EFFECTS OF CONVENTIONAL AND DEEP TILLAGE ON MUSTARD FOR EFFICIENT WATER AND NITROGEN USE IN COARSE-TEXTURED SOILS

Crops grown on coarse textured soils are prone to water and nutrient stresses owing to low water retention, poor inherent fertility, and rapid development of mechanical impedance to root growth. These stresses can be alleviated by enlarging rooting volume in the soil and/or by regulating the supply of water and nutrients. Field investigations were carried for 3 years to assess interactive effects of deep tillage, irrigation regime and nitrogen rate on root growth, dry matter accumulation, water use and yield of mustard in a loamy sand and a sandy loam soil. Treatments included combinations of two tillage systems: conventional tillage (CT) (one discing, two cultivations down to 10 cm depth, and a planking), and deep tillage (DT) (chiseling down to 35-40 cm followed by CT); three irrigation regimes: no irrigation (I0), 7 cm water 28 days after seeding (DAS) (I1), and two irrigations of 7 cm each at 28 DAS and at peak flowering (I2); and four nitrogen rates: 0, 40, 80 and 120 kg ha-1. The experiment was replicated three times in a split plot design with tillage and irrigation in main plots and nitrogen in sub-plots. Deep tillage and early irrigation enhanced the rooting density and the rate of dry matter accumulation of mustard, and as a consequence, there was greater depletion of profile stored water and better plant water status, particularly in the low water retentive loamy sand. Tillage enhanced the synergistic effects of irrigation and nitrogen on crop water use. Interaction effects of the three variables on grain yield were significant in this soil. Regression models relating relative yield to water supply and nitrogen rates showed that, for a given yield, more water and nitrogen were required for CT than for DT in the loamy sand indicating that tillage enhanced the utilization of water and nutrients. The magnitude of tillage effects was much less in the sandy loam.