Gallaher, C. M. 2007. Phosphorus availability in annual and perennial cropping systems. MS Thesis, Michigan State University, East Lansing, Michigan, USA.
Understanding mechanisms that promote efficient nutrient cycling is key to creating more sustainable agricultural landscapes. Many legumes have a unique ability to mobilize soil P. Phosphorus cycling was quantified at the Long Term Ecological Research (LTER) experiment at Kellogg Biological Station, in four systems initiated in 1989: 1) conventional corn-soybean-wheat, 2) organic corn-soybean-wheat with two years of red clover cover crops, 3) continuous alfalfa, and 4) a successional system, taken out of farmland in 1989. These treatments allow for comparisons between cropping systems with annual and perennial legumes and different intensities of legumes. In 2006, soybeans were planted as an assay of P bioavailability in the conventional, organic and alfalfa systems. Soil samples from the four systems, from 1992, 2001 and 2006, were analyzed for particulate organic matter phosphorus (POM-P), total organic P, total soil P, and soil extractable P (Bray P) to examine changes in soil P pools over time. Phosphorus bioavailability was greatest in the alfalfa system. Changes in soil pools occurred over time, with more P being stored in the organic and plant available soil pools in systems with a greater presence of legumes. Overall, these findings argue for an integrated approach to phosphorus nutrient management in low-input or organic agricultural systems, which utilize a variety of legumes to improve the bioavailability of P and build up P in soil pools with rapid turnover, such as POM-P.
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