Agricultural practices drive elevated rates of topsoil decline across Kenya, but terracing and reduced tillage can reverse this.
Agricultural practices drive elevated rates of topsoil decline across Kenya, but terracing and reduced tillage can reverse this.
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DOI：
10.1016/j.scitotenv.2023.161925
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发表时间：
2023-01
期刊：
影响因子：
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通讯作者：
C. Feeney;D. Robinson;A. Thomas;P. Borrelli;D. M. Cooper;L. May
中科院分区：
文献类型：
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作者：
C. Feeney;D. Robinson;A. Thomas;P. Borrelli;D. M. Cooper;L. May
随着农业用地面积的增加，以养活不断扩大的全球人口，土壤侵蚀可能会加速，造成不可持续的土壤和养分流失。这对肯尼亚至关重要，因为农田扩大以及径流和侵蚀造成的养分负荷正在助长淡水生态系统的富营养化和荒漠化。我们使用修订的通用土壤流失方程（RUSLE）预测土壤侵蚀率在肯尼亚全国目前的土地覆盖和潜在的自然植被。模拟自然植被条件可以确定在目前土地使用做法下侵蚀率升高的程度。这种方法利用新的数字土壤图和两个植被覆盖图来模拟表土（最高20厘米）的侵蚀速率，寿命（表土质量除以侵蚀速率），和横向养分通量（养分浓度乘以侵蚀速率）在这两种情况下。我们估计当前土地覆盖下的平均土壤侵蚀率约为5.5 t ha-1 yr-1，约为自然植被覆盖估计速率（约1.8 t ha-1 yr-1）的3倍，相当于全国表土流失约320 Mt yr-1。在目前的侵蚀速率下，土壤有机碳、氮和磷的年流失量分别为8.8Mt、315 Kt和110 Kt。此外，5.3%的表土（约3.1 Mha），包括> 25%的农田，寿命短（<100年）。另外还测试了一些设想方案，这些设想方案假定在耕地上采用梯田化和减少耕作的做法来减轻侵蚀。采用分区耕作建立梯阶梯田可以减少≥ 75%的土壤流失，最高可达87.1 t ha− 1 yr −1。这些减少与将农田转化为自然植被相当，表明大多数农业土壤可以成功保护。需要对建立梯田和减少耕作的农田进行广泛的长期监测，以验证我们的模型所示的这些农业支持措施的有效性。
As agricultural land area increases to feed an expanding global population, soil erosion will likely accelerate, generating unsustainable losses of soil and nutrients. This is critical for Kenya where cropland expansion and nutrient loading from runoff and erosion is contributing to eutrophication of freshwater ecosystems and desertification. We used the Revised Universal Soil Loss Equation (RUSLE) to predict soil erosion rates under present land cover and potential natural vegetation nationally across Kenya. Simulating natural vegetation conditions allows the degree to which erosion rates are elevated under current land use practices to be determined. This methodology exploits new digital soil maps and two vegetation cover maps to model topsoil (top 20 cm) erosion rates, lifespans (the mass of topsoil divided by erosion rate), and lateral nutrient fluxes (nutrient concentration times erosion rate) under both scenarios. We estimated the mean soil erosion rate under current land cover at ~5.5 t ha−1yr−1, ~3 times the rate estimated for natural vegetation cover (~1.8 t ha−1yr−1), and equivalent to ~320 Mt yr−1of topsoil lost nationwide. Under present erosion rates, ~8.8 Mt, ~315 Kt, and ~ 110 Kt of soil organic carbon, nitrogen and phosphorous are lost from soil every year, respectively. Further, 5.3 % of topsoils (~3.1 Mha), including at >25 % of croplands, have short lifespans (<100 years). Additional scenarios were tested that assume combinations of terracing and reduced tillage practices were adopted on croplands to mitigate erosion. Establishing bench terraces with zoned tillage could reduce soil losses by ≥75 %; up to 87.1 t ha−1yr−1. These reductions are comparable to converting croplands to natural vegetation, demonstrating most agricultural soils can be conserved successfully. Extensive long-term monitoring of croplands with terraces and reduced tillage established is required to verify the efficacy of these agricultural support practices as indicated by our modelling.