Influence of residual manure on selected nutrient elements and microbial composition of soil under long-term crop rotation

A study was conducted on a long-term field experiment at the University of Pretoria, South Africa, that was established in 1939. The aim was to investigate the effects of residual manure on the characteristics of the total and microbial biomass and their nutrient contents in the soil and on maize yield under long-term crop rotation. It was found that total C, N and available P levels were increased as a result of manure application. Seasonally, these nutrients exhibited variations that appeared to be related to influences of crop rotation. Long-term soil N content in an adjacent native site remained relatively constant while it tended to increase in the control and manured plots. Soil microbial biomass content of C, N, and P and microbial populations were affected by previous manure application, as well as by crop rotation. The biomass and numbers of microflora were generally higher in the manured plots. Manure application also resulted in higher maize yields and had substantial residual effects. Relationships between the different soil properties considered and crop yield are presented and their implications discussed.