Adaptation of the SIMPLE Model to Oilseed Flax (Linum usitatissimum L.) for Arid and Semi-Arid Environments

Abstract

Oilseed flax (Linum usitatissimum L.) is an important oil crop, and the SIMPLE model is a very effective tool to simulate crop production. In this study, to adapt the SIMPLE model for the overall improvement of flax production and yield, three promising cultivars of North China—Longya Hybrid No. 1, Baxuan No. 3 and Zhangya No. 2—were selected. Experiments were conducted in Dingxi, Wulanchabu, Datong and Zhangjiakou in Northern China from 2016 to 2020. The SIMPLE model was first calibrated and then evaluated for the simulation of flax growth and development and grain yield and biomass. A base temperature of 5 °C was used for phenology, with optimum temperatures from 16 to 20 °C for the third pair of true leaves to unfolded to the budding stage, and from 20 to 25 °C for the flowering stage. In the results, the average simulated value of aboveground biomass in Dingxi was 8772 kg ha−1, with a root mean square error (RMSE) of 1239 kg ha−1 (d-index = 0.69). The simulations were also good in the other three sites according to a comparison of the predicted and observed biomasses (RMSE 135 kg ha−1 and d-index 0.90 at Zhangjiakou, RMSE 280 kg ha−1 and d-index 0.95 at Wulanchabu, and RMSE 140 kg ha−1 and d-index 0.97 at Datong). Flax grain yield was well simulated compared with the observed values, with a RMSE of 55 kg ha−1 and a d-index of 0.96 for Dingxi, a RMSE of 63 kg ha−1 and a d-index of 0.93 for Wulanchabu, and a RMSE of 5 kg ha−1 and a d-index of 0.97 for Zhangjiakou, whereas the yield was somewhat underestimated for Datong (RMSE of 176 kg ha−1 and d-index of 0.91). Overall, the SIMPLE model provided satisfactory predictions under different environments and management. Care should be taken when transferring the SIMPLE-Flax model to other environments, as vernalization and day-length sensitivity are not included in this model.