April 2000 DIAS
r e D o r t N o. 28 • Plant Production
Lars J. Munkholm
T h e s p a d e a n a l y s i s
- a modification of the qualitative spade diagnosis for scientific use
M inistry o f Food, A g ric u ltu re an d Fisheries
K *
ti
I I
iir
II ;
lit
The spade analyses
- a modification of the qualitative spade diagnosis for scientific use
Lars J. M u n kh o lm
D e p a rtm e n t o f Crop Physiologi and Soil Science P. O. Box 50
D K -8830 Tjele D enm ark
DIAS re p o rt Plant Production no. 28 • A pril 2000
Publisher: Danish Institute o f Agricultural Sciences Tel. +45 89 99 19 OO Research Centre Foulum Fax +45 89 99 19 19 P.O. Box 50
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Preface
In th is re p o rt a m o d ificatio n o f th e quaU tative classical spade d iag n o sis is p resen ted . T h is w o rk h as b e e n carried o u t w ith in P ro ject 1.3 “ S oil fertility an d soil tilth as in flu en ced by o rg an ic farm in g p ra c tic e s an d so il tillag e” op erated u n d e r th e D an ish R e se a rc h C e n tre fo r O rg an ic F arm in g . In th e p ro ject th e soil tilth o f d ifferen tly m an ag e d soils h as b e e n in v e stig a te d by th e u se o f “h o listic” field m eth o d s as w ell as sp ecialised “ re d u c tio n istic ” lab o rato ry m eth o d s. W ide ran g es o f soil p hysical, b io lo g ical an d ch em ical p a ra m e te rs have b e e n m e a su re d in th e d ifferen tly m an ag e d soils. T he spade an aly sis w as th e m o s t in te g ra tin g an d h o listic an aly tical m eth o d ap p lied in the project.
In th e p ro cess o f d ev elo p in g th e spade an aly sis m an u al a n u m b er o f p erso n s h a v e g iv e n k in d a d v ice. A t th e in itiatio n o f th e w o rk K n u d Suhr, D en Ø k o lo g isk e L an d b ru g ssk o le a n d m y c o lle a g u e s Susarm e E lm h o lt an d K arl J. R asm ussen, D an ish In stitu te o f A g ricu ltu ra l S cien ce s (D IA S ) h av e co n trib u ted w ith h in ts an d go o d ideas. A n d rea B este a n d U lric h H am p l, S tiftu n g fu r Ö k o lo g ie u n d L an d b au , G erm an y h av e b een v ery helpftil an d p a rtic u la rly g iv en v a lu a b le in fo rm atio n o n w h ere to fin d o ld h ard ly accessib le literature. L astly , P e r S c h jø n n in g , D IA S h as c o n trib u te d w ith fruitfiil ideas and a critical rev iew from th e in itial d ev elo p in g p h ase to th e p u b lic a tio n phase.
In th e p ractical w o rk K resten M ey er, D IA S -B y g h o lm an d S tig T. R asm u ssen , D IA S -F o u lu m h av e assisted .
D a n ish In stitu te o f A g ricu ltu ra l S ciences D e p a rtm e n t o f C ro p P h y sio lo g y and Soil S cience N o v e m b e r 1999
L ars J. M u n k h o lm
S u m m a r y ... 5
S a m m e n d ra g ... 7
1. I n tro d u c tio n ... 9
2. B a c k g ro u n d ... 10
2.1. T h e sp ad e d ia g n o s is ... 10
2.2 O th e r m e th o d s ... 13
2.2.1 P e d o lo g ical soil p ro file d e s c rip tio n s ... 13
2 .2 .2 N u m e ric a l ev alu a tio n o f soil tilth ... 13
3. T h e sp ad e an aly sis m e th o d ... 14
3.1. H o w to u se th e sp ad e a n a ly s is ...15
4. M a te ria ls an d m e t h o d s ...15
4.1 L o n g -te rm soil m an ag e m en t e ff e c ts ...15
4.1.1 G ro u p I ...16
4 .1 .2 G ro u p I I ...16
4 .1 .3 G ro u p I I I ... 16
4.2 E ffects o f soil tillag e - G ro u p I V ... 17
4.3 A n a ly s is ... 17
5. R esu lts a n d d is c u ssio n ...18
5.1 L o n g -te rm so il m an ag e m en t e ff e c ts ...18
5.1.1 G ro u p I ... 18
5.1 .2 G ro u p I I ...19
5.1.3 G ro u p I I I ...20
5.2 E ffe c t o f so il tillag e - G ro u p I V ...21
5.3 G en eral d is c u ssio n ... 22
5.3.1 G en eral f in d in g s ... 22
5.3 .2 C o m p a c te d la y e r s ... 23
5.3.3 L o n g -term an d sh o rt-term e ffe c ts... 23
5.3.4 E v a lu a tio n o f th e spade an aly sis m e t h o d ...24
6. C o n c lu s io n s ...25
7. L ite ra tu r e ... 25
T a b le s a n d F ig u r e s ... 30 A p p en d ix A: R esu lts in d e ta ils ...A1 A p p en d ix B; T h e sp ad e a n aly sis m a n u a l...B1 C o n te n ts
O p tim al soil fertility is o f p articu lar im portance in org an ic farm in g w h e re p la n t p ro d u c tio n re lie s h e a v ily o n th e in h eren t p ro p ertie s and the accu m u lated effect o f p a st a n d p re s e n t soil m an ag e m en t. T he term ” soil tilth ” d escrib es the d esired soil stru ctu re in re la tio n to p lan t g ro w th . A sse ssin g soil tilth in th e field h as b een a ch allen g e to scien tists an d p ra c tic ia n s fo r cen tu ries. Jo h a n G ö rb in g fro m G erm an y d ev elo p e d the d escrip tiv e sp ad e d ia g n o sis m e th o d in th e y e a rs fro m 1920 to 1945. A n o th er G erm an, G erh ard t P reu sch en , re in tro d u c ed th e m e th o d in th e early 1980s as a to o l sp ecifically ap p licab le to ev alu a te soil tilth in o rg an ic farm in g . T h e k ey ele m e n ts in the P reu sch en sp ad e d iag n o sis are an ex am in atio n o f soil stru ctu re, ro o t g ro w th , so il fau n a, d e co m p o sitio n o f o rganic m atter and soil frag m en tatio n .
T h e P re u sc h e n sp ad e d iag n o sis is a q u alitativ e m eth o d th a t is h ig h ly d e p e n d e n t o n th e e x p e rie n c e an d sk ill o f th e operato r. In th is report a stan d ard ised “ se m i-q u a n tita tiv e ” field m e th o d to ev alu a te soil tilth in th e field is p resen ted an d evaluated.
S oil stru ctu re is d escrib ed acco rd in g to intern atio n al standard m ethods. N e w g u id e lin e s are p ro p o se d w h ere no clea r an d stan d ard ised m eth o d s o f d escrib in g sp ecific so il ch a ra c te ristic s w e re fo u n d in th e literature. T h is applies e.g. to th e d escrip tio n o f p o re an d ro o t g ro w th c h a ra c te ristic s an d d eg ree o f d eco m p o sitio n o f ap p lied o rganic m atter.
T h e sp ad e an aly sis m eth o d w as tested on fo u r gro u p s o f soils each co n sistin g o f tw o o r th ree so ils w ith c o n trastin g lo n g -term o r sho rt-term soil m anagem ent. In all so ils th ree
ch a ra c te ristic lay ers w e re o bserved. A t th e to p a 5-8 cm intensely c u ltiv ated lay er w as fo u n d , w h ic h h a d a cru m b stru ctu re in m o st cases. In the m iddle (ap p ro x im a tely 7 -22 cm ) a d en ser, g ra n u la r o r su b -a n g u la r stru ctu red lay er w as found in m o st cases. A t the b o tto m a d en se, c o arse b lo c k y o r c o m p a c t m assiv e p lo u g h p an w as fo u n d - ex cep t fo r th e tre a tm e n t w ith d eep soil lo o sen in g . T h e o ccu rren ce o f p lo u g h pans co n firm s th e g en eral fin d in g o f p lo u g h p a n s in c u ltiv a te d D a n ish soils.
R o o t g ro w th w as restricted at the in terface b etw een all layers. A ra th e r w e a k ro o t re stric tio n w as o b se rv e d a t th e in terfa ce b etw een th e loose, intensely cu ltiv ated to p lay er an d th e m id d le layer. A sev ere ro o t gro w th restrictio n w as in m o st cases d etec ted a t the tra n sitio n to the p lo u g h p a n layer.
P o sitiv e lo n g -term effects o f a v ersatile cro p ro tatio n an d ap p licatio n o f o rg an ic m a n u re w as fo u n d - e x c e p t fo r th e G ro u p I soils. In th a t case n eg ativ e sh o rt-term effects o f in ten siv e tillag e an d tra ffic m ay h av e o v ersh ad o w ed p o sitiv e effects o f lo n g -term soil m an ag e m en t. T he sig n ific a n t e ffe c t o f tillag e an d traffic o n soil tilth w as also e v id e n t fi-om th e tilla g e trial
Summary
T he sp ad e a n aly sis w as a useful tool to describe th e p resen t soil tilth statu s o f th e soil. O n the b ack g ro u n d o f c o m p reh en siv e d a ta m aterial on soil m an ag e m en t o f th e p a st y ears, it w as p o ss ib le to ev alu a te lo n g an d sho rt-term effects o f soil m an ag em en t. G o o d c o rre la tio n s to p a ram eters m easu red by specialised q u an titativ e m ethods in the field an d in th e lab o rato ry h a v e b e e n found.
O p tim al fru g tb arh ed er i sæ rlig grad a f b ety d n in g i ø k o lo g isk jo rd b ru g , h v o r
p la n te p ro d u k tio n e n stæ rk t afh æ n g er a fjo rd e n s oprin d else og a f d y rk n in g sh isto rien . T e rm e n
” so il tilth ” e r e t b eg reb an v en d t i d en eng elsk sp ro g ed e v erd en til a t b esk riv e d en ø n sk ed e jo rd s tru k tu r i relatio n til plan tev æ k st. D et er svæ rt a t ov ersæ tte b e g re b e t til d an sk , m en b e g re b e t en ”b e k v e m ” jo r d k o m m er tæ tte st på. B ed ø m m else a f ” soil tilth ” i m ark en h a r v æ ret e n u d fo rd rin g fo r ag erd y rk eren g en n em århundreder. T y sk eren J o h ^ G ö rb in g u d v ik le d e i å ren e 1920 til 1945 sp ad ed iag n o sen til dette form ål. M eto d en b lev ta g e t op p å ny i sta rte n a f 19 8 0 ’e m e a f G e rh a rd t P reu sch en , so m e n m etode til a t b ed ø m m e ” soil tilth ” i sp ecielt ø k o lo g isk jo rd b ru g . I sp ad ed iag n o sen er n ø g leelem en tern e e n b esk riv else a fjo r d e n s stru k tu r o g sm u ld reev n e , ro d v æ k st, fau n a ak tiv itet, o m sæ tn in g a f tilfø rt o rg an isk s t o f
S p ad ed iag n o se m eto d e er e n b e sk riv en d e k v alitativ m eto d e og d e rfo r h a r o p eratø ren s u d d an n else o g erfarin g stor bety d n in g fo r resu ltatet a f besk riv elsen . I d en n e ra p p o rt p ræ se n te re s o g e v alu e res en ” sem i-k v an titativ ” m eto d e til b ed ø m m else a f ” soil tilth ” i de ø v erste 30 c m a f jo rd e n .
I d en fo re slå e d e sp ad e an aly se m an u al er v elb esk rev n e in tern atio n ale stan d ard m e to d er a n v e n d t til b esk riv else a fjo rd e n s struktur. D er er u d v ik let en v ejled n in g til b esk riv else a f e g en sk a b e r, h v o r stan d ard m e to d er ikke kunne findes i litteraturen. D ette g æ ld e r bla. fo r b e sk riv e lse a f p o re - og ro d sy stem sam t fo r b ed ø m m else a f o m sæ tn in g a f o rg a n isk stof.
S pade an a ly se n b lev ev alu e ret p å fire g ru p p er a f jo rd e r, d er h v e r in d eh o ld er to e lle r tre jo r d e m ed fo rsk e llig d y rk n in g sm æ ssig forhistorie. F o r alle jo rd e rn e fan d tes tre k a ra k te ristisk e lag. I d e ø v e rste 5-8 c m fan d tes et in ten st b earb ejd et lag g en erelt m ed k ru m m estru k tu r. I m id te n (o m k rin g 7-22 cm ) v a r d er e t m ere k o m p ak t lag m ed g ran u læ r eller su b a n g u læ r b lo k s tru k tu r i d e fleste tilfæ ld e. I b u n d en (22-30 cm ) fandtes e n k o m p ak t p lø jesål m ed g ro v b lo k s tru k tu r e lle r k o m p a k t m a ssiv stru k tu r - u n d tag en i en d y b d elø sn et jo rd . D ette b e k ræ fte r, a t p lø je så l er m e g e t u d b re d t i d an sk e landbrugsjorde.
R o d v æ k ste n v a r h æ m m et v ed o v erg an g en m ellem de ov en n æ v n te lag. V ed o v e rg a n g til m id te rz o n e n fan d tes e n svag h æ m n in g a f ro dvæ ksten. E n k raftig h æ m n in g a f ro d v æ k sten fan d tes i de fle ste tilfæ ld e v e d ov erg an g til piøjesålen.
G e n e re lt v a r d e r en g u n stig effek t a f e t alsid ig t sæ d sk ifte og tilfø rsel a f o rg an isk s t o f p å jo rd e n s ”tilth ” . F o r G ru p p e I jo rd e n e v a r ten d en sen d og modsat,- h v ilk et k an fo rk la re s m ed , at
d e n n e g ativ e e ffe k t a f intens jo rd b earb ejd n in g og tra fik h avde o v ersk y g g et de p o sitiv e la n g tid se ffe k te r a f e t a lsid ig t sæ d sk ifte og tilfø rsel a f o rg an isk s t o f Jo rd b e a rb e jd n in g sfo rsø g e t v iste o g så k la rt at jo rd b e a rb e jd n in g er a f sto r b e ty d n in g fo r jo rd e n s ”tilth ” . D e n ” ik k e-
Sammendrag
S p ad ean aly sen v a r e t an v en d elig t red sk ab til at b ed ø m m e jo rd e n s ak tu elle ” soil tilth ” status.
E t o m fa tte n d e k en d sk ab til jo rd e n e s d y rk n in g sh isto rie m u lig g jo rd e en ev a lu e rin g a f l a n g - og k o rttid s v irk n in g e r a f d y rk n in g sh isto rien på jo rd e n s ”tilth ” . D er fan d tes g o d e k o rre la tio n e r til jo rd fy s is k e og -b io lo g is k e p aram etre m ålt m ed sp ecialisered e k v an titativ e m e to d e r i m ark en o g i lab o rato riet.
S o il fertility a n d so il stru ctu re/p lan t in teractio n s are areas in w h ic h in te re st is in creasin g w o rld -w id e. T erm s like soil q uality, so il fertility an d soil tilth h av e b ec o m e w e ll-k n o w n am o n g so il sc ie n tists as w ell as p ractician s in agriculture. O ne o f th e m a in reaso n s fo r th is g ro w in g in te re st is th e in creased im p o rtan ce o f o p tim al soil fertility. T he u se o f m in eral fertilisers a n d p esticid es is in creasin g ly b ein g restricted in D en m ark an d o th e r co u n tries. T h is h a s re d u ced th e fa rm e r’s o p tio n s o f co m p en satin g fo r sub -o p tim al p lan t g ro w th b y ap p ly in g e x tra m in eral fertilisers o r p esticid es. T he g row ing in terest in su stain ab le fa rm in g sy ste m s h as p o ssib ly also cau sed m o re atten tio n on th e subject. In D en m ark o rg an ic farm in g in p a rtic u la r h as g a in e d m u c h atten tio n an d m any farm ers h av e c o n v erted to o rg an ic farm in g p ractices.
P resen tly a b o u t 5% o f th e ag ricu ltu ral area is m an ag ed according to o rg an ic fa rm in g p ractices (B o rg en , 1999). T he n eed fo r o p tim al soil fertility and soil stru ctu re is p a rtic u la rly im p o rtan t in o rg a n ic fa n n in g w h e re p lan t p ro d u ctio n relies m o re h eavily o n th e in h eren t p ro p ertie s (b asic m a te ria l an d the accu m u lated effect o f p a st and presen t soil m an ag e m en t). L a stly , th e fa c t th a t m o d e m a g ricu ltu ral practices m ay cause soil d eg rad atio n (ero sio n , c o m p a c tio n and d e p le tio n o f o rg an ic m atter) is p ro b ab ly also a reaso n th e atten tio n o n th e su b ject. In o rd e r to clarify w h a t is m e a n t by so il fertility an d a d esired structural state o f th e soil som e b ro ad ly u sed te rm s are p re se n te d an d d efin ed below .
S oil fe rtility : T h e in h eren t soil fertility o f the soil is a flm ction o f p aren t m aterial, c lim ate, th e d u ra tio n o f so il fo rm in g p ro cesses actin g o n th e soil and th e v eg eta tio n th a t h as e v o lv e d in re sp o n se to so il p ro p ertie s an d clim ate (K ing, 1990).
B o d en g are: In G erm an y th e term “ B o d en g are” has b e e n used fo r cen tu ries to d escrib e a soil w ith a n o p tim al soil structure. S ekera and B ru n n er (1943) d efin ed “B o d e n g a re ” sim p ly as the stab ility o f an o p tim al soil structure. T hey co n sid ered a cru m b stru ctu re as th e d e sire d soil stru ctu re in re la tio n to p lan t grow th. A cco rd in g to G örbing (1947 p. 112) “ B o d e n g a re ” h a s a b ro a d e r m e an in g - it can n o t ju s t be rep laced by “cru m b stru ctu re” . B y a “ G are” so il G ö rb in g u n d e rsta n d s a b io lo g ic a lly activ e soil th a t is the fu n d am en t fo r d ev elo p in g c ru m b stru ctu re in th e u p p e r 20 cm o f th e soil profile. “ G ar ist ein B oden, d essen K rü m elstru k tu r d u rc h das L eb en se lb st g e b ild e t w ird , v o n den W u rzlen aller den B o d en b e sied eln d en P flan zen b is z u d en M ik ro o rg a n ism e n , im h arm o n isch e n K räftesp iel m it allen p h y sik alisch en , c h e m isc h e n u n d k o llo id k e m isc h e n V o rg än g e im B o d en ” (G örbing, 1947 p. 177).
S o il tilth : S oil tilth is a m u ltifaceted characteristic. Several d e fin itio n s h av e b e e n p ro p o s e d fo r th is term . Y o d er (1 9 3 7 ) a d d ressed th e overall q u ality o f soil as a m e d iu m fo r p la n t g ro w th : so il tilth is a blanket term describing a ll the conditions that determine the degree o f fitness o f a soil a s an environment f o r the growth and development o f a crop plant. M o re re c e n t ap p ro a c h e s h ig h lig h t th e p h y sical p ro p erties o f th e soil the physical condition o f soil as
1. Introduction
W ith th e aim o f developing a quantitative understanding o f the concept o f soil tilth K arlen et al.
(1990) pro p o sed a n ew definition and introduced a term called tilth-form ing processes. Soil tilth w as defin ed as the physical condition o f a soil described by its bulk density, porosity, structure, roughness, and aggregate characteristic as related to water, nutrient, heat and air transport;
stimulation o f microbial and microfauna populations and processes; and impedance to seedling emergence and root penetration. Soil tilth form ing processes w ere defined as the combined action ofphysical, chemical, and biological processes that bond prim ary soil particles into simple and complex aggregates and aggregate associations that create specific structural or tilth conditions. A co m p reh en siv e rev iew on fo rm atio n an d stab ilisatio n o f soil tilth is g iv e n by H a d a s (1 9 9 7 ).
“ S oil tilth ” h as b e e n ch o sen as a g eneral term to describe th e d esired stru ctu ral state o f th e soil in th is p resen tatio n . A ssessin g soil tilth in th e field m ay be very d iffic u lt b e c a u se it is a q u a lita tiv e an d m u ltifaceted term . D espite that, som e field m eth o d s h av e b een p ro p o sed . T he so -calle d “ sp ad e d ia g n o sis” d ev elo p e d by G örbing in the 1930s (G ö rb in g , 1947) a n d m o d ified by P reu sch en (P reu sch en 1983, 1994) is an attem p t to assess soil tilth b y a sim p le q u alitativ e field m ethod.
In th is re p o rt a stan d ard ised “ sem i-q u an titativ e” field m ethod to ev alu a te soil tilth in th e field is p re se n te d an d ev alu ated . T he m eth o d is d ev elo p e d on th e b asis o f th e d e sc rip tio n o f the P re u sc h e n sp ad e d iag n o sis. It is en titled “ T he spade an aly sis” to signal ro o ts in th e “ sp ad e d ia g n o s is” c o m b in ed w ith a n ew approach.
2. Background
2.1. The spade diagnosis
T h e sp ad e d ia g n o sis w as d ev elo p e d in th e y ears b etw een 1920 an d 1945 by G ö rb in g (G ö rb in g , 1947) as a sim ple to o l fo r practician s (farm ers, ad v iso rs etc .) to ev alu a te soil fertility in the field.
G ö rb in g w as o rig in ally ed u cated as a ch em ist in food science. Ju s t a fte r th e c o n c lu sio n o f th e F irst W o rld W ar he d ed ica ted h is life to teach in g and research in ag ricu ltu re. H e h ad
e x p e rie n c e d fam in e in P alestin e an d S yria and hu n g ers in G erm an y an d w an ted to m a k e h is c o n trib u tio n to a v o id su ch cata stro p h es in th e future by securing a la rg e r an d m ore sta b le food su p p ly . H e started b y g iv in g lectu res a b o u t the p ro p er use o f esp ecially m in eral fe rtilise rs in p lan t p ro d u ctio n . H is w o rk o n d ev elo p in g the spade d iag n o sis w as in itiated on th e b ack g ro u n d o f q u e stio n s a sk ed by practician s in the field (e.g. “ w hy does m y w in te r b arley g ro w p o o rly in th is sp o t? ” o r “ w h at is w ro n g w ith m y w in ter ry e?” ). Such q u estio n s co u ld n o t a lw a y s be p ro p e rly an sw e re d by n u trie n t deficien cy only. A n in v estig atio n o f th e so il w as n e e d e d to g iv e a m o re co m p re h e n siv e ex p lan atio n . G örbing g ath ered k n o w led g e fo r 25 y ears b e fo re he p u b lish ed an y th in g a b o u t th e spade diagnosis. In th a t tim e he p e rfo rm ed m o re th a n 5 0 .0 0 0 sin g le sp ad e d iag n o ses. A ctu ally , S ekera and B ru n n er (1943) w ere the first w h o ra th e r b rie fly
10
d e sc rib e d th e G ö rb in g sp ad e d iagnosis. T he m ethod w as alm o st fo rg o tten fo r d e c a d e s u ntil P reu sch en a n d o th e rs rein tro d u c ed th e m eth o d ab o u t 20 y ears ago (D iez, 1982; P reu sch en , 1983). It w as re in tro d u c ed esp ecially as a to o l in o rganic farm in g to ev alu a te so il tilth a n d soil fertility (P reu sch en , 1983). In D en m ark th e spade d iag n o sis has b een in tro d u ced b y p io n e e rs in o rg an ic farm in g (S u h r e t al., 1995) and is still m ain ly u sed b y o rg an ic farm ers an d ad v iso rs.
G ö rb in g b ased h is e x am in atio n o n th e d escrip tio n an d classificatio n o f soil stru ctu re
(G ö rb in g , 1947). H e d escrib es th ree fu n d am en tal elem en ts in “ G are” (i.e. soil tilth ) fo rm atio n a n d stab ilisatio n : 1. A n adequate p H level (Ihne deficien cy w as a m a jo r p ro b le m a t th a t tim e), 2. P ro p e r m a n a g e m e n t o f ap p lied org an ic m atter and 3. B io lo g ically su itab le so il tillage.
H e fo c u se d o n an ev alu a tio n o f the u p p er 30 cm o f the soil p ro file u n less th ere w a s a sp ecific re a so n to in clu d e d ee p e r lay ers (e.g. p o o r d rain ag e o r an assessm en t o f th e n e e d fo r d e e p so il- lo o sen in g ). A m in im ally d istu rb ed soil b lo ck is tak en o u t w ith a so -called G ö rb in g sp ad e an d stu d ie d w h e n it lies h o rizo n tally above ground. A cco rd in g to G ö rb in g (19 4 7 ) a n d S e k e ra an d B rurm er (1 9 4 3 ) a cru m b soil structure is th e d esired soil structure in re la tio n to p la n t g row th.
T h e d e e p e r d o w n in the soil th e cru m b structure reach es th e better.
P re u sc h e n ex ten d e d the sp ad e d iag n o sis by a m o re co m p reh en siv e ex a m in a tio n o f ro o t g ro w th , fau n al activ ity an d d e co m p o sitio n o f o rganic m atter (P reu sch en , 1983). T he
P reu sch en sp ad e d iag n o sis is d ev elo p e d to evaluate th e co n n ectio n b etw e e n soil stru ctu re, soil fau n al a c tiv ity an d ro o t an d p lan t g ro w th in the field. P reu sch en h a s g iv en a d etailed
d e sc rip tio n o n w h at to lo o k fo r w h en p erfo rm in g th e spade d iag n o sis. T he k e y e le m e n ts in th e P reu sch en sp ad e d iag n o sis are a n ex am in atio n o f 1. soil stru ctu re (lay erin g , stru ctu ral u n its, d e n sity , co lo u r, m o istu re co n ten t), 2. ro o t g ro w th (n u m b er an d d istrib u tio n , ab n o rm al ro o t gro w th , ro o t n o d u les (leg u m in o u s p lan ts), 3. Soil fauna, 4. d e co m p o sitio n o f o rg an ic m a tte r an d 5. so il frag m en tatio n .
S oil stru c tu re : S oil tex tu re is ro u g h ly estim ated an d th e soil p ro file is d iv id e d into h o rizo n s th a t are m ark ed ly d ifferen t fro m each other. P reu sch en em p h asises e sp ecially th e n e e d to n o te c o m p a c te d la y e rs (e.g. tillag e p an s) and anaerobic layers th a t m ig h t im p ed e ro o t g row th.
F o r e a c h lay er so il co lo u r, th e stru ctu ral u n its an d th e deg ree o f c o m p a c tio n are d escrib ed . P reu sch en su g g est th a t th e b asis o f an o p tim al soil structure is th e fo rm atio n o f so il cru m b s. In acc o rd a n c e w ith G ö rb in g , P reu sch en co n sid ers a cru m b structure as th e d e sire d soil stru ctu re fo r p la n t g ro w th . T h e fu rth er d o w n th e pro file a cru m b structure is o b serv ed th e b etter.
P reu sch en d efin es “ g e n u in e” soil cru m b s as spherical, p o ro u s a g g reg ates w ith a ro u g h su rface. T h e “ g e n u in e ” soil cru m b s are m ain ly 2-4 m m an d are seld o m larg er th a n 5 m m in diam eter.
R o o t grovyth: P reu sch en g ives a th o ro u g h d escrip tio n o f w h at to lo o k fo r w h e n d e sc rib in g th e ro o t sy stem . P reu sch en states th a t it is im p o rtan t to ex am in e the ro o t sy stem o f b o th th e cro p an d w eed s. T h e n u m b er, size d istrib u tio n an d b ran ch in g o f th e ro o ts m u s t be d esc rib e d fo r each d e sig n a te d lay er in the profile. It is o f great im p o rtan ce to n o te ab n o rm al ro o t g ro w th c au sed b y e.g. co m p ac ted o r an aero b ic areas in th e soil. A b n o rm al o r su b -o p tim al ro o t g ro w th m ay a p p e a r as th ic k e n e d ro o ts an d stro n g ly ben d ed /d e flected roots. A cco rd in g to P re u sc h e n
(1 9 9 4 ), rh iz o sh e a th co n sistin g o f soil-organic m atter m aterial adh erin g to th e ro o ts is a sig n o f h ig h b io lo g ical activ ity in the soil. R h izo sh eath s are m ainly found o n th e ro o ts o f g rasses.
A c c o rd in g to M c C u lly (19 9 5 ) m o st d ico ty led o n s do not form rh izo sh eath s.
F o r leg u m in o u s p la n ts P reu sch en (1994) p ro p o ses to ch aracterise th e n u m b e r an d d istrib u tio n o f ro o t n o d u le s in th e profile. Id eally , the ro o t nodules should be relativ ely sp arse b u t e v en ly d istrib u te d o n th e leg u m in o u s ro o ts in the studied profile. T he Rhizobium b a c te ria n eed w ell- ae ra te d c o n d itio n s to fix ate n itrogen. T h erefo re m inim a! occu rren ce o f ro o t n o d u les in a n a re a o f th e so il m ay in d icate p o o r aeration.
Soil fauna: P reu sch en stresses th e im portance o f ex am in in g earth w o rm activity. T he o b serv ed ea rth w o rm s sh o u ld be noted. A lso th e n u m b er and d istrib u tio n o f earth w o rm b u rro w s m u s t be n o ted as w ell as su rface featu res in the earth w o rm burrow s. H e e m p h asises th a t su rface featu res c o n sistin g o f so il an d o rganic m atter sh ould co v er earth w o rm b u rro w s, id eally . T he o c c u rre n c e o f n a rro w straig h t b u rro w s w ith o u t su rface featu res in d icates a b io lo g ical w o rth le ss a re a a cco rd in g to P reu sch en (1994).
D ec o m p o sitio n o f o rg an ic m atter: T he deg ree o f d e co m p o sitio n o f ap p lied o rg an ic m a tte r is ex am in ed . T he con sisten ce , sm ell and co lo u r o f th e d e co m p o sin g o rg an ic m a tte r are
e v alu a ted . A fte r so m e tim e th e ap p lied o rganic m atter e.g. straw m u st be friable. I f it re m a in s firm an d w ith o u t sig n o f d eco m p o sitio n it indicates p o o r b io lo g ical activ ity in the soil. I f the m aterial g o es b la c k an d sm ells m u sty it sig n ifies anaero b ic d e co m p o sitio n .
S oil fra g m e n ta tio n : T h e P reu sch en sp ad e diag n o sis is co m p leted by liftin g up th e rest o f th e m aterial o n the sp ad e an d th en d ro p p in g th e soil on th e ground. T h e d eg ree o f soil
fra g m en tatio n is ev alu ated . Id eally , th e soil sh ould fragm ent into sm all p iece s w ith o u t any p e rsiste n t m a jo r c lo d s o r soil layers.
T h e P re u sc h e n sp ad e d iag n o sis g ives a co m p reh en siv e e x am in atio n o f soil features. It is a p ro b le m th a t th e d escrip tio n o f P reu sch en lacks d etailed guidelines. T h is im p lies th a t th e sp ad e d ia g n o sis d ep en d s on th e ex p erien ce o f the d escrip to r and th erefo re the resu lts m ay be hig h ly su b jectiv e.
S o b eliu s (1 9 9 5 ) has su g g ested a m o d ificatio n o f th e spade d iag n o sis. T h e d e sc rip tio n o f soil stru ctu re (lay erin g , co lo u r, grade, agg reg ate ty p e an d size, con sisten ce , po re size a n d n u m b e r o f p o res) fo llo w s th e F A O g u id elin es fo r soil d escrip tio n (F A O , 1990). A lso th e d e sc rip tio n o f n u m b e r an d size o f ro o ts fo llo w s th e FA O guidelines. In ad d itio n , S o b eliu s h as p ro p o se d a m o re d e ta ile d d e sc rip tio n o f ro o t grow th. R oot m o rp h o lo g y (b ran ch in g , th ick en in g , b e n d in g , rh iz o sh e a th s) an d ro o t n o d u les o n leg u m in o u s p lan ts are described. U n fo rtu n ately , h e h as n o t in clu d ed g u id e lin e s o n h o w to ev alu a te b iological activ ity in th e soil - ex cep t fo r a key to d e te rm in e e a rth w o rm species.
R e c e n tly , B este (1 9 9 9 ) h as p ro p o sed an ex ten d e d spade d iag n o sis th a t co m b in es a q u a lita tiv e d e sc rip tio n o f soil stru ctu re in th e 0 -30 cm layer w ith a q u an titativ e d e te rm in a tio n o f som e k ey p h y sic a l p aram eters. W et ag g reg ate stab ility is d eterm in ed by a sim p le m eth o d a p p lie d in
12
th e field. S h ear stren g th is d eterm in ed in situ in all layers w ith at v an e sh e a r ap p aratu s. C ore sam p les are ta k e n fo r d eterm in atio n o f w a te r co n ten t an d b u lk density.
2.2 Other methods
2.2.1 Pedological soil profile descriptions
M an y o f th e soil featu res describ ed in the P reu sch en spade d iag n o sis are also d e sc rib e d w h e n m a k in g a p ed o lo g ical d escrip tio n o f the soil profile. A n u m b er o f in tern atio n al g u id e lin e s fo r so il d e sc rip tio n h av e b een w o rk ed out (e.g. F A O , 1990; Soil S u rv ey D iv isio n S taff, 1993).
D an ish g u id e lin e s fo r soil d escrip tio n h ave b een set up by e.g. P etersen an d M ø b erg (19 8 7 ) a n d M a d se n a n d Jen sen (19 8 8 ) o n th e b asis o f th e in tern atio n al gu id elin es. T h e se g u id e lin e s m ay also be a p p lied to th e sp ad e d iag n o sis as su g g ested by S o b eliu s (1995).
It is w o rth n o tin g th a t th ere are sig n ifican t differen ces b etw een a sp ad e d iag n o sis a n d an o rd in ary so il p ro file d escrip tio n - p articu larly in th e objectives. T he p u rp o se o f a so il p ro file d e sc rip tio n is co m m o n ly to learn ab o u t soil g en esis an d /o r to be able to classify th e soil. T he o b je c tiv e o f th e sp ad e d iag n o sis is to evaluate th e p resen t soil m a n a g e m e n t strateg y by stu d y in g th e re la tio n b etw een th e soil structure, ro o t g ro w th and b io lo g ical activ ity in the u p p e r p a rt o f th e soil p ro file (P reuschen, 1983).
2.2.2 Numerical evaluation o f soil tilth T h e P e e rlk a m p m eth o d
In th e N e th e rla n d s in th e 1960s th ere w as a lo t o f activ ity in th e d ev e lo p m e n t an d te stin g o f d e sc rip tiv e soil e v alu a tio n field m ethods. E sp ecia lly the P eerlk am p m e th o d (P eerlk am p ,
1959) h as b e e n b ro ad ly u sed in th e N eth erlan d s an d elsew h ere (B o ek el, 1963; B atey , 1975, 1988). In th e P e e rlk a m p m eth o d th e soil is assig n ed an “ St” n u m b e r (1-9); S t 1 = p o o r, S t 9 = o p tim al so il tilth. W ith an o rd in ary spade soil b lo ck s are d ug o u t from th e so il (at le a st 10 sam p les). T he assig n m e n t o f th e in d ex is b ased o n a v isual e v alu a tio n o f th e stru ctu ral u n its (ty p e, shape, size, p o ro sity an d ru p tu re energ y in m o ist con d itio n ), soil p o ro sity an d ro o t g ro w th . P eerlk am p p ro p o sed a sep arate ratin g tab le fo r light an d h eav y soils. F o r h e a v y so ils a p o o r soil (S t 1) c o n sists o f large d en se clods, w ith evidence o f an aero b ic c o n d itio n s in som e areas. T h e ro o ts g ro w solely in the crack s b etw een th e clods. O n th e o th e r h a n d a fin e, loose c ru m b stru ctu re c h aracterises a n ideal heav y soil (S t 9). A p o o r san d y soil is c h a ra c te rise d by sin g le -g ra in stru ctu re, w h ereas a soil co n sistin g stable p orous soil ag g reg ates c h a ra c te rise s an o p tim a l san d y soil.
T h e P e e rlk a m p m e th o d h as b een b ro ad ly u sed in the N eth erlan d s an d in o th e r c o u n trie s as d e sc rib e d b y B atey (1975). B o ek el (19 8 2 ) u sed the m eth o d to study th e d e v e lo p m e n t o f soil tilth o v e r sev eral y e a rs (1 9 6 0 -1 9 8 2 ) fo r som e co m m ercial an d re se a rc h statio n field s in the N e th erlan d s. H e fo u n d a g en eral d ecrease in ratin g durin g th e 22 y ears o f study. T h is fin d in g w as e x p la in e d b y in creased p ro b lem s w ith soil co m p ac tio n due to th e u se o f in creasin g ly h e a v ie r tra c to rs an d im p lem en ts in m o d e m agriculture. B oekel (1 9 6 3 ) also fo u n d a p o sitiv e e ffe c t o f th e c o n te n t o f o rg an ic m a tte r o n soil tilth (i.e. h ig h er v isual ratin g ). B atey (19 7 5 )
n o ted th a t v isu al sco rin g m eth o d s - equal o r sim ilar to the P eerlk am p m eth o d - w ere e x te n siv e ly u sed in G reat B ritain in adv iso ry as w ell as in in v estig atio n al w ork.
T h e B atey m eth o d
In a so -calle d p ractical guide to the use an d m an ag em en t o f soil B atey (1 9 8 8 ) d escrib es p ro b le m s o f soil stru ctu re in m o d e m ag ricu ltu re and p resen ts a m eth o d o f n u m erically e v alu a tin g so il stru ctu re in th e field. T h e m eth o d resem b les to a g reat e x te n t th e P e e rlk a m p m eth o d . A sp ad efu l o f soil is d u g o u t an d gently b roken apart. T h e soil stru ctu ral u n its, the g rad e a n d th e co n siste n c e are assessed. T he soil o r soil layer is assig n ed a n u m b e r a c co rd in g to a ” soil stru ctu ral k ey ” . T h e index goes from S I to S7 w here S I is the best. S I so ils/so il layers are ch a ra c te rise d by fine aggregates, 1-6 m m in diam eter. S7 so ils/so il layers are c o m p a c t so ils/la y e rs w ith few o r no co m p o n en t ag g reg ates v isible w h ere a n a ero b ic c o n d itio n s m ay be detec ted .
3. The spade analysis method
T h e p resen ted sp ad e a n aly sis m eth o d is d ev elo p e d o n th e b asis o f the sp ad e d ia g n o sis as d e sc rib e d by P reu sch en (1983, 1994) an d S obelius (1995). T h e p u rp o se s o f the sp ad e a n aly sis are:
- to d esc rib e th e p re se n t status o f soil tilth
to relate th e p re se n t soil tilth status to past soil m an ag e m en t practices
- to g iv e a fo u n d atio n fo r m ak in g d ecisio n s on im p ro v ed soil m an ag e m en t (e.g. a ltered tilla g e , cro p ro tatio n an d fertilisation).
- to ev a lu a te th e e ffe c t o f im p lem en ted initiatives.
G u id e lin e s fo r sp ad e an aly sis d escrip tio n are presen ted in A p p en d ix B. T h e d e sc rip tio n o f soil lay erin g a n d b o u n d aries is carried o u t acco rd in g to th e g u id elin es o f M ad sen an d Jen sen (1 9 8 8 ) w ith slig h t m o d ificatio n s. Soil co lo u r is describ ed u sin g th e M u n sell c o lo u r c h art sy stem (M u n sell, 1975). E v alu atio n o f soil texture, grad es, an d ty p e s o f stru ctu ral u n its fo llo w s th e stan d ard soil d escrip tio n m eth o d s (M ad sen an d Jen sen , 1988). A sse ss m e n t o f a g g re g a te size an d soil co n sisten ce fo llo w s the FA O g u id elin es (F A O , 1990). E v a lu a tio n o f m a cro p o res, su rface featu res in m acro p o res, and o f n u m b er and size o f e a rth w o rm b u rro w s an d ro o ts is b ased e n th e d escrip tio n o f P etersen and M ø b erg (1 9 8 7 ) an d G rev e e t al. (1999).
In o rd e r to g e t a m o re co m p reh en siv e ch aracterisatio n o f po re and ro o t stru ctu re g u id e lin e s fo r e v a lu a tio n o f p o re co n tin u ity , ro o t bran ch in g and ab n o rm al ro o t g ro w th h av e b een w o rk e d o u t o n th e b asis o f the q u alitativ e d e scrip tio n s by P reuschen (1983, 1994) an d G rev e e t al. (1999).
C o n c e rn in g th e ch aracterisatio n o f ro o t n o d u latio n o n leg u m in o u s p lan ts th e g u id e lin e s are b ased o n P reu sch en (1 9 8 3 , 1994) and S obelius (1995). W h en d escrib in g soil faunal activ ity , ea rth w o rm s are ev alu a ted sep arately (n u m b ers, sp ecies and earth w o rm casts). O th e r soil
1 4
an im als are assessed as w ell as possible. T he gu id elin es fo r ev alu a tio n o f th e d eg re e o f d eco m p o sitio n o f o rg an ic m a tte r h av e b een b ased on the d e scrip tio n s o f P re u sc h e n (1 9 8 3 , 1994). In th e en c lo se d m an u al (A p p en d ix B ), a d escrip tio n o f sam pling, and
reco m m e n d a tio n s o n w h e n to perfo rm the analysis, n u m b er o f rep licates etc.
3.1. How to use the spade analysis
T h e m e th o d is ap p licab le fo r a n u m b er o f p u rp o ses in p ractical ag ricu ltu re as w ell as in a g ric u ltu ra l research . T he m eth o d m ay be u sed by practician s in m an y corm ections as d e sc rib e d b y G ö rb in g (1947). T he o b jectiv e o f th e in sp ectio n m ay be g en eral m o n ito rin g o f so il-p la n t in teractio n s. It m ay also be ap p lied m o re activ ely as a to o l a t th e o p eratio n al lev el in th e d ecisio n -m a k in g p ro cess in soil m anagem ent. F o r in stan ce th e m eth o d m ay b e a p p lie d to ev a lu a te seed b ed q u ality o r the deg ree o f d e co m p o sitio n o f n ew ly ap p lied o rg an ic m atter. It m ay also b e u sed p rio r to tillag e to d eterm in e the p ro p er d ep th a n d /o r in ten sity o f so il tillag e.
In ag ricu ltu ral research the m eth o d m ay be u sed as a first step in a h ierarch ical a n a ly sis o f e.g.
effe c ts o f soil m an ag e m en t sy stem s o n soil tilth. In th a t case it m ay be su p p le m e n te d b y o th e r q u a lita tiv e an d q u an titativ e field an d laboratory m eth o d s (S chjørm ing e t al., 1999). T h e sp ad e a n a ly sis m a y also be u sed m o re d irectly orien ted to assess th e p ro p e r d e p th o f sam p lin g o r th e p ro p e r d ep th an d ty p e o f tillag e actio n to be u sed in a tillag e trial.
4. Materials and methods
4.1 Long-term soil management effects
R esu lts fro m th e sp ad e an aly sis p erfo rm ed o n sites w ith d ifferen t soil m a n a g e m e n t are p re se n te d b elow . D etailed scien tific stu d ies o n th e state o f soil tilth h a v e b e e n c o n d u cte d on th e so ils in P ro je c t 1.3 op erated u n d er D an ish R esearch C entre fo r O rg an ic F arm in g . A d e ta ile d d e sc rip tio n o f b asic characteristics an d the selectio n o f th e so ils is g iv e n by
Schjørm ing e t al. (In prep.). Soil ty p e and p aren t m aterial is co m p arab le fo r so ils w ith in each o f th e fo u r g ro u p s o f so ils presented. Soil m an ag em en t d iffers w ith in each o f th e fo u r g roups.
T h ere is a d iffe re n c e in lo n g -term soil m an ag e m en t w ith in each o f th e g ro u p s I-III an d a d iffe re n c e in soil tillag e w ith in th e G roup IV (T able 1).
A ll soils in G roup I-III are developed on till plains from the W eichselian glacial stage. T he soils m ay all be classified as O xyaquic A griudolls according to Soil T axonom y (Soil S urvey Staff, 1998). T he clay content w as around 15% in the G roup I soils, 20% in the G roup II soils, and 18% in th e G roup III soils. T he G roup I soils are n o t n e ig h b o u rin g sites. T h ere is a b o u t 2 k m b etw e e n O rg -H (I) an d C o n v -H (I) an d a b o u t 25 k m b etw een C o n v -P (I) an d th e o th ers. T he G ro u p II a n d III soils are lo cated n ear each o th er (approx. 2 k m d istance). W ith in e a c h o f th ese g ro u p s th e tw o sites are lo cated aro u n d 25 0 m eters from each other. T he so ils are la b elled b y ’O rg ’ (O rg an ic) o r ’C o n v ’ (C o n v en tio n al) w ith an ’H ’ fo r ’A n im al H u s b a n d ry ’
m e a n in g a d airy fo d d er cro p p in g system and a ’P ’ fo r ’P la n t’ m ean in g a c ro p p in g sy stem fo r c ash cro p (p rim arily sm all g rain cereals) production.
4.1.1 Group I
T he so ils lab elled O rg -H an d C o n v -H h av e fo r d ecad es b een m an ag e d in a fo rag e cro p ro ta tio n (T ab le 1). T h ey h av e had a cro p ro tatio n w ith a m ix tu re o f a n n u al an d p e re n n ia l c ro p s an d an im al m an u re h a v e reg u larly b een applied. T he O rg -H soil has b een d e d ic a te d to b io d y n a m ic farm in g practices fo r alm o st 50 years. T h e C onv-H soil has b e e n c u ltiv ated m ain ly w ith c ereals fo r th e last 20 y ears b efore sam pling. A n im al m an u re has n o t b e e n a p p lie d fo r at least 10 y ears b u t straw has been incorporated into the soil. In th e y ear o f sam p lin g an d field testin g , sp rin g b arley w ith a g rass/clo v er m ix tu re u n d erso v m w as g ro w n o n O rg -H an d C o n v -H an d p eas on C onv-P.
F o r all G r. I so ils th e tillag e sy stem in clu d ed m o uldboard p lo u g h in g in th e a u tu m n p reced in g all n e w cro p s T h e soils had receiv ed co n trastin g tillage an d traffic in ten sity w ith in th e y e a r o f sa m p lin g an d field testin g . T he traffic intensity w as hig h on O rg-H an d C o n v -H d u e to p re p a ra tio n o f seed b ed , so w in g o f the sm all grain cereal c o v er cro p an d th e g ra s s/c lo v e r ley, an d ro llin g th e soil afterw ard s: T h is resu lted in a total o f 8 tracto r p asses b e tw e e n th e a u tu m n p lo u g h in g an d the sam p lin g at p lan t g erm in atio n in the spring (T ab le 1). O n the C o n v -P so il a sin g le p ass in th e field a fte r p lo u g h in g w as carried out. S eedbed p rep aratio n an d so w in g w ere p e rfo rm e d w ith a co m b in ed im plem ent.
T h e so ils had ap p ro x im ately sim ilar soil tex tu re and pH (T ab le 2). T he c o n te n t o f o rg an ic m a tte r an d read ily av ailab le K, M g an d P w as very h ig h for C onv-H . T h e co n te n t o f e x tra c ta b le P (O lsen -P ) w as low fo r C onv-P (0 1sen-P = 15 m g k g ‘‘ ~ P t= 1 .5 ) a n d very lo w fo r O rg -H (0 1 sen -P = 8 m g k g ’' ~ Pt= 0.8).
4.1.2 Group II
T h e so il lab elled O rg -H has b een m anaged acco rd in g to o rg an ic farm in g p ractices w ith a fo rag e cro p ro ta tio n since 1951 (T ab le 1). T he ro tatio n has included an n u al as w ell as
p eren n ial crops. T he referen ce soil, labelled C onv-H , h as b een m an ag e d co n v e n tio n a lly w ith a sim p le fo u r-c o u rse cash cro p rotation. Q uite h ig h am o u n ts o f an im al m an u re h av e b e e n a p p lie d a n n u ally to th is soil. T he soils had sim ilar tex tu ral co m p o sitio n s an d b o th h ad a hig h level o f read ily av ailab le K , M g and P (T ab le 2). T he o rg an ic m atter c o n te n t an d C E C w ere s lig h tly h ig h e r fo r th e O rg-H soil th an fo r th e C o n v -H soil, w h ereas th e pH w as h ig h e s t fo r the C o n v -H soil. In th e y e a r o f a n aly sis (1998) spelt (Triticum spelta) w as g ro w n on O rg-H a n d w in te r w h e a t (Triticum sativum) o n C onv-H .
4.1.3 Group III
T he so il la b e lle d O rg -H has b een m an ag ed acco rd in g to o rg an ic farm in g p ractices w ith a fo rag e c ro p ro ta tio n sin ce 1958 (T ab le 1). T he co n v en tio n ally m an ag ed referen ce soil, lab elled C o n v -P , has b een gro w n alm o st co n tin u o u sly w ith cereals fo r th e la st 20 years.
1 6
A n im al m an u re w as n o t ap p lied an d straw w as rem o v ed in m o st y ears o n th e C o n v -P soil. In 1998 S p elt (Triticum spelta) w as gro w n o n O rg-H and w in te r w h e a t (Tri/zcMW sativum) w as g ro w n o n C onv-H . T h e so ils h ad co m p arab le textural c o m p o sitio n s (T ab le 2). T h e O rg -H soil h a d a m u ch h ig h e r co n te n t o f org an ic m atter an d read ily av ailab le K , M g an d P th a n the C o n v -P soil. T h e C E C w as also h ig h e st fo r th e O rg-H soil, w h ereas th e pH w a s sim ila r fo r the tw o soils.
4.2 Effects o f soil tillage - Group IV
T h e tilla g e e x p erim en t w as in itiated u n d er P ro ject 1.3 u n d er D anish R esearch C e n tre fo r O rg an ic F arm in g . T he e x p erim en t w as estab lish ed in 1997 a t th e o rg an ically m a n ag e d R u g b a lle g å rd E x p erim en tal S tation, H o rsen s w here the fields w ere c o n v erted to o rg an ic fa rm in g p ractices in 1995. T he soil is a sandy loam d ev elo p e d on d ilu v ial clay , san d an d gravel. B eets w ere g ro w n in 1997 and spring b arley /p ea m ix w ith g ra ss/c lo v e r u n d e rs o w n in
1998 (T ab le 1). F o u r tillag e treatm en ts w ere carried out o n p lo ts in a ra n d o m ise d b lo c k d e sig n w ith fo u r rep licates. S pade a n aly sis w as carried o u t in tw o treatm en ts. T h e field d id n o t re c e iv e an im al m an u re in 1998. S am p lin g and m easu rem en ts to o k p lace in th e spring b a rle y /p e a m ix w ith g rass/clo v er undersow n.
T he traditional tillage treatm ent, labelled T T , included m ouldboard ploughing follow ed by secondary tillage an d drilling in one pass by a com bined im plem ent. A n im plem ent com p o sed o f subsoiler tines com bined w ith a rotovator and a drill w as used for th e non-inverting tillage, labelled N IT . T he depth o f subsoil loosening is flexible, but w as set at approxim ately m ax im u m d ep th (35 cm ) in 1998. T he tex tu re and th e g en eral chem ical c h aracteristics are at th e sam e level fo r b o th treatm en ts (T ab le 2).
4.3 Analysis
T h ree re p lic a te s o f th e sp ad e a n aly sis w ere perfo rm ed o n Gr. I soils at th e b e g in n in g o f Ju ly 1997. F o r G r. II an d III soils tw o rep licates o f th e sp ad e an aly sis w ere carried o u t o n each soil. T h e d istan ce b etw e e n sam p lin g p o in ts o n G r. I-III soils w as a p p ro x im a te ly 25. T h e sp ad e a n aly sis w as p e rfo rm e d a t th e en d o f Ju n e 1998 fo r G ro u p II an d at th e b eg in n in g o f Ju ly 1998 fo r G ro u p III. In th e tillag e e x p erim en t fo u r rep licates w ere carried o u t fo r each tre a tm e n t (i.e.
o n e p e r rep licate in th e field trial) in the b e g in n in g o f Ju ly 1998. T h ere is a ra th e r larg e sp atial tex tu ral v a ria tio n in th e field. B efo re the trial w as in itiated th e field w as c h a ra c te rise d in a 4 0 * 4 0 m g rid (R a sm u sse n e t al., 1995). B ased o n th o se resu lts areas w ith sim ila r te x tu re w ere selected fo r sam p lin g an d also fo r p erfo rm in g th e spade analysis. In all cases th e sam e o p e ra to r {the author) carried o u t the spade analyses.
5. Results and discussion
D e ta ile d re su lts are p resen ted in ap p en d ix A. T he p resen ted resu lts are a v erag es o f th e tw o o r th ree re p lic a te s a t each site.
5.1 Long-term soil management effects 5.1.1 Group I
T h e soil p ro file s c o u ld be d iv id ed into th ree ch aracteristic h o rizo n s in all soils. A lo o se an d c ru m b -stru c tu re d to p lay er (h arro w ed layer) w as follow ed by a rath er lo o se p lo u g h ed layer.
B e lo w 23 -2 5 c m a p lo u g h pan w as identified. T he soils had sim ilar soil c o lo u r an d m o istu re c o n te n t in all th ree h orizons. F ig u re 1 show s ph o to s o f soil b lo ck s fi-om th e C o n v -P an d O rg- H soils.
F o r th e C o n v -P so il a cru m b stru ctu re w as identified dow n to th e p lo u g h p an layer, w h ereas fo r th e o th e r tw o so ils (O rg-H and C o n v -H ) a cru m b stru ctu re w as fo u n d o n ly in th e h arro w e d to p layer. F o r th o se so ils the stru ctu re becam e d en ser w ith g ran u lar to su b -an g u lar b lo ck y u n its b e lo w th e to p layer. A t th e bottom a p lough pan w as identified. A p la te -stru c tu re d p lo u g h p an w as n o ted fo r th e O rg-H soil. C h aracteristics o f the p lo u g h p an w ere n o t d e sc rib e d fo r C o n v -P an d C onv-H .
A t all d ep th s th e so ils h ad a sticky and p lastic co n sisten ce w h en w et. W h en m o ist all th e soils w ere ch a ra c te rise d as friab le in th e to p layer. A friab le soil co n sisten ce w h en m o ist w as also fo u n d fo r th e m id d le lay er o f th e O rg-H and C onv-P soils. A slig h tly firm er soil w as fo u n d in th e m id d le lay er o f th e C o n v -H soil. W hen dry the O rg-H soil w as h ard in the to p an d m id d le lay er an d v ery h a rd in th e p lo u g h pan layer. In co m p ariso n , the C o n v -P an d C o n v -H soils w ere less h a rd in th e to p layer. T he C onv-P w as also less hard in th e m id d le layer.
T h e n u m b e r o f c o arse m acro p o res (> 2 m m in diam eter) d ecreased w ith d ep th fo r all soils fro m >5 p o re s dm"^ in th e to p layer to 1-5 p ores dm'^ in th e m id d le layer. T h e to p an d m id d le lay ers o f all so ils h ad ap p ro x im ately the sam e estim ated n u m b er o f m acro p o res. A sim ilar level o f fine m a cro p o res (0.5-2 m m in diam eter) w as likew ise estim ated fo r th e to p lay er o f all so ils. T h e C o n v -P soil had m ore fine m acro p o res in the m id d le lay er th an th e o th e r soils.
A ro u g h ly eq u al n u m b e r o f earth w o rm burro w s w as o b serv ed in the to p an d m id d le lay er o f all so ils (1-5 p o res dm '^). T h ere w as a tendency to a h ig h er n u m b er in th e to p lay er o f th e C o n v -P soil a n d a lo w er n u m b er in the m iddle layer o f th e C onv-H soil. T he c o n tin u ity an d o rie n ta tio n o f m acro p o res and earth w o rm burro w s w as d ifficu lt to ev alu ate. It w as d e fin ite ly im p o ssib le to ev alu a te th ese ch aracteristics fo r th e fine m acro p o res. N e v e rth e le ss a “ s lig h f ’ po re c o n tin u ity o f th e co arse m acro p o res w as estim ated in the to p lay er fo r all soils. In the m id d le lay er it w as estim ated as “ h ig h ” fo r the O rg-H an d C o n v -H an d as “m o d e ra te ” fo r th e C o n v -P soil. T h e co n tin u ity o f earth w o rm burro w s w as estim ated as “ h ig h ” in th e to p and m id d le lay er o f th e soils, ex cep t fo r the top lay er o f the C o n v -P soil w h ere it w as e stim a te d as
“ slig h t” . T he c o a rse m acro p o res and the earth w o rm b u rro w s w ere o rien ted d iffu se ly in th e top
lay er o f th e so ils (ex cep t fo r the earth w o rm bu rro w s in the O rg -H soil). In th e m id d le lay er th ey w e re o rie n te d m ain ly vertically.
A c o m p a riso n in ro o t g ro w th ch aracteristics b etw een all soils is n o t p o ssib le, b ecau se p e a w as g ro w n on th e C o n v -P soil an d spring b arley w ith g rass/clo v er u n d e rso w n w a s g ro w n o n th e o th e r soils. W h en co m p arin g th e O rg-H an d C onv-H soils a sim ilar n u m b e r o f c o arse an d fine ro o ts w ere fo u n d in th e profiles. T h e n u m b er o f co arse ro o ts (> 2 m m in d iam eter) w a s sim ila r in th e to p an d th e m id d le layers, w h ereas the n u m b er o f fine ro o ts (0 .5 -2 m m in d iam eter) d e c re a se d w ith d epth. T h is tren d w as also found fo r th e C onv-P soil. T h e n u m b e r o f ro o t n o d u le s o n th e p e a ro o ts in the C o n v -P soil also d ecreased w ith depth. A slig h t h a m p e rin g o f ro o t g ro w th w as o b serv ed at the in terface b etw een the h arro w ed to p lay er a n d th e m id d le lay er b e lo w fo r e sp ecially th e C onv-P soil. A m o re severe ro o t g ro w th re stra in w a s o b serv ed a t th e in terfa ce b etw e e n th e m id d le lay er and th e p lo u g h p a n at th e b o tto m o f th e p ro file fo r O rg -H an d C o n v -H soils.
T h e ty p e o f o rg an ic m a tte r u n d e r d eco m p o sitio n d iffered b etw een th e soils. In th e O rg -H so il o n ly ro o t re sid u e s w e re o b served, w hile in th e C o n v -H soil ra th e r p e rsiste n t ro o t a n d stu b b le re sid u e s o f th e p rev io u s m aize cro p occurred. In the C onv-P soil a large n u m b e r o f straw re sid u e s fro m th e p rev io u s cereal cro p w ere p resent. D ue to d iffe re n t ty p e s o f o rg an ic m a tte r b ein g p re se n t in th e so ils it is very d ifficu lt to com pare the ab ility o f the soils to d eco m p o se th e v is ib le o rg an ic m atter. T h is is ex p ressed as th e d eg ree o f d ec o m p o sitio n c h a racteristic an d v a rie d fro m m o d erate to go o d fo r the C onv-H and C onv-P soils to g o o d fo r th e O rg -H soil.
G en erally , the C o n v -P soil h ad th e m o st desirab le soil tilth o f the th ree stu d ied soils. It had cru m b stru ctu re to a g reater d ep th , less hard co n sisten ce w h en dry an d a larg er m acro p o ro sity . T h is d iffe re n c e ag rees w ith the d ifferen ce in b u lk d en sity (T able 2). T he tw o so ils g ro w n w ith fo rag e c ro p s h ad alm o st sim ilar characteristics. T h ere w as a ten d en c y to slig h tly p o o re r soil tilth fo r th e C o n v -H soil du e to a b lo ck ier stru ctu re in the m id d le lay er a n d a lo w e r estim a te d m acro p o ro sity . T h e less d esirab le soil tilth found on the O rg-H an d C o n v -H so ils is very lik ely d u e to sh o rt-term effects o f intensive soil tillag e an d traffic rath er th a n lo n g -te rm effects o f so il m an ag e m en t.
5.1.2 Group I I
T h ree d iffe re n t soil lay ers w ere d etec ted in b o th soils (T able 2, A p p en d ix A ). A t th e to p a lo o se a n d c ru m b -stru ctu red to p -la y e r w as observed. In the m id d le do w n to th e b o tto m o f th e p lo u g h e d la y e r a d en ser, b lo c k ie r soil w as noticed. A t th e b o tto m a d e n se r b u t ra th e r w eak p lo u g h p a n w ith a su b -an g u lar b lo ck y structure w as observed. T h e soil c o lo u r an d the m o istu re c o n te n t w e re q u ite sim ilar fo r th e soils. A p h o to o f a soil b lo ck fro m th e O rg -H so il is sh o w n in F ig u re 2.
T h e tw o so ils h ad a m atch in g soil structure (structural u n its, g rad e an d co n sisten ce ) th ro u g h o u t th e 30 c m d eep soil profile. T h e soils w ere sticky and p lastic in all lay ers w h en
w et. W h en m o ist, b o th soils had a ru p tu re resistance th a t in creased from friab le in th e to p lay er to v ery firm in th e b o tto m layer. T he soils d iffered in n u m b er o f m acro p o res (e sp e c ia lly earth w o rm b u rro w s) in the lo w er p arts o f the soil pro file and earth w o rm activ ity . T h e re w as an ex trem ely h ig h earth w o rm activ ity in O rg-H . A n ab u n d an ce o f c o arse m a c ro p o re s and earth w o rm b u rro w s (>5 p ores dm '^) w as found a t all d ep th s in the O rg -H soil. T he so ils had sim ila r n u m b e r o f fine m acro p o res in the top and m id d le lay er (>5 p o re s dm '^). A slig h tly lo w e r n u m b e r o f fin e m acro p o res w as found in the p lo u g h pan layer o f the O rg -H so il th a n in th e C o n v -H soil. In th e p lo u g h p an lay er a h ig h er c o n tin u ity o f co arse m a cro p o res an d b u rro w s w as estim a te d fo r th e O rg-H soil. M any d ifferen t h o rizo n tally an d v ertically b u rro w in g earth w o rm sp ecies w ere seen in the O rg-H soil but n o t identified.
In b o th so ils a slig h tly im peded ro o t g row th w as fo u n d at th e in terface b etw een th e m id d le lay er an d th e su b so il (w eak p lo u g h pan). T he bran ch in g o f th e ro o ts w as asse sse d e q u a lly fo r th e to p lay ers (m o d erate/stro n g ). In the p lo u g h p an lay er th e ro o ts w as less b ra n c h e d fo r th e C o n v -H so il th an fo r th e O rg -H soil. T he ab u n d an ce o f earth w o rm b u rro w s in O rg -H m ay h a v e c au sed a less restricted ro o t gro w th in the bottom lay er o f O rg-H . F o r b o th so ils a go o d d e g re e o f d e c o m p o sitio n o f straw and stu b b le w as observed.
In c o n c lu sio n , the soils h ad a v ery sim ilar an d rath er go o d soil tilth. T h ey had m ain ly cru m b stru ctu re in the p lo u g h ed lay er and a rath er w eak p lo u g h pan. T h ey d iffered m ain ly in e a rth w o rm activ ity , w h ere an ex trem ely high activity w as o b serv ed in the O rg -H soil.
5.1.3 Group III
In b o th so ils th ree layers w ere d etec ted (T ab le 3, A ppendix A ). T he p lo u g h ed lay er w as d iv id e d into a 6-7 cm d eep to p lay er w ith a m ainly cru m b ly stru ctu re and a d e n se r m ain ly b lo c k y stru ctu red lay er (7 -2 0 cm ). B elo w 20 cm d ep th a co m p ac t p lo u g h p a n w as fo u n d w ith a p re d o m in a n tly c o m p ac t m assiv e structure. T he soils had m atch in g soil c o lo u r in the p lo u g h e d layer. In th e p lo u g h p an lay er the soil w as b rig h ter in the C o n v -P th a n in O rg -H soil in d ic a tin g a lo w er c o n te n t o f o rganic m atter. A p h o to o f a soil b lo ck fro m each soil is sh o w n in F ig u re 3.
T h e C o n v -P soil h ad a d en ser and less fav o u rab le soil stru ctu re in th e w h o le 30 c m p ro file th a n O rg -H . E v e n in th e to p lay er a partially blo ck y stru ctu re w as fo u n d in th e C o n v -P soil. In th e O rg -H so il a cru m b stru ctu re w as o b serv ed in the to p lay er an d p artially in th e m id d le layer. A to ta lly m assiv e p lo u g h p an w as detected in the C onv-P soil, w h ereas it w as p a rtia lly b lo ck y in the O rg -H soil. T he u n fav o u rab le soil structure in esp ecially C o n v -P is also a p p a re n t from th e g rad e an d co n sisten ce o f the soil. T he C o n v -P soil d id n o t fractu re into a g g re g a te s (i.e. g rad e = m assiv e) in p art o f the m id d le and in th e p lo u g h p a n layer. O n th e o th e r h a n d th e O rg -H soil fractu red m o d erately into w hole ag g reg ates (i.e. g rad e =
“ m o d e ra te ” ) in m o st o f th e p ro file in O rg-H soil. T he rupture resistan ce o f m o ist soil in c re a se d from “ firm ” in th e to p lay er to “ex trem ely firm ” in th e p lo u g h p a n in th e C o n v -P soil. F o r th e O rg -H soil th e ru p tu re resistan ce w as classified as “ friab le” in th e u p p e r lay er an d “ very firm ” in th e p lo u g h p an layer.
20
C o n cern in g m acro p o res an d earth w o rm bu rro w s, no sig n ifican t d ifferen ce w as d ete c te d b etw een th e soils. D esp ite th at, a h ig h er n u m b er o f especially h o rizo n tally b u rro w in g ea rth w o rm s w a s o b serv ed in th e C onv-P soil com pared to the O rg -H soil. R o o t g ro w th w as sev erely h a m p e re d in b o th soils. A b n o rm al ro o t g ro w th w as seen in fo rm o f b e n d e d /d e fle c te d an d th ic k e n e d ro o ts at th e interface b etw een th e u p p er and th e m id d le lay er a n d m o st sev erely at th e cro ssin g to th e p lo u g h p a n layer. T he n u m b er o f coarse ro o ts w as lo w in b o th soils. T he n u m b e r o f fine ro o ts d ecreased w ith d ep th in bo th soils - alth o u g h m o st d rastica lly in the C o n v -P soil.
In b o th so ils a reas w ith p o o r d e co m p o sitio n (eith er slow o r an aero b ic d e c o m p o sitio n ) w ere fo u n d . M o st o f th e a p p lied o rg an ic m atter (straw and stu b b le) w as lo cated a t th e b o tto m o f th e p lo u g h layer. S o m e o f the m aterial w as eith er still to u g h (no sig n o f d e c o m p o sitio n ) o r w as b la c k a n d sm elled m u sty (anaerobic d e co m p o sitio n ) F ig u re 4.
In g e n e ra l b o th soils had a ra th e r p o o r soil tilth. A cru m b structure w as p re s e n t o n ly in th e to p h a rro w e d lay er an d severe ro o t restrictio n w as o b serv ed at the in terface b e tw e e n th e th ree layers. N e v e rth e le ss th e O rg -H soil h ad a m o re d esirab le soil tilth th an th e c o m p a c t a n d h ard C o n v -P soil.
5.2 Effect o f soil tillage - Group IV
T he so ils w ere b o th d iv id ed into th ree ch aracteristic layers (T ab le 4, A p p e n d ix A ). A n u p p er c ru m b stru ctu red lay er w as o b serv ed fo r b o th treatm en ts on top o f a d e n se r la y e r th a t rea c h e d to th e b o tto m o f th e p lo u g h ed o r o ld p lo u g h ed layer. A t the b o tto m a stro n g ly c o m p a c te d p lo u g h p an w as o b serv ed in th e T T treated soil and th e rem ain s o f an o ld p lo u g h p a n w as d e te c te d in th e N IT tre a te d soil. T he soils w ere “m o ist” in all layers an d h a d sim ila r soil c o lo u r w ith in th e sp ecifie d layers. T he d ifferen tly treated soils w ere slig h tly p la stic an d slig h tly stick y w h en w et. W h en m o ist the soils w ere friable in th e p lo u g h ed la y e r a n d firm in th e b o tto m layer. P h o to s o f a so il b lo ck from each soil are sh o w n in F ig u re 5. A n e x a m p le o f a c o m p a c t p lo u g h p an is illu strated in F ig u re 6.
A larg e n u m b e r o f fin e m acro p o res (>5 p o res dm '^) w as o b serv ed in all layers o f th e N IT tre a te d soil. In th e T T treated soil the n u m b er o f fine m acro p o res d ecreased fro m >5 p o res dm '^ in th e to p lay er to <1 o r 1-5 p o res dm '^ in th e p lo u g h p a n layer. T he estim a te d co n tin u ity o f c o arse m a c ro p o re s im p ro v ed from “ slig h t” in the to p lay er to “m o d e ra te /h ig h ” in th e b o tto m lay er fo r b o th treatm en ts. A d ifferen ce b etw een the treatm en ts w as foim d re g a rd in g th e c o n tin u ity o f e a rth w o rm burrow s. T he h ig h est c o n tin u ity w as estim ated fo r th e T T tre a te d soil. In b o th tre a tm e n ts a h am p ered ro o t gro w th w as no ticed - b u t m o st sev erely in th e T T treated soil (F ig u re 7). R estricted ro o t g ro w th w as n oticed at the cro ssin g to th e m id d le lay er a n d at th e in terfa ce b e tw e e n th e m id d le an d p lo u g h p an layer. T h e n u m b e r o f ro o t n o d u le s seem ed to b e n e g a tiv e ly affected by th e p o o r soil structure in th e p lo u g h p an lay er o f th e T T tre a te d soil. F e w e r ro o t n o d u les w ere o b serv ed in the T T treated soil th a n in th e N IT treated soil (F ig u re 8).
Some horizontally and vertically burrowing earthworms were observed in the investigated soil blocks o f the NIT treated soil. No earthworms were seen in the TT treated soil blocks.
The degree o f decomposition was assessed as “good” for both treatments.
In conclusion, both soils had a fairly good soil tilth down to the plough pan layer. The successful loosening o f the plough pan in the NIT treated soil means that this soil had the most desirable soil structure.
5.3 G eneral discussion 5.3.1 Generalfindings
In the nine investigated soils the 30 cm soil profile could be divided into three characteristic layers reflecting the past and present tillage practices. At the top a 5-8 cm deep intensely cultivated layer was found, where the soil in most cases had a cnmib structure. In the middle (approximately 7-22 cm) a denser crumb to blocky-structured layer was found. A dense, blocky to compact massive plough pan was found at the bottom o f all soils except for the deep loosened soil (NIT) in the tillage experiment. An increase in rupture resistance and a decrease in macroporosity with depth also reflected the general increase in density with depth.
Root growth was restricted at the interface between all layers. A rather weak root restriction was observed at the interface between the loose, intensely cultivated top layer and the middle layer. On the other hand, severe root growth restriction was seen at the transition to the plough pan layer. This was especially the case for the Group 111 soils and the TT treated soil in the tillage experiment. In the plough pan roots grew mainly in macropores in the form o f old root channels and earthworm burrows and only a few roots had grown into the bulk o f the soil. The nodulation o f pea roots seemed to be negatively affected by soil compaction (i.e.
“few” root nodules on pea roots in the plough pan in the TT treated soil, whereas it was
“common” for NIT treated soil).
Earthworm activity was evaluated on the basis o f the number and characteristics o f
earthworm burrows and the number and species identified while excavating the soil block. An evaluation o f earthworm activity should not rely solely on the latter. The soil block is too small a unit to give a representative sample of the number o f earthworms present in the soil.
Moreover some o f the earthworms would have escaped while digging out the sample. Lastly, a significant number o f vertically burrowing species like Lumhricus terrestris may be located below 30 cm depth.
In one case a clear difference in earthworm activity was noticed. The Org-H(II) soil had an extremely high activity compared to all the other soils including its counterpart (Conv-H(II)).
The degree o f decomposition o f organic matter was assessed “good” in most soils except for the Group III soils. In these soils with a prominent plough pan, areas o f poor decomposition were observed.
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5.3.2 Compacted layers
In all soils plough pans occurred. This agrees with other recent studies in Denmark that subsoil compaction occurs extensively in many Danish soils (e.g. Schjønning, 1989;
Schjønning and Rasmussen, 1989; Rasmussen et al. 1995). The development o f plough pans is caused by the traffic o f machinery on the soil surface and by the pressure and slippage o f tractor tyres in the furrow when ploughing. Harmful soil compaction is not a new problem (see e.g. Soane and Van Ouwerkerk, 1994), but the problems have supposedly escalated during recent years because o f a sharp increase in the size and weight o f agricultural
machinery. In the early work on the spade diagnosis the problem o f compacted plough pans is highlighted (Görbing, 1947 and Teipel, 1952 a, b). According to Teipel (1952a) Görbing assessed that plough pans were present in about 80% o f the many soils that he had
investigated throughout the years (1920-1947). Teipel found plough pans in more than 60% o f the 140 soils from Thüringen, Germany that were investigated by the spade diagnosis. The soils ranged from heavy clay soils to sandy soils. In recent years Preuschen (1994) has emphasised the negative impact o f tillage pans on soil tilth.
As a measure o f remedying and avoiding the formation o f plough pans Görbing proposed that primary cultivation was performed with a plough that combines an inverting tillage o f the upper 10-15 cm o f the soil with deep non-inverting soil loosening to more than 30 cm depth.
Hampl et al. (1995) advocates a similar primary tillage system as being particularly suitable in organic farming.
5.3.3 Long-term and short-term effects
There was no clear trend in the results o f the spade analysis concerning long-term effects o f different soil management. The application o f organic matter and a versatile crop rotation were expected to result in improved soil tilth as found by e.g. Reganold (1988). The results from the Group II and III soils support this hypothesis. Conversely, the results from the Group I soils show the opposite trend. The beneficial effects o f application o f organic manure and a forage crop rotation for the Org-H(I) and Conv-H(I) soils have probably been blurred by negative effects o f soil compaction in the plough layer. This finding agrees with e.g.
Munkholm et al. (1999a) who found that heavy soil compaction in early spring on wet soil after primary cultivation had a marked negative effect on soil structure in the seedbed (i.e.
increased penetration resistance and strength o f soil aggregates, and decreased soil fiiability).
Soil compaction o f the plough layer may be especially critical on the Org-H(I) soil, which has a very low Olsen-P content. On this soil, optimal growth conditions are needed to be able to extract the strongly bound P. This is the case for both the plant roots and the arbiscular mycorrhizal flmgi. The latter may take up a considerable part o f the P associated with the plant roots (George et al., 1995). The combination o f a compact and a soil low in plant available P may be one o f the main reasons for the generally low yield level recorded on the farm with the Org-H(I) soil (Jensen and BCristensen, 1998).
