Severe boron deficiency limiting grain legumes in the inner Terai of Nepal.

Lentils, chickpeas, and pigeon peas are important grain legumes grown in Nepal. They provide staple components of Nepalese diets by supplying vegetable protein, vitamins, and minerals that are otherwise only available in sparse amounts. Their cultivation also improves soil health through additions of fixed nitrogen and organic matter and by breaking cereal pest and disease cycles. However, their yields are generally low and unstable due to an array of biotic and abiotic constraints. Symptoms suggestive of micronutrient limitations had been observed prior to the 1990s, but it was difficult to differentiate these symptoms from those caused by other factors. For example, the poor podding of chickpea was usually attributed to Botrytis grey mould disease, until it was shown that boron (B) deficiency had a similar effect. In order to establish if any, and if so which, micronutrients were limiting chickpea, an omission trial was conducted in the field at the Research Station of the Grain Legume Research Programme, Rampur, Chitwan District, inner Terai in the 1993/94 season. In the absence of applied B, there was no yield as no pods formed, in comparison to a yield of 300 kg ha-1 in the full nutrient treatment. There was yellowing of younger leaves and typical ‘little leaf’ symptoms when B was omitted. Molybdenum (Mo) was also shown to be deficient for chickpeas at this site. Subsequent field trials established that the optimum rate of B to apply to the soil to correct the deficiency at this location was 0.5 kg ha. Further studies at this location confirmed positive responses of lentils and pigeonpea in terms of yield to B application. In lentil variety ILL-4605, absence of B reduced yield to 6% of the treatment with B; in the pigeonpea variety, Bageswari, the reduction was to 10% of the treatment with B. Lentils also responded to zinc. For all of these legumes, there were large genotypic differences in response to B, with exotic germplasm (e.g., lentil genotypes from the International Centre for Agricultural Research in Dry Areas [ICARDA] and chickpea and pigeonpea genotypes from the International Crop Research Institute for the Semi-Arid Tropics [ICRISAT]) being more susceptible to B deficiency than locally-derived ones. This indicates evolution of local genotypes to B-deficient conditions and scope for genetic enhancement to alleviate B deficiency. In the 1997/98 and 1998/99 seasons, on-farm trials were conducted to evaluate the extent of B deficiency in the inner Terai. Chickpea and mustard, crops known to be particularly susceptible to B deficiency, were used as test crops. Yield responses were widespread but variable, with responses of up to 560% in chickpea and 360% in mustard crops being recorded. Responsiveness decreased with increasing soil organic matter content. A critical concentration range of 15-20 ppm B was found for the shoot tips of chickpeas. The large responses to B obtained in these grain legumes, and appearance of symptoms likely to be due to B-deficiency in these and other crops in the central and eastern Terai, indicate a need for systematic