Organic fertilizer application increases the soil respiration and net ecosystem carbon dioxide absorption of paddy fields under water-saving irrigation

Abstract

Quantifying carbon sequestration in paddy soil is necessary to understand the effect of agricultural practices on carbon cycles. The objective of this study was to assess the effect of organic fertilizer addition (MF) on the soil respiration and net ecosystem carbon dioxide (CO₂) absorption of paddy fields under water-saving irrigation (CI) in the Taihu Lake Region of China during the 2014 and 2015 rice-growing seasons. Compared with the traditional fertilizer and water management (FC), the joint regulation of CI and MF (CM) significantly increased the rice yields and irrigation water use efficiencies of paddy fields by 4.02~5.08 and 83.54~109.97% (p < 0.05). The effects of organic fertilizer addition on soil respiration and net ecosystem CO₂ absorption rates showed inter-annual differences. CM paddy fields showed a higher soil respiration and net CO₂ absorption rates during some periods of the rice growth stage in the first year and during most periods of the rice growth stage in the second year. These fields also had significantly higher total CO₂ emission through soil respiration (total R_soil) and total net CO₂ absorption compared with FC paddy fields (p < 0.05). The total R_soil and net ecosystem CO₂ absorption of CM paddy fields were 67.39~91.55 and 129.41~113.75 mol m⁻², which were 27.66~135.52 and 12.96~31.66% higher than those of FC paddy fields. The interaction between water and fertilizer management had significant effects on total net ecosystem CO₂ absorption. The frequent alternate wet–dry cycles of CI paddy fields increased the soil respiration and reduced the net CO₂ absorption. Organic fertilizer promoted the soil respiration of paddy soil but also increased its net CO₂ absorption and organic carbon content. Therefore, the joint regulation of water-saving irrigation and organic fertilizer is an effective measure for maintaining yield, increasing irrigation water use efficiency, mitigating CO₂ emission, and promoting paddy soil fertility.