【作者】 王恩姮；

【导师】 赵雨森； 陈祥伟； Richard M. Cruse；

【作者基本信息】 东北林业大学 ， 水土保持与荒漠化防治， 2011， 博士

【摘要】 以东北典型黑土区耕地上壤为主要研究对象,采用田间机械作业过程与模拟机械压实试验相结合、田间季节性冻融过程与室内模拟冻融循环试验相结合的方法,从机械作业正负效益、季节性冻融循环特征等方而入手,研究了对土壤影响范围较深、影响程度较为强烈的机械作业和季节性冻融循环两个过程对典型黑土区土壤结构的影响。首先,通过对容重、硬度、孔隙度、团聚体分布及稳定性、三相比、速效养分等指标的测定与分析,研究了不同机械类型以及前期含水量对机械作业条件下黑土耕作区、非耕作区土壤结构特征、有效养分的影响,结果表明：(1)机械作业对黑土区耕地土壤结构存在正负两方面效应,总体表现为对表层耕作区土壤的疏松改良效果,和对耕作层下土壤的积累压实作用,大机械和中机械作业条件下的压实积累区分别在41-60cm和31～40cm土层范围。(2)大机械对耕作区土壤环境的改善调节作用明显优于中小机械,显著降低了表层耕作区土壤的容重,收获和深松作业后土壤容重分别较收获前降低了3.5%和7.2%(P<0.05),非毛管与毛管的比例(NCP/CP)显著增加,而由于中机械收获和整地深度不一致,在17.5-30cm深度产生了土壤再生板结。(3)大机械收获、整地作业可以显著增加土壤速效磷的含量,与收获前相比提高20.07%～380.91%,中机械作业时土壤速效磷的含量整体上呈现降低趋势；大、中机械作业对土壤速效氮的影响均不明显,显著增加了下层非耕作区土壤速效钾含量,提高幅度分别为10.04%～20.61%和17.05%～27.52%(P<0.05)。(4)前期含水量不同对机械压实后黑土土壤结构特征的变化具有显著影响。前期含水量较高时机械压实对土壤的影响范围较深,可达40cm,比较低前期含水量的影响范围增加了10cm。但高含水量时,从首次压实开始就体现了积累压实的作用。(5)综合黑土耕作区0～30cm范围内于筛团聚体和水稳性团聚体PA0.25、MWD、MWSSA、分维数D值和PAD0.25的变化,可以认为少次压实具有促进土壤团聚体团聚的作用,但同等负荷下多次积累压实会降低土壤的水稳定性和机械稳定性。其次,采用长期定位监测的方法对比分析了典型剖面、不同坡位(坡肩和坡脚)处季节性冻融特征；通过对容重、硬度、孔隙度、空隙比、饱和度、团聚体公布及稳定性等指标的测定和分析,研究了季节性冻融对黑土耕作区、非耕作区以及压实黑土结构特征的影响；星后采用美国中部黑土的原状土、填充土、团聚体样品,通过室内模拟实验,进行了冻融循环次数、含水量对孔隙结构、团聚体稳定性的研究,结果表明：(1)季节性冻融过程中(2008年10月～2009年6月),坡上部位的冻结强度较为明显,坡下部位积雪较深,坡上和坡下的最大冻结深度分别为229cm和191cm,坡上部位的平均冻结和解冻速度分别为1.17cm/d和2.83cm/d；而坡下部位则相应为1.03cm/d和2.60cm/d。(2)季节性冻融后,50～70cm上层范围的土壤结构较其上下土层更为敏感(P<0.05),耕作区土壤(0～30cm)风干团聚体量分散趋势,但大于0.25mm团聚体的水稳定性却显著增强(P<0.05)。土壤硬度以表层(0～10cm)变化最为显著,降低了84.11%(P<0.05),各层次土壤容重趋于一致,在1.10～1.11g/cm3之间。(3)冻融交替频度、程度以及水分条件的差异能够对典型黑土表层(0～10cm)团聚体组成、分布及分形特征产生不同的影响：无水分补充时,显著增加了>5mm干筛团聚体和>0.25mm水稳性团聚体的含量；有水分补充时则加剧了团聚体的拆分作用,显著增加了<2mm干筛团聚体和0.25～1mm水稳性团聚体的含量。(4)由于不同压实程度土体内水热运移规律和季节性冻融过程与特征差异所致,季节性冻融能够对压实土壤的团聚体、孔隙以及三相结构产生影响,呈现缓解并改善典型黑土耕作区压实土壤环境的趋势,但仅一季冻融循环作用均无法使各压实处理达到无碾压自然恢复的状态。(5)模拟冻融循环时,冻融循环对各粒级风干团聚体、水稳定性团聚体比例的影响均达到了显著水平(P<0.01),而前期含水量仅对小于5mm的水稳性团聚体分布比例有显著影响(P<0.01)。风干团聚体对冻融交替更加敏感,取样方式对风干团聚体的MWD影响显著(P<0.01)。(6)冻融循环能够显著增加0～40cm表层土壤平均孔隙的数目,显著降低40～80cm土层范围内平均孔隙面积以及Feret直径；含水量对粘化层(40～80cm)原状土柱柿内≥5mm孔隙的平均数目与平均面积的影响最为显著(P<0.05),冻融循环显著降低了粘化层(40～80cm)填充土柱的平均孔隙数目,相H比之下,含水量对填充土柱孔隙的影响较小。与此同时,在研究过程中借鉴柯布-道格拉斯生产函数边际递减效益的思想,构建了旱作土壤介质中“三相投入”与“结构产出”的土壤结构生产函数(GSSI)和土壤三相结构距离(STPSD),为定量化研究、分析和综合评价土壤结构状态与变化动态提供了新的综合指标及方法。研究的结果不仅可以为进一步深入系统研究东北黑土区土壤质量演变与管理提供理论参考和借鉴,而且对黑土资源的利用与保护、科学指导机械作业、恢复和改善黑土土壤结构与功能具有重要的现实意义。更多还原

【Abstract】 Agricultural machinery tillage and seasonal freeze-thaw cycles are two major processes affecting soil structure in black soil region of Northeast China. Combining practical machinery operation and natural freeze-thaw cycles with artificial machinery compaction in the field and artificial freeze-thaw cycles in the lab, the plus and minus benefits of machinery tillage, characterization of seasonal freeze-thaw cycles, and their effects on soil structure were studied based on typical black soil.Firstly, the effects of machinery type and antecedent water content on soil structure and soil available nutrient were investigated by measuring soil bulk density, soil strength, soil porosity, soil aggregate distribution and stability, three soil phases and availability of nitrogen, phosphorus, potassium. The results showed that(1)Machinery tillage had positive and negative influence on soil structure, soil in top cultivated layer can be loosened and ameliorated however the subsoil compaction was resulted. For heavy and medium machinery, subsoil compaction formed in the soil depth of 41～60cm and 31～40cm, respectively.(2)Heavy machinery did better in improving soil environment compared with medium machinery, soil bulk density under heavy machinery operation decreased significantly by 3.5% and 7.2% after harvesting and subsoiling and NCP/CP increased dramatically also(P<0.05);however during the soil depth of 17.5～30cm under medium machinery operation there was a new plow pan produced because of the depth difference between harvesting and subsoiling.(3)Heavy machinery harvesting and subsoiling could increase phosphorus availability by 20.07%～380.91% overall, and increase potassium availability by 10.04%～20.61%(P<0.05)in the subsoil; medium machinery operation presented a increase and decrease trend of phosphorus availability and increase potassium availability by 17.05%～27.52% (P<0.05)in the subsoil; both heavy and medium machinery had no significance on soil nitrogen availability.(4)Antecedent water content had a significant effect on soil structure under machinery operations. Higher water antecedent resulted in deeper subsoil compaction at 40cm, which was deeper by 10cm than lower water content. Soil compaction occurred at the first pass when water content was higher. (5)By analyzing aggregate distribution and stability indexes of PA0.25、MWD、MWSSA、D and PAD0.25 in top soil of 0～30cm, we could inferred that few traffic passes promoted soil aggregation however more traffic passes greater than 5 would reduce water stability and mechanical stability of soil aggregates.Secondly, we monitored natural seasonal freeze-thaw cycles in different positions along slop and imitated freeze-thaw cycles under different water condition. The effects of freeze-thaw cycles on soil structure were studied by measuring soil bulk density, soil strength, soil porosity, void ratio, soil saturation, soil aggregate distribution and stability. Results showed that (1)During seasonal freezing and thawing cycles of October,2008 to June,2009, soil on the higher elevation had more intensive freeze process with shallow snow depth; the biggest frozen depth in higher and lower elevation were 229cm and 191cm respectively. The speed of freeze and thaw processes were 1.17cm/d and 2.83cm/d in higher elevation position, which were 1.03cm/d and 2.60cm/d for lower elevation position.(2)Soil at depth of 50～70cm was more susceptive to seasonal freezing and thawing cycles(P<0.050; after seasonal freezing and thawing, dry aggregates in cultivated soil (0-30cm) layer dispersed and stability of water stable aggregates bigger than 0.25mm increased significantly(<0.05), soil strength in 0～10cm decreased by 84.11%(<0.05), bulk density were in the same value of 1.10～1.11g/cm.(3)Frequency, intensity and water condition could affect soil aggregates distribution and stability (0-10cm) significantly:dry aggregates bigger than 5mm and water stable aggregates bigger than>0.25mm increased when there was no extra water applied during freezing and thawing cycles; however soil aggregates dispersed more when applying water during freezing and thawing cycles, dry aggregates smaller than 2mm and water stable aggregates of 0.25～1mm increased significantly(P<0.05).(4)Seasonal freeze-thaw cycles could loosen and improve soil environment in cultivated layer compacted by tractor, but one seasonal freeze-thaw process would not make the compacted soil recover to the natural level.(5)During artificial freezing-thawing process, dry aggregates and water stable aggregates were influenced by the number of cycles significantly(P<0.01), antecedent water content could only affect water stable aggregates smaller than 5mm(P<0.01)。Dry aggregates were more susceptive than water stable aggregates, and the MWD of dry aggregates was affected by method of sampling soil(P<0.01).(6)From the image analysis results of CT, freeze-thaw cycles could increase the average number of pores of soil at depth of 0～40cm and decrease average number and Feret diameter of pores during soil depth of 40-80cm. For argillic layer (40-80cm), average number and area of pores with size bigger and equal to 5mm were influenced by antecedent water content significantly(P<0.05); The number of freeze-thaw cycles had more influence on the average number of pores compared with antecedent water content.Meanwhile, we constructed generalized soil structure index (GSSI)and soil three phases index (GSSI)based on the Cobb-Douglas production function, which can use to quantify and evaluate soil structure condition.Results from this research could offer the theory reference to further study quality and management of black soil and contribute realistic significance to guide machinery tillage and ameliorate soil structure and function of black soil.更多还原