Changes in Soil Hot-Water Extractable C,N and P Fractions During Vegetative Restoration in Zhifanggou Watershed on the Loess Plateau

The study was conducted in Zhifanggou Watershed,Shaanxi Province,China,to evaluate the effect of different vegetation types on hot-water extractable C,N and P fractions,with the aim to determine whether hot-water extractable fractions could be used as indicators of soil quality change in Loess Plateau.The six vegetation types established in 1975 were（i） Robinia pseudoacacia L.,（ii） Caragana korshinkii Kom.,（iii） Pinus tabulaeformis Carr.,（iv） P.tabulaeformis-Amorpha fruticosa L.,（v） R.pseudoacacia-A.fruticosa,and（vi） grassland.A cropped hillslope plot and a Platycladus orientalis L.native forest plot were used as references.The results indicated that the conversion of native forest to cropland resulted in a significant decline in the hot-water extractable C,N and P fractions.Hot-water extractable C,N,and P increased when cultivated land was revegetated,but after 30 years the amount of hot-water extractable C,N,and P in revegetated fields was still much lower compared to native forest.Hot-water extractable fractions increased more under mixed-forest than under pure-forest stands.Furthermore,there was a significant correlation between the hot-water extractable fractions and soil chemical and microbiological properties.The results showed that hot-water extractable fractions could be used as indicators of soil quality change on the Loess Plateau.     

黄土高原半干旱区人工林地土壤水分环境的研究

对黄土高原半干旱丘陵沟壑区主要造林树种林地水分进行了研究。结果表明,该区域不同树种林地土壤含水量很低,接近于凋萎湿度,2002年5月,6 m深土壤平均含水量为5.02%~5.12%,2003年5月为4.65%~6.35%,降水作用仅发生在地表至2 m左右土层内,在1.8~4.0 m有明显的土壤干化现象,含水量保持在凋萎湿度。土壤干层的存在是该区域林地和荒坡土壤水分分布的普遍规律,主要是由特殊的气候条件造成的土壤水分收支长期亏损的积累结果,并非林木生长的必然现象。     

Basic Soil Productivity of Spring Maize in Black Soil Under Long-Term Fertilization Based on DSSAT Model

Increasing basic farmland soil productivity has significance in reducing fertilizer application and maintaining high yield of crops. In this study, we defined that the basic soil productivity （BSP） is the production capacity of a farmland soil with its own physical and chemical properties for a specific crop season under local environment and field management. Based on 22-yr （1990-2011） long-term experimental data on black soil （Typic hapludoll） in Gongzhuling, Jilin Province, Northeast China, the decision support system for an agro-technology transfer （DSSAT）-CERES-Maize model was applied to simulate the yield by BSP of spring maize （Zea mays L.） to examine the effects of long-term fertilization on changes of BSP and explore the mechanisms of BSP increasing. Five treatments were examined： （1） no-fertilization control （control）; （2） chemical nitrogen, phosphorus, and potassium （NPK）; （3） NPK plus farmyard manure （NPKM）; （4） 1.5 time of NPKM （1.5NPKM） and （5） NPK plus straw （NPKS）. Results showed that after 22-yr fertilization, the yield by BSP of spring maize significantly increased 78.0, 101.2, and 69.4% under the NPKM, 1.5NPKM and NPKS, respectively, compared to the initial value （in 1992）, but not significant under NPK （26.9% increase） and the control （8.9% decrease）. The contribution percentage of BSP showed a significant rising trend （P〈0.05） under 1.5NPKM. The average contribution percentage of BSP among fertilizations ranged from 74.4 to 84.7%, and ranked as 1.5NPKM〉NPKM〉NPK〉NPKS, indicating that organic manure combined with chemical fertilizers （I.5NPKM and NPKM） could more effectively increase BSP compared with the inorganic fertilizer application alone （NPK） in the black soil. This study showed that soil organic matter （SOM） was the key factor among various fertility factors that could affect BSP in the black soil, and total N, total P and/or available P also played important role in BSP increasing. Compared with the chemical fertilization, a balanced chemical plus manure or straw fertilization （NPKM or NPKS） not only increased the concentrations of soil nutrient, but also improved the soil physical properties, and structure and diversity of soil microbial population, resulting in an iincrease of BSP. We recommend that a balanced chemical plus manure or straw fertilization （NPKM or NPKS） should be the fertilization practices to enhance spring maize yield and improve BSP in the black soil of Northeast China.     

Crop Yield and Soil Properties in the First 3 Years After Biochar Application to a Calcareous Soil

It remains unclear whether biochar applications to calcareous soils can improve soil fertility and crop yield. A long-term field experiment was established in 2009 so as to determine the effect of biochar on crop yield and soil properties in a calcareous soil. Five treatments were： 1） straw incorporation; 2） straw incorporation with inorganic fertilizer; 3）, 4） and 5） straw incorporation with inorganic fertilizer, and biochar at 30, 60, and 90 t ha-l, respectively. The annual yield of either winter wheat or summer maize was not increased significantly following biochar application, whereas the cumulative yield over the first 4 growing seasons was significantly increased. Soil pH, measured in situ, was increased by a maximum of 0.35 units after 2 yr following biochar application. After 3 yr, soil bulk density significantly decreased while soil water holding capacity increased with adding biochar of 90 t ha^-1. Alkaline hydrolysable N decreased but exchangeable K increased due to biochar addition. Olsen-P did not change compared to the treatment without biochar. The results suggested that biochar could be used in calcareous soils without yield loss or significant impacts on nutrient availability.     

Effects of Long-Term Organic Amendments on Soil Organic Carbon in a Paddy Field A Case Study on Red Soil

Soil organic carbon （SOC） is one of the main carbon reservoirs in the terrestrial ecosystem. It is important to study SOC dynamics and effects of organic carbon amendments in paddy fields because of their vest expansion in south China. A study was carried out to evaluate the relationship between the SOC content and organic carbon input under various organic amendments at a long-term fertilization experiment that was established on a red soil under a double rice cropping system in 1981. The treatments included non-fertilization （CK）, nitrogen-phosphorus-potassium fertilization in early rice only （NPK）, green manure （Astragalus sinicus L.） in early rice only （OM1）, high rate of green manure in early rice only （OM2）, combined green manure in early rice and farmyard manure in late rice （OM3）, combined green manure in early rice, farmyard manure in late rice and rice straw mulching in winter （OM4）, combined green manure in early rice and rice straw mulching in winter （OMS）. Our data showed that the SOC content was the highest under OM3 and OM4, followed by OM1, OM2 and OM5, then NPK fertilization, and the lowest under non-fertilization. However, our analyses in SOC stock indicated a significant difference between OM3 （33.9 t ha^-1） and OM4 （31.8 t ha^-1）, but no difference between NPK fertilization （27 t ha^-1） and nonfertilization （28.1 t ha^-1）. There was a significant linear increase in SOC over time for all treatments, and the slop of linear equation was greater in organic manure treatments （0.276-0.344 g kg-1 yr^-1） than in chemical fertilizer （0.216 g kg^-1 yr^-1） and no fertilizer （0.127 g kg^-1 yr^-1）.     

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

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

Soil Quality Assessment of Acid Sulfate Paddy Soils with Different Productivities in Guangdong Province,China

Land conversion is considered an effective measure to ensure national food security in China, but little information is available on the quality of low productivity soils, in particular those in acid sulfate soil regions. In our study, acid sulfate paddy soils were divided into soils with high, medium and low levels based on local rice productivity, and 60 soil samples were collected for analysis. Twenty soil variables including physical, chemical and biochemical properties were determined. Those variables that were significantly different between the high, medium and low productivity soils were selected for principal component analysis, and microbial biomass carbon （MBC）, total nitrogen （TN）, available silicon （ASi）, pH and available zinc （AZn） were retained in the minimum data set （MDS）. After scoring the MDS variables, they were integrated to calculate a soil quality index （SQI）, and the high, medium and low productivity paddy soils received mean SQI scores of 0.95, 0.83 and 0.60, respectively. Low productivity paddy soils showed worse soil quality, and a large discrepancy was observed between the low and high productivity paddy soils. Lower MBC, TN, ASi, pH and available K （AK） were considered as the primary limiting factors. Additionally, all the soil samples collected were rich in available P and AZn, but deficient in AK and ASi. The results suggest that soil AK and ASi deficiencies were the main limiting factors for all the studied acid sulfate paddy soil regions. The application of K and Si on a national basis and other sustainable management approaches are suggested to improve rice productivity, especially for low productivity paddy soils. Our results indicated that there is a large potential for increasing productivity and producing more cereals in acid sulfate paddy soil regions.     

Spatiotemporal Changes in Soil Nutrients:A Case Study in Taihu Region of China

The accurate assessment of the spatiotemporal changes in soil nutrients influenced by agricultural production provides the basis for development of management strategies to maintain soil fertility and balance soil nutrients. In this paper, we combined spatial measurements from 2 157 soil samples and geostatistical analysis to assess the spatiotemporal changes in soil organic carbon （SOC）, total nitrogen （TN）, available phosphorus （AP） and available potassium content （AK） from the first soil survey （in the 1980s） to the second soil survey （in the 2000s） in the Taihu region of Jiangsu Province in China. The results showed that average soil nutrients in three soil types all exhibited the increased levels in the 2000s （except for AK in the yellow brown soil）. The standard deviation of soil nutrient contents increased （except for TN in the paddy soil）. Agricultural production in the 20 years led to increases in SOC, TN, AP and AK by 74, 82, 89 and 65%, respectively, of the Taihu areas analyzed. From the 1980s to 2000s all the nugget/sill ratios of soil nutrients indices were between 25 and 75% （except for AK in the yellow brown soil in the 2000s）, indicating moderate spatial dependence. The ratio of AP in the yellow brown soil in the 2000s was 88.74%, showing weak spatial dependence. The spatial correlation range values for SOC, TN, AP and AK in the 2000s all decreased. The main areas showing declines in SOC, TN and AP were in the northwest. For AK, the main region with declining levels was in the east and middle of western areas. Apparently, the increase in soil nutrients in the Taihu region can be mainly attributed to the large increase in fertilizer inputs, change in crop systems and enhanced residues management since the 1980s. Future emphasis should be placed on avoiding excess fertilizer inputs and balancing the effects of the fertilizers in soils.     

黄土高原土壤干层初步研究

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

黄土高原土壤剖面粒度异常层及相关因素的响应初步分析

[目的]对黄土高原安塞县纸坊沟流域退耕林土壤1m剖面有机碳含量、粒度、全氮含量、碳氮比、碳酸钙含量进行分析,研究以粒度反映下的土壤异常层理化性质变化,以及各土壤物理化学的响应。[方法]对黄土高原上3个样地各随机选择3个10m×10m的样方并分坡上、坡中、坡下分别挖掘3剖面,间隔10cm采样,地表0～10cm分0～5和5～10cm2部分分别采样。每剖面采样11个,共99个样品,对其进行机碳含量、粒度、全氮含量、碳氮比、碳酸钙含量分析。[结果]3个样地土壤剖面存在a1、b1、b2、c1、c25个特征层,〈0.02mm粒径的土壤颗粒含量减少,〉0.02mm粒径的土壤颗粒含量增加,有机碳含量和C/N值（a1、b1、b2、c2）增加,但CaCO3含量上升趋势不明显。[结论]研究证明土壤特征层在黄土地区,尤其是侵蚀性黄土地区是普遍存在的,在现代土壤学和生态学研究领域应当给予重视。     

黄土高原土壤剖面粒度异常层及相关因素的响应初步分析

[目的]对黄土高原安塞县纸坊沟流域退耕林土壤1 m剖面有机碳含量、粒度、全氮含量、碳氮比、碳酸钙含量进行分析,研究以粒度反映下的土壤异常层理化性质变化,以及各土壤物理化学的响应。[方法]对黄土高原上3个样地各随机选择3个10 m×10 m的样方并分坡上、坡中、坡下分别挖掘3剖面,间隔10 cm采样,地表0～10 cm分0～5 cm和5～10 cm 2部分分别采样。每剖面采样11个,共99个样品,对其进行机碳含量、粒度、全氮含量、碳氮比、碳酸钙含量分析。[结果]3个样地土壤剖面存在a1、b1、b2、c1、c2 5个特征层,〈0.02 mm粒径的土壤颗粒含量减少,〉0.02 mm粒径的土壤颗粒含量增加,有机碳含量和C/N值（a1、b1、b2、c2）增加,但CaCO3含量上升趋势不明显。[结论]研究证明土壤特征层在黄土地区,尤其是侵蚀性黄土地区是普遍存在的,在现代土壤学和生态学研究领域应当给予重视。     

Changes in Organic Carbon Index of Grey Desert Soil in Northwest China After Long-Term Fertilization

Soil organic carbon （SOC）, soil microbial biomass carbon （SMBC） and SMBC quotient （SMBC/SOC, qSMBC） are key indexes of soil biological fertility because of the relationship to soil nutrition supply capacity. Yet it remains unknown how these three indexes change, which limits our understanding about how soil respond to different fertilization practices. Based on a 22-yr （1990-2011） long-term fertilization experiment in northwest China, we investigated the dynamics of SMBC and qSMBC during the growing period of winter wheat, the relationships between the SMBC, qSMBC, soil organic carbon （SOC） concentrations, the carbon input and grain yield of wheat as well. Fertilization treatments were 1） nonfertilization （control）; 2） chemical nitrogen plus phosphate plus potassium （NPK）; 3） NPK plus animal manure （NPKM）; 4） double NPKM （hNPKM） and 5） NPK plus straw （NPKS）. Results showed that the SMBC and qSMBC were significantly different among returning, jointing, flowering and harvest stages of wheat under long-term fertilization. And the largest values were observed in the flowering stage. Values for SMBC and qSMBC ranged from 37.5 to 106.0 mg kg1 and 0.41 to 0.61%, respectively. The mean value rank of SMBC during the whole growing period of wheat was hNPKM〉NPK_M〉NPKS〉CK〉NPK. But there were no statistically significant differences between hNPKM and NPKM, or between CK and NPK. The order for qSMBC was NPKS〉NPKM〉CK〉hNPKM〉NPK. These results indicated that NPKS significantly increased the ratio of SMBC to SOC, i.e., qSMBC, compared with NPK fertilizer or other two NPKM fertilizations. Significant linear relationships were observed between the annual carbon input and SOC （P〈0.01） or SMBC （P〈0.05）, and between the relative grain yield of wheat and the SOC content as well （P〈0.05）. But the qSMBC was not correlated with the annual carbon input. It is thus obvious that the combination of manure, straw with mineral fertilizer may be benefit to increase SOC and improve soil quality than using only mineral fertilizer.     

黄土高原沟壑区土壤抗蚀性的初步研究

通过对黄土高原沟壑区不同地类土壤抗蚀性的研究,发现林草地土壤抗蚀性能明显高于农田,表层土壤的抗蚀性能一般比下层土壤要强。研究表明土壤容重、大于0.25mm的土壤水稳性团聚体含量以及土壤渗透系数是决定土壤抗蚀性大小的主导因素。通过运用逐步回归分析方法,得到了可用于预报和确定土壤抗蚀性的回归方程。     

Soil Monitoring System as a Basic Tool for Protection of Soils and Sustainable Land Use in Slovakia

The purpose of soil monitoring system in Slovakia is better to protect the soils with regard to sustainable land use. The main objective is the observation of soil properties concerning the main threats to soil： soil contamination, salinisation and sodification, decline in soil organic matter （SOM）, soil compaction and erosion. Soil monitoring system in Slovakia is consistently running since 1993. Its importance consists of providing the information on changing spatial and temporal variations of soil parameters as well as the evolution of soil quality in topsoil and subsoil. Soil monitoring network in Slovakia is constructed using ecological principles, taking into account all main soil types and subtypes, SOM, climatic regions, emission regions, polluted and non-polluted regions as well as various land use. The results of soil monitoring of 318 sites on agricultural land in Slovakia have been presented. Soil properties are evaluated according to the main threats to soil relating to European Commission recommendation for European soil monitoring performance as follows： soil contamination, soil salinization and sodification, decline in SOM, soil compaction and erosion. The most significant change has been determined in physical properties of soils. The physical degradation was especially manifested in compacted and the eroded soils. About 50% of agricultural land is potentially affected by soil erosion in Slovakia. In addition, decline in SOM and available nutrients indicate the serious facts on evaluation and extension of soil degradation processes during the last period in Slovakia. Obtained measured data and required outputs are reported to Joint Research Centre （JRC） in lspra （Italy） and European Environmental Agency （EEA） in Copenhagen （Denmark）. Finally, soil monitoring system thus becomes a basic tool for protection of soils and sustainable land use as well as for the creation of legislatives not only in Slovakia, but in EU, too.     

Soil Organic Carbon Accumulation Increases Percentage of Soil Olsen-P to Total P at Two 15-Year Mono-Cropping Systems in Northern China

Soil organic carbon （SOC） and soil Olsen-P are key soil fertility indexes but information on their relationships is limited particularly under long-term fertilization. We investigated the relationships between SOC and the percentage of soil Olsen-P to total P （PSOPTP） under six different 15-yr （1990-2004） long-term fertilizations at two cropping systems in northern China. These fertilization treatments were （1） unfertilized control （control）; （2） chemical nitrogen （N）; （3） N plus chemical P （NP）; （4） NP plus chemical potassium （NPK）; （5） NPK plus animal manure （NPKM） and （6） high NPKM （hNPKM）. Compared with their initial values in 1989 at both sites, during the 1 lth to 15th fertilization years annual mean SOC contents were significantly increased by 39.4-47.0% and 58.9-93.9% at Gongzhuling, Jilin Province, and Urumqi, Xinjiang, China, under the two NPKM fertilizations, respectively, while no significant changes under the no-P or chemical P fertilization. During the 1 lth to 15th fertilization years, annual mean PSOPTP was respectively increased by 2.6-4.2 and 5.8-14.1 times over the initial values under the two chemical P fertilizations and the two NPKM fertilizations, but was unchanged in their initial levels under the two no-P fertilizations at both sites. Over the 15-yr long-term fertilization SOC significantly positively correlated with PSOPTP （r^2=0.55-0.79, P〈0.01）. We concluded that the combination of chemical P plus manure is an effective way to promote SOC accumulation and the percentage of soil Olsen-P to total P at the two mono-cropping system sites in northern China.     

Effects of Elemental Sulphur and Farmyard Manure on pH and Salinity of Calcareous Sandy Loam Soil and Some Nutrient Elements in Tomato Plant

The objective of this study was to evaluate the effects of elemental sulphur （S） and farmyard manure on soil pH, EC and N, S, P concentrations of tomato grown in a calcareous sandy loam soil. For this purpose, a pot experiment was conducted in greenhouse conditions. Sulphur was applied at 0, 50, 100, 150, 200, 400 mg kg~ and farmyard manure at 0, 3 ton da^-1 to the soil. Three weeks after applications, tomato seedlings were planted and 8 weeks later, the plants were harvested to determine N, S, P concentrations and dry matter yield. Soil pH and EC were determined in the soil samples taken at 3 different periods. Effects of sulphur and farmyard manure applications were not significant on N, P concentrations and dry matter yield of tomato plant. S concentration of tomato plant was increased by sulphur alone. Soil pH was decreased and soil EC was increased in both 2^nd and 3^rd soil sampling period by the sulphur applications. As a result of farmyard manure application, soil pH decreased in the 2^nd soil sampling period but increased in the 3^rd soil sampling period. Also, soil EC was significantly increased in 1^st and 3^rd soil sampling period. Farmyard manure had no significant effect on S supply to tomato plant. The N：S ratio of tomato plant was decreased by sulphur alone. However, the sulphur with farmyard manure applications decreased N：S ratio in lesser extend compared to the S applications.     

黄土高原陡坡耕地土壤侵蚀对土壤性质的影响

以137Cs示踪技术和室内分析的方法研究了黄土高原北部陡坡耕地土壤侵蚀对土壤养分流失的数量、变化规律及影响因素。结果表明,黄土高原陡坡耕地的土壤侵蚀对土壤中有机质、有效P的含量变化有很大影响,即随着土壤侵蚀速率的增大,土壤中有机质、有效P的含量也明显降低,对有效N的影响无明显规律,土壤侵蚀对土壤养分含量变化的影响规律是:有机质>有效P>有效N。土壤中较大颗粒(1—0.25mm)及细颗粒(<0.001mm)的含量随着土壤侵蚀的增加而呈下降趋势。坡度变化是影响该地区土壤养分流失变化的主导因子,在整个山坡的坡度范围内,随着坡度的增加,土壤的侵蚀速率也增大,土壤中有机质及有效P的含量也逐渐降低。     

黄土高原半干旱区旱作农田土壤干燥化研究

为了揭示黄土高原半干旱区旱作农田土壤干燥化发生规律,为黄土高原旱作农田土壤水分可持续利用和当地粮食生产的可持续发展提供科学依据,在黄土高原半干旱区固原、定西和海原3个有代表性的区域实地观测了不同类型旱作农田的深层土壤湿度,分析了旱作农田的土壤干燥化发生规律和土壤干层分布特征。结果表明:(1)黄土高原半干旱区固原、定西和海原各类农田0～600cm土层土壤湿度平均值分别为11.46%、14.37%、9.27%,各类农田土壤湿度均明显低于其土壤稳定湿度值,均发生了不同程度的土壤干燥化现象;(2)固原高产麦田和高产马铃薯田土壤干层厚度分别比低产农田土壤干层厚120cm和260cm;海原高产麦田和高产马铃薯田比低产农田土壤干层厚度厚20cm和80cm。黄土高原半干旱区随着旱作粮田产量的提高,农田深层土壤湿度逐渐降低,土壤干层逐渐加深和加厚。     

Soil Salinization in Some Irrigated Areas of the Kingdom of Bahrain

Monitoring and assessment of agricultural land degradation is of vital importance for better land and water management planning and reclamation. It requires setting baseline information and basic analysis at specific time and space. About 33 geo-referenced soil sampling spots were selected in two agricultural production locations in the Kingdom of Bahrain to assess the status and preliminary causes of land degradation. Soil samples were taken from 13 sites in Diraz location while 19 samples were taken from Budayyi location. The samples were taken to 90 cm depth at 30 cm intervals. Standard procedures were followed to determine soil physiochemical properties. In addition, field observations on farm condition, distance from the sea, method of irrigation and irrigation water source were taken. Some of the soil samples were deliberately taken from outside the irrigated basins among trees compared with samples taken from inside the actively growing area for comparison. The results indicated that the salinity level was significantly （P 〈 0.001） higher at the 0-30 cm soil depth compared with 30-60 cm or 60-90 cm depths in both locations. The distance from the sea did not show clear correlation with surface soil salinity in Budayyi area compared with Diraz. Both locations showed significantly higher salinity levels on samples taken outside the actively growing areas compared with those taken from within. The effect is more prominent at the 0-30 cm depth. The observed variability on salinity levels may be attributed to farm management practices and deteriorating quality of ground water. Thus, agricultural land degradation in Bahrain cannot be attributed to ground water deterioration alone. The use of tertiary treated sewage water （TSE） may ease the pressure on ground water, but the pH of the TSE should be carefully monitored and managed with proper studies on leaching requirements to avoid further salinity complications.     

Soil Nitrous Oxide Emissions Under Maize-Legume Intercropping System in the North China Plain

Many studies have focused on various agricultural management measures to reduce agricultural nitrous oxide （N2O） emission. However, few studies have investigated soil N2O emissions in intercropping systems in the North China Plain. Thus, we conducted a ifeld experiment to compare N2O emissions under monoculture and maize-legume intercropping systems. In 2010, ifve treatments, including monocultured maize （M）, maize-peanut （MP）, maize-alfalfa （MA）, maize-soybean （MS）, and maize-sweet clover （MSC） intercropping were designed to investigate this issue using the static chamber technique. In 2011, M, MP, and MS remained, and monocultured peanuts （P） and soybean （S） were added to the trial. The results showed that total production of N2O from different treatments ranged from （0.87＆#177;0.12） to （1.17＆#177;0.11） kg ha-1 in 2010, while those ranged from （3.35＆#177;0.30） to （9.10＆#177;2.09） kg ha-1 in 2011. MA and MSC had no signiifcant effect on soil N2O production compared to that of M （P＆lt;0.05）. Cumulative N2O emissions from MP in 2010 were signiifcantly lower than those from M, but the result was the opposite in 2011 （P＆lt;0.05）. MS signiifcantly reduced soil N2O emissions by 25.55 and 48.84%in 2010 and 2011, respectively （P＆lt;0.05）. Soil N2O emissions were signiifcantly correlated with soil water content, soil temperature, nitriifcation potential, soil NH4＋, and soil NO3-content （R2=0.160-0.764, P＆lt;0.01）. A stepwise linear regression analysis indicated that soil N2O release was mainly controlled by the interaction between soil moisture and soil NO3-content （R2=0.828, P＆lt;0.001）. These results indicate that MS had a coincident effect on soil N2O lfux and signiifcantly reduced soil N2O production compared to that of M over two growing seasons.