Impact of Irrigation Methods on Soil Salt Content and Their Differences in Whole Cotton Growing Season in Arid Area of Northwest China

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1 Nov., 2016 Journal of Resources and Ecology Vol. 7 No.6 J. Resour. Ecol (6) DOI: /j.issn x Impact of Irrigation Methods on Soil Salt Content and Their Differences in Whole Cotton Growing Season in Arid Area of Northwest China JIN Jianjun 1, RAN Shenghong 2,*, LIU Taotao 3 1. College of Resources Science and Technology, Beijing Normal University, Beijing , China; 2. Key Laboratory of Land Surface Pattern and Simulation, Institute of Geographical Sciences and Natural Resources Research, CAS, Beijing , China; 3. Northwest Institute of Eco-Environment and Resources, CAS, Lanzhou , China Abstract: Research for changes of soil water and salt is an important content of land sciences and agriculture sciences in arid and semi arid regions. In this paper, sampling in actual agricultural fields, laboratory analysis of soil samples and statistical analysis methods are used to quantitatively analyze soil salinity changes under different irrigation methods throughout the cotton growing season in Shihezi reclamation area. The results show that irrigation methods play an important role in soil salt content in the surface soil (0 20 cm) and sub-deep soil (40 60 cm), followed by deep soil layer ( cm) and root soil layer (20 40 cm). Furrow irrigation yields the maximum soil salt content in deep layer ( cm) or sub-deep layer (40 60 cm) and the maximum salinity occurs in the first half of the cotton growing season (June or earlier). In contrast, drip irrigation yields the maximum soil salinity in the root layer (20 40 cm) or sub-deep (40 60 cm), and this usually appears in the second half growing season (July or after). The ratio of chloride ion to sulfate ion (Cl /SO 4 2 ) and its change in the soil are on the rise under furrow irrigation, while the value first increased and then decreased with a peak point in June under drip irrigation. This suggests that furrow irrigation may shift the type of soil salinization to chloride ion type moreso than drip irrigation. Potassium and sodium ion contents of the soil show that soil sodium+potassium content will drop after the first rise under furrow irrigation and the value is manifested by fluctuations under drip irrigation. Potassium+sodium content change is relatively more stable in the whole cotton growth period under irrigation methods. The maximum of sodium and potassium content of the soil usually occur in deep soil layer ( cm) or sub-deep soil layer (40 60 cm) in most sample points under furrow irrigation while it is inconsistent in different sample points under drip irrigation. A nonparametric test for paired samples is used to analyze differences of soil salt content under different irrigation methods. This analysis shows that the impact of irrigation on soil salinity is most significant in July, followed by August, June, May, and April in most sample points. The most significant impact of irrigation methods occurs in the surface soil layer (0 20 cm), followed by deep layer ( cm), root layer (20 40 cm) and sub-deep (40 60 cm). These conclusions will be benefitial for mitigation of soil salinization, irrigation and fertilization and sustainable land use. Key words: soil salinity; soil water content; cotton growing season; arid area of northwest China 1 Introduction Water shortages and soil salinization are main limiting factors for development in arid northwest China, especially in reclamation in Xinjiang. Water-saving irrigation technology was introduced to Xinjiang at late 1990s and has been gradually implemented to facilitate irrigated agriculture development in Xinjiang. But it also raises some concerns, one Received: Accepted: Foundation: National Natural Science Foundation of China ( /U ). *Corresponding author: RAN Shenghong. ransh@igsnrr.ac.cn. Citation: JIN Jianjun, RAN Shenghong, LIU Taotao Impact of irrigation methods on soil salt content and their differences in whole cotton growing season in arid area of northwest China. Journal of Resources and Ecology. 7(6):

2 454 Journal of Resources and Ecology Vol. 7 No. 6, 2016 of which is whether the water-saving irrigation will make the arable land salinization worse or not. Most of the literature suggests that soil texture, especially salinization processes, will be stabilizing after years of change of irrigation methods (Lambert K. Smedema & Karim Shiati. 2002). So now is the critical period to assess the impacts of irrigation methods on agricultural land salinization in the reclamation region in Xinjiang in north-west China. The reasons for soil salinization in arable land in arid areas includes mainly natural factors, for example dry climate, closed terrain topography, higher salt content of the soil parent material, and human factors such as the changes of groundwater level, irrigation, drainage and so on (B. Hanson & D. May. 2004; Fethi Bouksila et al., 2013). Due to the relative stability of natural factors, since their change is difficult to be controlled by human activity, the current research in this area focuses on human factors contributing to soil salinization, such as irrigation methods, irrigation quota, irrigation water (water quality), time and frequency of irrigation and other factors on soil salinization processes (Nazirbay Ibragimov, et al. 2007; Qi Peipei et al., 2012 Ruoshui Wanga, et al., 2014). But the results are inconsistent. In studies on the impact of irrigation methods on soil water and salt processes, some scholars have applied analog data under laboratory control or sampling measurement data in the field to analyze the impact of irrigation methods on soil salinization. These studies include impacts of irrigation methods on process of soil salinization of arable land, physical properties, soil fertility and crop quality and yield. Research results show that the impact of irrigation methods on cotton soil includes many aspects, such as soil specific gravity, bulk density, porosity and aggregate structure, mechanical composition, etc. In general, the current irrigation management practices favor salt leaching out of the root zone and soil salinization could be controlled as long as a reasonable regulation of irrigation frequency and amount of irrigation could be implemented (Yaohu Kanga et al., 2012; Mark Altaweel & Chikako E. Watanabe. 2012). However, some other scholars have different opinions and even draw opposite conclusions. Some studies show that drip irrigation makes soil salt content increase in different soil layers and most of the salt content accumulates in soil layer cm. The longer the drip irrigation time, the more severe the accumulated soil salt (Li Yuyi et al., 2007; Liu Qingsheng, 2008). Results from other research is inconsistent with this, and may even be opposite due to the combined effect of irrigation method, soil type, drainage patterns and other factors. Some scholars may regard the combined effect about changes in soil water and salt as an effect of a single factor, which results in a bias conclusion which is not entirely consistent with the actual situation. This paper will use statistical analysis to quantitatively assess the impact of irrigation methods on soil salinization based on the data which from actual cotton fields samples and laboratory analysis in Shihezi reclamation area. The potential for better irrigation management and policy implications will also be discussed. 2 Data and research methods 2.1 Study area Shihezi reclamation area was selected as study area. It is located in the middle of north Tianshan mountains, which has a typical continental arid climate, with annual precipitation of mm which mainly concentrated in the summer. Precipitation from April to August accounted for 56% to 70% of precipitation throughout a year. Annual evaporation is from l000 to 1500 mm and the evaporation from April to August accounts for 65% to 70% of the annual amount of evaporation. The soil type is alluvial plain soils and most are saline soil and meadow marsh soil due to the lower alluvial watered conditions. Strong evaporation forces accompany with the arid climate, soil salt resulted from weathering crust, poor circulation groundwater circulation, over-exploitation of water resources, inappropriate irrigation practices and other human activities have played an important role on migration and changes of soil water and salt in Shihezi reclamation area. Drip irrigation technology has been introduced in the study area in 1996 and began to be promoted in the whole reclamation area by The ppopularity of advanced irrigation methods emerged from their ability to alleviate the water shortage problem to some extent, but it will also change soil water and soil salt content and their distribution. This paper focuses on the impact of irrigation methods on soil water and soil salt distribution in cotton irrigation in Shihezi reclamation area, as well as changes of soil water and soil salt in the whole cotton growing season. It will provide a scientific basis for the moderate development of arable land and establishment of a reasonable system of irrigation to prevent soil salinization in arid areas in general. 2.2 Soil samples collection and laboratory analysis Sample selection and sampling methods. In order to minimize the impact of climate, topography, soil types and other natural factors on the experimental data, sample sites were selected based on the following principles: Firstly, weather patterns, geology and geomorphology type in plots are consistent or similar natural conditions; Secondly, the soil type of selected plots are the same in order to ensure soil permeability are similar; Thirdly, each sample site must have different plots with furrow irrigation and drip irrigation methods in order to do a comparative study. Based on these principles, this paper selected Liuhudi, Tongshucun, Xindoucun and Huxicun as sample sites and two adjacent plots under different irrigation methods are selected in each sample site for soil sampling. Figure 1 is the location of sampling points.

3 JIN Jianjun, et al.: Impact of Irrigation Methods on Soil Salt Content and Their Differences in Whole Cotton Growing Season in Arid Area of Northwest China 455 Fig.1 The location of sample sites Sampling time. Soil samples are collected in 4/5/6/7/8, Each time represent a different portion of the cotton growing season. Indicators and laboratory analysis methods. Eight types of salt ion in soil (Cl /SO 2 4 /CO 2 3 /HCO 3 /Na + /K + /Ca 2+ /Mg 2+ ) and soil moisture and ph values were measured (Bao Shidan. 2008). Soil samples from the field (aluminum box packing) will be immediately weighed and suspended with 5:1 ratio of soil and water for salt extraction. Water-soluble salt will be measured according to the method in "agrochemical soil analysis (third edition)": CO 2 3 and HCO 3 content were measured by dual indicator neutralization assay; Cl content was determined by titration with AgNO 3 ; SO 2 4 content was measured by indirect EDTA complexometric titration; Ca 2+ and Mg 2+ content were determined by EDTA titration; K + and Na + content were measured by flame photometer. 2.3 Research methods Using the data obtained above, SPSS software was used to analyze for significant differences of soil salt content under different irrigation methods. Nonparametric rank sum testtwo paired sample Wilcoxon signed rank test-was used to analyze for significant differences in soil salinity data points under different irrigation methods, because the overall distribution of the data is unknown. Then the main salt ion (chloride, sulfate ions, sodium ions and potassium ions) contents and their changes were analyzed. Finally the coupling relation between soil water and soil salt was studied in an attempt to reveal the effect of irrigation methods on the relation between soil water and salt content and their changes. 3 Results Based on the laboratory analytical data from four sample sites, for a total 80 mixed soil samples (four sample sites 5 months 4 soil layers = 80 samples), we studied soil salinity under different irrigation methods and its changes. The soil salt contents were compared quantitatively in different soil layers and in different portions of the cotton growing season. 3.1 Soil salt content and their changes under different irrigation methods Because soil salinity background and groundwater level is different in different sample sites, the impact of irrigation methods on soil salt content in different sample sites is different due to the combined effect of multiple factors. In order to minimize the interference of other factors, the soil salt contents and their changes over time are compared to that of one under different irrigations only in a sample site. These results are shown in Fig. 2. Fig.2 soil salinity changes with the seasons under different irrigation methods

4 456 Journal of Resources and Ecology Vol. 7 No. 6, 2016 Figure 2 shows that soil salinity with drip irrigation is higher than that with furrow irrigation in most of the sample sites (three sample sites from all four samples sites: Tongshucun, Xindoucun and Huxicun). In addition, under drip irrigation, soil salinity is marginally increased and then decreased in the cotton growth period, while soil salinity under furrow irrigation method varies in different sites. To analyze the transport of soil salinity, focusing on the impact of irrigation method, soil salinity and their changes in different soil layers were quantitatively analyzed for all sample sites. 3.2 Changes of soil salinity in 4 soil layers over time under different irrigation methods In order to assess the impact of irrigation methods on spatial and temporal distribution of soil salinity, soil salt content and their changes over time in different soil layers were compared under different irrigation methods in the 4 sample sites. The results are shown in Fig. 3 to Fig. 6. (1) Soil salinity and its changes over time under different irrigation methods in Liuhudi (Fig. 3) Figure 3 shows that the maximum soil salt content occurs in sub-deep layer (40 60 cm) and the minimum occurs in surface layer (0 20 cm) under furrow irrigation. In most soil layers, salt content rose after an initial drop and reached the lowest value in July. Under drip irrigation, the difference of soil salt content in different layers is evident before June and the maximum of soil salt content occurs in sub-deep layer (40 60 cm) while the minimum occurs in the surface layer (0 20 cm). Then the difference decreased. In short, soil salinity fluctuations over time and the two local maxima of soil salt content appeared in May and July. (2) Soil salinity and its changes over time under different irrigation methods in Tongshucun. Figure 4 shows that soil salt content in different soil layers increased before June and then decreased in Tongshucun under furrow irrigation. Under drip irrigation, the maximum of soil salt content occurs in sub-deep layer and the minimum occurs in surface layer (0 20 cm) and the soil salt increased from April to July. In the deeper the soil layer, soil salinity changes little with time. (3) Soil salinity and its changes over time under different irrigation methods in Xindoucun. Figure 5 shows that the soil salt content increases with increasing soil depth under furrow irrigation in Xindoucun. It is similar under Drip Irrigation but the differences of soil salinity among soil layers are smaller than under furrow irrigation. The maximum of soil salinity occurred in May under furrow and in July under drip irrigation in all soil Fig.3 Soil salt content and its change under different irrigation methods in Liuhudi (2013) Fig.4 Soil salt content and its change under different irrigation methods in Tongshucun (2013) Fig.5 Soil salt content and its change under different irrigation methods in Xindoucun (2013)

5 JIN Jianjun, et al.: Impact of Irrigation Methods on Soil Salt Content and Their Differences in Whole Cotton Growing Season in Arid Area of Northwest China 457 Fig.6 Soil salt content and its change under different irrigation methods in Huxicun (2013) layers in Xindoucun. (4) Soil salinity and its changes over time under different irrigation methods in Huxicun. Figure 6 shows that the maximum soil salinity occurred in sub-deep layer (40 60 cm) or deep layer ( cm) under furrow irrigation, while it occurred in root layer (20 40 cm) under drip irrigation in Huxicun. This indicates drip irrigation may make soil salt accumulate in upper soil layers. From the perspective of temporal change, soil salinity fluctuated under furrow irrigation and it decreased under drip irrigation throughout the cotton growing season in all soil layers. Based on all sample data from Figs. 3 6, it can be concluded that furrow irrigation methods yield the maximum of soil salinity in deep layer ( cm) or sub-deep layer (40 60 cm); while drip irrigation yields the maximum of soil salinity in the root layer (20 40 cm) or sub-deep (40 60 cm). From the temporal point of view, furrow irrigation can produce soil salinity fluctuations with maximum soil salinity appearing earlier (May-June) and drip irrigation can produce soil salinity changes in a way that is more stable with the maximum soil salinity appeared to be postponed (June- July). Because the effects of irrigation methods on soil salinity are not entirely consistent in the 4 sample sites, some main types of soil salt ion content and their changes under different irrigation methods are analyzed quantitatively. 3.3 Spatial and temporal distribution of major soil anion (Cl, SO 2 4 ) contents under different irrigation methods Soil chloride and sulfate ion contents, and their ratio, are an important basis to determine type of soil salinization and to assess the degree of salinization. The impact of irrigation methods on soil salinization should be reflected by the main salt ions, especially chloride ion and sulfate ion content and their changes. Chloride and sulfate ion contents and their changes in different soil layers are compared under different irrigation methods and throughout the cotton growing season. (1) Soil chloride ion content and its changes under different irrigation methods Figure 7 shows that soil chloride ion contents under drip irrigation are greater than those under furrow irrigation in most of the sample sites (3 sample sites out of 4%, 75%). Changes in the range of soil chloride ion content during the cotton growing season under furrow irrigation are bigger than those under drip irrigation. The maximum soil chloride ion content under furrow irrigation occurred in June, while the maximum occurred in July under drip irrigation. This shows that drip irrigation methods might make chloride ions accumulate in the top soil layer. In the first half of cotton growing season (April-June), the minimum soil chloride ion content occurred at the top soil layer, and it increased with the increasing soil depth with both irrigation methods. However, it was different in the second half of the cotton growing season: soil chloride ion content maintained this vertical distribution under furrow irrigation but increased, with the maximum occurring in the top soil layer in July and August, under drip irrigation. The differences among different soil layers under furrow irrigation are larger than those under drip irrigation. (2) Soil sulfate ion content and its changes under different irrigation methods Figure 8 shows that the difference of soil sulfate ion content between furrow irrigation and drip irrigation is not evident. The minimum of soil sulfate ion content occurred in the top soil layer (0 20 cm) and the maximum occurred in the sub-deep soil layer (40 60 cm). This suggests that drip irrigation methods might make sulfate ions accumulate in the upper soil layer. Soil sulfate ion content increased before June and then showed a downward trend, with the maximum sulfate ion content occurring in May or June, while soil sulfate ion content fluctuated under drip irrigation in the cotton growing season. The maximum sulfate ion content appeared in May and July, which may have resulted from the irrigation methods and irrigation frequency. (3) Chloride/sulphate and its changes with different irrigation methods The ratio of chloride and sulfate ions is an important basis for determining the type of soil salinization. Cl 2 /SO 4 and its changes in different soil layers with different irrigation methods are quantitatively analyzed. the results are shown in Fig. 9. Figure 9 shows that the ratio Cl /SO 2 4 increased over time during the whole cotton growing season with furrow irrigation, while the ratio fluctuated and was relatively stable with drip irrigation. This indicates that furrow irrigation

6 458 Journal of Resources and Ecology Vol. 7 No. 6, 2016 Fig.7 Soil Cl content and its change under different irrigation methods, 2013 Fig.8 Soil SO 4 2 content and its change under different irrigation methods, 2013

7 JIN Jianjun, et al.: Impact of Irrigation Methods on Soil Salt Content and Their Differences in Whole Cotton Growing Season in Arid Area of Northwest China 459 Fig.9 Ratio Cl /SO content under different irrigation methods, 2013 may transform soil salinization type to chloride ion type, while drip irrigation s impact on the change of soil salinization type is not evident. 3.4 Spatial and temporal distribution of soil Na + + K + content with different irrigation methods Soil sodium and potassium contents and their distribution are closely related to irrigation and fertilization management. Spatial and temporal distribution of soil Na + + K + content with different irrigation methods are shown in Fig. 10. Fig.10 shows that soil sodium+potassium content drops after the an initial rise with furrow irrigation in most sample sites (3 out of 4 sample sites), while it fluctuated while remaining more stable throughout the cotton growth period with drip irrigation. In addition, the maximum of sodium and potassium content occured in the deep ( cm) or sub-deep (40 60 cm) soil layers with furrow irrigation, while the difference of soil sodium and potassium content among soil layers is not evident with drip irrigation. As previously mentioned, different irrigation methods will lead to differences of soil salinity. These differences are not only reflected in the fact that soil salt content with drip irrigation is slightly larger than that with furrow irrigation, but they are also reflected in the differences in spatial and temporal distributions of different types ions and their changes under different irrigation methods. The significance of differences are analyzed in the following discussion, i.e. we would like to know the impact of irrigation on soil salinity is statistically significant or not. 4 Discussion 4.1 Difference analysis of soil salinity under different irrigation methods As mentioned above, the soil salinity of every sampling point under different irrigation methods and those from across the whole cotton growing season are different, indicating that the irrigation methods have some impacts on soil salinity and its temporal and spatial distributions. To test the significance of these differences in soil salinity under different irrigation methods the nonparametric Wilcoxon signedrank test was used. The differences between soil salinity under different irrigation methods were first analyzed and the results are shown in Table 1. From Table 1, it can be seen that the differences between soil salinities under different irrigation methods in the surface soil (0 20 cm), deep layer ( cm) and root layer (20 40 cm) are statistically significant at the 0.05 level, while the differences between soil salinities in the second deep layer (40 60 cm) are statistically significant at the 0.1 level. The results show that the impacts of irrigation methods on soil salinity in different soil layers are different, of which the strongest significance is evident in the soil surface (0 20 cm), followed by the deep layer ( cm), the

8 460 Journal of Resources and Ecology Vol. 7 No. 6, 2016 Fig.10 Soil Na + +K + content and its change under different irrigation methods, 2013 root layer (20 40 cm), and the sub-deep (40 60 cm). This further demonstrates that the drip irrigation method will result in soil salinity aggregation in the surface soil (0 20 cm). The differences between soil salinity under different irrigation methods (drip irrigation vs. furrow irrigation) in different months are then analyzed, and the results are shown in Table 2. Table 1 Significance test results on the differences between soil salinity under different irrigation methods (drip irrigation vs furrow irrigation)* Soil depth 0 20 cm cm cm cm Sig. value Z *: Nonparametric correlation samples Wilcoxin signed rank test Table 2 Significance test results on the differences between soil salinity under different irrigation methods (drip irrigation vs furrow irrigation) in different months* Months Sig.-value Z *: Nonparametric correlation samples Wilcoxin signed rank test Table 2 shows that the most significant difference in soil salinity changes resulting from irrigation methods during the whole cotton growth period is in July, followed by August, June, May and April. This result shows that the soil salinities under different irrigation methods are closest in April, while the differences are largest in July. 4.2 Mechanism of irrigation methods impact on soil salinity of cotton field (1) Impact of soil water content In soil, salt comes with water and leaves with water. Changes in the method of irrigation have a direct impact on the water transportation law. This paper first analyzes the seasonal variation of soil moisture under different irrigation methods for each sample. Figure 11 shows the distribution of soil moisture in different growing seasons under different irrigation methods. Figure 11 shows that most of the samples are consistent with the law of soil water and salt content change. The change in soil water is greater than the change in soil salt content. Compared with the flood irrigation method, the water usage is less under the drip irrigation method. However, the irrigation frequency is greater, which makes the change of soil water content in the whole cotton growing season less under the drip irrigation method. The changing

9 JIN Jianjun, et al.: Impact of Irrigation Methods on Soil Salt Content and Their Differences in Whole Cotton Growing Season in Arid Area of Northwest China 461 Fig.11 soil water (right Y-axis) and soil salt content (left Y-axis) change in different layers under different irrigation methods (A: 0 20 cm; B: cm; C: cm; D: cm) trend of soil salinity is quite similar to the trend of soil moisture. From the vertical perspective, soil salinity increases with the soil depth and this phenomenon is more pronounced under the furrow irrigation method than under the drip irrigation method. From the temporal perspective, under the furrow irrigation method, the soil water and salt contents decrease first and increase later, while the water and salt content of the soil under drip irrigation is relatively stable throughout the growing season. In short, the furrow irrigation method makes the soil salinity show a clear stratification law. But as time goes, the magnitude of the stratification becomes smaller. The drip irrigation method makes soil salinity changes with irrigation time and irrigation water amounts and it is relatively stable in the cotton growing season, thus making the soil salinity distribution become controllable. Overall, under the drip irrigation method, the reduction in the total amount of water usage per unit of land area did not bring the total reduction in the salt content of the soil, suggesting that drip irrigation could lead to salt retention in the monitored soil (0 100 cm) while furrow irrigation may make some salt into the unsampled soil below 100 cm.

10 462 Journal of Resources and Ecology Vol. 7 No. 6, 2016 (2) Impact on groundwater levels Changes in groundwater levels have an important impact on soil salinization. Water-saving irrigation may lead to the decline in total irrigation water amount but it may raise the groundwater levels. The groundwater level in the study area had been 9 12 m for many years. But in our four selected study sample points, the altitude of the samples under drip irrigation is less than that of the samples under furrow irrigation, that is, the groundwater level of sample points under drip irrigations is higher than that under flood irrigations (Table 3). This may be one possible reason for the higher soil salinity in most sample points under drip irrigations. Table 3 Altitude of every sample point (m) Sample point names Irrigation methods Liuhudi Tongshu Village Xindou Village Furrow Drip Furrow Drip Furrow Drip Furrow Huxi Village Drip Altitude Conclusions Based on laboratory analysis data for soil samples for salt content and their changes in whole cotton growing season, the differences of soil salt between with drip irrigation and furrow irrigation yielded the following conclusions: (1) Irrigation methods (whether drip irrigation or furrow irrigation) can play a role in temporal and spatial distribution of soil salinity. The maximum soil salt content usually occured in deep soil layer ( cm) or sub-deep soil layer (40 60 cm) with furrow irrigation while the maximum usually occured in the root soil layer (20 40 cm) or subdeep soil layer (40 60 cm) with drip irrigation. The maximum soil salt content usually occured in the first half of the growing season (June or earlier) with furrow irrigation while the maximum usually occured in the second-half of the growing season (July or later) with drip irrigation. (2) The transport mode of different types of ions is different with different irrigation methods. The ratio Cl /SO 4 2 increases during the whole cotton growing season in most soil layers with furrow irrigation while the ratio is fluctuating and relatively stable with drip irrigation. This indicates that furrow irrigation may transform the soil salinization type to the chloride ion type, while drip irrigation s impact on the change of soil salinization type is not evident. (3) The differences of soil salt content among fields with different irrigation methods are inconsistent. The impacts of irrigation methods on soil salinity in different soil layers are different, with the greatest significance evident in the soil surface (0 20 cm), followed by the deep layer ( cm), the root layer (20 40 cm), and the sub-deep layer (40 60 cm). This further demonstrates that the drip irrigation method will result in soil salinity aggregation in the surface soil (0 20 cm). In addition, the most significant difference in soil salinity changes resulted from irrigation methods in the whole cotton growth period occurred in July, followed by August, June, May and April. This result shows that the soil salinities under different irrigation methods are most similar in April and most different in July. (4) The differences of soil salt content with different irrigation methods are significant. But these differences are not same in different sample sites. This suggests the presence of other factors that have greater impact on soil salinity, such as topography (terrain), the background value of soil salinity, groundwater level, irrigation water quality, crop type, and so on. Recognition of these factors and their impact difference will be an important part of future work. Acknowledgements Authors would like to express their thanks to Professor Minghua Zhang and Dr. Mike who work in University of California, Davis. They give some very good suggestions on this paper. Professor Wang Shuangming and his graduate students who work in Shihezi University provide help in soil sample collecting and sample analysis. Thanks! References B. Hanson, D. May Effect of subsurface drip irrigation on processing tomato yield, water table depth, soil salinity, and profitability. Agricultural Water Management. 68 (3): Bao Shidan Agricultural chemistry analysis of soils[m]. Beijing: China Agriculture Press. (in Chinese) Fethi Bouksila, Akissa Bahri, Ronny Berndtsson, et al Assessment of soil salinization risks under irrigation with brackish water in semiarid Tunisia. Environmental and Experimental Botany. 92(6): Lambert K. Smedema. Karim Shiati Irrigation and salinity: a perspective review of the salinity hazards of irrigation development in the arid zone. Irrigation and Drainage Systems. 16: Li Yuyi, Zhang Fenghua, Pan Xudong, et al Changes of salt accumulation in soil layers with different landforms in Manas River Valley in Xinjiang Region of China. Transactions of the Chinese Society of Agriculture Engineering. 23(2): (in Chinese) Liu Qingsheng, Liu Gaohuan, Zhao Jun The Indication function of soil type and soil Texture and land type to soil salinization levels. Chinese Agricultural Science Bulletin. 24(1): (in Chinese) Mark Altaweel, Chikako E. Watanabe Assessing the resilience of irrigation agriculture: applying a social-ecological model for understanding the mitigation of salinization. Journal of Archaeological Science. 39 (4): Nazirbay Ibragimov, Steven R. Evett, Yusupbek Esanbekov, et al Water use efficiency of irrigated cotton in Uzbekistan under drip and furrow irrigation. Agricultural water management. 90 (1-2): Qi Peipei, Ran Shenghong, Zhang Kai Effects of different irrigation modes and corps on soil salinization on shihezi reclamation area, China. Journal of Agro-Environment Science. 31(4): (in Chinese) Ruoshui Wang, Shuqin Wan, Yaohu Kang, et al Assessment of secondary soil salinity prevention and economicbenefit under different drip line placement and irrigation regime innorthwest China. 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11 JIN Jianjun, et al.: Impact of Irrigation Methods on Soil Salt Content and Their Differences in Whole Cotton Growing Season in Arid Area of Northwest China 463 金建君 1, 冉圣宏 2, 刘韬韬 3 1. 北京师范大学资源学院, 北京 ; 2. 中国科学院地理科学与资源研究所, 中国科学院陆地表层格局与模拟重点实验室, 北京 ; 3. 中国科学院西北生态环境资源研究院, 兰州 摘要 : 土壤水盐变化研究是干旱半干旱区土地科学和农业科学的重要研究内容之一 本文通过对棉田的野外土壤取样和实验室定量分析, 结果表明灌溉方式对棉田土壤表层 (0 20 cm) 和次深层 (40 60 cm) 土壤含盐量的影响最大, 其次是深层 ( cm) 和根层 (20 40 cm): 漫灌使得土壤含盐量的最大值出现在深层 ( cm) 或次深层 (40 60 cm), 而滴灌使得土壤含盐量的最大值出现在根层 (20 40 cm) 或次深层 (40 60 cm) 同时, 灌溉方式对土壤 Cl 2 /SO 4 也有影响 : 漫灌使其增大而滴灌则会使其先升后降, 在棉花生长中期的 7 月份达到最大值, 这意味着灌溉方式可能对棉田土壤的盐渍化类型具有一定的影响 ; 最后本文还采用配对样本的非参数检验对灌溉方式导致的这种土壤含盐量差别的显著性进行了分析, 认为这种差别在棉花的不同生长期的显著性有所不同 关键词 : 土壤盐渍化 ; 土壤水含量 ; 棉花生长季 ; 华北干旱区