Field, plant, to leaf: A meta-analysis on crop water use efficiency response to potassium fertilization

Applying potassium (K) fertilizer to fields is considered to be an important agricultural production practice to improve crop water use efficiency (WUE). However, the magnitude of crop WUE response to K fertilization has only been reported for individual regions, crops and scales due to lack of extensive and complete global datasets. Here we quantified the responses of crop WUE to K fertilization at the three scales of field-population (WUEfield), whole-plant (WUEplant) and single-leaf (WUEleaf) through synthesizing 797 paired observations from 81 field -based studies worldwide. Meta-analysis results showed that K fertilization increased WUEfield, WUEplant and WUEleaf of crops by 19.0%, 12.0% and 29.9%, respectively, with the key factors influencing this being crop type, mean annual precipitation and soil pH, respectively. It should be noted that the magnitude of WUEfield, WUEplant and WUEleaf response to K fertilization was significantly positively correlated with mean annual precipitation, while significantly negatively correlated with soil pH, which implying that K fertilization is an effective way to improve crop WUE in the region with humid climate or acidic soil. Furthermore, the conclusive findings of this meta-analysis showed that the relative importance of environmental factors in the magnitude of the WUEfield, WUEplant and WUEleaf response to K fertilization was 49.8%, 68.8% and 82.0%, respectively, which indicated that climatic characteristics and soil properties were drivers of crop WUE response to K fertilization rather than management practices. Overall, our meta-analysis provides new insight into the crop WUE response to K fertilization from field, plant, to leaf was driven by environmental factors and highlights the great potential of improved field K fertilization strategies in developing sustainable agriculture under the condition of climate change.