David J. Fallow

Infiltration under constant head and falling head conditions.

Prediction of the infiltration of water into field soils requires knowledge of the field-saturated hydraulic conductivity and a second parameter, such as the matric flux potential (corresponding to field saturation), or the Green and Ampt wetting-front pressure head, or the alpha parameter. Analytical solutions of 1-D infiltration under both constant and falling-head conditions are reviewed and several new solutions are developed based on the Green and Ampt assumptions. A laboratory experiment using the falling head technique is analyzed using several approximate analytical solutions.

Assessing the temporal stability of spatial patterns in crop yields using combine yield monitor data

Using previous years’ yield patterns may be one method of breaking a field into management zones for the purpose of site-specific management. For this method to be useful there must be temporal stability of yield patterns and there must be a sound method of assessing the spatial-temporal stability of yield in a field. To this end, a method was developed to give a non-biased estimate of the within-field spatial-temporal stability of yield. The method determined the probability that the normalized yield for all years available at a given location in the field fit within the accuracy limits of the combine. Combine accuracies of ± 2.5%, 5% and 10% of the field mean yield and gridded data of 3 m, 6 m, and 9 m cell sizes, as well as crop choice were all included in the model to assess its sensitivity to changes in these factors. The resulting spatial-temporal stability maps were well correlated with visual estimations of the spatial yield patterns. The model results were highly influenced by the inputted combin...

Temporal and Spatial Variability of Water Surplus in Ontario, Canada

The temporal variability in estimated water surplus in 12 climatic regions of the province of Ontario, Canada, and its spatial distribution throughout most of the province are discussed in this paper. Surplus water is that which results from precipitation that runs off the land surface and that which drains through the soil profile to the water table and through subsurface drainage. A one-dimensional, deterministic model (DRAINMOD) that simulates soil water flow, including plant uptake, evapotranspiration, and freeze/thaw conditions, was used to estimate the water surplus. Simulations were performed using daily climatic data from January 1954 to December 2001 for each region. A reference corn crop and the predominant local soil conditions in each region, with the hydraulic properties for each layer in the soil profile, were used as model inputs. There was considerable year-to-year variability in annual water surplus in all regions caused by both precipitation and soil conditions. It was the least (~150 mm) in three regions and it exceeded 350 mm in another three regions, where winter snowfall is the greatest as a result of these regions being in the lea of one of the Great Lakes. The variability in water surplus generally increased as average water surplus increased.