SOIL PHYSICAL PROPERTIES AND AGGREGATE ASSOCIATED C, N, AND P IN ORGANIC AND CONVENTIONAL CROPPING SYSTEMS

Authors: Green, V; Cavigelli, Michel; Dao, Thanh; Flanagan, Dennis

Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/17/2005
Publication Date: 10/1/2005
Citation: Green, V.S., Cavigelli, M.A., Dao, T.H., Flanagan, D.C. 2005. Soil physical properties and aggregate associated c, n, and p in organic and conventional cropping systems. Soil Science. 170:822-831

Interpretive Summary: Organic farming, which is growing in popularity, has been proposed as a sustainable alternative to conventional farming practices. However, it is not known how organic farming affects soil erosion risk and loss of nutrients in eroded sediments. We compared soil erosion risk and the amount of nutrients that may be lost from farm fields during erosion in grain-based conventional (no-till and chisel till) and organic cropping systems and in a forest. We did this by determining soil bulk density, soil aggregate stability, soil aggregate distribution and the amounts of carbon, nitrogen, and phosphorus in different sized aggregates. Results indicate an increased risk of nutrients being transported with eroded soil from organic and chisel till soils compared to no-till soils. These differences are likely the result of tillage breaking down the soil aggregates in the chisel till and organic soils while the lack of tillage in the no-till systems preserves the structure of the soil and thus keeps it from eroding as readily. Organic farming has many benefits; however, farmers must take into account potential erosion risk and water quality issues with organic farming when selecting sustainable farming practices. Developing an organic, no-till or minimum till cropping system that promotes soil structural stability will optimize nutrient conservation and reduce the risk of nutrient transport in humid to sub-humid regions.

Technical Abstract: Organic farming, which is growing in popularity, has been proposed as a sustainable alternative to conventional farming practices. However, it is not known how organic farming affects soil erosion risk and loss of nutrients in eroded sediments. We compared soil erosion risk and the amount of nutrients that may be lost from farm fields during erosion in grain-based conventional (no-till and chisel till) and organic cropping systems and in a forest. We did this by determining soil bulk density, soil aggregate stability, soil aggregate distribution and the amounts of carbon, nitrogen, and phosphorus in different sized aggregates. No-till and forest soils had lower bulk density and greater aggregate stability than did chisel till and organic soils. Carbon, nitrogen, and phosphorus concentrations were greater in large aggregates than in small aggregates regardless of cropping system. Since there were more large aggregates in the no-till soils than in the other soils, the amount of carbon, nitrogen and phosphorus was greatest in large aggregates in no-till soils. The amount of carbon, nitrogen and phosphorus was greates in small aggregates in the organic and chisel till soils. These results indicate an increased risk of nutrients being transported with eroded soil from organic and chisel till soils compared to no-till soils. These differences are likely the result of tillage breaking down the soil aggregates in the chisel till and organic soils while the lack of tillage in the no-till systems preserves the structure of the soil and thus keeps it from eroding as readily. Organic farming has many benefits; however, farmers must take into account potential erosion risk and water quality issues with organic farming when selecting sustainable farming practices. Developing an organic, no-till or minimum till cropping system that promotes soil structural stability will optimize nutrient conservation and reduce the risk of nutrient transport in humid to sub-humid regions.