No description available.

No description available.

No description available.

The effect of level and timing of nitrogen (N) fertilizer application on grain yield (YLD), grain protein (GPC), and breadmaking ability of four hard red spring wheat cultivars and on soil residual nitrate was investigated. Nitrogen fertility caused an increase in YLD, lodging, several yield components, GPC, and breadmaking quality and caused a reduction in N harvest index and grain ash, and N use efficiency (NUE) resulting in an increase in soil residual NO$ sb3$-N. Split N application reduced lodging, tillers and spikes m$ sp{-2}$ and caused an increase in grain weight, GPC, loaf volume and NUE. Grain yield increases were largely due to increases in the grain spike$ sp{-1}$ and tillers n$ sp{-2}$. Absolute protein content was found to be critical in determining GPC. Cultivars showed plastic responses to N. Despite its high YLD and flour yield, Hege 155-85 may be risky to produce because of its high dependence on N. Mineralization of N occurred during winter. Marked differences existed between the sites.

Soybean growth with respect to N fertilizer rates, plant population densities and two cultivars was investigated on three Quebec soils at four sites. Soybean nodulation, growth, grain yields and nutrient uptake at three developmental stages were investigated. Soil nitrate levels after harvest were also studied. / N fertilizer application depressed soybean nodulation consistently, but improved soybean growth where initial soil nitrate levels were low. Grain yield was increased at one site with added N, where soybean growth was stressed by low initial soil nitrate levels (below 17 kg N/ha) and severe summer drought. Soybean N and K uptake were increased with increased N fertilizer but P uptake was not affected. Residual soil nitrate content in the 0-50 cm depth in the fall of the crop year increased linearly and this effect carried over to the following spring. / Plant population had little effect on individual plant nodulation but increased fresh nodule mass per unit area. Plant biomass, grain yield and nutrient uptake were increased with increased population densities. / The cultivar Apache had better nodulation potential and grain yield potential and was better adapted to intensive management practices with high plant populations than the cultivar Maple-Arrow.

Nitrous oxide (N2O) produced from agricultural activities must be determined if management procedures to reduce emissions are to be established. From 1994 to 1996, N20 emissions were determined under continuous corn and corn-legume rotations in different soils of Quebec. Continuous corn was studied on four sites, two from a long-term experiment, a Ste. Rosalie heavy clay (Humic Gleysol) and a Chicot sandy loam (Gray-Brown Luvisol), at 0, 170,285 and 400 kg N ha-1, and two from a corn rotation study, a Ste. Rosalie clay (Humic Gleysol) and an Ormstown silty clay loam (Humic Gleysol). Treatments in the rotation study included no-till (NT) and conventional tillage (CT), monocropped corn, monocropped soybean-, corn-soybean; and soybean-corn-alfalfa phased rotations. Nitrogen rates of 0, 90, and 180 kg N ha-1 for corn and 0, 20, and 40 kg N ha-1 for monocropped soybean were used, and soybean/alfalfa with no fertilizer N following corn. Rates of N2O emissions were significantly affected by N fertilization, tillage and soil moisture content. Generally, N2O emissions were higher in the NT systems, with corn, and increased with increasing N rates. Increased nitrogen applications led to linear increases in N2O emission over the three years for both Ste. Rosalie (2) and Ormstown soils at a rate of 1.0 to 1.6 percent of added N. The N 2O emission rates were significantly related to soil denitrification rates, water filled pore space, and soil NH4+ and NO3-- concentrations in all three years. A corn system using conventional tillage, legumes in rotation and reduced N fertilizer would decrease N2O emission from agricultural fields.

No description available.

No description available.

Nitrogen fertilizer use suffers from low efficiencies and increased residual NO$ sb3$ in the soil. The purpose of this study was to compare N fertilizer efficiency by a comparison of three N sources, three rates of N fertilization, and three application times of N fertilizer. Grain corn yields increased with increases in N rates, and split applications of N were superior to preplant incorporated (PPI) fertilizer. Grain N uptake was associated to grain yield and N uptake. Stover yields increased with increased N and varied with application times of N, but the effects were not as pronounced as with grain yields. Soil NO$ sb3$ generally increased with increases of added N but not with split application of N compared to PPI N. Soil NO$ sb3$ in the spring in control plots was related to grain yield response to added N but not to stover yield response.

Thesis (Ph. D. - Soils, Water and Engineering)--University of Arizona, 1985. / Includes bibliographical references (leaves 179-182).