Department of Sustainable Agriculture Sciences, Rothamsted Research, Harpenden, UK.
Department of Computational and Analytical Sciences, Rothamsted Research, Harpenden, UK.
Glob Chang Biol. 2018 Jun;24(6):2563-2584. doi: 10.1111/gcb.14066. Epub 2018 Feb 28.
We evaluated the "4 per 1000" initiative for increasing soil organic carbon (SOC) by analysing rates of SOC increase in treatments in 16 long-term experiments in southeast United Kingdom. The initiative sets a goal for SOC stock to increase by 4‰ per year in the 0-40 cm soil depth, continued over 20 years. Our experiments, on three soil types, provided 114 treatment comparisons over 7-157 years. Treatments included organic additions (incorporated by inversion ploughing), N fertilizers, introducing pasture leys into continuous arable systems, and converting arable land to woodland. In 65% of cases, SOC increases occurred at >7‰ per year in the 0-23 cm depth, approximately equivalent to 4‰ per year in the 0-40 cm depth. In the two longest running experiments (>150 years), annual farmyard manure (FYM) applications at 35 t fresh material per hectare (equivalent to approx. 3.2 t organic C/ha/year) gave SOC increases of 18‰ and 43‰ per year in the 23 cm depth during the first 20 years. Increases exceeding 7‰ per year continued for 40-60 years. In other experiments, with FYM applied at lower rates or not every year, there were increases of 3‰-8‰ per year over several decades. Other treatments gave increases between zero and 19‰ per year over various periods. We conclude that there are severe limitations to achieving the "4 per 1000" goal in practical agriculture over large areas. The reasons include (1) farmers not having the necessary resources (e.g. insufficient manure); (2) some, though not all, practices favouring SOC already widely adopted; (3) practices uneconomic for farmers-potentially overcome by changes in regulations or subsidies; (4) practices undesirable for global food security. We suggest it is more realistic to promote practices for increasing SOC based on improving soil quality and functioning as small increases can have disproportionately large beneficial impacts, though not necessarily translating into increased crop yield.
我们评估了通过分析英国东南部 16 个长期实验中处理措施的土壤有机碳（SOC）增加率来增加土壤有机碳（SOC）的“4 per 1000”计划。该计划设定了在 0-40cm 土壤深度中 SOC 库存每年增加 4‰的目标，持续 20 年。我们在三种土壤类型上进行了实验，提供了 7-157 年间的 114 个处理措施比较。处理措施包括有机添加物（通过反转犁耕进行翻耕）、氮肥、将牧场引入连续的耕地系统以及将耕地转换为林地。在 65%的情况下，0-23cm 深度的 SOC 增加率超过 7‰，相当于 0-40cm 深度的 SOC 每年增加 4‰。在两个运行时间最长的实验（>150 年）中，每年每公顷 35 吨新鲜材料（相当于约 3.2t 有机碳/公顷/年）的厩肥应用在最初 20 年内使 23cm 深度的 SOC 增加了 18‰和 43‰。每年超过 7‰的增加持续了 40-60 年。在其他实验中，厩肥的施用量较低或并非每年都施，在几十年内 SOC 每年增加 3‰-8‰。其他处理措施在不同时期的 SOC 年增加率在 0-19‰之间。我们得出的结论是，在大面积的实际农业中实现“4 per 1000”目标存在严重限制。原因包括：（1）农民没有必要的资源（例如，厩肥不足）；（2）一些（尽管不是全部）有利于 SOC 的措施已经得到广泛采用；（3）对农民来说不经济的措施——有可能通过改变法规或补贴来克服；（4）对全球粮食安全不利的措施。我们认为，更现实的做法是基于提高土壤质量和功能来推广增加 SOC 的措施，因为小的增加可能会产生不成比例的巨大有益影响，尽管不一定转化为作物产量的增加。
