Contribution and fate of maize residue-15N and urea-15N as affected by N fertilization regime.

Wencheng Ding,Shutian Li,Shaomin Huang,Ping He,Debjani Sihi

doi:10.1371/journal.pone.0210176

Abstract

Increasing amounts of crop residues are being returned to croplands. Understanding nitrogen (N) availability in crop residues under various N fertilization regimes is important in optimizing N management. Pot experiments were conducted to investigate the contribution, fate and residual effects of urea and maize residue-N using a 15N isotope technique. Four N regimes were tested: three basal–topdressing ratios of N applied as urea (100–0, 75–25, 50–50) and one basal application of 75% N as urea and 25% N as manure (75U+25M). An average of 31.4% wheat N uptake was derived from urea, 9.2% from maize residue, and 59.5% from the soil in the first season. During the growing stages of wheat, maize residue contributed 0.3–4.8% and 3.1–13.2% to soil mineral and microbial biomass N, respectively, and those originated from urea was 1.0–4.2% and 4.6–16.8%, respectively. Regarding the fate of urea and residue-N after the first season, 35.9% and 16.9% of urea-15N and residue-15N were recovered by wheat, 28.1% and 46.9% remained in the soil, and 36.0% and 36.2% were lost. The contribution of urea to crop N uptake and N recovery efficiency increased, while that of residue-N decreased with increasing proportion of topdressing N. Substituting 25% mineral N with manure decreased the urea-15N loss without negative effects on crop dry matter and N uptake. Residual urea-15N and maize residue-15N from the previous season contributed 3.9% and 3.0% to summer maize N uptake. Additionally, 29.3% of residue-15N remained in the soil after the second season, while only 18.6% of urea-15N remained. Our study suggests that fertilizer and crop residue are actively involved in soil N transformation and plant N nutrition, emphasizing the capacities of organic residues to sustainably supply nutrients. Considering the utilization of both N fertilizer and maize residue, we may suggest a 75–25 split in N fertilizer application, but more appropriate options need to be further assessed under different cropping systems.

Highlights

Most agricultural soils are depleted of indigenous N and require large quantities of N to be applied in the form of mineral fertilizer
To maximize the utilization of N fertilizer and organic residues, the first step is to identify their roles playing in crop growth
Contribution and fate of maize residue-15N and urea-15N as affected by N fertilization regime contribution to crop uptake from maize residue, fertilizer, and the soil is approximately 1:3:6 with little change occurring across growth stages

Summary

Introduction

Most agricultural soils are depleted of indigenous N and require large quantities of N to be applied in the form of mineral fertilizer. China produces approximately 925 million tons of crop residues annually [11], with 34.2%, 33.1% and 14.5% of the total nutrient resources originating from maize, rice, and wheat residues, respectively [12]. Winter wheat-summer maize rotation is the dominant crop system in the North China Plain, where Fluvo-aquic soils have poor soil fertility because of its calcareous nature, frequent tillage and lack of organic matter [8]. Crop residue retention can effectively improve crop productivity, soil fertility, and enhance nutrients use efficiency by recycling them through the soil [15,16]. A meta-analysis showed that crop residue retention increased yield by 5.2%, 6.4% and 5.6%, respectively for rice, wheat and maize in China [17]. Increasing crop yield with crop residue retention depends on many other practices, such as water and fertilization management. Numerous factors, such as inherent N content, C/N ratio, lignin and polyphenol concentrations in crop residues, soil properties and climatic conditions, play important roles in decomposition and nutrient release from crop residue [18,19,20]

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Conclusion