Abstract
Soil water potential (Ψ) controls the dynamics of water in soils and can therefore affect greenhouse gas fluxes. We examined the relationship between soil moisture content (θ) at five different levels of water potential (Ψ = 0, −0.05, −0.1, −0.33 and −15 bar) and greenhouse gas (carbon dioxide, CO2; nitrous oxide, N2O and methane, CH4) fluxes. The study was conducted in 2011 in a silt loam soil at Freeman farm of Lincoln University. Soil samples were collected at two depths: 0–10 and 10–20 cm and their bulk densities were measured. Samples were later saturated then brought into a pressure plate for measurements of Ψ and θ. Soil air samples for greenhouse gas flux analyses were collected using static and vented chambers, 30 cm in height and 20 cm in diameter. Determination of CO2, CH4 and N2O concentrations from soil air samples were done using a Shimadzu Gas Chromatograph (GC-14). Results showed that there were significant correlations between greenhouse gas fluxes and θ held at various Ψ in the 0–10 cm depth of soil group. For instance, θ at Ψ = 0 positively correlated with measured CO2 (p = 0.0043, r = 0.49), N2O (p = 0.0020, r = 0.64) and negatively correlated with CH4 (p = 0.0125, r = −0.44) fluxes. Regression analysis showed that 24%, 41% and 19% of changes in CO2, N2O and CH4 fluxes, respectively, were due to θ at Ψ = 0 (p < 0.05). This study stresses the need to monitor soil water potential when monitoring greenhouse gas fluxes.
Highlights
IntroductionAgriculture is a significant source of carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4)and the contribution to the emissions of these gases mainly depend on agricultural management practices (e.g., fertilizer applications, methods of irrigation, tillage, manure applications, crop cultivation, burning crop residues, etc.) [1,2,3]
Agriculture is a significant source of carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4)and the contribution to the emissions of these gases mainly depend on agricultural management practices [1,2,3]
The matric potential has been a useful way to describe the availability of soil water and the ability of plants to extract it
Summary
Agriculture is a significant source of carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4)and the contribution to the emissions of these gases mainly depend on agricultural management practices (e.g., fertilizer applications, methods of irrigation, tillage, manure applications, crop cultivation, burning crop residues, etc.) [1,2,3]. Agricultural soils can constitute either as a net source or sink of these greenhouse gases (GHG) [4,5]. Several authors have found significant correlation between soil water and GHG fluxes [12,13]. Other authors have suggested that GHG fluxes are greater at certain levels of water in the soil and decline as water content declines [12,14]. There are only few studies relating soil water content and its energy state (water potential) to GHG fluxes [15]. The objective of this study was, to assess the relationship between soil moisture (θ) held at five different levels of water potential
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