Effects of irrigation methods on distribution characteristics, stability and nutrient contents of calcareous brown soil aggregates

A field experiment was conducted at the Hancun Experimental Base of the Wheat Research Institute, Shanxi Agricultural University, from 2016 to 2021 to explore the effects of different irrigation methods (continuous micro-sprinkler irrigation, SI; continuous drip irrigation, DI; continuous flooding irrigation, FI; and annual rotation of flooding irrigation and micro-sprinkler irrigation, RI) on the distribution characteristics, stability, and nutrients contents of calcareous brown soil aggregates. After five years of positioning, >0.25 mm aggregates weight percentage of machine-stable aggregates (DR_0.25) and water-stable aggregates (WR_0.25), mean weight diameter (MWD), geometric mean diameter (GMD), destruction rate (PAD), fractal dimension (D), and nutrients (organic carbon, available phosphorus, and available potassium) contents of soil water-stable aggregates were determined. In addition, the correlations among the distribution characteristics, stability, and nutrients contents of soil water-stable aggregates were analyzed. The main results were as follows: 1) In the 0–10 cm soil layer, the dominant particle sizes of mechine-stable soil aggregates of treatments SI, DI, and RI were 0.5–1 mm, that of treatment FI was <0.25 mm. In the 10–20 cm soil layer, the dominant particle sizes of mechine-stable soil aggregates of treatments DI, FI, and RI were > 5 mm, while that of treatment SI was 0.5–1 mm; that for all treatments were > 5 mm in the 20–50 cm soil layer. The dominant particle size of the water-stable aggregate of the four treatments was <0.25 mm in the 0–50 cm soil layer, but the highest percentage of weight was observed in FI. 2) SI and DI effectively increased WR_0.25, reduced D, and resulted in higher MWD and GMD overall in the 0–50 cm soil layer, as well as decreased PAD in the 30–50 cm soil layer compared to FI and RI. However, the aggregates stability indices of treatments FI and RI were largely affected by the soil depth. 3) Compared to FI and RI, SI and DI resulted in higher contents of organic carbon, available phosphorus, and available potassium in soil water-stable macro-aggregates (>0.25 mm), and had obvious advantages in increasing available phosphorus content in the 0–30 cm soil layer and available potassium content in the 30–50 cm soil layer. 4) The results of the correlation analysis showed that the relationships between soil depth, WR_0.25, MWD, GMD, PAD, D, and nutrients (organic carbon, available phosphorus, and available potassium) contents of soil water-stable macro-aggregates were significant (P<0.05) or extremely significant (P<0.01). Overall, SI and DI were more advantageous in improving the structure and properties of soil, promoting the formation of soil macro-aggregates, and increasing the level of stability and nutrients contents of water-stable aggregates, and should be popularized and applied.