ALBERT

Description: In response to Kyoto Protocol commitments, countries can elect agricultural carbon sinks to offset emissions from other sectors, but they need to verify soil organic carbon (SOC) stock change. We summarize issues we see as barriers to obtaining accurate measures of SOC change, including: soil depth, bulk density and equivalent soil mass, representation of landscape components, experimental design, and the equilibrium status of the SOC. If the entire plow depth is not considered, rates of SOC storage under conservation compared with conventional tillage can be overstated. Bulk density must be measured to report SOC stock on an area basis. More critical still is the need to report SOC stock on an equivalent mass basis to normalize the effects of management on bulk density. Most experiments comparing SOC under differing management have been conducted in small, flat research plots. Although results obtained from these long-term experiments have been useful to develop and validate SOC prediction models, they do not adequately consider landscape effects. Traditional agronomic experimental designs can be inefficient for assessing small changes in SOC stock within large spatial variability. Sampling designs are suggested to improve statistical power and sensitivity in detecting changes in SOC stocks over short time periods. Key words: Soil organic carbon change, agroecosystems, experimental design, sampling depth

Description: Sustainability of forest ecosystems and climate change are two critical issues for boreal forest ecosystems in Canada that require an understanding of the links and balance between productivity, soil processes and their interaction with natural and anth ropogenic disturbances. Forest ecosystem models can be used to understand and predict boreal forest ecosystem dynamics. EFIMOD 2 is an individual tree model of the forest-soil ecosystem capable of modelling nitrogen feedback to productivity in response to changes in soil moisture and temperature. It has been successfully applied in Europe, but has not been calibrated for any forest ecosystem in Canada. The objective of this study was to parameterize and validate EFIMOD 2 for jack pine in Canada. Simulated and measured results agreed for changes in tree biomass carbon and soil carbon and nitrogen with increasing stand age and across a climatic gradient from the southern to northern limits of the boreal forest. Preliminary results from scenario testing indicate that EFIMOD 2 can be successfully applied to predict the impacts of forest management practices and climate change in the absence of natural disturbances on jack pine in the boreal forest of Canada. Model development is underway to represent the effects of natural disturbances. Key words: EFIMOD 2, forest soil, carbon, nitrogen, model, jack pine

Description: Environment and management effects on the N supply to crops are not well understood. We assessed the influence of tillage system (conventional tillage or no-till), N fertilizer (0 or 60 kg N ha-1) and year on N sources and supply of a Dark Brown Chernozem loam soil, and N utilization by spring wheat (Triticum aestivum L.) in 2 yr. The main N source was mineralized N; only 14–23% of wheat N was derived from fertilizer, and non-exchangeable ammonium made no measurable contribution. Soil NO3 and exchangeable NH4 content at sowing and net N mineralization during the growing season (Nmin) were influenced more by year than by N addition and tillage. Nmin was 90–100 kg N ha-1 in 1999, a moist growing season but only 21–39 kg N ha-1 in 2000, a drier year. In both years, soil inorganic N to 60 cm at sowing averaged about 60 kg N ha-1 of which half was N mineralized since the previous harvest. Year accounted for 65–81% of the variation in N uptake. Fertilization increased N uptake and wheat yields, especially in 2000, but fertilization and tillage had no effect on post-heading N uptake and N translocation. Nitrogen use efficiency (NUE) and N recovery were lower with N applied and not affected by tillage. Our study indicated that available N was affected more by environment than management. In dry conditions, when Nmin is low, N application may be more effective in increasing yield and N uptake than in wet years, an observation that may merit further attention. Key words: Available N, N mineralization, N recovery, N use efficiency, non-exchangeable ammonium, tillage

Description: Despite the seriousness of the erosion problem in the Nakhla watershed, there are still only limited data on the rates of soil loss on cultivated land on steep slopes. Thus, there is a need for more information for optimizing strategies for soil conservation. Recent concern over problems of soil degradation and the off-site impacts of accelerated erosion has highlighted the need for improved methods of estimating rates and patterns of soil erosion by water. In this paper, soil erosion and deposition rates have been studied using the 137Cs technique in upstream part in the Nakhla watershed on cultivated soils (Larbaa Beni Hassan area), which is known to suffer soil erosion. Multiple transect sampling was established parallel to the slope, and 137Cs inventories were determined for the sampling points. After establishing the local reference inventory (3073 Bq m-2), soil erosion and deposition rates were estimated using the 137Cs inventories on all the transects with three calibration models: proportional model (PM), mass balance model 1 (MBM1) and mass balance model 2 (MBM2). The magnitude of the soil erosion rates depends on many factors, including the location of sampling, the local topography, and the soil properties. Estimated soil erosion rates for the study area varied from 0.4 to 28.9 t ha-1 yr-1 using PM; from 0.5 to 66.9 t ha-1 yr-1 using MBM1; and from 0.4 to 56.4 t ha-1 yr-1 using MBM2. The deposition ranged, respectively, from 0.3 to 8.0 t ha-1 yr-1 for PM, from 0.4 to 14.5 t ha-1 yr-1 for MBM1, and from 0.3 to 11.5 t ha-1 yr-1 for MBM2. The sediment delivery ratio is about 98%. For one selected plot, L11, the erosion rates show a clear relationship with the range of slopes in its three different horizontal parts. Estimates of soil redistribution rates were interpolated by means of kriging, using Surfer 7.0 software. Two representative transects were selected to identify the contribution of tillage on 137Cs redistribution by using mass balance model 3. It is observed that the pattern of 137Cs redistribution is dominated by water erosion and that the contribution of tillage redistribution remain is smaller. Key words: 137Cs method, soil erosion, erosion rate, soil redistribution, conversion models

Description: Soil phosphorus (P), which is potentially a risk for environmental contamination, is currently interpreted using soil P saturation in North America. Our objective was to assess the ratio of P to aluminum (Al) in the Mehlich-III (M-III) soil test to build P requirement models for corn and soybean. We analyzed 129 corn and 19 soybean P fertilizer trials. For corn, the (P/Al)M-III ratio improved soil fertility classification compared with PM-III alone. The critical PM-III value as determined by the Cate-Nelson procedure was found to be 31.5 mg PM-III kg-1, close to published values. The critical (P/Al)M-III ratios of 0.025 for 〉 300 g clay kg-1 soils and 0.040 for ≤ 300 g clay kg-1 soils differed significantly between the two soil groups. For (P/Al)M-III ratios above 0.214, there was no positive response to added P for all soils regardless of texture. Using published critical environmental (P/Al)M-III ratios of 0.076 for 〉 300 g clay kg-1soils and 0.131 for ≤ 300 g clay kg-1 soils as benchmarks values, agri-environmental P requirement models were built using conditional expectations of 50 to 80% of computed optimum P values within a soil class. A validation study supported the low critical (P/Al)M-III ratios and the 50% conditional expectation model except for a high carbon soil which was outside the application range of the models. However, banded P decreased corn yield at four validation sites although the model predicted positive response to P. Soybean did not respond to P except at extremely low fertility levels ((P/Al)M-III ≤ 0.02) and behaved as a P-mining crop even in low-P soils. Corn-soybean rotations can reduce soil P to low (P/Al)M-III ratios with minimal agronomic risk. Key words: Soil phosphorus saturation, Mehlich-III soil extraction method, soil fertility classification, soil texture, fertilizer P requirement model, corn, soybean

Description: Vegetated buffer strips (VBS) are often recommended as a management practice that farmers can use to help mitigate the environmental effects of runoff from agricultural fields. Previous research has shown that VBS can be effective at trapping phosphorus (P) and other farm-sourced environmental contaminants. This project measured the effectiveness of established vegetated strips at decreasing P in runoff from agricultural fields in Manitoba. Paired samples of runoff, taken at the field edge and in the vegetated strip, indicated that in 11 of the 22 cases sampled (50%), P concentrations in the runoff decreased (on average 30%) as the flow passed through the vegetated strip. In 7 of the 22 case (32%) there was no difference; however, in four of the 22 cases (18%), runoff P concentrations increased, indicating the vegetated strip had become a source of runoff P. Soil samples from the VBS showed high available P concentrations at positions within the vegetated strip along the runoff flow path, and in 7 of 10 cases these concentrations were higher (33% on average) than in the field soil. Although the observations and numerical results suggest that VBS can be effective at removing P in runoff, perhaps the major limitation in this flat-land region is that runoff tends to flow through rather small portions of the VBS, and these may not have sufficient capacity to retain the runoff P in the longer term. Key words: Vegetated filter strips, VBS, VFS, manure, soluble, particulate, ortho, riparian

Description: The sensitivity of soil organic matter decomposition to temperature change is critical tothe global carbon balance and to whether soils will respond with positive feedback to climate change. Forest cover determines litter composition, which controls to a large extent soil organic matter quality and its sensitivity to temperature. The effect of temperature on soil organic matter decomposition was studied along a latitudinal gradient encompassing sugar maple, balsam fir and black spruce forest types. Long-term laboratory soil incubations conducted at four different temperatures were used to discriminate the effect of temperature from that of organic matter quality on decomposition rates. The specific C mineralization rate of the humus layer was highest for balsam fir sites, intermediate for one sugar maple site and lowest for black spruce sites and the other sugar maple site. However, considering the total C pools of the FH layer and of the top 20 cm of mineral soil, it was estimated that coniferous sites exhibit a higher C efflux than sugar maple soils at any given temperature. Estimated C mineralization rates in the field using the temperature records for each individual site showed the same trends despite cooler temperature regimes for the coniferous sites. The Q10 respiration rates of the humus layer of all sites increased as the temperature got warmer. A significant effect of temperature on the pool size of labile C in the mineral soil was detected for some sites suggesting a potential long-term loss of C upon warming. The low estimated C evolution rates of sugar maple soils were perhaps due to the greater decomposition activity within the L layer, before the litter C enters underlying soil pools. These observations suggest that coniferous soils are not more resistant than deciduous forests to increasing their specific rates of soil heterotrophic respiration upon warming. Key words: Soil organic carbon, forest type, forest composition, warming, long-term incubation, labile carbon

Description: Forested peatlands store significant amounts of soil carbon (C) compared with upland forests and are strongly influenced by climatic parameters. Carbon stocks at peatland margins, although likely to be most sensitive to changes in climate, have not been well quantified, making it difficult to predict their response to climate change. The purpose of this study was to characterize the physical environment and associated changes in C stocks across the forested margins of two boreal fens. Peat depth increased and water table depth decreased toward the peatland centre, and these parameters acted as the controlling environmental variables. Above-ground biomass C was primarily derived from tree biomass and decreased from upland to peatland, despite an opposite trend in understorey (herbaceous and shrubby) biomass stocks. Leaf area index was related to peat depth through a negative power function and increased linearly with above-ground tree biomass. Total ecosystem C increased from upland to peatland, with minimum and maximum values of 270 and 2100 Mg C ha-1, respectively, and was largely dominated by soil C stocks, even at the upland end of the gradient. Although numerous small trees toward the peatland interior might allow a rapid increase in tree biomass C with lowering water tables, it seems likely that this would be a limited response, overshadowed in the long term by declines in the more substantial soil C stocks. Key words: Peatlands, carbon stocks, biomass, soil, leaf area index, peat depth

Description: Modelling soil organic carbon (SOC) stock changes in agroecosystems can be performed with different approaches depending on objectives and available data. Our objective in this paper is to describe a scheme for developing a dynamic SOC algorithm for calculating net greenhouse gas emissions from Canadian farms as a function of management and local conditions. Our approach is flexible and emphasizes ease of use and the integration of available knowledge. Using this approach, we assessed the performance of several SOC models having two or more compartments for some common agroecosystems in Canada. Analysis of long-term data for conventional management practices at different sites (n = 36) in Canada, including recent model applications in the literature on some of those data, indicated that the results obtained with two-compartment models, such as the Introductory Carbon Balance Model (ICBM) and Modified Woodruff Model (MWM), yielded results comparable to those of a multi-compartment model (CENTURY). The analysis also showed that a model such as ICBM need stuning to be applied to management and conditions across Canada. Two-compartment models programmable in a simple spreadsheet format, though they may not supplant more complex models in allapplications, offer advantages of simplicity and transparency in whole-farm analyses of greenhouse gas emissions. Key words: Virtual Farm, soil organic carbon, soil disturbance, C inputs, Introductory Carbon Balance Model (ICBM), CENTURY, Modified Woodruff Model (MWM).

Description: Dairy manure is important for corn (Zea mays L.) production in New York. Optimizing corn yield while minimizing environmental loss with manure nutrients is often a challenge. A potential tool for improving N management is the Illinois Soil Nitrogen Test (ISNT), which estimates amino sugar N, a pool of potentially mineralizable N for corn uptake. The objectives of this study were to determine (1) the short-term effects of manure applications on ISNT-N, and (2) the longer-term impacts of annual additions of composted and liquid dairy manure on ISNT-N. A 6-wk incubation study showed that NH4-N from manure temporarily (〈 2 wk) increased ISNT results. A 4-yr field study was conducted with annual spring applications of two rates of composted dairy manure (45 and 77 Mg ha-1) and two liquid dairy manure rates (63.5 and 180 kL ha-1). Results showed that ISNT-N slightly decreased over time in check plots (no manure or fertilizer additions) and that increases in ISNT-N over time in compost and liquid manure amended plots were consistent with changes in N credits currently given to manures in New York. Our results suggest that the ISNT accounts for N in previously applied compost and manure amendments, but that samples should not be taken within 2-wk following manure addition. Key words: Amino sugar, compost, Illinois Soil Nitrogen Test, nitrogen, manure, nutrient management