Changes in terrestrial surface dry and wet conditions on the Loess Plateau(China) during the last half century

This paper, using a revised Penman-Monteith model, computed the terrestrial surface humidity index of the Loess Plateau （China） based on climatic factors of monthly mean temperature, maximum temperature, minimum temperature, relative humidity, precipitation, wind speed and sunshine duration observed on the plateau from 1961 to 2008. The temporal-spatial distribution, anomaly distribution and sub-regional temporal variations of the terrestrial surface dry and wet conditions were analyzed as well. The results showed a decreasing trend in the annual average surface humidity from the southeast to the northwest in the research anna. Over the period of 1961-2008, an aridification tendency appeared sharply in the central interior region of the Loess Plateau, and less sharply in the middle part of the region. The border region showed the weakest tendency ol; aridification. It is clear that aridification diffused in all directions from the interior region. The spatial anomaly distribution of the terrestrial surface dry and wet conditions on the Loess Plateau can be divided into three key areas： the southern, western and eastern regions. The terrestrial annual humidity index displayed a significantly descending trend and showed remarkable abrupt changes from wet to dry in the years 1967, 1977 and 1979. In the above mentioned three key areas for dry and wet conditions, the terrestrial annual humidity index exhibited a fluctuation period of 3-4 years, while in the southern region, a fluctuation period of 7-8 years existed at the same time.

Revegetation with artificial plants improves topsoil hydrological properties but intensifies deep-soil drying in northern Loess Plateau,China

Knowledge about the effects of vegetation types on soil properties and on water dynamics in the soil profile is critical for revegetation strategies in water-scarce regions, especially the choice of vegetation type and human management measures. We focused on the analysis of the effects of vegetation type on soil hydrological properties and soil moisture variation in the 0–400 cm soil layer based on a long-term（2004―2016） experimental data in the northern Loess Plateau region, China. Soil bulk density（BD）, saturated soil hydraulic conductivity（Ks）, field capacity（FC） and soil organic carbon（SOC） in 2016, as well as the volumetric soil moisture content during 2004–2016, were measured in four vegetation types, i.e., shrubland（korshinsk peashrub）, artificial grassland（alfalfa）, fallow land and cropland（millet or potato）. Compared with cropland, revegetation with peashrub and alfalfa significantly decreased BD and increased Ks, FC, and SOC in the 0–40 cm soil layer, and fallow land significantly increased FC and SOC in the 0–10 cm soil layer. Soil water storage（SWS） significantly declined in shrubland and grassland in the 40–400 cm soil layer, causing severe soil drought in the deep soil layers. The study suggested that converting cropland to grassland（alfalfa） and shrubland（peashrub） improved soil-hydrological properties, but worsened water conditions in the deep soil profile. However, natural restoration did not intensify deep-soil drying. The results imply that natural restoration could be better than revegetation with peashrub and alfalfa in terms of good soil hydrological processes in the semi-arid Loess Plateau region.

Effects of Tillage Methods on Soil Available Phosphorus and Available Potassium in the Loess Plateau

In order to find out the effects of long-term no-tillage operation on soil available phosphorus and available potassium in the loess plateau, a suitable high-yield and high-efficiency tillage technology system was established. In the Changwu loess plateau agri-ecological experiment station of the Northwest A&F University of Changwu County, Shaanxi Province, the no-tillage experimental field for three consecutive years was selected. In September 2015, no-tillage, tillage, and rotary tillage were carried out before winter wheat was sowed. After the harvest of winter wheat in 2016, the contents of available phosphorus and available potassium in 0-30 cm soil layer under three tillage methods were analyzed. The results showed that in the 0-30 cm soil layer, the soil available phosphorus and available potassium decreased with the increase of the soil depth in the three tillage methods. The content of available phosphorus and available potassium in 10-20 cm soil layer and 20-30 cm soil layer decreased by 16.07%, 32.74%, 15.54% and 27.08%, respectively, and there were significant differences ( P <0.05). Under different tillage methods, the soil available phosphorus content in the 0-10 cm soil layer significantly reduced by 11.31% compared with no-tillage. The soil available potassium content under tillage and rotary tillage significantly reduced by 6.16% and 4.97%, respectively ( P <0.05). Compared with no-tillage, the soil available phosphorus content in the 20-30 cm soil layer significantly reduced by 18.12%. The soil available potassium content under tillage and rotary tillage methods significantly reduced by 17.17% and 9.22%, respectively ( P <0.05). Therefore, in the long-term no-tillage dry loess plateau, it is necessary to conduct proper tillage or rotary tillage.

Long Term Effects of Farming System on Soil Water Content and Dry Soil Layer in Deep Loess Profile of Loess Tableland in China

Soil water is strongly affected by land use/cover in the Loess Plateau in China. Water stored in thick loessal soils is one of the most important resources regulating vegetation growth. However, soil water in the deep loess proifle, which is critical for maintaining the function of the“soil water pool”is rarely studied because deep proifle soil samples are dififcult to collect. In this study, four experimental plots were established in 2005 to represent different farming systems on the Changwu Tableland：fallow land, fertilized cropland, unfertilized cropland, and continuous alfalfa. The soil water content in the 15-m-deep loess proifles was monitored continuously from 2007 to 2012 with the neutron probe technique. The results showed that temporal variations in soil water proifles differed among the four farming systems. Under fallow land, the soil water content increased gradually over time, ifrst in the surface layers and later in the deep soil layers. In contrast, the soil water content decreased gradually under continuous alfalfa. The distributions of soil water in deep soil layers under both fertilized and unfertilized cropland were relatively stable over time. Thus farming system signiifcantly affected soil water content. Seven years after the start of the experiment, the soil water contents in the 15-m-deep proifles averaged 23.4%under fallow land, 20.3%under fertilized cropland, 21.6%under unfertilized cropland, and 16.0%under continuous alfalfa. Compared to measurements at the start of the experiment, both fallow land and unfertilized cropland increased soil water storage in the 15-m loess proifles. In contrast, continuous alfalfa reduced soil water storage. Fertilized cropland has no signiifcant effect on soil water storage. These results suggest that deep soil water can be replenished under the fallow and unfertilized farming systems. Dry soil layers （i.e., those which have soil water content less than the stable ifeld water capacity） in the subsoil of the Changwu Tableland region can be classiifed as either temporary dry soil layers or persistent dry soil layers. Temporary dry soil layers, which typically form under annual crops, often disappear during wet years. Persistent dry soil layers generally develop under perennial vegetation. Even after removing the vegetation, persistent dry soil layers remain for several decades. This study provides information useful for the conservation and utilization of soil water resources in the Loess Tableland.

Influence of environmental factors on land-surface water and heat exchange during dry and wet periods in the growing season of semiarid grassland on the Loess Plateau

On the basis of information from the project ＂Land-surface Processes and their Experimental Study on the Chinese Loess Plateau＂, we analyzed differences in land-surface water and heat processes during the main dry and wet periods of the semiarid grassland growing season in Yuzhong County, as well as the influences of these environmental factors. Studies have shown that there are significant differences in changes of land-surface temperature and humidity during dry and wet periods. Daily average normalized temperature has an overall vertical distribution of ＂forward tilting＂ and ＂backward tilting＂ during dry and wet periods, respectively. During the dry period, shallow soil above 20-cm depth is the active temperature layer. The heat transfer rate in soil is obviously different during dry and wet periods. During the dry period, the ratio of sensible heat flux to net radiation （H/Rn） and the value of latent heat flux to net radiation （LE/Rn） have a linear relationship with 5-cm soil temperature; during the wet period, these have a nonlinear relationship with 5-cm soil temperature, and soil temperature of 16℃ is the critical temperature for changes in the land-surface water and heat exchange trend on a daily scale. During the dry period, H/Rn and LE/Rn have a linear relationship with soil water content. During the wet period, these have a nonlinear relationship with 5-cm soil water content, and 0.21 m^3 m^-3 is the critical point for changes in the land-surface water and heat exchange trend at daily scale. During the dry period, for vapor pressure deficit less than 0.7 kPa, H/Rn rises with increased vapor pressure deficit, whereas LEIRn decreases with that increase. When that deficit is greater than 0.7 kPa, both H/Rn and LE/Rn tend to be constant. During the wet period, H/Rn increases with the vapor pressure deficit, whereas LE/Rn decreases. The above characteristics directly reflect the effect of differences in land-surface environmental factors during land-surface water and heat exchange processes, and indirectly reflect the influences of cloud precipitation processes on those processes.

Soil water depletion depth by planted vegetation on the Loess Plateau

Evapotranspiration of much planted vegetation exceeds precipitation, and this can deplete soil water and cause a deep dry layer in the soil profile, which is a serious obstacle to sustainable land use on the Loess Plateau, China. This study aimed to determine water depletion depth of planted grassland, shrub, and forest in a semiarid area on the Loess Plateau. Soil moisture of five vegetation types was measured to >20 m in depth. The vegetation types were crop, natural grasse, seven-year-old planted alfalfa (Medicago sativa L.), 23-year-old planted caragana (Caragana microphylla Lam.) shrub, and 23-year-old planted pine (Pinus tabulaeformis L) forest land. Through comparing moisture of planted alfalfa grass, caragana shrub, and pine forest to crop and natural grassland, the depth and amount of soil water consumed by grassland, caragana brush and pine forest was determined. The depth of soil water depleted by alfalfa, caragana brush, and pine forest reached 15.5, 22.4 and 21.5 m, respectively.

两大优势产区‘红富士’苹果园土壤和叶片营养诊断研究

【目的】通过对中国环渤海和黄土高原两大优势产区‘红富士’苹果园土壤有效养分和叶片矿质元素含量的测定及营养状况诊断,为苹果园科学施肥提供理论依据。【方法】根据土壤有效养分分级标准及叶片DRIS诊断法,采用DPS V7.05软件进行LSD单因素方差分析和差异性显著分析,对两大产区树龄15—20年的高产(>37 500 kg.hm-2)、低产(<37 500 kg.hm-2)园土壤和叶片营养状况进行诊断。【结果】环渤海产区土壤有机质、碱解氮、速效磷、速效钾有效养分均值分别为10.9 g.kg-1、73.21 mg.kg-1、70.22 mg.kg-1、169.2 mg.kg-1;黄土高原产区土壤有机质、碱解氮、速效磷、速效钾有效养分均值分别为11.7g.kg-1、56.46 mg.kg-1、14.91 mg.kg-1、135.78mg.kg-1;除有机质外,碱解氮、速效磷、速效钾有效养分含量为环渤海产区高于黄土高原产区;环渤海产区叶片N、P、K、Ca、Mg、Fe、Mn、Cu、Zn、B、Mo各养分元素含量均值分别为2.73%、0.18%、1.15%、9.63 g.kg-1、2.86g.kg-1、87.97 mg.kg-1、124.02 mg.kg-1、13.36 mg.kg-1、15.64 mg.kg-1、35.09 mg.kg-1、0.51 mg.kg-1;黄土高原产区叶片N、P、K、Ca、Mg、Fe、Mn、Cu、Zn、B、Mo各养分元素含量均值分别为2.72%、0.18%、1.17%、10.23 g.kg-1、2.99 g.kg-1、88.69 mg.kg-1、116.39 mg.kg-1、10.85 mg.kg-1、15.94 mg.kg-1、39.55 mg.kg-1、0.51 mg.kg-1。通过DRIS法对两大优势产区叶片营养诊断结果表明,环渤海产区低产园叶片最缺乏的元素为Ca、K,其次是Fe、N、Zn,最不缺乏的是Cu、Mo;黄土高原产区低产园叶片最缺乏的元素是P、K,其次是N、Zn、Cu等,最不缺乏的是B、Ca。【结论】环渤海、黄土高原产区土壤有效养分状况均为有机质中等偏低、缺氮;环渤海产区富P少K;黄土高原产区贫P缺K。低产园叶片诊断表明,黄土高原产区树体营养平衡状况优于环渤海产区,两产区均具有很大的增产潜力。建议环渤海产区增加K、N、Ca、Fe和Zn施用,黄土高原产区增加P、K、N、Zn、Cu、Mn、Fe施用,同时重视有机肥施用。

黄土区土壤干化研究进展

全面回顾了国内对土壤干化研究所取得的成果,包括土壤干化的分布及在不同尺度上的分异特征、土壤干层类型、土壤干化的形成原因及其危害、量化指标、防治对策等。同时对这些研究成果作了简单的对比分析,指出了目前研究所面临的问题和不足。并指明今后该领域的研究应结合当前退耕还林还草的总体目标。探索土壤干化的形成机理,提出统一的量化指标,为黄土区退耕还林还草的生态恢复与重建工程提供参考。

黄土高原土壤干层初步研究

在详细描述土壤干层现象和类型的基础上 ,分析了土壤干层的成因 ,即低降水高蒸发、水土流失、植被类型选择失当、群落生产力过高和群落密度过大等 ,指出土壤干层的危害主要表现为使局部小气候环境趋于旱化、土地退化、植被生长衰退、天然下种更新不良及加大造林难度等 ,最后提出了缓解土壤干层对黄土高原生态环境的恢复和重建的意义和重要性。

长期施肥条件下黄土旱塬土壤NO_3^-N的淋溶分布规律

在黄土旱塬区 ,长期施肥对土壤剖面NO3- N含量和分布有显著影响 .施用化学氮肥 ,土壤剖面中出现NO3- N的淋溶与深层累积 ,而施用磷肥和有机肥有减弱NO3- N向更深层淋溶的作用 .单施氮肥处理 (N) ,NO3- N的累积峰深度最大 ,为 1 2 0～ 2 0 0cm ;N、P有机肥配施处理 (NPM ) ,NO3- N的累积峰值最高 ,但峰深度降低至 60～ 1 2 0cm ;N、P配施 (NP)累积深度为 80～ 1 4 0cm .不施氮肥 ,分布在土壤剖面中NO3- N含量显著降低 .氮肥用量愈大 ,NO3- N的累积量愈大 .N、P配施可以有效降低NO3- N累积 .在同一氮肥用量下 ,NO3-

黄土高原半干旱区气候变化对春小麦生长发育的影响——以甘肃定西为例

利用黄土高原半干旱区春小麦生长发育定位观测资料、加密观测和对应平行气象观测资料,分析气候变化对春小麦生长发育的影响,以及春小麦穗干重生长与气象条件的关系。结果表明,研究区域降水量年际变化呈下降趋势,降水量变化曲线线性拟合倾向率为-15.796 mm/10a。降水量存在3 a、6 a的年际周期变化。气温年际变化呈上升趋势,气温变化曲线线性拟合倾向率为0.362℃/10a。作物生长季干燥指数呈显著上升趋势,干燥指数变化曲线线性拟合倾向率为0.12/10a,20世纪90年代初至2009年明显趋于干旱化。春小麦播种到成熟约需110—130 d,期间≥0℃积温为1500—2000℃,降水量为150—200mm,日照时数为800—1300 h。春小麦在播种后38 d开始,穗干重由缓慢生长转为迅速生长阶段;在播种后50 d,穗干重生长速度最大;播种后63 d开始,穗干重生长从迅速生长又转为缓慢生长。对春小麦生长发育全生育期而言,受气候变暖的影响,乳熟—成熟期每10 a缩短2—3 d、全生育期每10 a缩短4—5 d。气温对春小麦产量形成除出苗期和成熟期外,其余为负效应,孕穗期对气温变化十分敏感;降水量的影响函数同热量的影响函数呈反相位分布,除出苗期和成熟期降水量为负效应外,其余时段降水量对春小麦产量形成均为正效应,春小麦拔节—抽穗期对降水量变化十分敏感。

黄土高原北部人工灌草植被土壤干燥化过程研究

黄土高原北部水蚀风蚀交错区是典型的生态脆弱区,人工灌草植被土壤干燥化发生频繁。土壤干化层的形成影响生物小循环并削弱水文大循环,严重制约植被建设成效和区域生态稳定。为阐明人工灌草植被土壤干燥化过程,并确定适宜的种植年限,选择该区典型人工灌草植被-柠条和苜蓿为研究对象,分析两种植被土壤水分和地上生物量随生长年限的变化特征。结果表明:2-8年生柠条和1-7年生苜蓿对剖面土壤水分消耗强烈,并随生长年限呈快速下降趋势,9-12年生柠条和8-11年生苜蓿1.0-4.0 m剖面含水量分别降低至8.2%-9.0%和8.5%-10.5%之间,并处于相对稳定状态。4-5年生柠条地1-1.4 m开始产生干层,6年生柠条地干层深度达2.4 m,干层厚度为1.4 m;9-12年生柠条地干层深度超过4.0 m。2-4年生苜蓿地无干燥化;5年生苜蓿生长季末土壤干层深度达3.6 m,干层厚度为2.6 m,且7年生以后土壤干层的深度超过4.0 m。因此,为调控土壤干层,减少深层土壤干化的发生,建议柠条和苜蓿的生长年限分别不要超过6年和5年,其对应的地上最大干生物量分别为5050 kg/hm^2和1980 kg/hm^2。研究结果可为黄土高原北部生态脆弱区人工灌草植被管理与土壤干层调控提供科学依据。

黄土旱塬Hybrid-Maize模型适应性及春玉米生产潜力估算

通过对Hybrid-Maize玉米高产模型进行田间验证,应用该模型对黄土旱塬春玉米生产潜力进行初步估算。结果表明,Hybrid-Maize模型在黄土旱塬表现出较好模拟效果,总生物量、秸秆生物量和籽粒产量模拟值与实测值间具有极显著线性相关性,其决定系数分别为0.9469、0.8164和0.9650,回归系数分别为1.0198、0.9787和1.1844,接近于1。黄土旱塬区多年光温生产潜力和气候生产潜力因品种不同有所差别,对多年平均光温籽粒和总生物量生产潜力,紧凑型玉米品种分别为13.25和22.45t/hm2,平展型玉米品种分别为12.32和20.62t/hm2,年际变化小;对多年平均气候籽粒和总生物量生产潜力,紧凑型玉米品种分别为11.97和19.94t/hm2,平展型玉米品种分别为11.37和18.63t/hm2,年际波动大。在黄土旱塬区,玉米产量潜力挖掘的主要途径应集中在提高密度和水分限制条件下,Hybrid-Maize玉米模型在指导玉米高产栽培上具有较好应用。

黄土高原土壤干层评定指标的改进及分级标准

土壤干层是黄土高原普遍存在的特殊土壤水文现象,研究其现状、成因、防治、调控措施等对科学认识区域植被承载力、土地生产力以及低效林草改造和可持续植被建设等有重要理论与生产指导意义,而合理通用评判指标与分级标准是开展土壤干层研究的基础。目前黄土高原土壤干层尚无统一评判指标与分级标准,给区域土壤干层研究带来困难。本文在已有研究成果的基础上,提出用土壤有效水饱和度/不饱和度作为土壤干层评判指标,并给出其分级标准。该评判指标计算简单,具通用性和可比性,可望成为土壤干层的通用评判指标。

黄土高原沟壑区小流域土壤干层的分布特征

以长武王东沟小流域为研究对象,从土壤干层的量化指标、分级评述和分布特征等3个方面初步探讨了黄土高原沟壑区小流域的土壤干层问题,并就小流域内的植被建设中的一些问题提出了几点看法。结果表明:在王东沟小流域内,土壤干层已成为一个普遍存在的水分现象,不同程度地影响植物生长和植被的恢复,并具有如下特点:①土壤干层的干燥化程度和干层厚度都表现为林地大于果园,果园大于草地,农地最小;②同一种植被类型由于密度、生物量、树龄、坡度、坡向以及坡位不同,其土壤干层的干燥化程度和深度也不相同。

黄土高原土壤干层形成原因分析

以丰水年洛川人工林地深层土壤水分恢复为依据,采用高精度土壤含水量测量与逐层分析技术,以含水量变化率为主要指标,研究洛川2004年1月-2005年5月不同植被土壤水分的季节变化与水量平衡。结果显示,降水渗深以内表层土壤水分受气候和植被生长影响,呈明显季节变化;渗深以下深层土壤水分,中产农田和梨树林砍伐后基本维持平衡,苹果林地持续减少并以春季减少最多。研究表明,黄土高原深层土壤水分呈低水平循环状态,易形成土壤干层,而季节干旱是土壤干层形成的直接驱动力;"低降水、高蒸发"的气候特点是黄土高原土壤干层形成的决定因素,半湿润半干旱气候中的干旱特征对黄土高原自然地理环境产生广泛而深刻的影响。

黄土旱塬长期施肥下硝态氮深层累积的定量研究

在黄土旱塬长期定位测定结果表明 ,长期过量或不平衡使用氮肥将导致硝态氮在土壤深层的严重积累。不同施肥处理对比 ,14年后 0～ 2 0 0 cm硝态氮的累积量 NPM>N>NP>M,对应的硝态氮累积率分别为 2 0 .3%、30 .98%、15 .4 9%和 8.5 1%。化肥配比试验表明 ,土壤剖面 NO3- N的累积量与累积率一般随氮肥用量的增加而增加 ,而且 ,NO3- N累积深度随氮肥用量的递增而加深。氮磷严重失调时 ,硝态氮累积率剧增 ,15年后最大累积率达到 4 2 .3% (单施氮 180 kg/ hm2 处理 )。在施氮引起 NO3- N严重累积的情况下 ,配施磷肥可以明显的减少硝态氮的累积数量和累积率 ,而且随磷肥用量的增加减少幅度愈大。从土壤氮素平衡来看 ,加大施氮量降低氮素利用率 。

黄土塬区3种豆科牧草对土壤水分的消耗利用研究

在田间完全旱作条件下采用3个密度和2种播种方式观察了3种多年生豆科牧草生长第2年对土壤水分的消耗利用情况.结果表明：苜蓿主要耗水深度在2～3 m,最深可达5 m,其中、高密度处理3 m以上土壤水分含量都在稳定田间持水量之下,已经开始形成土壤下伏干层;沙打旺耗水深度在0～2 m,最低含水量（11.61%）处于80～100 cm,在雨季可以恢复到稳定田间持水量之上;达乌里胡枝子主要耗水深度在1 m以上,最低含水量也在稳定田间持水量之上.单播沙打旺、苜蓿和达乌里胡枝子全生长期内对土壤水分的消耗分别为249.9、180.2和136.6 mm,水分利用效率分别是29.39、26.04和8.91 kg·mm-1·hm-2.混播、加大播种密度都会增加3种牧草土壤水分消耗,降低土壤储水量,提高干草产量和水分利用效率,但影响程度因牧草种类、播种方式以及不同的生长时段而异.

黄土高原水土保持建设的环境效应

水土保持是黄土高原生态恢复和重建的基础,但在有效拦蓄径流和泥沙的同时,水土保持建设改变了水分和养分的静态分布格局和动态循环过程,并由此对区域的环境产生影响。分析了水土保持建设对水文环境和土壤环境的影响及其研究动态。不同水保措施都能在一定程度上调节和控制水文过程,改善流域的水质,提高土壤的质量,提高土壤的含水率;而人工林草植被不同程度地减少了土壤含水率。同时对黄河断流以及土壤干层与水土保持建设的关系进行了探讨。

吴旗县不同植被类型土壤干层特征分析

吴旗县位于黄土高原暖温带半干旱地区,由于降雨量较少以及地表的蒸发和植物的蒸腾,使土壤水亏损严重,部分植被下的土壤中出现了土壤干层。为了系统比较不同植被类型下土壤干层特点,通过对吴旗不同植被0～9.0m土壤水分的实地测量和分析,得出以下结论:除农地外,其它植被类型下都不同程度的存在着土壤干层,干层严重程度,林地大于灌木林地,灌木林地大于草地;草地存在临时干层和永久干层,永久干层深度可以达到4.0m。测量当时,灌木林没有临时干层,存在永久干层,深度3.0～8.4m;杏树林不存在临时干层,油松林临时干层则很严重,杏树林和油松林永久干层深度分别在8.0m和9.0m以上。临时干层的出现取决于降水的补充,因此可能与采样时间有关。通过对吴旗县土壤干层的分析可以为进一步研究土壤干层和植被建设提供借鉴。