The performance of a subsurface irrigation system in a clay soil was investigated under field conditions from 1989 to 1991. It was found that subsurface irrigation could be practised successfully in some clay soils of Quebec. The 10 m drain spacing was found to be better than the 20 m drain spacing in terms of keeping a uniform water table between the drains. The water table distribution between the drains was found to be a factor of the applied hydraulic head. The relationship between the applied hydraulic head and the midspan water table elevation could not be determined due to unfavourable weather conditions during the study period. The soil moisture content was found to follow the same behavior as the water table elevation, however, the relationship between these two parameters could not be properly established. It was also found that under the same applied hydraulic head, the drain spacing did not affect the soil moisture distribution. Subsurface irrigated plots were found to make better use of rain water than drained only plots since they did not permit the formation of well-defined pathways (macropores) allowing rainfall to move below the root zone without wetting it. It was also found that subsurface irrigation did not alter the soil structure appreciably and that autumn drainability was not affected in 1990 and 1991.

No description available.

No description available.

The main objective of this research was to determine the short-term effects of cropping on the aggregation and the carbohydrate fraction of a marine clay soil. When compared to a fallow (bare soil) control, cropping to barley and alfalfa for two seasons resulted in significant increases in the size and stability of soil aggregates. The increase in water-stable aggregates $>$2.0 mm was at the expense of aggregates $<$1.0 mm. Under corn, soil aggregation was not different than under fallow. After two seasons, soil under barley or alfalfa contained 15 to 25% more carbohydrates than the fallow or corn treatments. The partial correlation (r = 0.63, P = 0.001) which was observed between carbohydrate content and mean weight diameter of water-stable aggregates, and periodate oxidation tests strongly suggested that carbohydrates were at least partly responsible for the increase in macro-aggregate stability. The remaining cropping effects were removed by tetraborate which suggest the participation of more-humified though ill-defined organic matter. The nature of the changes in organic matter was further investigated using particle size fractionation. Compared to the fallow control, cropping to barley and alfalfa resulted in an enrichment in carbon, nitrogen, and carbohydrates in the sand fraction. The carbohydrate composition of the soil and of its size fractions, determined by liquid chromatography, suggested that cropping treatments had only little effect on the origin of the soil carbohydrates.

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Mole drainage is an inexpensive form of drainage particularly suited to clay soils. / Mole drainage is approved by Le Conseil des Productions Vegetales du Quebec to drain clay soils with low hydraulic conductivity. A few known trials on this technique of drainage have been done in Ontario and Alberta. In England and New Zealand, this technique is widely used. The large surface of heavy clay soil cultivated in Abitibi-Temiscamingue makes this region an excellent choice for trying this technique. / Two sites established on two soil series (Palmarolle, Roquemaure) have been moled in Abitibi-Temiscamingue. These soils represent 21% of the cultivated land in this region. Twelve plots have been moled at varied depths, spaces and lengths. Physical and chemical soil properties have been measured to identify their influence on mole drainage stability. Water table, rainfall and the stability of the mole drains were monitored for three summers. Mole drain stability was observed with a borescope. Maturity growth and yield of a hay crop, and three types of cereals were measured. / The mole drainage technique is satisfactory in heavy clay. The organic matter (${>2 %}$), the water content of the soil (${>40 %}$) at moling time and a small amount of rainfall (${<6}$ mm) in the first week after moling positively influenced the stability of the mole drains. Some mole drains have kept 75% of their initial opening after three years of life. The water table was lower on one mole drained site. The yield of the hay and the three cereals were higher on the moled parcels. (Abstract shortened by UMI.)

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No description available.