W.L.J. van Rensburg

The quantification of rangeland condition in a semi-arid grassland of southern Africa

The degradation gradient technique was used to quantify rangeland, condition in areas ranging from poor, trampled areas close to watering points to well managed areas in a semi-arid, sweet grassland of southern Africa. Ecological values were linked to species by means of their individual positions on the degradation gradient. These species were further classified according to ecological index values. Identification of indicator species for purposes of rangeland condition assessment was done by using the correlations between the relative composition and the rangeland condition value of a species. Index values and Gaussian distribution curves were used in calculations to determine rangeland condition. The accuracy of these methods was tested and the best results were obtained by using the species curves of Themeda triandra and other species which dominate at other positions along the gradient. The advantage of this technique lies in its simplicity and ease of use. Another advantage is the fact that only the...

Effect of slope and plant cover on run-off, soil loss and water use efficiency of natural veld.

Abstract Run‐off and soil loss were monitored from a climax, subclimax and pioneer veld, each on a 5,9%, 4,1% and 2,1% slope, by means of a rainfall simulator on a Valsrivier soil form. With rainfall intensity, soil moisture content at the beginning of each rain storm, and soil texture the same for each treatment, plant cover and composition had a significant (positive) (P≤0,05) influence on the amount of soil loss and run‐off that occurred, as against the insignificant influence of the slope. An average of 6,2 t/ha soil loss and 80,6% run‐off of the amount of water applied occurred from the pioneer veld (0,7% basal cover) on the steepest slope. In all the successional stages more run‐off and less soil loss occurred from wet soil than from dry soil. Significant (P≤0,01) relationships between basal and canopy cover were obtained with run‐off and soil loss. The climax, subclimax and pioneer veld produced on average 0,57 g, 0,23 g and 0,07 g aboveground phytomass for each litre of water evapotranspirated.

Ranking of grass species according to visible wilting order and rate of recovery in the central orange free state

Abstract A number of grasses were ranked according to the order in which they wilted with diminishing moisture availability, and according to their ability to recover after water replenishment. Digitaria eriantha and Digitaria argyrograpta were the most sensitive to moisture stress, whereas Sporobolus fimbriatus and Panicum stapfianum were last to show signs of wilting. The latter two grass species were the first to recover from wilting during optimum soil water conditions. The leaf water potential and soil water content at which each grass species wilted were recorded.

Influence of soil pH and fertilization on the dry matter production, chemical composition and digestibility of perennial grasses: I. Anthephora pubescens nees 1

Reports the results of a study conducted to investigate the influence of soil pH and fertilization on the dry matter production, chemical composition and organic matter digestibility of Anthephora pubescens evaluated in pots; The influence of soil pH and fertilization (N, P and Zn) on the dry matter (DM) production, chemical composition (crude protein, P, K, Ca, Mg and Zn content) and organic matter (OM) digestibility of Anthephora pubescens Nees was evaluated in pots. The highest DM production was obtained in the neutral soil medium (pH 6,5 in H 2 O) and alkaline (pH 7,5 in H 2 O) soil mediums adversely affected DM yield, crude protein (CP), Zn content and OM digestibility of A. pubescens . Fertilization invariably increased DM production. Keywords: anthephora pubescens ; botany; chemical composition; crude protein; digestibility; dm yield; dry matter production; fertilization; Grasses; k; organic matter; perennial grass; Perennial grasses; ph; phytomass; soil culture; Soil pH; yield; zn Journal of the Grassland Society of Southern Africa.

The influence of nitrogen and defoliation on production and water‐use efficiency of Lolium multiflorum cv. Midmar

Abstract The objective of this study was to investigate the influence of different nitrogen fertiliser application levels in combination with different defoliation intervals on the dry matter (DM) production and water‐use efficiency of ryegrass (Lolium multiflorum,) cv. Midmar. In a field trial, four nitrogen levels (0, 150, 300 and 450 kg N ha−1) were combined with five defoliation intervals (every 2, 4, 6 and 8 weeks and twice a season). Soil moisture levels were measured with a neutron hydroprobe and were used to schedule irrigation. The dry matter production, nitrogen‐use efficiency (NUE), plant DM content and water‐use efficiency were influenced (P<0.01) by nitrogen level, defoliation interval, and the interaction between these factors. Total DM production varied from 64 to 20 922 kg DM ha−1. Dry matter production per unit of applied N decreased with an increase in N level within a defoliation interval. The plant DM content varied from 14.0% to 35.6%. The plant DM content decreased (P<0.05) with incr...

Influence of soil PH and fertilization on the dry matter production, chemical composition and digestibility of perennial grasses : II panicum maximum JACQ 1

Abstract The influence of soil pH and fertilization (?, ? and Zn) on the dry matter (DM) production, chemical composition (crude protein, P, K, Ca, Mg and Zn content) and organic matter (OM) digestibility of Panicum maximum Jacq. was evaluated in pots. Panicum maximum grew best in a neutral (pH 6,5 in water) to a slightly alkaline (pH 7,5 in water) soil medium. Soil acidity (pH 4,5 in water) adversely affected DM yield as well as the crude protein (CP), P, Ca and Zn content of the above ground phytomass. Fertilization invariably increased DM production, CP content, Zn content and OM digestibility.