Otimização dos processos de calibração e validação do modelo cropgro-soybean

Abstract

Crop models are important tools to improve the management and yield of agricultural systems. These improvements are helpful to meet the growing food and fuel demand without increase the crop areas. The conventional approach for calibrating/validating a crop model considers few to many experiments. However, few experiments could lead to higher uncertainties and a large number of experiments is too expensive. Traditionally, the classical procedure use to share an experimental dataset one part to calibrate and the other to validate the model. However, if only few experiments are available, split it could increase the uncertainties on simulation performance. On the other hand, to calibrate/validate the model using several experiments is too expensive and time consuming. Methods that can optimize these procedures, decreasing the processing time and costs, with a reliable performance are always welcome. The first chapter of this study was conducted to evaluate and compare a statistically robust method with the classical calibration/validation procedure. These two procedure, were applied to estimate the genetic coefficients of the CROPGRO-soybean model, using multiple experiments. The cross-validation leave-one-out method, was applied to 21 experiments, using the NA 5909 RG variety, across a southern state of Brazil. The cross-validation reduced the classical calibration/validation procedure average RMSE from 2.6, 4.6, 4.8, 7.3, 10.2, 677 and 551 to 1.1, 4.1, 4.1, 6.2, 6.3, 347 and 447 for emergence, R1, R3, R5, R7 (days), grains.m-2 and kg.ha-1, respectively. There was stability in the estimated ecotype and genetic coefficient among the 21 experiments. Considering the wide range of environment conditions, the CROPGRO-soybean model provided robust predictions of phenology, biomass and grain yield. Finally, to improve the calibration/validation procedure performance, the cross-validation method should be used whenever possible. For the second chapter of this study, the main objectives were to evaluate the calibration/validation uncertainties using different numbers of experiments and to find out the minimum number of experiments required for a reliable CROPGRO-Soybean simulation. This study also used 21 field experiments (BMX Potencia RR variety) sown in eight different locations of Southern Brazil between 2010 and 2014. The experiments were grouped in four classes (Individual sowings, season/year per location, experimental sites, and all data together). As the grouping level increase, the developmental stages RRMSE (%), decreased from 22.2% to 7.8% from individual sowings to all data together, respectively. The use of only one individual sowings experiment could lead to a RRMSE of 28.4, 48, and 36% for R1, LAI and yield, respectively. However, the largest decrease occurred from the individual sowings to the season/year per location. Then, is recommended, use at least the season/year per location (early, recommended and late sowing dates) class. It will allow understand the behavior of the variety, avoiding the high costs of several experiments and keeping a reliable performance of the model.