Effects of super absorbent polymer on crop yield, water productivity and soil properties: A global meta-analysis

Abstract

Super absorbent polymer (SAP) is well recognized to be one of the potential technologies for improving crop yields and water productivity (WP). However, the effects of SAP on crop yields and WP remain inconsistent and vary with environment and application conditions. In this work we conducted a meta-analysis of 1504 paired data points from 310 papers published before July 2022 to evaluate the effect of SAP on crop yield and WP considering SAP attributes, initial soil properties, and experimental conditions. The SAP addition to soil resulted in average increases of 12.8% and 17.2% on yield and WP respectively. Increases in yield and WP after SAP application were the highest in tuber crops, while the greatest economic benefits were observed in vegetable crops. The increase in WP was higher in rainfed conditions (18.3%) than in irrigated conditions (14.8%). The highest improvement in WP was observed in the SAP with organic-inorganic hybrid compound types, the banding/hole application method, and the fine-grained structure. In addition the effectiveness of WP response to SAP significantly positively correlated with the initial soil pH and the soil bulk density, and was negatively correlated with N fertilizer rates, water supply, initial soil organic matter (SOM) and total nitrogen. The improvement in WP was closely related to the increased in water stable aggregates (WSA), soil porosity, SOM, available nitrogen, phosphorus and potassium after SAP application. These results suggest that the effects of SAP application on crop yield and WP are dependent on soil properties. By integrating the impacts of environmental conditions, our findings can help to tailor-make SAP application measures for different environmental conditions to fully achieve the benefits of SAP application.