Comparisons between subsurface trickle-(drip) and furrow-irrigated leaf lettuce, scheduled by AZSCHED and by tensiometers were made to evaluate their effects on crop coefficient, crop water use, nitrogen uptake and nitrogen leaching. A field experiment with four treatments and five replications was conducted during the fall-winter 1994-95 growing season at The University of Arizona's Campus Agricultural Center. Results showed that there was no significant difference at 95% confidence level among treatments, with respect to crop coefficients. A Fourier series was fitted to represent the Growing Degree Days (GDD)--Crop coefficient (Kc) relationship that can be recommended for irrigation scheduling of leaf lettuce at any geographical situation and planting date. A table of Kc for "days after thinning" was derived for Tucson-AZ. Marketable yield averaged 25.0 Mg ha⁻¹ with crop water use efficiency of 9.8 Kg of marketable yield per cubic meter of water (including rainfall). The 1994-95 growing season was not typical for Tucson-AZ. There was 181 mm of rainfall compared to the long term average of 91 mm. Based on the studied condition we could also conclude that, for supplementary irrigation, that is typical of humid areas, there is no difference if one irrigate leaf lettuce by short-end-closed furrow or subsurface - trickle irrigation, scheduled either by tension of 20 kPa or AZSCHED software, concerning yield and nitrogen uptake. The risk of nitrogen leaching is higher for furrow irrigation systems than for drip.

No description available.

No description available.

Concerns over water quality have led to required removal of 50 % of dairy manure phosphorus (P) from the impaired Bosque River Watershed. Application of composted dairy manure (CDM) to sod and moving P off the watershed with sod has prompted a study using box lysimeters to determine NO3--N and P leaching from transplanted sod grown with CDM and inorganic fertilizer as well as sprigs top-dressed with CDM. Treatments were applied to lysimeters filled with a silica sand medium. Three leaching events were imposed, leaching 0.07 to 0.09 % of the total P applied and 0.09 to 1.43 % of total N applied. Concentrations of P in leachate averaged 0.04 to 0.25 mg L-1. Top-dressed CDM on sprigs leached statistically greater amounts of NO3--N than both transplanted sod treatments and greater P than the fertilizer grown sod. After the third leaching event, all treatments received an additional application of P, 100 kg ha-1 as CDM for manure-grown sod and sprigs, 50 kg ha-1 as triple superphosphate for fertilizer-grown sod. An additional three leachings were imposed. Top-dressed sprigs and transplanted sod leached similar amounts of P following the additional P application. Applied nutrients appeared to stay mainly in the sod layer and in the sand medium just below the sod layer. Top-dressed CDM appears to exhibit greater leaching losses of NO3--N than transplanted manure-grown sod and greater N and P losses than transplanted fertilizer grown sod.

The problem of domestic solid wastes buried in landfill sites is viewed from the aspect of leachate contamination and migration in the substrate. Generally, this occurs through the penetration of the contaminant into the liner material. This study assesses the efficiency of natural clay barriers as an expedient economic lining material. / Various chemical constituents of the landfill leachate of an actual waste containment site at Lachenaie (35 km east of Montreal) were determined from samples collected from specially designed basins. / In companion laboratory tests, these leachate samples were permeated through laboratory columns that contained the natural clay compacted at the optimum water content. The columns were constructed so as to permit simulation of slow, saturated, anaerobic flow of leachate through the clay lining surrounding the landfill and leachate basins. Leachates were permeated through the soil columns for periods of four to five months, during which effluents were collected periodically and analyzed for different chemical species and physical parameters. These chemical analyses measured changes in the concentration of: (a) cations (Na, K, Ca, and Mg), (b) anions (Cl, HCO$ sb3$, and CO$ sb3$), (c) total organic carbon (TOC), and (d) heavy metals (Fe, Zn, Pb, and Cu). The physical parameters measured included: (a) pH, and (b) specific conductivity. / Subsequent to the leaching tests, the column contents were cut into six sections and analyzed to determine the distribution profiles of the adsorbed and retained contaminants at various time durations. / Predictions, using a dispersion-convection model for concentration profile development for either adsorbed or retained contaminants, were compared with the experimentally determined profiles (both in leaching columns and landfill laboratory model). / Another set of experiments was also conducted to evaluate the effect of some organic fluids on the geotechnical properties of different clay soils (natural clay and two reference clay soils: illite and kaolinite). / The results from this study have demonstrated that the natural clay soil can be used to adequately contain the different contaminant species usually present in the leachate solutions. Furthermore, the data suggested that under favourable soil conditions, landfill leachates containing low levels of trace metals will not pose a substantial contamination threat to the subsurface environment, provided that a proper thickness of barrier is used. (Abstract shortened with permission of author.)

The effects of sulfur dispersing agents (SDAs) in the oxygen pressure leaching of nickel concentrate at medium temperature were investigated. Liquid sulfur-aqueous solution interfacial tensions and liquid sulfur-sulfide mineral contact angles were measured at 140ºC, 690 kPa overpressure by nitrogen, and 1.0 mol/L NiSO₄. The effects of SDAs including lignosulfonate, Quebracho, o-phenylenediamine (OPD), and humic acid were evaluated by the calculation of the work of adhesion in the liquid sulfur-sulfide mineral-aqueous solution systems. It was found that the sulfide mineral surface is sulfophobic at pH from 4.1 to 4.5 due to the hydrolysis of nickel (II) ions to nickel hydroxide and the deposition of nickel hydroxide on the mineral surface. These findings apply to four different sulfide mineral systems, including pentlandite, nickeliferous pyrrhotite, pyrrhotite, and chalcopyrite. Lignosulfonate, Quebracho, and humic acid were found to significantly reduce the work of adhesion indicating they should be effective SDAs. OPD is ineffective in changing the work of adhesion of sulfur on the mineral sulfides indicating that it is not a good candidate for sulfur dispersion. The adsorption behavior of SDAs, including lignosulfonate, Quebracho, OPD, and humic acid on elemental sulfur and on nickel sulfide concentrate was investigated. Lignosulfonate, Quebracho, and humic acid were characterized by their infrared spectra. The charge changes on elemental sulfur surface were characterized by the measurement of the electrokinetic sonic amplitude (ESA) in the absence or presence of SDAs. The adsorption of lignosulfonate on molten sulfur surface was calculated by the Gibbs Equation. The adsorption of lignosulfonate, Quebracho, and humic acid on the nickel concentrate was investigated at ambient temperature. The adsorption of lignosulfonate, Quebracho, and humic acid on the nickel concentrate was found to be monolayer adsorption, which was fitted to the Langmuir adsorption isotherm. Electrostatic interaction and ion-binding are the possible mechanisms for the adsorption of lignosulfonate and humic acid on the nickel concentrate. Quebracho is adsorbed on the nickel concentrate through hydroxyl and sulfonate groups. OPD cannot adsorb on the molten sulfur surface. OPD undergoes chemical change in aqueous solution in the presence of ferric at ambient temperature. Oxygen pressure leaching experiments were performed at 140 or 150ºC under 690 kPa oxygen overpressure. The particle size of the nickel concentrate was found to be an important factor in leaching. During the leaching of nickel concentrate with P₈₀ of 48 µm, the SDAs were believed to be fully degraded before nickel was fully extracted. At most 66% nickel was extracted in the presence of 20 kg/t OPD. Fine grinding (P₈₀ of 10 µm) was sufficient for 99% nickel recovery at low pulp density while at high pulp density, the nickel extraction increased from 95% to 99% with addition of SDAs. Based on the leaching results on a nickel concentrate sample (-44 µm), OPD had the effect of increasing the nickel extraction to about 99%, followed by Quebracho (83%), lignosulfonate (72%), and humic acid (61%). It is suggested that the oxidation product of OPD is effective in solving the sulfur wetting problem in leaching. 97% nickel was recovered in the presence of 5 g/L chloride ion. Chloride ion has an effect to enhance the performance of lignosulfonate under leaching conditions.

The export of nitrogen (N) and phosphorus (P) from agricultural catchments is a major problem worldwide. The export of these nutrients is largely driven by storm events, and the hydrologic response of catchments varies within and between storm events. Antecedent soil moisture and rainfall rates have both been shown to affect the discharge and nutrient export from agricultural catchments, but their relationship to nutrient export is not fully understood. Currently, there are no studies that examine the leaching of both nitrate and phosphate from soil pools under the combined influence of differences in soil moisture and rainfall rates. The objectives of this study were to examine the combined effect of antecedent soil moisture and rainfall rates on the hydrologic response of soil and the export of nitrate and phosphate from the soil. The approach used intact soil monoliths in two experiments to first characterize the hydrologic response of the soil, and secondly to assess how the hydrologic response of the soil affects the leaching of nitrate and phosphate from soil pools. Differences in antecedent soil moisture and rainfall rates influenced both the amount of discharge and the hydrologic flow paths in the soil. As was expected, antecedent soil moisture governed the depth of discharge, with more discharge (runoff ratios= 0.89 to 0.91) produced by wet soil and the least runoff produced by dry soil (runoff ratios= 0.08 to 0.14) although this was not affected by the rainfall rate. Instead, rainfall rates predominantly affected hydrologic flow paths in the soil, with preferential flow at the beginning of the leaching period under high intensity rainfall (especially in wet soil), and predominantly matrix flow occurring under low intensity rainfall. The rainfall intensity did not appear to affect discharge volume. The mass of both nitrate and phosphate exported was higher under low intensity rainfall, ranging from 11.2 to 60.1mg/mU+00B2 and 77 to 4980μg/mU+00B2, respectively and from 0.9 to 34.4mg/mU+00B2 and 18.4 to 732μg/mU+00B2, respectively under high intensity rainfall. Antecedent soil moisture was significantly positively correlated with the depth of discharge produced, which also had a significant positive relationship with the mass of nitrate and phosphate exported (Spearman’s ρ= 0.75 to 0.81, p= <0.001), with greater masses of both nutrients exported from wet soil than dry soil. Soil moisture had contrasting influences on the nitrate concentrations in leachate, where nitrate concentrations and soil moisture were negatively related under low intensity rainfall and positively related under high intensity rainfall. Concentrations of phosphate in leachate were more variable, with no clear relationship to soil moisture, discharge, rainfall rate or soil phosphate pools. Antecedent soil moisture and the rainfall rate have a combined influence on the concentration of nitrate in leachate and an influence on the mass of both nitrate and phosphate exported. Although different hydrologic flow paths (matrix, preferential) were observed under the variable antecedent conditions and rainfall rates, this did not appear to affect nutrient fluxes from soil. This may be related to available nutrient pools and distributions in the soil in the current study. Understanding of the influence of flow types on the export of soil nutrient pools requires further study in a lab and a comparison of the breakthrough of nitrate and phosphate from soil pools with that of a conservative tracer (chloride). Nutrient and tracer breakthrough could then be compared to the hydraulic conductivity of the soil and the progression of the wetting front to fully understand the flow paths occurring and their effect on nutrient leaching.

In response to environmental concerns about NO3- leaching research has shifted toward the increased incorporation of nitrogen-fixing legumes, such as red clover, into agroecosystems to promote tighter cycling of nitrogen (N). Although more sustainable than fertilized systems, red clover still has the potential to contribute to leaching. The objective of this study was to ascertain the contribution of red clover to soil NO3- when grown in mixture with bluegrass. Soil solute samples were collected at 15 and 45 cm depth using ceramic suction lysimeters from two experimental pastures in Nova Scotia in 2009. The concentration of NO3--N in the soil solute of bluegrass-red clover mixtures was 10 to 25 times higher in Truro, and 5 to 16 times greater in Nappan, compared to the corresponding unfertilized pure bluegrass stand. Neither sub-surface irrigation nor two distinct red clover cultivar mixtures were found to significantly alter NO3- leaching patterns.

This research examined field measurements and the HYDRUS 1-D (version 4.12) model to quantify annual movement of NO3-N through two soils of different HSG groups (B and C) using a Cl tracer and examine leaching losses attributed to the winter months (November 2007 – April 2008). Field and model data confirmed potential leaching losses ~ 72% (Cl mass recovery) over these months. Differences in Cl and nitrate-N mass recovery indicated potential N losses via other processes such as denitrification and/or immobilization. The 200 kg N ha-1 treatment was most indicative; site’s B and C had 1% and 9% losses, respectively. Both sites exhibited ~ 96-99 % loss of soil nitrate-N and Cl of the fall-applied N and Cl by September 2008. Monthly crop sampling demonstrated ~ 1% soil mineral-N remained at harvest (November 2008). These findings further support the effectiveness of applying N in the spring than the fall. / M.Sc. Thesis / Agriculture and Agri-Food Canada, Ontario Ministry of Agriculture, Food and Rural Affairs and the Canadian Water Network

No description available.