ALBERT

Description: In a previous study a nitrogen mineralization model was developed by combining the potentially mineralizable nitrogen (No) with functions representing the effect of temperature and soil moisture on the mineralization rate constant (k). The model performed well in predicting the amount of net nitrogen mineralized during a growing season when soil was incubated in plastic bags placed in incubators or buried in the field. In the present study a similar model was used to estimate net nitrogen mineralized in situ from Wood Mountain loam an Orthic Brown soil at Swift Current, Saskatchewan under (a) summerfallow, (b) cropped-dryland and (c) cropped-irrigated conditions. Model output showed good agreement to field measurements especially for the first 45–60 d, but thereafter tended to underestimate the measured data particularly under cropped-dryland conditions. During a growing season the cropped-irrigated system predicted 69 kg ha−1 net nitrogen mineralized, but 81 kg ha−1 was measured; the corresponding values for summerfallow were 64 and 86 kg ha−1, and for cropped-dryland 36 and 52 kg ha−1, respectively. The model is not dynamic since it does not allow for No to be replenished continuously by nitrogen derived from decomposition of fresh residues and rhizosphere microbial biomass. Net nitrogen mineralized from this source might explain at least part of the underestimate predicted by the model. Other sources of possible discrepancy could be imprecision in measuring the mineralization of nitrogen and in estimating the parameters in the model. Nonetheless, it was established that one of the main shortcomings of the model was that it underestimated the amount of nitrogen mineralized whenever the soil became very dry and was then rewetted by rainfall. This was probably because the latter process resulted in large flushes in mineral nitrogen in situ while in the laboratory estimate of No and k, this effect is not adequately simulated. Key words: Q10, No, N mineralization, rate constant, temperature function

Description: In the early 1980s, an internal Agriculture Canada review, carried out as a result of a request from the Province of Saskatchewan, indicated a need to determine whether there were any sites in the Province that posed a possible B toxicity problem. The soil and irrigation water quality (SAR, pH, EC, B concentration) and the B content of alfalfa (Medicago sativa L.) were assessed at 29 irrigation projects in Saskatchewan. Langmuir and Freundlich B adsorption equations were determined for another 13 soils that allowed assessment of the effect of soil zone and texture on these relationships. It was found that, except for a few locations where crops sensitive to B may experience some problems, water quality with respect to B was acceptable for most projects. The survey showed that salinity posed more of a threat to production under irrigation than did B toxicity. Boron toxicity was closely associated with salinity problems. Freundlich equations described the data for the 13 soils best; K values ranged between 0.24 and 2.04. These values were not affected by soil zone; coarse-textured soils had K values less than 0.5 and fine-textured soils values greater than 1.5. Data presented in our study can be used to determine where the irrigation practice of individual irrigation projects in Saskatchewan is appropriate for maintaining proper salt balance in the soils so as not to impede plant growth. Key words: Boron toxicity, alfalfa, SAR, Freundlich isotherm

Description: Data from an 18-yr crop rotation study carried out on a Brown loam soil at Swift Current, Saskatchewan, were used to estimate equations that relate spring wheat straw yields, and N and P content of grain and straw to moisture use (MU). Moisture use was defined as soil moisture content in 0- to 120-cm depth at seeding, less soil moisture content at harvest, plus growing season precipitation. Grain yields were also related to straw yields and to N content of the straw. Potential net N mineralization (Nmin) in summerfallow (periods during the growing season with negative Nmin omitted) was related (r = 0.74**) to precipitation received during the spring to fall period. An attempt to relate apparent net Nmin (determined by N balance) in cropped systems to growing season precipitation or to MU was not successful. Highly significant linear regressions were obtained for straw yields, grain N and P contents vs. MU, and for grain yield vs. straw yield (r = 0.66** – 0.83**), but the other relationships were less reliable (r = 0.41** – 0.55**) though still significant. We discussed how these relationships might be used to estimate fertilizer N requirements, for examining N immobilization-mineralization, and for estimating residue sufficiency for erosion control on summerfallowed land. Key words: Straw:grain ratio, N uptake, P uptake, crop residues, N mineralization

Description: The effects of crop rotation and fertilization on the quantitative relationship between spring wheat (Triticum aestivum L.) yields (y), available spring soil moisture (AvSpSM), and growing season precipitation (GSP) were determined from an experiment conducted on a loam soil in the Brown soil zone of southwestern Saskatchewan for the period 1967–1984. Moisture used (MU) was defined as[Formula: see text]and AvSpSM as volumetric moisture content at time of planting minus the lowest soil moisture measured at harvest. For discussion of moisture use characteristics GSP was defined as precipitation received from 1 May to 31 Aug.; for predictive equations GSP was more effective if GSP was taken as 1 May–31 July. When the 18-yr data were analyzed, the relation of y to MU was curvilinear. If data for 1 or 2 yr (1970 and 1983) with skewed distribution of GSP were omitted, the relationship between y (kg ha−1) and MU (mm) for well-fertilized fallow- and stubble-seeded wheat combined was[Formula: see text](where GSP = 1 May to 31 July). This equation performed well when it was used to estimate yields of fallow- and stubble-seeded wheat in 1985 and 1986. Stubble-seeded wheat required 68 mm of moisture to produce the first kilogram per hectare of grain; fallow-seeded wheat required about 46 mm. There was no effect of fertilizer on these lower threshold values, but the yield increase per millimetre of MU tended to be greater for the better fertilized rotations. The main difference in our y vs. MU relationships compared to those reported for the period 1925–1950 was that the lower threshold level of MU for grain production decreased from about 140 mm to the values cited above; this has resulted in substantially greater moisture use efficiency in recent years likely due to better, more timely crop management and the improved cereal varieties now used. When y was related to AvSpSM and GSP (1 May to 31 July) analyzed as separate variables, the relationship was only improved in terms of coefficient of determination (R2) value when a quadratic model was used. However, the latter did not predict the 1985 and 1986 yields as well as the y vs. MU relationship did. For fallow-seeded wheat, the relative effect of GSP on yield variability was about 5.4 times as great as that of AvSpSM; for stubble-seeded wheat it was only 1.5 times as great. GSP was equally important in affecting yields of wheat grown on fallow or stubble. The grain-filling period was confirmed as the most important for the occurrence of precipitation for both fallow- and stubble-seeded wheat, but precipitation at or near seeding time was almost as important for stubble-seeded wheat since this ensures the establishment of an adequate plant stand. Key words: Available moisture, growing season precipitation, timeliness of precipitation, regression analysis

Description: Four approaches for calculating downlink interferences for shaped-beam antennas are described. An investigation of alternative mixed-integer programming models for satellite synthesis is summarized. Plans for coordinating the various programs developed under this grant are outlined. Two procedures for ordering satellites to initialize the k-permutation algorithm are proposed. Results are presented for the k-permutation algorithms. Feasible solutions are found for 5 of the 6 problems considered. Finally, it is demonstrated that the k-permutation algorithm can be used to solve arc allotment problems.