Contemporary Global Issue of Rising Water Scarcity for Agriculture: The Quest for Effective and Feasible Soil Moisture and Free-Water Surface Conservation Strategies

There is the need to take seriously the task of conserving soil moisture in agricultural fields and free-water surfaces in reservoirs, especially in recent years of climate change. Many strategies exist for achieving this task and improving the productivity of arable soils. These strategies traditionally come under biological and physical or mechanical measures. Some other relatively new techniques operate neither on physical nor on biological principle. All these measures which operate on different principles frequently overlap. The principles involved, together with the prospects and constraints of the key techniques of conserving soil moisture found in the literature, are reviewed in this paper. Among other considerations, the effectiveness and/or practicability of any one of the techniques depend upon soil type, topography, climate, scale of production, level of technology, and socio-economic status. Such agronomic practices as conservation tillage and live vegetation mulch that maintain infiltration rates often appear to be more beneficial in the long run than engineering structures, especially those that lead to blocking of waterways on the soil surface. However, this review reveals that none of the soil moisture conservation strategies could be credited as universally applicable. Consequently, an integrated approach to soil water management and conservation, where feasible, is considered more appropriate. This is because the different principles involved in the techniques identified to be compatible would readily complement and strengthen one another. Such a multi-mechanistic approach is expected to result in improved efficacy in conserving water resources in soils and open reservoirs.

Development of Steel Slag-Based Solidification/Stabilization Materials for High Moisture Content Soil

To solve the problems of high moisture content,high viscosity,and poor engineering mechanical properties of soil,this paper using with steel slag(SS)and desulfurization ash(DS)as initial raw materials,realizing the coop-erative treatment of solid waste and solidification of silt soil.The synergistic utilization of SS and DS can reduce the production cost of curing agent and promote its own consumption.According to blended cement of various SS contents and inspected compressive strength performances,the most suitable raw materials ratio was selected.The best formula for this curing agent is cement:steel slag=3:7 with 5%DS,and its 28-day compressive strength can reach 30 MPa.The experiment shows that the effect of DS and Na_(2)SO_(4) reagent with the same quality on early compressive strength improvement of cement and SS system is not much different.In this study,the mineral composition and microstructure of different gel system blocks were characterized by XRD,SEM and EDX,and a large number of webbed structures were found in the SEM test,which was not seen in previous studies.Besides,unconfined compressive strength(UCS),water resistance,and toxic characteristic leaching procedure(TCLP)were used to evaluate silt solidified soil properties.The results demonstrated that the solidified silt could meet not only the standard of general subgrade;but also has a partial stabilization effect of heavy metal ions.

Effects of the Dicranopteris linearis root system and initial moisture content on the soil disintegration characteristics of gully erosion

Benggang erosion is caused by a special type of gully erosion in southern China that seriously endangers the local ecology and environment.In this study,typical Benggang collapsing-wall soils were used as the study area to investigate the effects of different initial moisture contents and dicranopteris linearis root weight densities,as well as their interactions on disintegration in orthogonal test method.The results showed that the rate of soil disintegration decreased as a linear function of the initial moisture content.The soil disintegration rate tended to rise and then fall as the root weight density increased,reflecting an optimum root weight density of 0.75-1.00 g/100 cm3.The incorporation of dicranopteris linearis roots was most effective for soil consolidation in the shallow layers of soil.In addition,the disintegration rate of the collapsing-wall soils increases as the soil layer deepened.The dicranopteris linearis root system and initial moisture content had an interactive effect that was more pronounced in deeper soils.However,the combined effect of these processes was always dominated by the initial moisture content.Moderate initial soil moisture content(0.20-0.24 g/g)and the addition of a high root density in dicranopteris linearis(0.75-1.00 g/100 cm3)were the optimal combinations that reduced the disintegration rate.In conclusion,maintaining a suitable natural moisture content in collapsing-wall soils and taking measures that use plants to consolidate soil can effectively prevent and control the occurrence of Benggang erosion.The results of this study provided further insight into the factors that influence soil disintegration and offered a scientific basis for soil erosion management in the southern China.

Utilizing a new soil effective temperature scheme and archived satellite microwave brightness temperature data to estimate surface soil moisture in the Nagqu region, Tibetan Plateau of China

Since the early 2000s, many satellite passive microwave brightness temperature （BT） archives, such as the Advanced Microwave Scanning Radiometer for the Earth Observing System （AMSR-E） BTs, have become the useful resources for assessing the changes in the surface and deep soil moistures over both arid and semi-arid regions. In this study, we used a new soil effective temperature （T scheme and the archived AMSR-E BTs to estimate surface soil moisture （SM） over the Nagqu region in the central Tibetan Plateau, China. The surface and deep soil temperatures required for the calculation of regional-scale T were obtained from outputs of the Community Land Model version 4.5 （CLM4.5）. In situ SM measurements at the CEOP-CAMP/Tibet （Coordinated Enhanced Observing Period Asia-Australia Monsoon Project on the Tibetan Plateau） experimental sites were used to validate the AMSR-E-based SM estimations at regional and single-site scales. Furthermore, the spatial distribution of monthly mean surface SM over the Nagqu region was obtained from 16 daytime AMSR-E BT observations in July 2004 over the Nagqu region. Results revealed that the AMSR-E-based surface SM estimations agreed well with the in situ-based surface SM measurements, with the root mean square error （RMSE） ranging from 0.042 to 0.066 m3/m3 and the coefficient of determination （R2） ranging from 0.71 to 0.92 during the nighttime and daytime. The regional surface soil water state map showed a clear spatial pattern related to the terrain. It indicated that the lower surface SM values occurred in the mountainous areas of the northern, mid-western and southeastern parts of Nagqu region, while the higher surface SM values appeared in the low elevation areas such as the Tongtian River Basin, Namco Lake and bog meadows in the central part of Nagqu region. Our analysis also showed that the new T^scheme does not require special fitting parameters or additional assumptions, which simplifies the data requirements for regional-scale applications. This scheme combined with the archived satellite passive microwave BT observations can be used to estimate the historical surface SM for hydrological process studies over the Tibetan Plateau regions.

Temperature effect on the reference frequency of FDR soil moisture sensor

The FDR automatic soil moisture sensor must determine reference frequency in the air and water. Experimental studies show that the water reference frequency is influenced by water temperature. The variation of the reference frequency of the sensor is measured with the change of the water temperature,then analysis the influence of the volume water content measurement of the sensor,analysis found that the error is not more than 3% for the measurement of the volumetric water content of the temperature.

Elevated Carbon Dioxide and Soil Moisture on Early Growth Response of Soybean

Interactions between elevated [CO2] and soil water availability have the potential impact on crops and future food security of the world. The study was conducted to investigate vegetative growth response of soybeans under two [CO2] (380 and 800 μmol mol-1) with three soil moisture levels in controlled environment. Slow growth rate and altered crop phenology of soybeans were observed under elevated [CO2] at early stage (V-3/V-4), but showed positive physiologically response at later stage (R3) indicating adoptive mechanism of plants to high [CO2]. Elevated [CO2] decreases the number of leaves by 23% and 14% and reduces in leaf areas by 11.7% and 9.7% compared with ambient [CO2] at 29 and 44 days after planting (DAP), respectively. Adaptive mechanism of plants to high [CO2] produced 39% and 83.7% greater leaf number and leaf areas, respectively at later stage (R3) of the crop growth (59 DAP). There was a reduction in a specific leaf area (SLA) at 29 DAP (22.2%) but an increase at 44 DAP (1.4%) and 58 DAP (8.5%) under elevated [CO2]. Dry matter production of plants was increased significantly for elevated [CO2]. Increase in leaf C (<1%) and reduction in N concentration (6.0% - 9.5%) increased the C:N ratio of soybean leaves (4.4% - 12.98%) under elevated [CO2]. Elevated [CO2] with normal soil moisture condition produced a maximum number of pods (54.8% - 122.4%) and an increase in dry weight of pods (29.8% - 56.6%). Plants under elevated [CO2] produced significantly greater numbers of root nodules per plant by 114% compared with plants under ambient [CO2] at 44 DAP. These results show a direct and interactive effect of elevated [CO2] and soil moisture on plant growth that will affect not only the global food security but also nutritional security.

Dried earth layers of artificial forestland in the Loess Plateau of Shaanxi Province

By determining the earth moisture content of artificial forestland between 0 and 6 m deep in the Loess Plateau of Shaanxi province, the vertical change of moisture content, distribution and formation causes of a dried earth layer are researched. The results show that the average moisture content is 9.3%-9.5% between 2 and 4 m under artificial forest of over 10 year＇s growth in Guanzhong Plain, and chronic weak dried earth layers are developed which show that the dried earth layers are distributed extensively on the Loess Plateau. The southern boundary of the dried earth layer has reached the northern foot of the Qinling Mountains. When precipitation reaches 600 mm, there are weak dried earth layers between 2 and 4 m under artificial forest of more than 10 years old. When the precipitation is between 400 and 500 mm, there are moderate dried earth layers. When precipitation is above 800 mm, there are no dried earth layers. There are no dried earth layers under meadow land, corn land and less than 5 years old of artificial forestland in central and southern parts of the Loess Plateau. The development of dried earth layers under cypress forest is weaker than broad-leaved forest. Under the same climatic conditions, the development of dried earth layers under the loess tableland is nearly at the same level as the 2nd and 3rd river terrace. Dried earth layers developed in membrane water zone, and the buried depth is small and motion velocity is slow in the Loess Plateau, which is the direct water factor of the formation of the dried earth layer, while differences of tree age and tree species are the plant factors that consumed much moisture. From the depth of the gravity water and the membrane water in Guanzhong Plain, it is clear that the formation cause of dried earth layers is mainly due to natural factors. The dried layers generally develop in middle-aged artificial forestland that consumed too much moisture, which is the general character of earth moisture in subhumid and semiarid zones. The appearance of dried layers doesn＇t show that the forest doesn＇t develop in this area; this is depended on their development intensity. Artificial forest of Chinese poplar, locust tree and Chinese scholartree consuming less water can be planted in the areas where dried earth layer developed weakly, but can not be planted in the areas where dried earth layer developed intensely.

Carbon fixation and influencing factors of biological soil crusts in a revegetated area of the Tengger Desert,northern China

Biological soil crusts （BSCs） are an important type of land cover in arid desert landscapes and play an important role in the carbon source-sink exchange within a desert system. In this study, two typical BSCs, moss crusts and algae crusts, were selected from a revegetated sandy area of the Tengger Desert in northern China, and the experiment was carried out over a 3-year period from January 2010 to November 2012. We obtained the effec- tive active wetting time to maintain the physiological activity of BSCs basing on continuous field measurements and previous laboratory studies on BSCs photosynthesis and respiration rates. And then we developed a BSCs carbon fixation model that is driven by soil moisture. The results indicated that moss crusts and algae crusts had significant effects on soil moisture and temperature dynamics by decreasing rainfall infiltration. The mean carbon fixation rates of moss and algae crusts were 0.21 and 0.13 g C/（m2.d）, respectively. The annual carbon fixations of moss crusts and algae crusts were 64.9 and 38.6 g C/（m2.a）, respectively, and the carbon fixation of non-rainfall water reached 11.6 g C/（m2.a） （30.2% of the total） and 8.8 g C/（m2.a） （43.6% of the total）, respectively. Finally, the model was tested and verified with continuous field observations. The data of the modeled and measured CO2 fluxes matched notably well. In desert regions, the carbon fixation is higher with high-frequency rainfall even the total amount of seasonal rainfall was the same.

Effects of irrigation on precipitation in the arid regions of Xinjiang,China

Soil moisture is an important parameter for the interaction between soil and atmosphere. It is the sec- ond important factor that influences climate change, next to sea surface temperature （SST）. Most previous studies focused on the monsoon regions in East China, and only a few laid emphases on arid environments. In Xinjiang, which is located in Northwest China, the climate is typically arid and semi-arid. During the past 20 years, the pre- cipitation in Xinjiang has shown a significant increasing trend, and it is closely related to oasis irrigation. This paper aims at discussing whether abnormal soil moisture in spring can be the signal to forecast summer precipitation. The effects of abnormal soil moisture due to farm irrigation in spring in arid environments on regional climate are inves- tigated by using a regional climate model （RegCM3）. The results indicate that positive soil moisture anomaly in irrigated cropland surface in May led to an increase in precipitation in spring as well as across the whole summer. The impact could last for about four months. The effects of soil moisture on the surface air temperature showed a time-lagging trend. The summer air temperature declined by a maximum amplitude of 0.8℃. The increased soil moisture could enhance evaporation and ascending motion in the low troposphere, which brought in more precipi- tation. The soil moisture affected regional weather and climate mainly by altering the surface sensible and latent heat fluxes.

Effects of soil substrate heterogeneity and moisture on interspecific competition between Alternanthera philoxeroides and four native species

Aims Clonal plant species have the potential for high relative performance in heterogeneous environments,and this might increase the com-petitive ability and invasiveness of introduced clonal plant species.It was hypothesized that clonal species whose performance responds more to heterogeneity of a resource have higher competitive ability in habitats where this resource is more heterogeneous and that this relationship is stronger when other resources are less limiting.Methods To test these hypotheses,the perennial clonal herb Alternanthera philoxeroides,which is invasive in China,was grown alone or with each of four clonal perennial,co-occurring herbs native to China,i.e.Alternanthera sessilis,Cynodon dactylon,Hemarthria altissima and Wedelia chinensis.Plants were given homogeneous or het-erogeneous soil substrate crossed with low and high levels of soil moisture.Important Findings Effects of heterogeneity on the accumulation of mass and ramets and on competitive effect and response of A.philoxeroides differed between native species and interacted with effects of soil moisture.A.philoxeroides reduced the final total mass or ramet number of the native species except A.sessilis,and the negative competitive effects on H.altissima and C.dactylon were more pronounced in heterogeneous than in homogeneous soil.Competitive response of A.philoxeroides was more negative to A.sessilis than to the other native species.Across native species,the competitive response of A.philoxeroides was more negative in heterogeneous than in homo-geneous soils at low moisture level,but the reverse was true at high moisture level.Results do not consistently support either hypoth-esis,but do suggest that competitive ability can be partly explained by individual species traits such as size,and that some competi-tive effects and responses are emergent properties of interspecific interactions.

INFLUENCE OF SOIL MOISTURE AND VEGETATION ON CLIMATE CHANGES INDUCED BY THERMAL FORCING

A land-process scheme has been incorporated in a vertical one-dimensional time-dependent atmospheric model and numerical experiments have been performed with the coupled model to examine influences of soil wetness and vege- tation on climate changes associated to thermal forcing.It is showed that response of land-surface temperature to the thermal forcing becomes small with increase of soil water content and vegetation cover.Furthermore,the response is more obvious in arid climate region than in humid one.The result also shows that there exist two patterns of corre- sponding relation between variations in air temperature and humidity on the land surface in response to hydrologic and thermal focing.

保墒措施对山南地区人工林土壤水分时空特征的影响——以雪松人工林为例

为探究山南地区人工林在不同保墒措施下土壤含水率的变化,以雪松人工林为研究对象,共设计覆盖、滴灌处理4个,各处理分别为稻草覆盖、地膜覆盖、滴灌和地膜覆盖加滴灌,并设对照处理1个,对雪松人工林0~20 cm和20~40 cm土层的土壤含水率进行测定。结果表明:1年中各种保墒措施下雪松人工林的土壤含水率均呈“几”字型分布,且不同保墒措施在不同季节的效果不同。不同处理20~40 cm土层土壤含水率的大小为地膜覆盖加滴灌的>地膜覆盖的>稻草覆盖的>滴灌的>对照的。地膜覆盖加滴灌处理在全年的保墒效果均最佳,0~20 cm土层的土壤含水率可达29.32%,20~40 cm土层的土壤含水率可达29.7%,均明显高于对照处理的。不同土层的土壤含水率随季节性变化大,春、冬季浅土层与深土层的土壤含水率接近,夏季0~20 cm浅土层的土壤含水率低于20~40 cm深土层的,秋季0~20 cm浅土层的土壤含水率略高于20~40 cm深土层的。地膜覆盖加滴灌是山南地区雪松人工林土壤水分保持的最佳保墒措施。

红壤丘陵区马尾松林和湿地松林物候特征的时空变异及影响因素

【目的】探究马尾松林和湿地松林物候期的时空变异及影响因素,为红壤丘陵区森林碳汇时空格局精准评估与预测提供理论支撑。【方法】基于2017—2021年的数码相机时间序列数据,提取29块样地(马尾松林18块,湿地松林11块)的有效叶面积指数(LAIe)时空动态。采用有效叶面积指数的广义双重逻辑斯蒂模型确定物候期指标(生长季开始时间,SOS;生长季结束时间,EOS;生长季长度,LOS)。利用变异系数表征物候期时空变异幅度。通过皮尔逊相关分析和线性混合模型,解析气候(干旱指数、空气温度、降水量、饱和水汽压差、光合有效辐射)、土壤(土壤温湿度、土层厚度、石砾含量)和生物因子(林分密度、林下植被丰富度)对物候期的驱动作用。【结果】1)马尾松林和湿地松林物候特征均为单峰曲线(但马尾松林无明显峰值)。与马尾松林相比,湿地松林的SOS较晚,但LAIe的季节变化幅度更大且值更高。2)马尾松林的物候期在时空尺度上不如湿地松林稳定。马尾松林的SOS、EOS、LOS在空间上的变异系数和SOS在时间上的变异系数均大于湿地松林。3)在年际尺度上,马尾松林的SOS和EOS分别与早春和旱季0~120 cm土层的土壤含水量呈负相关和正相关;湿地松林的EOS与旱季0~60 cm土层的土壤含水量呈正相关。4)在空间尺度上,马尾松林物候期受林分密度、草本层物种丰富度和0~60 cm土壤石砾含量影响。【结论】马尾松林和湿地松林的物候特征在曲线峰值、SOS、LAIe变化幅度和数值大小等方面存在明显差异。湿地松林的物候期在时空尺度上更稳定。种内、种间竞争强度和土壤资源异质性共同驱动了红壤丘陵区马尾松林物候的时空变异格局。

放牧显著降低中国草地生态系统土壤含水量

本研究利用Meta分析方法,对中国草地生态系统已开展的258个关于放牧对于中国草地生态系统土壤含水量的试验结果进行综合分析。结果表明:放牧对中国草地0-30 cm土壤含水量影响的平均效应值为-0.111,降低幅度约10.51%,达到0.01显著性检验水平。放牧对表层土壤0-10 cm土层影响影响最高,随着土层加深,平均效应值均呈现降低趋势,且放牧分别对草甸草原、典型草原和荒漠草原土壤含水量影响作用最强。温度、降水量、海拔和土壤容重4种环境因子贡献率最大。放牧分别可解释93.90%、87.66%、90.64%的对0-10、10-20和20-30 cm土层的效应值变异。全球增温可能会显著降低放牧草地土壤含水量,为了提升草地土壤含水量应采用轻度放牧制度。本研究为明晰放牧草地生态系统水分变化提供了理论基础。

土壤水分动态变化对重楼生长发育的影响

通过测量重楼样地样本植株生长数据,采用土壤动态监测仪测量重楼样地10 cm、20 cm、30 cm深度土壤水分动态数据,分析土壤水分、土壤温度动态变化对重楼生长发育的影响,得出:A样地重楼样本植株生长发育略优于B样地重楼样本植株;A样地土壤10 cm、20 cm深度水分随深度增加均匀增加,30 cm深度土壤水分较充裕,更适宜重楼生长,B样地土壤水分随深度增加较不明显,且20 cm深度土壤水分高于30 cm深度土壤水分,对重楼植株根系吸水及获取养分可能产生一定影响;A样地土壤10 cm、20 cm、30 cm深度土温递减相对均匀,这为重楼根部生长发育、吸水、呼吸作用等创造相对稳定的温度环境;B样地不同深度土温递减落差较大,这对重楼根系发育、吸水、呼吸作用等产生一定影响。

地膜覆盖保墒灌溉的土壤水、热以及作物效应研究

通过小区试验研究了不同的地膜覆盖保墒灌溉措施对土壤水分动态变化、土壤微生物、土壤温度、玉米生长状况、生理生态指标以及产量等的影响。结果表明，地膜覆盖后0-50cm土壤含水量覆膜的明显高于未覆膜处理，在玉米整个生育期内，未灌溉处理的地膜0-20cm的含水量较对照平均提高6．1％，20—50cm较对照平均提高3．38％，50—100cm较对照平均提高1．57％。覆膜后耕层土壤细菌、赦线菌、真菌平均分别是对照的4．1倍、2．08倍和2．41倍。覆膜后叶片光合和蒸腾速率均较对照有所增加，相同灌溉量条件下，地膜处理的玉米产量较对照平均增产14．24％、9．4％和11．15％，对于覆膜或不覆膜处理，其产量均随着灌溉水量的增加而增加。

旱作麦田秸秆覆盖的生态综合效应研究

研究了秸秆覆盖春小麦田土壤温度、水分、养分和微生物数量的变化趋势,结果表明:秸秆覆盖对表层(0～10cm)土温变化有明显的调节作用,在低温时有增温作用,高温时有降温作用;覆盖有一定的抑蒸保墒作用,可提高作物水分利用效率9.61%～20.93%,其保水作用主要发生在上层土体0～40cm,并随覆盖量的增加而增强;覆盖后0～40cm土体中土壤全N、全P在一个生长季节后变化不明显,但土壤有机质、速效钾含量有所增加;覆盖处理后小麦生育时期土壤细菌、放线菌和真菌的数量均高于对照,形成了不同时期新的土壤微生物区系,改变了土壤生物学活性。适量秸秆覆盖有利于寻求适宜作物生长发育的水热组合,具有良好的农田综合效应,可提高产量12.47%～29.63%。

东北黑土区农林复合土壤效应

以黑土区小黑杨—大豆、长白落叶松—大豆和红皮云杉—大豆农林复合系统及大豆纯农地土壤为对象,通过对土壤水分物理性质,有机质、N、P、K等指标的测定与分析,对比研究了不同农林复合模式对黑土区土壤物理性质与土壤养分环境的影响。结果表明:农林复合生态系统能够显著改善黑土区土壤结构,提高土壤养分质量分数,增加表层土壤的有机质和C/N。其中以小黑杨—大豆模式效果最好,土壤含水量可达41.20%,总孔隙度和土壤密度分别为60.60%、1.02g/cm3,CP/NCP高于大豆纯农地,且该模式在提高土壤有机质、水解氮及有效磷质量分数方面最为突出;长白落叶松—大豆和红皮云杉—大豆模式的速效钾质量分数较高。

太湖地区主要水稻土水力特征及其影响因素

通过田间和室内试验研究了太湖地区3种主要水稻土(白土、黄泥土和乌栅土)的水分特征以及影响因素,得出了各种土壤每一土层的容重、质地、有机质、土壤团聚度、土壤结构系数和土壤水分特征曲线,比较了3种主要水稻土类型的土壤基本物理性质和水分特征状况,并根据水分特征曲线得出了这3种土壤的田间持水量、有效水含量和萎蔫系数。结果表明:土壤田间持水量和有效水含量均与容重呈极显著的线性负相关,有效水与土壤粘粒含量也呈显著的线性负相关;而土壤的田间持水量和有效水含量与土壤有机质、结构系数、团聚度呈极显著的线性正相关,萎蔫系数与质地也呈显著的线性正相关。

结实期土壤水分和氮素营养对水稻产量与品质的交互影响

杂交籼稻汕优63和粳稻武育粳3号种植于土培池,于始穗期进行0N(0g/m2)、NN(中氮,4.5g/m2)和HN(高氮,9.0g/m2)3种施氮量处理,于抽穗后7d至成熟期设置了WW(保持浅水层)、MD(轻度落干,土壤水势保持-25kPa)和SD(重度落干,土壤水势保持-50 kPa)3种土壤水分处理,研究了结实期土壤水分和氮素营养对水稻产量与品质的交互影响。在各施氮水平下,产量、糙米率、精米率和整精米率均以MD处理最高,垩白粒率和垩白度均以MD处理最低。在0N下,SD处理降低了产量、碾磨品质、外观品质和食味品质;在MN或HN下,SD处理的产量、碾磨品质、外观品质和食味品质与WW的差异不显著或显著优于WW。说明土壤水分和氮素营养对水稻产量和品质的影响存在着明显的互作效应,结实期土壤水势为-25kPa、粒肥的施氮量为45kg/hm2,稻米的品质较优、产量最高。