紫色土坡耕地土壤属性差异对耕层土壤质量的影响

坡耕地是一个区域最易发生水土流失的土地利用类型,其严重的水土流失、面源污染和耕层退化现象直接威胁着坡耕地持续利用以及当地粮食安全、生态安全;耕层土壤质量对自然因素和人为耕作活动的影响较为敏感。以南方3个地点紫色土坡耕地耕层土壤质量为研究对象,从土壤属性角度,对比分析了重庆合川、江西兴国、云南楚雄不同耕层垂直深度土壤养分特征、土壤物理性质、土壤水库特征、耕作性能差异性及其形成原因。结果表明:(1)坡耕地耕层土壤有机质表现为云南楚雄(28.80g/kg)江西兴国(9.03 g/kg)重庆合川(8.80 g/kg);除全钾含量外,土壤全量养分和速效养分的含量表现为云南楚雄江西兴国重庆合川;坡耕地耕层速效养分垂直分布变化规律基本一致,主要表现为土壤速效养分主要在0—20 cm土层富集,而20—40 cm和40—60 cm土层无显著差异。(2)不同地点紫色土坡耕地耕层土壤物理性质差异明显,以重庆合川坡耕地土壤物理质量最差,表现为土壤砂粒含量60%、土壤容重最大(1.43 g/cm3)、土壤总孔隙度(45.97%)和毛管孔隙度(34.36%)最小;从坡耕地耕层土壤物理性质垂直变化特征看,耕作层(0—20 cm)优于心土层(20—40 cm)和底土层(40—60 cm)。(3)紫色土坡耕地耕层土壤初始入渗率以江西兴国坡耕地耕层最大(0.32 mm/min),而以重庆合川坡耕地耕层最小(0.19 mm/min);土壤稳定入渗率和平均入渗率均表现为云南楚雄重庆合川江西兴国;坡耕地耕层土壤最大有效库容以云南楚雄最好(873.311 t/hm~2),说明云南楚雄紫色土坡耕地耕层土壤具有较好的抵御季节性干旱能力;不同地点坡耕地耕层土壤总库容、死库容、兴利库容、滞洪库容、最大有效库容在垂直方向变化表现为耕作层(0—20 cm)大于心土层(20—40 cm)和底土层(40—60 cm)。(4)不同地点紫色土坡耕地耕层土壤抗剪强度和贯入阻力均呈现出相同变化规律,土壤抗剪强度表现为重庆合川(15.39 kg/cm~2)云南楚雄(14.74 kg/cm~2)江西兴国(10.66 kg/cm~2),而土壤贯入阻力值为重庆合川(424.83 k Pa)云南楚雄(252.50 k Pa)江西兴国(188.87 k Pa),这种土壤力学性能的变化说明重庆合川紫色土坡耕地耕层土壤具有较好抵抗剪切破坏的能力和较大耕作阻力。上述研究结果可为不同地点紫色土坡耕地耕层土壤质量诊断、坡耕地合理耕层评价提供理论依据和数据支持。

Effect of different soil properties on plow-layer soil quality of sloping farmland in purple hilly areas

As the most easily eroded land-use type, severe soil degradation of the plow layer (as a shallow soil layer), deterioration of soil properties, and gravel process, could restrict the sustainable utilization of slope farmland, which also directly threatens local food security and ecological security. Plow-layer soil quality is highly sensitive to both natural factors and artificial farming tillage. Taking the plow-layer soil quality of three slope farmlands in the southern purple hilly area (Hechuan-Chongqing, Xingguo-jiangxi, and Chuxiong-Yunnan) as examples, this study mainly analyzed the differences in soil physical properties, soil reservoir characteristics, and soil nutrient characteristics of slope farmlands, and their vertical distribution characteristics, from the perspective of soil properties, so did the forming causes at the same time. The results indicated the following. (1) The soil organic matter of the plow-layer in the three locations in decreasing order was as follows: Chuxiong-Yunnan (28.80 g/kg) > Xingguo-jiangxi (9.03 g/kg) > Hechuan-Chongqing (8.80 g/kg). With the exception of total soil potassium content, other contents such as total soil nutrients and available soil nutrients, could be arranged in the following order: Chuxiong-Yunnan > Hechuan-Chongqing > Xingguo-jiangxi. The vertical characteristics of available soil nutrients in the plow-layer of slope farmland showed the same distribution, being mainly concentrated in the 0-20-cm soil layer. However, there were no significant differences between the 20-40-cm soil layer and the 40-60-cm soil layer. (2) The soil physical properties of the plow-layer of slope farmlands among the three purple hilly locations showed significant differences. The soil physical quality of the plow-layer in Hechuan-Chongqing was the worst, with the characteristic of soil sand content > 60%, maximum soil bulk density of 1.43 g/cm³, minimum soil total porosity of 45.97%, and capillary porosity of 34.36%. From the viewpoint of the plow-layer vertical characteristics of slope farmland, the soil physical properties of the tillage layer (0-20 cm) were better than those of the subsoil (20-40 cm) and bottom layer (40-60 cm). (3) The initial soil infiltration rate of the plow-layer in the Xingguo-jiangxi slope farmland was the largest (0.32 mm/min), and the initial soil infiltration rate in Hechuan-Chongqing plow-layer was the lowest (0.19 mm/min). The soil infiltration rate and the average soil infiltration rate both showed the same order of Chuxiong-Yunnan > Xingguo-jiangxi > Hechuan-Chongqing. The soil maximum effective capacity of the plow-layer in Chuxiong-Yunnan slope farmland was the best (873.311 t/hm²), which indicated that such plow-layers of slope farmland have better resistance to seasonal drought. Plow-layer vertical characteristics, such as the total storage capacity, dead storage capacity, active storage capacity, flood detention storage capacity, and maximum effective capacity, all showed the same order: tillage layer (0-20 cm) > subsoil layer (20-40 cm) > bottom layer (40-60 cm). (4) The soil shear strength and the soil penetration resistance of the plow-layer among the three slope farmland locations showed the same regular changes. The soil shear strengths of the plow-layer were Hechuan-Chongqing (15.39 kg/cm²) > Chuxiong-Yunnan (14.74 kg/cm²) > Xingguo-jiangxi (10.66 kg/cm²), whereas the soil penetration resistances of the plow-layer were Hechuan-Chongqing (424.83 kPa) > Chuxiong-Yunnan (252.50 kPa) > Xingguo-jiangxi (188.87 kPa), which indicated that the plow-layer soil of slope farmland in the Hechuan-Chongqing purple hilly area has better resistance to shear stress and greater resistance to farming tillage. These results could provide a theoretical basis and supporting data not only for soil quality diagnosis but also for rational plow-layer evaluation for slope farmlands in different purple hilly areas.