Coupling impacts of planting date and cultivar on potato yield

Potato is one of the major food crops in agro-pastoral ecotone (APE) in North China, with a total yield accounting for 46.8% of total grain yield in the region. Therefore, yield stability of potato is of significance for food security in the region. Due to the shortage of surface water and groundwater resources, potato is mostly produced under rainfed condition in the APE. Thus, there is large variation in rainfed potato yield due to high variability of annual and season precipitation. Adjustment in planting date and selection of cultivars were both effective ways of adapting to climate change, but there were few studies on the exploration of the impacts of coupling planting date and cultivar type on potato yield under rainfed condition in the APE. In this study, the APSIM-Potato model were calibrated and validated by serial planting date and cultivar experiments of potato in 1981-2010 to analyze the optimal combinations of planting date and cultivar by focusing on yield and guaranteeing rate of yield of rainfed potato. The results showed that APSIM-Potato model performed well in simulating phenology and fresh yield under different planting dates and cultivars of potato. The range of root mean square errors (RMSE) between the observed and simulated phenology was 0-6.3 days for the calibration years and 2.1-4.2 days for the validation years under different combinations of planting date and cultivar type. The range of normalized root mean square error (NRMSE) between the observed and simulated yields under different combinations of planting date and cultivar type was 0.3%-3.9% for the calibration years and 0.9%-7.6% for the validation years. Under rainfed condition, the range of simulated fresh yield of potato under different combinations of planting date and cultivar was 0-28 914 kg·hm^-2 for the period 1981-2010, with an average of 10 494 kg·hm^-2. Planting mid-maturing cultivar 'Kexin_1' in late planting date (1^st June) produced fresh yield of 12 153 kg·hm^-2, which was respectively 16.3% and 7.0% higher than that under early planting season (26^th April) and the middle planting (15^th May) in the APE during 1981-2010. Moreover, the simulated fresh potato yield of 'Kexin_1' under late planting date was respectively 18.7% and 17.2% higher than that of early-maturing cultivar 'Favorita' and late-maturing cultivar 'Desiree'. Planting mid-maturing cultivar at late planting date (1^st June) guaranteed higher simulated fresh yield than the average in 66.7% years of 1981-2010. The study showed significant interaction among planting date, cultivar and environment in potato production in the APE in North China. Under rainfed condition, postponing planting date and selecting mid-maturity cultivar of potato was the most effective way of adapting to the warming and drying climatic conditions. This provided a reference for adapting to climate change and ensuring stable and high potato yield in the region.