Drying-wetting cycles consistently increase net nitrogen mineralization in 25 agricultural soils across intensity and number of drying-wetting cycles

Abstract

An increase in extreme weather events such as heavy rainfall and extreme drought causes intensive and frequent drying-wetting (DW) cycles, which have strong effects on the availability of nitrogen (N) for plant growth and development. How the effects of DW cycles on N turnover vary with the intensity and number of DW cycles and soil properties has not been clearly addressed, which hinders predicting soil biogeochemical cycles in a changing world. Herein, we examined the response of net N mineralization in agricultural soils measured at a standard temperature (25 °C) to DW cycles varying in intensity and number. A total of 25 soils differing in texture and organic matter content were collected to create a soil property gradient. We also established the relationships of DW cycle effects on net N mineralization to soil properties. The DW cycles significantly increased N mineralization by 11.05 ± 0.66 mg kg−1 (+81.7%), and the increase was consistent across DW intensities and numbers for most soils. The release of inorganic N was dependent on soil properties, while the regulation of soil properties on DW effects varied with DW intensity, with stronger regulation under intense DW cycles (60% to 0% field capacity) than under moderate DW cycles (100% to 20% field capacity). The effect of intense DW cycles on NH4+ increased with clay content but decreased with soil pH and sand content. The effect on NO3− has opposite responses to these soil properties when compared with the effects on NH4+. The effect on total inorganic N increased with soil pH and inorganic N concentration. These results indicated that DW cycles have the potential to increase N availability in agricultural soils and highlighted the underestimation of N availability predicted with averaged soil moisture instead of real-time soil moisture under changing soil moisture conditions.