Land resources. Adopting such soil conservation measures as matching crops closely to soil types, using farming methods appropriate to the terrain, enhancing the soil with organic matter, terracing steep hillsides, ringing farm plots with soil-anchoring trees, and managing watersheds better can reduce loss of productive agricultural land due to soil erosion and degradation (98). Farmers also can protect the land by adopting low-till or no-till farming and rotating crops, thus giving soils a chance to recover nutrients.

In many degraded areas land rehabilitation has proved to be so time-consuming, labor-intensive, and expensive that it is virtually impossible. India, for example, has grappled with land degradation in arid and semiarid regions for decades but with little result (98). Other places, however, have had more success. In 1979, for example, after an extensive land rehabilitation project, China increased food production by some 70% in Mizhi County on the Loess Plateau. The project, carried out in cooperation with the United Nations Development Program, helped farmers turn steep slopes over to permanent vegetation, terrace other slopes, and control gully erosion by erecting small dams of rocks and sandbags. Many farmers also replaced annual crops with perennials, such as alfalfa, which hold the soil in place (98).

Water resources. The world needs a "blue revolution" as much as it needs another Green Revolution. Based on the UN medium population projection, over 4 billion people would be affected by water shortages in the year 2050. By then, for example, in Nigeria only about 900 cubic meters would be available per person, compared with 3,200 cubic meters per person in 1990 (26).

A water-short world is an unstable world. More than 200 river systems cross international borders; nearly 100 countries share just 13 major rivers and lakes (26, 73). Water use practices in upstream countries can affect water supplies in downstream countries. Disputes can arise, especially where countries with rapid population growth and limited arable land and water supplies vie for access to water. For example, Ethiopia plans to divert more of the Blue Nile's waters for irrigated agriculture, while Egypt, downstream, depends on the Nile's waters for its very existence (41).

These Indian women use a community stand pipe for drinking and washing. By the year 2050 over 4 billion people may be affected by water shortages. The world needs a "blue revolution" as much as another Green Revolution.

Instead of a "first come, first served" approach to water management, countries and regions need to manage distribution and use of water resources to ensure that everyone gets a fair share. Guaranteeing access to water supplies also would help food-deficit countries improve their agricultural production. Some countries have successfully negotiated agreements over use of water resources—for example, India and Bangladesh, which share the Ganges, the largest and most important river on the Indian subcontinent (14).

With the prospect of less water per person, countries must conserve available water resources and manage them better than in the past. Many strategies and technologies exist to help save water and distribute it equitably. These include building reservoirs and small catchment dams to collect water during the rainy season for use during the dry season, allowing aquifers to recharge, reducing leaks in urban water pipes, protecting watersheds by planting trees to reduce erosion, and recycling municipal waste water for agricultural use (98, 99).

Since irrigation water is wasted almost everywhere, there is great scope in the short run for water conservation in agriculture (97, 98, 99). In particular, the following steps can encourage efficient use of water and can promote conservation:

• Improving the design of irrigation systems and using technologies better suited to climate and terrain can greatly reduce waste and improve crop yields. For example, Israeli farmers use drip irrigation: each plant receives water through its own little drip tube. With this technique they have increased the efficiency of irrigation by as much as 95%. Over the past 20 years Israel's food production has doubled without using any more water (26).
• Pricing water at its real value, instead of subsidizing it, can have an immediate effect on water use, encouraging farmers to save water and use it more efficiently (73).
• For some agricultural purposes waste water from households and municipalities ("brown water") can substitute for fresh water. For example, in Calcutta sewage lagoons are used to raise carp and irrigate vegetable gardens (26). In most cases sewage water needs to be pretreated in order to eliminate pathogens.
• Water harvesting and low-cost irrigation schemes can help poor farmers meet their water needs. Water harvesting involves digging holes to collect runoff for irrigating crops, pastures, and trees during dry months. Where this technique has been used, as in Kenya, Burkina Faso, and Niger, crop yields are twice those produced by dryland farming methods (99).
• Reforesting upland watersheds can reduce water runoff and raise soil moisture levels, helping to recharge groundwater aquifers and capturing more water for human use (26, 99).