High biomass yielding winter cover crops can improve phosphorus availability in soil

Abstract

We investigated the effects of high biomass yielding winter cover crops, namely grazing vetch ( Vicia dasycarpa L.) and oats ( Avena sativa L.), on soil phosphorus (P) availability in low fertiliser input maize-based conservation agriculture systems. Soil samples were collected from the 0–50-mm depth of experimental plots after 4 years of maize–winter cover crop rotations. A sequential fractionation scheme was used to separate total soil P into labile, moderately labile and non-labile organic P (P o ) and inorganic (P i ) pools. Labile P pools included microbial biomass-P as well as P i and P o pools extracted using 0.5 M NaHCO 3 and 1.0 M HCl. The non-labile P pools were humic-P and 1.0 M H 2 SO 4 extracted P. Soil on the maize–winter cover crop rotations had higher HCl-P i and total P than the soil on the maize–fallow rotation. The cover crops had no significant ( p >0.05) effect on NaHCO 3 -P o , NaHCO 3 -P i , HCl-P o , fulvic acid-P and recalcitrant H 2 SO 4 -P fractions. Non-application of fertiliser increased accumulation of humic-P on the maize–oats rotation. Cover crop biomass input explained 73% of the variations in microbial biomass-P and 33% of variations in total labile P. Phosphorus concentration of young maize plants was significantly increased by the cover crops, with a positive correlation to HCl-P i ( r s =0.90). This contribution from winter cover crops to P availability in the surface soil suggests that, in the long term, fertiliser P could be reduced in such systems.