Preparing South Asia for prime time

Most farmers in the High Barind Tract of northwest Bangladesh can grow only one crop per year, transplanted summer rice. By the time this is harvested, the soil surface has begun to dry out, and subsequent crops struggle to get going. Only those who can afford to irrigate their land from deep tube wells can hope for a reliable winter harvest, whether of boro (winter) rice or an alternative such as wheat. However, in the last two years, 10,000 hectares of the High Barind Tract have yielded two excellent winter crops of rainfed chickpea.

Farmers have been using minimum tillage to reduce soil moisture loss and planting short-duration chickpea varieties introduced by researchers from the Plant Sciences Research Programme of the UK Department for International Development. The plants' early maturity minimises the impact of end-of-season drought. Key to success is priming the chickpea seeds prior to sowing to help the seedlings achieve good establishment. The rewards to farmers have been encouraging; two crops per year instead of one, one of them a chickpea crop that tolerates drought, needs few inputs and fetches a high price at the market.

Steroids for seeds?

credit: Centre for Arid Zone Studies

Seed priming - the practice of soaking seed in water overnight prior to sowing - is well known to enhance crop establishment (See Seed priming: a simple but successful solution [99-4]). More novel is the use of priming water as a medium for growth-boosting supplements. Chickpea, like other legumes, relies on soil-borne molybdenum to facilitate the development of root nodules that house the nitrogen-fixing rhizobia bacteria that turn legume roots into nitrogen fertiliser factories. The research team in Bangladesh found that adding a pinch of sodium molybdate to the priming water bears impressive results. In trials, chickpea seeds primed with sodium molybdate and rhizobium yielded, on average, 60 per cent more than seeds primed with water alone.

Other trials in eastern India looked more specifically at the action of the sodium molybdate. Two sets of seeds were compared, one set primed with sodium molybdate and rhizobium and a control set initially primed with plain water, with rhizobium later applied to the seeds' surface. The seeds primed with both rhizobium and sodium molybdate yielded 25 per cent more than the rhizobium-only control.

Molybdenum and rhizobium are not the only supplements that can be administered in priming water. In Pakistan, wheat and chickpea have responded well to the addition of zinc sulphate, and preliminary data suggest that priming seed with phosphate stimulates early root growth, allowing better uptake of soil phosphorus. With nitrogen, phosphorus and molybdenum all deficient in large areas of Africa and Asia, the potential of enhanced priming would seem huge. Molybdenum in particular is deficient in the acidic soils that cover a lot of eastern India from West Bengal to Orissa, and much of eastern Africa. Legume growth in these regions suffers as a result.

A viable technology?

But is seed priming with mineral or organic supplements a realistic option for poor farmers? How available is sodium molybdate, for example? In fact, this obscure-sounding compound is typically available on the shelves of agricultural suppliers in South Asia, where it is applied to soil to boost legume growth. The advantage of administering the dose through priming water is that it greatly reduces the amount needed. One jar, sufficient to treat a hectare of land, will prime seeds for an entire village.

Yet, despite the simplicity of seed priming, interest and uptake has been patchy. Extension departments comment that as a single, stand-alone technology, seed priming is not 'substantial' enough to merit its own promotion campaign, though the use of the technique to tackle soil nutrient deficiencies could change that view. Furthermore, in situations where poor crop establishment is a major constraint to production, as it is with rainfed winter crops in the High Barind Tract, seed priming could be the precise tool needed.

Quick-growing rice

Efforts by the DFID-funded Plant Sciences Programme to increase the popularity of growing winter crops in the area are also being helped by the introduction of shorter-duration rice plants. These varieties, selected in farmer-participatory trials in Nepal, have now undergone 'mother and baby' trials in Bangladesh, with great success. Of the 11 varieties brought from Nepal, all reached maturity earlier than the varieties currently being grown in Bangladesh, and most had considerably better yields, more than 30 per cent better in some cases. The best of the Nepali rice varieties matured three to four weeks sooner than the most popular variety in Bangladesh, with superior grain yield, grain quality and resistance to lodging.

The shorter duration of the first crop also gave farmers more time to get their second crop established, reducing pressure on labour at a busy time of year. Although the newly introduced varieties were originally intended for summer cultivation, many farmers decided to grow them during the winter season, with comparably good results. But for those without the water resources to sustain a winter rice crop, planting a primed, short-duration winter chickpea crop could be an excellent alternative.

Mother and baby trials: the central (mother) site allows researchers to test the widest range of technologies using a conventional experiment design. At the same time, the smaller (baby) trials allow participating farmers to select the technologies they are specifically interested in and those which are best suited to their needs. (See also Turning the wheels of technology Developments 00-4)