Temporal dynamics of paddy soil structure as affected by different fertilization strategies investigated with soil shrinkage curve

The paddy soil presents strong structural dynamics due to tillage and frequent Wetting/Drying (WD) cycles. Fertilization practices can affect soil structure and therefore may alter their dynamics. The aim of this study was to investigate the temporal dynamics of paddy soil structure as affected by fertilization strategies using soil shrinkage characteristics. Four long-term fertilization treatments were selected: no fertilization as a control (CK), mineral fertilizer (NPK), mineral fertilizer plus green manure (GM), mineral fertilizer plus green manure and swine manure (GSM). Undisturbed soil cores and bulk soil samples were collected four times during WD cycles. Soil physical properties and shrinkage curves were measured. The results showed that soil bulk density and aggregate stability increased during drying and decreased during wetting, while soil shrinkage capacity was on the contrary. Relative to CK and inorganic fertilization, the application of organic manure decreased soil bulk density and increased aggregate stability, but had no impact on soil shrinkage capacity. Detailed shrinkage analyses manifested the different shrinkage patterns for the different treatments. The GSM treatment had more structural shrinkage than the CK, NPK, and GM treatments because more inter-aggregate pores developed in the GSM treatment. The shrinkage behavior of organic fertilizer treated soils (GSM and GM treatments) was more stable during WD cycles than the NPK and CK treatments. Besides, the CK and NPK treatments had greater slopes at the inflection point (slopefroe,d), indicating the soil structure of the GM and GSM treatments was more stable than that of the CK and NPK treatments, which was confirmed by soil aggregate stability data._ These results suggest manure should be used to improve soil structure and increase soil stability. We also recommend soil shrinkage curves as a useful tool to study the structural properties, dynamics, as well as the quality of the paddy soil with a high shrinkage capacity.