Seasonal and spatial patterns of rainfall trends on the Canadian prairie

Non-Peer ReviewedWe used regression analysis to establish linear trends of annual and seasonal rainfall amounts and number of events at 140 stations with 40 years of record from 1956 to 1995 across the Canadian Prairie. There has been a significant increase in the rainfall amounts and number of events. Increase in annual rainfall was 51 mm or about 16% of the 40 yr mean while the number of rainfall events increased by 17 or about 29%. Spring (January to April) experienced proportionately the largest increase, with amount and number increasing by 46% and 64%, respectively. This may be related to the conversion of snow to rain as a result of climatic warming during this period. The increase in rainfall amount and number of events during summer (May to August) were similar to the annual patterns. There was no significant increase in rainfall amount and number of events during the fall season (September to December). The increases in rainfall amount and number of events were not uniform across the prairies, with the least increase in rainfall amount and number of events in southern Manitoba, and the largest increase in Alberta and Saskatchewan. Little or no change in amounts occurred in the northern portion of the prairie provinces. The results confirmed that the prairies are not getting drier, however, there are seasonal and spatial differences in rainfall trends

Precipitation trends on the Canadian prairie

Non-Peer ReviewedThe amount and timing of precipitation on the Canadian Prairie is critical to grain production. Information on the precipitation trend is therefore vital to this region. Regression analysis was used to establish linear trends of precipitation amounts and number of precipitation events at 37 stations with 75 years of record (prior to and including 1995) across the Canadian Prairie. There has been a significant increase in the number of precipitation events mainly due to an increase in the number of low-intensity events. As such precipitation events are not getting more intense. From 1921 to 1995 on the Canadian Prairie, the number of precipitation events (excluding events that are 0.5 mm or less) has increased by 16 events, and precipitation and rainfall amounts have increased by 0.62 mm and 0.60 mm per annum, respectively. During the period from 1921 to 1960 the trends in precipitation, rainfall and snowfall were not statistically different from zero. However, from 1961 to 1995, snowfall has declined by 0.95 mm per year. The trends in the most recent period (1961 to 1995) were also significantly different from those in the 1921 to 1960 period for snowfall. The difference in trends between the two periods for snowfall, combined with the inverse relationship in the rainfall-snowfall trends suggest that these trends may be related to climate change

Simulating nitrate leaching under dryland conditions: model validation for water and solute movement

Non-Peer ReviewedThere is an increased awareness of the possible leakage of nitrate out of agricultural systems and its potential to contaminate underground and surface water. This has led to the use of simulation mode s for studying the dynamics and movement of nitrate-nitrogen within and beyond the root zone of crops. Before these models can be applied to field situations they need to be tested and validated against realistic field conditions. We tested the water flow and solute movement portion of LEACHM (Leaching Estimation And CHemistry Model), and validated it with respect to moisture and chloride changes of a prairie soil under fallow conditions during the growing season. The retentivity and conductivity functions proposed by Campbell (1974), as used in the original version of the model behaved poorly for our soil. We modified the model using the Van Genuchten function and used this to simulate water content changes during the 1975 and 1976 growing seasons. The "pan coefficient" was used as an optimization factor to calibrate the 1976 moisture data. A pan coefficient of 0.4-0.5 was found to be appropriate under fallow while a value of 0.7 was used for wheat crop. Moisture distribution with depth, and changes with time, were well simulated by the model. The distribution of 171 kg/ha of chloride applied as KCl at a depth of 10 em was simulated using LEACHM. There was good agreement between the predicted and measured chloride distribution in 1975 and 1976

Spring emergence of Canadian Delia radicum and synchronization with its natural enemy, Aleochara bilineata

To characterize time of spring emergence following post-diapause development, Delia radicum (L.) (Diptera: Anthomyiidae) from Saskatchewan, Manitoba, and southwestern Ontario were collected in fall, maintained over winter at 1 °C, then transferred to higher constant temperatures until adult emergence. At each location there were "early” and "late” phenotypes. Truncated normal models of temperature dependency of development rate were fitted for each phenotype from each location. We provide the first evidence of geographic variation in the criteria separating these phenotypes. Separation criteria and models for early and late phenotypes at the two prairie locations, approximately 700 km apart, were indistinguishable, but differed from those for Ontario. Prairie phenotypes developed more slowly than Ontario phenotypes, and more prairie individuals were of the late phenotype. Poor synchronization of spring emergence could impair predation of D. radicum eggs by adult Aleochara bilineata Gyllenhal (Coleoptera: Staphylinidae). Aleochara bilineata from Manitoba were reared and development rates modelled as for D. radicum. Models of development rates for the two species, when combined with simulated soil temperatures for two prairie locations, suggest that emergence of adult A. bilineata is well synchronized with availability of D. radicum eggs in prairie canol

Fertilizer application and deep leaching of nitrate under long term crop rotation

Non-Peer ReviewedIt is commonly believed that the use of nitrogen fertilizers in agriculture will lead eventually to the loss of nitrate via leaching. The nitrate leached below the root zone has the potential to contaminate underground water. The results obtained from various long term crop rotation studies in Saskatchewan suggest that this common belief may not hold in general. This is especially true where nitrogen fertilizers were applied based on soil test recommendation and the land was continuously cropped. Under long term crop rotation studies in the Black Soil Zone at Melfort, the application of nitrogen fertilizer in recent years were based on the general recommendation for wheat. The deep core sample revealed that more nitrate was present in the soil profile under fertilized continuous wheat compared to the unfertilized plots. However, in the Black Soil at Indian Head, where fertilizer application was based on soil test values, similar amounts of nitrate were found below the root zone of fertilized and unfertilized plots after 34 years of continuous wheat. This was in spite of applying 1584 kg of N ha-1 to the fertilized plot over 34 years. A result similar to that at Indian Head was obtained from the crop rotation experiment in the Brown Soil Zone at Swift Current. In the Brown Soil Zone, the inclusion of a fallow phase in the rotation, increased the amount of nitrate found below the root zone although this system had received less fertilizer over the years than the continuously cropped plots. The fallow phase appeared to provide a window for the leakage of nitrate accumulated within the root zone. This was attributed to a better moisture (antecedent moisture) regime and higher amount of mineralized nitrate during the fallow phase. On the other hand, frequent summerfallow can deplete the soil of its N supplying power and this may eventually result in less nitrate leached as was found for the 2-yr rotation at Indian Head after 34 yr