Soil respiration, aggregate stability and nutrient availability affected by drying duration and drying-rewetting frequency

Abstract

Wetting dry soil is well known for generating respiration and nutrient pulses (the “Birch effect”), but the effects of frequent drying-rewetting (DRW) cycles, especially the effects regarding nutrient availability, have not been well investigated. This study was designed to determine how DRW frequency influences soil respiration, aggregate stability and nutrient availability. Soil was collected from Xishan Forest Farm in Beijing, China, incubated in a laboratory and subjected to 1, 2, 3, 4, 6, or 8 DRW cycles over 48 days, with a control treatment at constant moisture (CM). The results showed that the stability of soil aggregates was significantly promoted when the drying period exceeded 12 days, while the soil aggregate stability decreased when the number of DRW cycles exceeded 2 and declined with an increase in cycle frequency. Under DRW incubation, the cumulative respiration during the wetting period compensated for the lack of respiration in the drying period compared with that under CM. The soil NH4+ and NO3− contents increased after drying, but after DRW, the NH4+ content decreased while the NO3− content increased. These results indicate that DRW promoted soil nitrification and that this effect strengthened with an increase in the number of DRW cycles. The variation range of available P was small under different DRW frequencies, indicating that the soil environment exerted a certain buffering effect on the availability of P. The availability of K increased when the drought exceeded 12 days but decreased progressively with increasing DRW frequencies. We conclude that a duration of drying exceeding 12 days is an important factor influencing soil aggregates and the availability of K. The frequency of DRW cycles may be important for aggregates and the availability of N and K.