Agronomy and Horticulture Department


Date of this Version



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 Philisophy, Major: Agronomy. Under the Supervision of Professor Richard B. Ferguson.
Lincoln, Nebraska: December, 2008
Copyright (c) 2008 Akwasi A. Abunyewa.


Grain sorghum (Sorghum bicolor L. Moench) is the fifth world leading cereal after maize, wheat, rice and barley. The crop can yield reasonably well under adverse conditions of low soil water and high temperature. A three year field study was conducted in a transect across Nebraska where annual mean precipitation ranges from 300 to 900 mm yr-1 to evaluate management practices to optimize yield potential under water limiting conditions. Loss in grain yield due to planting configurations ranged from 20 to 30% with skip-row configurations compared to conventional planting configuration (s0) at the site with greatest precipitation. At a site with moderate precipitation, grain yield was reduced by 18% with plant two skip two configurations (s2) and was not significantly affected with plant one skip one configuration (s1). At sites with the lowest precipitation and significant soil water deficits, grain yield increased with s1 and s2 ranging between 5 and 123% over s0. Considering yield across all sites, s0 yield was greater than skip-row configurations when average yield was above 4.5 Mg ha-1. Water use efficiency was highest with skip-row configuration at low to medium in-season precipitation sites but lower at sites where the mean in-season daily precipitation was greater than 2.5 mm. Increased N rate resulted in increased grain yield with s0 but there were no significant response to N application after 100 kg N ha-1. With skip-row planting, raising N rate above 50 kg N ha-1 did not significantly increase grain yield. Conventional planting (s0) had significantly higher agronomic N use efficiency (AEN) and partial factor productivity of N applied (PFPN) than skip-row configurations. Water and nitrogen stress both resulted in significant increase of leaf and canopy reflectance. A model calibrated in a greenhouse study using a reciprocal index in the green and red edge and in the NIR ranges predicted chlorophyll content with RMSE ranging between 52 and 56 mg m-2.