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Five methods to measure the saturated hydraulic conductivity of Arizona irrigated soils were evaluated using the in-situ single ring, double ring, compact constant head permeameter methods, and with tempe cells (soil cores) in the laboratory. Ten Arizona irrigated soils were studied, and the textures of these soils ranged from sand to silty clay. Three water qualities were evaluated, namely the local water, gypsum in local water, and gypsum water (0.005M CaSO₄ · 2H₂O solution). Sites were selected to provide soils having a wide range of soil characteristics and detailed laboratory and field morphology data were measured including soil texture, bulk density, soil aggregation, stickiness, plasticity, moisture retention at various tensions, ECₑ, and pHₑ. The results showed that the double ring method was the better in-situ method. The relationships between soil properties and K(sat) were evaluated, and soil properties were examined as predictor variables for K(sat) in stepwise multiple-regression. Stepwise multiple-regression criteria were set at a probability of F to enter ≤ 0.5 and probability of F to remove ≥ 0.1. Six models are presented that can be used in predicting K(sat). Each model has a subset of field and laboratory predictor variables selected based on stepwise multiple-regression criteria, and with some personal judgment. Casewise diagnostics were used to test model performances.

Numerical simulations were performed to study two-dimensional infiltration from furrows. The simulations were carried out using the models SWMS_2D, HYDRUS-2D and HYDRUS-1D. The first model was used to evaluate the individual effect of soil and furrow parameters on cumulative infiltration and deep seepage. Cumulative infiltration was found to be more sensitive to saturated hydraulic conductivity, wetted perimeter and furrow spacing than the other parameters for relatively long times, while cumulative deep seepage was more sensitive to the same parameters except to the furrow spacing. It was verified that two-dimensional cumulative infiltration can be approximated using one-dimensional models, for example HYDRUS-1D, by combining the vertical and horizontal infiltrations. The two-dimensional cumulative infiltration is underpredicted by no more than 35% using this calculation. When steady state is reached the steady infiltration rate may be linearly related to the depth of the furrow. As a result, steady infiltration rate is dependent only on type of soil, water depth in the furrow and furrow width. Broocks-Corey soil hydraulic parameters were matched to the van Genuchten parameters by four different procedures. The method based on matching sorptivities produced the closest results to the van Genuchten solution for one- and two-dimensional cumulative infiltration. However, cumulative deep seepage was not accurately simulated. The SCS infiltration parameters were also matched but using an inverse problem methodology. The parameters obtained described cumulative infiltration reasonably well.

In the riparian corridor of the San Pedro River in southeastern Arizona, the fluxes of water and energy over three riparian vegetation groupings were monitored and modeled in order to determine their annual water use and water sources. In situ micrometeorological and soil moisture measurements were made from 1996-1998 at a floodplain grassland site composed mainly of the perennial floodplain grass, Sporobolus wrightii (sacaton), and a tree/shrub grouping dominated by Prosopis velutina (mesquite). The results indicate that the grassland obtained water only from the near-surface (recent precipitation), while the mesquite accessed moisture from deeper in the vadose zone and/or from the water table. Both of these sites exhibited little interaction with the underlying groundwater, suggesting that the majority of the groundwater use from riparian vegetation is limited to the areas of dense mesquite and the forest gallery adjacent to the river. Measurements of the forest gallery water use composed mainly of Populus fremontii (cottonwood) and Salix gooddingii (willow) were available for some shorter term periods in 1997. These measurements were used to calibrate the Penman-Monteith model for evaporation in order to determine the water use from the forest gallery for the entire growing season. The total seasonal water use from the forest was considerably less than potential evaporation estimates. Observations of soil moisture under two rangeland sites in the San Pedro Basin were examined in order to determine the magnitude and the depth of root zone recharge characteristics in this semiarid region. Intermittent TDR observations made from 1990 to 1998 show that deeper root zone recharge occurred primarily during the wintertime, when the plants were senescent and evaporation demand was diminished. A physically-based variably-saturated flow model was used to determine the wintertime recharge. Using an automatic calibration algorithm, the model proved capable of reproducing the observations with small error. Simulated wintertime infiltration amounts indicated that substantial, deeper root zone recharge did occur during wet winters, but that the large year-to-year variability of this recharge implies that deeper-rooted plants would still need access to moisture in shallow root zone.

The quantity of quartz and its size distribution was determined in soils formed from quartz free basaltic tephra on Greens Peak, Apache County, Arizona. The soils showed a decrease in quartz content from the east side to the west side of the peak. The percentage of averaged weighed quartz content in the upper soil horizons ranged from (36.1%-13.9%) on the east side and (19.9%-12.3%) on the west side. The content of quartz was higher in the surface soil horizons than in the lower horizons. Large amounts of quartz occurred in the sand and silt fraction, whereas no quartz was detected in the clay fractions. Quartz is concentrated mostly in the coarse silt (22-53 μm) fraction (50%). Quartz particle size distribution in these soils is dominantly in the range of 17-53 μm particle count based, and (17-63 μm) mass based. The abundance of silt and very fine sand quartz, and the paucity of aerosolic quartz 1-10 μm in these fractions is indicative of dust transported short distances from the local sources. It is suggested that the quartz was added as loess sized material of mainly local origin brought into the profiles by eolian transport.

Application of manure has been used to increase the nitrogen status of many arid and semi-arid agricultural soils, however, organic nitrogen contained in animal manures must be mineralized prior to utilization by crops. Nitrogen mineralization is, like other biological processes, affected by soil water status. This can be due to the direct influence of soil moisture and/or salt interactions on the nitrogen dynamics. It is critical to understand the interactive effects of salt and water on nitrogen in soils amended with organic fertilizer. Such knowledge may be used for improving and quantifying nitrogen use efficiency. Objectives of this study were (i) to examine the relative and interactive influences of soil osmotic and matric water potentials on nitrogen transformations in manure-amended and non-manured soils, (ii) to determine the extent of nitrogen mineralization over a range of soil water potentials, and (iii) to study the effect of manure addition on nitrogen dynamics in an agricultural desert soil. Gila fine sandy loam soil was treated by addition of varying amounts of distilled water, NaCl, and dairy manure and incubated at depth of 20 cm in 0.025 mm thickness Ziploc® bags. Ammonium nitrogen, nitrate nitrogen, gravimetric soil moisture content, and total soil water potential were measured weekly for 16 weeks. Our study showed a decrease in the amount of inorganic N released from both the non-manured and manure-amended soils at total soil water potentials of approximately -55 bars or less. Maximal amounts of inorganic-N were released at potentials of -23 to -3.5 bars. There was an accumulation in the amounts of NH₄-N released at potentials of -55 bars or less, presumably because of a reduction in net nitrification. The manure caused nitrogen immobilization especially during the early part of our study. Immobilization also occurred in non-manured soil, but this generally lasted only a few weeks. Immobilization was prolonged in soils with lower water potentials. Net N mineralization in the manure-amended soils was higher than in the non-manured soils when soil moisture content was at field capacity.

Eutrophication and cyanobacteria blooms are a growing problem in Missisquoi Bay of Lake Champlain in southern Quebec, and these are largely attributed to non-point source phosphorus and nitrogen (N) pollution from agricultural land in the surrounding watersheds. Residual soil N left after crop harvest contains soluble and particulate forms of N that are at risk of being transported from tile drained agricultural fields to waterways. This study aimed to find the sources of soluble N (mainly nitrate; NO3-N) and particulate organic N (PON) that are susceptible to loss, and the transport pathways by which they move to surface water through tile drained agricultural fields. Water samples were collected at the tile drainage outlet of fields with a clayey and a sandy soil during fall 2010, spring and fall 2011 and spring 2012. There was 1.3 times greater NO3-N concentration and 1.1 fold higher PON concentration in tile drainage water from sandy soil than clayey soil and electrical conductivity measurements indicated that preferential flow was the main pathway for PON loss from clayey soil. Using a dual stable isotopes of δ15N and δ18O of NO3 -N coupled with a mixing model, inorganic NH4 fertilizer was found to be the most important contributor to the NO3-N pool in tile drainage water within two weeks of fertilizer application; however, microbially-processed NO3-N was the main source (40 to 49% of NO3-N in tile drainage water) when crops were not growing in the field. Sources of PON in tile drainage water were manure N (47%) and plant residue N (20%) from topsoil layer of the clayey soil, while soil organic N (SON) contributed 94% of PON lost from the topsoil of the sandy soil. More specifically, the PON pool contained N-rich soil organo-mineral complexes from the top soil layer that reached the tile drains by preferential flow pathways. Decreasing NH4 inputs from fertilizer and allocating sufficient N credits to manure and legume residue inputs could reduce the buildup of NO3-N and organic N, thereby reducing NO3-N and PON losses from these sources. I conclude that source fingerprinting techniques using stable isotope tracers are an effective way of assembling information on the susceptibility of N inputs to loss and transport pathways, which need to be considered when choosing best management practices to reduce non-point source N pollution from the agricultural sector. / L'eutrophisation et les proliférations de cyanobactérie sont un problème croissant dans la Baie Missisquoi du Lac Champlain dans le sud du Québec. Celles-ci peuvent être largement imputées a une pollution en phosphore et azote (N) d'origine diffuse, provenant de terres agricoles dans les basins versants s'y déversant. L'azote résiduel du sol, qui demeure après la récolte, comprend des formes soluble et particulaires qui risquent d'être transportées des champs équipés d'une système de drainage souterrain vers les cours d'eau. Cette étude tenta d'identifier les sources d'azote soluble (principalement les nitrates; NO3-N) et d'azote organique particulaire (AOP) qui sont vulnérables aux pertes, et les voies de transport par lesquelles elles se rendent des champs agricoles équipés de systèmes de drainage souterrains aux eaux de surface. Des échantillons d'eau furent prélevés à l'exutoire du système de drainage souterrain de champs aux sols argileux ou sablonneux, à l'automne 2010, au printemps et à l'automne 2011, et au printemps 2012. Les concentrations en NO3-N et en AOP furent 1.3 et 1.1 plus élevées, respectivement, dans l'eau de drainage provenant du sol sablonneux que du sol argileux, Un suivi de l'électroconductivité du sol indiqua que l'écoulement préférentiel fut la principale voie des pertes en AOP dans le sol argileux. Le suivi d'isotopes stables (δ15N et δ18O) du NO3-N du sol et des eaux de drainage, en combinaison avec un modèle de combinaison, démontra que, dans les deux semaines après son épandage, l'engrais inorganique à base de NH4 contribua le plus au stock de NO3-N des eaux de drainage souterraines. Cependant, le NO3-N transformé par les microbes fut la principale source (40 à 49%) du NO3-N dans les eaux de drainage, lorsque les cultures étaient absentes. Or, 47% et 20% de l'AOP dans les eaux de drainage provint, respectivement, d'azote de fumier et d'azote des résidus de cultures ayant leur origine dans la couche arable du sol argileux, tandis que l'azote organique de la couche arable du sol sablonneux contribua 94% de l'AOP perdu. Plus particulièrement, le stock d'AOP de la couche arable contenait des complexes organominéraux riches en azote, qui se sont rendus au drains par des voies préférentielles d'écoulement. Une diminution des apports en NH4 provenant d'engrais, et une prise en compte des crédits d'azote associés au fumier et aux résidus de plantes légumineuses, pourrait réduire l'accumulation de NO3-N et d'azote organique, réduisant ainsi les pertes en NO3-N et AOP provenant de ces sources. Les techniques d'empreinte isotopique on donc permis de faire un suivi efficace des intrants azotées tout en générant de nouvelles connaissances sur la vulnérabilité des intrants azotées aux voies de perte et de transport. Celles-ci devront être considérées lors du choix et de la mise en œuvre de pratiques de gestion optimales dans le secteur agricole visant à réduire la pollution azotée diffuse.

Canola is the second most important oilseed crop after soybean. More than 90% of the canola crop grown in the world is transgenic. Before this crop is grown more extensively in Quebec, there is a need to assess environmental risks associated with genetically engineered canola, mainly Roundup Ready (glyphosate- resistant) and Liberty Link (glufosinate-resistant) varieties. We have conducted a field study to compare and contrast the fate and transport of glyphosate and glufosinate herbicides in soil (used in transgenic canola production), with trifluralin, a herbicide commonly used with non-transgenic (conventional) canola cultivars. Yield data were also collected in each test plot. Three treatments were assigned (type of transgenic canola, variety, and plant stage at which herbicide application was made), in quadruplicate, in a completely randomized block design set up at two sites: Emile A. Lods Agronomy Research Centre in the Macdonald Campus of McGill University and the Normandin site of Agriculture and Agri food Canada. Soil samples were collected from two depths, 0-0.15 m and 0.15-0.30 m, at different times (1, 7 and 20 days) after herbicide application, during the growing season. Non-significant yield differences were observed between herbicide-resistant and conventional canola grown in Quebec. Glufosinate was found to be the least persistent herbicide (half-life = 7 days), while trifluralin was found to have the longest persistence in the soil (half-life = 54 days). The overall order of persistence was Trifluralin > Glyphosate > Glufosinate. Negligible leaching was observed in case of glyphosate and glufosinate to a depth of 0.30 m. Since glyphosate was found to be highly adsorbed on to the topsoil at the Lods site, herbicide concentrations were recalculated for the top 2 mm of soil, as per published literature, and they were very high, thus heightening concerns for polluted surface runoff. Trifluralin was found at the lower depth (0.15-0.30 cm) at 7 and 20 days after herbicide application, with higher (relative to each herbicide's level in the soil one day after application) residual concentrations than herbicides used in herbicide resistant (HR) canola. / Le canola est au deuxième rang mondial, après le soja, comme culture oléagineuse. Plus de 90% de la récolte de canola provident de variétés transgéniques. Avant que cette culture prenne sa place au Québec il est nécessaire d'évaluer les risqué environnementaux associés au canola transgénique, en particulier les variétés Roundup Ready (tolérant au glyphosate) et Liberty Link (tolérant au glufosinate). Une étude au champ, nous a permis de comparer et mettre en contraste le devenir et le transport d'herbicides à base de glyphosate and glufosinate, utilisées dans la production de canola transgénique, dans le sol, avec la trifluraline, un herbicide servant au contrôle des mauvais herbes dans le canola non-transgénique (conventionnel). Le rendement fut évalue pour chaque parcelle. Trois traitements furent imposes (type de canola transgénique, variété, et étape de développement de la culture lors de l'application d'herbicide), avec 4 répétitions, dans un protocole complètement aléatoire et plans en blocs aléatoires complets, mis en place à deux sites: la Ferme Lods sur le campus Macdonald de l'université McGill, et au site Normandin d'Agriculture et Agroalimentaire Canada. Des échantillons de sol furent prélevés à deux profondeurs (0-0.15 m et 0.15-0.30 m), à différent moments (1, 7 et 20 jours) après l'application d'herbicide. Des différences non-significatives furent notées entre le rendement des variétés de canola résistantes aux herbicides et le canola conventionnel, cultivées au Québec. Le glufosinate se montra l'herbicide le moins persistant dans le sol (demi vie = 7 jours), tandis que la trifluraline se montra le plus persistant (demi-vie = 54 jours). Globalement, la persistance de ces herbicides suit l'ordre Trifluraline > Glyphosate > Glufosinate. Un niveau négligeable de lessivage jusqu'à une profondeur de 0.30 m fut observe pour le glyphosate et le glufosinate. Etant donné la forte liaison du glyphosate aux sols du site Lods, les concentrations recalculées pour the 2 mm en surface furent très élevées, représentant ainsi un certain risque de perte par ruissèlement. La trifluralin fut détectée dans la zone du sol la plus profonde (0.15-0.30 m) 7 et 20 jours après l'application d'herbicide application, et présenta des concentrations résiduelles plus élevés à 7 et 20 jours, sur une base relative aux niveaux présents dans le sol un jour après l'application des herbicides, que les herbicide appliqués aux variétés de canola résistantes aux herbicides.