Globally, 60-70 % of food production is rainfed agriculture and in sub-Saharan Africa over 95 % of the food production is rainfed agriculture (Falkenmark and Rockström 2005). Smallholders in the Limpopo River basin have little access to irrigation schemes and rain water is therefore their main source of water (Nyalungu 2005).
Traditional agricultural yields are strongly influenced by environmental conditions in the basin and average yields tend to be low, reflecting the low-input/output system. However, the contribution of rainfed agriculture to food security should not be underestimated and in years of good rains, subsistence agriculture can contribute substantial to household food requirements (FAO 2004).
Crops and Yields
In Botswana, the main subsistence crops are sorghum, maize, millet, beans, other pulses and oilseeds. Although yields are low, these crops form an important source of food and income for many families in the basin (FAO 2004).
Most districts in Mozambique have very limited access to agricultural-related services (irrigation, fertilizers, tractors etc.) and are therefore reliant on rainfed and floodplain farming. It is common practice for families to establish one plot in the fertile lowlands along the rivers (baixas) where they plant maize, nhemba beans, groundnuts, and manioc, and another plot in the highlands (serras) where they plant sorghum, millet, pulses and other drought-resistant crops. Yields range from 0.40 tonnes/ha for groundnuts to 0.8 tonne/ha for maize.
Harvesting rainfed crops in the Chokwé region of Mozambique.
Source: Qwist-Hoffmann 2010
( click to enlarge )
In South Africa, maize is the most important subsistence crop, even though it is not ideally suited to the drought-prone environment of the basin. The reason for this somewhat risky crop selection is that white-maize meal is an important part of the diet of many southern Africans (FAO 2004).
In Zimbabwe the the majority of the Limpopo River basin falls with the Natural Region V, the driest region of the country. Maize, sorghum, cotton, groundnuts and sunflower are commonly grown crops in the middle basin in Zimbabwe. As is true for the majority of the basin, subsistence crop yields are very low, ranging from 0.40 tonnes/ha for groundnuts to just under 1 tonne/ha for maize.
Green Water Potential
Green water is soil moisture used in rainfed agriculture, while Blue water is the surface and groundwater water extracted from rivers, lakes and aquifers for irrigation. Many of the large river systems of the region are nearing closure or are already closed, meaning that all of the blue water in these systems is largely already allocated (Falkenmark and Rockström 2005).
In the majority of the countries in southern Africa, green water supplies comprise over 80 % of the annual water used in the food sector. The majority of this water is used in the production of rainfed crops. In hyper-arid areas blue water plays more of a role, supplementing the inadequate availability of precipitation. Irrigated agriculture accounts for two-thirds of blue water withdrawals in southern Africa. Future demands will increasingly have to rely on more efficient uses of green water and improved rainfed agriculture.
There are inefficiencies in the use of green water that with improved management could help meet future water demands in sub-Saharan River basins (Falkenmark and Rockström 2005). “Importantly, the vast majority of farmers in southern hemisphere Africa practice rain-fed agriculture, often sub-optimally. Improving rainfed agriculture through dryspell mitigation by blending irrigation and dryland techniques therefore presents a huge potential for improving future food production in the region (Scholes and Biggs 2004).”
This is especially relevant to the Limpopo River basin where current blue water withdrawals for irrigation often exceed available blue water by 30 % in some areas (Nyalungu 2005).