Environmental Controls on Fallow Carbon Dioxide Flux in a Single‐Crop Rice Paddy, Japan

Abstract

Soil organic carbon (SOC) is one of the important measures of soil fertility and sustainability in arable lands. With continuous CO 2 flux measurements, this study assessed the SOC decomposition and its environmental controls at both half-hourly and season-long scales in a single-crop rice (Oryza sativa L.) paddy during three fallow periods between 2004 and 2007. Measurements were made on a gray lowland soil sited in eastern Japan using the eddy covariance method. Ecosystem respiration was strongly affected by soil water content measured at 0-0Á1 m depth. At 0Á5 m 3 m À 3 or more of soil water content, the baseline of ecosystem respiration decreased by 50% compared with that at 0Á2 m 3 m À 3 . The effect was quantified at half-hourly scale using an empirical multiple regression model, together with the soil surface temperature and the time after residue incorporation. At season-long scale, net biome production, which is equivalent to the change in the SOC pool during the fallow period, was estimated from the flux and ancillary data at 150 g C m À 2 in 2004-2005, 70 g m À 2 in 2005-2006, and 270 g C m À 2 in 2006-2007. Apparently, as much as 46 to 79% of the soil organic matter incorporated (crop residues, ratoon, and stable manure) was decomposed during the fallow period. Precipitation, or associated soil water content, was important for the carbon balance of the field at season-long scale because of its large interannual variability and relatively low permeability of the paddy soil.

Comparison of fallow season CO<SUB>2</SUB> efflux from paddy soil estimated using laboratory incubation with eddy covariance-based flux

“…They obtained a higher CO 2 evolution rate at the field capacity than that at 60 of the field capacity. This finding does not appear to be consistent with the negative correlation between CO 2 flux and soil moisture reported by Ono et al 2015 . In actual fields, soils were stacked and layered, and water continuously moves vertically and horizontally.…”

“…At a field scale, Ono et al 2015 measured the CO 2 fluxes during three FSs in a normally cultivated rice paddy in central Japan using the eddy covariance method and showed that approximately 50 of the crop residues left in the field after the harvest were decomposed during FS. The time course of the observed CO 2 flux during FS was positively correlated with soil temperature and negatively correlated with soil moisture under very wet conditions.…”

Precise and continuous measurement of plant heights in an agricultural field using a time-lapse camera

“…Meteorological data and ecological characteristics such as plant height, leaf area, and biomass have been monitored at the site since 1999 Ono et al, 2013 . A rectangular plot of 100 54 m was cultivated with 'Koshihikari' rice Oryza sativa L. using established methods. Further details of the site and experimental crop are given in previous studies Miyata et al, 2005;Saito et al, 2005;Mano et al, 2007;Ono et al, 2008Ono et al, , 2013Ono et al, , 2015 2.2 Plant height measurement method 2.2.1 Plant height measurement system A weatherproof time-lapse camera PlantCam, Wingscapes, Alabaster, AL, USA was used to capture images of rice plants at the site. The camera has a 4.0 megapixel CMOS sensor and the 35-mm-equivalent focal length is 45 mm lens field of view of 52° .…”

A Nondestructive Method to Estimate Plant Height, Stem Diameter and Biomass of Rice under Field Conditions Using Digital Image Analysis

“…A rectangular plot of 100 × 54 m was cultivated with 'Koshihikari' rice (Oryza sativa L.) using established methods, and the transplanting and harvesting date were May 2nd and September 11th, respectively. Further details of the site and experimental crop are given in previous studies Saito et al, 2005;Mano et al, 2007;Ono et al, 2008Ono et al, , 2013Ono et al, , 2015Mano, 2017).…”