Learning from a long-term crop rotation experiment

A crop rotation experiment was established in 1996/97 at three locations representing differ-ent soil types and climates. Three factors were tested: i) crop rotation with different propor-tions of N2-fixing crops, ii) with and without a catch crop, and iii) with and without animal manure. A green manure crop increased yields in the following cereal crops, but at the rota-tional level, total yields were larger in crop rotations without a green manure crop. There were positive effects of animal manure and catch crops on yield. However, except for the coarse sandy soil, the yield effects of catch crops and animal manure decreased over time when a grass-clover green manure was included in the rotation. The problems with perennial weeds increased over time depending on crop rotation and use of catch crops. This stresses the im-portance of considering long-term effects in the evaluation of crop management measures

Nitrogen use efficiency of cereals in arable organic farming

The effect of nitrogen (N) supply and weeds on grain yield of spring barley, winter wheat and winter rye was investigated from 1997 to 2004 in an organic farming crop rotation experiment in Denmark on three soil types varying from coarse sand to sandy loam. Two experimental factors were included in the experiment in a factorial design: 1) catch crop (with and without), and 2) manure (with and without). The apparent recovery efficiency of N in grains (nitrogen use efficiency, NUE) from NH4-N in applied manure varied from 29 to 38% in spring barley and from 23 to 44% in winter cereals. The NUE of above-ground N in catch crops sampled in November prior to the spring barley varied from 16 to 52% with the largest value on the coarse sandy soil and the smallest value on the sandy loam soil. The NUE of N accumulated in grass-clover cuttings varied from 14 to 39% with the lowest value on the coarse sandy soil, most likely due to high rates of N leaching. The NUE declined with increasing amounts of N accumulated in the grass-clover cuttings. This indicates that grain yields can be improved by removing the grass-clover cuttings and applying the N contained in the cuttings in spring to the cereal crops, possibly after fermentation in a biogas reactor

Plant protection in an organic crop rotation experiment for grain production

The plant protection carried out in the Danish crop rotation experiment is described. These measures can be quite different in the different systems. While mechanical weed control can be carried out in systems without catch crops, it is not possible to do so in systems with catch crops without affecting the establishment of the catch crop. The occurrence of weeds, pests and diseases is recorded, and the results are described. Since the results are only from the two first years of the experiments, it is not possible to conclude anything about the crop rotations as such. There are however differences related to the other experimental treatments in the experiment: the presence or absence of catch crops and manure. Only in very few cases are the differences statistically significant

Weed control in organic crop rotation experiments for grain production

Weed control methods in organic crop rotation experiments for grain production. Preliminary results

Sædskiftets og gødskningens betydning for udbytte i vårbyg

Effekten af kvælstofforsyning og ukrudt på kerneudbytter i vårbyg blev undersøgt fra 1997 til 2007 i et økologisk sædskifteforsøg på tre jordtyper i Danmark. Resultaterne viser at det er muligt at få tilfredsstillende udbytter ved at kombinere kvælstoffikserende efterafgrøder og en moderat mængde husdyrgødning

Incompatibility between fertility building measures and the management of perennial weeds in organic cropping systems

Fertility building measures are important components in improving the productivity of organic cropping systems without livestock. However, some measures seem to be incompatible with the control of perennial weeds that can have adverse effects such as significant weed competition. The influence of fertility building measures (N2-fixing crops in the crop sequence, cover crops and manuring) and the abundance of perennial weeds were studied in a long-term crop rotation experiment at two locations in Denmark. The aim was to gain insight into the factors that influence the growth of perennial weed species occurring in mixed stands. Data were obtained from three cycles of four-year arable crop rotations comprising various cash crops in rotations with and without annual whole-year grass-clover as green manure and subjected to four treatment combinations: with and without animal manure and with and without cover crops. Severe outbreaks of perennial weed problems did not occur at the location that had the highest soil fertility, whereas the other site demonstrated dynamic growth of Cirsium arvense and Elytrigia repens. Grain legumes tended to promote the growth of C. arvense, while manuring was neutral to C. arvense but beneficial to E. repens. Cover crops assisted the growth of E. repens since prolonged mechanical interventions were not possible. Compatibility was only achieved with grass-clover and C. arvense, meaning that green manure crops suitable for cutting and mulching could offer an important management option against C. arvense but not against E. repens

The Danish organic crop rotation experiment for cereal production 1997-2004

In 1997 a crop rotation experiment was initiated at three sites in Denmark. The objective of the experiment was to explore the possibilities for both short-term and long-term increases in organic cereal production through manipulation of crop rotation design on different soil types. The experiment included three factors (proportion of grass-clover in the rotation, catch crops and manure application) in a randomised factorial design. The main indicators measured in the experiment were crop yield, nutrient leaching and weeds. The crop rotation experiment has shown significant effects of location, crop rotation, catch crops and manure on yields, weed infestation, soil fertility and nutrient losses (Olesen et al., 2002; Schjønning et al., 2004; Askegaard et al., 2005a, b; Rasmussen et al., 2005, 2006). There were indications of changes of some of these effects over time as a result of the ‘buffering power’ of grass-clover, where the N2-fixation is affected by crop management and soil fertility. This buffering power will probably not only affect yields but also the risk of N losses, and there is a need to further investigate possibilities of controlling N supply to the crops better through improved use of green manure crops, catch crops and manure at the crop rotation level. Perennial weeds (especially C. arvense and E. repens) have proliferated severely in the crop rotation experiment at two of the three locations during the experimental period, and these weeds may seriously reduce yields in organic arable farming. Direct control of perennial weeds is typically carried out by stubble cultivation in autumn, reducing the possibilities for growing catch crops. The energy use, as well as the elevated risk for nutrient leaching, jeopardizes the sustainability of this practice, and therefore cultivation should be avoided (Rasmussen et al., 2006). The crop rotation experiment has shown that the occurrence of these weeds is significantly affected by the choice of crops and catch crops, and by the addition of manure. However, this needs to be further substantiated, and the effects of weed infestation on yields, as well as the interaction with fertility level needs to be quantified. Crop production in organic farming systems relies to a large extent on soil fertility for nutrient supply. The soil fertility must be maintained via choice of crop rotation and (green) manuring practices. Fertility building by such means requires a long-term integrated approach, rather than the short-term and targeted solutions common in conventional agriculture (Watson et al., 2002). It follows that, for studies of management effects on soil fertility, long-term cropping experiments are indispensable

Weed control in organic crop rotations for grain production

Weed management carried out in organic crop rotation experiments for grain production. Preliminary results

Konsekvenser af at nedsætte input af næringsstoffer på bedriften

I dag må der tilføres 70 kg kvælstof pr. ha i ikke-økologisk husdyrgødning. Hvis det blev besluttet at stoppe for denne mulighed, kunne det tænkes at have både direkte og indirekte indflydelse på udbytte,kvalitet,andre næringsstoffer end kvælstof,udvaskning af næringsstoffer,etablering af efterafgrøder samt ukrudt og andre skadevolder

Ukrudt i økologiske kornsædskifteforsøg

Der er igangsat forsøg med økologiske sædskifter på fire forskellige steder i Danmark, afspejlende forskellige klima- og jordbundsforhold. De fire sædskifter har forskellig andel af kvælstoffikserende afgrøder hhv. korn til modenhed, med og uden fangafgrøder og med og uden husdyrgødning. Forsøgene har været gennemført i 1997 og 1998. I forsøgene er bl.a. registreret ukrudt. Det er for tidligt at sige noget om ukrudtets udvikling i de forskellige sædskifter. Der er mest ukrudt i vintersæden begge forsøgsår alle steder. I 1997 er der i de vårsåede afgrøder mest ukrudt i byg/ært. Der er signifikant mest ukrudt i de gødede led af vinterhveden i forhold til de ugødede i Flakkebjerg 1997 og Foulum 1998. Ukrudtsbekæmpelsen har kun haft signifikant effekt på ukrudtets biomasse i vinterhveden i Foulum, hvor der i 1997 er mest ukrudt i de ubehandlede led, i 1998 er mest ukrudt i det børsterensede led, men næstmest i det ubehandlede. I Flakkebjerg var der i 1997 signifikant færrest ukrudtsplanter i havren i de ukrudtsharvede led. Der forekom i 1998 alm. kvik alle steder bortset fra i Foulum, og agertidsler i Flakkebjerg. Efter høst var der signifikant færre tidsler i parceller med efterafgrøde end uden