Calibration and evaluation of a Carbon Net Primary Productivity (CNPP) module based on the Simple model

The Carbon Net Primary Productivity (CNPP) module is an extension of the SIMPLE model designed to estimate above- and belowground biomass production and carbon assimilation. Developed for integration within the ProCarbon-Soil (PROCS) environmental carbon simulation framework, the module predicts carbon inputs both during and at the conclusion of crop cycles. Initial parameterization was conducted for soybean and maize using micrometeorological data, while wheat, bean, and perennial forage (Urochloa brizantha cv. Marandu) were parameterized utilizing agrometeorological experimental data and literature sources. Subsequently, reference cultivars were calibrated by grouping genotypes based on phenological traits and edaphoclimatic regions using farm-level datasets. Evaluation against micrometeorological sites demonstrated high accuracy in simulating leaf area index, evapotranspiration, and dry matter allocation for soybean and maize. While performance for wheat, bean, and forage was slightly constrained by data availability, the overall statistics validate the module’s efficacy across major Brazilian agricultural regions. Through its parsimonious parameter set, the CNPP module ensures robust calibration and high performance across diverse crops, genotypes, and management scenarios.