Corn and weed residue decomposition in northeast Ohio organic and conventional dairy farms

Increasingly, farmers claim that management practices can significantly influence soil quality. For instance, it is common practice for dairy farms in their rotation cycle to harvest grain and then leave stubble and weeds over winter on the soil surface before ploughing in spring ahead of planting crops. Corn stubble and weeds protect soil in winter, decompose through the seasons, and release nutrients that are utilized by crops and microorganisms. Also, plant residues may harbor increased soil decomposing organisms that feed up on them. Both conventional and organic farmers tend to follow these practices with the major difference that in the conventional systems, inorganic fertilizers and pesticides are applied. Organic matter breakdown in soils under different management (organic versus conventional as in this case) may be different because some inorganic chemicals are known to affect soil decomposers and also these might be less abundant in soils with less food resources, since the organic farmers rely totally on soil fertility derived from organic source. This hypothesis was tested in an on-farm decomposition study conducted in an organic and a conventional farm that grew corn (Zea mays L.) for dairy cattle feed, in Wayne County, OH. Mesh bags containing crop and weed residues were laid on the soil surface at the onset of winter and sampled thereafter to determine decomposition. Mass loss was significantly different among substrates, with crop residues decomposing faster than weeds. Mass and nitrogen (N) loss varied among substrates and variations were greater in summer. Between farms mass and N loss were significantly higher in the organic farm in summer. Earthworm population density was significantly higher in the organic farm. In summary, corn residues decomposed faster than weed residues, and differences in decomposition among substrates increased in summer. Decomposition was faster in summer at both farms, however, it was higher at the organic one, where more soil decomposers were found. The higher metabolic activity in the soil of the organic farm in warmer weather suggests a more active soil biota, which may be crucial for farms whose main or sole source of nutrients derives from organic matter decomposition.