Water and salt movement in different soil textures under various negative irrigating pressures

supported by the National High-Tech R＆D Program of China （2013AA102901）

Effects of Supplemental Irrigation Based on Testing Soil Moisture and Nitrogen Fertilization Amount on the Yield and Nitrogen Uptake of Winter Wheat

[Objective] This study aimed to determine the effects of supplemental irrigation on yield and nitrogen uptake in winter wheat. [Method] Three supplemental irrigation levels were set based on the target soil contents of 60%, 70% and 80%） at jointing stage of wheat. Moreover, three nitrogen levels （0, 195 and 255 kg/hm^2） were designed. The experimental plots were arranged fol owing a split-plot design. Zhoumai 18 was selected as the experimental material. [Result] Supplemental irrigation and nitrogen application in combination had significant or extremely significant effects on yield, yield components and nitrogen uptake in winter wheat. The interaction between irrigation and nitrogen fertilization had significant or extremely significant influence on the number of ears, number of grains per ear, 1 000-grain weight, grain yield and nitrogen accumulation in winter wheat. Under different combinations of supplemental irrigation and nitrogen application, the maximum yield of winter wheat was obtained at W2 N195, while the minimum at W1 N255. [Conclusion] With the increase of irrigation, negative effect of nitrogen on number of ears, number of grains per ear, 1 000-grain weight, grain yield and nitrogen accumulation decrease under lower nitrogen application rate.

Response of Soil Organic Carbon and Its Aggregate Fractions to LongTerm Fertilization in Irrigated Desert Soil of China

Irrigated desert soil samples in the Hexi Corridor of China were collected over a period of 23 years from a site where different fertilization methods had been used. Changes of soil organic carbon （SOC） and its water stable aggregate （WSA） size fractions were studied. The effects of various fertilization methods on the distribution of added organic carbon （OC） in different WSA size fractions were also analyzed. The results showed that the applied fertilizations for 23 years improved SOC concentrations and OC concentrations in all WSA size fractions compared to the non-fertilized treatment （CK）. In addition, fertilization obviously increased the OC stocks of2 mm, 0.25-2 mm and 0.053-0.25 mm WSA fractions, respectively. A signiifcant positive correlation was found between soil C gains and OC inputs （r=0.92, P〈0.05）, indicating that SOC may have not reached the saturation point yet at the site. The C sequestration rate was estimated by 14.02%at the site. The OC stocks in all of the〈2 mm WSA fractions increased with the increase of OC input amounts;and the conversion rate of the input fresh OC to the OC stock of〈0.053 mm WSA fraction was 1.2 and 2.6 times higher than those of the 0.25-2 mm and 0.053-0.25 mm WSA fractions, respectively. Therefore, the〈0.053 mm WSA fraction was the most important component for soil C sequestration in the irrigated desert soil.

Effect of different water application intensity and irrigation amount treatments of microirrigation on soil-leaching coastal saline soils of North China

In coastal regions, Bohai Gulf is one of the most affected areas by salinization. To study the effects of mocrosprinkler irrigation on the characteristics of highly saline sandy loam soil（ECe（saturated paste extract）=22.3 d S m^–1; SAR（sodium adsorption ratio）=49.0） of North China, a laboratory experiment was conducted. Five water application intensity（WAI） treatments（1.7, 3.1, 5.3, 8.8, and 10.1 mm h^–1）, five irrigation amount（IA） treatments（148, 168, 184, 201, and 223 mm） and three time periods of water redistribution（0, 24 and 48 h） were employed in the study. A compounding microsprinkler system was used for the WAI treatments, and a single microsprinkler was used for the IA treatments. The results indicated that, as soil depth increased, soil water content（θ） increased and then slightly decreased; with WAI and IA consistently increasing, the relatively moist region expanded and the average θ increased. Meanwhile, soil ECe increased as soil depth increased, and the zone with low soil salinity expanded as WAI and IA increased. Although the reduction of the average SAR was smaller than that of the average electrical conductivity of the ECe, these variables decreased in similar fashion as WAI and IA increased under microsprinkler irrigation. The average p H decreased as soil depth increased. Longer time periods of water redistribution led to lower salinity and slight expansion of the SAR zone. Considering the effects of leached salts in coastal saline soils, greater WAI and IA values are more advantageous under unsaturated flow conditions, as they cause better water movement in the soil. After leaching due to microsprinkler irrigation, highly saline soil gradually changes to moderately saline soil. The results provide theoretical and technological guidance for the salt leaching and landscaping of highly saline coastal environments.

Chemical fractions and potential mobility of lead in soils irrigated by sewage in Pearl River Delta,South China

The chemical fractions,i.e.,water soluble(WS),exchangeable(Ex),carbonate(Car),weakly organic(WO),Fe-Mn oxide(FMO),strongly organic(SO),residual(Res) fraction,of Pb in irrigated soils in South China were investigated by a modified Tessier sequential extraction technique.The results show that the chemical fraction of Pb in soil is mainly the Res fraction and followed by FMO fraction,and the WS,WO,FMO,and SO fractions in topsoils(0-10 cm) are higher than those in subsoils(30-40 cm).The sum of contents of WS and Ex fractions(SWE) in topsoils is significantly positively related with that in subsoils,indicating the strong mobility of Pb in WS and Ex fractions in soils,and the SWE in soils is higher than the German trigger value for the transfer path soil-plant,indicating the high bioavailability of Pb in soils of this area.Fortunately,SWE and the ratio of WS and Ex fractions(RWE) to the sum of all fractions generally decrease with the soil depth in soil profile and the RWE in soil profile is lower than 0.5%,indicating the low pollution risk for Pb in groundwater.In addition,soil particles,pH and Fe2O3 play an important role in the impact of mobility and chemical fractions of Pb in soils.

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.

The Impacts of Supplemental Irrigation Based on Soil Moisture Measurement and Nitrogen Use on Winter Wheat Yield and Nitrogen Absorption and Distribution

Based on split plot design method of field test,the impacts of supplemental irrigation based on soil moisture measurement and nitrogen use on winter wheat yield and nitrogen absorption and distribution were studied.Supplemental irrigation had three levels: 60%(W_1),70%(W_2) and 80%(W3) of the targeted relative water content at 0-40 cm of soil layer during jointing period of winter wheat.Nitrogen fertilization had three levels: not using nitrogen(N_0),using pure nitrogen of 195 kg/hm^2(N_(195)) and 255 kg/hm^2(N_(255)).Results showed that:(i)different supplemental irrigation and nitrogen fertilization significantly affected plant height and leaf area of winter wheat during key growth period.Under the same supplemental irrigation treatment,both plant height and leaf area of winter wheat showed as N_(255)> N_(195)> N_0(P <0.05).Plant height in N_(195) and N_(255)treatments was significantly higher than that in N_0 treatment,but there was not significant difference between N_(195) and N_(255)(P >0.05).Under the same nitrogen fertilization,plant height in W_2(569.4 m^3/hm^2) and W3(873.45 m^3/hm^2) treatments was significant higher than that in W_1(265.2 m^3/hm^2),but there was not significant difference between W_2 and W3(P >0.05).It illustrated that excessive nitrogen fertilization and supplemental irrigation did not significantly affect plant height and leaf area of winter wheat.(ii) Under the same nitrogen fertilization level,yield increase effect of winter wheat by supplemental irrigation showed a declining trend with nitrogen application amount increased.It illustrated that nitrogen fertilization and supplemental irrigation had certain critical values on the yield of winter wheat.When surpassing the critical value,the yield declined.When nitrogen fertilization amount was 195 kg/hm^2,and supplemental irrigation amount was 70% of field moisture capacity(569.4 m^3/hm^2),the highest yield 8500 kg/hm^2 could be obtained.(iii) During mature period of winter wheat,nitrogen accumulation amount of plant treated by nitrogen was significantly higher than that not treated by nitrogen(P <0.05).But under the treatments of W_2 and W3,nitrogen accumulation amount in N_(255) significantly declined when compared with N_(195)(P <0.05).Especially under W3(873.45 m^3/hm^2) level,nitrogen accumulation amount in N_(255) was even lower than N_0.Under the treatments of N_0 and N_(195),nitrogen accumulation amount of plant significantly increased with supplemental irrigation increased(P < 0.05).But under N_(255) treatment,there was not significant difference(P > 0.05).It illustrated that moderate supplemental irrigation and nitrogen fertilization could improve nitrogen absorption ability of winter wheat,but excessive supplemental irrigation and nitrogen fertilization were not favorable for plant's nitrogen absorption.(iv) Although the increase of supplemental irrigation during jointing period improved nitrogen absorption ability of winter wheat and promoted winter wheat absorbing more nitrogen,it inhibited nitrogen transferring and distributing to seed.Comprehensively considering growth condition of winter wheat and nitrogen risk condition,it is suggested that nitrogen application amount was 195 kg/hm^2,and supplemental irrigation reached 70% of field moisture capacity(569.4 m^3/hm^2),which could be as the suitable water and fertilizer use amounts in the region.

Change Numbers of Microorganisms under Vegetable Cultures of Irrigated Soils of Subtropical Zone of Azerbaijan

Number of microorganisms of soils of subtropic zones in a vegetable-fodder and vegetable-bean crop rotations compared with permanent cultivation of these cultures has been studied. The results of the analyses have shown that character of change of number of the basic physiological groups of microorganisms （a bacteria, sporeforming bacteria, actinomysetes and microscopic fungies） depends not only on soil-ecological conditions but also on the kind and biological features of cultivated cultures. In soils of subtropical zones the greatest number of organisms using organic nitrogen in food was observed on alluvial meadow-forestry soils and yellowish-gley soils. Gray-brown soils are rich in actinomycetes in comparison with alluvial meadow-forestry soils, but meadow-serozem is rich in spore-forming bacteria forms. A number of microscopic fungi of the studied soils were the least. High intensity of processes of mineralization was marked in meadow-serozem soils, the least in alluvial meadow-forestry and yellowish-gley soils. Under permanent cultures the quantity of microorganisms was less, and factor of mineralization is higher above, than in crop rotation.

Effects of Irrigation on Soil and Wheat Yield under Drought Conditions in Sichuan

In order to study the effective water-saving cultivation of wheat in Sichuan under drought conditions to reduce grain loss,the effects of different irrigation methods（ natural rainfall,artificial irrigation,and infiltrating irrigation） on soil physical characteristics and main agronomic characters and yield of wheat were analyzed. The results showed that different irrigation treatments at different growth stages had different effects on soil physical characteristics and agronomic characters of wheat. At the seedling and jointing stage,there were small differences between the treatments in soil compactness,soil bulk density,and soil water content. At the flowering and maturation stage,different irrigation treatments had great impacts on soil compactness,soil bulk density,soil water content,and agronomic characters of wheat. In the hilly areas of Sichuan Basin,infiltrating irrigation at the jointing stage was the best,and wheat yield increased significantly,2 113. 46 kg/hm^2 higher than that in the control.

Using side-dressing technique to reduce nitrogen leaching and improve nitrogen recovery efficiency under an irrigated rice system in the upper reaches of Yellow River Basin, Northwest China

The excessive nitrogen （N） fertilizer input coupled with flood irrigation might result in higher N leaching and lower nitrogen recovery efficiency （NRE）. Under an intensive rice system in the Ningxia irrigation region, China, environmental friendly N management practices are hreavily needed to balance the amount of N input for optimum crop production while minimize the nitrogen loss. The objective of this study was to determine the influences of side-dressing （SD） technique in mechanical transplanting systems on the NRE, N leaching losses and rice yield in anthropogenic-alluvial soil during two rice growing seasons （2010-2011）. Four fertilizer N treatments were established, including conventional urea rate （CU, 300 kg ha-1 yr-1）; higher SD of controlled-release N fertilizer rate （SD1,176 kg ha-1 yr-1）; lower SD of controlled-release N fertilizer rate （SD2, 125 kg ha-1 yr-1）; and control （CK, no N fertilizer）. Field lysimeters were used to quantify drainage from undisturbed soil during six rice growing stages. Meanwhile, the temporal variations of total nitrigen （TN）, NO3--N, and NH4＋-N concentrations in percolation water were examined. The results showed that SD1 substantially improved NRE and reduced N leaching losses while maintaining rice yields. Across two years, the averaged NRE under SD1 treatment increased by 25.5% as relative to CU, but yet the rice yield was similar between two treatments. On average, the nitrogen loss defined as TN, NH4＋-N, and NO3--N under the SD1 treatment reduced by 27.4, 37.2 and 24.1%, respectively, when compared with CU during the study periods. Although the SD2 treatment could further reduce N leaching loss to some extent, this technique would sharply decline rice yield, with the magnitude of as high as 21.0% relative to CU treatment. Additionally, the average NRE under SD2 was 11.2% lower than that under SD1 treatment. Overall, the present study concluded that the SO technique is an effective strategy to reduce N leaching and increase NRE, thus potentially mitigate local environmental threat. We propose SD1 as a novel alternative fertilizer technique under an irrigated rice-based system in Ningxia irrigation region when higher yields are under consideration.

Ecotoxicity assessment of soil irrigated with domestic wastewater using different extractions

The toxicity of soil irrigated with treated domestic wastewater （site A） and untreated gray wastewater （site B） were investigated. Soil extracts were prepared using distilled water, acid solvent （0.1 mol·L-1 HCl）, and organic solvent （acetone：petroleum ether：cyclohexane= 1：1：1） to understand the type of pollutants responsible for the ecotoxicity associated with wastewater irrigation. The soil toxicity was assessed using a luminescence inhibition assay with Vibrio fischeri for acute toxicity, a micronucleus assay with Vicia faba root tips and a single cell gel electrophoresis assay of mice lymphocytes for genotoxicity. The physicochemical properties and the heavy metal （HM） contents of the irrigated soil were also analyzed. The results indicated that the wastewater irrigation at site A had no effects on the soil properties. With the exception of Pb, Zn, Fe, and Mn, the accumulation of HMs （Cu, Ni, and Cr） occurred. However, the irrigation at site A did not result in obvious acute toxicity or genotoxicity in the soil. The soil properties changed greatly, and HMs （Cu, Ni, and Cr） accumulated in site B. There were significant increases in the acute toxic and genotoxic effects in the soils from site B. The ecotoxicity in site B came primarily from organic-extractable pollutants.