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Exotherm characteristics of dormant apple, pear, peach, plum, grape, persimmon, and black walnut buds were investigated from late autumn to early spring. Differential thermal analysis indicated differences in the high-temperature exotherm (HTE) and low-temperature exotherm (LTE) among the fruit species and sampling dates. According to exotherm characteristics and cold hardiness, the species tested could be divided into two groups, those without LTE (apples and pear) and those with LTE (grape, persimmon, black walnut, peach, and plum). The later group with LTE could be further categorized into two sub-groups those possessing three stages of hardiness development (peach and plum group) and those with five stages of hardiness development (grape, persimmon, and black walnut). In peach and plum group HTE and no LTE could be detected in the first and last stages when bud water content was higher than 55%. The second stage both HTE and LTE could be detected when bud water content was between 40% and 50 %. In the grape, persimmon, and black walnut group the first stage with only HTE was from bud formation to deep supercooling initiation when bud water content was higher than 52%. The second stage with both HTE and LTE was when bud water content was between 40% and 48%. The third stage when only LTE could be detected and bud water content was usually lower than 40%. The fourth stage was from HTE reappearance to LTE disappearance before bud swell. The fifth stage was from LTE disappearance to when only HTE could be detected. No detection of LTE in the buds of apple and pear and no detection of HTE in the buds of grape, persimmon and black walnut were both closely associated with water status in the buds.

Exotherm characteristics of dormant apple, pear, peach, plum, grape, persimmon, and black walnut buds were investigated from late autumn to early spring. Differential thermal analysis indicated differences in the high-temperature exotherm (HTE) and low-temperature exotherm (LTE) among the fruit species and sampling dates. According to exotherm characteristics and cold hardiness, the species tested could be divided into two groups, those without LTE (apples and pear) and those with LTE (grape, persimmon, black walnut, peach, and plum). The latter group with LTE could be further categorized into two subgroups, those possessing three stages of hardiness development (peach and plum group) and those with five stages of hardiness development (grape, persimmon, and black walnut). In the peach and plum group, HTE and no LTE could be detected in the first and last stages when bud water content was >55%. In the second stage, both HTE and LTE could be detected when bud water content was between 40% and 50%. In the grape, persimmon, and black walnut group, the first stage with only HTE was from bud formation to deep supercooling initiation when bud water content was >52%. The second stage with both HTE and LTE was when bud water content was between 40% and 48%. The third stage when only LTE could be detected and bud water content was usually <40%. The fourth stage was from HTE reappearance to LTE disappearance before bud swell. The fifth stage was from LTE disappearance to when only HTE could be detected. No detection of LTE in the buds of apple and pear and no detection of HTE in the buds of grape, persimmon, and black walnut were both closely associated with water status in the buds.

Sunburn can be caused either by heat stress or by UV-B radiation. Under natural conditions fruit sunburn is usually caused by the combination of both heat stress and UV-B radiation. To evaluate the use of reflectance spectroscopy in early detection of fruit sunburn, 5-year-old `Fuji' apple bearing trees growing in pot-in-pot system at the Lewis-Brown Horticulture Farm of Oregon State Univ. were used in the experiment. Fruit sunburn was monitored either under natural conditions or treated with UV-B, heat or both under controlled conditions after detached from the tree. Under natural conditions, the sun-exposed side of Fuji fruit has much higher anthocyanins than the shaded side. The increase in anthocyanins at the sun-exposed side is to protect the fruit from sunburn. When the temperature higher than 40 °C the sunburn symptom initiated first by change the color of the sun-exposed side from red to tan, then to yellow patches, and finally turn to brown and dark brown patches. The peel pigments analysis results indicated that anthocyanins decreased earlier than chlorophyll in the symptom development. The results of detached fruit exposure to 30,000μW/cm² UV-B lights or to 40 °C at control conditions for 2, 4, 6, 8, 10, and 12 hours indicated that high intensity UV-B lights or high temperature alone can cause sunburn respectively. The UV-B and temperature combination treatment enhanced the sunburn processes. The apples with sunburn caused under natural conditions or under UV-B and temperature controlled conditions were scanned by using reflectance spectroscopy of FOSS NIR system at different stage of the sunburn. The results indicted that Fuji apple sunburn can be efficiently detected at the early stage of sunburn in both natural and controlled conditions.

Differential exothermal characteristics in relations to bud water content and dormant periods were dynamically investigated within the buds of apple, pear, peach, plum, Grape, persimmon, and black walnut from late autumn to early spring. Differential thermal analysis (DTA) indicated that bud cold hardiness and two exotherms, the high temperature exotherm (HTE) and low temperature exotherm (LTE), were different among species and dormant periods. According to whether buds have deep supercooling during the dormant winter period the species tested can be divided into two groups. The first group, without supercooling, includes the buds of apple and pear, in which LTE was undetectable. The second group, with supercooling, includes the buds of peach, plum, grape, persimmon, and black walnut, in which LTE was detectable. The second group can be further divided into peach and plum subgroup, and grape, persimmon, and black walnut subgroup. Both HTE and LTE can be detected in the buds of peach and plum subgroup, in which bud cold hardiness can be further divided into three different stages; whereas in the buds of grape, persimmon and black walnut subgroup only LTE can be detected, in which bud cold hardiness can be further divided into five stages according to the detection dynamics of HTE and LTE. Bud differential exothermal characteristics and deep supercooling dynamics are closely related to bud water content and cold hardiness stages. No detection of LTE in the buds of apple and pear and no detection of HTE in the buds of grape, persimmon and black walnut were both closely associated with bud water content.

Grapevine cold hardiness is often assessed with differential thermal analysis (DTA) of excised dormant buds. Such small tissues are prone to rapid dehydration when exposed to air during sample preparation. We show that excised buds of grape cultivars `Vignoles' and `Norton' lose as much as 6.3% and 2.9% of their total water content, respectively, during a two-minute exposure to air at 24 °C. In order to assess the impact of moisture loss on cold hardiness measurements, we prepared dormant bud samples with reduced water content and subjected them to DTA. The results demonstrate a positive correlation between average gross bud water content and median low temperature exotherm (LTE_mean). In `Vignoles' and `Norton' buds, a 6.5% and a 4.3% reduction in gross water content, respectively, were sufficient to result in lower LTE temperatures (P < 0.001). The data suggest that even moderate dehydration of excised grape buds may influence the results of cold hardiness assessment by DTA. It is important that investigators be vigilant to the potential artifacts that can arise during sample preparation in order to ensure that the LTE temperatures of samples reliably characterize the cold hardiness of field populations.

Reserve nitrogen is an important factor for plant growth and fruiting performance in tree fruit crops. The fall foliar urea application appears to be an efficient method for increasing N reserves. The effect of fall foliar urea application on N reserves and fruiting performance were studied with four year old `Gala'/M26 trees grown in 20 gallon containers in a pot-in-pot system from 2001 to 2003 at the Lewis-Brown Horticulture Farm of Oregon State Univ.. The trees were either sprayed with 0 or 2 times 3% urea after harvest in October. Shoot and spur samples were taken at the dormant season for reserve N analysis. Fruit performance was recorded in the following growing season. The fall foliar application significantly increased spur N reserve and had the trend to increase shoot N reserve but not significantly. The fall foliar application significantly increased tree fruit set and cluster fruit set. With normal fruit thinning, fall foliar urea application has the trend to increase both tree yield and average fruit size; without fruit thinning, fall foliar urea application has the trend to increase tree yield. These results indicate that fall foliar urea application an effective method to increase reserve N for maintaining tree yield.

Near-infrared (NIR) reflectance spectroscopy was used to determine the chemical composition of fruit and nut trees. Potted almond and bench-grafted Fuji/M26 trees were fertigated during the growing season with different N levels by modifying the Hoagland to create different levels of nitrogen and carbohydrates in plant tissues during dormancy. Dried, ground, and sieved shoot, shank, and root samples were uniformly packed into NIR cells and scanned with a Foss NIRSystem 6500 monochromator from 400 to 2500 nm. Statistical and multiple linear regression methods were used to derive a standard error of performance and the correlation between NIR reading and standard chemical composition analysis (anthrone, Kjedahl and Ninhydrin methods for carbohydrate, total N, and amino acid analysis, respectively) were determined. The multiple determination coefficients (R ²) of apple and almond tissues were 0.9949 and 0.9842 for total nitrogen, 0.9971 and 0.9802 for amino acid, and 0.8889 and 0.8687 for nonstructural carbohydrate, respectively.

One-year-old (Old Home) OH87 and OH97 pear rootstocks were grown in 2-gallon containers under natural conditions at Corvallis, Ore., in in 1999. Uniform plants were harvested during August and September, and total leaf area, new shoot number and length, and root growth were measured. The kinetics of NH₄ ⁺ and NO₃ ^- uptake by new roots of both rootstocks were determined with the ion-depletion technique. OH87 had larger total leaf area, and more and longer shoots than OH97. Total root biomass was similiar between the two rootstocks, but OH87 had a larger proportion of new roots and more extension roots than OH97. Both rootstocks had lower Km values for NH₄ ⁺ absorption than for NO₃ ^- and therefore both had greater absorptive power for NH₄ ⁺ than for NO₃ ^- at the low nutrient concentrations. The maximum uptake rates (V_max) of OH97 were similiar for both NH₄ ⁺ and NO₃ ^- absorption, but OH87 had a much higher maximum uptake rate for NO₃ ^- than for NH₄ ⁺.

Nitrogen is one of the most important nutrition factors affecting grapevine growth performance and berry quality. Leaf pigments contents and leaf areas are the important indicators of grapevine nitrogen status and plant performance. In order to find a efficient way to nondestructively measure leaf nitrogen and pigments status, the SPAD meter, CCM-200 and CM-1000 chlorophyll meter in comparisons with FOSS NIR system were used in measuring leaf nitrogen, leaf chlorophyll, carotenoids, flavonoids and anthocyanins in 7-year-old Pinot Noir grape with different rate of N treatments. The results indicate that the reading of all these meters have a good relationship with leaf N, leaf chlorophyll and leaf area. But the accuracy among these meters was different, in which the accuracy of FOSS NIR is better than that of the SPAD meter, CCM-200 and CM-1000. There is the good relationship between leaf nitrogen contents, leaf area, leaf chlorophyll and carotenoids contents. Flavonoids and anthocyanins have the inverse relationship with leaf N contents and leaf area. FOSS NIR system can be use for nondestructive assessing nitrogen, leaf chlorophyll, carotenoids, flavonoids and anthocyanins whereas the other meters can only used for nondestructive assessing leaf nitrogen and leaf chlorophyll. These results indicate it is possible to use nondestructive spectral methods as the precision viticulture tools to manage vineyards nitrogen fertilization and grapevine performance.

The accuracy of nondestructive optical methods for chlorophyll (Chl) assessment based on leaf spectral characteristics depends on the wavelengths used for Chl assessment. Using spectroscopy, the optimum wavelengths (OW) for Chl assessment were determined by using 1-year-old almond (Prunus dulcis), poplar (Populus trichocarpa × P. deltoides), and apple (Malus ×domestica) trees grown at different rates of nitrogen fertilization to produce leaves with different Chl concentrations. Spectral reflectance of leaf discs was measured using a spectroradiometer (300 to 1100 nm at 1-nm intervals), and total Chl concentration in leaf discs was extracted and determined in 80% acetone. The OW for nondestructive Chl assessment by reflectance spectroscopy was estimated using 1) the coefficient of determination (r ²) from simple linear regression; 2) reflectance sensitivity analysis (a measure for changes of spectral reflectance on unit change in leaf Chl concentration); and 3) the first spectral derivative method. Our results indicated that the first derivative method can be used only to identify OW in the red edge region of the spectrum, whereas r ² and reflectance sensitivity analysis can be used to identify the OW in both the red edge and green regions. Our results indicate that using simple linear r ² in combination with reflectance sensitivity and/or the first derivative analyses is a reliable method for determining OW in plant leaves tested. Two optimum wavebands with larger r ², smaller root mean square error, and higher reflectance sensitivity were found in red edge (700 to 730 nm) and green (550 to 580 nm) regions, respectively, which can be used as common OW for Chl reflectance assessment in poplar, apple, and almond leaves tested. Single-wavelength indices if developed with OW were even more accurate than those more wavelength indices that developed without using OW. The accuracy of indices can be further improved if indices developed by using one OW and one Chl-insensitive wavelength from near infrared (NIR) (750 to 1100 nm) in the form of R_NIR/R_OW or (R_NIR – R_OW)/(R_NIR + R_OW).