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ARS Home » Pacific West Area » Salinas, California » Crop Improvement and Protection Research » Research » Publications at this Location » Publication #304484
Title: Soil phosphorus mobilization in the rhizosphere of cover crops has little effect on phosphorus cycling in California agricultural soils

Author
item MALTAIS-LANNDRY, G. - Stanford University
item SCOW, K. - University Of California
item Brennan, Eric

Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/14/2014
Publication Date: 8/28/2014
Citation: Maltais-Landry, G., Scow, K., Brennan, E.B. 2014. Soil phosphorus mobilization in the rhizosphere of cover crops has little effect on phosphorus cycling in California agricultural soils. Soil Biology and Biochemistry. 78:255-262.

Interpretive Summary: This study used two long-term studies in California to understand if mixtures of legumes and cereal cover crops can reduce losses of phosphorus (P) and increase P availability for subsequent cash crops. Various organic and conventional systems were studied where cover crops were in rotation with grains and tomatoes, or high-value vegetables (lettuce and broccoli). Although legume cover crops can increase P availability in their root systems, this is not likely to have a major effect on P dynamics in these systems because legume biomass is relatively low in these mixtures. However, cereal cover crops can take up a substantial amount of P and therefore reduce the risk of P losses from runoff and leaching.

Technical Abstract: External phosphorus (P) inputs to agricultural soils are needed to replace soil P removed by harvest and maintain soil fertility. Alternative fertilization approaches that maintain soil fertility while reducing P inputs could improve current practices that often result in excessive P application and P fixation in soil pools of low plant availability. Cover crops may provide P benefits and lower the need for P inputs by reducing losses from soils and increasing mobilization of soil P bound to soil minerals or organic matter. We studied the potential of legume (fava bean, vetch, pea) and cereal (rye, wheat, oats) cover crops to reduce P losses and increase P mobilization across various organic and conventional management practices in two long-term systems trials in California. We measured cover crop biomass and nutrient content, P-mobilizing compounds (pH, organic acids, phosphatase activity) and soil P fraction changes in the rhizosphere. Cereals generally produced more biomass with similar P content compared to legumes, resulting in higher P uptake. However, higher C:P and C:N in cereal biomass suggest that delayed mineralization could limit P recycling benefits. Legumes, especially fava bean, had the largest effect on rhizosphere properties by reducing pH and increasing organic acids concentrations and phosphatase activity, but we found no indication of higher soil P availability with legumes. Furthermore, we found no strong effect of management practices on mobilization, but higher P input increased cover crop biomass and P uptake in some cases. Our results suggest that reducing P losses using cereals is more promising to lower external P input requirements in California agriculture than mobilizing soil P with legumes.