晋西黄土区退耕年限对土壤物理性质的影响

【目的】为评价晋西黄土区退耕年限对土壤物理性质的影响,并为该地区水土保持林构建提供依据。【方法】以山西吉县蔡家川小流域的农地为对照,对晋西黄土区5种典型退耕还林林分(包括自然恢复山杨林、刺槐×侧柏人工混交林、油松×刺槐人工混交林、刺槐人工纯林和油松人工纯林)的土壤物理性质进行了连续23年的定位观测。【结果】(1)所有人工林土壤密度随退耕年限呈现先上升(退耕后前1~4年)后下降(退耕后4~23年间)的趋势,在10~15年下降至一个比初始值更低的值后逐渐趋于平稳;自然恢复林随退耕年限土壤密度呈不断下降趋势,最高下降幅度为11.21%(0~20 cm土层)。(2)人工林土壤总孔隙度在前10~15年呈先下降后上升的趋势,自然恢复林土壤总孔隙度随恢复年限上升趋势越来越缓慢,0~20 cm土层和20~40 cm土层累积变化率为1.4%和0.6%。(3)5种典型林分的毛管孔隙度均随退耕年限增加呈上升趋势,其中人工林内20~40 cm土壤层的毛管孔隙度变化大于0~20 cm土层,自然恢复林0~20 cm土层和20~40 cm土层的累积变化率分别为2.5%和1.5%左右。【结论】退耕年限对土壤物理性质影响显著(P <0.05),4种人工林中土壤物理性质的变化主要发生在退耕后的前10~15年内,其中刺槐×侧柏混交林对土壤物理性质的改良效果更明显,建议该地区人工林恢复类型应以刺槐×侧柏混交林为主。

Effects of converting years from farmland to forestland on soil physical properties in the loess area of western Shanxi Province,northern China

Objective] This paper aims to evaluate the effects of converting time from cropland to forestland on soil physical properties, and provide a basis for the construction of soil and water conservation forests in the region. Method] The 23 years positioning continuous monitoring was taken on soil physical properties under five typical forests, including one natural restoration Populus davidiana plantation, two mixed plantations of Platycladus orientalis and Robinia pseudoacacia, Pinus tabuliformis and Robinia pseudoacacia, two pure plantations of Robinia pseudoacacia and Pinus tabuliform, and taking the corn farmland as control. Result](1) With the increase of converted years, the soil bulk density(BD) under the four plantations increased first and then decreased to a stable value, which was lower than initial value at about 10-15 years. In the natural restoration forest(NF), BD showed a downward tendency with the highest decreasing range of 11.21% at 0-20 cm soil depth.(2) The soil total porosity(TP) under the 4 plantations decreased first and then increased to a stable value, which was higher than initial value at about 10-15 years.The cumulative changing rates of TP at the soil depths of 0-20 cm and 20-40 cm were 1.4% and 0.6%,respectively under NF.(3) The capillary porosity(CP) under the five typical forests all showed an increasing trend with the increase of converting time. The CP at 0-20 cm changed more than at 20-40 cm in the plantations;the cumulative changing rates of CP at 0-20 cm and 20-40 cm were 2.5% and 1.5%,respectively under NF. Conclution] The converted years showed a significant effects on soil physical properties(P < 0.05) under the typical forests, while for the plantations, the change of BD and TP mostly occurred in the first 10-15 years. The mixed forests of Pinus tabuliformis and Robinia pseudoacacia should be the prioritized for the artificial vegetation restoration in the research area based on its remarkable improvement effects on soil physical properties.