The Water Environment and Implications for Productivity

• Published in: Journal of biogeography 1990-07, Vol.17 (4/5), p.513-520
• Main Authors: McCown, R. L., Williams, John
• Format: Article
• Language: English
• Subjects: Agricultural productivity; Australia; Dry seasons; Grasses; Legumes; Pastoralism; Pastures; Productivity; Rain; Savanna Management for Pastoral Industries; Savanna soils; Savannas; Soil infiltration; Soil water
• ISSN: 0305-0270; 1365-2699
• DOI: 10.2307/2845384

Water deficits constrain productivity of herbivores on savanna grassland in two ways. The lack of soil water in the dry season causes a nutritional stress due to the low protein concentration and low dry matter digestibility of dead tropical perennial grass tissue. Less frequently, lack of rain in the growing season causes feed shortages in the subsequent dry season. The first part of this paper deals with simulation of these effects using weather data and describing the variation which occurs in northern Australia. Options for reducing the impact of the annual dry season include sowing a pasture legume, singe dry legume leaf is relatively nutritious. The second part of the paper examines variation imposed by the water climate on legume production potential and on the risk of spoilage due to out-of-season rainfall. Thirdly, the paper examines the effects of nitrogen and phosphorus deficiencies and the consequences of mismanagement of the soil surface on the water constraint. It is concluded that the substantial progress in reducing nutritional stress of the annual dry season has changed the nature of the problem of periodic droughts. Whereas formerly the main impact of nutritional stress was high cattle mortalities, now genetically better adapted cattle survive by consuming a greater proportion of the low quality herbage with the aid of mineral supplements. The sowing of legumes increases average carrying capacity and increased pasture utilization. Both innovations increase the risk of overgrazing in years of below-average pasture production. Avoidance of accelerated land degradation as a result of loss of buffering capacity inherent to the former extensive system will require skilful management.