Effect of soil texture on N2O emissions in Southern NSW irrigated wheat. Griffith, New South Wales, 2013

Brief description

Soil texture is a major driver of soil-derived N2O emissions as it controls the soil aeration status thereby influencing the processes of nitrification and denitrification. We used a novel measurement system that combines weighing lysimeters with automated chambers to study the effect of soil texture on GHG and water balance at sub-daily time resolution from three soil types of variable texture: 1) Banna Sand (BS), 2) Hanwood Loam (HL), and 3) Mundiwa Clay Loam (MCL), all from southern New South Wales, Australia. Six intact soil cores (diameter = 0.75 m, depth = 1.2 m) were collected from each soil type, half of which were planted with wheat while rest left bare. Four cores from each soil type were measured for N2O, CH4 and CO2, as well as soil temperature, moisture and evapotranspiration (ET). Remaining two cores from each soil type were destructively sampled to measure seasonal changes in mineral N, pH and DOC. Leaching losses of water, nutrients and dissolved GHGs were also measured. N2O emissions were in the order MCL>HL>BS. Greatest response of N2O to irrigation and rainfall events was observed in MCL while BS and HL showed negligible to short-lived response suggesting nitrification as the major process for N2O emissions in the coarse-textured soils (BS and HL) and and denitrification in the fine-textured soils (MCL). Plants had a significant effect on N2O emissions with cores planted with wheat showed significantly larger N2O emissions compared to cores left bare; however, the magnitude of this effect was variable among soil types and was in the order MCL>HL>BS. Leaching losses of water and N were greatest in BS followed by HL while no leaching occurred in MCL. Plant uptake significantly reduced the leaching losses of water and nutrients. A denitrification experiment was also conducted by adding 60% enriched K15NO3 to all cores followed by manual gas sampling for 15N2O and 15N2 fluxes and soil sampling for changes in soil mineral N, as well as losses through leaching below root-zone. Samples from this 15N experiment are currently being analysed.