Spatial and temporal projected distribution of four crop plants in Egypt

This study focuses on the management of the local agroecosystems in order to adapt planting or sowing practices for the projected climate change scenarios. It is projected that there will be increased air temperature throughout all four seasons in the coming 100 years, from the southern towards the northern parts of Egypt. The objective of this study is to investigate the influence of that increased air temperature on the spatial and temporal distribution of four of the major economic crops in Egypt. The study species are cotton (Gossypium barbadense L., cv. Giza 89), wheat (Triticum aestivum L., cv. Gemiza 9), rice (Oryza stiva L., cv. Sakha 101) and maize (Zea mays L., cv. Hybrid 10). Optimum air temperature allowing maximum growth for each of the study crop cultivars and the current and projected air temperature patterns in the future years were used for projection of the seasonal and crop distribution maps in the years 2005, 2025, 2050, 2075 and 2100. Results showed that sowing dates of a target crop may be managed in order to allow maximum predicted planting area in the same region. The current maximum area suitable for planting the Cotton crop in Egypt (104 thousand Fadden/year; one Fadden = 0.96 hectare or 0.42 acre) showed few variations over the coming hundred years. In this case, the sowing dates should be changed from the hotter months (February to April) to the cooler months (January to February). Alternatively, a great reduction in the area planted by Wheat crop was predicted in the coming 100 years. Despite the early planting, a reduction of about 147 thousand Fadden/year was projected by the year 2075. On the other hand, with earlier sowing dates, the maximum areas that are planted by Rice and Maize may not be greatly affected by the projected increase in air temperature.     

Soil chemical changes under irrigated mango production in the Central São Francisco River Valley,Brazil

Irrigated areas in Brazil's Central S?o Francisco River Valley have experienced declines in productivity, which may be a reflection of changes in soil chemical properties due to management. This study was conducted to compare the chemical composition of soil solutions and cation exchange complexes in a five-year-old grove of irrigated mango (Mangifera indica L. cv. Tommy Atkins) with that of an adjacent clearing in the native caatinga vegetation. A detailed physiographic characterization of the area revealed a subsurface rock layer, which was more undulating than the current land surface, and identified the presence of a very saline and sodic (1045 microS cm(-1), sodium adsorption ratio [SAR] = 5.19) ground water table. While changes in concentrations of Ca, Mg, and K could be attributed to direct management inputs (fertilization and liming with dolomite), increases in Na suggested average annual capillary rise from the ground water table of 28 L m(-2). Accordingly, soil salinity levels appeared to be more dependent on surface elevation than the elevation of the rock layer or sediment thickness. The apparent influence of land surface curvature on water redistribution and the solution chemistry was more pronounced under irrigated mango production. In general, salinity levels had doubled in the mango grove and nearly tripled under the canopies, after only five years of irrigation. Though critical saline or sodic conditions were not encountered, the changes observed indicate a need for more adequate monitoring and management of water and salt inputs despite the excellent water quality of the S?o Francisco River.     

Water and nitrogen management effects on water and nitrogen fluxes in Florida Flatwoods

The effects of water and fertilizer best management practices (BMPs) have not been quantified for groundwater nitrogen (N) beneath seepage irrigated vegetable fields with shallow water table environments. This effect was evaluated by a 3-yr study conducted in the Flatwoods of south Florida for watermelon ( cv. Mardi Gras and Tri-X 313) and tomato ( cv. BHN 586) using three treatments of water and inorganic fertilizer N (N) rates: (i) high fertilizer and water rates with seepage irrigation (HR), (ii) recommended fertilizer and water rates (BMP) with seepage irrigation (RR); and (iii) RR with subsurface drip irrigation (RR-SD). These treatments were implemented on six hydraulically isolated plots. The N rate treatments for high (HR) and recommended (RR and RR-SD) were based on a grower survey and BMP recommendations, respectively. Water applied, water table depth, and soil moisture content were regularly monitored for each treatment. Plant, soil, and groundwater N sampling and analyses were conducted for each season of the 3-yr study. The average water applied in HR (187 cm) was greater than RR (172 cm) and RR-SD (94 cm). Soil N maintained in crop beds for HR was significantly higher than RR and RR-SD. Soil solution analyses showed that N leached beneath HR (112 mg L) was greater ( = 0.053) than RR (76 mg L) and RR-SD (88 mg L). Shallow groundwater concentrations of dissolved inorganic nitrogen (NH-N + NO-N) were higher ( = 0.02) in HR (37 mg L) compared with RR (15 mg L) and RR-SD (19 mg L). Decreased N and water table levels can improve groundwater quality by reducing N leachate in shallow water table environments with seepage irrigated vegetable production systems.     

Estimating yields of salt- and water-stressed forages with remote sensing in the visible and near infrared

In arid irrigated regions, the proportion of crop production under deficit irrigation with poorer quality water is increasing as demand for fresh water soars and efforts to prevent saline water table development occur. Remote sensing technology to quantify salinity and water stress effects on forage yield can be an important tool to address yield loss potential when deficit irrigating with poor water quality. Two important forages, alfalfa (Medicago sativa L.) and tall wheatgrass (Agropyron elongatum L.), were grown in a volumetric lysimeter facility where rootzone salinity and water content were varied and monitored. Ground-based hyperspectral canopy reflectance in the visible and near infrared (NIR) were related to forage yields from a broad range of salinity and water stress conditions. Canopy reflectance spectra were obtained in the 350- to 1000-nm region from two viewing angles (nadir view, 45 degrees from nadir). Nadir view vegetation indices (VI) were not as strongly correlated with leaf area index changes attributed to water and salinity stress treatments for both alfalfa and wheatgrass. From a list of 71 VIs, two were selected for a multiple linear-regression model that estimated yield under varying salinity and water stress conditions. With data obtained during the second harvest of a three-harvest 100-d growing period, regression coefficients for each crop were developed and then used with the model to estimate fresh weights for preceding and succeeding harvests during the same 100-d interval. The model accounted for 72% of the variation in yields in wheatgrass and 94% in yields of alfalfa within the same salinity and water stress treatment period. The model successfully predicted yield in three out of four cases when applied to the first and third harvest yields. Correlations between indices and yield increased as canopy development progressed. Growth reductions attributed to simultaneous salinity and water stress were well characterized, but the corrections for effects of varying tissue nitrogen (N) and very low leaf area index (LAI) are necessary.     

Irrigation of broccoli and canola with boron- and selenium-laden effluent

Selenium (Se), boron (B), and salinity contamination of agricultural drainage water is potentially hazardous for water reuse strategies in central California. To demonstrate the feasibility of using plants to extract Se from drainage water, Se accumulation was determined in canola (Brassica napus L.) and broccoli (Brassica oleracea L.) irrigated with drainage effluent in the San Joaquin Valley, California. In the 2-yr field study, both crops were irrigated with a typical drainage water containing Se (150 microg L(-1)), B (5 mg L(-1)), and a sulfate dominated salinity (EC of 7 dS m(-1)). Total dry matter yields were at least 11 Mg ha(-1) for both canola and broccoli, and plant tissue Se concentrations did not exceed 7 mg kg(-1) DM for either crop. Based on the amount of soluble Se applied to crops with drainage water and the estimated amount of soluble Se remaining in soil to a depth of 90 cm at harvest, both canola and broccoli accumulated at least 40% of the estimated soluble Se lost from the soil for both years. Applied Se not accounted for in plant tissue or as soluble Se in the soil was presumably lost by biological volatilization. This study suggests that irrigating two high value crops such as canola and broccoli with Se-laden effluent helps manage Se-laden effluent requiring treatment, and also produces economically viable Se-enriched crops. Future research should focus on managing residual salt and B in the soil for sustaining long time water reuse strategies.     

Nitrogen- vs. phosphorus-based dairy manure applications to field crops: nitrate and phosphorus leaching and soil phosphorus accumulation

Management of animal manures to provide nutrients for crop growth has generally been based on crop N needs. However, because manures have a lower N/P ratio than most harvested crops, N-based manure management often oversupplies the crop-soil system with P, which can be lost into the environment and contribute to eutrophication of water bodies. We examined the effects of N- vs. P-based manure applications on N and P uptake by alfalfa (Medicago sativa L.), corn (Zea mays L.) for silage, and orchardgrass (Dactylis glomerata L.), leaching below the root zone, and accumulation of P in soil. Treatments included N- and P-based manure rates, with no nutrient input controls and inorganically fertilized plots for comparison. Nitrate concentrations in leachate from inorganic fertilizer or manure treatments averaged 14 mg NO(3)-N L(-1), and did not differ by nutrient treatment. Average annual total P losses in leachate did not exceed 1 kg ha(-1). In the top 5 cm of soil in plots receiving the N-based manure treatment, soil test P increased by 47%, from 85 to 125 mg kg(-1). Nitrogen- and P-based manure applications did not differ in ability to supply nutrients for crop growth, or in losses of nitrate and total P in leachate. However, the N-based manure led to significantly greater accumulation of soil test P in the surface 5 cm of soil. Surface soil P accumulation has implications for increased risk of off-field P movement.     

Vetiver (Vetiveria zizanioides) responses to fertilization and salinity under irrigation conditions

Vetiver (Vetiveria zizanioides) has not been widely introduced in arid and semi-arid regions where irrigation, fertilization, and salinity are important factors in plant growth. The main objective of this study was to determine the response of vetiver to fertilization (fertigation) and salinity and their interactions under irrigated conditions. The experiment was conducted in a greenhouse in 10-L pots. Combined effects of three nutrients concentrations and three salinity levels of electrical conductivity (EC) 1, 3 and 6 dS/m in the irrigation water on growth and transpiration of vetiver plants and the content of different elements in their foliage were studied. Similar contents of 3.7 g/kg Na, 5.77 g/kg Ca and 2.55 g/kg Mg were found in the foliage of all the plants irrigated with the different fertilizer and salinity levels. Concentrations of 59 mg/L N and 36.1 mg/L K in the irrigation water were sufficient for vetiver plants needs at the different salinity levels tested. The salinity threshold (the maximum EC in the soil solution that does not cause a significant yield reduction) for vetiver was between 3 and 6 dS/m. A concentration of 15.2 mg/L P in the irrigation water was the optimum value for vetiver growth in the three salinity levels, resulting in an average content of 5.95 g/kg P in plant foliage. It is suggested that vetiver is sensitive to excess P (>8.66 g/kg). Increasing EC in the irrigation water to 6 dS/m decreased plant foliage biomass mainly due to an increase in the osmotic potential of the irrigation water and high Cl⁻ concentration in the foliage.     

Modeling nitrogen and water management effects in a wheat-maize double-cropping system

Excessive N and water use in agriculture causes environmental degradation and can potentially jeopardize the sustainability of the system. A field study was conducted from 2000 to 2002 to study the effects of four N treatments (0, 100, 200, and 300 kg N ha(-1) per crop) on a wheat (Triticum aestivum L.) and maize (Zea mays L.) double cropping system under 70 +/- 15% field capacity in the North China Plain (NCP). The root zone water quality model (RZWQM), with the crop estimation through resource and environment synthesis (CERES) plant growth modules incorporated, was evaluated for its simulation of crop production, soil water, and N leaching in the double cropping system. Soil water content, biomass, and grain yield were better simulated with normalized root mean square errors (NRMSE, RMSE divided by mean observed value) from 0.11 to 0.15 than soil NO(3)-N and plant N uptake that had NRMSE from 0.19 to 0.43 across these treatments. The long-term simulation with historical weather data showed that, at 200 kg N ha(-1) per crop application rate, auto-irrigation triggered at 50% of the field capacity and recharged to 60% field capacity in the 0- to 50-cm soil profile were adequate for obtaining acceptable yield levels in this intensified double cropping system. Results also showed potential savings of more than 30% of the current N application rates per crop from 300 to 200 kg N ha(-1), which could reduce about 60% of the N leaching without compromising crop yields.     

Simulating the Impacts of Irrigation Levels on Soybean Production in Texas High Plains to Manage Diminishing Groundwater Levels

There is an increasing need to strategize and plan irrigation systems under varied climatic conditions to support efficient irrigation practices while maintaining and improving the sustainability of groundwater systems. This study was undertaken to simulate the growth and production of soybean [Glycine max (L.)] under different irrigation scenarios. The objectives of this study were to calibrate and validate the CROPGRO‐Soybean model under Texas High Plains’ (THP) climatic conditions and to apply the calibrated model to simulate the impacts of different irrigation levels and triggers on soybean production. The methodology involved combining short‐term experimental data with long‐term historical weather data (1951–2012), and use of mechanistic crop growth simulation algorithms to determine optimum irrigation management strategies. Irrigation was scheduled based on five different plant extractable water levels (irrigation threshold [ITHR]) set at 20%, 35%, 50%, 65%, and 80%. The calibrated model was able to satisfactorily reproduce measured leaf area index, biomass, and evapotranspiration for soybean, indicating it can be used for investigating different strategies for irrigating soybean in the THP. Calculations of crop water productivity for biomass and yield along with irrigation water use efficiency indicated soybean can be irrigated at ITHR set at 50% or 65% with minimal yield loss as compared to 80% ITHR, thus conserving water and contributing toward lower groundwater withdrawals. Editor's note: This paper is part of the featured series on Optimizing Ogallala Aquifer Water Use to Sustain Food Systems. See the February 2019 issue for the introduction and background to the series.     

Arsenic availability from chromated copper arsenate (CCA)-treated wood

Lumber used to construct raised garden beds is often treated with chromated copper arsenate (CCA). This project aimed to determine (i) how far As, Cu, and Cr had diffused away from CCA-treated wood surfaces in raised garden beds under realistic conditions, (ii) the uptake of these elements by crops, and (iii) the effect of CCA solution on soil bacteria. This study showed that As, Cu, and Cr diffuse into soil from CCA-treated wood used to construct raised garden beds. To determine crop uptake of these elements, contaminated soil 0 to 2 cm from the treated wood was obtained from two different beds (40-50 mg kg(-1) As); control soil was collected 1.5 m away from the treated wood (<3-10 mg kg(-1) As). Four replicates of carrot (Daucus carota var. sativus Hoffm. cv. Thumbelina), spinach (Spinacia oleracea L. cv. Indian Summer), bush bean (Phaseolus vulgaris L. cv. Provider), and buckwheat (Fagopyrum esculentum Moench cv. Common) were grown in pots containing these soils in a greenhouse. After harvest, plant materials were dried, ground, digested, and analyzed for As by inductively coupled plasma-hydride generation (ICP-HG). Concentrations of As in all crops grown in contaminated soils were higher than those from control soils. The levels of As in the crops remained well below the recommended limit for As set by the United States Public Health Service (2.6 mg kg(-1) fresh wt.). To determine if bacteria in soils 0 to 2 cm from the treated wood had higher resistance to Type C chromated copper arsenate (CCA-C) solution than those from reference soils, dilution plates were set up using quarter-strength tryptic soy agar (TSA) media and 0 to 22.94 g L(-1) (0-1.25% v/v) CCA-C working solution. The microorganisms from soils adjacent to treated wood had greater growth on the CCA-amended media than those from reference soils outside the bed.     

Influence of plant growth on degradation of linear alkylbenzene sulfonate in sludge-amended soil

Widespread application of sewage sludge to agricultural soils in Denmark has led to concern about the possible accumulation and effects of linear alkylbenzene sulfonate (LAS) in the soil ecosystem. Therefore, we have studied the uptake and degradation of LAS in greenhouse pot experiments. Sewage sludge was incorporated into a sandy soil to give a range from very low to very high applications (0.4 to 90 Mg dry wt. ha(-1)). In addition, LAS was added as water solutions. The soil was transferred to pots and sown with barley (Hordeum vulgare L. cv. Apex), rape (Brassica napus L. cv. Hyola 401), or carrot (Daucus carota L.). Also, plant-free controls were established. For all additions there was no plant uptake above the detection limit at 0.5 mg LAS kg(-1) d.w, but plant growth stimulated the degradation. With a growth period of 30 d, LAS concentrations in soil from pots with rape had dropped from 27 to 1.4 mg kg(-1) dry wt., but in plant-free pots the concentration decreased only to 2.4 mg kg(-1) dry wt. When LAS was added as a spike, the final concentration in soil from planted pots was 0.7 mg kg(-1) dry wt., but in pots without plants the final concentration was much higher (2.5 mg kg(-1) dry wt.). During degradation, the relative fraction of homologues C10, C11, and C12 decreased, while C13 increased.     

Goals and remedial strategies for water quality and wildlife management in a coastal lagoon--a case-study of Ringkøbing Fjord, Denmark

The aim of this work is (1) to discuss approaches and tools to set management goals using operational indicators for coastal management (i.e., indicators that are easy to measure, understand and predict) and validated predictive models and (2) to discuss remedial strategies for sustainable coastal management regarding water quality and the abundance of fish, waterfowl and large aquatic plants. These approaches are exemplified using data from Ringkøbing Fjord, Denmark, which has undergone two major regime shifts during the last decades. This work discusses the changes taken place during the period from 1980 to 2004 (when there are good empirical data). For Ringkøbing Fjord, which is a very shallow, well-oxygenated lagoon dominated by resuspension processes, we have targeted on the following operational indicators, which are meant to reflect seasonal median values for the entire defined coastal area (the ecosystem scale) and not conditions at individual sites or data from shorter time periods: Secchi depth (as a standard measure of water clarity) and chlorophyll-a concentrations (as a key measure of algal biomass). The operational indicators are regulated by a set of standard abiotic factors, such as salinity, suspended particulate matter (SPM), nutrient concentrations (N and P), coastal morphometry and water exchange. Such relationships are quantified using well-tested, general quantitative models, which illustrate how these indicators are interrelated and how they reflect fundamental aspects of coastal ecosystems. We demonstrate that the regime shift in the lagoon can be modelled and quantitatively explained and is related to changes in salinity and nutrient inflow. A very important threshold is linked to increased salinities in the lagoon. For example, when the mean annual salinity is higher than about 9.5‰, large numbers of saltwater species of clams can survive and influence the structure and function of the ecosystem in profound ways. The model also illustrates the dynamic response to changes in nutrient loading. We have presented several management strategies with the goal of keeping the Secchi depth at 2 m, which would stimulate the growth of higher aquatic plants, which are fundamental for fish production and bird abundance in the lagoon. Given the fact that the Secchi depth depends on many variable factors (temperature, TP-inflow from land, salinity, changes in biomasses of macrophytes and clams, which are accounted for in these simulations), our results indicate that in practice it will likely be very difficult to reach that goal. However, it would be realistic to maintain a Secchi depth of 1.5 m if the variability in salinity is minimized and the mean salinity is kept at about 10.2‰.     

Nitrate-nitrogen concentrations in the perched ground water under seepage-irrigated potato cropping systems

Excessive nitrogen rates for potato production in northeast Florida have been declared as a potential source of nitrate pollution in the St. Johns River watershed. This 3-yr study examined the effect of N rates (0, 168, and 280 kg ha(-1)) split between planting and 40 d after planting on the NO(3)-N concentration in the perched ground water under potato (Solanum tuberosum cv. Atlantic) in rotation with sorghum sudan grass hybrid (Sorghum vulgare x Sorghum vulgare var. sudanese, cv. SX17), cowpea (Vigna unguiculata cv. Iron Clay), and greenbean (Phaseolus vulgare cv. Espada). Soil solution from the root zone and water from the perched ground water under potato were sampled periodically using lysimeters and wells, respectively. Fertilization at planting increased the NO(3)-N concentration in the perched ground water, but no effect of the legumes in rotation with potatoes on nitrate leaching was detected. Fertilization of green bean increased NO(3)-N concentration in the perched ground water under potato planted in the following season. The NO(3)-N concentration in the soil solution within the potato root zone followed a similar pattern to that of the perched ground water but with higher initial values. The NO(3)-N concentration in the perched ground water was proportional to the rainfall magnitude after potato planting. A significant increase in NO(3)-N concentration in the perched ground water under cowpea planted in summer after potato was detected for the side-dressing of 168 kg ha(-1) N applied to potato 40 d after planting but not at the 56 kg ha(-1) N side-dress. Elevation in NO(3)-N concentration in the perched ground water under sorghum was not significant, supporting its use as an effective N catch crop.     

Spatial Analysis of Soil Salinity and Soil Structural Stability in a Semiarid Region of New South Wales,Australia

Salt-affected soils are a major threat to agriculture especially in the semiarid regions of the world. The effective management of these soils requires adequate understanding of not only how water and, hence, solutes are transported within the soil, but also how soil salinity and sodicity spatially interact to determine soil structural breakdown. For sustainable agricultural production, information on quantitative soil quality, such as salinity, is required for effective land management and environmental planning. In this study, quantitative methods for mapping indicators of soil structural stability, namely salinity and sodicity, were developed to assess the effect of these primary indicators on soil structural breakdown. The current levels of soil salinity, as measured by electrical conductivity (EC) of the soil/water suspension, soil sodicity, represented by exchangeable sodium percentage (ESP), and aggregate stability, were assessed. Remote sensing, geographical information system (GIS), and geostatistical techniques-primarily regression-kriging and indicator-kriging-were used to spatially predict the soil sodicity and salinity. The patterns of salinity (EC) and sodicity (ESP > 5%) were identified. The effect of land use on these soil quality indicators was found to be minimal. Co-spatial patterns were elucidated between sodic soils (defined by ESP > 5%) and highly probable mechanically dispersive soils predicted from indicator-kriging of ASWAT scores. It was established that the incorporation of EC with ESP into an objective index, called electrolyte stability index (ESI = ESP/EC), gave a good indication of soil dispersion, although the threshold ESI value below which effective structural breakdown might occur is 0.025, which is twice as small as the expected 0.05. The discrepancies between ESI and ASWAT scores suggest that other soil factors than salinity and sodicity are affecting soil structural breakdown. This calls for further investigation. The study provides valuable information in the form of risk zones of soil structural breakdown for land management. These zones, with a probability of mechanical soil dispersion of >0.70, require immediate management attention with greater monitoring and amelioration techniques, particularly gypsum or lime application and/or altered cultivation techniques.     

Radionuclide transport above a near-surface water table: III. Soil migration and crop uptake of three gamma-emitting radionuclides, 1990 to 1993

This paper summarizes the vertical distributions of 22Na, 137Cs, and 60Co above controlled water tables in deep and shallow lysimeters during a four-year experiment. The activity concentration profiles were all determined at the time of harvest of a winter wheat (Triticum aestivum L. cv. Pastiche) crop. Activity concentrations in different crop tissues were determined and crop uptake expressed as both an inventory ratio (IR) and a transfer factor (TFw), weighted to account for root and radionuclide distributions within the soil profile. Experimental variates were subjected to analysis of variance to determine the single and combined effects of the soil depth and the year of the experiment on the results obtained. Each radionuclide showed significant variations in activity concentration with soil depth, but the significance of these variations from year to year was dependent on radionuclide. A distinction in the behavior of weakly sorbed (22Na) and more highly sorbed (137Cs and 60Co) radionuclides was observed. The former exhibited significant variations in its distribution in the soil profile from year-to-year whereas the latter did not. Relatively high TF, values for 22Na were maintained throughout the experiment, whereas for 137Cs and 60Co, the highest TFw values were recorded in 1990 followed by a significant decline in 1991, with TFw remaining low in 1992 and 1993. The TFw values were, in general, significantly higher for deep lysimeters than for shallow lysimeters. This is thought to provide evidence of enhanced radionuclide absorption by the relatively small fraction of roots in the vicinity of the deeper water table.     

Assessment of the use of industrial by-products to remediate a copper- and arsenic-contaminated soil

Two water treatment sludges (WTS-A, WTS-B), two red muds (RM), and red gypsum (RG), all rich in iron oxy-hydroxides, were added to a soil highly polluted with As and Cu at 2% (w/w) to reduce metal bioavailability. Because the amendments increased soil pH to approximately 6, a lime treatment to the same pH and an unamended treatment were included for comparison. All the amendments had significant positive effects on the soil microbial biomass and growth of ryegrass (Lolium multiflorum Lam. cv. Avance), but only WTS-A improved lettuce (Lactuca sativa L. cv. Tom Thumb) growth. The mineralization of added ammonium nitrogen was not significantly affected by the treatments, while a physiologically based extraction test (PBET) showed that bioaccessibility of As was low (< 5%) and decreased only in the WTS-A treatment. Concentrations of As in soil pore water and extractable As only decreased in the WTS and RG treatments. In contrast, Cu concentrations in soil pore water and extractable Cu decreased in all treatments, by more than 84% in the WTS, RM, and RG treatments. Non-isotopically exchangeable As and Cu were present in colloids in the soil pore water. Untreated soil had < 4% isotopically exchangeable As and this decreased by approximately 50%, with WTS, RM, and RG. The labile Cu pool represented a large proportion (34%) of the total Cu pool, and the isotopically exchangeable and soluble Cu were strongly correlated with soil pH. Acidification of the treated soils showed that the labile As and Cu both increased in the treated soils compared with untreated soils. The significance of the treatment effects on soil fertility and potential off-site transport of As and Cu to ground water are discussed.     

Controlled drainage and wetlands to reduce agricultural pollution: a lysimetric study

Controlled drainage and wetlands could be very effective practices to control nitrogen pollution in the low-lying agricultural plains of northeast Italy, but they are not as popular as in other countries. An experiment on lysimeters was therefore carried out in 1996-1998, with the double aim of obtaining local information to encourage the implementation of these practices and to gain more knowledge on the effects involved. Controlled drainage + subirrigation and wetlands were all considered as natural systems where alternative water table management could ameliorate water quality, and were compared with a typical water management scheme for crops in the open field. Eight treatments were considered: free drainage on maize (Zea mays L.) and sugarbeet (Beta vulgaris L.), two treatments of controlled drainage on the same crops, and five wetland treatments using common reed [Phragmites australis (Cav.) Trin. ex Steud.], common cattail (Typha latifolia L.), and tufted sedge (Carex elata All.), with different water table or flooding levels. Lysimeters received about 130 g m 2 of N with fertilization and irrigation water, with small differences among treatments. The effects of treatments were more evident for NO3-N concentrations than for the other chemical parameters (total Kjeldahl nitrogen, pH, and electrical conductivity), with significantly different medians among free drainage (33 mg L(-1)), controlled drainage (1.6 and 2.6 mg L(-1)), and wetlands (0.5-0.7 mg L(-1)). Referring to free drainage, NO3-N losses were reduced by 46 to 63% in controlled drainage and 95% in the average of wetlands. Wetlands also reduced losses of total dissolved solids from 253 g m(-2) (average of crop treatments) to 175 g m(-2) (average of wetlands).     

SOIL SALINITY PREDICTION USING ARTIFICIAL NEURAL NETWORKS1

ABSTRACT: This study explores the applicability of Artificial Neural Networks (ANNs) for predicting salt build‐up in the crop root zone. ANN models were developed with salinity data from field lysimeters subirrigated with brackish water. Different ANN architectures were explored by varying the number of processing elements (PEs) (from 1 to 30) for replicate data from a 0.4 m water table, 0.8 m water table, and both 0.4 and 0.8 m water table lysimeters. Different ANN models were developed by using individual replicate treatment values as well as the mean value for each treatment. For replicate data, the models with twenty, seven, and six PEs were found to be the best for the water tables at 0.4 m, 0.8 m and both water tables combined, respectively. The correlation coefficients between observed salinity and ANN predicted salinity of the test data with these models were 0.89, 0.91, and 0.89, respectively. The performance of the ANNs developed using mean salinity values of the replicates was found to be similar to those with replicate data. Not only was there agreement between observed and ANN predicted salinity values, the results clearly indicated the potential use of ANN models for predicting salt build‐up in soil profile at a specific site.     

Rye cover crop and gamagrass strip effects on NO3 concentration and load in tile drainage

A significant portion of the NO3 from agricultural fields that contaminates surface waters in the Midwest Corn Belt is transported to streams or rivers by subsurface drainage systems or "tiles." Previous research has shown that N fertilizer management alone is not sufficient for reducing NO3 concentrations in subsurface drainage to acceptable levels; therefore, additional approaches need to be devised. We compared two cropping system modifications for NO3 concentration and load in subsurface drainage water for a no-till corn (Zea mays L.)-soybean (Glycine max [L.] Merr.) management system. In one treatment, eastern gamagrass (Tripsacum dactyloides L.) was grown in permanent 3.05-m-wide strips above the tiles. For the second treatment, a rye (Secale cereale L.) winter cover crop was seeded over the entire plot area each year near harvest and chemically killed before planting the following spring. Twelve 30.5x42.7-m subsurface-drained field plots were established in 1999 with an automated system for measuring tile flow and collecting flow-weighted samples. Both treatments and a control were initiated in 2000 and replicated four times. Full establishment of both treatments did not occur until fall 2001 because of dry conditions. Treatment comparisons were conducted from 2002 through 2005. The rye cover crop treatment significantly reduced subsurface drainage water flow-weighted NO3 concentrations and NO3 loads in all 4 yr. The rye cover crop treatment did not significantly reduce cumulative annual drainage. Averaged over 4 yr, the rye cover crop reduced flow-weighted NO3 concentrations by 59% and loads by 61%. The gamagrass strips did not significantly reduce cumulative drainage, the average annual flow-weighted NO3 concentrations, or cumulative NO3 loads averaged over the 4 yr. Rye winter cover crops grown after corn and soybean have the potential to reduce the NO3 concentrations and loads delivered to surface waters by subsurface drainage systems.     

Responses of red-osier dogwood to oil sands tailings treated with gypsum or alum

The application of composite or consolidated tailings (CT) technology provides Alberta's oil sands industry with a means of reducing the volume of the fines fraction in extraction tailings and allows for faster reclamation and revegetation of mining sites. This study examined the effects of coagulant aids (gypsum and alum), used in the production of CT, on the ion content, growth, and survival of greenhouse-grown red-osier dogwood (Cornus sericea L. subsp. sericea). Seedlings were planted in gypsum-CT and alum-CT substrates, and compared with those planted in reclamation material (salvaged peat and till). The seedlings were bottom-watered with one of the following: (i) Hoagland mineral solution prepared in deionized water (Epstein, 1972); (ii) Hoagland solution in gypsum-based CT release water; or (iii) Hoagland solution in alum-based CT release water. Pore water of CT substrates and CT release waters had similar chemical characteristics, including salinity levels. However, plants in CT substrates had higher concentrations of ions (particularly Na and B), reduced growth, and higher mortality than plants in reclamation material and treated with CT waters. The presence of H2S indicated low-oxygen conditions in the CT substrates, while in the reclamation materials with CT release water treatments, no evidence of sulfides was observed. Low-oxygen conditions in the CT substrate treatments may have interfered with plant exclusion mechanisms for Na and B. Therefore, substrate properties may modify responses of reclamation plants to pore water chemistry due to the effects on oxygen availability to roots.