Simulation of Soil Water and Nitrogen Under Different Management Practices in Maize-Wheat Rotation

Abstract

Water and nutrients availability affect the crop yield. Soil mulching (plastic or straw) may improve crop yield by reducing evaporation and improving soil quality. Climatic and soil conditions, crop species and water availability sometimes oppose the effects of mulching. Field experiments were conducted on a loam soil for two years (2014-15 and 2015-16) to assess the effects of irrigation and nitrogen fertilizer under plastic and straw mulches on maize (Zea mays L.) and wheat (Triticum aestivum L.) growth, yield, water use efficiency and soil properties. Treatments involved three irrigation levels [60% field capacity (I1), 80% field capacity (I2) and 100% field capacity (I3)] and three mulches [control (M0), plastic film (M1) and rice straw mulch (M2)] in Study-I. Irrigations in main plots and mulches in sub-plots were arranged in a split-plot arrangement with randomized complete block design. Irrigations were applied to fill the soil moisture deficit at pre-decided field capacity levels with intervals of 7 days for maize and 15 days for wheat. Soil water contents and bulk density were determined at 15 cm intervals up to 45 cm depth one day before each irrigation to determine the amount of irrigation. A cut-throat flume was used to apply the measured amount of irrigations to each plot. In Study-II seven treatments were tested including nitrogen and mulch omission plots (T0) and three nitrogen management practices (single split, two splits and three splits) and two mulched conditions (plastic film and straw mulch). The plots were arranged in a randomized complete block (RCB) design with three replications. For one split whole nitrogen was applied at sowing for maize and wheat. For two splits nitrogen was applied at sowing and 12-leaf stage (V12) and for three splits nitrogen was applied at sowing, 4-leaf stage (V4) and 12-leaf stage (V12) in maize. For wheat nitrogen was applied at sowing and crown root stage in two splits and at sowing, crown root stage and tillering in three splits. In both studies soil volumetric water contents in 0-160 cm depth at 20 cm intervals in soil profiles were measured in each depth at every 7 days using TDR in each plot. Soil samples were also taken up to 160 cm depth at 20 cm intervals with an auger every month. The concentrations of NH4+-N and NO3--N were determined after the extraction of fresh soil samples. WHCNS (Water Heat Carbon Nitrogen Simulator) model was used to simulate soil water content, nitrate concentration and ammonium concentration in soil profile. Results indicated that maize and wheat grain yield increased with increase in irrigation levels, and the maize yield in plastic film treatment was 28-32% more than that under no mulch treatment. While straw mulch increased wheat yield by 17-23%. xviii Mulching also enhanced the water storage in soil at harvest and decreased the total water use by maize and wheat. Mulching decreased the water use by maize from 552.98 mm in M0 to 485.79 mm in plastic film mulch (M1) and from 378.63 mm in M0 to 336.76 mm in straw mulch (M2) by wheat. There was no significant effect of irrigation levels on water use efficiency (WUE) of maize and wheat but was affected significantly by the different mulches. The WUE of maize in plots under plastic film were 10.2 and 11.4 kg ha-1 mm-1 during 2014 and 2015 which were 22 and 36%, respectively more than that under non-mulched plots. The water use efficiency of wheat was 19-25% more than that of control in straw mulch. Maximum grain yield of maize was recorded for treatment T5 (plastic film + nitrogen in three splits) which was 75.6 and 81.4% more than that of T0 (control) during 2014 and 2015 respectively. T6 (straw mulch + nitrogen in three splits) increased grain yield of wheat by 40.7% during 1st year while 46.9% during 2nd year. Total water use by maize was 1.12 and 4.4% lower than that of control in 2014 and 2015, respectively. T6 reduced the total water use by wheat by 0.8 and 1.2% over that of control in 2014-15 and 2015-16, respectively. Water use efficiency of maize increased by 77.7% during 2014 and 87.8% during 2015 in T5 as compared to that of T0. T6 increased water use efficiency of wheat by 41.8 and 48.8% over that of T0 in 2014-15 and 2015-16, respectively. Straw mulching significantly decreased soil bulk density with an increase in soil porosity, hydraulic conductivity, infiltration rate, soil organic matter, active carbon and water stable aggregates in 0-15 cm and 15-30 cm soil layers in both studies. For both studies, predicted and observed soil water contents and nitrate concentrations at all depths were in agreement. However, simulated ammonium contents were not close to measured values at all depths. A significant relationship was observed between measured and simulated values of soil water and nitrate concentration for both studies. The data show that plastic and straw mulches can increase yield, WUE and soil quality under conditions of limited water availability. Nitrogen applied in three splits under plastic film for maize and under straw mulch for wheat significantly improved growth and yield of respective crops. Nitrogen fertilization under mulched conditions significantly decreased the total water use and increased the water use efficiency in both crops. The WHCNS model was acceptable in simulating soil water and nitrogen in the study area.