Afloopstudies vanaf natuurlike veld in verskillende suksessiestadia van die sentrale oranje‐vrystaat

Uittreksel

Afloopbane met ‘n helling van 4,13% is gebruik om die afloopverliese, fitomassaproduksie en waterverbruiksdoel‐treffendheid (WVD: Bogrondse fitomassa geproduseer in verhouding tot die evapotranspirasieverliese), van natuurlike veld in verskillende suksessiestadia vir die periode Julie 1977 tot Junie 1983 te monitor.

Hoogsbetekenisvolle verskille (P < 0,01) in afloopverliese tussen die klimaks‐, subklimaks‐ en pioniergrasbedekte afloopbane, het oor die proefperiode voorgekom. Onderskeidelik 1,01, 1,55 en 2,94% van die totale neerslag wat oordie ses jaar voorgekom het, het vanaf die klimaks‐, subklimaks‐en pioniergrasbedekkings afgeloop.

Die klimaksgrasbedekking wat die hoogste fitomassaproduksie oor die ses jaar gelewer het, het ‘n afname in produksie getoon soos wat die reenval tussen seisoene afgeneem het, terwyl die pioniergrasbedekking ‘n toename in fitomassaproduksie getoon het, met ‘n afname in reënval.

Die WVD van die klimaksgrasbedekking is onderskeidelik gemiddeld twee en vier keer (P < 0,01) meer doeltreffend as die subklimaks‐ en pioniergrasbedekking oor die ses jaar.     

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 reaction of Anthephora pubescens to N, P and K fertilization was evaluated from 1976 to 1983. Dry matter production at N levels of 0; 75 and 150 kg/ha were 1,9; 2,2 and 2,3 ton/ha respectively. This relative poor reaction to N was related to rainfall variations and the initial low soil P status. A significant N × P interaction was recorded. Dry matter production increased from 1,6 ton/ha at the NO × PO treatment to 2,8 ton/ha at the 150 kg N/ha × 20 kg P/ha treatment. Anthephora responded poorly to K fertilization and the mean dry matter production was 2,1; 2,2 and 2,2 ton/ha with 0; 75 and 150 kg K/ha respectively.

The mean crude protein content of A. pubescens increased from 6,5 % at the NO level to 8,8 % with 150 kg N/ha. The P content of plant material increased from 0,13 % at the PO level to 0,20 % with 20 kg P/ha. The Zn content of plant material dropped to sub‐optimal levels during the trial.     

Influence of stocking rate and grazing system on plant basal cover and botanical composition of veld in the northern cape 1

Abstract

Changes in basal cover and botanical composition were recorded at four stocking rates, both under continuous and rotational grazing in the Northern Cape. The experiment was conducted with cattle. Results suggested that heavier stocking rates could be applied under rotational grazing than under continuous grazing without veld deterioration occuring. After four seasons, botanical composition deteriorated only under continuous grazing. Plant basal cover decreased significantly at the heavy stocking rates, both under rotational and continuous grazing. This result illustrates the danger of grazing strategies based on an injudicious increase in stock numbers.

Basal cover was found to be a better indicator of trends in veld condition than botanical composition, despite annual fluctuations resulting from rainfall variability. Changes in the botanical composition apparently occur only where veld deterioration is more advanced.     

Influence of stocking rate and grazing systems on available grazing in the northern cape 1

Abstract

The influence of rotational and continuous grazing systems, each applied with four stocking rates, on the above‐ground phytomass of veld was determined over four years.

Grazing systems showed a significant influence on available herbage during one year only. Increased stocking rates brought a progressive decline in above‐ground phytomass. During the fourth season (1980/81) the average grazing pressures at stocking rates of 10 ha, 7 ha, 5,5 ha and 4 ha/Large stock unit were 5 984 kg, 3 417 kg, 2 390 kg and 1 238 kg and 1 238 kg phytomass/Large stock unit, respectively. At the end of the fourth season (July, 1981) there was reserve grazing available on the various stocking rates for approximately 579 days, 337 days, 202 days and 76 days, respectively. The risk of high stocking rates in the marginal rainfall regions, is emphasised.     

Die invloed van vog‐ en ontblaringsbehandelings in hidrologiese eenhede op natuurlike veld van die sentrale oranje‐vrystaat

Die invloed van al die kombinasies van twee intensiteite (3 en 6 cm ontblaringshoogtes) en twee frekwensies (een en vier keer per jaar) van ontblaring, is onder drie verskillende vogbehandelings, onder natuurlike veldtoestande, vir die periode Julie 1978 tot Junie 1981, ondersoek. Die invloed van die vog‐ en ontblaringsbehandelings is geëvalueer in terme van die basale bedekking, botaniese samestelling, fitomassaproduksie en waterverbruiksdoeltreffendheid (WVD: Is die fitomassa geproduseer in verhouding tot die evapotranspirasie).

Die verskillende vogbehandelings waaraan die veld onderwerp is, het meegebring dat daar aan die einde van die 1980/81‐seisoen hoogs betekenisvolle verskille in basale bedekking en botaniese samestelling tussen die drie vogbehandelings voorgekom het.

Vog toon die grootste invloed op weiveldproduksie van al die veranderlikes wat toegepas is. Die intensieteit en frekwensie van ontblaring het die produksie tot ‘n mindere mate beinvloed.

Die waterverbruiksdoeltreffendheid van die grasse onder vogbehandeling 1, naamlik normale reënval, het toegeneem met ‘n afname in ontblaringsintensiteit. Onder vogbehandeling 2, naamlik optimale grondvogtoestande, neem die WVD van die grasse toe met ‘n toename in ontblaringsfrekwensie. Hoe strawwer ontblaar is (3 cm hoogte in plaas van 6 cm hoogte) onder optimale grondvogtoestande, hoe hoër is die waterverbruiksdoeltreffendheid.     

Laboratory confirmation of African horsesickness in the western Cape: application of a F(ab')2-based indirect ELISA

Recently a suspected outbreak of African horsesickness in the Western Cape Province resulted in the deaths of four foals and one adult horse. Spleen samples from these animals were subjected to analysis by an enzyme-linked immunosorbent assay (ELISA) which uses F(ab')2 fragments of immunoglobulins to detect African horse sickness virus (AHSV) antigens. The results of the immunoassay were compared with those obtained by isolation followed by serotyping as is currently applied by the Reference Centre at the Veterinary Research Institute, Onderstepoort. Samples of spleen tissue from the four foals contained sufficient antigen to be readily detectable by ELISA. A marginally positive signal was obtained with the tissue from the adult horse. This sample was inoculated onto VERO cells and four days were allowed for viral multiplication. Subsequently, when the cell culture was assayed by F(ab')2-ELISA, a much higher absorbance value than that obtained with the original spleen sample resulted, thus confirming the presence of AHSV in the initial specimen. The F(ab')2-ELISA has potential to be used as an initial diagnostic test to screen for AHSV.