ENHANCED SYSTEM MODELS AND DECISION SUPPORT TOOLS TO OPTIMIZE WATER LIMITED AGRICULTURE
Location: Agricultural Systems Research Unit
Title: Simulating dryland water availability and spring wheat production under various management practices in the Northern Great Plains
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 1, 2012
Publication Date: January 7, 2013
Citation: Qi, Z., Bartling, P.N., Jabro, J.D., Lenssen, A.W., Iversen, W.M., Ahuja, L.R., Ma, L., Allen, B.L., Evans, R.G. 2013. Simulating dryland water availability and spring wheat production under various management practices in the Northern Great Plains. Agronomy Journal. 105:37-50.
Interpretive Summary: The RZWQM2 model was calibrated to simulate soil water content, total above ground biomass, and grain yield of spring wheat grown in 2004-2010 under various management practices near Sidney, MT. The model performance was acceptable for predicting soil water and yield. Long-term weather data was applied to the RZWQM2 model to investigate water availability and yield differences under different management practices. The results showed ecological management lead yield loss, and a large water deficit existed under this dryland condition. Fallowing the field every other year would result in significant reduction in economic return. The simulations also suggested early planting dates and higher seeding rates would increase spring wheat yield in the North Great Plains.
Agricultural system models are useful tools to synthesize field experimental data and to extrapolate the results to longer periods of weather and other cropping systems. The objectives of this study were: 1) to quantify the effects of planting date, seeding rate, and tillage on spring wheat production in a continuous spring wheat system using RZWQM2 model under a dryland condition, and 2) to extend the results to longer term weather conditions and a wheat-fallow rotation. Measured soil water content, crop yield, and total above ground biomass in a 7-year field experiment (2004-10) conducted on a Williams loam (fine-loamy, mixed, superactive, frigid, Typic Argiustolls) at the Rasmussen dryland site near Sidney, MT were used to calibrate and validate the RZWQM2 model. Treatments were two tillage practices (conventional and no-till) and two plant management practices (conventional and ecological). The conventional plant management had customary planting dates and customary seeding rate for the region, whereas the ecological planting management, designed to control weeds, consisted of late planting dates (about 3-4 wks later) and a 33% higher seeding rate. Results showed that the model performance was acceptable in terms of soil water, yield, and biomass simulation under both management practices; however, there was a large unexplained variation in the measured biomass. The crop production was significantly affected by changes in temperature and rainfall pattern from year to year. The hydrologic analysis under long-term climate variability showed a large water deficit (32.3 cm) for the spring wheat crop; and, the actual ET of spring wheat during the growing season was 23.5 cm, about 70% of the annual precipitation of 34.5 cm. Fallowing the dryland every other year conserved 4.2 cm water for the following wheat year, of which only 1.7 cm water was taken up by wheat, resulting in a yield increase of 249 kg ha-1 (13.7%). However, the annualized average total yield decreased 782 kg ha-1 (43.1%) due to one year fallow; thus the spring wheat-fallow rotation was not economical. Other long-term simulations showed that optimal planting dates ranged from March 1 to April 10, and the seeding rate with optimum economic return was 3.71 and 3.95 × 106 seeds ha-1 for conventional and ecological management treatments, respectively. Tillage impacts on water and crop yield were minimal.