Using NCSWAP to simulate seasonal nitrogen dynamics in soil and corn

• Published in: Plant and soil 1995-12, Vol.177 (2), p.235-247
• Main Authors: Dou, Z. (Pennsylvania State Univ., University Park, PA (USA). Dept. of Agronomy), Fox, R.H
• Format: Article
• Language: English
• Subjects: Agricultural soils; Agrology; AZOTE; CICLO BIOGEOQUIMICO; Corn; CYCLE BIOGEOCHIMIQUE; CYCLING; ESTACIONES DEL ANO; FERTILIDAD DEL SUELO; FERTILITE DU SOL; Fertilizers; MODELE DE SIMULATION; Modeling; MODELOS DE SIMULACION; Nitrates; NITROGEN; NITROGENO; SAISON; SEASONS; SIMULATION MODELS; Simulations; SOIL FERTILITY; Soil water; Tillage; ZEA MAYS
• ISSN: 0032-079X; 1573-5036
• DOI: 10.1007/BF00010130

The objective of this study was to determine if a re-calibrated version of the computer model NCSWAP (version 36) could accurately predict corn growth and soil N dynamics in conventionally tilled (CT) and no-till (NT) corn supplied with legume green manure or ammonium nitrate as N sources. We also attempted to ascertain the reasons for limitations in the model's ability to simulate corn growth and soil N dynamics found by our colleagues in a previous study and to propose potential improvements. The model was calibrated to accurately simulate total available N (N in plant above-ground biomass plus soil nitrate in the 0 to 45 cm profile) for a control and a fertilizer CT treatment in the 1992 growing season. To do so, input values defining the quantities of active soil organic N had to be reduced to 19% of the values proposed by the model developers and a solute transport factor defining the mobile vs. immobile fractions of soil nitrate adjusted from 0.8 to 0.2. The discrepancies between the proposed values and the lower values employed in this study might be due to the uncertainties in quantitatively describing soil N mineralization processes and the way they are handled in the model, as well as the lack of a component simulating macroporous-influenced water flow and solute transport in the model. With the current version, until one knows how to predict what these values are, the model needs to be re-calibrated for each experimental site and condition and thus is of limited value as a general model. With no further adjustment of input values, model validation success was mixed. The model accurately predicted total available N for treatments in the second year of the experiment that had the same N source and tillage as the treatments used for the calibration year but with the different weather and growing conditions. However, total available N was underpredicted where legume green manure was the N source and overpredicted with no-till cultivation. The model was accurate in simulating seasonal corn growth for nearly all the treatments, judged by nonsignificant mean difference (MD) values and highly significant correlation coefficients (r). Prediction of seasonal soil nitrate concentration was less accurate compared to total available N and corn growth variables. Potential improvements in the model's simulation of a no-till system as well as for predicting corn harvest yield and seasonal soil nitrate concentration where N deficiency occurs were discussed.