Nitrous Oxide Emissions from Sorghum Crops with Distinct Cropping Histories. Kingaroy, Queensland, 2012 - 2013 [Theme: Integrated Cotton and Grain Cropping Systems]

N2O emissions were measured in plots planted with sorghum (Sorghum bicolor L.) following two distinct cropping histories. One crop rotation (hereafter called legume ley pasture-cereal) included two seasons of alfalfa pasture (Medicago sativa, L., summers 2009/2010 and 2010/2011), one season of maize (Zea mays, L., summer 2011/2012) and one season of sulla pasture (Hedysarum coronarium L., winter 2012) prior to sowing sorghum. The other crop rotation (hereafter called grass ley pasture-cereal) consisted of two seasons of a mixed rhodes grass (Chloris gayana, K.) and alfalfa pasture (summers 2009/2010 and 2010/2011), one season of maize (Zea mays, L., summer 2011/2012) and one season of wheat (Triticum aestivum L., winter 2012). Both crops were terminated in November 2012 with all residues returned to the soil as a mulch before being incorporated into the soil with four shallow cultivations.
Two N fertilisation rates were tested on each cropping history, resulting in a total of four treatments. The first N application rate was designed to achieve maximum yield potential and was representative of farming practices of the region. The synthetic N rate used in L70 was reduced compared to G100 to assess whether the estimated 30 kg N ha-1 resulting from the mineralisation of the sulla residues would have been available to sorghum.

本研究对种植于两种不同种植历史样地中的高粱（Sorghum bicolor L.）的一氧化二氮（N₂O）排放进行了测定。其中一种轮作模式（下文简称豆科饲草轮作-谷物轮作）在播种高粱前，依次经历两季紫花苜蓿（Medicago sativa L.）草地种植（2009/2010年夏季、2010/2011年夏季）、一季玉米（Zea mays L.）种植（2011/2012年夏季）以及一季驴食草（Hedysarum coronarium L.）草地种植（2012年冬季）。另一种轮作模式（下文简称禾本科饲草轮作-谷物轮作）则包含两季混合罗得斯草（Chloris gayana）与紫花苜蓿的草地种植（2009/2010年夏季、2010/2011年夏季）、一季玉米（Zea mays L.）种植（2011/2012年夏季）以及一季小麦（Triticum aestivum L.）种植（2012年冬季）。两种前作均于2012年11月终止种植，全部秸秆残体以覆盖物形式还田，随后通过四次浅耕将残体翻入土中。
针对每种种植历史设置两个氮肥施用量梯度，共计形成4种处理。第一种氮肥施用量旨在实现作物最高产量潜力，符合该区域的常规农事操作规范。与G100处理相比，L70处理的人工合成氮肥施用量有所降低，以此探究驴食草残体矿化所释放的预估30 kg N·ha⁻¹氮素是否可被高粱吸收利用。