APSIM-Tropical Pasture model parameterization for simulating Marandu palisade grass growth and soil water in irrigated and rainfed cut-and-carry systems

Process-based models such as the Agricultural Production Systems Simulator (APSIM) can be useful to simulate pasture growth and development. This aim of the study is to parameterise the APSIM-Tropical Pasture model to simulate Marandu palisade grass (Urochloa brizantha cv. Marandu), irrigated and rainfed, under cut-and-carry management. Parameterisation was performed with experimental data collected in Piracicaba, SP, Brazil (Experiment 1: 11 growth cycles), and Sao Carlos, SP, Brazil (Experiment 2: 9 growth cycles). In both experiments, aboveground live biomass, leaf, stem, crown and dead material mass, specific leaf area (SLA), leaf area index (LAI) and height were assessed. In Experiment 1, soil water content was measured with a capacitance probe, at depths from 0 to 0.9 m. Calibration was performed for base temperature, light extinction coefficient and radiation use efficiency. The calibrated model proved to be accurate in simulating living biomass, leaf mass, LAI and height for all tested variables. In the irrigated system, the statistics presented values between 0.64 and 0.86 for coefficient of determination (R-2), between 0.59 and 0.70 for efficiency coefficient (NSE) and between 0.88 and 0.95 for the Willmott's agreement index (d). For these same variables, in the rainfed system, R-2 values ranged from 0.70 to 0.86; NSE from 0.54 to 0.70; and average d was 0.93. The simulation of soil water content showed satisfactory results for rainfed pasture, but was less precise for the irrigated treatment. The calibration of the APSIM-Tropical Pasture model for Marandu palisade grass resulted in efficient simulations of pasture growth under cut-and-carry management.