Water, together with seeds and fertilizers, is a major input for agriculture. Agriculture accounts for 80 per cent of human water use at global level. Clean water is a renewable resource that, despite its global abundance, may be scarce locally. More than 30 countries experience chronic water shortages or droughts. Optimum levels of plant nutrients help crops use water more efficiently.

Fertilizer Use and Water Availability

The amount of water required to grow various food and forage crops is considerable, ranging from 300 to 2,000 litres per kilogram of harvested crop product. Fertilizers increase Water Use Efficiency (WUE) by increasing rooting depth and density, as well as the crop's ability to withstand drought stress. Where water and plant nutrients are scarce and WUE by crops is low, increasing the nutrient availability to a level that is not limiting during plant growth leads to a crop production increase that is accompanied by a water use efficiency increase. There is considerable synergy between irrigation and fertilizer use; the yield increase resulting from the use of the two production factors together is greater than the yield increase from either factor alone.

The Green Revolution of the 1960s and 1970s led to spectacular increases in food production in several developing countries, e.g. in India, Pakistan and, to a lesser extent, Bangladesh and Nepal. Large increases in cereal yields were achieved in a very short time through the combination of several factors, including adoption of new high-yielding varieties, sufficient availability of water through irrigation and fertilizer application. Contrary to Asia, where cereal yields doubled between 1970 and 1994, to reach three tonnes per hectare, yields increased slowly in Africa at an average rate of ten kilograms per hectare per year, for a production level of about one tonne per hectare. One important reason is the relative availability of water and nutrients in many areas of Sub-Saharan Africa; when infiltration of water into the soil exceeds 250 mm, nutrient deficiencies override water shortages as the factor limiting crop productivity. These nutrient deficiencies are such that the crop can absorb only 10 to 15 per cent of total rainfall, the excess being lost through evaporation, deep percolation and run-off. Supplying extra nutrients under such circumstances can increase water uptake.

Poor inherent soil fertility of many tropical soils is exacerbated by soil loss via erosion, particularly loss of organic matter. While soil erosion contributes to the run-off of nutrients and other agricultural inputs, loss of organic matter leads to the degradation of the soil's structure and to a reduction of the soil's ability to retain water. This can be counterbalanced using sources of organic matter, such as farmyard manure, which are recognized for their important role in providing plant nutrients and improving the soil's structure and water retention ability.

Irrigation and Water Use Efficiency (WUE)

Irrigated agriculture improves food security by reducing the risk of crop failure. By providing a sufficient and timely water supply to crops, irrigation favours the plant's capacity to absorb the applied nutrients and, thus, contributes positively to fertilizer use efficiency. Fertigation, which combines irrigation with fertilization, maximizes the synergy between these two key agricultural inputs.

At present, irrigated agriculture in developing countries covers 20 per cent of the arable land, but accounts for 40 per cent of total crop production and 60 percent of the cereal production. Agriculture accounts for 60 to 90 per cent of total water withdrawals in developing countries. Irrigation efficiency in developing countries is projected to increase from 43 per cent to 50 per cent by 2030, thus saving 330 billion cubic metres of water per year.

According to the Food and Agriculture Organization of the United Nations (FAO),

irrigated agriculture will account for 47 per cent of crop production in 30 years. Better Water Use Efficiency will help to contain the resulting increase in agricultural withdrawals of water.

IFA's Position

IFA advocates the optimal use of fertilizers and water resources with appropriate integrated management systems that are compatible with food security and sustainability objectives.

IFA, in collaboration with other stakeholders, promotes management practices that have the potential to enhance Water Use Efficiency, in particular the appropriate use of fertilizers and fertigation.

December 2002