Periodic Flooding and Drying Decreases Colloidal Phosphorus Loss Potentials in the Intensive Calcareous Vegetable Fields

Abstract

Heavy manure application in protected vegetable fields with calcareous soils is commonplace in China leading to elevated phosphorus (P) loss to water. In addition, periodic flooding and drying events are an additional agricultural management strategy, which can increase the colloid-facilitated migration of P. However, newly generated minerals during the redox cycles also showed intense adsorption on P. To investigate the loss potential of colloidal P to water, soils from a 12-year vegetable field received long-term manure in the North China Plain were sampled and incubated based on different water regulation treatments including flooding (F), partially wet (W) and alternate flooding and drying (FW) events for 30 d. Soil water dispersible colloids (WDC) were extracted and characteristics of P and P-binding materials were quantified, including content, form, size-distribution, chemical composition and colloidal stabilities. Colloidal mineralogical analysis was also conducted and it enabled deeper insights into the controlling mechanism of P loss to water from soil. The results showed that most of water dispersible P (WDP) existed in the colloidal phase (0.6-1000 nm). The FW treatment significantly reduced the release of WDP and promoted the conversion from molybdenum unreactive phosphorus (MUP) to molybdenum reactive phosphorus (MRP) compared with the F or W treatments. In the drying period, the decline of pH, the enhancement of electric conductivity (EC) and WDC-associated calcium (Ca) and magnesium (Mg) were observed but the subsequent reflooding process partially neutralized these effects. Adsorption and cementation by the newly generated calcium/magnesium minerals increased the sizes and stabilities of colloidal P. In summary, controlled flooding and drainage when managed correctly have a role to play in mitigating P loss from calcareous soil in vegetable protected fields.

Keywords: Periodic flooding and drying, Colloidal P, P loss potentials, Intensive vegetable fields, Calcareous soil