Cover crop and tillage effects on soils transitioning to organic production
Abstract
Organic agriculture is a system-scale method of managing on-farm fertility, environmental impact and disease and pest control. Farmers depend on organic amendments, such as compost and cover crops, to supply the nitrogen necessary to grow cash crops. No-till agriculture is also used as a way of improving soil physical structure and decreasing fuel inputs into farm management. Both cover crops and no-till can lead to insufficient nitrogen and nitrogen immobilization if improperly managed, especially during the period of transition into organic production. Two experiments were performed to study the effect of cover crops and no-till on a field transitioning to organic production and a field in its first years of organic production in west-central Indiana. The effects of a leguminous cover crop on soil physical properties and cash crop yield were examined, as well as the timing of nitrogen mineralization following cover crop incorporation and bedding. Greater soil nitrate-N and ammonium-N concentrations were found following the cover crop treatment compared to the bare treatment, as well as increased percent nitrogen in the above-ground biomass of the cash crop. There was not a yield increase associated with the increased soil nitrogen, although disease and insect pressure may have obscured the effects. In one of the two years, soil wet aggregate stability following crop harvest was improved in the cover crop treatment, despite having been tilled to incorporate the cover crop residues. In a different experiment, the effects of tillage and different cover crops on soil physical properties, nitrogen mineralization and cash crop yield were also investigated. Soil wet aggregate stability and permanganate-oxidizable carbon were increased following cover crop treatments, as well as in the no-till subtreatment compared to the tilled treatment. Bulk density was not affected by cover crop treatment or tillage treatment. The hairy vetch (Vicia villosa) cover crop had the greatest total nitrogen content and also the greatest soil nitrate-N and ammonium-N concentrations following tillage. The tilled subtreatments had greater soil nitrate-N and ammonium-N than the no-till subtreatments throughout the entire experiment, although this may be partially due to the summer-long drought. No yield data were collected for the cash crop due to a late-season hailstorm, but the plants in the no-till plots were smaller and less vigorous than the plants in the tilled plots, possibly due to decreased nitrogen availability in the no-till plots. These results demonstrate the effectiveness of legumes in supplying nitrogen in organic systems as well as the importance of cover crops in the recovery of aggregates post-tillage. Soil wet aggregate stability and permanganate-oxidizable carbon were good indicators of management changes, as differences were registered within a year of establishment. Additional years of research should be performed to monitor the cumulative effects of cover crops and tillage in an organic system.
Degree
M.S.
Advisors
Kladivko, Purdue University.
Subject Area
Agronomy|Soil sciences
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