Wheat and rice farming on the vast Indo-Gangetic plains, affected by excessive salts in the soil, can be cost-effectively improved by treatment with gypsum and organic manure followed by sowing with salt-tolerant crop varieties, a study says. Published last month in Agroecology and Sustainable Food Systems, the study says that India has 2.8 million hectares of land, mostly in the Indo-Gangetic alluvial plains, that are ‘sodic’ and that can be recovered by treating it for excess sodium. Sodic soils restrict the movement of water and air in the soil, affecting the growth of plants. Associated problems include shallow wetting zones, temporary waterlogging and diminished water storage in the root zone, researchers behind the study explain.
Globally, more than 833 million hectares of land have salt-affected soils, especially in the arid or semi-arid environments of Africa, Asia and Latin America, according to the Food and Agriculture Organization (FAO). Between 20 and 50 percent of irrigated soils are too salty, leaving more than 1.5 billion people worldwide to face challenges caused by soil degradation. Currently, soil remediation of sodic soils in India relies on the addition of 50 percent gypsum followed by cultivating traditional varieties of rice and wheat on the land. But, this is increasingly unaffordable for smallholders who farm on the upper Indo-Gangetic plains which extend over 150,000 square kilometres’. Each hectare of sodic soil requires 12 to 16 tons of gypsum for remediation which, at 4,570 per ton, is beyond the reach of small and marginal farmers (those having less than one hectare of land), the study says. The researchers estimated that 60 percent of the total cost of reclamation goes towards gypsum—a mineral which is becoming scarce because of demand for non-agricultural uses.
According to the study, conducted in the Hardoi district on the Indo-Gangetic plains of Uttar Pradesh state, treatment using 25 percent gypsum, 10 percent magnesium and press mud (organic fertilizer made from sugar cane residue), followed by sowing with salt-resistant varieties of wheat and rice, doubled crop productivity. India, a major sugarcane grower, produces about 12 million tons of press mud annually. Press mud contains nutrients, organic matter and high amounts of calcium sulphate, which supplies calcium directly to the soil to replace excess sodium.