Biological Systems Engineering


First Advisor

Dr. William L. Kranz

Second Advisor

Dr. Suat Irmak

Third Advisor

Dr. Haishun Yang

Date of this Version



Sharma, S. (2017). Use of Long Term Weather Data and Spatially Delineated Field Attributes to Predict Water and Energy Conservation from Variable Rate Irrigation (Master's thesis), University of Nebraska-Lincoln.


A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Agricultural and Biological Systems Engineering, Under the Supervision of Professor William L. Kranz. Lincoln, Nebraska: December 2017

Copyright (c) 2017 Sahil Sharma


The declining levels of the Ogallala aquifer calls for more judicious use of water. Studies have shown that VRI has the potential for water savings. But adoption of VRI is still very low. The major reason is lack of information on the returns from the VRI systems and its feasibility in different fields. Also, a quantification of the required reduction in prices of VRI is necessary. So, an economic return analysis of VRI strategies was done to compare it to uniform irrigation management (UIM) using a water balance model based on long term weather data and field properties for a field near Elgin, Nebraska, containing four soil textures, for a period of 1988-2016. Five strategies were established to work on the study, namely, Field Capacity-VRI, Driest Soil Trigger-VRI, Water Mining-VRI, CUIM and Total IUM. Thirteen field distributions were developed to study the variation in the field requirements of VRI and results were quantified based on three cost factors (100%, 75%, and 50%).

The water balance model predicted irrigation amounts and frequencies for the five strategies which were used to determine the total water applied, total cost of application as well as an input for the AquaCrop model to simulate the yields. Irrigation costs were calculated based on three prices of VRI ($21,379, $16,034 and $10,690) and profits were calculated for each strategy and distribution and savings were established by comparing profits with those of CUIM.

Results indicate that VRI is not feasible for the field near Elgin, NE, at present costs because an average yearly application reduction of 2.4% was not able to justify the 4% yearly decline in monetary savings as compared to CUIM. TIUM is recommended for the field as it showed $2907 yearly savings on CUIM. It was also observed that VRI worked best in fields where water mining is justified, that is, the fields with higher variation in water holding capacities soils with the more wet soils covering at least 60% of area. Also, a reduction of at least 25% in the initial costs was considered essential for VRI to be beneficial.

Adviser: William Kranz