Soil nitrate accumulation, leaching and crop nitrogen use as influenced by fertilization and irrigation in an intensive wheat–maize double cropping system in the North China Plain

There is a growing concern about excessive nitrogen (N) and water use in agricultural systems in North China due to the reduced resource use efficiency and increased groundwater pollution. A two-year experiment with two soil moisture by four N treatments was conducted to investigate the effects of N application rates and soil moisture on soil N dynamics, crop yield, N uptake and use efficiency in an intensive wheat–maize double cropping system (wheat–maize rotation) in the North China Plain. Under the experimental conditions, crop yield of both wheat and maize did␣not␣increase significantly at N rates above 200 kg N ha⁻¹. Nitrogen application rates affected little on ammonium-N (NH₄-N) content in the 0–100 cm soil profiles. Excess nitrate-N (NO₃-N), ranging from 221 kg N ha⁻¹ to 620 kg N ha⁻¹, accumulated in the 0–100 cm soil profile at the end of second rotation in the treatments with N rates of 200 kg N ha⁻¹ and 300 kg N ha⁻¹. In general, maize crop has higher N use efficiency than wheat crop. Higher NO₃-N leaching occurred in maize season than in wheat season due to more water leakage caused by the concentrated summer rainfall. The results of this study indicate that the optimum N rate may be much lower than that used in many areas in the North China Plain given the high level of N already in the soil, and there is great potential for reducing N inputs to increase N use efficiency and to mitigate N leaching into the groundwater. Avoiding excess water leakage through controlled irrigation and matching N application to crop N demand is the key to reduce NO₃-N leaching and maintain crop yield. Such management requires knowledge of crop water and N demand and soil N dynamics as they change with variable climate temporally and spatially. Simulation modeling can capture those interactions and is considered as a powerful tool to assist in␣the␣future optimization of N and irrigation managements. Section Editor: L. Wade     

Consecutive seasonal effect on yield and water productivity of drip deficit irrigated sorghum in saline soils

Drought stress destructively affects the growth and productivity of sorghum crop, especially under saline soils. Therefore, Field trials were performed to determine the influence of water stress on water productivity (water productivity for grain, (G-WP) and water productivity for forage, (F-WP), yield of sorghum and soil properties in salt-affected soil (8.20 dS m^?1) under different sowing dates and irrigation regimes. The summer sowing (SS) was performed on 1 April while fall sowing (FS) was established on 2 August. The irrigation regimes were; 100, 90, 80, and 70% of crop evapotranspiration (ETc). The findings displayed that the fodder and grain yields were increased by 23% and 26% under SS compared to FS over the two seasons 2017 and 2018, respectively. Among irrigation levels, the maximum values of grain and fodder yield were given by 100% of ETc, while a non-significant difference was observed between 100% and 90% of ETc. Moreover, the maximum values of G-WP (1.31%) and F-WP (9.00%) were recorded for 90% of ETc. Interestingly, the soil salinity was decreased in 0–0.6 m depth, and more decline was noted in 0–0.2 m depth using 90% of ETc. The highest salt accumulation withinside the soil profile was recorded under 70% of ETc in comparison to 100% of ETc. Thereupon, under water scarcity, application of 90% of ETc is recommended with SS to save 10% of the applied irrigation water without a significant decrease in grain yield (GY).     

Effects of irrigation frequencies on soil salinity and crop water productivity of fodder maize

This study was carried out at the experimental station of Department of Irrigation and Drainage, Sindh Agriculture University, Tandojam to investigate the effect of different irrigation frequencies on soil salinity and crop productivity. Four irrigation frequencies i.e. Irrigation after 7 days (T1)_, Irrigation after 14 days (T2), Irrigation after 21 days (T3), and Irrigation after 28 days (T4) were applied to fodder maize. The results showed significant effect of treatments on soil salinity. The EC of soil slightly increased under all treatments for all depths as compared to pre-treatments. At treatment T1, the salt amount was most noticeable and the highest EC (1.85) was observed at top surface of soil while the lowest (1.65) EC was observed under T4 at the comparable depth however, EC decreased at deeper depths under all treatments. The pH, SAR and ESP of soil decreased at all treatments however this decrease was more pronounced under T1 as compared to other treatments. The highest SAR was observed under T4 (9.40) while the lowest (8.00) under T1 for the matching depths. Similarly, the highest ESP was observed under T4 (11.40) while the lowest (10.15) under T1 for the similar depths. The results on the analysis of variance were non-significant between soil salinity parameters observed for pre-experiment. However, the results of analysis of variance on pH, EC, SAR and ESP showed significant differences between treatments in the post experiment. The maximum plant height, stem girth, number of leaves per plant and fodder yield were observed when the maize fodder was irrigated with a 7 day frequency and it was followed by other irrigation frequencies. Similarly, crop water productivity was 4.5, 4.2, 3.9 and 3.0 kg m⁻³ under T1, T2, T3, and T4 treatments, respectively. These results revealed that T1 produced the maximum crop water productivity as compared to rest of the treatments. The farming community is thus recommended to apply irrigation, to maize fodder crop, with 7 day frequency in order to get maximum fodder yield.     

Microbial contamination of vegetable crop and soil profile in arid regions under controlled application of domestic wastewater

Increasing lack of potable water in arid countries leads to the use of treated wastewater for crop production. However, the use of inappropriate irrigation practices could result in a serious contamination risk to plants, soils, and groundwater with sewage water. This research was initiated in view to the increasing danger of vegetable crops and groundwater contamination with pathogenic bacteria due to wastewater land application. The research was designed to study: (1) the effect of treated wastewater irrigation on the yield and microbial contamination of the radish plant under field conditions; (2) contamination of the agricultural soil profile with fecal coliform bacteria. Effluent from a domestic wastewater treatment plant (100%) in Jeddah city, Saudi Arabia, was diluted to 80% and 40% with the groundwater of the experimental site constituting three different water qualities plus groundwater as control. Radish plant was grown in two consecutive seasons under two drip irrigation systems and four irrigation water qualities. Upon harvesting, plant weight per ha, total bacterial, fecal coliform, fecal streptococci were detected per 100 g of dry matter and compared with the control. The soil profile was also sampled at an equal distance of 3 cm from soil surface for fecal coliform detection. The results indicated that the yield increased significantly under the subsurface irrigation system and the control water quality compared to surface irrigation system and other water qualities. There was a considerable drop in the count of all bacteria species under the subsurface irrigation system compared to surface irrigation. The bacterial count/g of the plant shoot system increased as the percentage of wastewater in the irrigation water increased. Most of the fecal coliform bacteria were deposited in the first few centimeters below the column inlet and the profile exponentially decreased with increasing depth.     

Influence of soil texture and crop management on the productivity of miscanthus (Miscanthus × giganteus Greef et Deu.) in the Mediterranean

Biomass productivity is the main favorable trait of candidate bioenergy crops. Miscanthus × giganteus is a promising species, due to its high‐yield potential and positive traits including low nutrient requirements and potential for C sequestration in soils. However, miscanthus productivity appears to be mostly related to water availability in the soil. This is important, particularly in Mediterranean regions where the risk of summer droughts is high. To date, there have been no studies on miscanthus responses under different soil conditions, while only a few have investigated the role of different crop managements, such as irrigation and nitrogen fertilization, in the Mediterranean. Therefore, the effects of contrasting soil textures (i.e. silty‐clay‐loam vs. sandy‐loam) and alternative agricultural intensification regimes (i.e. rainfed vs. irrigated and 0, 50, 100 kg ha^?1 nitrogen fertilization), on miscanthus productivity were evaluated at three different harvest times for two consecutive years. Our results confirmed the importance of water availability in determining satisfactory yields in Mediterranean environments, and how soil and site characteristics strongly affect biomass production. We found that the aboveground dry yields varied between 5 Mg ha^?1 up to 29 Mg ha^?1. Conversely, nitrogen fertilization played only a minor role on crop productivity, and high fertilization levels were relatively inefficient. Finally, a marked decrease, of up to ?40%, in the aboveground yield occurred when the harvest time was delayed from autumn to winter. Overall, our results highlighted the importance of determining crop responses on a site‐by‐site basis, and that decisions on the optimal harvest time should be driven by the biomass end use and other long‐term considerations, such as yield stability and the maintenance of soil fertility.     

A methodology for measuring drainage and nitrate leaching in unevenly irrigated vegetable crops

The objective of our study was to establish a methodology to determine drainage and nitrate leaching in unevenly irrigated vegetable crops. It was conducted in a tomato crop (Lycopersicum esculentum Mill) with drip irrigation in the summer of 2000 in the Ebro Valley, Spain. Two soil management techniques and two irrigation treatments were evaluated bare soil (S1) and soil mulched with black plastic (S2), with irrigation calculated according to the Crop Evapotranspiration (ETc) for bare soil (R1) and for mulched soil (R2). Volumetric soil water content (θv) was measured weekly to 1 m depth in six positions transverse to the drip line. Drainage was calculated by applying the water balance equation to the data from: (i) all six positions (method 1) and (ii) to the positions located under the plants and between the rows, respectively (method 2). Soil solution was extracted at 1 m depth with porous ceramic cups and analysed for nitrate. Nitrate leached to 1 m depth was calculated as the product of volume of drainage accumulated weekly and the nitrate concentration of the soil solution. Drainage and nitrate leaching were evaluated for two different crop periods crop establishment and crop growth. Method 2 produced results that were not significantly different from those from method 1. However, method 1 was more accurate and identified more differences between treatments. The greater drainage occurred during the crop establishment period, which also favoured the leaching of nitrates previously stored in the soil profile and later applied as fertilizer before planting. During establishment the crop was unable to use all available nitrate and the quality of groundwater deteriorated. The results suggest that further studies are required to adjust crop coefficients (Kc) to the actual needs of tomato crops grown with drip irrigation under bare soil and plastic mulching conditions.     

Cairo-East Bank effluent re-use study 3 — Effect of field crop irrigation with secondary treated wastewater on biological and chemical properties of soil and groundwater

Large scale field trials were conducted in fertile soil and desert (virgin) soil to evaluate the effect of irrigation with secondary treated wastewater from two wastewater treatment plants in Cairo on biological and chemical properties of soil and groundwater. Soil samples were taken for physical and chemical analysis after crop harvest. Groundwater monitoring wells were installed in and around the experimental soil sites. Considerable amounts of macronutrients (NPK) were applied to the grown crops through the treated wastewater irrigation: N (19–79%), P (23–181%) and K (85–357%) of the recommended fertilizer rates according to the crop and the experimental site. Soil physical and chemical analysis showed that both soils are widely variable in water holding capacity, organic matter, pH value, CaCO₃, salinity, cation exchange capacity, and soil bulk density in the topsoil (0–30 cm). Groundwater samples which were examined for the presence of pathogenic bacteria (salmonella), faecal coliform bacteria and helminth ova. At the virgin soil site, 10–57% of the samples from each well contained salmonella, whereas at the fertile soil, salmonella was not detected in five wells, and the occurrence in the other four wells was 10–20% of the samples. The numbers of faecal coliforms were similar at both sites, in the range 10²–10³ MPN per 100 mL. Small numbers of parasite ova were also found in the majority of wells, with a greater number occurring at the virgin soil. The groundwater in both sites was similar and of poor quality, and would be unsuitable for potable or irrigation purposes.     

Enhancing water use efficiency and grain yield of wheat by optimizing irrigation supply in arid and semi-arid regions of Pakistan

The lack of good irrigation practices and policy reforms in Pakistan triggers major threats to the water and food security of the country. In the future, irrigation will happen under the scarcity of water, as inadequate irrigation water becomes the requirement rather than the exception. The precise application of water with irrigation management is therefore needed. This research evaluated the wheat grain yield and water use efficiency (WUE) under limited irrigation practices in arid and semi-arid regions of Pakistan. DSSAT was used to simulate yield and assess alternative irrigation scheduling based on different levels of irrigation starting from the actual irrigation level up to 65% less irrigation. The findings demonstrated that different levels of irrigation had substantial effects on wheat grain yield and total water consumption. After comparing the different irrigation levels, the high amount of actual irrigation level in semi-arid sites decreased the WUE and wheat grain yield. However, the arid site (Site-1) showed the highest wheat grain yield 2394 kg ha^?1 and WUE 5.9 kg^?3 on actual irrigation (T₁), and with the reduction of water, wheat grain yield decreased continuously. The optimal irrigation level was attained on semi-arid (site-2) with 50% (T₁₁) less water where the wheat grain yield and WUE were 1925 kg ha^?1 and 4.47 kg^?3 respectively. The best irrigation level was acquired with 40% less water (T₉) on semi-arid (site-3), where wheat grain yield and WUE were 1925 kg ha^?1 and 4.57 kg^?3, respectively. The results demonstrated that reducing the irrigation levels could promote the growth of wheat, resulting in an improved WUE. In crux, significant potential for further improving the efficiency of agricultural water usage in the region relies on effective soil moisture management and efficient use of water.     

A county‐level estimation of renewable surface water and groundwater availability associated with potential large‐scale bioenergy feedstock production scenarios in the United States

This study examines fresh renewable water resources available for bioenergy feedstock production in the United States. The impacts of feedstock irrigation on surface and groundwater resources available to nonbioenergy sectors were quantified using a pair of water availability indexes: streamflow availability index and percolation flow availability index. The two metrics were applied to both historical (2008) and three possible future biomass production scenarios from the 2016 U.S. Billion‐Ton Report at the county level. For both historical and future scenarios, we found that the consumptive irrigation requirements for bioenergy feedstock account for <0.01% of annual streamflow in all but three counties in Nebraska. Results suggest that the irrigation demand of future biomass production could be supplied by annual renewable groundwater flow in about 94% of feedstock‐growing counties that use groundwater for irrigation, representing about 92% of production tonnage. Counties that require irrigation from nonrenewable groundwater resources are mostly located in the Northern Plains and Pacific regions. We also evaluated the sensitivity of crop water footprint estimation to soil moisture carryover by comparing blue water estimates from six different empirical and process‐based methods. Our findings suggest that accounting for preseason soil moisture is critical for representative blue water estimation, so that the irrigation water consumption is not overestimated. This is especially true in the Corn Belt region, where blue water estimates with and without preseason soil moisture would be about 1.9 versus 45.5 billion m³/year under the historical scenario. This difference is smaller in semiarid regions like the High Plains, but the blue water estimate can still triple if soil moisture is not considered. From the perspective of renewable surface water and groundwater resources, scaling feedstock production up in the High Plains and California will require careful planning integrated with water management strategies to improve water resource conservation.     

Arsenic uptake and accumulation in rice (Oryza sativa L.) irrigated with contaminated water

Long-term use of arsenic contaminated groundwater to irrigate crops, especially paddy rice (Oryza sativaL.) has resulted in elevated soil arsenic levels in Bangladesh. There is, therefore, concern regarding accumulation of arsenic in rice grown on these soils. A greenhouse pot experiment was conducted to evaluate the impact of arsenic-contaminated irrigation water on the growth and uptake of arsenic into rice grain, husk, straw and root. There were altogether 10 treatments which were a combination of five arsenate irrigation water concentrations (0–8 mg As l^–1) and two soil phosphate amendments. Use of arsenate containing irrigation water reduced plant height, decreased rice yield and affected development of root growth. Arsenic concentrations in all plant parts increased with increasing arsenate concentration in irrigation water. However, arsenic concentration in rice grain did not exceed the maximum permissible limit of 1.0 mg As kg^–1. Arsenic accumulation in rice straw at very high levels indicates that feeding cattle with such contaminated straw could be a direct threat for their health and also, indirectly, to human health via presumably contaminated bovine meat and milk. Phosphate application neither showed any significant difference in plant growth and development, nor in As concentrations in plant parts.     

咸水灌溉条件下土壤水盐分布特征

通过设置3种灌水量水平（100%ET_c、80%ET_c、60%ET_c）和3种灌水水质水平（0.7、3和6 g·L^-1）,研究了咸水灌溉条件下春小麦120 cm土层内水分动态和盐分累积特征.结果表明：水分在农田土壤中的分布主要受灌水量和土壤质地的影响,充分灌溉使水分存贮在较深土层中,而非充分灌溉则使水分存贮在表层;在相同灌水量的条件下,土体内的盐分积累程度随着灌溉水矿化度的增大而加剧;在相同矿化度条件下,土体内的盐分含量及积盐深度随着灌水量的增加而增大.在作物整个生育期内,连续使用咸水灌溉将导致土壤积盐,且非充分灌溉较充分灌溉更易使土壤表层积盐.     

Effect of Rural Sewage Irrigation Regime on Water-Nitrogen Utilization and Crop Growth of Paddy Rice in Southern China

Reclaimed water irrigation has become an effective mean to alleviate the contradiction between water availability and its consumption worldwide. In this study, three types of irrigation water sources (rural sewage’s primary treated water R1 and secondary treated water R2, and river water R3) meeting the requirements of water quality for farmland irrigation were selected, and three types of irrigation water levels (low water level W1 of 0–80 mm, medium water level W2 of 0–100 mm, and high water level W3 of 0–150 mm) were adopted to carry out research on the influence mechanismS of different irrigation water sources and water levels on water and nitrogen use and crop growth in paddy field. The water quantity indicators (irrigation times and irrigation volume), soil ammonium nitrogen (NH₄⁺-N) and nitrate nitrogen (NO₃⁻-N), rice yield indicators (thousand-grain weight, the number of grains per spike, and the number of effective spikes), and quality indicators (the amount of protein, amylose, vitamin C, nitrate and nitrite content) of rice were measured. The results showed that, the average irrigation volume under W3 was 2.4 and 1.9 times of that under W1 and W2, respectively. Compared with R3, the peak consumption of rice was lagged behind under R1 and R2, and the nitrogen form in 0–40 cm soil layers under rural sewage irrigation was mainly NH₄⁺-N. The changes of NO₃⁻-N and NH₄⁺-N in the 0–40 cm soil layer showed the trend of declining and then increasing. The water level control only had a significant effect on the change of NO₃⁻-N in the 60–80 cm soil layer. Both irrigation water use efficiency and crop water use efficiency were gradually reduced with the increase of field water level control. The nitrogen utilization efficiency under rural sewage irrigation was significantly higher than that under R3. Compared with the R3, rural sewage irrigation could significantly increase the yield of rice, and as the field water level rose, the effect of yield promotion was more obvious. It was noteworthy that the grain of rice under R1 monitored the low nitrate and nitrite content, but no nitrate and nitrite was discovered under R2 and R3. Therefore, reasonable rural sewage irrigation (R2) and medium water level (W2) were beneficial to improve nitrogen utilization efficiency, crop yield and crop quality promotion.

     

极端干旱条件下燕麦垄沟覆盖系统水生态过程

围绕极端气候条件下沟垄沟覆盖系统水文过程和水生产力变化问题开展两年的大田试验研究。以裸燕麦坝莜3号品种为材料,于2010年和2011年在甘肃定西进行,以充分灌溉为对照组,设置平地无种植、垄沟无覆膜种植、垄沟覆膜种植、裸地4个处理(此4个处理均无灌溉),测定生育期降雨、气温、0—140 cm土壤剖面水分变化、作物生长和产量等指标。结果表明,2010年和2011年分别为阶段性极端干旱和全生育期极端干旱两个类型,均导致所有处理组中土壤剖面60—100 cm的"土壤干层"现象,垄沟覆膜处理对"土壤干层"现象具有显著的缓解效应。与对照组相比,垄沟覆膜处理显著促进了收获期土壤剖面贮水量的回升,其贮水量分别提高了41.2 mm(2010年)和22.4 mm(2011年),全生育期水分利用效率和水生产力分别提高了1.7、0.4 kg·hm-2·mm-1(2010年)和6.5、9.8 kg·hm-2·mm-1(2011年)。另外,垄沟覆膜处理组的地上生物量比对照组降低了30.5%(2010年)和67.42%(2011年),但收获指数较对照分别提高了33.4%(2010年)和55.6%(2011年)。研究表明,垄沟覆膜处理促进了降水向土壤水和作物水的转化效率,显著地缓解了作物水分供需矛盾,是应对极端气候变化的重要生态策略。     

Silicon-mediated growth and yield improvement of sunflower (<Emphasis Type="Italic">Helianthus annus</Emphasis> L.) subjected to brackish water stress

Silicon is known to compensate crop yield losses under diverse biotic and abiotic stress conditions; however, reports about its protective role for plants exposed to brackish water stress are very limited. A pot culture experiment was conducted to assess the beneficial effect of silicon supplementation (0 and 100 mg/kg) in alleviating growth adversities of brackish water (saline, sodic, alkaline, and saline–sodic water) stress in two contrasting sunflower cultivars, SF-187 (salt tolerant), and Hysun-33 (salt sensitive) grown in greenhouse. Results demonstrated that hostile growth environments, mainly the combined stress of saline–sodic water, severely affected the physiological attributes, growth, yield, and yield contributing components in sunflower. However, the response to brackish water stress differed genotypically, with greater magnitude of damage to the Hysun-33 as compared to SF-187 genotype. It hampered plant growth due to membrane damage and reduced water uptake, but silicon supplementation minimized the negative effects of stress by limiting toxic Na⁺ ions uptake, improving membrane stability, and increasing relative water contents caused by higher silicon and K⁺ uptake that eventually led to improved biomass yield. The response was further evaluated at yield level and data regarding head diameter, achene yield, and 100 achene weight were taken. Results indicated that silicon supplementation to growth medium of saline and/or sodic water treated plants significantly enhanced the head diameter (22–30%), thus ultimately producing 15–25% higher achene yield, and weight of the biological harvest of both sunflower genotypes. Overall, the beneficial effect of silicon supplementation was more evident in Hysun-33 (salt sensitive) as compared to SF-187 (salt tolerant) genotype. Taken together, the results of this study suggest silicon fertilization as a potential strategy to increase crop productivity under brackish water stress; however, experimental trials at farmer field level should be conducted before setting any recommendations.     

The effect of brackish water irrigation on the above- and below-ground development of pollarded Acacia saligna shrubs in an arid environment

The regrowth capacity after pollarding of a short-rotation plantation of Acacia saligna (Labill.) H. Wendl. was investigated in a field trial. This shrub has been proposed as a provider of biomass (fuelwood and fodder) in an arid environment, using local marginal water resources such as surface runoff and brackish groundwater. The specific objective of this study was to examine the effects of water quality, irrigation frequency and annual runoff flooding onthe above- and belowground development of the pollarded shrubs. Treatments consisted of drip-irrigation with freshwater or brackish water, at low (twice a month) or high (weekly) frequency, with or without annual freshwater flooding, and on a well-watered basis (twice a week) without flooding. Each 15?×?5 m² plot contained four rows of four shrubs. After 5 years of growth, the shrubs were pollarded to a height of 1.5 m and during the subsequent year of regrowth, root development was monitored non-destructively using the minirhizotron, shoot growth was estimated from trunk cross-sectional area and allometric equations (obtained at the end of the measuring period by measurements and destructive sampling), and plant water status was monitored by measuring pre-dawn leaf water potential. Dry fodder (leaves and thin branches) production was between 3.50 and 9.75 t ha^?1 and dry wood was between 3.50 and 15.50 t ha^?1. The highest biomass production was obtained in the well-watered freshwater treatment, which also had the highest number of roots and highest predawn leaf water potential throughout the year. Shrubs irrigated with brackish water at low frequency without supplemental flooding produced the lowest yields. Water quality significantly affected shoot development only in the well-watered treatments although root development was reduced wherever brackish water was applied. Flooding the plots with freshwater once a year led to an increase in the number of roots outside the drip-irrigation zone, especially in brackish water treatments. A continued root growth with time was observed in all treatments even though the shoots were pollarded. In fact total root increments and aboveground biomass production were positively linearly related. Moreover the linear response of shoot and root increments to increasing water availability and not to water quality suggests that irrigation frequency was the main factor determining the regrowth capacity and amount of above- and belowground biomass production. Based on the above, runoff water and brackish groundwater could be used in a complementary manner for the sustainable production of fuelwood and fodder in a short-rotation plantation of this shrub.     

Short–rotation woody crops: A prospective method for phytoremediation of agricultural land at risk of salinisation in southern Australia?

Growing short–rotation woody crops (SRWC) in rotation with conventional agriculture (phase farming with trees) is a prospective method for ameliorating degraded soils, particularly those at risk from salinisation. This work details changes in soil water storage and crop and pasture growth in the first 2 years after harvesting SRWCs at two sites in Western Australia between 2002 and 2004.This trial has demonstrated that where the roots of SRWCs can penetrate deeply into the subsoil, it is possible to develop soil water deficits large enough to subsequently allow several decades of conventional agriculture before groundwater recharge is resumed. At one site, Eucalyptus polybractea dried the soil to 10 m, creating a soil water deficit of 1350 mm within 6 years of planting. It is estimated that annual crops and pasture could be grown at this site for 68 years before the soil again reaches field capacity. Further work is required to determine where in the landscape SRWCs can develop these large soil water deficits.Reduced soil fertility limited crop and pasture growth in the first year after the SRWC at one site, while reduced plant–available water limited crop and pasture growth for 2 years after the SRWC at the other. Monitoring is continuing to determine longer-term changes in soil water content and crop and pasture productivity.     

Deficit irrigation affects seasonal changes in leaf physiology and oil quality of Olea europaea (cultivars Frantoio and Leccino)

The olive tree is a traditionally nonirrigated crop that occupies quite an extensive agricultural area in Mediterranean-type agroecosystems. Improvements in water-use efficiency of crops are essential under the scenarios of water scarcity predicted by global change models for the Mediterranean region. Recently, irrigation has been introduced to increase the low land productivity, but there is little information on ecophysiological aspects and quality features intended for a sagacious use of water, while being of major importance for the achievement of high-quality products as olive oil. Therefore, deficit irrigation programmes were developed to improve water-use efficiency, crop productivity and quality in a subhumid zone of Southern Italy with good winter–spring precipitation. The response of mature olive trees to deficit irrigation in deep soils was studied on cultivars Frantoio and Leccino by examining atmospheric environment and soil moisture, gas exchange and plant water status, as well as oil yield and chemical analysis. Trees were not irrigated (rainfed) or subjected to irrigation at 66% and 100% of crop evapotranspiration (ET_C), starting from pit hardening to early fruit veraison. Improvements in the photosynthetic capacity induced by increasing soil water availability were only of minor importance. However, plant water status was positively influenced by deficit irrigation, with 66% and 100% of ET_C treatments hardly differing from one another though consistently diverging from rainfed plants. The effect of water stress on photosynthesis was mainly dependent on diffusion resistances in response to soil moisture. Leccino showed higher instantaneous water-use efficiency than Frantoio. Crop yield increased proportionally to the amount of seasonal water volume, confirming differences between cultivars in water-use efficiency. The unsaturated/saturated and the monounsaturated/polyunsaturated fatty acid ratios of the oil also differed between cultivars, while the watering regime had minor effects. Although irrigation can modify the fatty acid profile, polyphenol contents were scarcely affected by the water supply. Irrigation to 100% of ET_C in the period August–September might be advisable to achieve high-quality yields, while saving consistent amounts of water.     

再生(污)水灌溉生态风险与可持续利用

作为一个农业大国,水资源贫乏及地域分布不均匀造成了我国严重的农业用水危机。为缓解我国农业用水危机,污水灌溉及再生水灌溉已成为解决农业灌溉水源不足的一项重要措施。在总结污水灌溉及再生水灌溉生态风险的基础上,针对国内研究现状,分析了我国再生水灌溉利用的可行性。研究发现,再生水灌溉的污染风险远小于污水灌溉,且再生水灌溉还具有回用成本低、减少农作物生产成本等经济效益,以及减少污染物向水环境中排放、改善土壤质量等环境效益。与污水灌溉相比再生水在农业灌溉上具有较大的应用前景,应加大其推广与应用的力度。最后,根据国内外的研究现状,提出了一些再生水灌溉可持续管理措施及其安全利用的相关建议。     

微咸水滴灌对土壤酶活性、CO2通量及有机碳降解的影响

利用微咸水灌溉是解决干旱区水资源短缺的重要途径.通过田间小区滴灌试验,研究了不同矿化度微咸水(0.31、3.0、5.0 g·L^-1,NaCl浓度)对土壤过氧化氢酶、蔗糖酶、多酚氧化酶、β-葡萄糖苷酶和纤维素酶活性的影响,采用土壤碳通量和物料袋法研究了土壤CO₂通量和有机碳降解对微咸水滴灌的响应.结果表明: 微咸水(3.0 g·L^-1)处理下蔗糖酶、β-葡萄糖苷酶、纤维素酶的活性分别比淡水处理降低31.7%～32.4%、29.7%～31.6%、20.8%～24.3%,而土壤多酚氧化酶活性则随灌溉水矿化度提高而显著升高,在膜下微咸水、咸水处理多酚氧化酶较淡水处理提高2.4%、20.5%.土壤微生物生物量碳和微生物熵均随灌溉水矿化度提高呈降低趋势,而代谢熵则呈升高趋势.不同处理对土壤CO₂通量影响表现为淡水＞微咸水≥咸水,且膜下CO₂通量显著高于膜间(P<0.05),棉花吐絮期(9月20日)膜下淡水处理较咸水和微咸水处理的CO₂通量分别升高29.8%、28.2%,微咸水滴灌显著降低了土壤CO₂通量.不同矿化度微咸水滴灌对有机物(棉花和苜蓿秸秆)的降解率表现为淡水＞微咸水＞咸水,膜下有机物降解显著高于膜间.在培养第125天时,咸水、微咸水、淡水处理的膜间棉花秸秆回收率分别为39.7%、36.3%、30.5%,膜间苜蓿秸秆回收率分别为46.5%、36.5%、35.4%.微咸水灌溉明显抑制了北疆滴灌棉田土壤酶活性,造成土壤微生物量和CO₂通量下降,土壤有机物降解率降低,使绿洲农田土壤生物性状变差.     

微咸水滴灌对土壤酶活性、CO2通量及有机碳降解的影响

利用微咸水灌溉是解决干旱区水资源短缺的重要途径.通过田间小区滴灌试验,研究了不同矿化度微咸水(0.31、3.0、5.0 g·L^-1,NaCl浓度)对土壤过氧化氢酶、蔗糖酶、多酚氧化酶、β-葡萄糖苷酶和纤维素酶活性的影响,采用土壤碳通量和物料袋法研究了土壤CO₂通量和有机碳降解对微咸水滴灌的响应.结果表明: 微咸水(3.0 g·L^-1)处理下蔗糖酶、β-葡萄糖苷酶、纤维素酶的活性分别比淡水处理降低31.7%～32.4%、29.7%～31.6%、20.8%～24.3%,而土壤多酚氧化酶活性则随灌溉水矿化度提高而显著升高,在膜下微咸水、咸水处理多酚氧化酶较淡水处理提高2.4%、20.5%.土壤微生物生物量碳和微生物熵均随灌溉水矿化度提高呈降低趋势,而代谢熵则呈升高趋势.不同处理对土壤CO₂通量影响表现为淡水＞微咸水≥咸水,且膜下CO₂通量显著高于膜间(P<0.05),棉花吐絮期(9月20日)膜下淡水处理较咸水和微咸水处理的CO₂通量分别升高29.8%、28.2%,微咸水滴灌显著降低了土壤CO₂通量.不同矿化度微咸水滴灌对有机物(棉花和苜蓿秸秆)的降解率表现为淡水＞微咸水＞咸水,膜下有机物降解显著高于膜间.在培养第125天时,咸水、微咸水、淡水处理的膜间棉花秸秆回收率分别为39.7%、36.3%、30.5%,膜间苜蓿秸秆回收率分别为46.5%、36.5%、35.4%.微咸水灌溉明显抑制了北疆滴灌棉田土壤酶活性,造成土壤微生物量和CO₂通量下降,土壤有机物降解率降低,使绿洲农田土壤生物性状变差.