Evaluation of Yield Advantage and Water Productivity of Maize-Groundnut InterCropping Systems in the Dry Zone of Sri Lanka using Agricultural Production Systems sIMulator (APSIM)

Abstract

The APSIM (Agriculture Productions Systems SImulator)–Maize & Groundnut model has been utilized on a global scale to assess the effects of various farming practices on the growth of maize and groundnut intercropping. However, limited attention has been given to modeling the crop productivity (t/ha) and water productivity (t/ha/m3 ) of maize and groundnut intercropping under conditions such as rainfed or rainfed with supplementary irrigation, in tropical SouthAsia. To address this gap, we tailored and assessed the APSIM–Maize & Groundnut intercropping model for two widely cultivated Sri Lankan varieties: Pacific (Maize) and Lanka Jumbo (Groundnut). The APSIM model was introduced to simulate the growth, development, and yields of maize-groundnut intercropping in the Dry Zone of Sri Lanka, utilizing field experimental data. The model calibration process involved utilizing the first set of data to determine varietal parameters. The simulation results demonstrated a high level of agreement between the simulated values and the actual measurements during the growing periods as RMSE and RRMSE values for maize yield were 0.89 t/ha and 11.37% while that for groundnut was 0.108 t/ha and 7.7%. RMSE (Root Mean Square Error) quantifies the average prediction error in the same units as the target variable. RRMSE (Relative RMSE) normalizes RMSE by the range of observed values, providing a percentage-based measure for better comparison across datasets with different scales. The model accurately predicted grain yield for maize and groundnut under moisture-limited field conditions, showcasing a strong fit with the observed data. This fit was consistent across various factors, including cultivation year, season, time of planting (i.e., with rainfall or based on specific planting dates), variety, and water management practice (e.g., completely rainfed or rainfed with supplementary irrigation). Traditionally, many maize farmers grow this crop as a standalone crop. However, introducing groundnut as a secondary crop alongside maize offers advantages such as additional income and enhanced soil fertility. It was evident from the results that maizegroundnut intercropping can be used to get a high yield with a limited amount of water during periods of low rainfall such as the yala season and it is a very good solution to water scarcity. In situations where rainfall or other essential factors are delayed, employing crop modeling with APSIM becomes crucial to augment reliance on supplemental water resources and meet the specific requirements for maize and groundnut crops