Evaluation of DSSAT CERES-Maize Model in Simulating Soil Mineral Nitrogen (NH4+ and NO3-) and Yield of Corn in North Central Oklahoma.

The CERES-Maize of DSSAT v4.6 model was used to simulate soil mineral nitrogen and corn yield in a silt loam and loam soil in north central Oklahoma. The data used for validation was obtained from a two-year study of conventional tillage and no till corn (Zea mays L.) during 2016 and 2017. Urea ammonium nitrate (28-0-0) was used as nitrogen source with six N treatments which include 0, 40, 80, 120, 160, and 200 pounds/acre each replicated three times arranged in a randomized complete block design in two locations. Both fields were initially sampled a week prior to pre-plant fertilization and sequentially sampled afterwards at four (4) growth stages of corn (V2, V4, V8 and VT). Soils collected were submitted to Oklahoma State University’s Soil, Water and Forage Analytical Laboratory (SWAFL) within forty-eight (48) hours from sampling. These samples were then analyzed for extractable NH4⁺, NO3^- using 1.0 M KCl and were simultaneously measured on a flow-injection analyzer. The ammonium is analyzed using the salicylate method, and the nitrate is measured using the cadmium reduction method.  Total extractable N (NH4⁺ + NO3^-) was then calculated.

The model’s inputs included site information, daily weather data, soil properties, soil initial conditions, irrigation and fertilizer management and crop performance data. Overprediction by the model on the soil mineral nitrogen (NH4⁺ and NO3^-) was observed. The model also overpredicted yield across treatments. Results obtained from experiment (Yo) and simulation (Ys) has the following relationships expressed as Ys= 1.0634Yo with R² =0.77 for extractable ammonium, Ys=0.4396Yo with R² =0.76 for extractable nitrate and Ys=1.21Yo with R² =0.89 for corn grain yield. The study showed that improvement of the DSSAT’s CERES-Maize is needed before it can be used to confidently simulate yield and soil mineral nitrogen at different vegetative stages of corn under conditions in north central Oklahoma.