Soil Surface Fluxes of Greenhouse Gases in an Irrigated Maize‐Based Agroecosystem

Abstract

An understanding of the effect of fertility management on soil surface fluxes of CO2, N2O, and CH4 is essential in evaluating C sequestration measures that attempt to increase the amount of crop residue returned to the soil through increased fertilizer inputs. In this study, soil surface CO2 flux was measured over a 27‐mo sampling period in continuous maize (Zea mays L.) plots managed under either an intensive fertility regime (M2) or recommended best management (M1). Flux was significantly higher in the M2 treatment on only 2 d during the first growing season. Annual estimates of soil surface CO2 flux, based on a modified exponential equation that incorporates leaf area index (LAI) to predict temporal changes in soil respiration, averaged 11550 kg C ha−1 yr−1 for both treatments (approximately 31.64 kg C ha−1 d−1 on average). Within row soil surface CO2 flux was, on average, 64% higher than between row flux. Plant population did not significantly affect measured soil surface CO2 flux. While fertility management had no significant effect on CH4 flux, N2O flux as measured on 3 d during the 2000 growing season was significantly higher in the M2 treatment. In 2001, no significant differences in N2O flux were observed, possibly due to changes in N management and irrigation method. Electrical conductivity measured during the 2000 and 2001 growing seasons was significantly higher in the M2 treatment while pH measured during the 2001 season was significantly lower for M2.

Daily soil surface CO2 flux during non-flooded periods in flood-irrigated rice rotations

“…As displayed in the variability of all soil surface CO 2 flux measurements within the same sampling date generally increased throughout the cropping season until after harvest. In accordance with past research (Amos et al 2005), increasing soil surface CO 2 flux throughout the growth period was expected due to crop maturing and soil temperature increases related to seasonal changes.…”

“…Smaller soil surface CO 2 flux in the late-season crops compared to the early-season crops may be explained by the different growth stages of crops during the time of sampling (Amos et al 2005). Root respiration has been estimated to constitute 40 to 60 % of the CO 2 emitted from the soil (Raich and Schlesinger 1992), so soils containing more mature crops have the ability to produce greater soil surface CO 2 emissions due to increased root respiration from greater photosynthetic rates (Kuzyakov and Cheng 2001;Amos et al 2005).…”

“…Root respiration has been estimated to constitute 40 to 60 % of the CO 2 emitted from the soil (Raich and Schlesinger 1992), so soils containing more mature crops have the ability to produce greater soil surface CO 2 emissions due to increased root respiration from greater photosynthetic rates (Kuzyakov and Cheng 2001;Amos et al 2005). On 23 June 2010, late-season crops had been planted 3 days prior to CO 2 flux measurements, whereas the non-flooded, earlyseason rotations had been planted approximately 3 weeks prior to measurement on this date (Table 1).…”

“…Like the 23 June 2010 sampling date, smaller quantities of soil surface CO 2 flux in late-season crops could be associated with crop maturity during the time of measurement (Raich and Schlesinger 1992;Kuzyakov and Cheng 2001;Amos et al 2005). In that, the late-season rice and soybean crops were less mature than the early-season rice, soybean, and corn crops.…”

Are the Fractionation Corrections Correct: Are the Isotopic Shifts for 14C/12C Ratios in Physical Processes and Chemical Reactions Really Twice Those for 13C/12C?

“…This requires a sustained input of dead carbon to the pots equal to one-third of the contemporary carbon respired by the plant roots themselves. Data from maize field studies (Amos et al 2005) show soil fluxes during the growing season of 50-150 kg C/ha-d for densities of ~10 5 plants/ha. Taking the median flux value and assuming that 50% of this is from root respiration (Bond-Lamberty et al 2004), the minimum deadcarbon input required is (1/3)(0.5)(10 5 g/ha-d)/(10 5 plants/ha), or about 0.17 g C per plant per day.…”