RICE-wheat is a major cropping pattern of the rice growing areas of the country, occupying about 1.8 million hectares. However, wheat yield in rice-growing areas are lower than that of the neighbouring irrigated areas. One of the major factors limiting wheat yield is late planting of wheat after rice, particularly ‘basmati’ rice.
Pre-irrigation or rainfall at the time of preparation of land further delays wheat plantation by 2-3 weeks. Wheat planted late after mid-November causes losses in grain yield at the rate of one per cent per day per hectare. This conflict between rice and wheat can be resolved in several ways as by developing early maturing rice and late maturing wheat varieties, mechanical harvesting of rice or by planting wheat directly at zero- tillage.
By Atique Rehman
RICE-wheat is a major cropping pattern of the rice growing areas of the country, occupying about 1.8 million hectares. However, wheat yield in rice-growing areas are lower than that of the neighbouring irrigated areas. One of the major factors limiting wheat yield is late planting of wheat after rice, particularly ‘basmati’ rice.
Pre-irrigation or rainfall at the time of preparation of land further delays wheat plantation by 2-3 weeks. Wheat planted late after mid-November causes losses in grain yield at the rate of one per cent per day per hectare. This conflict between rice and wheat can be resolved in several ways as by developing early maturing rice and late maturing wheat varieties, mechanical harvesting of rice or by planting wheat directly at zero- tillage.
Soil resources are suffering from degradation over the last few years. Much of it has lost up to one half of its native organic matter content. Evidence suggests that growth in cereal yields has begun to decline in many high potential areas, possibly owing to soil nutrient mining, declining levels of organic matter, increasing salinity, falling water tables and the build up of weed, pathogens and pest populations. The major contributors to this trend are the tilling of soil with disc, plow and cultivator in preparing the land for seeding, using chemical fertilisers instead of natural manures. The challenge facing the region, therefore, is to further increase productivity while making agriculture more efficient, ecologically sound and sustainable.
In recent years, drought has been a factor in crop production and farmers have come to realise the full effects of soil erosion. Traditional farming systems in rice-wheat cropping areas are heavily reliant on tillage to prepare a fine seed-bed for wheat sowing. There has been a cultural belief that ploughing the land many times is a heavy toll for soil health and overall productivity.
It has been shown through research and farmer experience that excessive tillage removes surface residues which protect the soil. More tillage causes more erosion and soil degradation, especially in warmer areas where the top soil layer is thin. The most desirable form of tillage is to leave a protective cover of leaves, stems and stalks from the previous crop on the surface of soil.
Zero-tillage means planting of seed directly on no tilled soil after the harvest of the previous crop. It is introduced by the International Maize and Wheat Improvement Centre (CIMMYT).
The best way to avoid delay in planting wheat after rice is to adopt appropriate relay cropping system technology at zero-tillage. Relay cropping of wheat at zero-tillage has been reported to produce wheat yields comparable to that obtained at traditionally prepared seed bed. Zero-tillage allows early and timely sowing of wheat crop and reduces the cost of production through lesser use of fossil fuels and herbicides etc. In zero- tillage crops are planted with minimum disturbance of soil by placing the seeds in a narrow slit 3-4cm wide and 4-7cm deep without land preparation.
Many variables contribute to yield potential, including growing season precipitation, temperature, fertiliser placement, crop rotations, and type of seeding implement. With the proper equipment and good crop management techniques, producers have shown that there is a good probability that yields will be equivalent or better under zero-tillage systems than with conventional tillage systems. With zero-tillage technology, farmers can produce more for less cost, with fewer inputs as well as saving on diesel fuel, tractor time and conserving irrigation water.
Sowing with zero-tillage offers the benefits of retained surface residues and reduced soil water losses. Zero-tillage seeding systems can provide higher spring soil moisture and lower evaporation losses compared with conventional tillage systems. By increasing soil water through better retention of snow and rainfall and decreasing evaporation losses which is one of the limiting crop production factors in dry land farming, farmers can increase the yields.
Zero-tillage sowing may improve soil condition over time. Long term zero- tillage seeded fields are higher in the availability of organic nitrogen than in fields seeded using conventional methods. This is supported by the experience of many long time zero-tillers who have reduced their fertiliser rates from soil test recommendations without suffering yield decreases.
Crop rotation is fundamental to zero-tillage, since this promotes adequate biomass levels for permanent mulch cover; it also assists in the control of weeds, pests and diseases, as well as in improving the physical condition of the soil. Soil erosion is reduced by about 90 per cent and soil biological activity and bio-diversity are maximised.
The early-established wheat crop shades weeds more effectively, reducing their growth and the need for herbicides. This can be explained by the fact that conventional land preparation disturbs the soil and brings weed seeds to the surface. The rice stubbles and higher plant density under zero-tillage leave less room for weeds. In a field study at six locations in rice area, 43 per cent less weed density was observed at zero-tillage compared to conventional tillage.
Since it enables wheat to take advantage of residual moisture from rice, zero-tillage saves farmers around one million liters of water per hectare, compared with conventional practices. This water represents an actual savings which is important for farmers, who are eventually charged more for water and related expenses or it may be used elsewhere for productive agriculture. By burning an average of 60-70 litres less diesel fuel per hectare sown, tractors emit much less carbon dioxide under zero-tillage, which shows that this practice is also an environment-friendly. Zero-tillage also reduces the level of drudgery for crop establishment which provides better quality of life to the farmer.
A potent constraint in adopting zero-tillage in rice-wheat system, is the attack of stem borer (Scirpophaga incentulas), a harmful pest of rice. Presently farmers are required to uproot and incorporate rice stubbles by the end of February and to delay planting of rice nurseries after 20th May in order to destroy larvae surviving in rice stubbles before rice planting in the following year.
