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Timothy L. Righetti

Nitrogen, boron, and zinc are the major deficiencies encountered in Oregon tree fruit production. Much of our current management strategies are based on studies evaluating the uptake and plant mobility of labeled N, Zn, and B. Because mature trees differ from young plants, most of our experiments are conducted on fully bearing trees. Nitrogen strategies emphasize applying minimal amounts to avoid excess vigor and poor fruit quality. Our goal is to produce moderately vigorous trees with low fruit N, while still maintaining adequate tree reserves for early spring growth. Labeled 15N studies suggest that the later N is applied, the less is partitioned into leaves and fruit, with more N incorporated into storage tissues. Postharvest foliar applications of urea can also produce high bud N levels in combination with moderate vigor and low fruit N. Partitioning differences from various timings also result in different utilization efficiencies, especially if one considers N losses from pruning. Early N applications may have smaller efficiencies because pruning losses are greater. Although plant B is thought to be immobile, foliar-applied B is rapidly mobilized out of the leaf. Postharvest foliar B applications are an excellent way to ensure that buds have adequate B levels the following spring. Unlike N and B, Zn is not mobilized out of the leaf where it is applied. Sprays directly to young tissues in the spring are the only practical ways of increasing Zn levels.

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Enrique E. Sánchez and Timothy L. Righetti

This study was carried out on mature `Delicious' apple trees (Malus domestica Borkh.) on EM 9 rootstock. Labeled B (99.63 Atom % 10B) was applied as boric acid. Treatments were postharvest foliar B at 375 mg·L–1, postharvest foliar B (375 mg·L–1) plus urea (2.5% wt/vol), and a soil application at the same per-tree rate as the foliar treatments (16 g boric acid/tree). Postharvest foliar B applied with or without urea was efficiently transported from the leaves into storage tissues for the next year's growth. However, soil-applied B remained mostly in the roots while very little was translocated to the above-ground portions of the tree at full bloom. When urea was added to a foliar B spray, the amount of B in the roots and flower clusters increased at full bloom. Although increasing the efficiency of foliar B applications may not be necessary, combining urea and B into a single application is recommended when growers want to apply both N and B. Shoot leaves from all treatments collected late in the season (midsummer) had similar B concentrations, even though treatments altered the amount of added B that was present in different tree tissues early in the season.

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Enrique E. Sanchez and Timothy L. Righetti

`Cornice' pear trees (Pyrus communis L.) were fertilized with ammonium nitrate depleted in “N in Spring 1987 and 1988. In Aug., Oct., and Nov. 1988, midleaves on current season shoots were sampled at three positions from the periphery to the center of the canopy. Total N/cm' of leaf area remained almost constant through October, even though percent N concentration declined as specific leaf weight (SLW) increased. Furthermore, there was no substantial net change in either labeled or unlabeled N in either treatment until senescence began in October. Peripheral leaves contained higher levels of both reserve and newly acquired N than did less-exposed leaves. Despite large differences in N/cm2 for October samples, by November leaves from both high (HN) and low N (LN) trees exported similar percentages of their total N. The average N export to storage tissues irrespective of tree N status was 71%, 61%, and 52% for peripheral, medium, and interior leaves, respectively. The export of N was influenced more by the leaf position in the plant canopy than the nutritional status of the tree.

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Timothy L. Righetti and Michael D. Halbleib

Agriculture is changing. State-of-the-art computer systems that use GPS (global positioning systems) data, GIS (geographic information systems) software, remotely sensed images, automated sampling, and information analysis systems are transforming growers' ability to produce their crops. Currently, the farm service and agricultural sales industry, rather than the grower direct most information technology applications. Precision agriculture must become an information-driven and grower-driven process. Data evaluation has to be made simpler, less time consuming, and inexpensive. The purpose of this paper is to outline potential strategies and demonstrate how information can be processed and evaluated with readily available and inexpensive analytical tools.

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Kris L. Wilder, Timothy L. Righetti, and Arthur Poole

Cranberry (Vaccinium macrocarpon Ait.) is an important crop in Oregon. However, nutrient critical levels have not been established. Since developing nutrient critical levels usually requires time-consuming and expensive field trials, we chose to use the Diagnosis and Recommendation Integrated System (DRIS), which can use survey data to determine critical levels. We analyzed 139 cranberry samples collected from the southern Oregon coastal area over a three-year period. Leaf concentrations for N, P, K, S, Ca, Mg, Mn, Fe, Cu, B, and Zn in bearing uprights collected in mid-August were matched with the corresponding yields. DRIS was employed to obtain norms and critical levels from this survey data. To test our DRIS norms and critical levels, we evaluated two published experiments (Torio and Eck, 1969 and Medappa and Dana, 1969) where fertility treatments altered mineral concentrations and affected yield. Both ratio-based and critical concentration diagnoses were useful. Changes in the Nutrient Imbalance Index was a good predictor of yield response.

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Habib Khemira, Timothy L. Righetti, and Anita N. Azarenko

Fruit tree responses to foliar urea sprays are variable. We hypothesized that such variability is a function of leaf age-related changes in urea-N mobility after urea is absorbed. Two experiments were conducted to study the distribution of urea-derived N in shoots and branches of apple (Malus ×domestica Borkh.) trees. Urea labeled with 15N was applied to young expanding leaves in spring and to senescing spur leaves in fall. At the low concentrations used [0.5%, 1%, and 2% (w/v)], very little spring-applied 15N was found in tissues other than the treated leaf. Fall-applied urea-15N, however, was detected in high concentrations in dormant buds and bark of the spurs to which the treated leaves were attached. Almost no N was exported to neighboring tissues. The following spring, there was some redistribution of labeled N to adjacent buds. Foliar urea sprays applied immediately after harvest contributed most to bud N; less urea-N was exported to the buds following later fall applications.

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David R. Sandrock, Anita N. Azarenko, and Timothy L. Righetti

Nitrogen accumulation patterns were established for Weigela florida (Bunge.) A. DC. `Red Prince' (fast growth rate) and Euonymus alatus (Thunb.) Sieb. `Compactus' (slow growth rate). From these, daily and biweekly N delivery schedules were designed to match N supply with N accumulation patterns of each taxon. Delivery schedules were sliding scales in that total N applied was controlled by independent increases (or decreases) of N concentration and solution volume. Daily and biweekly N delivery schedules were tested against a constant N rate (200 mg·L-1) and Osmocote 18N-2.6P-9.9K (The Scotts Co., Marysville, Ohio). Plants were grown in 3.8-L containers in 7 douglas fir bark: 2 sphagnum peatmoss: 1 silica sand (0.65 mm; by volume) outdoors in full sun on a gravel pad for 142 d. Within each taxon, Weigela and Euonymus grown with sliding-scale N fertilization schedules had similar total dry weights, leaf areas, and total plant N contents to plants grown with a constant N rate (200 mg·L-1) or Osmocote 18N-2.6P-9.9K. Sliding-scale liquid fertilization based on plant N requirements introduced less total N to the production cycle and resulted in higher N uptake efficiency than fertilization with a constant N rate of 200 mg·L-1. In general, liquid N fertilizer treatments resulted in plants with higher shoot to root ratios than plants treated with Osmocote 18N-2.6P-9.9K. Weigela and Euonymus treated with biweekly schedules were similar to plants treated with daily schedules (same total amount of N delivered with each treatment).

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David Sugar, Timothy L. Righetti, Enrique E. Sanchez, and Habib Khemira

Management of pear (Pyrus communis L.) trees for low N and high Ca content in the fruit reduced the severity of postharvest fungal decay. Application of N fertilizer 3 weeks before harvest supplied N for tree reserves and for flowers the following spring without increasing fruit N. Calcium chloride sprays during the growing season increased fruit Ca content. Nitrogen and Ca management appear to be additive factors in decay reduction. Fruit density and position in the tree canopy influenced their response to N fertilization. Nitrogen: Ca ratios were lower in fruit from the east quadrant and bottom third of trees and from the distal portion of branches. High fruit density was associated with low N: Ca ratios. Nutritional manipulations appear to be compatible with other methods of postharvest decay control.

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Hannah G. Rempel, Bernadine C. Strik, and Timothy L. Righetti

The effects of 15N-labeled fertilizer applied to mature summer-bearing red raspberry (Rubus idaeus L. `Meeker') plants were measured over 2 years. Four nitrogen (N) treatments were applied: singularly at 0, 40, or 80 kg·ha-1 of N in early spring (budbreak), or split with 40 kg·ha-1 of N (unlabeled) applied at budbreak and 40 kg·ha-1 of N (15N-depleted) applied eight weeks later. Plants were sampled six times per year to determine N and 15N content in the plant components throughout the growing season. Soil also was sampled seven times per year to determine inorganic N concentrations within the four treatments as well as in a bare soil plot. There was a tendency for the unfertilized treatment to have the lowest and for the split-N treatment to have the highest yield in both years. N application had no significant effect on plant dry weight or total N content in either year. Dry weight accumulation was 5.5 t·ha-1 and total N accumulation was 88 to 96 kg·ha-1 for aboveground biomass in the fertilized plots in 2001. Of the total N present, averaged over 2 years, 17% was removed in prunings, 12% was lost through primocane leaf senescence, 13% was removed through fruit harvest, 30% remained in the over-wintering plant, and 28% was considered lost or transported to the roots. Peak fertilizer N-uptake occurred by July for the single N applications and by September for the last application in the split-N treatment. This uptake accounted for 36% to 37% (single applications) and 24% (last half of split application) of the 15N applied. Plants receiving the highest single rate of fertilizer took up more fertilizer N while plants receiving the lower rate took up more N from the soil and from storage tissues. By midharvest, fertilizer N was found primarily in the fruit, fruiting laterals, and primocanes (94%) for all fertilized treatments; however, the majority of the fertilizer N applied in the last half of the split application was located in the primocanes (60%). Stored fertilizer N distribution was similar in all fertilized treatments. By the end of the second year, 5% to 12% of the fertilizer acquired in 2001 remained in the fertilized plants. Soil nitrate concentrations increased after fertilization to 78.5 g·m-3, and declined to an average of 35.6 g·m-3 by fruit harvest. Seasonal soil N decline was partially attributed to plant uptake; however, leaching and immobilization into the organic fraction may also have contributed to the decline.

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Timothy L. Righetti, David R. Sandrock, Bernadine Strik, and Anita Azarenko

Two approaches for estimating the amount of nitrogen (N) in plant tissues derived from labeled fertilizer were evaluated for two tissue types (root and shoot) in three different genera. In the first, atom percentage values obtained by mass spectrometry were converted to the portion of N derived from the fertilizer (NDFF). In the second, the slope of the regression line for the relationship between total N and labeled fertilizer N was used to represent the incremental increase in fertilizer N for each unit increase in total N. These two approaches were applied to data collected during container experiments. Unless a plot of total N versus labeled fertilizer N passes through the origin, conventional ratio-based estimates of the amount of NDFF for plants or tissues are often misleading. When nonzero intercepts occur, NDFF is dependent on the size (total N content) of the tissue or plant. Nonzero intercepts were frequently encountered. An analysis of regression lines describing the relationship between total N gain and fertilizer N produces a different interpretation than evaluations of the NDFF for treatment means. When an analysis of covariance was used to account for differences in total N between tissues and genera, results were generally consistent with the graphical observations and regression analysis. If only ratio-based approaches are used, it is difficult to determine if there are real physiological differences among treatments, genera, and tissues or if differences in NDFF are size-related. Because the data easily can be analyzed several ways, simultaneously evaluating data with ratio-based NDFF, covariates, and regression is appropriate.