The Impacts of Conservation Agriculture on Water Use and Crop Production on the Loess Plateau: From Know-What to Know-Why

Abstract

Due to the scarce irrigation water supply in the Loess Plateau, efficient use of rainwater is critical for the improvement of sustainable crop production. Conservation agriculture (CA) has been regarded as an ideal field management strategy to profoundly benefit water use and therefore crop production. However, it remains unclear as to how crop production and water use respond to annual precipitation and how CA practices affect crop production through regulating water use. In this study, a meta-analysis based on field observations was conducted to investigate the relationship between water use and crop production. The results showed that annual precipitation of 300 mm yr−1 is a threshold to ensure relatively high crop production and water use efficiency (WUE), and 600 mm yr−1 is the most favorable rainfall level for crop production and WUE. Evapotranspiration (ET) was linearly related to annual precipitation, except that it was not the lowest when annual rainfall <300 mm yr−1. Although straw mulching is more important than tillage reduction, tillage reduction is still necessary to combine with straw mulching to obtain a higher production of crop. Crop production, ET, and WUE kept increasing as experimental duration increased, indicating that extending CA term is essential to further improve water use and crop production. We further proposed mathematical equations to prove that the increase in transpiration plays a critical role in water use and crop production improvement. WUE is not necessarily related to the increase in yield, and, therefore, higher transpiration rather than increased WUE should be the target for crop production improvement. The results also suggest that evaporation and transpiration are not presented separately, which limits investigation of the effective use of water by identifying transpiration. Overall, annual precipitation is essential for the levels of crop production, ET, and WUE on the Chinese Loess Plateau. Reasonable CA practices, especially long-term application, could improve water use and crop production through increasing transpiration. However, a better future understanding of the relationship between crop production and water use needs more detailed information about the effective use of water at field scales.