Biological Systems Engineering

 

First Advisor

Suat Irmak

Date of this Version

4-2020

Comments

A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Biological Engineering (Agricultural and Biological Systems Engineering), Under the Supervision of Professor Suat Irmak. Lincoln, Nebraska: April 2020

Copyright 2020 Ali T. Mohammed

By request of the author, this dissertation is temporarily under embargo to allow sections to be submitted for article publication. Full text will be made available at a later date.

Abstract

Declining the quantity and quality of freshwater resources in many parts of the world, including Midwestern USA, especially in the light of rapidly growing world’s population and changing climate, imposes significant and, in some cases imminent, challenges for producers, policy- and decision-makers to produce more yield with less water and other inputs, particularly in water scarcity regions.

There is not comprehensive previous research has quantified and evaluated coupled impacts of irrigation rates and nitrogen timing management strategies and their interactions on maize (Zea mays L.) productivity and its various attributed efficiency index metrics under different irrigation methods under the same environment conditions and under the same soil and crop management practices simultaneously.

Extensive field experiments were conducted for maize during the 2016 and 2017 growing seasons in three large scale fields under center pivot (CP), subsurface drip irrigation (SDI) and furrow irrigation (FI) methods at full irrigation treatment (FIT), 80% FIT, 60% FIT and rainfed treatment (RFT) with three N application timing treatments. N application timing treatments that were imposed are: (i) traditional (NT); pre-plant application (TN) treatment, (ii) non-traditional-1 (NT-1); in-season three time N applications, and (iii) non-traditional-2 (NT-2); in-season four time N applications. The overall objectives of the study were to quantify and compare numerous maize plant physiological and biophysical properties, maize production, soil water dynamics, crop evapotranspiration (ETc), crop water productivity, yield response factor (Ky), N use efficiency indices, and developing new functions between nitrate-N vs. total water supply; seasonal irrigation water; and yield to account for nitrate-N driving factors.

Main effects of N treatments, irrigation methods, and year were (p<0.05) impacted response variable. The highest yields were in order of CP > SDI > FI across all treatments, both NT-1 and NT-2 were higher (p<0.05) than NT, whereas, NT-1 and NT-2 were statistically equal. SDI-80% FIT-NT-1 showed the lowest (p<0.05) total soil residual nitrate-N content. CP-FIT-NT-1 showed the highest mean total soil water content.

Results should provide invaluable data and information will improve synergy between nutrition and water, maximize maize and soil productivity, increase farmer’s profit, stakeholder awareness, and protect environmental quality for the study area.

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