DRAINMOD, a water management simulation model for artificially-drained soils, was evaluated for a Virginia Coastal Plain soil by comparing predicted and measured water table depths from a subirrigation/controlled drainage site over a period of three years. Water table elevations predicted by the model were in good agreement with measured water table elevation data with an average deviation of 9.47 cm for the three years of record. The YIELD version of DRAINMOD was used to predict corn yield for the subirrigation/controlled drainage site. Average corn yield predictions by the model agreed reasonably well with the observed average corn yield data with relative errors of 19.2, 4.4, and 8.1 percent for 1984, 1985, and 1986, respectively. Additionally, corn yields predicted for a conventional drainage system were considerably lower than those predicted for subirrigation/controlled drainage, reaffirming the need for irrigation of corn in the Coastal Plain region of Virginia. Research results indicate that DRAINMOD is a powerful tool for the design and evaluation of subirrigation/controlled drainage practices in the Virginia Coastal Plain. Simulations were performed for a 20-year period to determine the effects of system design on corn yield. An economic analysis was performed to determine optimal system design for maximizing profits from corn production. A drain spacing of 21.3 m, a drain depth of 110 cm, and a 65 cm weir depth were the design parameters recommended as optimal for maximizing profits from subirrigation/controlled drainage of corn on a Myatt fine sandy loam soil in the Virginia Coastal Plain. / Master of Science

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Thesis (M.Sc. (Agriculture)) --University of the North, 1985 / Refer to the document / University of the North, HSRC (Human Science Research Council), and Lebowa Project Committee

The purposes of this thesis are to examine experimental results obtained with subsurface irrigation of maize in 1988, and to provide preliminary plans and an economic analysis for the subsurface irrigation of maize in Richelieu County, Quebec. A mean increase in maize yield of 3.7 % was observed in 1988 on experimental plots with subsurface irrigation at the Charbonneau farm. However, a review of results obtained at the same experimental site from 1982 to 1988 indicated that the mean increase in maize yield with subsurface irrigation was 29 %. / Plans for two possible water supply systems designed to provide 180 mm a year of irrigation water for the subsurface irrigation of 1,250 ha in Richelieu County were considered. An economic analysis indicates that subsurface irrigation using groundwater has the greatest net benefits with an internal rate of return of 22.92 % and benefit to cost ratios of 1.90, 1.72 and 1.56 for discount rates of 8 %, 10 % and 12 % respectively. However, much of the groundwater in this region is saline and its use for irrigation may need to be restricted. Subsurface Irrigation using surface water from the Yamaska River was also profitable with an internal rate of return of 17.31 % and benefit to cost ratios of 1.66, 1.46 and 1.30 for the same discount rates.

A field subirrigation experiment, using saline-sodic water, was carried out on a loamy sand soil in southwestern Quebec. The experimental field was divided into 16 plots with 4 treatments; saline-sodic water, "fresh" water, controlled drainage and non-irrigated. Each treatment had four replicates. Maize yield, hydraulic conductivity, salt concentration, and salt movement through the soil were recorded in all plots. / No significant difference in maize yield occurred between plots irrigated with saline-sodic or fresh water in any of the three years. Irrigated maize plots yielded approximately 30% more than non-irrigated plots. / Hydraulic conductivity reductions in the saline plots were noted in May 1986, after the first snowmelt. From statistical analysis carried out, it appears that the saline-sodic water had an effect on hydraulic conductivity, significant at the 0.05 level. / From the measurements taken from piezometer stations, located throughout the field, salt concentrations and salt movement through the saturated soil profile were determined. Using salt concentration data from both irrigation water and soil water, an average effective field porosity was calculated with a computer program. The results obtained were within 4% of those obtained in laboratory tests. Moreover, the program was then used to model the salt balance of the soil from May 85 to May 87. Results indicated that most salts were removed with the rainfall and snowmelt of the winter months of 85/86 and 86/87.

Field water table measurements were taken at two sites in Southern Quebec in order to validate DRAINMOD, a field scale water table management model. Two growing seasons of data were collected on a loamy sand soil near Sorel, Quebec and one year of data on a clay soil to the south-west of Montreal. Several water table management schemes were investigated, ranging from conventional subsurface drainage to automated subsurface irrigation. / DRAINMOD was used to simulate the measured water table fluctuations and relative corn crop yields over the growing season. Verification of the model was needed to determine if it could be a useful tool in the design and operation of water table management systems for the Quebec region. / It was found that DRAINMOD output closely simulated the water table fluctuations for conventional drainage and subsurface irrigation plots provided no exceptional circumstances existed. More study is needed in some areas such as bedded fields and in the use of fluctuating water level control structures.

No description available.

No description available.

No description available.