Nitrous Oxide Emissions from an Andosol Upland Field Cropped to Wheat and Soybean with Different Tillage Systems and Organic Matter Applications

Abstract

To elucidate effects of tillage systems and organic-matter applications on N2O emissions, we assessed seasonal patterns and magnitudes of N2O emissions from Andosol upland soil growing wheat and soybeans using different tillage systems (conventional tillage and no-tillage) and organic-matter applications (crop-residue, crop-residue and cattle manure, and none). Mean N2O emissions during June 2008-October 2010 were 41-134 mgN m-2yr-1. The N2O emissions were observed immediately after manure application, fertilizer application, and during the later growing season in soybean-cropped soil. ANOVA revealed that the kind of crop and the organic-matter applications affect N2O emissions, unlike tillage systems. Greater N2O emissions in soil with residues and manure suggest that NO3--N determines N2O production by denitrification. Additionally, N2O emissions are greater in soybean-cropped soil, probably because of denitrification. The presence of fresh organic matter such as shed roots and degraded root nodules, NO3--N, or NO2--N under wet soil conditions is necessary for N2O production by denitrification. The water-filled pore space (WFPS) in no-tilled soil is consistently greater than that in conventionally tilled soil, but it does not affect N2O emissions, suggesting that soil wetness changes are the cause: tillage is not the sole limiting factor for N2O production in well-aerated soil. Greater N2O emissions during warm, wet periods of the growing season imply that emissions are related to climatic conditions that affect the soil environment and the resultant microbial activity. Nevertheless, N2O emissions from the study site with light-colored Andosol resembled those from Andosol, but were less than those from the other soil types such as those of Brown Forest soil, Brown Lowland soil, Grey Lowland soil, Wet Andosol, and Peat soil. Light-colored Andosol of this study site has lower background emissions. © 2011, The Society of Agricultural Meteorology of Japan. All rights reserved.