Effects of Soil Fertility, Elevation, and Phosphorus of Differing Solubility on Legume Performance for Nutrient Cycling Enhancement in the Bolivian Andes.

To improve modeling of the way that legume crops and biological nitrogen fixation can enhance nutrient cycling and nitrogen (N) and phosphorus (P) availablility in smallholder cropping systems of highland Bolivia, we conducted multilocation experiments on farm plots in Potosí, Bolivia in 2006-2007. These experiments tested the response of legume crop N uptake, above- and below-ground biomass fractions, and N fixation to mean site temperature, added P in rock phosphate and soluble form, and site soil parameters including soil P fractions, texture, and pH. Olsen P and soil texture were the most significant covariants in explaining interaction between legume response to applied P, and were combined to form a single covariant for combined analysis of 16 experiments. Site P fertility as measured by Olsen P was associated with increases in legume biomass and N uptake (N fixation plus soil uptake). The overall model for the experiments indicated a positive response of legume N uptake to soluble P as triple superphosphate at all sites. Sites with low soil clay content and low Olsen P also showed a positive response of legume N uptake to rock phosphate addition. There were also significant responses to P addition of root biomass and shoot:root ratio.