Best Management Practice for Potassium Application in Potato in Northwest China

During 2012 to 2013, 30 field trials with two treatments (OPT and OPT-K) were conducted in randomly selected rainfed and irrigated farmers' potato fields in Inner Mongolia and Gansu Provinces. The objective was to study tuber yield response and agronomic efficiency of K, soil indigenous K supply and productivity for K recommendation. The effect of K fertilizer source and time of application on potato tuber yield and quality were also studied in the two provinces. The average soil exchangeable K was 97 and 164 mg/kg in rainfed fields and 171 and 198 mg/kg in irrigated fields in Inner Mongolia and Gansu, respectively. The relationship between soil exchangeable K and relative yield (yield with no K/yield with K × 100%) showed that the critical level of soil exchangeable K at 90% relative yield was 99 mg K/kg for rainfed potato and 137 mg K/kg for irrigated potato.

In Inner Mongolia, K application increased potato tuber yield by an average of 1.7 t/ha (11%) and 2.2 t/ha (8%) and starch content by 0.7 and 0.6%, while it decreased reducing sugars by 0.3 and 0.25% for rainfed and irrigated potato, respectively. In Gansu, K fertilizer application significantly increased tuber yield by an average of 2.0 t/ha (8%) and 2.7 t/ha (8%) and starch content by 0.8 and 0.2%, while it decreased reducing sugars by 0.04% for rainfed and irrigated potato, respectively. The average agronomic efficiency (AE) of K fertilizer was 26.5 kg tuber/kg K₂O and 15.7 kg tuber/kg K₂O for rainfed and irrigated potato, respectively, in Inner Mongolia. These AE values in Gansu were 31 kg tuber/kg K₂O and 41 kg tuber/kg K₂O, respectively. In Inner Mongolia, the average indigenous K supply and tuber productivity were 52.7 kg/ha and 13.9 t/ha for rainfed potato and 118 kg/ha and 25 t/ha for irrigated potato, respectively. In Gansu, the mean indigenous K supply and tuber productivity were 172 kg/ha and 23.5 t/ha for rainfed potato, 246 kg/ha and 30 t/ha for irrigated potato, respectively. Tuber yield of rainfed potato was not related with soil exchangeable K, but the tuber yield of irrigated potato increased with the increase of exchangeable K in the soil. Potassium fertilizer application rates could be recommended based on AE (kg tuber/kg K₂O), target yield (Y_t, t/ha), and no K yield (Y₀, t/ha); i.e. recommended K (kg K₂O/ha) = (Y_t – Y₀) × 1000/AE. In rainfed and irrigated conditions, K fertilizer sources did not significantly affect tuber yield and quality, except that MOP significantly lowered the reducing sugar content. The best management practice for K fertilizer application in potato production of this region was to apply 100% KCl as basal or 50% as basal and 50% as topdressing either in rainfed or irrigated conditions.