Sanya Nanfan Research Institute of Hainan University, Hainan University, Sanya, 572025, China; College of Tropical Crops, Hainan University, Haikou, 570228, China.
Sanya Nanfan Research Institute of Hainan University, Hainan University, Sanya, 572025, China.
Environ Pollut. 2022 Nov 15;313:120100. doi: 10.1016/j.envpol.2022.120100. Epub 2022 Sep 5.
As the only "tropical base of agricultural production" in China, Hainan lsland is vigorously developing high-value agriculture and is becoming the province with the highest proportion of cash crops. However, this intensive farming with large nutrient inputs has caused cropland degradation, nitrogen (N) and phosphorus (P) overloads and water pollution, which have been reversed to initiate the construction of free trade ports. Here, we systematically review the status, driving factors, and environmental impacts of cropland degradation and nutrient overload with quantified evaluations and compared with other global tropics. Over the last 30 years, the soil pH in Hainan decreased by 0.3 units, and the soil organic carbon (SOC) decreased by 20%. This soil degradation has consequently aggravated nutrient losses, caused low use efficiency, and has required farmers add additional large nutrient to maintain harvests. P overuse is more serious than N overuse in Hainan due to the misuse of high P content compound fertilizers. The current N and P usage densities were 4% and 66% higher than the national average per crop season, i.e., 301 kg N ha and 98 kg P ha, respectively, and the application rates were even higher for vegetables, i.e., 43% and 115% higher than the national average for vegetables. Consequently, water quality degradation occurred. The nutrient contents of several estuaries have exceeded the Class III standards. Potential improvement strategies are proposed: (i) Organic materials must be recycled to curb the declines in SOC and pH, and more benefits would be obtained by together use of biochar. (ii) Nutrient quotas must be implemented to balance nutrient budgets and reduce excessive surpluses and losses. (iii) The service functions of ecological protection zones for water and soil conservation must be strengthened. These strategies also apply to other global tropics that face similar challenges of soil and ecological degradation.
作为中国唯一的“热带农业生产基地”，海南岛大力发展高价值农业，正在成为现金作物比例最高的省份。然而，这种集约化的农业种植方式，投入了大量的养分，导致耕地退化、氮（N）磷（P）过载和水污染，这反过来又促使海南开始建设自由贸易港。在这里，我们系统地回顾了耕地退化和养分过载的现状、驱动因素和环境影响，并进行了量化评估，与其他全球热带地区进行了比较。在过去的 30 年里，海南的土壤 pH 值下降了 0.3 个单位，土壤有机碳（SOC）下降了 20%。这种土壤退化导致养分损失加剧，利用率降低，农民需要额外投入大量养分来维持产量。由于高磷含量复合肥的误用，海南的磷过度使用比氮过度使用更为严重。目前，海南每茬作物的氮和磷用量密度比全国平均水平分别高出 4%和 66%，即 301 公斤/公顷和 98 公斤/公顷，而蔬菜的施用量甚至更高，即比全国平均水平高出 43%和 115%。因此，水质发生了退化。几个河口的营养含量已经超过了 III 类标准。我们提出了一些可能的改进策略：（i）必须回收有机物质，以遏制 SOC 和 pH 值的下降，并且通过生物炭的共同使用会获得更多的好处。（ii）必须实施养分配额，以平衡养分预算，减少过度的盈余和损失。（iii）必须加强水土保持生态保护带的服务功能。这些策略也适用于其他面临类似土壤和生态退化挑战的全球热带地区。
