Studies to increase profitability and N use efficiency in winter wheat (Triticum aestivum L.) production are needed to develop more sustainable agricultural systems in the 480‐ to 650‐mm precipitation zone of northern Idaho and eastern Washington. Field experiments were conducted on Latahco silt loam (fine‐silty, mixed, frigid Argiaquic Xeric Argialboll) soils east of Moscow, ID, during the 1982–1983, 1983–1984, 1985–1986 and 1986–1987 growing seasons. Fifteen different N placement‐source‐application timing treatments were arranged in a randomized complete block design with five replications. Fertilizer placements were (i) surface broadcast, (ii) band 50 mm below the seed, and (iii) combinations of surface broadcast and banded below the seed placements. Times of application treatments were (i) fall, (ii) spring, and (iii) various fall‐spring splits. All treatments were evaluated with two N sources: NH4NO3 (AN) and urea (U). Parameters evaluated were (i) winter wheat stand counts, (ii) early‐season plant biomass, (iii) grain yield, and (iv) apparent N use efficiency (NUE). Placement, N source and time of application had minimal impacts on winter wheat stand counts and early season biomass production. Both winter wheat grain yield and apparent NUE were greatest when N applications were split between fall and spring. Splitting time of N application resulted in apparent NUE of 58 to 61%, compared with 52 to 55% and 51 to 53% for fall only and spring only N applications, respectively. Grain yield and apparent NUE differences attributable to N source and N placement were not significant. Based on this study, ideal N management in the 480‐ to 650‐mm precipitation zone would utilize AN, U, or comparable N sources and split N applications where as little as 25% of the N is banded below the seed or surface broadcast in the fall, with the remainder applied as a spring topdress prior to Zadoks growth stage 24. This proposed management will improve both profitability and water quality by increasing both grain yield and N use efficiency when compared with systems currently employed.
Fall-applied N is poorly utilized by winter wheat (Triticum aestivum L.) in northern Idaho, because heavy winter precipitation leaches much of the N from the root zone. Nitrogen-use efficiency can be improved by spring application. This study evaluates two N fertilizer sources, urea-ammonium nitrate solution (UAN; 32% N) and prilled ammonium nitrate (AN; 34% N), as spring topdress materials and determines the growth stage at which N application would produce maximum yield. Four field studies were established on cropland initially containing less than 50 kg NOrN ha -•. Winter wheat was seeded at 90 kg ha-• at each site. Nitrogen was topdressed at 100 kg ha-• in the spring as either UAN, AN, or a UANbromoxynii/MCP A [3,5-dibromo-4-hydroxybenzonitrile/( 4-chloro-2-methylphenoxy) acetic acid) tank mix at eight different growth stages. Parameters evaluated included: (i) leaf burn, (ii) stand vigor, (iii) tillering, (iv) weed control, and (v) yield. Temporary yellowing of plant leaves was noted following UAN applications at air temperatures > l4°C. The degree of yellowing or leaf burn exhibited a significant curvilinear correlation with air temperature (R 2 =0.89). Nitrogen application date affected stand vigor, tillering, weed control, and yield, with the best ratings occurring with N applications before Zadoks' growth stage 31. When study sites and N sources were pooled, yields were 5. 4, 4.9, 4.8, 4.6, 4.3, 4.1, 3.6, and 3.1 Mg ha-• for wheat fertilized at growth stages 22, 24, 26, 28, 31, 32, 37, and 43, respectively. Significant N source X time of application interactions for winter wheat yield were observed at three study sites. At early N application dates (growth stages) yield differences attributable to AN or UAN were not observed; however, when N was applied after growth stage 31, UAN plots produced yields between I and 24% (average 6%) greater than AN-fertilized plots. This was attributable to dry soil conditions that reduced AN movement into the soil plant-root zone, coupled with foliar absorbtion of UAN by wheat plants.Additional Index Words: Nitrogen-use efficiency, Ammonium nitrate, Urea-ammonium nitrate, Leaf burn, Weed control, Fertilizerherbicide tank mix, Triticum aestivum L.
In semi‐arid climates, seed is often sown into soil with inadequate water for rapid germination. Distinguishing between adequate and marginal water can be difficult. Planting decisions become increasingly complicated when one considers possible differences between cultivars. This study was designed to measure the soil water potential limits for rapid, adequate, and marginal germination of winter wheat (Triticum aestivum L.). Laboratory data showed that germination was rapid (3 to 4 d) in soil at water potentials above ‐1.1 MPa and slower (4 to 5 d) at water potentials that ranged from ‐1.1 to ‐1.6 MPa. Below ‐1.6 MPa, less than half of the experimental units achieved the cut‐off criteria of 75% germination with 5‐mm radical length within 25 d. Six cultivars varied in time to germination by an average of 0.34 d, and two randomly selected seed lots of each cultivar differed by an average of 0.20 d. We conclude that variation between seed lots may be as important as variation between cultivars when looking for seed with superior germination under marginal soil water contents.
Glyphosate resistance in S. tragus highlights the imperative need to diversify weed control strategies to preserve the longevity and sustainability of herbicides in semi-arid cropping systems of the Pacific Northwest. © 2017 Society of Chemical Industry.
Nitrogen use efficiency by cereal crops may be increased by the placement of fertilizer with the seed; however, high N concentrations often cause injury and reduce both germination and emergence. Two studies were conducted under controlled greenhouse conditions to evaluate factors affecting emergence of winter wheat (Triticum aestivum L.) planted with seed‐banded N fertilizers. Soil from the Ap horizon of a Palouse silt loam (fine‐silty, mixed, mesic Pachic Ultic Haploxeroll) was used in both studies. Two N materials (ammonium nitrate and urea) were banded with the winter wheat seed (‘Stephens’) at N rates of 0, 11, 22, 33, 44, 55, and 66 kg ha−1, and placed in soils at soil matric potentials of −0.15, −0.25, and −0.35 MPa. The tolerance of five winter wheat cultivars ‘Daws’, ‘Hill 81’, ‘Nugaines’, ‘Peck’, and Stephens to sulfur‐coated urea (SCU) materials SCU‐10, SCU‐20, and SCU‐30 was evaluated in a separate study. Nitrogen rates of 0, 50, 100, and 150 kg ha−1 were used at a soil matric potential of −0.20 MPa. In the first study significant N source × water potential (P < 0.0003) and water potential × N rate (P < 0.0001) interactions were observed. In the second study, significant N source × N rate × cultivar (P < 0.0001), N source × N rate (P < 0.0001), and N source × cultivar (P < 0.0001) interactions were found. The N source, N application rate, soil‐water potential, and winter wheat cultivar main effects were all significant for winter wheat emergence. Ammonium nitrate reduced winter wheat emergence 5 to 26% less than urea when comparable quantities of N were placed with the seed. Winter wheat emergence decreased as soil‐water potential decreased (became more negative). These studies demonstrated how the evaluated factors are interrelated with regard to winter wheat emergence. Consequently, guidelines routinely used for seed‐banded N fertilization that only consider N application rate should be modified to also consider N source and soil moisture.
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