Time And Rate Of Nitrogen Fertilization Influence Maize Nitrogen Use Efficiency And Soil Enzyme Activity

University of Minnesota Ph.D. dissertation. September 2018. Major: Land and Atmospheric Science. Advisors: Paulo Pagliari, Jeffrey Coulter. 1 computer file (PDF); viii, 164 pages.Experiments were conducted from 2014 to 2016 comparing single (fall and spring) and split applications of differing nitrogen (N) rates for maize (Zea mays L.) on an irrigated Hubbard-Mosford loamy sand complex at Becker, a non-irrigated Normania loam soil at Lamberton, and a non-irrigated Nicollet clay loam soil at Waseca, MN. Fall and spring treatments were applied at recommended and 125% of recommended rates based on University of Minnesota guidelines for the different locations. Split-application treatments consisted of Sp, a two-way split (one-half of the N applied before planti and one-half applied at the six-leaf collar stage of maize phenological development (V6) and TSp, a three-way split (one-third of the N applied pre-plant, one-third at the V6 stage, and one-third at the silking stage of maize phenological development (R1) stage. Nitrogen rates varied by location and were based on University of Minnesota guidelines. All sites were planted to soybean [Glycine max L. (Merr.)] in 2013 and to maize in 2014 to 2016. At Becker, applying N fertilizer at the recommended rate as a three-way split improved maize grain and biomass yield, maize nutrient uptake, and nitrogen use efficiency (NUE). At Lamberton, grain yield, nutrient uptake, and NUE parameters did not differ among treatments applied at recommended rates, regardless of application time. At Waseca, applying the recommended N rate as either a two- or three-way split improved grain yield and NUE compared with fall or pre-plant application, while recommended N rates maximized nutrient uptake. Soil enzyme activity fluctuated across the growing season and decreased over time, particularly in the coarse-textured soils at Becker. Although microbial activity declined annually, there was no significant change in glucosidase activity. There was a decline in acid phosphatase activity in coarse- but not finer-textured soils. At Becker, applying N fertilizer as a three-way split increased sulfatase activity compared with applying N fertilizer in the fall or pre-plant. Enhanced understanding of how site-specific soil and weather characteristics influence these responses could increase maize yield and nutrient uptake while reducing the potential for nitrogen loss to the environment