Digitized by Kansas Correctional Industries

A field experiment was conducted on a homogeneous sandy soil and a layered soil of southern Quebec from 1988 to 1990. This was done in order to evaluate the yield response of indeterminate soybean to subsurface irrigation and to determine the performance of subsurface irrigation in a layered soil. It was found that indeterminate soybean varieties increase their yield by approximately 30% for two out of three years. Soybean are very sensitive to competition between themselves as well as with weeds. This sensitivity is increased during subsurface irrigation. Weeds were more prominent in the irrigated area. It was concluded that the soybean yields are functions of water table depth, percent weed and plant population density. The minimum allowable water table depth for soybean was found to be 45 cm. At a water table depth greater than 95 cm no yield response was observed. / Water table management is not only possible but very functional in the layered soils of southern Quebec. It was found that surplus water did not drain from the irrigated area until the water table anywhere in this area was 10 cm higher than the elevation of the overflow pipe in the control chamber. It was therefore concluded that a water table depth range of 10 cm should be included in the design of the water table control system to allow for the effects of rain.

A field lysimeter experiment was conducted on a sandy loam soil during the growing seasons of 1989 and 1990. The experiment tested the effects of four water table treatments on soybean (Glycine max) yields. The water table depths were 40, 60, 80, and 100 cm in depth. / Yields were measured in terms of: total seed mass per plant, number of seeds per plant, number of pods per plant, number of seeds per pod, and speed protein content at harvest. / The water management simulation model DRAINMOD, was used to develop irrigation and drainage strategies for soybean production. Three water table management methods were tested with each of three water table depths. The methods were conventional drainage, controlled drainage, and subirrigation, and the water table depths were 40, 60, 80, and 100 cm. / It was shown that for the driest year highest yields are obtained with subsurface irrigation and a weir setting of 40 cm. For the average year, highest yields are obtained with subirrigation and a 60 cm weir setting. For the wet years, best results are found when controlled drainage is used with 80 cm weir setting. It was found that in all but the driest and wettest years controlled drainage improved yields by 10% or more.

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Typescript (photocopy). / Digitized by Kansas Correctional Industries

A field lysimeter experiment was conducted on a sandy loam soil during the 1990 and 1991 growing seasons. The experiment tested the effects of different watertables on soybean yields, and on moisture distribution and nitrogen concentration of the soil profile. The watertable depths were 40, 60, 80, and 100 centimeters (cm). / Yields were measured in terms of number of beans per plant, number of pods per plant, number of beans per pod, and seed protein content at harvest. / Soil samples collected at depths of 30 and 70 cm from the soil surface were analyzed for moisture content and NO$ sb3 sp-$-N and NH$ sb4 sp+$-N concentrations. / The experimental results showed that controlled watertable management increased the yield and decreased soil NO$ sb3 sp-$-N levels. The best results from the watertables tested were found to be at 60 and 80 cm. This is suggested as the range of watertable depths that should be maintained for optimum soybean production.

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