短周期杉木人工林不同林龄土壤肥力综合评价

为探讨不同生长发育阶段林地土壤肥力状况及地力衰退趋势,分析影响地力衰退的主要影响因子,以不同林龄(2、4、6、8和11 a)杉木短周期小径材培育人工林的土壤样本为研究对象,检测土壤有机质、全氮、全钾、全磷、水解性氮、速效钾、有效磷、有效铁、交换性钙、交换性镁含量和pH值共11个土壤肥力指标,分析不同林龄土壤养分差异及其变化趋势。结果表明:除土壤pH值外,土壤主要肥力指标的变化幅度较大,有机质、全氮、水解性氮、速效钾、有效磷含量在不同土层和不同林龄间均存在极显著差异(P<0.01);随着林龄的增长,林地土壤有机质和氮磷肥消耗较大,其中,表土层(0~20 cm)有机质、水解性氮、有效磷含量到11 a主伐时的降幅均超过30%,但不同林龄间各肥力指标差异不显著;采用改进后的Nemerow法计算的土壤肥力综合指数为0.412~0.530,土壤肥力等级为Ⅲ级(P_综<0.9),土壤肥力较低,相比较而言,土壤中有机质和氮肥含量较充足,而交换性阳离子极为贫乏;有机质、速效钾、水解性氮、有效磷含量与综合肥力指数呈显著或极显著正相关(R_偏~2>0.8),是影响土壤肥力的主要因子;土壤肥力综合指数随林龄增大而降低,11 a主伐期比造林初期(2 a)下降22.26%,但不同林龄间各单项肥力指数及综合肥力指数均不存在显著差异(P>0.08)。在该栽培模式的超短经营周期内,随着林龄增大及林木生长对土壤养分的消耗,林地土壤肥力出现一定程度的退化现象,但并未达到显著水平,有必要通过提高整地质量、改良土壤、林粮间作、增施有机肥及氮磷钾肥等措施适度增加土壤肥力,维持林地长期生产力。

Comprehensive evaluation of soil fertility in different stand ages in a Chinese fir short rotation plantation

This study aimed to analyze the differences in soil nutrients at different ages and the trend in the change of soil degradation,to evaluate the fertility of soil,and to discuss the primary influencing factors in Chinese fir short rotation and small-size timber plantation.Soil samples from Chinese fir planted forest were collected at 2,4,6,8,and 11 years,and a total of 11 soil fertility indices were tested,namely content of organic matter,total nitrogen,total potassium,total phosphorus,available nitrogen,available potassium,available phosphorus,available iron,exchangeable calcium,exchangeable magnesium,and pH value.These studies can provide the basis for site selection,soil management,and rational operation of Chinese fir planted forests in this region.The results showed that the main soil fertility indices,in addition to the pH value,changed significantly.There were significant differences in the contents of organic matter,total nitrogen,available nitrogen,available potassium,and available phosphorus in different forest ages and soil layers.Soil organic matter,nitrogen,and phosphorus fertilizer were consumed more rapidly with an increase in forest age.The content of organic matter,hydrolytic nitrogen,and available phosphorus in the surface soil layer(0-20 cm)decreased by more than 30%from 2 years to 11 years,but there was no significant difference in fertility indexes among different ages.The improved Nemerow method was used to calculate the soil fertility index.This value ranged from 0.412 to 0.530,and the soil fertility level wasⅢ,which indicates low soil fertility.Soil organic matter and nitrogen content were abundant,and exchangeable cations were extremely poor in comparison.Organic matter,available nitrogen,available potassium,and available phosphorus were significantly or extremely significantly positively related to fertility index(partial correlation coefficient R~2>0.8),and were found to be the primary factors affecting soil fertility.The comprehensive index of soil fertility decreased with the increase in stand age,and decreased by 22.26%in 11 years of rotation compared with that at 2 years after planting.However,there were no significant differences(P>0.08)between the individual fertility index and comprehensive fertility index in different forest ages.The results showed that soil fertility had degenerated to a certain degree,but not to a significant level with the increase in age and the consumption of soil nutrients by tree growth in the super-short operating cycle of the cultivation mode.This can moderately increase soil fertility and maintain long-term forest productivity by enhancing the quality of site preparation,improving soil moderately,and increasing organic fertilizer and tree-crop interplanting.