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Spatially variable N fertilizer application may reduce environmental impacts and increase the economic return of N fertilization. To achieve these benefits, N recommendations must account for within-field differences in the amount of N required to produce a unit of yield (unit N requirement, UNR). Component analysis was used to determine the sources of variation in the UNRs of winter wheat (Triticum aestivum L.) among landscape positions. The UNRs were divided into two components, N uptake efficiency (plant N/N supply) and N utilization efficiency (grain yield/plant N) observed in N rate trials (0-140 kg N ha-1 fall applications) established on footslope, south backslope, shoulder, and north backslope positions of two farms for 2 yr. Variation in the UNR among the 16 landscape positions studied was most associated with differences in N uptake efficiency (r = -0.80), although N utilization efficiency (r = -0.62) also contributed to the variation. Nitrogen uptake efficiency among landscape positions declined as more fertilizer was required to reach optimum yield (r = -0.56) due to low N fertilizer uptake efficiencies (delta plant N/delta N fertilizer). Nitrogen fertilizer uptake efficiency was related to the degree of apparent N loss (r = -0.87), indicating that N availability limited N uptake efficiency among landscapes. Overall, low N fertilizer uptake efficiencies ( 50%) indicate the need to reduce N losses and lower UNRs, particularly on north-facing back-slopes susceptible to N leaching.

Recent research in the Palouse region of eastern Washington has suggested that traditional seeding rates may not be adequate to maximize winter wheat (Triticum aestivum L.) yield on all landscape positions. Low spike densities due to reduced light intensities, longer snow cover, and cool temperatures result in lower than expected yields on north-backslope (N-backslope) landscape positions. The objective of this experiment was to determine if higher seeding rates could increase spike density and yield. Three seeding rates, 1.0X standard grower rate (1.0X), 1.5X standard rate (1.5X), and 2.0X standard rate (2.0X), were tested on toeslope, south-backslope (S-backslope), shoulder, and N-backslopes at two locations, Farmington and Pullman, WA, in 1992 and 1993. The 1.5X and 2.0X treatments were established with an additional seeding operation perpendicular to the 1.0X drill passes. Increasing seeding rates resulted in greater spike density on all landscape positions. Spike density of wheat seeded at the 2.0X rate was from 11% greater on the S-backslope to 24% greater on the N-backslope in comparison with the 1.0X rate. Yield, however, only increased on the N-backslope with wheat seeded at the 2.0X rate yielding 10.3% more than wheat seeded at the 1.0X rate. On the three other landscape positions, a reduction in kernel number per spike resulted in no yield increase. Based on expected costs, the 2.0X seeding rate would increase net return on the N-backslope by $2.35/acre given $3.55/bu wheat. Research is needed to determine if similar yield increases could be achieved without making a perpendicular drill pass to double the seeding rate, which would increase net returns by $13.23/acre.

Winter wheat (Triticum aestivum L.) yield varies greatly among landscape positions in the Palouse region of eastern Washington, yet N fertilizer is typically applied uniformly. Varying N fertilizer rates within fields to match site-specific N requirements can increase fertilizer use efficiency; however, spatially variable N management programs are limited by their ability to predict site-specific yield potentials and the resultant N requirements. The objective of this study was to ascertain the role of yield components and soil properties in determining soft white winter wheat grain yield and protein when N application rates are varied among landscape positions. Nitrogen fertilizer (0 to 140 kg N ha −1 ) was fall-applied on footslope, south-backslope, shoulder, and northbackslope landscape positions at each of two farms in 1989 and in 1990. Grain yield among landscapes varied by up to 55% in 1990 and by up to 33% in 1991. Landscape position grain yields increased by 199 kg ha −1 /(cm precipitation+soil water reduction) (r 2 = 0.51) and by 706 kg ha −1 per 100 spikes m −2 (r 2 = 0.76). Grain protein concentration among landscapes increased by 2.7 g kg −1 per each increase of 10 kg residual soil NO 3 -N ha −1 (r 2 = 0.82). The large differences in grain yield among landscape positions may justify spatially variable N application. Improved N management should favorably reduce soft white winter wheat protein concentrations by minimizing high residual N levels as well as improve net returns and reduce environmental degradation. The basis for this improved N management may be site-specific yield estimates calculated from soil water availability and spike density

Spatially variable N application may improve N use efficiency, grain yield, and net returns of winter wheat (Triticum aestivum L.) in fields exhibiting wide ranges of soil characteristics. The objectives of this study were to (i) determine the variability in optimal economic grain yield and in the amount of N required to produce a unit of grain at optimum yield, the unit N requirement (UNR), among landscape positions; (ii) evaluate landscape position as a criterion for dividing fields into units of equal productivity; and (iii) assess the economic benefits of spatially variable N fertilizer application [...]

Increased rates of seeding and N fertilization have accounted for higher yields with new cultivars of several crops. Our objective was to evaluate the new meadowfoam cv. Floral (Limnanthes floccosa Howell subsp. grandiflora Arroyo) × Oregon Limnanthes ORL77-84 (L. alba Hartw. ex Benth. subsp. alba). Combined effects of seeding rate (1.5, 4.0, and 6.5 million seeds ha −1 ), February applied N topdress rate (0, 80, and 160 kg ha −1 ), and irrigation (none, pre-bloom, and pre- and post-bloom) were evaluated near Corvallis, Oregon in 1987-1988 and 1988-1989. Seeding rate, N rate, and irrigation effects on all measured variables were independent of each other. Seed yield, Seed oil content, and oil yield increased 45, 5, and 50%, respectively, while lodging did not increase as seeding rate increased from 1.5 to 6.5 million seeds ha −1 []

Meadowfoam (Limnanthes alba Hartw. ex Benth. subsp. alba cv. Mermaid) seed yield and oil yield vary among years. Consistent high oil yield is needed to encourage profitable commercialization. Field experiments were conducted at Oregon State University in 1987-1988 and 1988-1989 on an Amity silt loam (fine-silty, mixed, mesic Argiaquic Xeric Argialboll) to test the hypothesis that light and temperature effects before the beginning of rapid elongation of stems influence oil yield through alteration of phytomass (total aboveground dry matter) development. Shade-cloth and a transparent floating crop cover were used to alter light and temperature, compared to the control. Cover early, cover early plus late, and shade treatments were applied on 22 Jan. 1988 and 24 Jan. 1989 [...]

Meadowfoam (Limnanthes alba Hartw. ex Benth. subsp. alba cv. Mermaid) is protandrous and entomophilous. Flower number and phenology, stigma receptivity, and timely honey bee pollination are highly weather dependent and were hypothesized to cause seed yield variation. The objective of this field experiment was to use a synchrony index, which is an estimated of flower receptivity and pollination timing synchrony, to relate variation in seed yield to number of open flowers and foraging honey bee (Apis mellifera L.) density (.)

The literature lmacks information on seasonal patterns of meadowfoam (Limnanthes R. Br. spp.) dry matter production and nonstructural carbohydrate quantities and their relationship with seed yield. To provide this information, three meadowfoam lines (85-765, 85-729 and «Mermaind») with contrasting seed yield performance were grown in 1987-1988 and 1988-1989 at the Oregon State University Schimidt Farm

Future development of high-yielding meadowfoam (Limnanthes R. Br. spp.) cultivars may be enhance if relationships between oil yield, yield components, and agronomical, phenological, and morphological traits can be established. To identify such relationships, two half-sib L. floccosa Howell ssp. grandiflora Arroyo × L. alba Hartw. ex Benth ssp. alba lines, ORL85-765 and ORL85-729, and Mermaid' meadowfoam were grown and compared in solid stand in 1987-1988 and 1988-1989 at the Oregon State University Schmidt Farm (...)

Site-specific management of inputs in agricultural production is receiving increased attention because of new technologies and concerns about excessive input use. This paper provides a microeconomic analysis of its implications. It shows that profit decreases with an increase in the variability of input requirements, but that input and production effects can be quite complicated.