秦岭北麓不同林龄华北落叶松土壤速效钾变化规律

Seasonal dynamics of available K in soil for different ages of Larix principis-rupprechtii in the northern foot of the Qinling

【目的】土壤养分对华北落叶松的生长具有重要作用,钾素是植物所必需的大量营养元素之一,土壤中钾素对植物最有效的形态为速效钾,其能够直观地反映土壤可供植物利用的钾素水平。华北落叶松是北方人工林栽植的主要树种,具有生长快、木材优质、耐寒性好、水土保持效果好等优点。研究表明华北落叶松人工林种植初期长势良好,而近年来长势明显不良,因此有必要对秦岭北麓不同林龄华北落叶松林地土壤的养分特别是速效钾的变化规律进行研究。【方法】本研究选择土壤性质与林分基本特征相似的幼龄林(5a,10a),中龄林(20a),近熟林(30a)及成熟林(40a)等5种不同林龄华北落叶松人工林地。5a、10a、20a华北落叶松试验样地位于陕西省宝鸡市太白县太白林业局南滩实验苗圃林场,30a、40a试验样地位于西北农林科技大学火地塘教学试验林场。从5月开始,每月中旬采集各个样地的土壤样品,直到10月中旬落叶为止。每个林龄林地选5个不同的20 m×20 m样点,用土钻取剖面0—20 cm、20—40 cm、40—60 cm土层土壤,5个点混合均匀成一个土样,分析土壤速效钾含量。【结果】在不同月份,不同林龄的华北落叶松土壤的速效钾含量随土壤深度的增加有下降趋势。0—20 cm土层的速效钾含量相对于其他土层含量较高,其中,近熟林(30a)及成熟林(40a)土壤速效钾含量明显高于其他林龄的土壤;不同月份不同林龄华北落叶松土壤的速效钾含量差异显著(P<0.01)。研究区域不同林龄华北落叶松土壤速效钾含量达到中等及高水平。在不同华北落叶松生长季节0—20 cm土层速效钾含量呈先增加后降低的抛物线形变化。土壤速效钾含量与有机质含量有极显著的正相关关系(P<0.01),与土壤含水量达显著相关(P<0.05),与土壤pH呈显著负相关关系(P<0.05)。【结论】随林龄的增加,华北落叶松人工林土壤速效钾的含量不会降低。土壤有机质含量,土壤含水量与土壤pH会对土壤速效钾的含量产生影响。秦岭北麓华北落叶松人工林林地土壤速效钾含量丰富,供钾充足。

Objectives]Soil nutrients are important for growth of Larix principis-rupprechtii.The soil readily available K contents in 5a, 10a, 20a, 30a and 40a Larix principis-rupprechtii fields in northern foot of the Qinling were measured to find out their seasonal dynamics from May to October.[Methods]The plantation with Larix principis-rupprecht age of 5a, 10a, 20a, 30a and 40a was selected, where the basic stand characteristics of trees and soil properties were similar.The 5a, 10a and 20a plantations were located in Taibai County, Baoji in Shanxi Province in the northern foot of the Qinling Mountain, the 30a and 40a ones in the teaching experiment forest farm&nbsp;of Northwest A&F University in the same region.The soil samples of 5a, 10a, 20a, 30a and 40a Larix principis-rupprechtii were collected in the middle of each month from May 2012 to October 2012.Each sampling area was 20 m ×20 m,five points were chosen randomly in each plot and soil samples were collected after peel off the litter layer of soil surface.The 0-20, 20-40 and 40-60 cm soil samples were taken separately with 1 m soil drilling. The content of soil readily available K was analyzed.[Results] In different months content of soil available K for different ages of Larix principis-rupprechtii was declined from the soil depth of 0-20 cm to 20-40 cm.On the soil depth of 0-20 cm, soil available K content in 30 a and 40 a plantations are higher than that in other ages of plantations.Soil available K content varies significantly in the tested months( P<0.01) .Without fertilization, the soil available K contents are in middle and high levels.In 0-20 cm of soil, soil available K contents show parabolic variation from spring to autumn.The soil available K content is extremely significant and positively correlated with the soil organic matter content ( P<0.01 ) , significantly with the soil water content ( P<0.05 ) , and significant negatively correlated with soil pH (P<0.05).[Conclusions] The elongation of Larix principis-rupprechtii growth ages will not reduce the soil available K content.The content of soil organic matter, water and pH affect the soil available K content.The soils in the Larix principis-rupprechtii plantations in the northern foot of the Qinling are abundant in available K, in other word, the supply of available potassium to Larix principis-rupprechtii is adequate.