Short-term response of rangeland botanical composition and productivity to fertilization (N and P) in a semi-arid climate of South Africa

This study examined the short-term response of rangeland to annual (1993/94 to 1996/97 seasons) application of fertilizer [all combinations of 0; 10; 30 and 50 kgha−1nitrogen (N), with 0 and 10 kgha−1of phosphorus (P)] in terms of aboveground phytomass production, crude protein content, seasonal rain-use efficiency (S-RUE), nutrient use efficiency, botanical composition, basal cover and soil compaction. After 4 years of fertilization, the botanical composition of the high N-fertilized plots changed from a climax to subclimax vegetation.Elionurus muticus showed the greatest decrease in frequency (62%) due to N fertilization. Phosphorus fertilization only, had an insignificant (p>0·05) influence on species composition and basal cover over the 4 years. The production increased (p⩽0·01) with the application of N together with P, compared to applying only N (1074vs. 823 kgha−1). The more fertilizer applied, the more sensitive to drought the climax grasses became. Nitrogen and phosphorus fertilization significantly (p⩽0·01) affected S-RUE. The highest S-RUE of 6·64 kg phytomass ha−1mm−1and 0·23 kg crude protein ha−1mm−1were obtained with fertilizer application of 50 kgN plus 10 kgPha−1. On average over the 4 years, nutrient use efficiency with N+P application for all treatments was lower than without P. The increases in plant production per kg N applied, both with and without P were 28·00 and 29·81 kg respectively. Soil compaction increased with increase in N fertilization. These results confirm the vulnerability of native grasses in dry areas, following change in soil fertility.