No abstract

Sorption and degradation of the herbicide 2,4-D [2,4-dichlorophenoxyacetic acid] were determined for 123 surface soils (0 to 15 cm) collected in 2002 and in 2004 between 49 degrees to 60 degrees north longitude and 110 degrees to 120 degrees west latitude in Alberta, Canada. The soils were characterized by soil organic carbon content (SOC), pH, electrical conductivity, soil texture, cation exchange capacity, carbonate content, and total soil microbial activity. The 2,4-D sorption coefficients, Kd and Koc, were highly variable with coefficients of variation of 89 and 59%, respectively, at the provincial scale. Both Kd and Koc were well described by regression models with SOC and soil pH as variables, regardless of scale. Surprisingly, variations in 2,4-D mineralization were much smaller than variations in sorption. Variability in total 2,4-D mineralization was particularly low, with a coefficient of variation of only 7% at the provincial scale. Average 2,4-D half-lives in ecoregions ranged from 1.7 to 3.5 d, much lower than the field dissipation half-life of 10 d reported for 2,4-D in general pesticide property databases. Regression models describing degradation parameters were generally poor or not significant because 2,4-D mineralization was only weakly associated with measured 2,4-D sorption parameters and soil properties. As such, regional variations in herbicide sorption coefficients should be measured or calculated based on soil properties, to assign distinct pesticide fate model input parameters when estimating 2,4-D off-site transport at the provincial scale. Spatial variations in herbicide degradation appear less important for Alberta as 2,4-D half-lives were similar in soils across the province. The rapid mineralization of 2,4-D is noteworthy because 2,4-D is widely used in Alberta and perhaps adaptation of soil microbial communities allowed for accelerated degradation regardless of soil properties or the extent of 2,4-D sorption by soil.

There is no published information on the impact of volunteer barley on wheat yield loss or on the economics of controlling barley with a herbicide. With the registration of imazamox-resistant wheat, it is now possible to control volunteer barley in wheat. Thus, the likelihood of growing wheat in rotation with barley may increase. Field experiments were conducted in 2003 and 2004 at Beaverlodge, Lacombe, and Edmonton, AB, Canada, and Saskatoon, SK, Canada, to determine the impact of volunteer barley on yield of imazamox-resistant spring wheat seeded at relatively low (100 kg ha−1) and high (175 kg ha−1) rates. Barley was seeded at different densities to simulate volunteer barley infestations. Regression analysis indicated that wheat-plant density influenced the effects of volunteer barley interference on wheat yield loss, economic threshold values, and volunteer barley fecundity among locations and years. Economic thresholds varied from as few volunteer barley plants as 3 m−2at Beaverlodge in 2003 and 2004 to 48 m−2at Lacombe in 2003. In most cases, wheat yield loss and volunteer barley fecundity were lower and economic thresholds were higher when wheat was seeded at the higher rate. For example, averaged over both years at Beaverlodge initial slope values (percentage of wheat yield loss at low barley density) were 4.5 and 1.7%, and economic threshold values of volunteer barley plants were 3 m−2and 8 m−2at low and high wheat seeding rates, respectively. Results indicate that volunteer barley can be highly competitive in wheat, but yield losses and wheat seed contamination due to volunteer barley can be alleviated by seeding wheat at a relatively high rate.

, J. 2008. Selection and establishment of Alberta agricultural soil quality benchmark sites. Can. J. Soil Sci. 88: 399Á408. Forty-three benchmark sites were established to monitor soils across the agricultural regions of Alberta. Soil chemical and physical properties were examined in an initial pedological investigation in 1997. This paper describes site selection and presents results from the initial pedological investigation. Ninety-five percent of the chosen sites were representative of their provincial ecodistrict, with only two profiles being darker and higher in organic carbon than expected. The majority of selected sites were gently undulating loam soils on morainal parent materials in the dryland regions of Alberta. Soil texture, cation exchange capacity, calcium carbonate content, and soil pH reflected regional differences in quaternary geology and agricultural practices across Alberta. Southern Alberta was characterized by high pH, sandier-textured soil profiles, whereas the Peace Lowlands, being derived from marine shale deposits, exhibited finer soil textures and higher cation exchanges capacities. Owing to climatic and vegetative differences, organic carbon levels were significantly greater in northern Alberta compared with the south, but were found to differ based on soil horizon and slope position. Upper slopes typically had lower organic carbon levels, particularly in the A horizon. Similar results were observed for total soil N, although other soil nutrients differed in relation to soil properties, slope and ecoregion. Data collected will provide: (a) the basis for a detailed Alberta soil quality assessment, (b) data for future modeling efforts, and (c) data necessary to identify temporal changes in soil properties, yield and management relationships. Quatre-vingt-quinze pour cent des sites se´lectionne´s sont repre´sentatifs de leur e´codistrict provincial, deux profils seulement e´tant plus sombres et contenant plus de carbone organique que pre´vu. La plupart des sites retenus se caracte´risent par un sol loameux faiblement ondule´, assis sur une base morainique dans les re´gions arides de l'Alberta. La texture du sol, le pouvoir d'e´change cationique, la teneur en carbonate de calcium et le pH du sol refle`tent les variations re´gionales au niveau de la ge´ologie du Quaternaire et les pratiques agricoles en usage en Alberta. Le sud de la province se de´marque par un pH e´leve´et un sol a`texture plus sablonneuse, alors que les basses terres de la rivie`re de la Paix, issues de de´poˆts de schiste argileux marins, pre´sentent une granulome´trie plus fine et une meilleure capacite´d'e´change des cations. La concentration de carbone organique est sensiblement plus e´leve´e dans le nord que dans le sud de la province en raison des diffe´rences au niveau du climat et de la ve´ge´tation, mais elle varie avec l'horizon du sol et la situation de la pente. Les pentes en hauteur contiennent habituellement moins de carbone organique, surtout dans l'horizon A. Les auteurs ont observe´des re´sultats simil...