半干旱黄土丘陵区纯林土壤腐殖质异化特征及与其他性质的关系

纯林长期生长或多代连栽必然会导致土壤腐殖质含量和构成发生异化,探究这种异化特征及其与土壤其他性质的关系可以为纯林管理或混交改造提供科学依据。通过对半干旱黄土丘陵区南泥湾林场8种典型纯林土壤腐殖质及其他性质进行系统检测,结果表明:(1)侧柏林土壤腐殖质含量最高(34.61 g/kg),腐殖化程度和稳定性一般;白榆和白桦林土壤的腐殖质含量中等(19.69—23.58 g/kg)、腐殖化程度和稳定性最佳;茶条槭和小叶杨林土壤的腐殖质含量(20.59—22.53 g/kg)和构成均为中等水平;油松、沙棘和刺槐林土壤的腐殖质质量较低(11.77—13.81 g/kg),且腐殖化程度较低,稳定性相对最差;(2)与胡敏酸含量存在显著相互促进作用(P0.05)的土壤性质为CEC、N、微生物量和蛋白酶活性(相关系数0.769—0.926,下同),存在显著相互抑制作用的为有效Cu(-0.793);与富啡酸存在显著相互促进作用的为N、CEC、微生物量、蔗糖酶和磷酸酶活性(0.836—0.955),存在显著相互抑制作用的为有效Cu(-0.822);与胡敏素存在显著相互促进作用的为N、CEC、微生物量、磷酸酶活性和有效Zn(0.766—0.951),存在显著相互抑制作用的为脱氢酶活性(-0.784)。(3)腐殖质构成与其他性质的相关性均不显著(P0.05),其中相对有利于提高胡敏酸/腐殖酸含量之比的土壤性质为蛋白酶、蔗糖酶和过氧化氢酶活性,而不利的是脱氢酶活性;相对有利于提高胡敏酸/富啡酸含量之比的为速效K、CEC和脲酶活性,而不利的是脱氢酶活性。(4)总体而言土壤腐殖质含量较之腐殖质构成与其他性质之间具有更大的相关性;向土壤增施N肥可以促进腐殖质的形成,增加K肥则有利于腐殖质构成的改善,而通过混交改造或增加林下植被是促进纯林土壤腐殖质化过程和解决土壤退化的根本措施。

Humus differentiation and correlation with other soil properties under pure forest in semi-arid loess hilly area

Long-term growth or continued planting of pure forests which composed of one single species would cause soil humus differentiation both in content and composition, so studying the characteristics of humus differentiation and its correlation with other soil properties may provide scientific basis for the management and reformation of pure forests. In this study, 8 typical pure forest soils in Nanniwan forest station (which located at the semi-arid loess hill area) were sampled from 24 plots and their humus and other soil properties were measured systematically. The results showed that: (1) the soil from Platycladus orientalis forest had the highest humus content (34.61 g/kg) but moderate humification degree and stability; the soils from Ulmus pumila and Betula platyphylla had moderate humus content (19.69-23.58 g/kg) but highest humification degree and stability; the soils from Acer ginnala and Populus simonii forests had both moderate humus content (20.59-22.53 g/kg) and composition; the soils from Pinus tabulaeformis, Hippophae rhamnoides and Robinia pseudoacia forests had both low humus content (11.77-13.81 g/kg) and lowest humification degree and stability. (2) According to correlation analysis among humus content and other soil properties, humic acid had significant (P < 0.05) positive interaction with CEC, N (total and available N), microbe biomass and protease activity (correlation coefficient 0.769-0.926, the same below), but significant negative with available Cu (-0.793); fulvic acid had significant positive interaction with N, CEC, microbe biomass, sucrase and phosphatase activities (0.836-0.955), but significant negative with available Cu (-0.822); humin had significant positive interaction with N, CEC, microbe biomass and phosphatase activity and available Zn (0.766-0.951), but significant negative with dehydrogenase activity (-0.784). (3) According to correlation analysis among humus composition and other soil properties, no significant correlation (P > 0.05) among humus composition and other soil properties was observed. However, the ratio of humic acid/total humus acid would be enhanced by protease, sucrase and peroxidase to some extent, but restrained by dehydrogenase; the ratio of humic acid/fulvic acid would be enhanced by available K, CEC and urease to some extent, but restrained by dehydrogenase. (4) In general, humus content had more observable correlation with other soil properties than humus composition Increasing N fertilize and increasing K fertilize were helpful for the improvement of humus content and composition, respectively. Forming mixed forests or increasing the undergrowth was the essential measure to promote the soil humification process and to solve the problem of soil degradation.