Objective Evaluating the soil fertility of different forests by a variety of evaluation methods, analyzing the influences as well as differences and similarities of these evaluation methods on soil fertility comprehensive evaluation and providing a theoretical basis for forest soil nutrient management and sustainable development in South China.
Method Five kinds of forests, including Acacia spp. plantation, Cunninghamia lanceolate plantation, Eucalyptus urophylla plantation, Pinus massoniana plantation and broad-leaved mixed forest were chosen to measure and analyze bulk density, pH, organic matter, available phosphorus, available potassium, alkaline nitrogen and total nitrogen in soil at a depth of 0-20 cm. Single index evaluation was carried out by membership function and partial correlation analysis. Combined with correlation coefficient method, principal component analysis, grey correlation analysis and Nemerow index method, comprehensive evaluation of soil fertility was conducted for five forest stands.
Result The soil bulk density of five stands were ranged from 1.24 to 1.29 g·cm–3, and the values of pH were ranged from 4.11 to 4.24. The contents of organic matter were ranged from 21.43 to 28.18 g·kg–1, the contents of available phosphorus were ranged from 1.12 to 1.42 mg·kg–1, the contents of available potassium were ranged from 40.62 to 55.20 mg·kg–1, the contents of alkaline nitrogen were ranged from 106.12 to 132.28 mg·kg–1 and the contents of total nitrogen were ranged from 1.03 to 1.45 g·kg–1. According to the second national soil classification standards, the levels of organic matter and total nitrogen contents were above average values, while the level of available phosphorus content was low, the content of available potassium were ranged from low to below average level, and the content of alkaline nitrogen were ranged from above average to high level. The contents of organic matter, available potassium, available nitrogen and total nitrogen in broad-leaved mixed forest were significantly higher than those in some plantations. Organic matter played the most important role in soil fertility, while available phosphorus was a limiting factor affecting soil fertility. The results of comprehensive evaluation of four kinds of evaluation methods were consistent. The range of soil fertility from high to low was broad-leaved mixed forest > C. lanceolate plantation > P. massoniana plantation > A. spp. plantation > E. urophylla plantation.
Conclusion The soil fertility accumulation of broad-leaved mixed forest is better than those of other plantations, while the soil of E. urophylla plantation have low fertility. The applications of phosphorus and potassium fertilizer and the adjustment of soil acidity should be emphasized in the management of forest soil nutrients in South China.
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