Establishment and application of spring maize yield to evapotranspiration boundary function in the Loess Plateau of China

The yield to evapotranspiration (Y/ET) boundary function is a simple method for estimating water-limited yield potential and provides a guide for making proper crop management decisions in dryland areas. However, the original approach is arbitrary, and the boundary function is established without following any specific principles. In the present study, based on French & Schultz's boundary function concept and the quantile regression theory, and also linear interpolation to eliminate outliers, we developed an improved method in establishing the Y/ET boundary function. Taking spring maize in the Loess Plateau of China as a case study we selected fundamental data points obtained from 887 records found in 65 papers that were published between 1987 and 2014, and also linear interpolation to eliminate outliers. The results showed that the Y/ET boundary function was y = 60.5 × (x − 50) with a plateau yield of 15,954 kg ha−1 when ET exceeded 314 mm. Without film mulching, the Y/ET boundary function was y = 47.5 × (x − 62.3) with a plateau yield of 12,840 kg ha−1 when ET exceeded 325 mm. We further compared three different crop production methods (plastic film mulching, straw mulching, and no mulching) on maize production in the Loess Plateau. Among these methods, plastic film mulching was the most effective, since it increased the yield potential of spring maize, regardless ET, and hence, improved water use efficiency. Overall, this study provides novel insights into the establishment of the Y/ET boundary functions using specific principles that increase accuracy and help to identify the most profitable crop management systems.