Today, however, those same farmers, and South Asia's expanding population, face uncertainty. The area under rice and wheat has stabilized, and further expansion seems unlikely. At the same time, evidence suggests that growth in cereal yields has begun to slow in many high-potential agricultural areas, possibly owing to soil nutrient mining, declining levels of organic matter, increasing salinity, falling water tables and the build-up of weed, pathogen and pest populations. The challenge facing the region, therefore, is to further increase productivity while making agriculture more efficient, ecologically sound and sustainable.
The answer will not be more irrigation and chemical fertilizer. Instead, recent research indicates, farmers could produce more - and help conserve their natural resource base - by abandoning current land ploughing and harrowing practices in favour of "zero tillage", the simple technique of drilling seed into the soil with little or no prior land preparation.
Higher yields, lower costs. FAO says that conventional tillage with tractors and ploughs is a major cause of severe soil loss in many developing countries. "With the advent of tractors, farmers started to believe that the more you till the soil, the more yield you get," says José Benites, of AG's Land and Plant Nutrition Management Service. "The truth is that more tillage causes more erosion and soil degradation, especially in warmer areas where the topsoil layer is thin. In fact, soils in tropical countries generally do not need to be tilled. The most desirable form of tillage is to leave a protective blanket of leaves, stems and stalks from the previous crop on the surface. Zero tillage systems provide higher yields at less cost and also save on fuel use and tractor wear and tear."
The report cites the results of on-farm trials which show that reduced or zero tillage generally results in wheat yields that are higher than, or at least equal to, yields obtained using conventional practices. The simplest approach is surface seeding, already common in parts of eastern India and Bangladesh, where farmers broadcast wheat seed before their rice is harvested. Trials in Nepal have demonstrated that, provided there is sufficient soil moisture, this technique gives significantly higher yields than normal ploughing, partly because it allows farmers to plant 15 days earlier than usual. And since the cost of land preparation is zero, it also generates higher net income.
Another successful practice introduced from China is reduced tillage with two-wheel tractors, which use a shallow rotovator followed by a six-row seeding machine to prepare the soil and plant seed in one operation. In India, a four-wheel version saves time by tilling only the strip of land where the seed is planted, rather than the whole land surface. On higher yielding, more mechanized farmland in northwestern India and Pakistan, the report says, a tractor-pulled seed and fertilizer drill allowed farmers to place seed directly into the standing rice stubble without any ploughing. This approach also reduced weed problems - because the soil is disturbed less under zero tillage, fewer weed seeds are exposed and fewer germinate.
The consortium cautions that reduced and zero tillage entail adjustments in other crop management practices. For example, zero tillage requires careful timing of fertilizer application for surface-seeded wheat, and studies are needed to determine the effect of surface residues on soil organic carbon and total nitrogen in rice-wheat systems. In addition, some varieties of wheat do much better under zero tillage than others. Its report concludes: "For each of the tillage options, complementary practices need to be developed. It is time to strengthen research on these technologies so they can be adapted and promoted to farmers. The potential benefits to the farmer and the economy of the country far exceed any possible disadvantages."
Published January 2001