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- Author or Editor: R. Scott Johnson x
Minimal dormant pruning after the first and second growing seasons, followed by standard pruning thereafter, improved total tree yield in the 3rd, 4th, and 5th years after planting. Trees that were pruned in accordance with standard local practice had ≈50% yield compared to minimally pruned trees in years 3 through 5. Fruit from minimally pruned trees was sgnificantly smaller, but mathematical adjustment of crop load indicated that overall yield efficiency was improved in the 3rd and 4th years for trees receiving minimal pruning.
Foliar urea sprays offer an alternative to soil applied fertilizers which could greatly reduce the potential for nitrate pollution of groundwater, The approach in the past has been to apply relatively small doses of urea in order to minimize leaf phytotoxicity. Our approach is to apply relatively large doses in the fall when leaf phytotoxicity is not a serious concern. Results on peach trees in the field indicated rapid uptake of foliar applied solutions of 4.3 to 8.8% urea (w/w) (2.0 to 4.0% N). About 80-90% of the urea was absorbed by the leaf within 24 hours. Leaf N levels suggest the majority of this urea was translocated from the leaf into the tree within 1 week despite damage to the leaf. There were no negative effects on flowering, fruit set and production in the following year as long as a very low biuret formulation of urea was used.
Urea foliar sprays may be a more efficient and environmentally sound alternative to soil applied fertilizer N in the postharvest period in tree crop production in California. While tree crop sulfur (S) status can interact with tree N status to affect growth, we know of no study assessing tree crop leaf N and S dynamics following fall (postharvest) foliar urea applications. We conducted a field study to measure temporal dynamics of leaf N and leaf S (% dry weight basis) following postharvest urea sprays on prune (Prunusdomestica) and almond (Prunus dulcis). June-budded nursery stock prune (`French' on Myro 29C) and almond (`Price' on Lovell) trees were sprayed to dripping with 6.5% (w/w) and 10% (w/w) standard urea solutions, respectively. Prunes were sprayed on 1 Oct. 2003 and almonds on 18 Nov. 2003. Leaf samples were taken over a 3-week (almond) or 8-week (prune) period, beginning just before treatment. Foliar urea sprays significantly increased prune (23%) and almond (14%) leaf N compared to untreated control within 8 days of application. This affect was transient, as there were no differences in leaf N concentrations between treated and untreated trees at final leaf sampling. Urea sprays did not affect almond leaf S concentration relative to untreated trees. Prune leaf S was significantly reduced compared to untreated trees 8 days after treatment, but only on that sampling date. Remobilization of S from the leaves of control trees of either species was not apparent.
Six irrigation strategies were imposed on a block of O'Henry peach trees irrigated by fanjets. Treatments received different percentages of ET during the various stages of fruit growth and postharvest. ET was estimated by a large weighing lysimeter containing 2 trees and located in the center of the block. Fruit diameters were measured weekly and final fruit weights were determined at harvest. Adjusted fruit weights were estimated by statistically adjusting each treatment to the same fruit load.
Adjusted fruit weight correlated well with soil water content during the month before harvest but not during early stages of fruit growth. Treatments which applied 50% ET during early stages of fruit growth showed reduced fruit size at that time. However, with applications of 150% ET during the final fruit growth stage, fruit size recovered. Adjusted fruit weight also correlated with measures of tree water status including midday leaf water potential and canopy temperature.
Previous research with Mayfire nectarine demonstrated that seed length can be used as a developmental marker to predict the optimum date of girdling. Four years of study indicates that seed length also appears to be an effective physiologic marker for integrating early season heat accumulation. Seed length development was more highly correlated with heat accumulation (r=0.936) than with number of days after bloom (r=0.699). However, harvest date is more accurately predicted by number of days between 12mm seed length and harvest (30±1) than by degree-days between 12mm seed length and harvest (337±21).
One of the deterrents to the commercial adoption of controlled-environment agriculture (CEA) on a broad scale is the significant energy cost for lighting and thermal environmental control. Advances in energy conversion technologies, such as internal combustion engines (ICs), microturbines and fuel cells, offer the potential for combined heat and power (CHP) systems, which can be matched with the needs of CEA to reduce fossil-based fuels consumption. A principal concept delineated is that an integrated entrepreneurial approach to create business and community partnerships can enhance the value of energy produced (both electrical and heat). Energy production data from a commercial dairy farm is contrasted with energy use data from two greenhouse operations with varying energy-input requirements. Biogass produced from a 500-cow dairy combined with a 250-kW fuel cell could meet nearly all of the energy needs of both the dairy and an energy-intensive 740-m2 CEA greenhouse lettuce facility. The data suggest CEA greenhouses and other closely compatible enterprises can be developed to significantly alter agriculture, as we have known it.
Fruit quality, storage potential, and consumer acceptance were evaluated for `Elegant Lady' peach fruit from non-conventional and conventional fertilizer management systems. Conventional treatments were fertilized with synthetic sources of nitrogen (ammonium nitrate), while the non-conventional plots received organic sources of nitrogen such as vetch cover, biosolids compost, grass compost, chicken manure, or steer manure. Fertilization treatments were applied at high (300 N unit per acre) and low rates (100 N unit/acre) 2 years before the first postharvest evaluation. Evaluations were carried out for three seasons. There were no significant differences in fruit firmness (N) measured at different fruit positions, soluble solids concentration (%), pH, titratable acidity (% malic acid), water loss susceptibility (%), rate of softening, red color (%), or inking incidence. The incidence of flesh browning, mealiness, and flesh bleeding was only related to storage time and not to the fertilizer source. Therefore, the storage potential was not affected by the nitrogen fertilizer source. In our in-store consumer preference test during the 1995 season, 950 consumers did not perceive any taste differences between fruit from the different nitrogen fertilizer sources. Despite this, consumers still would prefer to buy fruit produced using an organic source of nitrogen rather than synthetic sources.