Soil carbon (C), nitrogen (N) and phosphorus (P) stoichiometry drives phosphorus lability in paddy soil under long-term fertilization: A fractionation and path analysis study.

Muhammad Qaswar,Huimin Zhang,Liu Kailou,Waqas Ahmed,Shi Xiaojun,Huang Jing,Xu Yongmei,He Zhongqun,Asad Shah,Waleed Asghar,Fan Hongzhu,Jiang Xianjun

doi:10.1371/journal.pone.0218195

Abstract

Soil C:N:P stoichiometry plays a vital role in nutrient cycling in ecosystems, but its importance to P transformation in paddy soil remains unclear. We investigated the effect of soil C:N:P stoichiometry on P mobility and uptake under long-term fertilization. Three treatments, CK (no fertilization), NPK (inorganic nitrogen, phosphorus and potassium fertilization) and NPKM (combined inorganic NPK fertilizer and manure application), were selected from two long-term experiments of paddy soil that were initiated in 1991 and 1982 in Chongqing and Suining, respectively. The results showed that in comparison the control treatment, under long-term fertilization, soil pH decreased. In comparison with the NPK and CK treatments, the NPKM treatment significantly increased soil nutrient contents, P uptake and phosphatase activities. In comparison to the CK treatment, the NPK and NPKM treatments significantly decreased soil C:N, C:P and N:P ratios. In comparison to NPK and CK treatments, the NPKM treatment decreased residual-P at both sites. Compared with CK treatment, the NPKM treatments increased labile-P and moderately labile-P by 987% and 144%, respectively, and NPK treatment increased these factors by 823% and 125%, respectively, at the Chongqing site. At the Suining site, with NPKM treatment, increases in labile-P and moderately labile-P were 706% and 73%, respectively, and with NPK treatment, the increases were 529% and 47%, respectively. In contrast, non-labile-P was significantly decreased with NPKM treatment in comparison to that with NPK and CK treatments. Moreover, increases in soil C:N and C:P ratios decreased the labile-P pools and increased non-labile-P pools. A path analysis indicated that soil C:N:P stoichiometry indirectly controlled P uptake by directly affecting P transformation from non-labile to labile-P pools. Moreover, the non-labile-P in soil with high SOM and P content directly affected P uptake, indicating that soil P transformation is mainly driven by soil C and P in paddy soil. In conclusion, understanding mechanism of P mobility influenced by soil C:N:P stoichiometry could be helpful to manage soil P fertility under long-term fertilization in paddy soils of these regions.

Highlights

Crop productivity is directly affected by P availability in agricultural soils [1]
In a previous study, Ahmed et al [21] found that the combined application of manure and inorganic fertilizers increased the labile-P fraction, and different soil properties showed different relationships with P fractions, the authors did not explain the mechanism of P pools transformation, mobility and uptake in paddy soils associated with soil nutrient stoichiometry
In the NPKM treatment, a half dose of the fertilizers was applied from an inorganic fertilizes, and the remaining half dose of nutrients was supplemented with pig fecal urine at the Chongqing site and fresh pig manure at the Suining site based on N content

Summary

Introduction

Crop productivity is directly affected by P availability in agricultural soils [1]. in some agricultural soils, the concentration of total P is naturally high, which can limit plant growth due to the low solubility and rapid conversion of P compounds to unavailable or poorly available P after fertilizer application [2]. To meet plant P requirements, excessive inorganic fertilization is a common practice in these regions, which causes environmental P losses and degraded soil fertility [16] In these regions, previous studies mainly focused on long-term fertilization effect on crop yields and soil fertility [14,17], and recommended, integrated nutrient management through the combination of applying inorganic fertilizer and manure addition to improve soil P fertility [18]. In a previous study, Ahmed et al [21] found that the combined application of manure and inorganic fertilizers increased the labile-P fraction, and different soil properties (pH, SOM, total P and Olsen-P) showed different relationships with P fractions, the authors did not explain the mechanism of P pools transformation, mobility and uptake in paddy soils associated with soil nutrient stoichiometry. C:N:P stoichiometry could be used as a powerful tool to understand nutrient cycling and

Objectives

Methods

Results

Discussion

Conclusion