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Paper of the Month November 2016

Simulating potential growth in a relay-strip intercropping system: Model description, calibration and testing

Abstract

Intercropping tends to have a higher productivity than traditional sole crops, mainly due to complementary resource use in time and space among different species. Intercropping may become more importantin a world that needs to produce 60–70% more food by 2050 with limited land and other agriculturalresources. To assess the role of intercropping in agricultural systems and its contribution to future foodsecurity, an intercrop model is needed for growth and yield predictions of intercrops under differentgrowing conditions. Strip intercropping is a prevalent intercropping system, but the existing intercropmodels are generally built for full mixtures and are less suitable for strip intercrops. Here we describe asimple intercrop model which is developed based on a sole crop model using the radiation use efficiency (RUE) concept and a strip intercrop light partitioning module. The model allows simulating the growthand yield of each intercropped species in relay-strip intercropping under potential growing conditions (only competition for light; other resources are assumed to be non-limiting), and the intercrop could varyin species combination, planting configuration, sowing densities and sowing dates. The daily inputs of themodel are temperature and radiation, and crop-specific parameters are required to simulate crop leaf areaindex (LAI), biomass and final yield. Data collected during two years (2013 and 2014) field experimentswere used to calibrate and test the model. The experiments consisted of two sole crop treatments (solewheat, SW and sole maize, SM) and three intercrop treatments (replacement intercrop, 6:2WM and add-row intercrops, 8:2WM and 6:3WM). The experiments were conducted in Wageningen, the Netherlands. Data of sole crops (SW and SM) and replacement intercrop (6:2WM) treatment were used to calibratethe model, and data of add-row intercrops (8:2WM and 6:3WM) were used to test the model. Bayesiananalysis was applied to calibrate RUE of wheat and maize in sole crops and intercrop. This calibrationprocedure resulted in posterior distributions of RUE for sole crops and intercrop, on the basis of whichdistributions of biomass and land equivalent ratio (LER) were simulated. Biomass accumulation and yieldof each species were simulated adequately but LAI was slightly overestimated compared to observations.The intercrop model allows simulating the contribution of border row effects to the productivity of inter-crops. It combines a simple structure with easy calibration and enables growth and yield simulations fora wide range of relay-strip intercrops. The model thus can be of value in exploratory land use studies toassess the role of intercropping.

Fang Gou, Martin K. van Ittersum, Wopke van der Werf (2017) Fields Crops Research 200: 122-142

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