Organic Farming Effects on Soil Physical Quality after 39 Years.

Abstract: Organic farming is an agricultural management strategy that aims to produce crops while enhancing soil and water quality as well as plant, animal and human health. The impact of organic farming on soil physical quality has not been, however, widely studied. The objective of this study was to determine the impact of organic farming practices on soil physical quality as compared with conventional farming practices after 39 years of management on a Sharpsburg silty clay loam in eastern Nebraska. This study also assessed relationships of soil physical properties with changes in soil organic C concentration. We hypothesized that long term organic farming will reduce soil compaction, improve hydraulic properties, and increase aggregation and organic C relative to conventional farming. Treatments were: 1) soybean-corn-soybean-winter wheat-soybean rotation receiving animal manure amendment (OAM), 2) alfalfa-alfalfa-corn-winter wheat-alfalfa rotation with green manure (alfalfa) amendment (OGM), 3) corn-soybean rotation under conventional practices with fertilizer and pesticide use (CR1), and 4) diversified rotation including corn-sorghum-soybean-winter wheat-soybean with fertilizer and pesticide use (DIR). Preliminary data collected in fall 2014 indicated that treatments affected wet aggregate stability. The DIR and OGM had 26% higher aggregate stability than CR1 for the 0-15 cm depth. Such differences may be due to the intensified crop rotations under DIR and OGM, which included alfalfa, grain sorghum, and winter wheat. Also, OAM and OGM tended to increase water infiltration compared with CR1 and DIR, but differences were not statistically significant. These trends may be due to possible increases in soil aggregation and organic matter content in the organic plots. A comprehensive characterization of soil physical properties including penetration resistance, shear strength, dry and wet aggregate stability, compactibility, bulk density, soil C concentrations, and other properties was conducted in fall 2015. Detailed results and will be presented and discussed at the meetings.