Wednesday, November 15, 2006

Phosphorus Availability in Annual and Perennial Cereal Legume Systems.

Courtney M. Gallaher, Michigan State University, Department of Crop and Soil Science, East Lansing, MI 48824 and Sieglinde Snapp, Michigan State Univ., A440A Plant & Soil Sci. Bldg., East Lansing, MI 48824-1325.

Understanding mechanisms that promote efficient nutrient cycling is key to creating more sustainable agricultural landscapes. Legumes have long been recognized for their role in cycling nitrogen, but it is also important to investigate their ability to efficiently recycle phosphorus. Phosphorus cycling was quantified in two corn soybean wheat rotation sequences, an alfalfa monoculture and an early successional (old field) system in the Long Term Ecological Research (LTER) experiment at Kellogg Biological Station in southwestern Michigan. The four treatments were initiated in 1990 and include 1) a conventional corn-soybean-wheat rotation, 2) an organic corn-soybean-wheat rotation with two years of red clover cover crops, 3) continuous alfalfa, and 4) a successional prairie taken out of farmland in 1989. These treatments allow for comparisons between cropping systems with annual and perennial legumes and different intensities of legumes (1 out of 3 years to continuous legumes). In 2006, soybeans were planted into microplots in these four treatments as an indicator crop, to examine whether phosphorus is more bioavailable in treatments with greater presence of legumes. To understand whether the presence of legumes in a crop rotation impacts phosphorus storage in different soil pools, soil samples from 1992 and 2006 were analyzed for phosphorus pools including particulate organic matter phosphorus (POM-P), total organic P, total soil P, Hedley fractionated pools and soil extractable P (Bray P). Deep soil samples from 2001 and 2006 were compared to see if the presence of legumes may shift phosphorus from inorganic pools deeper in the soil, to organic, more bioavailable pools at the soil surface.