Effect of Tillage Method and N Fertilizer Rates on Water and Nitrate Movement in Northern Khuzestan Soils

Irrigation management, soil tillage method and fertilizer management play important roles in increasing crop yield and water and solute movement in the soil profile. The present research was conducted to study the effects of a no-tillage system and nitrogen fertilizer on the mineral nitrogen movement and soil moisture under optimum irrigation conditions. The study was conducted at Safiabad Agricultural Research Center in silty clay loam soil and a warm, semi-arid climate. Two methods of corn seedbed preparation, including conventional tillage (CT) and no-tillage (NT) at three nitrogen levels (150, 225, 300 kg per hectare) were implemented. The nitrogen source was urea and was applied through fertigation in three equal splits at first irrigation, four-leaf and flowering stages. Nitrate and ammonium were measured before and 10 days after fertigation and after harvesting at 30 cm depth increments down to 120 cm. Inflow and outflow rates, soil moisture before and after irrigation, and bulk density were measured. The results indicated that no significant difference was observed between soil bulk density at the initial, middle and end of the cropping period for both tillage systems. The greatest moisture level was observed in the upper soil layer (0-20 cm) under NT (about 3%) for all pre-irrigation measurements. Inflow and outflow rates indicated that NT increased applied water and decreased runoff for every irrigation as a result of residues accumulated in the furrows. Nitrate concentration in the 0-30 cm soil layer for the two tillage methods was significantly higher than for the other layers (P<0.01). No significant differences were found between soil nitrate concentration and nitrate movement in soil layer for both tillage systems. Thus, nitrogen fertilizer application in the NT system with direct drilling on wheat residue is recommended at the same level recommended for CT. The levels of NH4-N in pre- and post-fertigation applications were generally low than the NO3-N level and no significantdifferences were found in the soil layers for both tillage systems.