ALLEVIATION OF SOIL PHYSICAL CONSTRAINTS FOR IMPROVED CROP PRODUCTION: A REVIEWNavjot Singh, Buta Singh Dhillon and Parminder Singh Sandhu
Soil degradation and the subsequent decline in crop yields are serious agricultural and economic problems. Soil degradation occurs both as nutrient depletion and structure deterioration because of reduced soil organic matter as well as increased bulk density, poor water infiltration and erosion. Current cropping system based on traditional ploughing and straw removal induce surface crusting and soil compaction which reduces infiltration rate and promote soil erosion and overall decrease in soil fertility. The major soil physical constraints found to impair soil quality and reduce crop growth includes soil crusting, soil compaction and high soil permeability. Soil compaction of agricultural land is an important form of physical degradation. The continuous use of implements years together develops a hard pan underneath which hinder the movement of water, prevents roots of many upland crops from penetration into the deeper soil layers and inhibits growth and yield of crops. Compaction has significant effects on bulk density, root length which ultimately leads to decrease in grain yield of Corn (Zea mays L.) by 14% and Soybean (Gylcine max L.) by 45 %. Negative impact of soil compaction on crop yield can often be alleviated by sub soiling. Subsoiling resulted in increase of seed cotton yield by 14 percent over no-subsoiling treatment. Controlled traffic farming has been shown to reduce soil compaction and improve soil health. Soil bulk density, pore size distribution, water content and infiltration rate changes towards a more desirable condition on the controlled traffic plots in a continuous 10 year controlled traffic experiment. Rain before emergence of the crops results in crust formation, leading to poor emergence. There is decrease in seedling emergence of cotton following crust formation due to simulated rain. Wheat straw mulch @ 6 t ha-1 used to cover the whole plot or 3 t ha-1 to cover the rows only showed a significant improvement in emergence count and rate of emergence as compared to control (crusted) treatment. Straw mulch decreases the crust strength by reducing the impact of rain drops on soil. Highly permeable coarse textured soils are characterized by low water retention capacity, excessive permeability, poor inherent fertility and prone to wind erosion. In these soils, fertilizer use efficiency is very low and nutrient loss was very high thus discouraging use of high level inputs. Compaction of highly permeable soils by six passes of 1.5 T tractor driven roller reduced water and nutrient losses, increase NO3-N content, increased moisture retention in the soil profile and reduced the irrigation requirements for crops. There is increase in mean soil bulk density from 1.55 g cm-3 to 1.79 g cm-3 and decrease in infiltration rate of soil from 5.7 cm hr-1 to 1.32 cm hr-1 with tractor wheel compaction of loamy sand soil.
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