Impact of Water and Nitrogen Management on Maize Actual Evapotranspiration, Soil Water Extraction and Crop Water Productivity in South Central Nebraska, USA
Document Type Article
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 Suat Irmak. Lincoln, Nebraska: May, 2013
Copyright (c) 2013 Daran R. Rudnick
Maize actual evapotranspiration (ETa), soil water extraction and crop water productivity was assessed for five nitrogen (N) levels 0, 84, 140, 196 and 252 kg ha-1 under fully-irrigated (FIT), limited irrigation (75% FIT) and rainfed conditions. Field experiments were conducted at the University of Nebraska-Lincoln South Central Agricultural Laboratory near Clay Center, Nebraska, USA, in 2011 and 2012. The study site was irrigated using a GPS-guided seven-span variable rate linear-move irrigation system (Valmont Industries, Valley, NE).
Seasonal cumulative ETa ranged from 426 (rainfed-196 kg ha-1) to 550 mm (FIT-196 kg ha-1) in 2011 and from 401 (rainfed-0 kg ha-1) to 535 mm (FIT-252 kg ha-1) in 2012. ETa increased with increasing irrigation application amount and, in general, ETa increased with increasing N application amount. A strong relationship was observed between the developed evapotranspiration-nitrogen use efficiency (ETNUE) index and applied N and dry grain yield.
The scale and source of soil physical properties data used in the developed stepwise plant soil water extraction model influenced both temporal and spatial soil water extraction amounts and patterns. The extraction analyses using site-specific soil physical properties performed best with a root mean square difference (RMSD) of 26.4 mm as compared with the soil water balance-determined ETa. Significant differences in soil water extraction occurred with depth with maximum extraction amounts and percentages occurring in the top 0.30 m depth. The results of this research demonstrated that the developed plant soil water extraction model can be effectively used to assess individual and soil profile water extraction amounts throughout the growing season for use in irrigation and nitrogen management.
The maximum grain yield results were 12.68 and 14.42 tons ha-1, which occurred under the FIT-252 kg ha-1 treatment, for the 2011 and 2012 growing seasons, respectively. Positive quadratic relationships were measured between crop (CWUE), irrigation (IWUE) and evapotranspiration (ETWUE) water use efficiencies and N application amount.
Advisor: Suat Irmak