Abstract

DUBE, Ernest; CHIDUZA, Cornelius  and  MUCHAONYERWA, Pardon. High biomass yielding winter cover crops can improve phosphorus availability in soil. S. Afr. j. sci. [online]. 2014, vol.110, n.3-4, pp.01-04. ISSN 1996-7489.

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 NaHCO₃ and 1.0 M HCl. The non-labile P pools were humic-P and 1.0 M H₂SO₄ 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 NaHCO₃-P_o, NaHCO₃-P_i, HCl-P_o, fulvic acid-P and recalcitrant H₂SO₄-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.

Keywords : conservation agriculture; cover crop biomass; no-till; phosphorus fertiliser; soil organic matter.

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