Potassium management in potato production in Northwest region of China

• Potassium increased tuber yield, enhanced commercial rate, mean tuber weight and starch content, reduced sugar content.
• In nearly 80% of the trials soil K was negative balance at current K application levels.
• The critical level of soil exchangeable K at 90% relative yield was 105 mg kg−1.
• Potassium could be recommended by relationships between yield response and agronomic efficiency and between uptake K and yield.

Field trials were conducted to study response of potato (Solanum tuberosum L) yield and quality to potassium (K) application, soil indigenous K supply (IKS) and productivity (IKP), K use efficiency and critical level of soil test K to establish scientific methods for K management in potato production. Results indicated that K application increased tuber yield by a range of −2.8 to 7.2 Mg ha−1 with an average of 3.2 Mg ha−1, 90% positive responses. Potassium application produced an average of 4.9 percentage more commercial rate, 11.3 g more mean tuber weight and 0.4 percentage more tuber starch content and 0.2 percentage less tuber sugar content than those of treatment without K application. The average agronomic efficiency of potassium (AEK) was 30.2 kg tuber kg−1 K2O, 56% observations was in 10–40 kg tuber kg−1 K2O. 79.2% of the observations showed negative K balance in potato fields with an average of 101.7 kg K ha−1 deficit. 87.5% of all the observations showed positive benefit from K application with an average return of US$715 ha−1. The average IKS and IKP was 141.8 kg K ha−1 and 25.9 Mg ha−1 which can be explained 25% and 30% of variations, respectively, by soil exchangeable K. Significant negative quadratic relationship (R2 = 0.75, P < 0.01) between yield response and relative yield, and significant linear relationship (R2 = 0.80, P < 0.01) between yield response and AEK were obtained. There was a significant relationship (R2 = 0.74, P < 0.01) between total uptake K by potato plant and total tuber yield. The critical level of soil exchangeable K at 90% relative yield was 105 mg kg−1 which can be a reference for K recommendation.