Rice cultivation contributes 11% of the global 308 Tg CH 4 anthropogenic emissions. The alternate wetting and drying (AWD) irrigation practice can conserve water while reducing CH 4 emissions through the deliberate, periodic introduction of aerobic soil conditions. This paper is the first to measure the impact of AWD on rice field CH 4 emissions using the eddy covariance (EC) method. This method provides continuous, direct observations over a larger footprint than in previous chamber-based approaches. Seasonal CH 4 emissions from a pair of adjacent, production-sized rice fields under delayed flood (DF) and AWD irrigation were compared from 2015 to 2017. Across the 2 fields and 3 years, cumulative CH 4 emissions in the production season were in the range of 7.1 to 31.7 kg CH 4 −C ha −1 for the AWD treatment and in the range of 75.7−141.6 kg CH 4 −C ha −1 for the DF treatments. Correcting for field-to-field differences in CH 4 production, the AWD practice reduced seasonal CH 4 emissions by 64.5 ± 2.5%. The AWD practice is increasingly implemented for water conservation in the mid-south region of the United States; however, based on this study, it also has great potential for reducing CH 4 emissions.

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12The quantification of transpiration and corresponding basal crop coefficients is crucial

Core Ideas The Lower Mississippi River Basin (LMRB) is agriculturally important and ecologically unique. The Delta‐Flux network will coordinate the activities of 17 eddy covariance towers. The network addresses the need for scaled C and water cycle observations. The network aims to promote sustainable, climate‐smart land management. Delta‐Flux is open to collaborators from strategic sites and relevant disciplines. Networks of remotely monitored research sites are increasingly the tool used to study regional agricultural impacts on carbon and water fluxes. However, key national networks such as the National Ecological Observatory Network and AmeriFlux lack contributions from the Lower Mississippi River Basin (LMRB), a highly productive agricultural area with opportunities for soil carbon sequestration through conservation practices. The authors describe the rationale to create the new Delta‐Flux network, which will coordinate efforts to quantify carbon and water budgets at seventeen eddy covariance flux tower sites in the LMRB. The network structure will facilitate climate‐smart management strategies based on production‐scale and continuous measurements of carbon and water fluxes from the landscape to the atmosphere under different soil and water management conditions. The seventeen instrumented field sites are expected to monitor fluxes within the most characteristic landscapes of the target area: row‐crop fields, pasture, grasslands, forests, and marshes. The network participants are committed to open collaboration and efficient regionalization of site‐level findings to support sustainable agricultural and forestry management and conservation of natural resources.

Surface renewal (SR) analysis is an interesting alternative to eddy covariance (EC) flux measurements. We have applied two recent SR approaches, with different theoretical background, that from Castellví (2004), SR Cas , and that from Shapland et al. (2012a, 2012b), SR Shap. We have applied both models for sensible (H) and latent (LE) heat flux estimation over heterogeneous crop surfaces. For this, EC equipments, including a sonic anemometer CSAT3 and a krypton hygrometer KH20, were located in two zones of drip irrigated orchards of late and early maturing peaches. The measurement period was June to September 2009. The SR Cas is based on similarity concepts for independent estimation of the calibration factor (, which varies with respect to the atmospheric stability. The SR Shap is based on analysis of different ramp-dimensions, separating the ones that are flux-bearing from the others that are isotropic. According to the results obtained here, there was a high 2 agreement between the 30-min turbulent fluxes independently derived by EC and SR Cas. The SR Shap agreement with EC was slightly lower. Estimation of fluxes determined by SR Cas resulted in higher values (around 11% for LE) with respect to EC, similarly to previously published works over homogeneous canopies. In terms of evapotranspiration, the root mean square error (RMSE) between EC and SR was only 0.07 mm h-1 (for SR Cas) and 0.11 mm h-1 (for SR shap) for both measuring spots. According to the energy balance closure, the SR Cas method was as reliable as the EC in estimating the turbulent fluxes related to irrigated agriculture and watershed distribution management, even when applied in heterogeneous cropping systems.