Impact of straw return on greenhouse gas emissions from maize fields in China: meta-analysis

Abstract

Introduction: An increase in the amount of greenhouse gases (GHGs) in the atmosphere causes global warming, and >14% of all GHG emissions come from agricultural activities. The three primary atmospheric GHGs are CO₂, CH₄, and N₂O; therefore, regulating GHG emissions from agroecosystems is important for global climate management. Straw return is an environmentally friendly agricultural practice that positively affects crop production and soil fertility. However, its effects on long-term GHG emissions remain controversial.

Methods: To examine the impact of straw return on GHG emissions from Chinese maize fields, 281 data pairs from 45 publications were assessed using a data meta-analysis.

Results: The findings demonstrated substantial increases in CO₂ and N₂O emissions of 140 and 40%, respectively. Methane emissions increased by 3% after straw return, and the maximum effect value of CO₂ emissions was 2.66 at nitrogen rates<150 kg/hm². The effect value of CH₄ emissions increased with an decrease in soil organic content, and the effect value of CH₄ emissions changed from negative to positive at concentrations >6 g/kg. With a nitrogen rate increase, N₂O emission effects under straw return initially increased and then decreased. N₂O emissions increased significantly when nitrogen rates were<250 kg/hm². The results of a random forest model showed that the most important factor affecting CO₂ and N₂O emissions from corn fields under straw return was the amount of nitrogen applied, and the most important factor affecting CH₄ emissions from corn fields under straw return was soil organic carbon content.

Discussion: This shows that a suitable straw return can achieve the mutually beneficial goal of guaranteeing food security and minimizing adverse effects on the environment.

Keywords: greenhouse gases; maize; meta-analysis; random forest; straw return.

Figure 1

Searching and filtering flowcharts.

Figure 2

The geographical distribution of the trial locations in the meta-analysis.

Figure 3

Summary of the overall effects of straw return in maize fields on CO₂, CH₄, and N₂O emissions. Blue squares are effect values; red line segments are 95% confidence intervals.

Figure 4

The effects of TN (g/kg), SOC (g/kg), nitrogen rate (kg/hm²), soil pH, soil type, average annual temperature (°C), rainfall (mm), plant method, and tillage method on CO₂, CH₄, and N₂O emissions from straw return in maize fields. Blue squares are effect values; red line segments are 95% confidence intervals.

Figure 5

The figure on the left illustrates the factors that impact greenhouse gas (GHG) emissions from soils where straw was returned. On the right side, the figure displays the relationship between CO₂ emissions and nitrogen fertilization rate (A, D), CH₄ emissions and organic carbon content (B, E), and N₂O emissions and nitrogen fertilization rate (C, F) under straw-returned conditions. "ns" indicates no significant difference, "*" indicates a significant difference (P < 0.05), and "**" indicates a strong significant difference (P < 0.01).

Figure 6

Conceptual map of the impact of straw returning on greenhouse gas emissions. The plus sign in red indicates an increase, while the minus sign in green indicates a decrease. The number next to the sign represents the corresponding effect value.