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Keywords:

  • biomass phosphorus;
  • goat manure;
  • inorganic phosphorus;
  • phosphorus cycling;
  • resin phosphorus

Abstract

High phosphate fixation necessitates the application of high rates of phosphorus (P) fertilizers to achieve reasonable crop yields in most tropical soils. The present study investigated the efficacy of goat manure in improving the effectiveness of fertilizer P for increasing maize yields. Treatments consisted of combinations of four rates of goat manure (0, 2.5, 5 and 10 g kg−1 equivalent to 0, 5, 10 and 20 t goat manure ha−1, respectively) and four rates of inorganic P (0, 45, 90 and 180 mg P kg−1 equivalent to 0, 90, 180 and 360 kg P ha−1, respectively) applied to 7 kg soil in pots. Maize (Zea maize L.) was sown immediately after application. Maize dry matter yields (maize yield) and the concentrations of resin P, soil microbial biomass P (biomass P), 0.5 mol L−1 NaHCO3 extractable inorganic P (NaHCO3-Pi) and 0.1 mol L−1 NaOH extractable inorganic P (NaOH-Pi) were determined 6 and 12 weeks after planting. After 12 weeks, maize yield increased with the addition of fertilizer P or goat manure separately and was further increased when they were applied together. These synergistic effects on maize yield were ascribed to enhanced P cycling because goat manure increased the concentration of biomass P, which in turn accounted for most of the observed variations (63%) in maize yield. The combination of biomass P and resin P, however, explained a greater proportion of the variations in maize yield (73%), suggesting that the usefulness of biomass P as an index of P availability would be enhanced if used in conjunction with resin P. These results indicated that goat manure application could be used to increase soil microbial biomass P, which in turn could improve the effectiveness of fertilizer P in the Eastern Cape, South Africa.