Soil water dynamics and deep soil recharge in a record wet year in the southern Loess Plateau of China

Terrestrial water cycles are influenced by hydrologic and textural properties of the deep loess layer in the Loess Plateau. Analyses of soil water profile distributions are needed to understand the regional water cycle processes and to guide agricultural production and sustainability. The objective of this study was to quantify the extent of deep soil water recharge and soil water profile dynamics during 1987-2003, especially in a record wet year of 2003, in common cropping systems in a semiarid-subhumid region of the southern Loess Plateau. The Chinese Ecological Research Network (CERN) site and a long-term rotation experiment site in a flat tableland were selected for this study. Soil moisture profiles were measured by a neutron probe to a depth of 6 m in 2003. The precipitation of 954 mm at the Changwu County Meteorological Station in 2003 was 63.4% higher than the long-term average (584 mm), and was a record high since 1957. Although cropping systems affected deep soil water recharge, the persistent dry soil layer formed between 2- and 3-m depths in croplands, resulting from many years of intensive cropping, was fully replenished in all cropping systems in 2003. Further frequency analysis indicated that the desiccated layer between 2- and 3-m depths would be fully recharged at least once in about 10 years for all existing cropping systems excluding continuous alfalfa. This finding should alleviate concerns about the formation of a permanent deep-soil desiccation layer as well as its potential impact on the long-term sustainability of the existing intensive cropping systems in the region.     

Crop yield and soil water restoration on 9-year-old alfalfa pasture in the semiarid Loess Plateau of China

The alfalfa pastureland in the semiarid Loess Plateau region of Northwest China usually has dry soil layers. A field experiment was conducted from October 2000 to October 2004 to examine soil water recovery and crop productivity on a 9-year-old alfalfa pasture. This experiment included six treatments: alfalfa pasture for 10-14 years, a conventional farming system without prior alfalfa planting, and four alfalfa-crop rotation treatments. For the rotation treatments, after 9 years of alfalfa selected crops were planted from 2001 to 2004 in the following sequence: (1) millet, spring wheat, potatoes, peas; (2) millet, corn, corn, spring wheat; (3) millet, potatoes, spring wheat, corn; (4) millet, fallow, peas, potatoes. The results showed that dry soil layers occurred in alfalfa pasture. We then plowed the alfalfa pasture and planted different crops. The soil water gradually increased during crop growth in the experimental period. The degree of soil water recovery in the four alfalfa-crop rotation treatments was derived from comparison with the soil water in the conventional system. After 4 years, the soil water recovery from the alfalfa-crop rotation systems at 0-500 cm soil depth was 90.5%, 89.8%, 92.2% and 96.7%, respectively. Soil total N content and soil respiration rate were high in the alfalfa-crop rotation systems. The yields of spring wheat in 2002, peas in 2003 and potatoes in 2004 in the alfalfa-crop rotation systems were not significantly different from yields in the conventional system. In the alfalfa-crop rotation systems, the yields of spring wheat and peas were greatly influenced by rainfall and were lowest in the dry year of 2004; the yields of corn and potatoes had a direct relationship with water use and were lowest in 2003. In summary, soil water in dry soil layers can recover, and crop yields in the alfalfa-crop systems were equal to those of the conventional system.     

黄土高原西部不同集雨保水措施下土壤水分变异特征

选择黄土高原西部丘陵区典型生态恢复区域,采用中子仪测定研究了不同集雨保水措施下油松林土壤水分变化,明确了不同措施下土壤水分动态特征和雨季前后土壤水分的亏缺与补偿情况。结果表明:不同集雨保水措施下土壤储水量差异明显。坡面覆膜集雨措施下各个土层土壤含水率均大于其他措施下土壤含水率。7月份各措施下土壤储水亏缺均有不同程度的缓解,坡面覆膜集雨、坡面覆膜集雨与集水槽结合2种措施下0~100 cm土层土壤储水亏缺状态得到有效缓解。坡面覆膜集雨措施对于有效利用降水有显著作用;树穴覆膜对于表层土壤水分的恢复有负面影响,但对深层土壤保水作用明显;燕尾式聚流坑对提高降水利用率和缓解土壤储水亏缺状态效果不佳。     

内蒙古河套灌区荒地水盐运移规律模拟

该文以内蒙古河套灌区为背景展开荒地水盐运移规律研究。在田间试验基础上,分析荒地土壤水盐的运移机理,利用HYDRUS-1D模型对荒地土壤水盐的迁移规律进行了模拟。荒地做为灌区盐分的贮存地,成为灌区水盐平衡的重要调节因素,荒地水盐动态研究对于干旱灌区具有重要意义。结果表明,强蒸发是荒地水盐运移的原动力,5 cm土层EC值上升了66.10%,20 cm土层EC值上升了63.89%。荒地在作物生育期是积盐的过程,在秋浇期是流失盐分的过程。经检验,HYDRUS－1D模型对盐渍化地区荒地水盐在垂直方向运移的模拟具有较高的精度,为区域水盐管理和灌区的可持续发展提供科学依据。     

Numerical simulations of water movement in a subsurface drip irrigation system under field and laboratory conditions using HYDRUS-2D

Due to the decreasing availability of water resources and the increasing competition for water between residential, industrial, and agricultural users, increasing irrigation efficiency, by methods like subsurface drip irrigation (SDI) systems, is a pressing concern for agricultural authorities. To properly manage SDI systems, and increase the efficiency of the water/fertilizer use while reducing water losses due to evaporation, the precise distribution of water around the emitters must be known. In this paper, the Windows-based computer software package HYDRUS-2D, which numerically simulates water, heat, and/or solute movement in two-dimensional, variably-saturated porous media, was used to evaluate the distribution of water around the emitter in a clay loam soil. The simulation results were compared with two sets of laboratory and field experiments involving SDI with emitters installed at different depths, and were evaluated using the root-mean-square-error (RMSE). The RMSE at different locations varied between 0.011 and 0.045 for volumetric water contents, and between 0.98 and 4.36 cm for wetting dimensions. Based on these values, it can be concluded that the correspondence between simulations and observations was very good.     

土壤湿度指数在黄土高原的适宜性评价

利用1992—2000年间黄土高原地区逐月降雨量、实测土壤湿度数据,结合GIS遥感技术、相关分析等方法,对基于TU-Wien变化检测算法,从ERS散射计数据反演获取的土壤湿度指数(SWI)或表层土壤湿度(SSM),从点和面2个尺度进行了验证。结果表明,在不同的土地利用、土壤质地和地形条件下,SWI或SSM与降水呈正相关(P<0.01)。时间序列方面,降雨、实测值和SWI或SSM基本上呈现出相同的变化趋势;空间分布上,降水和SWI具有相似的分布特征。在点尺度上,选取的7个站点的SWI与降水呈正相关(P<0.01),SWI和实测值的相关性随土层深度加深而下降,仅在10cm处达到显著水平(P<0.01)。对表层10cm的实测数据而言,降水和SWI的相关性要好于其与实测值的相关性。在黄土高原区域尺度上,SWI或SSM能够较为准确地揭示该地区表层土壤湿度的演变和空间分布特征。有长达20年(1992—2011年)之久的数据积累,并且可以免费及时获取的SWI或SSM,对于大范围实测土壤湿度数据匮乏的黄土高原地区而言,是一种具有较高利用价值的土壤湿度监测数据产品。     

Soil water dynamics and water use efficiency in spring maize (Zea mays L.) fields subjected to different water management practices on the Loess Plateau, China

Soil water supply is the main limiting factor to crop production across the Loess Plateau, China. A 2-year field experiment was conducted at the Changwu agro-ecosystem research station to evaluate various water management practices for achieving favorable grain yield (GY) with high water use efficiency (WUE) of spring maize (Zea mays L.). Four practices were examined: a rain-fed (RF) system as the control; supplementary irrigation (SI); film mulching (FM); and straw mulching (SM) (in 2008 only). The soil profile water storage (W) and the crop evapotranspiration (ET) levels were studied during the maize growing season, and the GY as well as the WUE were also compared. The results showed that mean soil water storage in the top 200 cm of the profile was significantly (P < 0.05) increased in the SI (380 mm in 2007, 411 mm in 2008) and SM (414 mm in 2008) compared to the FM (361 mm in 2007, 381 mm in 2008) and RF (360 mm in 2007, 384 mm in 2008) treatments. The soil water content was lower at the end of growing season than before planting in the 60-140 cm part of the profile in both the RF and FM treatments. Cumulative ET and average crop coefficiency (K_c) throughout the whole maize growing season were significantly (P < 0.05) higher in the SI (ET, 501 mm in 2007, 431 mm in 2008; K_c, 1.0 in 2007, 0.9 in 2008) treatment than in the other treatments. Both FM and SI significantly improved the GY. The WUE were increased significantly (23-25%; P < 0.05) under the FM treatment. It was concluded that both SI and FM are beneficial for improving the yield of spring maize on the Loess Plateau. However, FM is preferable because of the shortage of available water in the area.     

Particle-size effects on soil temperature, evaporation, water use efficiency and watermelon yield in fields mulched with gravel and sand in semi-arid Loess Plateau of northwest China

Gravel and sand mulch is an effective practice in conserving soil and moisture. However, the proportion of different particle size in this kind of mulch layer is an important factor to be considered in order to obtain optimal results from this practice. From 2005 to 2007, a series of experiments including one with watermelon were conducted in the semi-arid Loess Plateau of northwest China to determine the influence of particle size and its proportion in mulch layer on soil temperature, evapotranspiration, water use efficiency (WUE) and watermelon (Citrullus lanatus L.) yield. The treatments in no-watermelon experiments included particle sizes classified as <0.3, 0.3-1, 1-2, 2-4, 4-6, 6-8 and 8-10 cm mesh size or various rates of 2-6 cm pebble accounting for 0, 10, 20, 30, 40, 50, 60 and 70% with 30% 1-2 cm gravel-sand in mulch layer (as well as correspondingly decreasing sand proportions). The watermelon experiment included three particle sizes, 0.3-1, 1-2 and 2-6 cm. Soil temperature at 8:00 h was highest for the 1-2 cm treatment, and the daily average temperature at 14:00 h was highest for the 0.3-1 cm treatment. Soil temperature decreased with particle size increasing due to porosity enlarging. The relationship between soil temperature and particle size followed a quadratic or cubic curve. Soil temperature was increased by gravel-sand mulch plus plastic film. The increment of soil temperature was larger especially for 1-4 cm particle size. In the gravel-sand mulch layer having different size particles, the greater percentage being of 2-6 cm pebbles, increases porosity, and lowers soil temperature, and causes more evaporation. The results of the watermelon experiment showed that soil moisture before seeding would not affect the yield during the years of using gravel mulch. Watermelon yield and WUE were higher for 1-2 and 0.3-1 cm treatments than 2-6 cm treatments in later experiments during 2006 and 2007. In conclusion, 2-6 cm large size particles would not account for much in gravel-sand mulching layer. It would be better if the percentage of 2-6 cm particles was less than 30%.     

Effect of temporal variability in soil hydraulic properties on simulated water transfer under high-frequency drip irrigation

The effect of changes in the hydraulic properties of a loamy topsoil on water transfer under daily drip irrigation was studied over a cropping cycle. Soil water contents were measured continuously with neutron probes and capacitance sensors placed in access tubes (EnviroSMART) and were compared to predications made by the Hydrus-2D model. Three different sets of hydraulic parameters measured before and after irrigation started, were used.Our results demonstrated that, based on the assumptions used in this study, the accuracy of the Hydrus predictions is good. Graphical and statistical comparisons of simulated and measured soil water contents and consequently the total water storage revealed a similar trend throughout the monitoring period for the all three different sets of parameters. The soil hydraulic properties determined after irrigation started were found to be much more representative of the majority of the irrigation season, as confirmed by the accuracy of the simulation results with high values of the index of agreement and with values of RMSE similar in magnitude to the error associated with field measurements (0.020 cm³ cm⁻³). The highest RMSE values (about 0.04 cm³ cm⁻³) were found when the model used input soil parameters measured before irrigation started.Generally, changes in topsoil hydraulic properties over time had no significant effect on soil moisture distribution in our agro-pedo-climatic context. One possible explanation is that daily water application was conducted at the same time as maximal root water uptake. This meant the soil did not need to store total daily crop water requirements and consequently that the water redistribution phase represented a very short stage in the irrigation cycle. It is probable that irrigating in the daytime when crop evapotranspiration is highest could prevent the effects of a temporal change and other problems connected with the soil. Moreover, water will be always available for the crop. Further experiments are needed to justify the results and to study the effects of low frequency drip irrigation on soil hydraulic characterization and consequently on soil water transfer in order to improve irrigation scheduling practices.     

Effects of conservation tillage practices on winter wheat water-use efficiency and crop yield on the Loess Plateau,China

In the semi-humid to arid loess plateau areas of North China, water is the limiting factor for rain-fed crop yields. Conservation tillage has been proposed to improve soil and water conservation in these areas. From 1999 to 2005, we conducted a field experiment on winter wheat (Triticum aestivum L.) to investigate the effects of conservation tillage on soil water conservation, crop yield, and water-use efficiency. The field experiment was conducted using reduced tillage (RT), no tillage with mulching (NT), subsoil tillage with mulching (ST), and conventional tillage (CT). NT and ST improved water conversation, with the average soil water storage in 0–200 cm soil depth over the six years increased 25.24 mm at the end of summer fallow periods, whereas RT soil water storage decreased 12 mm, compared to CT. At wheat planting times, the available soil water on NT and ST plots was significantly higher than those using CT and RT. The winter wheat yields were also significantly affected by the tillage methods. The average winter wheat yields over 6 years on NT or ST plots were significantly higher than that in CT or RT plots. CT and RT yields did not vary significantly between them. In each study year, NT and ST water-use efficiency (WUE) was higher than that of CT and RT. In the dry growing seasons of 1999–2000, 2004–2005 and the low-rainfall fallow season of 2002, the WUE of NT and ST was significantly higher than that of CT and RT, but did not vary significantly in the other years. For all years, CT and RT showed no WUE advantage. In relation to CT, the economic benefit of RT, NT, and ST increased 62, 1754, and 1467 yuan ha⁻¹, respectively, and the output/input ratio of conservation tillage was higher than that of CT. The overall results showed that NT and ST are the optimum tillage systems for increasing water storage and wheat yields, enhancing WUE and saving energy on the Loess Plateau.     

Yield and seasonal water productivity of sunflower as affected by tillage and cropping systems under dryland conditions in the Limpopo Province of South Africa

Sustainable food production in semi-arid tropical countries can be achieved through efficient utilization of rainwater. A field experiment to assess the grain yield, seasonal water use (WU), water use efficiency (WUE) and precipitation use efficiency (PUE) of sunflower (Helianthus annuus L.) intercropped with cowpea (Vigna unguiculata L.) on two tillage systems was conducted during the 2007/2008 and 2008/2009 cropping seasons at the University of Venda (22°58′ S, 30°26′ E at 596 m above sea level). The experiment was configured as a 2 × 2 × 2 factorial design with three replications. The tillage treatments were conventional tillage (CT) (control) and in-field rainwater harvesting (IRWH) system. The IRWH is a special crop production technique that promotes runoff on 2.0-m wide no-till strip between crop rows and collects the runoff water in basins where it infiltrates into the soil profile. The treatments in the cropping system (CS) consisted of a sole crop (sunflower or cowpea) and an intercrop (sunflower × cowpea). Results of the experiment revealed that IRWH led to a significant (P < 0.05) increase in sunflower grain yield in the second season but cowpea grain yield was not influenced by tillage systems. IRWH resulted in significantly higher WU, WUE and PUE of both crops compared to CT system in the second season. The CS had significant effects on sunflower grain yield in both seasons but none on the cowpea grain yield. WU was significantly higher in intercrops than in sole cowpea and sole sunflower in the first and second season, respectively. WUE and PUE were significantly greater in sole sunflower than in the intercrops but less in the sole cowpea than in the intercrops.     

Effects of rainfall harvesting and mulching technologies on water use efficiency and crop yield in the semi-arid Loess Plateau, China

In semi-arid areas, crop growth is greatly limited by water. Amount of available water in soil can be increased by surface mulching and other soil management practices. Field experiments were conducted in 2005 and 2006 at Gaolan, Gansu, China, to determine the influence of ridge and furrow rainfall harvesting system (RFRHS), surface mulching and supplementary irrigation (SI) in various combinations on rainwater harvesting, amount of moisture in soil, water use efficiency (WUE), biomass yield of sweet sorghum (Sorghum bicolour L.) and seed yield of maize (Zea mays L.). In conventional fields without RFRHS, gravel-sand mulching produced higher biomass yield than plastic-mulching or straw-mulching. In plastic-mulched fields, an increasing amount of supplemental irrigation was needed to improve crop yield. There was no effect of RFRHS without plastic-covered ridge on rainwater harvesting when natural precipitation was less than 5 mm per event. This was due to little runoff of rainwater from frequent low precipitation showers, and most of the harvested rainwater gathered at the soil surface is lost to evaporation. In the RFRHS, crop yield and WUE were higher with plastic-covered ridges than bare ridges, and also higher with gravel-sand-mulched furrows than bare furrows in most cases, or straw-mulched furrows in some cases. This was most likely due to decreased evaporation with plastic or gravel-sand mulch. In the RFRHS with plastic-covered ridges and gravel-sand-mulched furrows, application of 30 mm supplemental irrigation produced the highest yield and WUE for sweet sorghum and maize in most cases. In conclusion, the findings suggested the integrated use of RFRHS, mulching and supplementary irrigation to improve rainwater availability for high sustainable crop yield. However, the high additional costs of supplemental irrigation and construction of RFRHS for rainwater harvesting need to be considered before using these practices on a commercial scale.     

Effects of gravel-sand mulch, plastic mulch and ridge and furrow rainfall harvesting system combinations on water use efficiency, soil temperature and watermelon yield in a semi-arid Loess Plateau of northwestern China

In the northwestern Loess Plateau of China, low precipitation results in poor crop yields, with a great fluctuation from year to year. The adoption of gravel-sand mulching has shown improvements in the growth of crops such as watermelon. The ridge and furrow rainwater harvest system (RFRHS) has been shown as an easy and efficient way to collect rainwater. A field experiment was conducted from 2007 to 2009 at Gaolan, Lanzhou, Gansu, China, to measure the effects of RFRHS, plastic mulch and gravel-sand mulch combinations on soil temperature, evapotranspiration (ET), water use efficiency (WUE) and watermelon yield. There were eight treatments: (1) flat gravel-sand mulched field, (2) RFRHS with a sand mulched furrow, entire plastic mulch and the ratio 1:1 of ridge and furrow, (3) RFRHS with a sand mulched furrow, entire plastic mulch and the ratio 4:3 of ridge and furrow, (4) RFRHS with a sand mulched furrow, entire plastic mulch and the ratio 5:3 of ridge and furrow, (5) RFRHS with a sand and plastic mulched furrow, bare ridge and the ratio 4:3 of ridge and furrow, (6) RFRHS with an entire plastic mulch and the ratio 4:3 of ridge and furrow, (7) conventional ridge planting with a plastic mulched ridge, and (8) flat gravel-sand mulched field plus 23 mm supplementary irrigation. Soil temperature for RFRHS with a gravel-sand plus plastic mulched furrow was slightly lower than that of flat gravel-sand mulch. The RFRHS caused a significant increase in watermelon yield and WUE. The increase in watermelon yield and WUE was greatly influenced by the ratio of ridge and furrow when RFRHS was combined with gravel-sand mulch. Watermelon yield was highest for the 1:1 ratio, and WUE was highest for the 5:3 and 1:1 ratios of ridge:furrow, and these were significantly greater than that of flat gravel-sand mulch, without or with irrigation. The use of ridge with plastic film mulch increased the beneficial effect of RFRHS on yield. The watermelon yield and WUE for non-plastic-mulched ridge were even lower than that of flat gravel-sand mulch. In summary, the findings suggest that RFRHS with gravel-sand mulched furrow plus plastic film mulch, and 1:1 ratio of ridge:furrow, would facilitate the use of limited rainfall most efficiently in improving watermelon yield, by reducing ET and increasing WUE in this semiarid region.     

新疆地下滴灌棉田一次性滴灌带埋深数值模拟与分析

由于灌水频率高、定额小,在新疆地区大面积应用膜下滴灌进行棉花种植时,常出现根系分布浅、植株易早衰等影响产量的问题,灌水湿润区域相对较深的地下滴灌可能是解决上述问题的方法之一。但因顾及机械耕作和多次使用,传统地下滴灌带通常埋深较大,致使苗期灌水及管理维护极其不便。随着工艺水平提高和生产成本降低,地下滴灌生产实际中采用一次性滴灌带已成为可能,本研究通过数值模拟方法来探讨地下滴灌一次性滴灌带的合理埋深问题。为了验证所建立的数值模型和选用的土壤物理参数,首先在新疆玛纳斯地区开展了地下滴灌田间试验,继而采用HYDRUS-2D/3D软件对该试验条件下的土壤水盐动态进行了模拟。结果表明,模拟值与实测值之间整体吻合较好,其中土壤含水量分布的平均绝对误差Me和均方根差Rm分别不高于0.034、0.040 cm~3/cm~3,相关系数R最小值为0.8,Nash效率系数Ns在0.34~0.62之间;含盐量Me、Rm也分别不超过3.31、4.24 g/kg,R最小值为0.6,Ns在-0.06~0.38之间,相关模型和参数较为合理可靠。在此基础上,对该地区不同滴灌带埋深(分别设为5、15、30 cm)情景下灌水过程中的水盐运动规律进行了进一步模拟与分析,结果表明:不同埋深导致土壤淡化和积盐区域分布不同,淡化区域主要集中在滴灌带附近,在远离滴灌带的湿润锋边缘出现积盐;随着滴灌带埋深加大,土面蒸发损失逐渐降低,但对表层土壤供水能力也相应减弱;综合考虑回收利用、棉花苗期水分供应、根区淡化脱盐需求及单方水的淡化脱盐效率等因素,当地地下滴灌棉田一次性滴灌带不宜埋设过深,建议布置在15 cm左右。     

黄土丘陵区土壤粒径分布单重分形和多重分形特征

利用单重分形和多重分形方法定量分析黄土丘陵区土壤粒径分布(PSD)特征,同时分析土地利用方式对PSD分形参数的影响。结果表明:研究区PSD呈现出非均匀分布,具有多重分形特征,PSD多重分形谱f(α)-α为不对称的上凸曲线。容量维数D0与土壤质地相关性不明显,信息维数D1、关联维数D2和多重分形谱宽Δα均与粘粒体积分数呈极显著正相关(P<0.01)。土地利用方式对粘粒、粉粒、砂粒体积分数和Dsilt值有显著影响(P<0.01)。多重分形分析为详细描述PSD提供了精确的方法和途径。     

A comparison of the water use of tree belts and pasture in recharge and discharge zones in a saline catchment in the Central West of NSW, Australia

Planting trees has been proposed as part of the solution to dryland salinity in Australia. The best location in the landscape and the spatial arrangement of trees however, is difficult to determine. This paper presents a case study of a field experiment that compared the water use of tree belts with that of pastures in recharge and discharge areas of a first order catchment in the Central West of NSW, Australia.The recharge tree belt and both pasture sites used very similar amounts of water but the discharge tree belt used double the water of the other three land uses by accessing groundwater. The discharge tree belt operated in an energy-limited environment, transpiring at a rate equivalent to atmospheric demand whereas the other three land uses were all water-limited. From a land management point of view, the establishment of more trees on the discharge site would have the biggest impact on reducing saline discharge and the least impact on the agricultural operations.     

Comparison of soil water content and corn yield in furrow and conventional ridge sown systems in a semiarid region of China

Water deficits and unusually warm soil temperatures can adversely affect conventional ridge sown systems. Increasingly serious water and temperature issues associated with global climate change may be problematic in the future, particularly in semiarid regions. This study explored the soil water and crop yield benefits of switching the sowing location of corn from ridges to furrows. Experiments were conducted over three years. Corn was grown in shallow furrow (SF) and deep furrow (DF) sown treatments until the V8 stage (eight visible leaf collars). New ridges were then built over the existing furrows. Grain yield was found to be higher in the SF and DF sown treatments than in a conventional ridge sown treatment (CR), especially in drought years. Switching sowing position from ridge to furrow could increase corn yield, directly, by improving soil moisture early in the growing season and, indirectly, by stimulating the growth of resource-capturing organs (e.g., leaves and roots). This simple and efficient approach to crop production in semiarid climates may be practical for the management of numerous agricultural systems, particularly those that are resource-limited, with greater vulnerability to the effects of global climate change.     

Life Cycle Assessment of biomass production in a Mediterranean greenhouse using different water sources: Groundwater, treated wastewater and desalinated seawater

An experimental biomass crop of Nicotiana tabacum was grown over a nine-month period inside a greenhouse situated in Almería, south-eastern Spain. Two irrigation methods corresponding to treated urban wastewater and groundwater, were arranged. No significant differences were observed in the total biomass produced on the treated wastewater and groundwater plots, which ranged from 17 to 28 kg m⁻², depending on plant density. Environmental Life Cycle Assessment (LCA) was applied in order to gain knowledge of the potential impacts of using either treated wastewater, groundwater, or desalinated water for irrigation. The LCA study included all the processes involved in agricultural production up to the final plant cutting. Since desalinated water was not actually used in the experiment, the experimental data from tobacco irrigated with groundwater was used in the LCA. Impact categories included were: global warming; acidification; water eutrophication; primary energy use; as well as aquatic and terrestrial ecotoxicity. Special attention was put on the ecotoxicity of emerging and priority pollutants in treated wastewater, as well as on soil quality impacts, namely soil organic carbon deficit and soil salinisation. The results show that using desalinated water leads to higher environmental impacts in several impact categories, including global warming, energy use, soil quality, and aquatic ecotoxicity. As an example, primary energy use increases by 80% and 50% as compared to using treated wastewater and groundwater, respectively. On the other hand, wastewater pollutants in irrigation water may involve a relevant contribution to terrestrial ecotoxicity. For this reason, the impact score of the wastewater-irrigated crop is 23% and 35% higher as compared to the crop using desalinated water and groundwater, respectively.     

A study of the effect of the interaction between site-specific conditions, residue cover and weed control on water storage during fallow

In the semiarid central region of Argentina the probability that rainfall meets crop requirements during growing season is less than 10%, therefore fallowing has been the most important practice to assure water availability during the growing season. Various site-specific and management factors have been identified as crucial for defining fallow efficiency (FE) and final available water contents (AW). The objective of the present study was to improve our knowledge about the interactions between residue cover, weed control, soil profile depth and water storage capacity (WSC) on FE. In 10 sites covering the environments of calcareous plains and sandy plains of the semiarid central region of Argentina and with different WSC, experiments with 3 different levels of residue cover (H, M, L) and with and without weed control (C and W respectively) during fallow were set up. A completely randomized block design with four repetitions and splits plots to consider weed control was used. Soil texture and organic matter were determined in samples of the A horizon (0.20 m). Bulk density, field capacity, permanent wilting point and soil water contents (monthly frequency) were measured at depth intervals of 0.20 m to the depth of the calcite layer or to 2.00 m depth. Soil temperature was taken in weekly intervals at 0.05 m depth and weed plants, separated by species, were counted at the end of fallow in 4 repetitions of 0.25 m² in each treatment. An empirical model was developed to predict final AW under these experimental conditions. Model parameters were: Residue level, weed control, WSC, profile depth, and rainfall during fallow. Site-specific conditions (WSC and profile depth) affected water storage during fallow; soils with highest values for both parameters showed highest final AW. Weed density was the most important factor that controlled AW, with on average 35 mm less AW in W than in C treatments. Residue level had a positive effect on final AW in both C and W treatments, with a difference of 18.5 mm between H and L. An interaction between residue level and weed density was observed, indicating weed suppression in H treatments. This was also confirmed by correspondence analysis between residue level and weed species which revealed that different species were related to each level. High residue levels also decreased soil temperature, thus affecting germination of post-fallow crops. The empirical model had an overall average prediction error of 13.7% and the regression between measured and predicted values showed a determination coefficient of 0.77.     

Econometric analysis of the determinants of adoption of rainwater harvesting and supplementary irrigation technology (RHSIT) in the semiarid Loess Plateau of China

Using a binary logistic regression model, this paper evaluates the determinants of farmers’ decisions to adopt rainwater harvesting and supplementary irrigation technology (RHSIT) and its elasticity of adoption in the rain-fed farming systems, based on a survey of 218 farmers in the semiarid areas of Loess Plateau in 2005. The results indicate that 12 variables are significant in explaining farmers’ adoption decisions. Farmers’ educational background, active labor force size, contact with extension, participation in the Grain-for-Green project, and positive attitudes towards RHSIT are some of the variables that have significantly positive effects on adoption of RHSIT, while farmer's age and distance from water storage tanks to farmers’ dwellings have significantly negative correlation with adoption. The probability of adoption also increases with increased targeting of institutional variables: credit obtained, assistance obtained, and technical training received. Farmers in villages that have more erosion problems are more likely to adopt RHSIT. Besides, the model indicates that a 1 unit increase in the diversity of irrigated crops grown by a household, especially high-value crops, results in a 6.98 times increase in the probability of RHSIT adoption. Variables such as family size, off-farm activity, level of family income, risk preference, and land tenure do not significantly influence adoption. This information will help prioritize the factors that affect adoption decisions and provide insight on pathways to increase the adoption of RHSIT.