Long term nitrogen and phosphorus application to veld

Abstract

The long term effects of a 5N x 3P factorial fertilizer application trial on hay yields, botanical composition and soil properties of veld are presented. Significant increases in hay yields were recorded during most years. There was a strong correlation (r = 0,757) between mean (over all 15 treatment combinations) annual hay yields and annual rainfall.

N and N + P fertilizer lowered the percentage basal cover of the tribe Andropogoneae. A notable exception of this tribe was Heteropogon contortus which increased significantly at the lower fertilizer levels. The basal cover of the tribe Paniceae generally increased with N and P fertilizer application. The reaction of the basal cover of the tribe Eragrosteae showed little by way of definite tendencies.

Increasing N and P levels generally resulted in decreases in soil pH, Ca, Mg, K and an increase in compaction of the soil surface layer. However, higher levels of N x P resulted in higher water infiltration rates than occurred in control plots, although initial infiltration rates were greatest in control plots. Despite certain undesirable effects of fertilizers on basal cover and certain chemical and physical properties of the soil, the fertilized plots maintained a high level of production.