Greenhouse Gas Fluxes following Tillage and Wetting in a Wheat‐Fallow Cropping System

Abstract

Little is known about the relative contributions of episodic tillage and precipitation events to annual greenhouse gas emissions from soil. Consequently, we measured carbon dioxide (CO2), nitrous oxide (NzO), and methane (CH4) fluxes from soil in wh eat-fallow cr opping system in western Nebraska using vented surface chambers, before and immediately after tillage and wetting with 5.1 cm of water, during the fallow period in 199511996. Replicated fallow management treatments included no-tillage, snbtillage, and plow representing a wide range in degree of soil disturbance. Soil bulk density, water-filled pore space, electrical conductivity (ECru), nitrate (NO3), and pH within top 30.5 cm soil, and soil temperature at 0 to 7.6 cm were measured to assess their correlation with variations in gas flux and tillage and wetting. Atmospheric concentrations above the soil (at ~40 cm) increased by 15% for COz and 9 to 31% for NzO and 6 to 16% for CH4 within I min after tillage and returned to background concentrations within 2 h. Except immediately after tillage, net CH~ flux was negative, from the atmosphere into soil, and is referred to as CH4 uptake. Overall, increases (1.5-4-fold) in CO~ and NzO losses from soil, and CH4 uptake by soil were short lived and returned to background levels within 8 to 24 h after tillage. Losses of CO~ and N~O increased to 1.7 and 5 times background emissions, respectively, for 24 h following wetting, while CH4 uptake declined by about 60% for 3 to 14 d after wetting. Water-filled pore space in the surface soil fell below 60% within 24 h after saturation and exhibited an inverse relationship (R z = 0.66) with CH4 uptake. A significant decline in soil NO3 and ECI:I in the top 7.6 cm occurred following wetting. Under our experimental conditions, and the expected frequency of tillage and wetting events, failure to include these short-lived episodic gas pulses in annual flux estimations may underestimate annual CO2 and N20 loss up to 13 and 24%, respectively, and overestimate CH 4 uptake by up to 18% in this cropping system. E NG-TERM EFFECTS of intensive soil and crop management practices have been known to influence COz, N20, and CH4 fluxes from soils (IPCC, 1996). But little is known about the immediate effects of agronomic practices on short-term COz, NzO, and CH4 pulses, and the magnitude of their contributions to annual flux. Because greenhouse gas emissions from soil occur due to complex biological, chemical, and physical processes, it is probable that short-term changes in soil properties immediately following tillage and irrigation or precipitation influence greenhouse gas fluxes. Significant changes in soil structure, porosity, and microhabitat occur immediately following tillage (Doran and Linn, 1994; Reicosky, 1997). This in turn may influ

Applicability of soil column incubation experiments to measure CO2 efflux

“…As a consequence, the CO 2 efflux under the T treatment was obviously higher than that under the NT treatment on the first day. Kessavalou et al (1998) and Reicosky and Archer (2007) reported results similar to those of the present study. No noticeable increase or decrease in the CO 2 efflux was observed after the first day of the incubation period (August 19 -January 14) (Fig.…”

Soil organic matter, biota and aggregation in temperate and tropical soils - Effects of no-tillage

“…The higher CH 4 -uptake and increased C sequestration, however, do not counterbalance the greater N 2 O-fluxes under NT; this results in an overall negative greenhouse gas balance of 214 kg CO 2 -equivalents·ha -1 ·yr -1 . However, it is evident from the error terms [126] for the (sub)tropical soils and from [13,16,17,25,48,117,158,159,171,174,178,179,199,215] for the temperate soils.…”

Meeting Cereal Demand While Protecting Natural Resources and Improving Environmental Quality

“…However, most of these estimates were obtained from small experimental field plots, which may not be representative of production-scale fields. Therefore, most currently used simulation models fail to account for large pulses of N 2 O emissions caused by spring thawing (130), rapid soil warming (131), tillage and irrigation events (132), and N application (120), which may greatly affect annual emission rates and the net global warming potential of an agroecosystem (133). And although C sequestration is often increased in systems that receive N fertilizer, the energy costs of N fertilizer and associated CO 2 emissions must also be included in the net greenhouse forcing budget (134).…”