Korttermyn invloed van strawwe droogte op veldtoestand en waterverbruiksdoeltreffendheid van grasveld in die sentrale Oranje‐Vrystaat

Abstract

Short‐term effect of severe drought on veld condition and water use efficiency of grassveld in the central Orange Free State. The impact of an intensive drought (1982/1983 and 1983/84‐growing seasons) on botanical composition, basal cover, mortality of grazing plants and water use efficiency (WUE) of veld in good, moderate and poor condition was identified. Increaser II species were apparently more capable of surviving drought than the Decreaser species. Under optimal soil moisture conditions the Decreaser species increased and the Increaser II species decreased. During the drought extensive grass mortality took place. Veld condition plays an important role in determining mortality during drought. Decreaser species have a high water requirement for optimal WUE, while Increaser II species can reach maximum WUE with less water. Under water stress conditions Increaser II species significantly (P≤0.01) do not use the water as efficiently as do Decreaser species. The WUE under water stress conditions for veld in good, moderate and poor condition was on average, during the study period, 0.90; 0.90 and 0.40 kg ha⁻¹ mm⁻¹, respectively, and towards under optimal water conditions, 2.47; 1.67 and 0.23 kg ha⁻¹ mm⁻¹, respectively.

Die impak van ‘n intense droogte (1982/83 en 1983/84‐seisoene) op botaniese samestelling, basale bedekking, mortaliteit van weiplante en waterverbruiksdoeltreffendheid (WVD) van veld in ‘n goeie, redelike en swak tocstand, is geïdentifiseer. Toenemer II spesies was beter in staat om ‘n droogte te oorleef as Afnemerspesies. Onder optimale grondwatertoestande het Afnemersoorte toegeneem, terwyl die Toenemer II spesies ‘n afname getoon het. Grootskaal‐se afsterwing van graspolle het gedurende die droogte voorgekom. Veldtoestand maak ‘n belangrike bydrae tot die afsterf van polle gedurende ‘n intense droogte. Afnemerspesies het ‘n hoë waterbehoefte vir optimale WVD, terwyl Toenemer II spesies met minder water ‘n optimum WVD kan bereik. Onder waterstremmingstoestande verbruik Toenemer II spesies water ook betekenisvol (P≤0.01) ondoeltreffender as Afnemer spesies. Die WVD onder waterstremmingstoestande van veld in goeie, redelike en swak toestand was gemiddeld, oor die proefperiode, onder‐skeidelik, 0.90; 0.90 en 0.40 kg ha⁻¹ mm⁻¹, en teenoor onder optimale watertoestande van onderskeidelik, 2.47; 1.67 en 0.23 kg ha⁻¹ mm⁻¹.

Additional index words:

• Basal cover
• drought
• species composition
• veld condition
• water use efficiency