Date of this Version
Thesis (M.S.)—University of Nebraska—Lincoln, 1955. Department of Agricultural Engineering.
Many research studies have been conducted to develop methods of estimating the water requirements of irrigated crops.From these studies have evolved tow basic methods for making irrigation estimates.These two methods are based on the two major factors affecting plant growth, namely, climate and soil moisture.
The method based on climatological data employs an empirical relationship between measurable weather factors and the use of water by irrigated crops.Climatological data are obtained during the season and substituted into the empirical relationship to calculate the water requirements of a crop over the previous period of use preceding irrigation.The water requirement is reduced by the amount of rainfall occurring in the period to obtain the irrigation requirement.
The soil-moisture method is based upon measuring the quantity of moisture present in the soil layer occupied by the roots of the crop.Measurements of soil moisture are made periodically or immediately before the scheduled time of irrigation.The irrigation requirement is the amount of water needed to fill the soil mantle to the capacity which the soil can hold against downward movement by gravity.Both of the above methods provide a means for estimating the amount of water required by irrigated crops.
The purpose of this study was to investigate methods for calculating the water requirements of irrigated crops.The investigation was designed to field test existing empirical relationships, which relate available weather data to water requirements.
Empirical relationships selected were based on weather data commonly recorded or available at Weather Bureau stations.Such relationships would permit the Weather Bureau or a similar agency to utilize the methods for reporting the daily water requirements of irrigated crops.The reported information along with daily rainfall amounts would be used by irrigators to determine the irrigation requirements of their crops.
In this project, the Blaney-Criddle formula was field-tested for controlling irrigation, and soil moisture studies were used as a check.Also, several other methods—Thornthwaite, pan evaporation, and a multiple regression equation –were evaluated for comparison with soil moisture deficit to determine their applicability in eastern Nebraska.
Advisor:Paul E. Schleusener