Root length density distribution and associated soil water dynamics for tomato plants under furrow irrigation in a solar greenhouse

Furrow irrigation is a traditional widely-used irrigation method in the world. Understanding the dynamics of soil water distribution is essential to developing effective furrow irrigation strategies, especially in water-limited regions. The objectives of this study are to analyze root length density distribution and to explore soil water dynamics by simulating soil water content using a HYDRUS-2D model with consideration of root water uptake for furrow irrigated tomato plants in a solar greenhouse in Northwest China. Soil water contents were also in-situ observed by the ECH_2O sensors from 4 June to 19 June and from 21 June to 4 July, 2012. Results showed that the root length density of tomato plants was concentrated in the 0–50 cm soil layers, and radiated 0–18 cm toward the furrow and 0–30 cm along the bed axis. Soil water content values simulated by the HYDRUS-2D model agreed well with those observed by the ECH_2O sensors, with regression coefficient of 0.988, coefficient of determination of 0.89, and index of agreement of 0.97. The HYDRUS-2D model with the calibrated parameters was then applied to explore the optimal irrigation scheduling. Infrequent irrigation with a large amount of water for each irrigation event could result in 10%–18% of the irrigation water losses. Thus we recommend high irrigation frequency with a low amount of water for each irrigation event in greenhouses for arid region. The maximum high irrigation amount and the suitable irrigation interval required to avoid plant water stress and drainage water were 34 mm and 6 days, respectively, for given daily average transpiration rate of 4.0 mm/d. To sum up, the HYDRUS-2D model with consideration of root water uptake can be used to improve irrigation scheduling for furrow irrigated tomato plants in greenhouses in arid regions.

Soil Water Distribution and Irrigation Uniformity Under Alternative Furrow Irrigation

Field experiments were conducted to investigate the spatial-temporal distribution and the uniformity of soil water under alternative furrow irrigation in spring maize field in Cansu Province. Results showed that during the crop growing season, alternative drying and wetting furrows could incur crops to endure a water stress. thus the adsorptive ability of root system could be enhanced. As there was no zero flux plane between irrigated furrows and non-irrigated furrows under alternative furrow irrigation, lateral infiltration of water was obviously increased, thus decreasing the deep percolation. Compared with the conventional irrigation, although the water consumption in alternative furrow irrigation was reduced, the uniformity of soil water was not obviously affected.

The Effects of Water and Fertilizer Coupling on Plant and Soil Nitrogen Characteristics and Fruit Growth of Rabbiteye Blueberry Plants in a Semi-Arid Region in China

To evaluate the effects of nitrogen(N)and irrigation coupling on the soil N distribution,plant N utilization,and fruit yield of rabbiteye blueberries(Vaccinium virgatum),a field experiment was designed using two factors(water and fertilizer application)with four levels of irrigation and three levels of fertilization,and a control.Under the different water and fertilizer combinations,N primarily accumulated in the leaves.Irrigation and N application within appropriate ranges(pure N≤29 g/plant and irrigation volume≤2.5 L/plant)significantly improved the blueberry fruit yield.Increases in water and N within these ranges promoted the effective accumulation of N in various organs and the absorption and utilization of N in the plants,which ultimately promoted blueberry yield.With increased N application rate,the nitrate N content of the 0–20 cm and 20–50 cm soil layers increased.With increased irrigation volume,the nitrate N content of the 0–20 cm soil layer decreased,while the nitrate content in the 20–50 cm soil layer increased.Low N and moderate water treatments resulted in high fruit yields and reduced nitrate N retention in the soil.Under these conditions,the economic input-output ratio was high and the soil N accumulation was low,and thus the economic and ecological benefits were maximized.

The characterization of soil profile distribution for nitrate leached in the paddy soil

Experiment was conducted for five successiveyears under large undisturbed monolith lysime-ters(2m×2m in square,l m in depth).Thesoil was silty clay loam texture and had a con-tent of total N 1.55 g/kg.The soil was flood-ed with penetration rate controlled at approxi-mate 3 mm per day in duration of double-riceseason and laid fallow and natural in winterand spring.Results showed that nitrate was the mainform of nitrogen in percolates.The change of

Distribution of the Si-deficiency rice soil in Hubei Province

There are about 1 million ha of Si-deficiency paddy soils in Hubei Province. Practically, it is essential to study the Si nutrient status in those Si-deficiency rice soil and its regional distribution before the application of Si-fertilizer. According to the analysis of 50 rice soil samples which collected from 20 counties/cities in Hubei Province, the available Si content in rice soils derived from different parent materials varied greatly. The Si content from high to low was in sequence of limestone, redpurplish sandy shale with carbonate, alluvium and lacustrine deposits, quaternary period red clay, granitic gneiss, and sandy shale. In addition, the Si content in rice soil was remarkably related with its pH. It seems that the pH 6.5 might be a demarcation line that divided the supplying Si ability of rice soils into the low and high categories (Table 1). Integrating the results with a critical soil Si-deficiency as 100 mg/kg, the evaluation index of soil Si supplying capability of a rice soil

Experimental Investigation of Soil Evaporation and Evapotranspiration of Winter Wheat Under Sprinkler Irrigation

Sprinkler irrigation is one of the typical irrigation technologies used for the winter wheat-summer maize double cropping system in the North China Plain. To evaluate the evapotranspiration （ET） of winter wheat under sprinkler irrigation in Beijing area, field experiments were conducted in growing seasons through 2005-2008, in the experimental station located in Tongzhou County, Beijing, China, with different irrigation depths. Results indicated that a relatively large variation of soil water content occurred within 0-40 cm soil layer. The seasonal ET of winter wheat generally increased with increasing irrigation amount, while the seasonal usage of soil water had a negative relationship with irrigation amount. Soil evaporation （Es） was about 25% of winter wheat ET during the period from reviving to maturity. Es increased while Es/ET decreased with increasing irrigation amount. Sprinkler irrigation scheduling with relatively large irrigation quota and low irrigation frequency can reduce Es and promote the irrigation water use efficiency.

Effects of soil conservation practices on soil erosion and the size selectivity of eroded sediment on cultivated slopes

Soil conservation practices can greatly affect the soil erosion process,but limited information is available about its influence on the particle size distribution(PSD)of eroded sediment,especially under natural rainfall.In this study,the runoff,sediment yields,and effective/ultimate PSD were measured under two conventional tillage practices,downhill ridge tillage(DT)and plat tillage(PT)and three soil conservation practices,contour ridge tillage(CT),mulching with downhill ridge tillage(MDT),and mulching with contour ridge tillage(MCT)during 21 natural rainfall events in the lower Jinsha River.The results showed that(1)soil conservation practices had a significant effect on soil erosion.The conventional tillage of DT caused highest runoff depth(0.58 to 29.13 mm)and sediment yield(0.01 to 3.19 t hm^(-2)).Compared with DT,the annual runoff depths and sediment yields of CT,MDT and MCT decreased by 12.24%-49.75%and 40.79%-88.30%,respectively.(2)Soil conservation practices can reduce the decomposition of aggregates in sediments.The ratios of effective and ultimate particle size(E/U)of siltand sand-sized particles of DT and PT plots were close to 1,indicating that they were transported as primary particles,however,values lower/greater than 1 subject to CT,MDT and MCT plots indicated they were transported as aggregates.The ratios of E/U of claysized particles were all less than 1 independently of tillage practices.(3)The sediments of soil conservation practices were more selective than those of conventional tillage practices.For CT,MDT and MCT plots,the average enrichment ratios(ERs)of clay,silt and sand were 1.99,1.93 and 0.42,respectively,with enrichment of clay and silt and depletion of sand in sediments.However,the compositions of the eroded sediments of DT and PT plots were similar to that of the original soil.These findings support the use of both effective and ultimate particle size distributions for studying the size selectivity of eroded sediment,and provide a scientific basis for revealing the erosion mechanism in the purple soil area of China.

Effects of digestate application depth on soil nitrogen volatilization and vertical distribution

This study investigated the effect of the digestate application depth on soil nitrogen volatilization and vertical distribution in black loam soil and sandy loam column.The contents of soil moisture,TKN(total Kjeldahl nitrogen),ammonium nitrogen,nitrate nitrogen,and the extent of ammonia volatilization were tested by applying digestate at depths of 0 cm,2 cm,6 cm,10 cm,15 cm and 20 cm,respectively.The experimental results showed that ammonia volatilization mainly occurred in the first 10 days and reduced significantly when the application depth was deeper than 10 cm.At the same application depth,compared with the black loam,the nitrogen loss in sandy loam through ammonia volatilization was less,and the penetration depth of nitrate nitrogen and ammonium nitrogen were all deeper.In the same soil,nitrate nitrogen penetrated deeper than ammonium nitrogen at all application depths.

Aggregate-associated changes in nutrient properties,microbial community and functions in a greenhouse vegetable field based on an eight-year fertilization experiment of China

Soil aggregation,microbial community,and functions(i.e.,extracellular enzyme activities;EEAs)are critical factors affecting soil C dynamics and nutrient cycling.We assessed soil aggregate distribution,stability,nutrients,and microbial characteristics within>2,0.25-2,0.053-0.25,and<0.053 mm aggregates,based on an eight-year field experiment in a greenhouse vegetable field in China.The field experiment includes four treatments:100%N fertilizer(CF),50%substitution of N frtilizer with manure(M),straw(S),and manure plus straw(MS).The amounts of nutrient(N,P20,and K20)input were equal in each treatment.Results showed higher values of mean weight diameter in organic amended soils(M,MS,and S,2.43-2.97)vs.CF-amended soils(1.99).Relative to CF treatment,organic amendments had positive effects on nutrient(i.e.,available N,P,and soil organic C(SOC))conditions,microbial(e.g,bacterial and fungal)growth,and EEAs in the>0.053 mm aggregates,but not in the<0.053 mm aggregates.The 0.25-0.053 mm aggregates exhibited better nutrient conditions and hydrolytic activity,while the<0.053 mm aggregates had poor nutrient conditions and higher oxidative activity among aggregates,per SOC,available N,available P,and a series of enzyme activities.These results indicated that the 0.25-0.053 mm(<0.053 mm)aggregates provide suitable microhabitats for hydrolytic(oxidative)activity.Interestingly,we found that hydrolytic and oxidative activities were mainly impacted by fertilization(58.5%,P<0.01)and aggregate fractions(50.5%,P<0.01),respectively.The hydrolytic and oxidative activities were significantly(P<0.01)associated with nutrients(SOC and available N)and pH,electrical conductivity,respectively.Furthermore,SOC,available N,and available P closely(P<0.05)afected microbial communities within>0.25,0.25-0.053,and<0.053 mm aggregates,respectively.These findings provide several insights into microbial characteristics within aggregates under dfferent frilization modes in the greenhouse vegetable production system in China.

Pedodiversity: a controversial concept

The concept of pedodiversity and its measurement methodology proposed and developed by Ibá?ez research term is introduced. An attempt to apply pedodiversity to analyze spatial soil variation and distribution patterns on the global scale is briefly demonstrated. Furthermore, constructive comments and criticisms on pedodiversity and its measurement from the noted pedologists and ecologists are outlined. Finally, potential applications of pedodiversity in soil science and other relevant disciplines are discussed.

Effects of irrigation water salinity on soil salt content distribution,soil physical properties and water use efficiency of maize for seed production in arid Northwest China

In order to explore the use of groundwater resources,field experiments were conducted for three consecutive years during 2012-2014 in the Shiyang River basin of Northwest China.Irrigation was conducted using four different water salinity levels that were arranged in a split plot design.These four water salinity levels were s0,s3,s6 and s9(0.71,3,6 and 9 g/L,respectively).The soil salt content,soil bulk density,soil porosity,saturated hydraulic conductivity,plant height,leaf area index and yield of maize for seed production were measured for studying the effects of saline water irrigation on soil salt content distribution,soil physical properties and water use efficiency.It was observed that higher salinity level of irrigation water and long duration of saline water irrigation resulted in more salt accumulation.Compared to initial values,the soil salt accumulation in 0-100 cm soil layer after three years of experiments for s0,s3,s6 and s9 was 0.189 mg/cm3,0.654 mg/cm3,0.717 mg/cm3 and 1.135 mg/cm3,respectively.Both greater salt levels in the irrigation water and frequent saline water irrigation led to greater soil bulk density,but poorer soil porosity and less saturated hydraulic conductivity.The saturated hydraulic conductivity decreased with increase in soil bulk density,but increased with improvement in soil porosity.It was noted that the maize height,leaf area index and maize yield gradually decreased with increase in water salinity.The maize yield decreased over 25%and the water use efficiency also gradually declined when irrigated with water containing 6 g/L and 9 g/L salinity levels.However,maize yield following saline water irrigation with 3 g/L decreased less than 20%and the decline in water use efficiency was not significant during the three-year experiment period.The results demonstrate that irrigation with saline water at the level of 6 g/L and 9 g/L in the study area is not suitable,while saline water irrigation with 3 g/L would be acceptable for a short duration together with salt leaching through spring irrigation before sowing.

Field study and regression modeling on soil water distribution with mulching and surface or subsurface drip irrigation systems

The soil water status was investigated under soil surface mulching techniques and two drip line depths from the soil surface(DL).These techniques were black plastic film(BPF),palm tree waste(PTW),and no mulching(NM)as the control treatment.The DL were 15 cm and 25 cm,with surface drip irrigation used as the control.The results indicated that both the BPF and PTW mulching enhanced the soil water retention capacity and there was about 6%water saving in subsurface drip irrigation,compared with NM.Furthermore,the water savings at a DL of 25 cm were lower(15-20 mm)than those at a DL of 15 cm(19-24 mm),whereas surface drip irrigation consumed more water.The distribution of soil water content(θv)for BPF and PTW were more useful than for NM.Hence,mulching the soil with PTW is recommended due to the lower costs and using a DL of 15 cm.Theθv values were derived using multiple linear regression(MLR)and multiple nonlinear regression(MNLR)models.Multiple regression analysis revealed the superiority of the MLR over the MNLR model,which in the training and testing processes had coefficients of correlation of 0.86 and 0.88,root mean square errors of 0.37 and 0.35,and indices of agreement of 0.99 and 0.93,respectively,over the MNLR model.Moreover,DL and spacing from the drip line had a significant effect on the estimation of θv.

Measuring and modeling two-dimensional irrigation infiltration under film-mulched furrows

Furrow irrigation with film-mulched agricultural beds is being promoted in the arid region of northwest China because it improves water utilization. Two-dimensional infiltration patterns under film-mulched furrows can provide guidelines and criteria for irrigation design and operation. Our objective was to investigate soil water dynamics during ponding irrigation infiltration of mulched furrows in a cross-sectional ridge-furrow configuration, using laboratory experiments and mathematical simulations. Six experimental treatments, with two soil types （silt loam and sandy loam）, were investigated to monitor the wetting patterns and soil water distribution in a cuboid soil chamber. Irrigation of mulched furrows clearly increased water lateral infiltration on ridge shoulders and ridges, due to enhancement of capillary driving force. Increases to both initial soil water content （SWC） and irrigation water level resulted in increased wetted soil volume. Empirical regression equations accurately estimated the wetted lateral distance （Rl） and downward distance （Rd） with elapsed time in a variably wetted soil medium. Optimization of model parameters followed by the Inverse approach resulted in satisfactory agreement between observed and predicted cumulative infiltration and SWC. On the basis of model calibration, HYDRUS-2D model can accurately simulate two-dimensional soil water dynamics under irrigation of mulched furrows. There were significant differences in wetting patterns between unmulched and mulched furrow irrigation using HYDRUS-2D simulation. The Rd under the mulched furrows was 32.14% less than the unmulched furrows. Therefore, film-mulched furrows are recommended in a furrow irrigation system.

Tannic acid and saponin for removing arsenic from brownfield soils: Mobilization, distribution and speciation

Plant biosurfactants were used for the first time to remove As and co-existing metals from brownfield soils. Tannic acid （TA）, a polyphenol, and saponin （SAP）, a glycoside were tested. The soil washing experiments were performed in batch conditions at constant biosurfactant concentration （3%）. Both biosurfactants differed in natural pH, surface tension, critical micelle concentration and content of functional groups. After a single washing, TA （pH 3.44） more efficiently mobilized As than SAP （pH 5.44）. When both biosurfactants were used at the same pH （SAP adjusted to 3.44）, arsenic mobilization was improved by triple washing. The process efficiency for TA and SAP was similar, and depending on the soil sample, ranged between 50%-64%. Arsenic mobilization by TA and SAP resulted mainly from decomposition of Fe arsenates, followed by Fe3＋ complexation with biosurfactants. Arsenic was efficiently released from reducible and partially from residual fractions. In all soils, As（V） was almost completely removed, whereas content of As（III） was decreased by 37%-73%. SAP and TA might be used potentially to remove As from contaminated soils.

Unraveling the size distributions of surface properties for purple soil and yellow soil

Soils contain diverse colloidal particles whose properties are pertinent to ecological and human health, whereas few investigations systematically analyze the surface properties of these particles. The objective of this study was to elucidate the surface properties of particles within targeted size ranges（i.e. 〉 10, 1-10, 0.5-1, 0.2-0.5 and 〈 0.2 μm） for a purple soil（Entisol） and a yellow soil（Ultisol） using the combined determination method. The mineralogy of corresponding particle-size fractions was determined by X-ray diffraction.We found that up to 80% of the specific surface area and 85% of the surface charge of the entire soil came from colloidal-sized particles（〈 1 μm）, and almost half of the specific surface area and surface charge came from the smallest particles（〈 0.2 μm）. Vermiculite,illite, montmorillonite and mica dominated in the colloidal-sized particles, of which the smallest particles had the highest proportion of vermiculite and montmorillonite. For a given size fraction, the purple soil had a larger specific surface area, stronger electrostatic field, and higher surface charge than the yellow soil due to differences in mineralogy.Likewise, the differences in surface properties among the various particle-size fractions can also be ascribed to mineralogy. Our results indicated that soil surface properties were essentially determined by the colloidal-sized particles, and the 〈 0.2 μm nanoparticles made the largest contribution to soil properties. The composition of clay minerals within the diverse particle-size fractions could fully explain the size distributions of surface properties.

Seismic responses of subway station with different distributions of soft soil in Tianjin

In connection with the practical project of Kunming Road station of Tianjin subway Line 3, the paper established a two-dimensional finite element model with visco-elastic boundary by using ANSYS and analyzed seismic responses of subway station with different distribution of soft soil. The nonlinear dynamic properties of soft soils are modeled by the KINH. And obtain the response rules about displacement and internal force on subway station in the general field soil and five different distributions of soft soil. Provide reference for improving the seismic performance of subway stations in Tianjin soft soil.

Sorption and phase distribution of ethanol and butanol blended gasoline vapours in the vadose zone after release

The sorption and phase distribution of 20% ethanol and butanol blended gasoline （E20 and B20） vapours have been examined in soils with varying soil organic matter （SOM） and water contents via laboratory microcosm experiments. The presence of 20% alcohol reduced the sorption of gasoline compounds by soil as well as the mass distribution of the compounds to soil solids. This effect was greater for ethanol than butanol. Compared with the sorption coefficient （Kd） of unblended gasoline compounds, the Kd of E20 gasoline compounds decreased by 54% for pentane, 54% for methylcyclopentane （MCP） and 63% for benzene, while the Kd of B20 gasoline compounds decreased by 39% for pentane, 38% for MCP and 49% for benzene, The retardation factor （R） of E20 gasoline compounds decreased by 53% for pentane, 53% for MCP and 48% for benzene, while the R of B20 gasoline compounds decreased by 39% for pentane, 37% for MCP and 38% for benzene. For all SOM and water contents tested, the Kd and R of all gasoline compounds were in the order of unblended gasoline 〉 B20 〉 E20, indicating that the use of high ethanol volume in gasoline to combat climate change could put the groundwater at greater risk of contamination,

An attempt to find a suitable place for soil moisture sensor in a drip irrigation system

Determination of an appropriate location for monitoring soil water content (SWC) is a keyfactor in efficient use of water in precision agriculture, however, the main challenge is thedynamic movement of water and root development in the soil profile. The objective of thisstudy was investigating how SWC distribution in a loam soil profile at two growth stages ofmaize may impact the suitable location for SWC monitoring in a drip-tape irrigation system.A new concept, Average Moisture Representative Surface (AMRS) was proposed to determine the surface of the soil profile, which represent the average soil moisture of the wettedvolume. SWC samples were taken during two irrigation intervals (48~52 days after planting(DAP) and 68~73 DAP) and root growth pattern was studied through root length density (RLD)at 50 and 100 DAP. The results revealed that a non-uniform wetting pattern after irrigationlimits the appropriate locations for SWC monitoring to point measurements and with time,SWC depletion resulted in enlarging AMRS. At the end of growing season, an increase of rootgrowth around the drippers increased the variation of root water uptake in different soil layers, and thus optimal place for soil sensors was limited to the upper layers, where the maximum root water uptake occurred. Overall, it is recommended to install soil sensors, such astensiometers and TDRs at a horizontal distance of 5~20 cm from the crop and a depth of10~20 cm from the soil surface while drip-tape is aligned close to the maize row.

Soil and land resources for agricultural production:General trends and future scenarios-A worldwide perspective

Based on the global distribution of land and soil quality and the world population,future trends in the agricultural use of land and soil resources are described,which will severely compromise future global food and fiber production through the increase and the spatial changes of world population,through the loss of fertile land caused by insufficient soil management and through urbanisation and industrialization Moreover,future changes in life style and the increasing demand for food and bioenergy,trough changes in world economy,through climate change and a worldwide decrease in fresh water supply,sustainable land use for the production of food and fiber will be under threat.Until 2050 global food production must be doubled for satisfying global needs.Our scenarios should help to preview future changes,to counterbalance and to mitigate possible negative impacts,thus sustaining global food security.