Effects of potassium application on yield and potassium balance of sweet potato field in China: A meta-analysis

Objectives Sweet potato is a potassium-loving crop, and its production relies heavily on K fertilizer application. This study was designed to integrate existing research results and quantitatively analyze the effects of K application on sweet potato yield and K balance. We aim to clarify sweet potato yield's response characteristics to K application under different factors, thus, providing theoretical guidance for K application.

Methods This study collected literature on the effect of K application on sweet potato yield published in China from 2000 to 2020. In total, 548 datasets were collected and subjected to a meta-analysis to analyze the effect of K application on yield increase and the influence of different K application rates on K balance.

Results K application increased sweet potato yield by 18.0% compared with no K application (P<0.05) . The increase on sweet potato yield though K fertilizer application was significantly (P<0.001) affected by yield level of the control group. The higher the yield recorded in the control plot, the lower the sweet potato yield's response to K fertilizer application. At low and medium yield levels of the control group (≤25 t/hm² and 25−35 t/hm²), the optimal K application rate was 225−300 kg/hm² and 300−375 kg/hm², respectively. At high yield levels >35 t/hm²), there was no significant (P>0.05) yield response to different K application. Soil organic matter (SOM), total N, available P, and available K (P<0.001) affected the yield increase effect of difference K application. The effect of K application on sweet potato yield was higher when SOM>20 g/kg, total N>1 g/kg, available P=10−20 mg/kg and available K (AK)≤50 mg/kg. The effect of K application on sweet potato yield showed a parabola trend with an increase in the K quantity applied. The appropriate K application rate for maximum yield was 225−300 kg/hm² when AK≤50 mg/kg, 300−375 kg/hm² when AK between 50 and 100 mg/kg, and not necessary when AK>100 mg/kg. The required K application rate was >225 kg/hm² to maintain soil K balance when sweet potato straw was not returned to the field, and that was >75 kg/hm² when straw was returned to the field.

Conclusions In China, the K application enhances sweet potato yields. K application has a strong relationship with SOM, total N, available P, and available K. Maintaining soil K equilibrium also necessitates potassium application. Specific soil conditions should dictate the K treatment regime for sweet potato production.