基于投影寻踪的土壤养分综合评价及影响因素研究

客观、精准研究土壤综合养分及影响因素,可为农作物科学施肥提供参考依据。以陕西省旬邑县苹果种植区为研究区,选取有机质、碱解氮、速效钾和有效磷为评价指标,将投影寻踪综合评价法运用到土壤养分评价中,根据最佳投影方向,计算土壤养分综合投影指数(comprehensive projection index, CPI),并依据经验等级对应投影值,从而评价土壤养分等级,基于普通克里格和GIS绘制土壤养分综合指数等级分布图,并利用随机森林的importance()函数分析影响因素对养分含量的重要性。结果表明:研究区CPI的变幅为0.653～1.516,平均值1.022,变异系数为14.746%,呈中等程度变异,同时CPI属于Ⅲ级和Ⅳ级;基于80%训练集和20%验证集的精度交叉验证,球面函数为最优理论模型;土壤综合养分的总体空间分布格局:除土桥、职田和湫坡头镇东部的养分等级高,土壤养分等级从西部向东部递减,从高到低的面积比例为:14.415︰28.522︰35.450︰20.115︰1.498,土壤综合养分属于中等及偏下水平,且主要分布在东部;高程、气温和坡度等因子是影响区域土壤养分的主导因子,且每项影...

Study on Comprehensive Evaluation and Influencing Factors of Soil Nutrients Based on Projection Pursuit

The objective and accurate study of comprehensive soil nutrients and their influential factors can provide reference for scientific fertilization of crops. The apple-planting area in Xunyi County of Shaanxi Province was selected as the study object. The comprehensive evaluation of projection pursuit was applied to comprehensively assess soil nutrients including organic matter, alkali hydrolysable N, available K and available P. The comprehensive projection index of soil nutrients was calculated according to the optimum projection direction. Soil nutrient level was evaluated according to the level of experience corresponding projection value. The spatial distribution of comprehensive soil nutrients was mapped by ordinary Kriging method and GIS, and the importance function of random forests was used to analyze the importance of influencing factors on nutrient contents. The results showed that the CPI variation in the study area was 0.653-1.516 with an average of 1.022, the variation coefficient was 14.746%, which was moderate. Moreover, CPI were in grades of III and IV. The spherical function was the optimal theoretical model by the accuracy of the cross-validation based on 80% training set and 20% verification set. The spatial distribution pattern of soil nutrients was as follows: except the high grades in Tuqiao, Zhitian, and the eastern part of Qiupotou towns, the integrated soil nutrient grade decreased from the west to the east in the study area, and the area ratio of comprehensive levels of soil nutrients from high to low was: 14.415 : 28.522 : 35.450 : 20.115 : 1.498. The comprehensive levels of soil nutrients were medium or low, and were mainly distributed in the eastern part. Soil nutrients were mainly affected by elevation, temperature and slope, and the influence degree of each factor varied greatly. The above results are consistent with the actual conditions in the area, thus can provide scientific bases for improving soil fertility of the local orchards and new ideas for comprehensive evaluation of soil nutrients.