Effect of straw incorporation on methane emission in rice paddy: conversion factor and smart straw management

Abstract

Abstract Straw incorporation is strongly recommended in rice paddy to improve soil quality and mitigate atmospheric carbon dioxide (CO 2 ), via increasing soil organic carbon (SOC) stock. However, straw application significantly increased methane (CH 4 ) emission during rice cultivation, and then its incorporation area was not expanded effectively. To find the reasonable straw management practice which can reduce CH 4 emission without productivity damage, the effect of straw incorporation season and method on CH 4 emission was investigated at six different textured paddy fields in South Korea for 2 years. A straw was applied right after rice harvesting in autumn, and the other right before rice transplanting in spring. In the autumn application, straw was applied with two different methods: spreading over soil surface or mixing with soil. Straw application significantly increased seasonal CH 4 flux by average 28–122% over 197–590 kg CH 4 ha −1 of the no-straw, but its flux showed big difference among straw applications. Fresh straw application before transplanting increased seasonal CH 4 flux by approximately 120% over the no-straw, but the autumn application reduced its CH 4 flux by 24–43% over 509–1407 kg CH 4 ha −1 of the spring application. In particular, the seasonal CH 4 flux was approximately 24% lower in straw mixing with soil after autumn harvesting than 423–855 kg CH 4 ha −1 in straw spreading over surface. However, CH 4 fluxes were not significantly discriminated by soil and meteorological properties in the selected condition. Straw application slightly increased rice grain yield by approximately 4% over the no-straw, but rice productivity was not statistically different among straw applications. Spring straw application increased CH 4 intensity which means seasonal CH 4 flux per grain yield by the maximum 220% over the no-straw. Autumn straw application significantly decreased CH 4 intensity by average 24–65% over the spring straw application. In particular, CH 4 intensity in straw mixing with soil treatment was not statistically different with the no-straw. Therefore, autumn straw application with mixing inner soil could be a reasonable straw management practice to decrease CH 4 emission impact with improving soil productivity.