Kröbel, R., Campbell, C. A., Zentner, R. P., Lemke, R., Steppuhn, H., Desjardins, R. L. and De Jong, R. 2012. Nitrogen and phosphorus effects on water use efficiency of spring wheat grown in a semi-arid region of the Canadian prairies. Can. J. Soil Sci. 92: 573-587. Water use efficiency (WUE) has often been analyzed for semiarid environments, but fallow-containing cropping systems were assessed inappropriately. Further, these short-term studies are unlikely to correctly assess weather variability impacts in such environments. We assessed the impact of fertilizer N and P on water use efficiency (WUE) and precipitation use efficiency (PUE) of spring wheat (Triticum aestivum L.) from a 39-yr long-term crop rotation study in semi-arid southwestern Saskatchewan. In the rotation experiment, continuous wheat (Cont W) with N P or P fertilizer only, and fallow-wheat-wheat (F-W-W) with N P, P only, or N only were studied. We calculated WUE using: (i) Yield (Y)/[water use (WU)/potential water use (PET)]; (ii) Y/WU; (iii) Y/WU with a fallow phase element added; and (iv) Y/harvest-to-harvest precipitation (PUE). The WUEs in the rotation experiment were generally greater for treatments with N P fertilizer, and greatest after an increase of N application coupled with favourable soil water conditions in the final decades of this study. In cases (i) and (ii), WUE for F-W-W was greater than for the Cont W-treatment. In case (iii), the WUEs were 5.7, 4.5, 3.9, 3.6, and 3.6 kg ha^-1 mm^-1 water for Cont W (N P), Cont W (P), F-W-W (N P), F-W-W (P), and F-W-W (N), respectively. For PUE [case (iv)] the values were 4.0, 3.1, 3.4, 3.0, and 2.9, respectively. We concluded that case (ii) was most appropriate for continuous cropping and case (iii) for systems including fallow, while case (iv) was usable in general.

Benke, M. B., Goh, T. B., Karamanos, R., Lupwayi, N. Z. and Hao, X. 2012. Retention and nitrification of injected anhydrous NH₃as affected by soil pH. Can. J. Soil Sci. 92: 589-598. Anhydrous ammonia is an economical and extensively used fertilizer, yet loss after injection can reduce its agronomic efficiency. A laboratory experiment was conducted to examine how soil properties affect ammonia retention and nitrification following anhydrous NH₃ injection using 10 different Canadian prairie soils. Soils were also injected with atmospheric air for comparison. Following injection, soils were incubated for up to 216 h at field capacity. Among the soil properties studied [pH (1:2 water), clay, total N, and organic C contents], only pH was negatively related (R²=0.55, n=10, 24 h incubation) to percentage injected N retained by soil. The amount of N retained by soil 24 h following injection was 92±2% (mean±SEM) when pH <6, compared with 64±2% when pH>7.5. Rate of nitrification increased (P<0.001) about 48-96 h following injection and was greater in pH>7.5 than pH<6 soils. There was no difference (P>0.05) in bacterial diversity between ammonia- and air-injected soils. The slower nitrification rates suggest that potential leaching and denitrification losses in acid soils could be smaller than in alkaline soils.

Ramnarine, R., Wagner-Riddle, C., Dunfield, K. E. and Voroney, R. P. 2012. Contributions of carbonates to soil CO₂emissions. Can. J. Soil Sci. 92: 599-607. Carbon dioxide (CO₂) is released in soil as a by-product of microbial and root respiration, but soil carbonates may also be a source of CO₂ emissions in calcareous soils. Global estimates of inorganic carbon range from 700 to 900 Pg as carbonates stored in soils, representing a significant potential source of CO₂ to the atmosphere. While previous studies have focused on the total CO₂ efflux from the soil, our goal was to identify the various sources and their contribution to total CO₂ emissions, by measuring the isotopic signature of the CO₂ emitted from the soil. Calcareous Luvisolic silt loam soil samples were obtained from conventional tillage (CT) and no-tillage (NT) plots in southern Ontario, Canada. Soil samples (root- and residue-free) were laboratory-incubated for 14 d and the isotopic signature of the CO₂ (δ¹³C_CO2) released was analyzed using isotope ratio mass spectrometry. Isotopic measurement was essential in quantifying the abiotic CO₂ production from carbonates, due to the unique δ¹³C signature of carbonates and soil organic matter. A two-end member mixing model was used to estimate the proportion of CO₂ evolved from soil carbonates and soil organic matter decomposition. Analysis of emitted CO₂ collected after the 14-d incubation indicate that the proportion of CO₂ originating from soil inorganic carbon was 62 to 74% for CT soil samples, and 64 to 80% for NT soil samples. Further work is recommended in the quantification of CO₂ emissions from calcareous soils, and to determine the transferability of laboratory results to field studies.

Olatuyi, S. O., Akinremi, O. O., Flaten, D. N. and Lobb, D. A. 2012. Solute transport in a hummocky landscape: I. Two-dimensional redistribution of bromide. Can. J. Soil Sci. 92: 609-629. Bromide has been widely used in field studies to estimate nitrate leaching in agricultural soils. This study examined the impacts of crop response to nitrogen fertilization on the vertical and lateral redistribution of bromide in the fall and spring seasons in a hummocky landscape. The study was carried out near Brandon, Manitoba, in 2007 and 2008, using two separate plots (Site-2007 and Site-2008). The plots were delineated into three landscape positions as upper (UPP), middle (MID) and lower (LOW) slope. A microplot at each landscape position received ¹⁵N labelled fertilizer (KNO₃) at the rates of 0, 90 and 135 kg N ha^-1, and KBr at the rate of 200 kg Br^- ha^-1. Site-2007 was seeded to canola while Site-2008 was seeded to winter wheat. Soil samples were taken within the microplot to a depth of 120 cm for vertical distribution, and up to 200 cm away from the microplot for lateral distribution of Br^- in the top 20 cm depth. The downward movement of Br^- in the soil was reduced under N fertilization. This resulted in the accumulation of Br^- in fertilized plots, and a greater lateral movement of Br^- in fertilized compared with unfertilized plots. The greatest vertical and lateral movement of Br^- occurred at the LOW slope position. In the fall season following Br^- application, 55 and 15% of the Br^- applied were recovered in the vertical and lateral components of the landscape, respectively. Estimated loss of Br^- due to vertical and lateral movement was 47% in the unfertilized treatment and 36% with N fertilization. The order of Br^- loss in the two dimensions was: LOW (48%)>MID (40%)>UPP (37%). The study shows that crop response to N fertilization reduced the vertical movement of solute, thereby providing an experimental support for the “Campbell hypothesis”which states that N fertilization and proper rate of N application reduces nitrate leaching.

Olatuyi, S. O., Akinremi, O. O. and Hao, X. 2012. Solute transport in a hummocky landscape: II. Vertical and seasonal redistribution of bromide and¹⁵N-labelled nitrate. Can. J. Soil Sci. 92: 631-643. Bromide (Br^-) tracer is often used to estimate potential nitrate-nitrogen (NO₃-N) leaching in soil. An alternative is to use ¹⁵N-labelled fertilizer to provide a direct measure of NO₃-N leaching losses. We employed a dual application of Br^- and ¹⁵N to estimate NO₃-N leaching in a hummocky landscape. The study was carried out near Brandon, Manitoba, in 2007 and 2008, using two separate plots (Site-2007 and Site-2008). The plots were delineated into three landscape positions as upper (UPP), middle (MID) and lower (LOW) slope. A microplot at each landscape received KBr at the rate of 200 kg Br^- ha^-1, and ¹⁵N-labelled KNO₃ fertilizer at the rates of 0, 90 and 135 kg N ha^-1. Site-2007 and Site-2008 were seeded to canola and winter wheat, respectively. Soil samples were taken in the fall and spring. The soil samples for the 90 and 135 kg N ha^-1 fertilization treatments were analyzed for vertical distribution of Br^-, ¹⁵N, and NO₃-N. The smallest amounts of Br^-, nitrogen derived from ¹⁵N-labelled fertilizer (NDFF), and NO₃-N were measured in the soil profile (0 to 120 cm) at the LOW slope position for both N fertilizer rates. The greatest amounts were at the MID slope, indicating that the downward movement of solute followed the order of: LOW>UPP>MID (P<0.05). Crop uptake of fertilizer N was 35 and 63% in canola and winter wheat, respectively, while Br^- uptake was negligible. In the absence of crop uptake, Br^- transport was similar to that of NDFF as 38% of each solute was lost between fall and spring in Site-2007 and 33% in Site-2008. Unlike Br^- and NDFF, NO₃-N distribution remained unchanged between fall and spring measurements, possibly due to its replenishment from native soil N sources. The dual tracer technique, as used in this study, showed the limitations of using soil profile NO₃-N alone as an indicator of nitrate leaching and for making treatment comparisons.

Zhu, J., Tremblay, N. and Liang, Y. 2012. Comparing SPAD and atLEAF values for chlorophyll assessment in crop species. Can. J. Soil Sci. 92: 645-648. This research had the objective of determining whether a new light transmittance meter, the atLEAF, could be used as a less expensive alternative to the SPAD meter. Both meters measure transmittance through leaf surfaces in wavelengths associated with chlorophyll, and both provide an indirect method for determining the nitrogen status of crop canopies. The current study compared SPAD and atLEAF values under different conditions and for six crop species (canola, wheat, barley, potato and corn). The results indicated strong correlations among laboratory leaf chlorophyll (Chl) content, SPAD values, and atLEAF values. Equivalent performances were observed for SPAD and atLEAF values in different environments regardless of crop species. Therefore, the atLEAF Chl meter can be used as an inexpensive alternative to the SPAD-502 meter.

Biswas, A., Chau, H. W., Bedard-Haughn, A. K. and Si, B. C. 2012. Factors controlling soil water storage in the hummocky landscape of the Prairie Pothole Region of North America. Can. J. Soil Sci. 92: 649-663. The Prairie Pothole Region (PPR) in North America is unique hummocky landscape containing hydrologically closed topographic depressions with no permanent inlet or outlet. Knowledge about the controls of soil water distribution in the landscape is important for understanding the hydrology in the PPR. In this study, we investigated the correlation between soil water storage and different controlling factors over time. Time domain reflectometry and neutron probe were used to measure soil water storage up to 1.4 m depth over 4 yr along a 576-m long transect at St. Denis National Wildlife Area, Saskatchewan, Canada, which represent a typical landscape of the PPR. Soil and vegetation properties were measured along the transect, and various terrain indices were calculated from the digital elevation map of the study area. Soil texture (e.g., correlation coefficient, r=-0.57 to -0.73 for sand) provided one of the best explanations for the variations in soil water storage by controlling the entry and transmission of water within soil in the semi-arid climate of study area. Bulk density (r=-0.22 to -0.56), depth of A horizon, (r=0.18 to 0.49), C horizon (r=0.29 to 0.69), and CaCO₃ layer (r=0.31 to 0.79) influenced the water transmission through soil and were correlated to soil water storage. Beside soil properties, topographic wetness index (r=0.47 to 0.67), slope (r=-0.41 to -0.56), convergence index (r=-0.29 to -0.60), and flow connectivity (r=0.27 to 0.60) were also correlated to soil water storage. However, multiple linear regressions showed a consistent high contribution from soil properties such as sand, organic carbon, depth of CaCO₃ layer, and bulk density in explaining the variability in soil water storage. A substantial contribution from topographic variables such as wetness index, gradient, and solar radiation was also observed. Therefore, unlike other geographic regions, the soil-water storage variations in the PPR are controlled by a combination of soil and terrain properties with dominant control from soil characteristics at the field scale.

Nazmi, L., Asadi, H., Manukyan, R. and Naderi, H. 2012. Influence of tillage displaced soil on the productivity and yield components of barley in northwest Iran. Can. J. Soil Sci. 92: 665-672. In hilly landforms subject to long-term cultivation, erosion has denuded the upper slope positions of topsoil, and accumulated topsoil in the lower slope positions. Slope gradient and position effects aggregation processes, which in turn impact soil productivity. A field experiment was conducted to assess the tillage-induced soil displacement and its effects on the soil properties and barley (Hordeum vulgare var. Sahand) biomass production for three different landscapes. The study was conducted on a hill slope seeded with barley (1.4-10.1° slope) located in the Mollaahmad watershed of the Ardabil province in northwestern Iran. For this purpose, soil samples were collected from four slope positions in a grassland as well as an agricultural field (dryland). A field experiment was conducted to evaluate the effects of slope gradient and position on barley growth and soil quality. Soil generally had lower organic carbon, available phosphorus, calcium carbonate equivalent, soil water content and mean weight diameter of soil aggregates in the farmland than the grassland, and in the upper slope positions than in the lower slopes. Significantly higher barley growth indices were associated with lower slope positions. Agronomic productivity of the soil was lowest for landscapes with the highest slope gradient. The relationships between tillage erosion and yield components were found to be significant. Spike weight and slope position had the largest contribution for the explanatory capacity of canonical variables (tillage erosion and yield components) estimated when compared with other parameters (slope gradient, dry matter, spike number, grain yield and 1000-grain weight). The findings in this study can be used as a tool to assist farmers, soil and water conservationists, and other policymakers in decision making regarding the use of lands.

Miller, J. J., Bremer, E., Beasley, B. W., Drury, C. F., Zebarth, B. J. and Larney, F. J. 2012. Long-term effect of fresh and composted cattle manure on the size and nutrient composition of dry-sieved soil aggregates. Can. J. Soil Sci. 92: 673-683. Application of feedlot manure to cropland may impact the size distribution and nutrient content of soil aggregates. The objective of this study was to determine the effects of fresh or composted feedlot manure containing straw or wood-chip bedding on dry-sieved aggregate size distribution and nutrient contents. Surface (0-15 cm) soil samples were obtained from a long-term field experiment where treatments were fresh (FM) or composted manure (CM) containing straw or wood-chips applied annually at 0 (control) or 77 Mg ha^-1 yr^-1 for 11 yr. Air-dried soil samples were separated using a rotary sieve into six aggregate size fractions ranging from <0.47 mm to >12.7 mm. Total C, total N, C:N ratio, soil mineralizable N (41-d incubation), total P, soil test P, and P saturation index were determined on the six aggregate fractions. The amendments significantly (P≤0.05) increased the proportion of smaller (<0.47 mm) aggregates and decreased the proportion of the larger (>12.7 mm) aggregates relative to the unamended control. The geometric mean diameter (GMD) was also lower and wind erodible fraction (WEF) was greater for the amended treatments than unamended control. We attributed this manure effect to increased organic matter content in the soil making the aggregates more friable and susceptible to breakdown by tillage. Carbon, N, and P concentrations were not shifted to smaller aggregate sizes where root growth and nutrient uptake are generally greater. The exception was mineralizable N, which tended to be greater in the finer<0.47 mm fraction. Mineralizable soil N in all aggregate sizes =0.47 mm was reduced for wood-chip compared with straw bedding, and resulted in net N immobilization in aggregate sizes =1.2 mm. Phosphorus sorption was lower in soil amended with wood-chips compared with straw bedding for aggregates =0.47 mm. Long-term manure application may shift soil aggregates from larger to finer fractions because of greater friability and suggests that these soils should be managed to avoid the greater risk of wind erosion.

Evans, C. R. W., Krzic, M., Broersma, K. and Thompson, D. J. 2012. Long-term grazing effects on grassland soil properties in southern British Columbia. Can. J. Soil Sci. 92: 685-693. Although grazing effects on soil properties have been evaluated on various temperate grasslands, no study has dealt with these effects in the southern interior of British Columbia. The objective of this study was to determine the effects of spring versus fall season grazing as well as grazing [at a moderate rate of 0.6 animal unit months (AUM) ha^-1] versus non-grazing by beef cattle on selected soil properties. Effects were determined 20 and 30 yr after the establishment of the field experiment. Soil properties were determined for the 0- to 7.5-cm, 7.5- to 15-cm, and 15- to 30-cm depths. In comparison with fall grazing, spring grazing had greater soil bulk density, greater mechanical resistance within the top 15 cm of the soil profile, higher pH, and lower polysaccharides. This was true for both 20 and 30 yr of treatment. Grazing effects on aggregate stability were observed only after 30 yr with spring grazing leading to a more stable structure with a mean weight diameter (MWD) of 1.5 mm and 32% and 10% of aggregates in the 2- to 6-mm and 1- to 2-mm size fractions, respectively, compared with a MWD of 1.0 mm and 20% and 6% under fall grazing. Greater soil bulk density, mechanical resistance, and pH were observed under the grazed treatment relative to the control without grazing, but as we used a moderate stocking rate the impacts were not as great as in previous studies, which used heavy stocking rates. Our findings show that long-term grazing at a moderate stocking rate of 0.6 AUM ha^-1 did not have critical detrimental effects on soil properties as some land managers and ranchers have suggested.