Effective management of legumes for maximizing biological nitrogen fixation and other benefits

The importance of legumes in sustainable crop production systems is well recognized. In the rice and wheat cropping systems of the Indo-Gangetic Plain, several legumes such as chickpea, lentil, pea, soybean, groundnut, mung bean, black gram, cowpea, and pigeonpea are grown depending upon rainfall pattern, water resources, geo-morphological features, domestic needs, and cropping systems. In the rice-wheat sequential cropping, short-duration legumes such as mung bean and cowpea offer great promise, but at present their adoption is negligible due to several management and social constraints. The productivity of legumes in general is low due to low genetic yield potential and sub-optimal management practices. Several studies under the All India Coordinated Pulses Improvement Project (AICPIP) have clearly shown that with better management, the present level of productivity of most of the legumes could be almost doubled. Tillage, planting time, plant population, plant nutrition, irrigation, and weed management considerably influence biological nitrogen fixation and productivity of legumes and therefore their management needs to be optimized for the agroecological regions and production systems. A decrease in nodulation and nitrogenase activity in many legumes has been observed due to late planting, high plant population, drought, excess moisture, high dose of mineral nitrogen, and soil application of herbicides (oxyfluorfen, linuron, oxadiazon, and metribuzin). Enhanced nodulation and higher yield have been reported with timely planting, application of 20-40 kg sulfur ha-1 along with 17.5-26.5 kg phosphorus ha-1, dual inoculation with Rhizobium and vesicular-arbuscular mycorrhizal fungi, irrigation at critical growth stages under moisture stress conditions, and efficient weed management. Deficiency of micronutrients such as zinc, molybdenum, and iron, which impair nodulation and grain yield, have been observed in some of the area