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A 2-yr study was conducted to investigate the effects of application date, landscape position and a urease and nitrification inhibited formulation of urea on the efficiency of fall-banded N fertilizer under Manitoba conditions. To date, no studies have investigated how these factors interact to influence the efficiency of fall-banded N in western Canada. The effects of landscape position were apparent at three of the four sites, with significantly greater grain yields, straw yields and total recovery of N in the high landscape positions than in the low landscape positions. In the high landscape positions, there were no significant differences in crop response or recovered N among application dates in the fall and spring. However, in the low landscape positions, grain yields, grain yield increases and apparent recovered fertilizer N in the aboveground portion of the crop and in the soil (0–120 cm) were significantly greater for spring and late fall applications, when compared with early and mid-fall applications. At one site in the first year of the study, early fall-banded N with the urease and nitrification inhibitors produced greater increases in grain yield than early fall-banded N without the inhibitors in the low landscape positions. However, overall there was little agronomic benefit to the use of the additives, as there were few significant differences in crop yields or N uptake by the crop with the inhibitors than without, in either year or landscape position. The results demonstrate that selection of suitable timing for application of fertilizer N to optimize crop yields is much more critical for poorly drained areas within a field, or for poorly drained fields, than for better drained land. Key words: Fall-banded N, spring-banded N, landscape position, N-(n-butyl) thiophosphoric triamide (NBPT), Dicyandiamide (DCD), wheat (Triticum aestivum)

The practice of placing granular Cu fertilizers with the seed of cereals and oilseeds has been expanding in western Canada mainly due to the high cost of applying the minimum suggested broadcast and incorporation rate of 3.5 kg Cu ha-1. The hypothesis made is that annual applications of small amounts of Cu in the order of 1 kg Cu ha-1 will satisfy the Cu requirement of a crop and, over a period of years, have the same effect as a single broadcast and incorporated application. We tested this hypothesis in a number of experiments aimed at assessing the effectiveness of seedrow placement of a variety of Cu products (sulphate, oxysulphate and chelated) at various rates (0 to 4 kg Cu ha-1) in the year of application, its residual effect after four annual applications and whether it can be combined with foliar Cu applications to provide an agronomic and economic solution both in the short and longer terms. Annual seedrow applications of up to 4 kg ha-1 were both agronomically and economically inferior to broadcasting and incorporation of 4 kg ha-1 as Cu sulphate; the former provided a statistically significant grain yield increase only in 3 of 10 site-years and only when the Cu fertilizer was in sulphate or chelated forms. However, yield increases thus obtained were neither economical nor as good as those obtained with broadcast and incorporated copper sulphate. The residual effects of seedrow-applied Cu at rates up to 4 kg ha-1 were very small compared to a single, 4-yr old broadcasting and incorporation of 4 kg Cu ha-1, and were obtained primarily after 3 yr of annual applications and with sulphate or chelated products only. However, average yield increases as a result of residual effects in the fifth year were approximately 35% of those obtained with broadcasting and incorporation. Combining seedrow with foliar applications did not have any agronomic or economic advantage, since most benefit arose from the latter. Key words: Broadcast and incorporation, sulphate, oxysulphate, chelate, residual

Copper is a nutrient known for its lack of mobility in soils. This phenomenon affects fertilizer product and placement options when attempting to correct Cu deficiencies. A column experiment was designed to directly compare the mobility of Cu sulphate (CuSO4 5H2O) and a chelated Cu fertilizer (CuEDTA) in five soils with different levels of organic matter (2 to 108 g kg-1 organic C) and clay (4.1 to 34.9%). The movement of Cu, supplied as Cu sulphate and CuEDTA, through a 10- cm column of soil was examined during a 10-d period by monitoring the Cu concentration in leachate following daily additions of 2 cm deionized water and subsequently assaying the soil columns, in 1-cm increments, for DTPA-extractable Cu (DTPACu). Copper sulphate was virtually non-mobile in all soils with at least 20 g kg-1 organic C and 10% clay. However, in a soil with 2 g kg-1 organic C and 4% clay, Cu sulphate moved as much as 7 cm. The restricted mobility of Cu sulphate in all but one soil in this study suggests that in most western Canadian Prairie soils, having relatively high levels of organic matter and clay, Cu supplied as Cu sulphate should be regarded as immobile from an agronomic perspective. In contrast, a portion (2 to 46%) of the CuEDTA moved through the entire 10 cm column of all soils within 3 d, i.e., following three daily additions of 2 cm of water. The enhanced mobility of the chelated Cu is of agronomic significance in that it suggests that this Cu source is more likely to move into the root zone without incorporation and provide adequate feeding sites for a crop when placed in or near the seedrow. Key words: Cu mobility, Cu sulphate, Cu chelate, soil texture, organic matter, leachate

Criteria for assessment of the Cu status of prairie soils were developed in the early 1980s and are currently in use with some modifications. Although there appears to be a reasonable agreement on the soil critical value of 0.4 mg kg-1 soil based on DTPA-extractable Cu, a marginal range that extends between 0.4 and 1.2 mg DTPA-Cu kg-1 soil is used to generate fertilizer recommendations. The objective of this study was to verify the existing soil critical value and identify the frequency of agronomic as well as economic response of spring wheat to Cu fertilization on soils with levels both below and above the critical value. We carried out a large number (52) of trials with spring wheat (Triticum aestivum L.) between 1991 and 2000 in all three Prairie Provinces and compiled a large number of spring wheat experiments conducted in western Canada (63) by a number of researchers. Fifty-nine trials carried out on soils containing marginal and sufficient Cu levels were evaluated and were compared to 56 experiments on soils containing deficient levels. A number of methods of placement and products were compared. Agronomic responses were obtained in 41 of the 115 experiments and only by broadcasting either 3 to 5.5 kg Cu ha-1 as CuSO4·5H2O or 0.5 to 2 kg Cu ha-1 as Cu-sulphonate and incorporating the product or by foliar application of 0.22 kg Cu ha-1. Calibration of the DTPA-extractable Cu test using a Mitscherlich type of function verified the soil critical value of 0.4 mg Cu kg-1 soil. Statistically significant grain yield responses were obtained in 87, 16 and 0% of trials carried out on soils containing 0.8 mg DTPA-extractable Cu kg-1 soil. Economic responses, defined as those where Cu application yielded a 2:1 return on the cost of fertilizer in the year of application, varied depending on the price of wheat and ranged between 19 to 45% in deficient soils for a price range of $100 to $200 t-1 of wheat grain; economic responses on marginal and sufficient soils occurred in 6% and none of the cases, respectively. Hence, fertilization of soils with DTPA-extractable Cu levels >0.4 mg kg-1 is associated with very high risk. Key words: DTPA-extractable, calibration, soil critical value, deficient, marginal, agronomic, economic

A 3-yr program was carried out in central Alberta to evaluate the immediate and residual contributions of various fertilizer sulfur sources to the pool of plant-available sulfate in soil. Three elemental sulfur products, a finely-divided suspension and two elemental sulfur + bentonite products, and ammonium sulfate were applied at various rates (0–120 kg S ha−1) in factorial arrangement with various supplemental rates of sulfate (0–40 kg S ha−1). Temporal patterns of plant-available sulfur release varied significantly among fertilizer S sources, suggesting different agronomic niches for the various forms. While ammonium sulfate and the finely divided S suspension provided almost immediate correction of S deficiency, the S-bentonite products appeared be better suited to long-term maintenance of soil S fertility. The relatively slow release of plant-available S in the latter products was attributed to ineffective dispersion of the products in the soil. These slow-release characteristics need to be considered in the formulation of fertilizer recommendations on soils previously amended with S-bentonite products. Key words: Oxidation, plant availability, residual effect, S fertilizers

Sulfur deficiency has become a widespread limitation to crop production in western Canada. A variety of S sources are commercially available to alleviate these deficiencies but not all are equally effective. Three elemental S products (a finely-divided suspension and two elemental S + bentonite) and ammonium sulfate were compared over a 3-yr period in central Alberta. These products were applied to barley and canola at various rates (0–120 kg S ha−1) in a factorial arrangement with various supplemental rates of sulfate-S (0–40 kg ha−1) in two experiments Fertilizers affording effective and reliable alleviation of S deficiency in the year of application included sulfate forms and finely-divided elemental S products that can be readily mixed into the soil. The residual benefits of the various fertilizer products examined appeared to be comparable despite large differences in short-term availability. The absence of appreciable residual advantage of slow-release elemental S products was attributed to the short duration of S assimilation by canola and barley and the susceptibility to leaching of S oxidized after that period. Key words: Barley, canola, residual, rotation, S fertilizer, uptake, yield

Growth chamber and laboratory studies were conducted to investigate the distribution and plant availability of copper (Cu) fractions in Saskatchewan soils. These studies included an examination of the distribution of Cu fractions in 27 soils and an evaluation of plant availability of native and added Cu fractions in beans (Phaseolus vulgaris L.) grown in seven soils. The soils in these experiments were selected to give a wide variation in physical and chemical properties. Total Cu content of the 27 soils ranged from 6.5 to 39.0 μg g−1 with an average of 21.0 μg g−1. A seven-step sequential fractionation showed that most of the total Cu (49.0–78.0%) was present in the residual fraction (Res-). The percentages of soil Cu in the exchangeable (Ex-), Pb-displaceable (Pb-), acid soluble (Aci-), Mn oxide bound (MnO-), organically associated (OM-) and Fe, Al oxide bound (FeO-) fractions averaged 2.2, 1.5, 2.0, 4.8, 7.9 and 11.1%, respectively. Amounts of Cu in MnO-, FeO-, Res- fractions and total Cu were interdependent and varied directly with DTP A- extractable Cu and clay content. The growth chamber experiment showed that the most of the applied Cu was accumulated in MnO-, OM-, FeO-, and Res- fractions. Therefore, sesquioxides and organic matter are the major components responsible for the adsorption of added Cu. The concentration of Cu and its uptake into navy beans were positively correlated with DTPA-extractable Cu, MnO-Cu, FeO-Cu and total Cu, which in turn were correlated with clay content. Plant Cu concentration and uptake can be predicted by an equation which includes DTPA-extractable Cu and clay content. These results showed that DTPA-extractable Cu is a good predictor of Cu availability in prairie soils. Key words: Cu fractions, distribution, availability, DTPA-extractable Cu, clay content, navy beans

The distribution of Zn in soil fractions was determined for 27 representative prairie soils from Saskatchewan. Total Zn in the 27 soils under study ranged from 19.0 to 106.6 μg g−1 with an average of 62.0 μg g−1. A sequential fractionation showed that 0.2–2.4% of total Zn was exchangeable, 0.4–8.1% was Pb-displaceable, 0.4–4.3% was acid soluble, 1.6–9.7% was associated with Mn oxides, 0.6–4.4% was associated with organic matter and 0.9–5.1% was associated with Fe + Al oxides. Most of the total Zn was present in residual form (66.9–91.0%). Amounts of Zn in exchangeable and Pb-displaceable fractions varied inversely with soil pH and extractable P. DTPA-extractable Zn was correlated with Zn in most of the fractions, except Fe oxide-Zn, residual-Zn and total Zn. This result indicates that DTPA extractable-Zn contains Zn from Mn oxides and organic matter associations in addition to the exchangeable and adsorbed forms. The amount of total Zn was correlated with clay content and cation exchange capacity thus reflecting differences in parent materials. Key words: Soil Zn, Zn fractions, Prairie soils, pH, clay content

The uptake of native and applied fractions of lead (20 and 100 μg Pb/g soil) by alfalfa and bromegrass was studied in a growth chamber experiment using three soils. The applied soil lead treatments did not affect dry matter (DM) yield but the concentration of lead in the plant tops was found to increase twofold when the amount of lead added to soil was increased fivefold (mean values for both crops 3.8 and 8.7 ppm in the 20 and 100 ppm Pb treatments, respectively). Added sulphur gave significant DM yield response in both crops on all soils but did not significantly alter the lead concentration in the aboveground DM. Lowering the temperatures and reducing the photoperiod to simulate autumn conditions resulted in a significant increase of lead concentration in plants grown on the 100 ppm Pb treatment, which was attributed to the corresponding reduction in the DM yields of the plants. High concentrations of lead (mean 132 ppm) were found in the fine roots of both crops in comparison with lead levels in main roots (mean 33 ppm). Lead extracted by various extractants from soil samples at the end of the growth chamber experiment indicated that applied lead was rapidly immobilized with the higher lead concentrations in the soil solution being found in the soil with the lowest organic matter and clay content.

Four soils of different physical and chemical characteristics were treated with 10 ppm lead in the form of PbCl2 labelled with lead-210 (2.5 mCi/g 207Pb) and subjected to a 7-wk incubation period. The extractability of the added lead was assessed using 12 extractants. Almost complete recovery (93–98%) of the applied lead was obtained with 6 N HNO3. Large amounts of the applied lead [Formula: see text] could be extracted by chelating agents (DTPA and EDTA). Relatively small amounts were exchangeable with 0.5 M BaCl2 (0.1–4%) and N NH4OAc (1–11%). Proportionally slightly higher amounts were extracted with 2.5% AcOH and 0.5 M NaHCO3. Only traces could be found in the 0.05 M CaCl2 extract.

Rather marked variations in δa15N values were obtained in a study carried out on samples taken from four soils belonging to the Weyburn soil association. The δa15N of the total N of well-drained depressional profiles dropped sharply with depth and, in contrast, for upper slope positions was relatively constant to a depth of approximately 5 m. This characteristic enrichment in the heavier isotope of total nitrogen of surface horizons may represent long-term immobilization of partially oxidized ammonium N into the organic N fraction; δa15N of the total N more closely represents past soil-forming processes while that of the nitrate N appears to reflect, in addition, recent N cycle stresses.

The relative effectiveness of Zn-sulphate (ZnS), Zn-EDTA (ZnE), low-yield ammonium-based lignosulphonate (ZnLY) and high-yield sodium-based lignosulphonate (ZnHY) for bean production was tested in growth chamber and incubation experiments. ZnS and ZnLY were more effective than ZnE and ZnHY in correcting Zn deficiency of bean plants. While biomass production was best with ZnS, ZnLY was more effective in increasing Zn-content in the foliage and in the formation of strong chelates in the soil. Key words: Zn-sulfate, Zn-EDTA, lignosulphonate, spent sulphite liquor, sulphite pulping

The objective of this study was to determine changes in N dynamics in an Orthic Black Chernozem as a result of two tillage practices (conventional and zero tillage) using the variations in the natural 15N abundance of different soil-N fractions. After 14 yr, no significant differences in isotope composition of total soil-N between the two tillage practices could be found. However, changes were detected in the natural 15N abundance of the acid-hydrolyzable N and various organo-mineral size fractions which led to useful comparisons of the nature of N under the two systems. The N-content of the hydrolyzable-N fraction was similar at the 0- to 4- and 8- to 16-cm depth under both tillage practices, while it was significantly different at the 4- to 8-cm depth. The δa15N of this fraction was consistently higher than that of total soil N at all depths only under zero tillage. This was associated with the presence of more labile N compounds under zero tillage. No differences in the isotopic composition of the organomineral size fractions were found at the 0- to 4-cm depth. At the 4- to 8- and 8- to 16-cm depths, the δa15N values of the finer particle size fractions were higher under zero tillage than under conventional tillage. This indicates a more labile nature of the N associated with these size fractions under zero tillage. Key words: δa15N, conventional tillage, zero tillage, total N, acid-hydrolyzable fraction, particle size fractions

Nitrogen isotopic fractionation during ammonium adsorption by clay colloids was shown to occur in two time-dependent stages. A rapid 15N enrichment of the NH4+ in solution was followed by a gradual depletion until, after an 8- to 10-h equilibrium period, the δa15N of the NH4+ in solution was approximately 1; this value was significantly lower than the initial value of 2.3 for the NH4Cl used in these experiments. The isotopic equilibrium constant (ke) for the ammonium adsorption reaction was greater than unity, and higher for the Ca2+- than K+-saturated clay colloids.

Cerenkov radiation counting was found to be an excellent method of radioassay of 210Pb in aqueous extracts of soils and acid digests of plant material. The use of polyethylene vials and a wavelength shifter 7-amino-1,3-naphthalene-disulfonic acid greatly improved the counting efficiency. Color quenching was the main factor in lowering counting efficiency but could be corrected using the channels ratio method. Extracts of soils having high organic matter contents showed severe color quenching. Pretreatment of these extracts with 30% H2O2 greatly increased the counting efficiency.

The variability in DTPA-extractable micronutrients was studied for the A and B horizons of a cultivated site and its native prairie counterpart. The results showed that there was a high degree of variability in samples taken every meter on a 46-m long transect. There were large differences among the cultivated and native prairie soils, the two soil horizons and the four micronutrients studied. In cultivated fields, larger numbers of samples were required for Cu and Mn than for Zn and Fe to obtain a precise estimate of the mean. The number of samples becomes critical as deficiency levels are approached. Key words: Soil sampling, sample size, soil variability

Wheat (Triticum aestivum L.) was grown in rotation with maize (Zea mays L.) and soybeans (Glycine max L.) as first crops at the National Irrigation Research Station, Nanga, Zambia. Two nodulating soybean cultivars used in the first season of the rotation were compared for their ability to support symbiotic N2 fixation by Bradyrhizobium japonicum using a nonnodulating cultivar as a reference crop and the 15N isotope dilution technique. All first crops received two levels of P (0 or 30 kg P ha−1). The legumes received a blanket application of 20 kg N ha−1, whereas maize received two rates of N (20 and 60 kg N ha−1). There were no benefits of residual P from the first crops to the succeeding wheat. However, the yields of wheat grown on plots where fixing legumes had been grown the previous season were significantly higher than those where maize had preceded. The superior wheat yield in the soybean-wheat rotation over the maize-wheat rotation was attributed to residual N from biological N2 fixation by the preceding legume crop. The benefits were greater when the lower yielding soybean cultivar preceded wheat in the rotation presumably due to its lower soil N demand. Key words: 15N isotope dilution, B. japonicum, N fixation, residual P, residual N, crop rotation

A survey of the DTPA-extractable Cu levels of approximately 1000 fields representing a large number of soil types in Saskatchewan suggested that, under current cropping systems, Cu deficiencies appear to be concentrated in the Grey Soil Zone. They are especially probable in seven soil associations, which include light Transition of Grey and Brownish-Grey Podzolic soils. Soil criteria for detecting Cu deficiencies in cereal crops cannot be fully documented using conventional calibration tests and techniques. However, data from 21 field trials and a growth chamber study indicated that the critical level of DTPA-extractable Cu in these soils is approximately 0.4 mg∙kg−1 for cereals. Large spatial variability of DTPA-extractable Cu levels has been found to occur in a level field, thus suggesting that the Cu status of a field may not be adequately described by assessing the Cu levels of composite field samples. Key words: DTPA-extractable Cu, soil survey, critical level, spatial variability

A growth chamber experiment was conducted to assess the Mn and Cu nutrition of canola (Brassica napus L. 'Westar') and whether S nutrition has an impact on the Mn and Cu nutrition of this crop. Three rates of Mn (0, 25, and 50 mg kg−1), three of Cu (0, 5, and 10 mg kg−1) and three rates of S (10, 20, and 30 mg kg−1) were applied in all combinations to canola grown on an organic soil. High Mn:Cu ratios (> 15) led to Cu deficiency, which, at 10 and 20 mg S kg−1, was alleviated by Cu additions. The Mn-induced Cu deficiency was self-corrected at the 30 mg S kg−1 application rate. This was attributed to the alleviation of a Cu × Mo antagonistic effect through addition of S. Key words: Canola, available soil Mn and Cu, Mn × Cu × S interaction, S × Mo interaction, Cu × Mo interaction

Current criteria for predicting zinc (Zn) deficiency in Saskatchewan soils are based on DTPA-extractable Zn values. DTPA-extractable Zn levels in 12% of 1200 samples taken across Saskatchewan contained less than 0.5 mg Zn kg−1 soil and would be classified as potentially Zn deficient. However, 23 field trials in 1982, 1983 and 1984 with spring wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), lentils (Lens esculenta Moench.), peas (Pisum sativum L.), alfalfa (Medicago sativa L.), corn (Zea mays L.) and flax (Linum usitatissimum L.) produced only one significant response to Zn fertilization. No yield benefits due to either annual or residual application of Zn fertilizer were obtained even on high lime soils or those containing DTPA-extractable Zn levels below 0.5 mg kg−1 soil. Hence, current soil criteria to identify Zn deficiencies under the prevailing cropping systems must be revised to reflect these findings. Key words: DTPA-extractable Zn, crop response, critical level

A growth chamber experiment with six organic soils was conducted to assess the Cu and Mn nutrition of spring wheat grown on organic soils. Three rates of Cu (0, 5, and 10 μg∙g−1 of equivalent volume of a fsl) and three rates on Mn (0, 25, and 50 μg∙g−1 of equivalent volume of a fsl) were applied in all combinations to spring wheat grown on six organic soils. Normal growth of wheat plants was achieved only in soils and treatments where a proper balance on Mn and Cu was achieved. Dry matter yield responses at 45, and 60 days and grain yields reflected the significance of this balance. The major conclusion from this study is that normal wheat growth was achieved on organic soils only when the DTPA-extractable soil (soil: extractant ratio of 1:5) Mn/Cu ratio was between 1–15. At Mn/Cu ratio below 1 and above 15, yield reducion and death of plants occurred due to Mn and Cu deficiency, respectively. Key words: Organic soils, spring wheat, available soil Mn and Cu, Mn/Cu interaction, Mn/Cu ratio

The δa15N for the total and nitrate soil N from surface samples taken from recharge and discharge areas associated with a saline seep differ significantly. Suggested reasons for these differences are included. These data suggest that the nitrate moving towards the surface with the soluble salts is depleted in the heavier isotope; the very high δa15N for total and nitrate N of surface samples suggests that denitrification has been a dominant process operating in the saline seep area. Incubation studies carried out on Ap samples taken from the recharge and discharge areas have verified that the δa15N (and perhaps also the nature of the mineralizable organic nitrogen) from a "mature" and "recent" saline profile are different from each other, and distinctly different from that of the recharge area.

The nature of the P-induced Zn deficiency in bean plants was studied in a growth chamber experiment using three pedogenically different soils. Application of P (0, 40, 80 and 160 mg P kg−1 soil) resulted in significant dry matter (DM) yield increases. Maximum DM yields were attained at the 40 mg P kg−1 application rate. Application of Zn (0, 5 or 10 mg Zn kg−1 soil) without P application had no effect on DM yields of bean plants. However, Zn application in combination with P application resulted in significant DM yield responses. There was no evidence that the P-induced Zn deficiency was a result of differences in soil characteristics or influence of P on the water soluble plus exchangeable, organically bound, Mn- and Fe-oxide bound or residual Zn fractions. The Zn concentration in bean plant tops was significantly reduced due to P application and the magnitude of the reduction was greatest with the first increment of applied P (40 mg P kg−1 soil). Application of P induced Zn deficiency, at least partly, by stimulation of growth and subsequent dilution of tissue Zn concentration. Translocation of Zn from roots to tops appeared to be restricted at 80 and 160 mg applied P kg−1 soil treatments, as evidenced by the reduction of Zn uptake in non-Zn treatments. Thus, plant dilution effects and reduced translocation of Zn from roots to tops were the two mechanisms responsible for the observed P-induced Zn deficiency in this study. Key words: P × Zn interaction, plant availability, plant uptake, soil Zn fractions, soil P, Zinc-65

The systematic decline in δa15N (per mill 15N excess) of plant material with application of fertilizer under field conditions was verified in a growth chamber experiment with soil columns. The δa15N of NO3−-N in the zones of the high NO3−-N accululation was lower than that of the soil-derived NO3−-N but not necessarily lower than the δa15N of the fertilizer material as was the case in previously reported field experiments. Calculation of the fate of the fertilizer N based on the principle of isotopic dilution provided semi-quantitative estimates of the added N found in the plant, the soil, and the leachate.