Textbox 1 Method of establishment of reduced standard N rates in Denmark based on working papers and notes from The official committee on standard N rates, nitrogen prognosis and nitrogen in animal
7.4 Hypothesis 3: More grass weeds survive herbicide treatments resulting in higher weed coverage at harvest
A comparison of Apera spica-venti coverage at harvest against year did not reveal any signifi-cant correlation, although weed coverage tended to be higher in recent years than previously following application of reduced herbicide doses. The results may have been affected by the fact that Apera spica-venti often wilted and was partly vanished at harvest time, making it difficult to distinguish between this grass weed and other plant residues.
Figure 7.7 shows the effect of reduced herbicide doses versus year and it is obvious that un-satisfactory effects were more common in recent years than in the beginning of the 10-year period. It is likely that a reduced efficacy explains the observed trend towards higher weed coverage at harvest, although it should be stressed that environmental factors, in particular soil moisture, will be an important parameter determining whether surviving weeds will con-tinue to grow during the summer.
y = 5,0173Ln(x) - 3,0007 R2 = 0,1598
0 5 10 15 20 25 30 35 40 45 50
0 50 100 150 200 250 300
Apera spica-venti density (plants/m2)
Yield increase (hkg/ha)
Figure 7.6 Apera spica-venti density in control plots versus yield increase following application of the recommended herbicide dose in winter wheat herbicide trials carried out by the Danish Agricultural Advisory Service from 1998 to 2007.
Conclusions: High grass weed densities resulted in higher yield increases following applica-tion of recommended and reduced herbicide doses, but the analysis of the DAAS data set could not confirm the hypothesis that grass weed densities have increased during the last 10 years.
7.4 Hypothesis 3: More grass weeds survive herbicide treatments resulting in higher weed coverage at harvest
A comparison of Apera spica-venti coverage at harvest against year did not reveal any signifi-cant correlation, although weed coverage tended to be higher in recent years than previously following application of reduced herbicide doses. The results may have been affected by the fact that Apera spica-venti often wilted and was partly vanished at harvest time, making it difficult to distinguish between this grass weed and other plant residues.
Figure 7.7 shows the effect of reduced herbicide doses versus year and it is obvious that un-satisfactory effects were more common in recent years than in the beginning of the 10-year period. It is likely that a reduced efficacy explains the observed trend towards higher weed coverage at harvest, although it should be stressed that environmental factors, in particular soil moisture, will be an important parameter determining whether surviving weeds will con-tinue to grow during the summer.
0 20 40 60 80 100 120
1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
Year
Percent effect
Figure 7.7 Effect of reduced herbicide doses on Apera spica-venti in winter wheat herbicide trials carried out by the Danish Agricultural Advisory Service from 1998 to 2007. Efficacy was assessed in April.
When plotting weed density at spraying versus weed coverage at harvest a positive correlation was found for control plots, whereas no correlation was seen for plots treated with the rec-ommended dose. For plots treated with reduced herbicide doses a weak correlation was ob-served, supporting the conclusion that the effect of reduced doses in some experiments was insufficient to prevent residual weeds at harvest.
Conclusion: In recent years a decreasing effect of reduced herbicide dosages was observed, but no clear evidence was found supporting the hypothesis that grass weed coverage at har-vest has increased during the last 10 years.
7.5 Conclusions
The analysis of the DAAS data set and previous research supported our first hypothesis, that early sowing leads to increasing problems with grass weeds. We could, however, not confirm that Apera spica-venti densities have increased in recent years, but our analysis confirmed that Apera spica-venti is a very competitive weed species and an increase in density could lead to higher yield losses if not controlled satisfactorily. Similarly, we could not confirm that Apera spica-venti coverage at harvest has increased in recent years, but we did find indications that the effect of reduced doses has diminished within the last years, suggesting that residual weeds at harvest and the associated seed production could become a problem in the future.
0 20 40 60 80 100 120
1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
Year
Percent effect
Figure 7.7 Effect of reduced herbicide doses on Apera spica-venti in winter wheat herbicide trials carried out by the Danish Agricultural Advisory Service from 1998 to 2007. Efficacy was assessed in April.
When plotting weed density at spraying versus weed coverage at harvest a positive correlation was found for control plots, whereas no correlation was seen for plots treated with the rec-ommended dose. For plots treated with reduced herbicide doses a weak correlation was ob-served, supporting the conclusion that the effect of reduced doses in some experiments was insufficient to prevent residual weeds at harvest.
Conclusion: In recent years a decreasing effect of reduced herbicide dosages was observed, but no clear evidence was found supporting the hypothesis that grass weed coverage at har-vest has increased during the last 10 years.
7.5 Conclusions
The analysis of the DAAS data set and previous research supported our first hypothesis, that early sowing leads to increasing problems with grass weeds. We could, however, not confirm that Apera spica-venti densities have increased in recent years, but our analysis confirmed that Apera spica-venti is a very competitive weed species and an increase in density could lead to higher yield losses if not controlled satisfactorily. Similarly, we could not confirm that Apera spica-venti coverage at harvest has increased in recent years, but we did find indications that the effect of reduced doses has diminished within the last years, suggesting that residual weeds at harvest and the associated seed production could become a problem in the future.
In conclusion, although grass weeds cause significant yield losses, our analyses of the DAAS dataset do not suggest that the observed stagnation in winter wheat yields can be attributed to increasing problems with grass weeds.
7.6 References
Amann A, Zwerger P. & Hurle K. (1992) Einfluss von Saattermin und Grundboden bearbei-tung auf die Populationsdynamik von Alopecurus myosuroides Huds. in verschiedenen Kulturen. Zeitschrift für Pflanzenkrankheiten und Pflanzenschutz, Sonderheft XIII, 269-276.
Andreasen, C., Stryhn H. & Streibig J.C. (1996) Decline of the flora in Danish arable fields.
Journal of Applied Biology 33, 619-626.
Andreasen, C. & Stryhn H. (2008) Increasing weed flora in Danish arable fields and its im-portance for biodiversity. Weed Research 48, 1-9.
Christensen, S. (1993) Herbicide dose adjustment and crop weed competition. Brighton Crop Protection Conference-Weeds, 1217-1222.
Christensen, S., Rasmussen, G., Olesen, J.E. & Jørgensen L.N. (1996) Weed management for integrated wheat production. Proceedings Second International Weed Control Congress, Copenhagen, Denmark, 1003-1008.
Jensen, J.E. & Petersen, P.H. (2006) Økonomi ved efterårsbehandling af ukrudt i vintersæd.
Præsentation ved Efterårsmøde 2006 i Middelfart.
Olsen, C.C., Jørgensen, L.N., Rasmussen, G. & Pedersen, J.B. (1997) Integreret vinterhvede-dyrkning-såtider og udsædsmængder. Danmarks JordbrugsForskning, Grøn Viden Markbrug nr. 184.
Melander, B. (1995) Impact on drilling date on Apera spica-venti L. and Alopecurus myosu-roides Huds. in winter wheat. Weed Research 35, 157-166.
Moss, S.R. (1985) The effect of drilling date, pre-drilling cultivations and herbicides on Alo-pecurus myosuroides (blackgrass) populations in winter wheat. Aspect of Applied Biol-ogy 9, 31-39.
In conclusion, although grass weeds cause significant yield losses, our analyses of the DAAS dataset do not suggest that the observed stagnation in winter wheat yields can be attributed to increasing problems with grass weeds.
7.6 References
Amann A, Zwerger P. & Hurle K. (1992) Einfluss von Saattermin und Grundboden bearbei-tung auf die Populationsdynamik von Alopecurus myosuroides Huds. in verschiedenen Kulturen. Zeitschrift für Pflanzenkrankheiten und Pflanzenschutz, Sonderheft XIII, 269-276.
Andreasen, C., Stryhn H. & Streibig J.C. (1996) Decline of the flora in Danish arable fields.
Journal of Applied Biology 33, 619-626.
Andreasen, C. & Stryhn H. (2008) Increasing weed flora in Danish arable fields and its im-portance for biodiversity. Weed Research 48, 1-9.
Christensen, S. (1993) Herbicide dose adjustment and crop weed competition. Brighton Crop Protection Conference-Weeds, 1217-1222.
Christensen, S., Rasmussen, G., Olesen, J.E. & Jørgensen L.N. (1996) Weed management for integrated wheat production. Proceedings Second International Weed Control Congress, Copenhagen, Denmark, 1003-1008.
Jensen, J.E. & Petersen, P.H. (2006) Økonomi ved efterårsbehandling af ukrudt i vintersæd.
Præsentation ved Efterårsmøde 2006 i Middelfart.
Olsen, C.C., Jørgensen, L.N., Rasmussen, G. & Pedersen, J.B. (1997) Integreret vinterhvede-dyrkning-såtider og udsædsmængder. Danmarks JordbrugsForskning, Grøn Viden Markbrug nr. 184.
Melander, B. (1995) Impact on drilling date on Apera spica-venti L. and Alopecurus myosu-roides Huds. in winter wheat. Weed Research 35, 157-166.
Moss, S.R. (1985) The effect of drilling date, pre-drilling cultivations and herbicides on Alo-pecurus myosuroides (blackgrass) populations in winter wheat. Aspect of Applied Biol-ogy 9, 31-39.
8 Soil tillage effects on the development of winter wheat yields in Denmark Per Schjønning 1), Jens J. Høy 2) & Lars J. Munkholm 1)
1) Aarhus University, Faculty of Agricultural Sciences (DJF), Department of Agroecology and Environment
2) Agrotech – Institute for Agri Technology and Food Innovtion
8.1 Introduction
Soil tillage is a key operation in arable farming and fulfils several purposes, which may be integrated in three main characteristics:
• Crop residues and applied organic manures are incorporated into the soil, enhancing decomposition of organic matter and removing pest sources from the very surface
• Traffic-induced hardpans in the top soil layers are loosened, which facilitates root growth, water infiltration and soil aeration
• Weeds are suppressed
Tillage for establishing a new crop is most often a two-step procedure with a primary tillage operation for obtaining the benefits described above, and a secondary tillage operation for creating a seedbed optimizing seed germination and early plant growth. The primary tillage operation in Denmark has traditionally included moldboard ploughing to a depth of 20-25 cm (Rasmussen, 1999). However, recent experience has shown that plough-less tillage (often labelled reduced tillage) is possible prior to many crops (Olesen et al., 2002). A major driver towards reduced tillage systems is the reduction in costs and the ability to till a larger area with the same man-power. The same holds for the trend towards power-take-off (pto) harrows that are very efficient in creating a seedbed nearly irrespective of the soil water content.
This chapter reviews the knowledge of tillage effects on winter wheat yield for Danish soil and climatic conditions. An initial text section highlights some key soil characteristics that should be kept in mind when addressing soil tillage from a soil functional perspective and not an efficiency approach. Next, one section deals with ploughless tillage, while a final section addresses tillage for seedbed preparation.
8.2 Soil structure, self-organization, soil organic matter and principles in tillage