NSW Department of Primary Industries, Orange Agricultural Institute, 1447 Forest Rd, Orange, NSW, 2800, Australia; Graham Centre for Agricultural Innovation (an Alliance Between NSW Department of Primary Industries and Charles Sturt University), Wagga Wagga, NSW, 2650, Australia.
Central West Farming Systems (CWFS), NSW Department of Primary Industries, Agricultural Research and Advisory Station, 1 Fifield Road, Condobolin, NSW, 2877, Australia.
J Environ Manage. 2020 May 1;261:110192. doi: 10.1016/j.jenvman.2020.110192. Epub 2020 Mar 2.
Understanding the drivers of soil organic carbon (SOC) change over time and confidence to predict changes in SOC are essential to the development and long-term viability of SOC trading schemes. This study investigated temporal changes in total SOC, total nitrogen (N), and carbon (C) fractions (particulate organic carbon - POC, resistant organic carbon - ROC and humus organic carbon - HOC) over a 16-year period for four contrasting farming systems in a low rainfall environment (424 mm) at Condobolin, Australia. The farming systems were 1) conventional tillage mixed farming (CT); 2) reduced tillage mixed farming (RT); 3) continuous cropping (CC); and 4) perennial pasture (PP). The SOC dynamics were also modelled using APSIM C and N modules, to determine the accuracy of this model. Results are presented in the context of land managers participating in Australian climate change mitigation schemes. There was an increase in SOC for all farming systems over the first 12 years (total organic C, TOC% at 0-10 cm increased from 1.33% to 1.77%), which was predominately in the POC% fraction (POC% at 0-10 cm increased from 0.14% to 0.5%). Between 2012 and 2015, there was a decrease in SOC back to starting levels (TOC = 1.22% POC = 0.12% at 0-10 cm) in all systems. The PP system had higher TOC%, POC% and HOC% levels on average and higher SOC stocks to 30 cm depth at the final measurement in 2015 (PP = 30.43 t C ha; cropping systems = 23.71 t C ha), compared to the other farming systems. There was a decrease in TN% over time in all farming systems except PP. The average C:N increased from 14.1 in 1999 to 19.7 in 2012, after which time the SOC levels decreased and C:N dropped back to 15.8. The temporal change in SOC was not able to be represented by the AusFarm model. There are three important conclusions for policy development: 1) monitoring temporal changes in SOC over 12 years did not indicate long-term sequestration, required to assure "permanence" in SOC trading (i.e. 25-100 years) due to the susceptibility of POC to degradation; 2) without monitoring SOC in reference land uses (e.g. CT cropping system as a control in this experiment) it is not possible to determine the net carbon sequestration, and therefore the true climate change mitigation value; and 3) modelling SOC using AusFarm/APSIM, does not fully represent the temporal dynamics of SOC in this low rainfall environment.
了解土壤有机碳（SOC）随时间变化的驱动因素以及预测 SOC 变化的信心，对于 SOC 交易计划的制定和长期可行性至关重要。本研究调查了在澳大利亚康多布林（Condobolin）一个低降雨量环境（424 毫米）下，四种不同农业系统在 16 年内的总 SOC、总氮（N）和碳（C）分数（颗粒有机碳-POC、抗有机碳-ROC 和腐殖质有机碳-HOC）的时间变化。这些农业系统分别为 1）常规耕作混合农业（CT）；2）少耕混合农业（RT）；3）连作（CC）；和 4）多年生草地（PP）。还使用 APSIM C 和 N 模块对 SOC 动态进行了建模，以确定该模型的准确性。结果是在参与澳大利亚缓解气候变化计划的土地管理者的背景下提出的。在最初的 12 年内，所有农业系统的 SOC 都有所增加（0-10cm 处的总有机碳，TOC%从 1.33%增加到 1.77%），主要是在 POC%分数中（0-10cm 处的 POC%从 0.14%增加到 0.5%）。2012 年至 2015 年间，所有系统的 SOC 均恢复到初始水平（0-10cm 处的 TOC=1.22%，POC=0.12%）。在 2015 年的最后一次测量中，PP 系统的 TOC%、POC%和 HOC%水平平均较高，SOC 储量在 30cm 深处较高（PP=30.43tCha；种植系统=23.71tCha），与其他农业系统相比。除了 PP 系统外，所有农业系统的 TN%随时间呈下降趋势。C:N 平均值从 1999 年的 14.1 增加到 2012 年的 19.7，此后 SOC 水平下降，C:N 下降回 15.8。SOC 的时间变化无法用 AusFarm 模型来表示。对于政策制定有三个重要结论：1）监测 SOC 在 12 年内的时间变化并不能表明长期封存，因为 POC 容易降解，因此需要保证 SOC 交易的“永久性”（即 25-100 年）；2）如果不监测参考土地利用中的 SOC（例如，在本实验中，将 CT 耕作系统作为对照），则无法确定净碳封存量，从而无法确定真正的气候变化缓解价值；3）使用 AusFarm/APSIM 对 SOC 进行建模并不能完全代表低降雨量环境中 SOC 的时间动态。
