Assessment of Soil Fertility of Mulberry Orchards Based on Combined Soil Nutrient Grades and Main Component Analysis

Soil fertility is synthetically expressed by various soil factors and can greatly affect the yield and quality of crops.Identifying soil fertility and the limiting factors are the basis of fertilizer application in mulberry orchard.In this study,14 soil fertility indexes were analyzed from 50 soil samples from 25 mulberry orchards in Hai’an County of Jiangsu Province,and then soil fertility was assessed by using the combining method of soil fertility grade and main component analysis.The results showed that soil fertility was high generally in the investigated orchards and the fertility of top layer(0 20 cm) was higher than that of lower(20 40 cm).However,considerable differences in soil fertility existed among different orchards,organic matter,nitrogen and potassium were partially deficient,phosphorus,magnesium,manganese and zinc were deficient only in several orchards,but iron and copper were higher in all orchards.Four main components were isolated and they reflected about 85% of all soil information of orchard,and the first main component was integrative nutrient factor,contributing to 44.41%;the second main component was pH factor,contributing to 24.03%;the third and fourth main component were related to the negative and positive function of zinc,contributing to 8.92% and 7.52%,respectively.Furthermore,the total 25 orchards were classified into four varieties representing different fertility conditions.These results suggested that the method of soil nutrient grades was detailed but the method of main component analysis was integrative,they were complementary and their combination could better assess soil fertility of mulberry orchard.