Enhanced topsoil P leaching in a short term flooded calcareous soil with combined straw and ammonium nitrogen incorporation

Abstract Straw incorporation (SI) coupled with ammonium nitrogen (AN) application is a management strategy for storing organic carbon (OC) and optimizing vegetable yields in intensively managed calcareous soils of North China. However, during short term flooded conditions, the resulting soil acidification and subsequent Fe reduction processes may affect the transformation of soil Fe/Al-bound phosphorus (Fe/Al-P) and the mobility of phosphate in soil. This study was conducted simulating the condition of short term flooding in order to investigate P leaching and the contents of soil inorganic P fractions, Fe(III) reduction and P adsorption kinetics in calcareous soil with four treatments; control (C), straw powder incorporation (SI), SI with subsequent AN elution (SN) and SI with subsequent sulfuric acid elution (SH). The results showed that the SI treatment promoted the transformation of Ca-bound P (Ca-P) in soil to Fe/Al-P due to acidification but had no effect on P leaching. The SN treatment significantly decreased the topsoil Fe/Al-P content and maximum P sorption capacity through Fe(III) reduction, whereas it increased the total amount of P leached under flooded conditions by 86.8%. In contrast, SH promoted Fe/Al-P accumulation as well as increase the soil maximum P sorption capacity in the topsoil, leading to a decrease in P leachate of 38.1% compared with the SI treatment. The SN treatment was responsible for high P mobility through promotion of Fe(III) reduction and inhibition of acidification processes. Such findings in the present study highlight that 1) SI coupled with AN induced the Fe(III) reduction releasing associated P while 2) SI coupled with acidification significantly inhibited the P leaching, which is of environmental benefit. However, the results presented herein were limited to a single soil type. Future studies should validate the processes found in the present study across other soil types.