Search

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.

Nitrogen use efficiency (grain weight per unit of N supplied from soil or fertilizer) can be reduced by overfertilization, suboptimal yields, and N losses. Nitrogen is typically fall-applied in eastern Washington for soft white winter wheat (Talcum aestivum L.) production, and is therefore subject to overwinter losses or accumulation in deep soil layers. Increasing grain protein levels of soft white winter wheat have been attributed in part to excessive N application rates and high residual N levels. Spring N applications were evaluated over four site-years as an option to all-fall applied N for reducing N inputs and improving N use efficiency, thereby allowing producers to mainlin productivity while controlling grain protein. Five to six N rates ranging from 0 to 140 kg ha −1 for the all-fall N applications were compared with fall-spring split applications of 134 to 140 kg total N ha −1 . Nitrogen was applied in the spring by topdressing (TD) or with a spoke-wheel point-injection (PI) system. A 15 N experiment was conducted at two locations during the second year to quantify N uptake from fertilizer and soil N. High preplant residual N conditions resulted in limited responses to added N. Nitrogen use efficiency was 26 to 44% lower in the 140 kg ha −1 fall-applied N treatments than in the zero-N control. Reduced N use was related to N losses from the system and to decreased N utilization efficiency (grain weight produced per unit plant N). Spring-applied N, with point injection or topdressing, maintained or increased N use efficiency compared with equivalent all-fall N rates of 134 and 112 kg N ha −1 . More 15 N-labeled fertilizer (7-16% more) was recovered with a split N application than with fall-applied N at the same total rate of 112 kg N ha −1 . At maturity, 68% of plant N was from soil sources with a split application, compared with 80% with an all-fall application. These results suggest spring-N applications with point injection or topdressing can improve fertilizer N recovery and N use efficiency over preplant applications in dryland winter wheat

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

Grain protein of soft white winter wheat (Triticum aestivum L.) produced in eastern Washington has increased above market-desired levels over the past decade, when subnormal precipitation and overfertilization contributed to excessive residual soil N levels. A field study was conducted over four site-years to (i) examine N effects on the yield-protein relationsbip of soft white winter wheat under high soil N conditions, (ii) determine if split N applications can maintain yield and reduce grain protein, and (iii) evaluate midseason grain analysis as a predictor of final grain protein. Nitrogen rates ranged from 0 to 140 kg N ha −1 ; timing treatments were fall preplant N and spring topdressed or point-injected N. High yields (> 5900 kg ha −1 ) were produced witbout fertilizer N, and yield responses to N ranged from 0 to 22%. Fall N > 56 kg N ha −1 increased yield in only one site-year; yields were reduced due to excess N fertilization in another site-year in conjunction with shallow N depletion and poor water extraction from deeper soil layers. In two of four site-years, yield increased with a 50% fall-50% spring point-injected N compared with 100% fall application at 84 kg total N ha −1 . Protein > 100 g kg −1 was produced in site-years where most soil N was depleted below the 90-cm depth; shallow N depletion was associated with lower protein. Grain N concentration at maturity was highly correlated with grain N concentration at the late milk and soft dough stages. Preharvest predictions of final grain protein may be useful in segregating grain at harvest for marketing purposes. Under high residual soil N levels, reduced N rates and split N applications between fall and spring can maintain high yields and reduce grain protein

Inadequate interpretation of cultivar test results can lead to poor cultivar selection by growers and loss of farm income. Analysis of cultivar mean yields does not allow comparison of predicted cultivar responses at different yield levels. Traditional tests of significance are inappropriate for nonacademic clients of applied research. This study introduces cumulative probabilities (CP) as an alternative method of expressing predicted cultivar response across the range of possible yields. Cumulative probabilities, computed using the mean and standard deviation of each cultivar in a normal probability density function, express the probability growers have of obtaining or exceeding given yields when planting each cultivar [...]

Farmer conducted on-farm research is an effective tool for development of crop management practices. The randomized complete-block experimental design is being used in on-farm tests, with blocks consisting of two or more long, narrow, sideby-side plots. This study examined the relationship between plot length and experimental error, and assesses the probable statistical outcome of on-farm tests performed in the dryland region of the Pacific Northwest, USA. Fourteen trials were conducted in wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) fields to measure yield variance of combine-width plots ranging in length from 250 to 1500 ft. The relationship between plot length and variance for each site followed a logarithmic decay model (average r 2 = 0.88) [...]

Release of mediocre and interior cultivars can have costly and deleterious consequences for breeders, crop improvement associations, and growers. Multilocational testing of new cultivars in replicated small-plot trials over several years has traditionally been used to screen new cultivars prior to release. Single-replicate on-farm tests (SROFTs) of spring barley (Hordeum vulgare L.) cultivars were conducted by eastern Washington growers from 1990 to 1992 to compare with the results obtained from replicated small-plot trials. The comparison of interest was the risk of releasing inferior barley cultivars and the similarity of cultivar response in the two testing systems [...]

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 [...]

Crop growth modeling can be useful in crop management, but previous rice crop models lack the morphologically accurate phenological detail needed for practical application. We designed a rice crop management model, CARICE, for scheduling management actions on the farm and evaluating consequences of alternative management strategies. A simple rice crop productivity model was expanded to include (i) phenology, based on leaf stage; (ii) tiller development, to establish yield components; (iii) assimilate partitioning by developmental stage, (iv) assimilate partitioning patterns of California cultivars; and (v) a direct-seeded cultural system [...]

Initial management strategies, such as established plant stand, significantly affect rice (Oryza sativa L.) crop development, grain yield, and final profits. Critical rice plant population for optimum yield differs greatly among various cultural systems. The objectives of this study were to: (i) characterize effects of increasing plant population on tillering, yield components, yield, and phytomass development in continuously flooded, direct water-seeded rice culture; and (ii) identify which crop development parameters are associated with optimum grain yield in this cultural system (...)