Replacing nitrogen in mineral fertilizers with nitrogen in maize straw increases soil water-holding capacity

Soil water-holding capacity decreases due to long-term mineral fertilizer application. The objective of this study was to determine how replacing mineral fertilizer with maize straw affected the soil water retention curve, soil water content, soil water availability, and soil equivalent pore size. Replacement treatments in which 25% (S₂₅), 50% (S₅₀), 75% (S₇₅), and 100% (S₁₀₀) of 225 kg ha^-1 nitrogen from mineral fertilizer (CK) was replaced with equivalent nitrogen from maize straw were conducted for five years in the Loess Plateau of China. The Gardner model was used to fit the soil water retention curve and calculate the soil water constant and equivalent pore size distribution. The results indicated that the Gardner model fitted well. Replacing nitrogen from mineral fertilizer with nitrogen from straw increased soil specific water capacity, soil readily available water, soil delayed available water, soil available water, soil capillary porosity, and soil available water porosity over time. S₂₅ increased field capacity and wilting point from the fourth fertilization year. S₅₀ enhanced soil readily available water, soil delayed available water, soil available water, and soil available water porosity from the fifth fertilization year, whereas S₂₅ and S₇₅ increased these from the third fertilization year or earlier. Soil specific water capacity, soil readily available water, soil delayed available water, soil available water, soil capillary porosity, and soil available water porosity could better reflect soil water-holding capacity and soil water supply capacity compared with field capacity and wilting point.