Survival and inoculum production of Gibberella zeae (Schwein.) Petch (anamorph Fusarium graminearum (Schwabe)), the causal agent of Fusarium head blight of wheat and barley, was related to the rate of wheat (Triticum aestivum L.) residue decomposition. Infested wheat residue, comprising intact nodes, internodes, and leaf sheaths, was placed in fiberglass mesh bags on the soil surface and at 7.5- to 10-cm and 15- to 20-cm depths in chisel-plowed plots and 15 to 20 cm deep in moldboard-plowed plots in October 1997. Residue was sampled monthly from April through November during 1998 and every 2 months through April to October 1999. Buried residue decomposed faster than residue placed on the soil surface. Less than 2% of the dry-matter residue remained in buried treatments after 24 months in the field, while 25% of the residue remained in the soil-surface treatment. Survival of G. zeae on node tissues was inversely related to the residue decomposition rate. Surface residue provided a substrate for G. zeae for a longer period of time than buried residue. Twenty-four months after the initiation of the trial, the level of colonization of nodes in buried residue was half the level of colonization of residue on the soil surface. Colonization of node tissues by G. zeae decreased over time, but increased for other Fusarium spp. Ascospores of G. zeae were still produced on residue pieces after 23 months, and these spores were capable of inducing disease. Data from this research may assist in developing effective management strategies for residues infested with G. zeae.

Comparisons between no‐till and conventional‐till management are often confounded by variation in both tillage and residue placement. The objective of this research was to separate the tillage variable from the surface‐residue variable associated with no‐till and conventional‐till management comparisons in irrigated continuous corn (Zea mays L.) production. Two Nebraska locations (Mead and Clay Center) with differences in soil types and climate were selected. Four tillage‐residue treatments [NT‐NR (no‐till, residue removed), NT‐R (no‐till, surface residue), T‐NR (till, residue removed), T‐R (conventional till, surface residue)] were fertilized by either broadcasting at planting or sidedressing at the 6‐leaf stage with rates of 0, 56, 112, and 168 kg N ha−1. At Clay Center, grain yields and total N accumulation were similar for all tillage‐residue treatment combinations in all years when the highest fertilizer N rate was used. In 2 of 3 yr at Mead, grain yields and total N accumulation were less for no‐till than conventionaltill treatments, but in 1 yr the yields and total N accumulations were greater in no‐till than conventional‐till treatments. At Mead, surface residue resulted in lower grain yields and total N accumulation compared with bare soil at lower N rates, but not at greater N rates, in 2 of 3 yr. Sidedressing fertilizer N was generally a more efficient N placement than broadcasting. Differences between tillage and residue effects at Clay Center and residue effects at Mead were overcome with higher rates of fertilizer N. Tillage effects at Mead did not appear to be N‐related. The data suggest that tillage may be necessary to maintain optimum production levels on finer‐textured soils when spring soil temperatures are cool and slow to warm. When spring soil temperatures are warm, no‐till strategies can be used for optimum production levels on these soils.

Discount payments associated with low grain protein concentration in hard red spring wheat (HRSW, Triticum aestivum L.) in recent years has increased interest for using controlled-release N fertilizers to increase protein concentration while maintaining optimal grain yields. Field experiments were conducted during 6 site-years in Minnesota from 2007 to 2009 to examine eff ects of a polymer-coated urea (PCU, Environmentally Smart Nitrogen [ESN], Agrium Inc., Calgary, AB, Canada) and non-coated urea on grain yields and protein concentrations of two HRSW cultivars, Alsen and Knudson, that vary in grain yield and protein concentration potentials. Polymer-coated urea and urea were applied in spring at six rates that supplied 0 to 110 kg N ha -1 in 2007 and 0 to 168 kg N ha -1 in 2008 and 2009. Because of genetic diff erences, Knudson produced greater grain yield than Alsen in environments (site-years), which were cooler and drier early in the growing season and the yield diff erences between the two cultivars increased with increasing N rates. In the same environment, PCU decreased grain yield compared with urea, which could be related to a reduced N release early in the growing season. Compared with urea, higher N (at Zadoks scale 85) and protein concentrations (at Zadoks scale 92) with PCU were observed due to increased N availability later during the growing season. To increase wheat protein concentrations from using PCU, future studies should evaluate diff erent mixtures of PCU and urea.

The economic benefit of using controlled-release N fertilizers on hard red spring wheat (HRSW, Triticum aestivum L.) depends on its cost/price ratio, grain yield, and availability of discount and/or premium prices for protein concentration. The objective of this study was to evaluate the effect of five different proportions (0, 25, 50, 75, and 100%) of polymer-coated urea (PCU) in the N fertilizer mixture applied at three different N rates on (i) HRSW grain yield and protein concentration and (ii) whole-plant dry matter and total N accumulation, and (iii) also to perform an economic analysis. As the proportion of PCU in the fertilizer mixture increased, the grain yield decreased in Environment 1 and remained the same in Environment 2. Cool dry conditions in Environment 1 delayed N release from PCU causing N deficiencies during the critical yield-development phase and resulting in lower grain yield as the PCU proportion increased. In contrast, this was not the case in Environment 2. As the proportion of PCU in the fertilizer mixture increased, protein concentrations increased in both environments indicating that PCU increases soil-N availability later in the growing season, regardless of the early season weather conditions. The proportion of PCU in the fertilizer mixture did not affect total N accumulation and post-harvest soil NO 3 -N concentrations. The results of this study suggest that adding a portion of PCU in the fertilizer mixture can increase HRSW grain protein concentration and provide economic benefits to producers if discount prices are around $20 per Mg or greater.

Developing solutions to atmospheric environmental problems requires a better understanding of chemical processes occurring in each component of the ecosystem. Volatile NH3 loss from plant foliage complicates the assessment of NH3 emissions from agricultural activities. The objective of this study was to use 15N methodology to identify time of occurrence, magnitude, and direction of NH3 exchange between corn (Zea mays L.) fertilized with enriched 15N and the atmosphere during reproductive growth. Ammonia was collected by drawing air over leaves, ear shoots, and whole plants and trapping the NH3 on oxalic acid‐impregnated filter disks. Filter disks were analyzed by ANCA‐MS procedures for total N and atom % 15N. An exchange of NH3 between corn plants and the atmosphere was found to occur during all sampling periods. This suggests that the release and capture of free NH3 is an active component of the metabolic processes taking place in corn plants during reproductive growth. For corn under non‐limiting N fertility, the direction, rate, and magnitude of NH3 exchange from leaves does not appear to be a function of ambient atmospheric NH3 concentrations. Determining the true loss or gain in N between corn plants and the atmosphere during reproductive growth is very difficult as a result of this continuous exchange of NH3. The amount of net N lost from a corn crop will be less than the amount indicated by measurements of isotopic loss, because both interchange between plants and deposition on soil and plants may take place within the field.