Is Irrigation Water Causing Degradation in Black Soils

Groundwater is the major or the only source of supplemental irrigation in the arid, semi-arid and coastal regions. Poor quality irrigation water in shrink–swell soils (i.e. Vertisols or black cotton soils) causes poor drainage (due to low saturated hydraulic conductivity (sHC)), increase in pH (due to soil reaction), high exchangeable sodium/magnesium percentage and increase in bulk density of soil. Therefore, quality of irrigation water is a key issue in irrigated agriculture, particularly in black soils where due to high clay content of the shrink–swell type of soil, the drainage problem is more likely. In India, shrink–swell soils (Vertisols) developed in the alluvium derived from the weathering of Deccan basalt, are found mostly in the Peninsular region extending from 845N to 260N lat. and 680E to 8345E long. Majority of shrink–swell soils (Vertisols) covering nearly 76.4 mha (ref. 3) in India occur in the lower piedmont plains or valleys, or in microdepressions. The shrink–swell soils contain a high proportion of swelling clays such as smectites. However, their unique physical properties are the greatest limitation to the dominantly low-input agriculture requiring careful management in order to tap the potential and at the same time avoiding any further decline in soil quality. A thorough understanding of the quality of these soils is crucial to develop and implement farming practices that will keep them productive for the current and future generations. Vertisols of the Purna Valley, which is spread over the districts of Amravati, Akola and Buldhana in Maharashtra, are generally free from any perceptible evidence of salt efflorescence on the soil surface. However, they do have the problem of poor drainage conditions. This adverse physical condition of the soil is due to its poor hydraulic conductivity caused by inadequate soil drainage, which in turn is mainly caused due to the impairment by sodium in the exchange complex. Additionally, there are other factors and processes that are inherently related to the development of sodicity in these shrink– swell soils. These additional factors/ processes are not yet understood completely. Considerable portion of these soils is reported to have developed salinity and waterlogging. The Soil Survey Department of Maharashtra has also reported this problem on both banks of the Purna River. Moreover, the soil in these areas generally remains waterlogged even after the rains which disrupts the sowing of kharif crops on several occasions. As a consequence, farmers are unable to maintain a sustainable production of agricultural crops. The present study was undertaken in four tehsils (i.e. blocks) of Amravati district dominant in black soils where, despite the low level of sodicity (exchangeable sodium percentage (ESP)  5), the soils have severe drainage problem, causing water stagnation in the rainy season which adversely affects the sowing or post-sowing operations in the kharif season. Crop failure due to lack of stored moisture is another problem in this part of Maharashtra dominated by these soils. The use of natural freshwater (viz. river or well) for irrigation aggravates the physical condition of the soil to such an extent that many farmers are forced to abandon irrigated agriculture in most parts of the district. In Maharashtra, the total irrigated area is 4.2 mha,