Search Results

You are looking at 1 - 10 of 18 items for

  • Author or Editor: R.S. Johnson x
  • Refine by Access: All x
Clear All Modify Search
Open access

R.S. Johnson and S.A. Weinbaum

Abstract

The pistachio (Pistacia vera L.) industry in California is based largely on a single pistillate (i.e., nut-producing) cultivar (Kerman) supported by seedling rootstocks of P. atlantica Desf. Data were collected and analyzed for tree growth and productivity of 113 mature ‘Kerman’ trees/P. atlantica seedlings over two cycles of alternate bearing. Tree size as estimated by trunk cross-sectional area varied 4-fold among the trees analyzed; tree yields, averaged over 4 years, varied 8-fold within the plot, and cropping efficiency (yield/cm2 of trunk cross-sectional area) varied 3-fold among the trees within the orchard. The severity of alternate bearing also was calculated. Eight superior trees were identified within the orchard that not only had higher average yields and cropping efficiencies, but also exhibited much more regular cropping patterns (i.e., reduced severity of alternate bearing) than adjacent trees and the orchard as a whole.

Open access

R.S. Johnson and D.F. Handley

Abstract

The response of fruit size and fruit size distribution was studied in four peach (Prunus persica L. Batsch.) cultivars (May Crest, June Lady, Elegant Lady, O’Henry) ranging in maturity date from late May to early August (75 to 150 days after bloom). Mature, open-vase trees were thinned to fruit levels ranging from 150 to 2200 fruit per tree. The slopes of the linear relationships between fruit weight and fruit number per tree were consistent among cultivars, but their y-intercepts increased proportionate to maturity date. The standard deviation of individual fruit weights tended to decrease with increasing fruit number per tree and increased with later-maturing cultivars. However, the coefficient of variation remained nearly constant among cultivars. Mean fruit weight generally dropped off with successive harvests, especially on trees with heavy fruit loads. Heavy fruit loads also delayed maturity in all four cultivars. This study measured the variation of fruit weight response to thinning, information that is needed for a detailed economic analysis of thinning to different fruit loads.

Open access

R.S. Johnson and A.N. Lakso

Abstract

The relationship of leaf area and stem weight, with stem length at different times during the year, was studied on 5 apple (Malus domestica Borkh.) cultivars. Leaf area was related linearly to stem length, but the slope differed by up to 2-times between cultivars. Stem dry weight increased curvilinearly with respect to stem length and showed less variation among cultivars than did leaf area. These 2 relationships combined indicated that the stem constitutes an increasing proportion of the total shoot weight with increasing stem length. Dormant stems had a greater weight per unit length than stems of growing shoots. Both stem length and leaf area showed strong fitting linear relationships with accumulated growing degree-days, but the stem length relationship showed less variability among cultivars than did leaf area.

Open access

R.S. Johnson and A.N. Lakso

Abstract

A computer model simulating the C balance of a growing ‘Jonamac’ apple (Malus domestica Borkh.) shoot was constructed to estimate the time of first net carbohydrate export from the shoot. The model was based on measurements of net photosynthesis and dark respiration rates and estimates of the dry weight in the different components of the shoot. Under the prevailing weather of 1981, the model indicates that a shoot growing to a final length of 50 cm became a net exporter of carbohydrates 19 days after budbreak, a time corresponding to a shoot 4 cm long with 10 unfolded leaves. Assuming the same early growth rates, a shoot with a final length of 2 cm starts exporting at 15 days after budbreak. The total export of carbohydrates remains higher from short shoots than long shoots until 36 days after budbreak, indicating that short shoots supply greater amounts of carbohydrates to the rest of the plant during this early period. The model estimates the total import of carbohydrates from reserves of about 165 mg for the long shoot and 80 mg for the short shoot. In each instance, these reserves only accounted for about 20% of the total carbohydrates used by the shoot up to that point. The remainder was supplied by current photosynthates.

Open access

R.S. Johnson and A.N. Lakso

Abstract

A computer model of a growing apple (Malus domestica Borkh.) shoot was used to estimate the effects of light and temperature on the C balance of a shoot. Long-term average solar radiation (langley/day) and maximum and minimum temperatures from Geneva, N.Y., were used as weather inputs. To simulate other weather conditions, solar radiation was increased or decreased by 150 langley/day, and maximum and minimum temperatures increased or decreased by 5.6°C. Both a short shoot of 2 cm and a long shoot of 50 cm final length were simulated. The model output indicated that increased light reduced carbohydrate import and caused earlier and greater export. Increased temperature increased carbohydrate import and the subsequent rate of carbohydrate export. The short shoot had a greater initial rate of C export and continued to export more total carbohydrates than the long shoot for about 30 to 50 days after budbreak. Slow leaf area development at a given temperature had little effect on carbohydrate import but delayed the beginning of export.

Open access

Frederick S. Davies and Charles R. Johnson

Abstract

Moderate and severe water-stress, as determined by decreases in stomatal conductance, resulted in significant reduction of leaf area and plant weight in 1-year-old containerized ‘Bluegem’ rabbiteye blueberry. Drought-tolerance appeared to be intermediate to other plant species based on a number of physiological factors. Critical water potential for stomatal closure was −2.2 MPa, transpiration ratio averaged 222 g of water transpired per g dry matter produced and relative water content changed 6.4% per 1.0 MPa change in water potential.

Free access

R.S. Johnson, D.F. Handley, and T.M. DeJong

Early maturing peach trees [Prunus persica (L.) Batsch cv. Regina] growing on a deep sandy loam soil were subjected to three levels of postharvest irrigation over 4 years. The control treatment was irrigated with ≈ 10 to 15 cm of water at 2- to 3-week intervals, the medium treatment received a single irrigation (20 to 30 cm) in early August, and the dry treatment was not irrigated between early to mid-June and mid-October. All received a predormancy irrigation of 10 to 15 cm in mid- to late October. Flower and fruit density were greater in the dry treatment than the control. The occurrence of double fruit was also greatly increased in the dry treatment but not in the medium treatment, when compared with the control. After normal commercial hand thinning, yields and fruit size were no different among the three treatments over all 4 years. Vegetative growth as measured by dormant pruning weights, trunk radial growth, and canopy shaded area was reduced in the dry treatment, but there was no indication of progressively declining vigor. Soil moisture determinations indicate that water use by the control occurred mainly in the upper soil profile. In the dry treatment, as the upper profile dried, water was extracted progressively deeper, down to at least 300 cm. The main disadvantage of severe postharvest water stress was the substantial increase of double fruits.

Open access

K.D. Larson, T.M. DeJong, and R.S. Johnson

Abstract

Peach trees (Prunus persica L. Batsch cv. Regina) were subjected to three levels of postharvest irrigation between 15 June and 15 Oct. 1983. Wet-treatment (control) trees were irrigated at 3-week intervals, medium-treatment trees received one, and dry-treatment trees received no postharvest irrigations. Significant differences in seasonal patterns of stomatal conductance were found among all treatments, with conductance varying in proportion to irrigation level. Wet-treatment pre-dawn water potential (ψw) remained nearly constant at −0.3 MPa throughout the postharvest season, whereas the dry-treatment readings became more negative as the season progressed. Differences in mid-day ψw were less distinct, but generally reflected pre-dawn water status. The seasonal increase in trunk radius of the dry-treatment trees was reduced by 33% relative to either wet or medium treatments. The amount of daily trunk radial shrinkage was inversely proportional to irrigation level. Dormant pruning weights were 13% less in dry treatments than wet treatments. Return bloom of dry-treatment trees in Spring 1984 was 30% and 40% greater than medium- and wet-treatment return bloom, respectively. Dry-treatment fruit set was 70% greater than medium- or wet-treatment fruit set. Following fruit thinning, there were no significant differences among treatments for fruit yield or fruit size, but fruit maturity was slightly delayed in the dry treatment.

Free access

S.J. Browning, T.P. Riordan, R.K. Johnson, and J. Johnson-Cicalese

Buffalograss [Buchloë dactyloides (Nutt.) Engelm] is a drought-resistant, dioecious species, native to the Central Great Plains, which shows excellent potential as a low-maintenance turfgrass. Although buffalograss can be propagated vegetatively, there is a need for seeded turf-type cultivars. To assist in developing seeded cultivars, heritabilities of turf characteristics were estimated. Heritabilities from maternal half-sib analyses ranged from h2 = 0.04 ± 0.03 for the 1988 uniformity rating to h2 = 0.62 ± 0.26 for the 1989 spring color rating. Heritability estimates calculated from offspring-parent regression were also variable and generally lower than maternal half-sib analysis. The results suggest that some turf characteristics are highly heritable and that growing conditions markedly affect heritability estimates.

Free access

S.P. Castagnoli, T.M. DeJong, S.A. Weinbaum, and R.S. Johnson

Premature defoliation of peach and nectarine (Prunus persica L. Batsch) trees resulting from foliar applications of ZnSO4 reduced N remobilization that typically occurs during leaf senescence. Leaf N remobilization in unsprayed control trees ranged from 45% to 50%, irrespective of tree N status. Leaf N remobilization in trees receiving foliar applications of ZnSO4 ranged from a positive influx of N into the leaf to ≈30% of the N remobilized, depending on ZnSO4 application timing and method of expressing leaf N levels. Early ZnSO4 applications resulted in less N remobilization. Measuring leaf N on an area basis was a more precise indicator of N remobilization than N per unit dry weight, because leaf weight per unit area changes during leaf senescence.