Browsing by Subject "N fertilizer"

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    Corn production and environmental implications under varying nitrogen and management practices
    (2013-12) Maharjan, Bijesh
    Economic and environmental issues combined have increased the need for better understanding of the fate of nitrogen (N) applied to crop production systems. The objectives of this dissertation were to evaluate the effects of different N sources including conventional urea (CU), polymer-coated urea (PCU), stabilized urea with chemical inhibitors (IU), and anhydrous ammonia (AA) on N losses and yield. Besides N sources, their interaction with placement (deep- versus shallow-banded; broadcast/incorporation versus subsurface banding), tillage management (conventional tillage versus no tillage) and irrigation management (irrigated versus rain fed) were also studied. In the first experiment, split-applied CU increased yield and N uptake compared with preplant applied PCU or IU and decreased nitrate (NO3-) leaching compared with PCU in a sandy loam soil. Direct soil-to-atmosphere nitrous oxide (N2O) emissions were significantly less with IU or split-U than with PCU and there was a trend for greater emissions with split-U than with IU (P =0.08). Irrigation significantly increased NO3- leaching during the growing season, but had no effect on direct N2O emissions in the same experiment. Indirect emissions due to NO3- leaching were estimated to be 79-117% of direct emissions using the default value of EF5, thus signifying the potential importance of indirect emissions in evaluating management effects on N2O emissions. In the second experiment, no-till significantly increased N2O emissions in fertilized treatments in a dry year and decreased crop yield in the control treatment in a silt loam soil. There were no significant differences in N2O emissions, grain yield or NO3- leaching potential with AA placement depth. In the third experiment, mid-row banding (MRB) significantly increased N2O emissions compared to broadcast/incorporation (BI) for PCU and CU in silt loam soils. Nitrous oxide emissions were correlated to a greater extent with soil nitrite (NO2-) intensity than with nitrate (NO3-) intensity; N intensity being a measure of integrated N concentrations over time. Compared to BI, MRB reduced NH3 volatilization loss and the CU treatment had greater NH3 loss than PCU or IU had. All these experiments highlighted the significant roles that N and other management practices can play in mitigating N losses.
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    Time And Rate Of Nitrogen Fertilization Influence Maize Nitrogen Use Efficiency And Soil Enzyme Activity
    (2018-09) Davies, Benjamin
    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.