Soil nutrient contents, microbial properties and maize yield under long-term legume-based crop rotation and fertilization: a comparison of residual effect of manure and NPK fertilizers

Abstract

A study was conducted in a field experiment that has been ongoing for over 60 years at the University of Pretoria, South Africa. The aim was to compare the residual effects of manure and NPK fertilizers on selected soil nutrients, microbial properties, C and N inputs, maize tissue nutrient concentration and yield under long-term crop rotation. Total organic C, total N and available P levels were increased owing to residuai effects of manure alone or in combination with NPK fertilizers. C input in NPK-fertilized plots was about 47% higher than in manured plots. The estimated fixed N ranged from 52 kg ha⁻¹ in the NPK plots to 164 kg ha⁻¹ in the control plots. Increases in nutrient contents of manured plots were not reflected in microbial properties of the soil. Microbial biomass and numbers were generally higher in the NPK-fertilized than in the manured plots. The differential responses were attributed largely to differences in decomposability of organic materials. Organic material in the NPK treatment appeared to have higher turnover rates than in other treatments, suggesting that C limitation in soils of low C but good nutrient supply may be compensated by the high turnover rate of available organic materials.