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.
Highlights
The scarce available water for crop use represents one of the key limiting factors largely constraining agricultural production in arid and semi-arid areas [1,2]
The decreased R2 indicates that the changes in yield, ET, and water use efficiency (WUE) are more sensitive to the changes in annual precipitation, and natural precipitation is critical to crop growth and yield improvement under dry climatic conditions
Crop production by adopting conventional tillage (CT) was significantly higher than that of two tillage practices without residue retention, i.e., CT and reduced tillage (RT), but was significantly lower than no tillage (NT) that combined tillage reduction and residue retention (Figure 3a). This indicates that tillage reduction of NT is still necessary to combine with straw mulching to obtain a higher production of crop, despite the relative importance of straw mulching being higher than tillage reduction [26,30]
Summary
The scarce available water for crop use represents one of the key limiting factors largely constraining agricultural production in arid and semi-arid areas [1,2]. Rain-fed farming land in China accounts for nearly 25 Mha, mainly in the Chinese Loess Plateau [3]. The intensive evaporation and low rainwater supply has been worsening as an essential constraint to crop production in dry land [6,7,8]. Given water as the key limiting factor to increasing crop productivity, management strategies that can significantly improve water use play a critical role in crop production increase and food security [2,8,10,11,12,13]
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