Cover crop biomass

Inhibitive effects are especially influenced by amount of cover crop biomass and soil management. Weed dry matter was reduced when rye residues were greater than 3.7 Mg ha-1 (Crutchfield et al. 1985), and when wheat residues were greater than Mg ha-1 (De Almeida 1985). Fisk et al. (2001) reported that burr medic (Medicago polymorpha L.) and barrel medic (M. truncatula Gaertn.) reduced by 70% weed dry weights while weed density was not affected if were no-till seeded as winter-killed cover crops into winter wheat (Triticum aestivum L.) stubble. 

Malik, R.K. Green, T.H. Brown, G.F. Beyl, CA. Sistani, K.R. Mays, D.A. Biomass production of short-rotation bioenergy hardwood plantations affected by cover crops. Biomass Bioenerg. 2001,21, 21-33. 

Weed seedling emergence was stimulated when living cover crop biomass was incorporated into the soil. Stimulation for morningglory ranged from 172 to 409%... 

When determining the potential influence of cover crops on the physicochemical state of Cecil A no-till soils or tilled soils, there are a variety of factors that are of interest. Among them are above- and below-ground cover crop biomass, morphology of cover crops (as related to shading and root distribution), soil temperature, soil moisture, soil compaction, soil pH, chemical composition of cover crops before and after glyphosate desiccation (e.g., C/N ratio and phenolic acid content), soil C/N ratio, soil nitrate-N, and soil phenolic acid content. 

The organic treatment had higher microbial biomass C and N, enzyme activity and potentially mineralisable N (Cunapala and Scow 1998) and different microbial community composition phospholipid fatty acid than the conventional treatment (Bossio ef al. 1 998). There were minimal differences between treatments in residue decomposition (Cunapala et al. 1998). Cover crops and higher irrigation frequency in the organic treatment may have contributed to the differences (Cunapala and Scow 1998). 

To produce uniformly distributed high-residue (>6 t ha biomass), grass-legume cover crop mixtures on permanent controlled-traffic raised beds, keeping the soil continuously covered using diverse rotations of cash and cover crops. 

In summary, organic no-till systems are recommended only where high-residue cover crops can be grown and managed properly, and when productivity of cash crops is favourably affected by root and shoot biomass (surface residue mulch) of the cover crops. Research and grower experience have shown that organic no-till systems are most likely to succeed ... 

Residues of hairy vetch following desiccation with a contact herbicide in Maryland reduced weed emergence during the first 4 weeks after desiccation (Teasdale, 1993 Teasdale and Daughtry, 1993). However, as hairy vetch residues decomposed, weed emergence became similar to that without a cover crop and a comparable weed biomass resulted. A living mulch of hairy vetch in the no-treatment control or a dead mulch in the mowed treatment improved weed control during the first 6 weeks of the season, but weed control deteriorated thereafter. 

Fig. 3.14 Mean total phenolic acid (femlic acid equivalents) content of 0-2.5 cm Cecil soil samples taken during the 1992 and 1993 growing season for reference plots (no-cover crop) and cover crop plots. In 1992 cover crops were desiccated with glyphosate in April. In 1993 cover crops were desiccated with glyphosate at two time periods (April and May) and living biomass was tilled into plots in May. The absence of standard error bars indicates that the error bars are too small to be visible. Figure based on data from Blum et al. (1997). Henry A Wallace Institute for Alternative Agriculture Inc, data used with permission of Cambridge University Press...

Adding Hoagland s solution in addition to sunflower tissues eliminated the inhibitory effects of sunflower tissues on pigweed seedling biomass. Thus, it would appear that nutrients in plant tissues mixed into soil might modify plant-plant allelo-pathic interactions differently than nutrients/fertilizer directly applied to surface of the soil or mixed into the soil. The functional role of nutrients in small grain and clover cover crop residues is presently not known. 

Crambe could be cultivated as a cover crop. The decomposition and nutrient release from crop residues of crambe in the implementation of no-tillage system has been reported. Heinz et al. (2011) have reported that the kinetics of residue decomposition in crambe were similar to those of nutrient release with an initial rapid phase followed by a slower one. K, P, and Mg are released more quickly for subsequent crops, while the increased speed of nutrients release occurred around 15 days after the biomass management. Due to a high content of glucosinolates, crambe could also be used as a crop for biofumigation. 

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