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

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.

土壤质地是驱动土壤源氧化亚氮（N₂O）排放的核心因素，其通过调控土壤通气状况，进而影响硝化作用（nitrification）与反硝化作用（denitrification）过程。本研究采用一种集成称重式蒸渗仪（weighing lysimeters）与自动气室的新型监测系统，针对澳大利亚新南威尔士州南部三种质地各异的土壤类型——1) 班纳砂土（Banna Sand, BS）、2) 汉伍德壤土（Hanwood Loam, HL）及3) 芒迪瓦粘壤土（Mundiwa Clay Loam, MCL），以亚日时间分辨率探究土壤质地对温室气体（GHG）与水分平衡的影响。每种土壤类型采集6根原状土芯（直径0.75 m，深度1.2 m），其中一半种植小麦，另一半设置为裸地对照组。针对每种土壤类型的4根土芯，测定其氧化亚氮（N₂O）、甲烷（CH₄）与二氧化碳（CO₂）排放通量，以及土壤温度、含水率与蒸散发（ET）。剩余的2根土芯则进行破坏性采样，以测定矿质氮（mineral N）、pH值与溶解性有机碳（DOC）的季节动态变化。同时还测定了水分、养分与溶解性温室气体的淋失通量。氧化亚氮排放通量遵循MCL>HL>BS的顺序。氧化亚氮排放对灌溉与降雨事件的响应在MCL中最为显著，而BS与HL的响应程度极弱且持续时间短暂，这表明粗质地土壤（coarse-textured soils，BS与HL）中氧化亚氮的主要产生过程为硝化作用，细质地土壤（fine-textured soils，MCL）则以反硝化作用为主。种植小麦对氧化亚氮排放具有显著影响，种植小麦的土芯其氧化亚氮排放量显著高于裸土土芯；但该效应的强度因土壤类型而异，整体遵循MCL>HL>BS的顺序。水分与氮素的淋失通量以BS最高，HL次之，而MCL未发生淋失现象。植株吸收作用显著降低了水分与养分的淋失通量。本研究还开展了反硝化实验：向所有土芯添加丰度为60%的¹⁵N标记硝酸钾（K¹⁵NO₃），随后手动采集气体样品以测定¹⁵N₂O与¹⁵N₂通量，同时采集土样以分析土壤矿质氮的变化，并测定根区以下的淋失损失。目前该¹⁵N标记实验的样品仍处于分析阶段。