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Leguminous pre-crops are an important source of green manure in organic crop rotations for improving soil fertility and achieving high yields of cereals. We aimed to study the potential of various leguminous species, other than the traditionally cultivated red clover (Trifolium pratense L.), as green manure pre-crops for subsequent cereals. The use of different legume species enables to exploit advantages of specific legumes in organic cereal production. In order to test the legumes as pre-crops for cereals, we carried out trials located in the temperate climate zone of northeast Europe (58°44'59.41'' N, 26°24'54.02'' E). We sowed the following perennial legumes as pre-crops: red clover, alsike clover (Trifolium hybridum L.) and Washington lupine (Lupinus polyphyllus Lindl.), biennial white sweet clover (Melilotus albus Medik.) and annual Alexandria clover (Trifolium alexandrinum L.), and crimson clover (Trifolium incarnatum L.). Timothy (Phleum pratense L.) was used as a control. The leguminous pre-crops were followed by three spring cereals (barley, oat and spring wheat) and two winter cereals (rye and winter wheat). We tested the first-year after-effect (all cereals) and second-year aftereffect (only barley and oat) of pre-crops on the grain yield of cereals. Perennial and biennial legume species produced the highest dry matter yield and contained the highest amount of nutrients, especially nitrogen, compared to annual species. All subsequent cereals produced significant extra yields after each leguminous pre-crop in the following two years, although the effect was smaller in the second year. The most suitable pre-crops for spring cereals were red and alsike clover followed by lupine, whereas the best pre-crops for winter cereals were sweet clover and annual clovers. Our results show the potential of various leguminous precrop species as valuable sources of green manure in organic crop rotation. [ABSTRACT FROM AUTHOR]

This study examined whether the N release pattern during decomposition of plant materials used as green manures can be modified in the short term through mixing plant materials with different levels of easily degradable compounds. In a lysimeter study, white clover shoots were mixed with perennial ryegrass shoots or chicory roots. Leaching of clover N was decreased more by inclusion of chicory than by ryegrass. However, decreased leaching losses over the non-growing season did not lead to enhanced N uptake by the crop during the following growing season. [ABSTRACT FROM AUTHOR]

Microbial communities are integral parts of the soil and their activity is very important to the functioning of the soil but the impact of different factors on soil microbial community composition is not well researched. Many studies have focused only on a few species. The aim of this study was to investigate the impact of treatment and sampling date on soil pH, abundance of total number of bacteria, molds, yeasts, mesophilic spore-forming bacteria, Fusarium spp., actinomycetes, azotobacteria, cellulose decomposers, denitrifying and nitrifying bacteria in organically (ORGGRM – green manure, and ORGFYM – green manure, solid cattle manure) and conventionally (CONFYM – solid cattle manure + mineral fertilizer and pesticides) cultivated soil. Fertilization with manure had positive direct- and after-effect (p<0.05) on the total number of bacteria, mesophilic spore-forming bacteria, nitrifying bacteria and cellulose decomposers, even in the CONFYM treatment. The abundance of yeasts was higher (p<0.05) in ORGFYM treatment (3.35×103) and 34–48% lower in CONFYM and ORGGRM treatments. The abundance of molds, Fusarium spp., and actinomycetes during the study in different treatments was similar but their abundance was significantly higher (p<0.05) when the weather in the sampling time was warm and humid. The negative impact of pesticides in CONFYM treatment occurred on the total number of bacteria, yeasts, molds, and denitrifying bacteria. The yeasts were most sensitive to pesticides; in study years, when the use of pesticides was very intensive, their abundance in CONFYM treatment decreased 72% compared with the ORGFYM treatment. The 4-year test results showed that although green manuring is considered an important management practice in organic cultivation, to maintain and increase the abundance of microbes in different microbial communities it is important to use other organic fertilizers such as animal manure in addition to green manure. [ABSTRACT FROM AUTHOR]

Cover crops can be used to reduce leaching and erosion, introduce variability into crop rotation and fix nitrogen (N) for use by the main crops, less is however known about effects on weeds. The effects on weed seed bank, weed growth and grain yield of 4 years of annual undersown clover and ryegrass alone and in combination, and one of the 4 years with clover or clover + grass as green manure, were studied in oat and spring wheat at two experimental sites in south-eastern Norway. These treatments were compared with no undersown crop (control) and with weed harrowing. In contrast to many results in the literature, the undersown clover in this study did not suppress annual weeds, but fertilized the weeds as well as the cereals. Undersown clover resulted in a statistically significant increase of grain yield at the two sites to 116% and 121% of control. During the 4-year period relative seed bank and density of emerged weed (dominated by Spergula arvensis) increased significantly about 4.5 and 10 times respectively in the undersown clover plots at Apelsvoll. At Kise both ryegrass alone and ryegrass mixed with clover significantly suppressed the weed biomass to 70% and 74% of control respectively. It is concluded that fertilization effects of undersown clover may have dominated and overriden the competitive effects. One whole-season clover green manure did not increase the mean yield, but resulted in a significant drop in seed bank size the following year, because of limited weed establishment in an established ley. Only a slight increase in average weed biomass was observed at one of the two experimental sites. The weed seed bank and the weed biomass were essentially kept at steady state during the experimental period in harrowed plots, but harrowing decreased grain yield significantly at both sites. [ABSTRACT FROM PUBLISHER]

Single and combined effects were studied of root length, burial depth, cutting and competition from a seasonal green manure crop on the growth and development of C. arvense from roots found in the upper soil layer. The experiment was performed under field conditions and partly repeated in a green house. The green manure consisted of a mixture of phacelia, common vetch, red clover and Italian ryegrass. Root fragments of 5 and 10 cm length were buried at 5 and 15 cm soil depth, simulating soil tillage. Use of green manure alone reduced growth of C. arvense more than any other single factor (81–99%), while root length and burial depth were more variable in their effect (0–96% reduction). Combined treatments involving both green manure, deep root burial (15 cm) and short root length (5 cm) reduced growth of C. arvense consistently by 95–100%. At the minimum regenerative capacity of C. arvense the number of leaves was 3–7 in plots with no green manure, at which time cutting had the greatest effect on regrowth the following year. The level for minimum regenerative capacity was not possible to decide for C. arvense growing in competition with green manure. Combined multiple treatments in spring, including use of green manure and mechanical operations in the upper soil layers, appear to be a potential means of reducing C. arvense infestations. [ABSTRACT FROM PUBLISHER]

By restricted access to manure, nitrogen (N) supply in organic agriculture relies on biological N-fixation. This study compares grain yields after one full-season green manure (FSGM) to yields with repeated use of a green-manure catch crop. At two sites in south-eastern Norway, in a simple 4-year rotation (oats/wheat/oats/wheat), the repeated use of ryegrass, clover, or a mixture of ryegrass and clover as catch crops was compared with an FSGM established as a catch crop in year 1. The FSGM treatments had no subsequent catch crops. In year 5, the final residual effects were measured in barley. The yield levels were about equal for grains with no catch crop and a ryegrass catch crop. On average, the green-manure catch crops increased subsequent cereal yields close to 30%. The FSGM increased subsequent cereal yields significantly in two years, but across the rotation the yields were comparable to those of the treatments without green-manure catch crop. To achieve acceptable yields under Norwegian conditions, more than 25% of the land should be used for full-season green manure, or this method combined with green-manure catch crops. The accumulated amount of N in aboveground biomass in late autumn did not compensate for the N removed by cereal yields. To account for the deficiency, the roots of the green-manure catch crops would have to contain about 60% of the total N (tot-N) required to balance the cereal yields. Such high average values for root N are likely not realistic to achieve. However, measurement of biomass in late autumn may not reflect all N made available to concurrent or subsequent main crops. [ABSTRACT FROM AUTHOR]

A field experiment was conducted in 2004-2006 to investigate the effect of green manure treatments on the yield of oats and spring barley. In the experiment, different green manure crops with undersowing and pure sowing were compared for amounts of N, C, and organic matter driven into soil and their effect on cereal yield. The spring barley field had a total of 41.7-62.4 kg N ha-1 and 1.75-2.81 Mg C ha-1 added to the soil with straw, weed, and roots, depending on the level of fertilisation; with red clover, and both common and hybrid lucerne undersowing, with barley straw and roots, the values were 3.45-3.96 Mg C ha-1 and 139.9-184.9 kg N ha-1. Pure sowings of these three leguminous green manure crops had total applications of 3.37-4.14 Mg C ha-1 and 219.7-236.8 kg N ha-1. The mixed and pure sowing of bird's-foot trefoil provided considerably less nitrogen and carbon to the soil with the biomass than with the other leguminous crops. Application of biomass with a high C/N ratio reduced the yield of the succeeding spring cereals. Of the green manures, the most effective were red clover and both common and hybrid lucerne, either as undersowing or as pure sowing. Undersowings with barley significantly increased the N supply for the succeeding crop without yield loss of the main crop compared with the unfertilised variant. Compared with ploughing-in of green manure in autumn, spring ploughing gave a 0.2-0.57 Mg ha-1 larger grain yield. [ABSTRACT FROM AUTHOR]

A study carried out in Uppsala, Sweden, compared three legumes: red clover (Trifolium pratense), lucerne (Medicago sativa) and yellow sweet clover (Melilotus officinalis) as a green manure for an early and late crop of Iceberg lettuce (Lactuca sativa crispa). Differences between the treatments were only apparent in the early crop of lettuce. With the early crop, the dry matter content of the leguminous green manure was more significant in effect on yield than its nutrient content. Red clover and lucerne provided approximately the same level of nutrients as yellow sweet clover, but despite this gave lower yields of Iceberg lettuce than the yellow sweet clover. A possible reason for this was that the higher amount of dry matter supplied by the yellow sweet clover had a positive effect on soil structure and thus improved lettuce rooting and water uptake. The results indicate that at farm level, reliability of biomass production is more important in choice of a green manure crop than chemical and morphological properties of the species. [ABSTRACT FROM AUTHOR]