喀斯特峰丛坡地不同土地利用方式下土壤N、P空间变异特征

Spatial heterogeneity of soil nitrogen and phosphorus under different land use patterns in depressions between karst hills

基于网格点(5 m×5 m)采样法采集土壤样品,利用经典统计学和地统计学方法,研究了喀斯特峰丛坡地不同土地利用方式(火烧迹地、刈割地、草地、封育地)下表层(0～20cm)土壤氮、磷的空间变异特性。结果表明:研究区4种不同土地利用方式土壤全氮(TN)、全磷(TP)、速效氮(AN)、速效磷(AP)均为中等程度变异,含量分别为5.40～6.26 g.kg-1、1.24～1.44 g.kg-1、365.87～507.32 mg.kg-1、3.91～8.04 mg.kg-1,封育地、火烧迹地土壤质量优于草地和刈割地;4种土地利用方式中火烧AN、火烧AP、刈割AN、封育TN的半方差函数最佳拟合模型为球状模型,火烧TN、刈割TN、刈割AP最佳拟合模型为指数模型,其他指标的最佳拟合模型均为高斯模型。刈割TP、火烧TP、草地TP、刈割TN、火烧AP、草地AP、封育TP表现为强烈的空间自相关性,其他土壤养分表现为中等的空间自相关。4种土地利用类型土壤TN与AN、TP与AP具有相似的空间分布格局。火烧、刈割处理TN和AN呈凹形分布,TP和AP呈单峰分布特征,中下坡含量最高,往两端含量逐渐降低;草地TN、AN、TP、AP 4种养分含量均随着坡位的升高而降低;封育样地中4种养分呈类似凹形分布,中间含量低,两端略微升高。土地利用方式的变化改变了喀斯特峰丛坡地土壤养分质量,造成了土壤养分空间格局的变化,因此,在地形破碎、土层浅薄的喀斯特地区进行生态恢复与重建时,应采取合理土地利用方式,进行保护和适度开发,提高喀斯特退化生态系统土壤质量。

Soil samples were collected from the depressions between karst hills by grid sampling method （5 m×5 m）, and the spatial heterogeneity of soil nitrogen and phosphorus in surface layer （0-20 cm） under different land use patterns （burned land, mowing land, grassland, and fenced land） were investigated by classic statistics and geo-statistics. In the study area, the soil total nitrogen （TN）, total phosphorus （TP）, available nitrogen （AN）, and available phosphorus （AP） under the four land use patterns showed a moderate variation, with the contents being 5.40-6.26 g·kg^-1, 1.24-1.44 g·kg^-1, 365.87-507.32 mg·kg^-1, and 3.91-8.04 mg·kg^-1, respectively. The soil quality of fenced land and burned land was superior to that of grassland and mowing land. The soil AN of burned land, AP of burned land, AN of mowing land, and TN of fenced land were fitted well by spherical model; the soil TN of burned land, TN of mowing land, and AP of mowing land were fitted well by exponential model; and the other soil nutrient variables were fitted well by Gaussian model. A strong spatial autocorrelation occurred for the soil TP of mowing land, TP of burned land, TP of grassland, and TN of mowing land, AP of burned land, AP of grassland, and TN of fenced land, while a moderate spatial autocorrelation existed for the other variables. The soil TN and AN as well as the soil TP and AP under the four land use patterns showed the similar spatial distribution pattern. The soil TN and AN of burned land and mowing land presented a concave distribution, while the TP and AP showed a unimodal distribution. The soil TN, TP, AN, and AP in grassland all decreased with slope position, while these soil nutrients in fenced land presented concave distribution. Land use pattern changed the soil nutrient quality in the depressions between karst hills, and caused different spatial patterns of soil nutrients. Therefore, in the ecological restoration and reconstruction of karst region with broken landform and shallow soil, it should adopt rational land use pattern, protection, and moderate development to improve the soil quality of degraded ecosystems.