Effect of long‐term fertilization on the transformations of water‐extractable phosphorus in a fluvo‐aquic soil

Abstract

Improved information on water‐extractable soil P (Pw) and its distribution in various forms is needed to assess its bioavailability and environmental impact. This study investigated Pw in a fluvo‐aquic soil solution in relation to the continuous application of inorganic fertilizer (NPK) and wheat straw–soybean‐based compost for 15 y. Phosphatase‐hydrolysis techniques were used to fractionate organic P (Po) in water extracts of soil into phosphomonoester (Pom) and phosphodiester (Pod). In comparison with the noncomposted treatments, compost application significantly increased the levels of inorganic P (Pi) and Po. Pom was the main form in water‐extractable soil Po (71%–88%), in which sugar phosphate (Pos) occupied 48%–75%, inositol hexakisphosphate (Pop) comprised 13%–23%, and Pod only accounted for a small percentage (11%–26%). Long‐term compost application significantly increased the content of Pom, Pos, and Pod, but decreased the Pop content; the ratio of Pom to Po increased significantly in compost‐treated soil, but the ratio of Pop to Po and Pod to Po significantly decreased. Thus, the equilibrium of phosphatase involved P transformations shifted to Pi in compost‐treated soil. The phosphomonoesterase and phosphodiesterase activities were significantly higher in compost‐treated soil, which favored the transformations of Pod into Pom and Pom into Pi. The ratio of Po to Pw in water extracts of compost‐treated soil was similar to that of control soils with no fertilizer input (CK), but was significantly lower than in NPK treatment, which demonstrated that a larger increase occurred for soil Pi in water extracts of compost‐treated soil. Long‐term compost application in the fluvo‐aquic soil changed the composition of Pw, promoted the rate of P transformations in soil solution, and significantly increased soil P bioavailability.

Organic and Inorganic Carbon in Paddy Soil as Evaluated by Mid-Infrared Photoacoustic Spectroscopy

“…It has been observed previously that SOC does not increase continuously even under conditions of great C input [32]. This was also verified in a long-term manure fertilization experiment conducted on a Fluvo-aquic soil [33]. Soil organic carbon increased during the first five to eight years, but thereafter a balance was reached.…”

Distribution and Enzyme Activities in the Soil around the Fertilizes

“…Each plastic pipe (length× diameter = 23cm ×5cm) was filled orderly with 180.0 g of soil at one end, fertilizer in the middle and another 180.0 g of soil at the other end. Fertilizers were separated from the soil with a nylon cloth, which has been shown to be an ideal material for the interface between soil and fertilizers [16,17], since this material enables water, nutrient, and microbial exudates to pass freely. Fertilizers placed between two nylon cloths included chemical fertilizer (urea), mixture of chemical and organic fertilizers in a ratio of 7:3 (urea + rapeseed straw), and organic fertilizer (rapeseed straw), respectively.…”

Nitrogen migration and transformation characteristics of the soil in karst areas under the combined application of oxalic acid and urea inhibitors

“…When nitrogen fertilizers are applied to soil, fertilizer microsites are formed near the fertilizer, with nutrient concentrations significantly different from the soil overall. In the fertilizer microsites of tidal soils, most of the applied phosphorus was immobilized, mainly within 2 mm of the soil at the point of application ( Du et al., 2012 ). In the fertilizer microsites of Paddy soil, water-soluble phosphorus, and effective phosphorus gradually decreased with increasing temperature ( Chen et al., 2014 ).…”