The ability of peach leaves to absorbed and translocated foliarly applied 15N-urea in mature peach (Prunus persica) trees was determined. Urea uptake experiments were conducted in June, October, and November 1995. Peach leaves absorbed ≈80% of the urea within 48 hr of application in all three experiments based on urea rinsed from leaf surfaces. Similarly, leaf 15N content reached a peak 48 hr after application. Translocation of 15N out of leaves, however, was more rapid in October then November. In October, 24% of the 15N remained in the leaves 2 weeks after application, while, in November, 80% stayed in the leaves and fell to the orchard floor. Thus, applying urea in mid November did not allow enough time for the N to be transported out of the leaves before leaf abscission. Timing of foliar urea application is critical to maximize N transport into perennial tissues of peach trees. 15Nurea resorption out of leaves and into perennial tree parts (roots, trunk, current year wood, etc.) is discussed.
Richard C. Rosecrance, Scott Johnson, and Steven A. Weinbaum
Richard C. Rosecrance, Steven A. Weinbaum, and Patrick H. Brown
The effect of crop load on nutrient and starch storage in mature, alternate-bearing pistachio trees was examined. Tree storage pools were estimated from the differences in nutrient and starch contents of perennial tree parts between dormancy (the period of highest nutrient and starch content) and following spring flush (the period of lowest nutrient and starch content). Following a lightly cropping (off) year, trees contained significantly larger N, P, and K storage pools than following a heavily cropping (on) year. The relative contribution of leaf nutrient resorption to tree nutrient storage pools varied depending on the crop load. Nutrient storage is a function of net leaf nutrient resorption and current uptake from the soil. Leaf nutrient (N, P, and K) resorption was a more significant component of nutrient storage in on-year than off-year trees. The contribution of nutrient storage to shoot (i.e., leaves, fruit, current-year wood) nutrient contents was evaluated following the spring flush (May) and nut fill (September) periods. Nutrient storage pools are an important source of nutrients during the spring flush of growth, but nutrient demands during nut fill are met primarily by current nutrient uptake from the soil. The relationships between nutrient storage and uptake are discussed.
Steven A. Weinbaum, Wesley P. Asai, David A. Goldhamer, Franz J.A. Niederholzer, and Tom T. Muraoka
There is legitimate concern that excessive fertilizer nitrogen (N) application rates adversely affect groundwater quality in the San Joaquin Valley of California. A 5-year study was conducted to assess the interrelationships between N fertilization rates, tree productivity, leaf [N], soil [NO– 3], tree recovery of isotopically labeled fertilizer N, and NO– 3 leaching. High N trees recovered <50% as much labeled fertilizer N in the crop as did trees previously receiving low to moderate fertilizer application rates. Our data suggest that the dilution of labeled N in the soil by high residual levels of NO– 3 in the soil had a greater effect than tree N status (as expressed by leaf N concentration) on the relative recovery of fertilizer N.
Steven A. Weinbaum, Wesley Asai, David Goldhamer, and Franz J.A. Niederholzer
A project to study the interrelationships between leaf N conc., relative tree yield (RTY), nitrate leaching and fertilizer N recovery was established in 1990. Collection of pretreatment baseline data was followed by differential rates of N fertilization. Significant differences in leaf N conc. and RTY were obtained in 1992 and 1993, respectively. RTY is defined as tree yield in 1993 expressed as a percentage of pretreatment (1990) yield. 15N-depleted (NH4)2SO4 was applied postharvest in 1993 to 17 trees differing in RTY and leaf N conc., and recovery of labelled N in the blossoms of these trees (March, 1994) will be discussed.
Edwin J. Reidel, Patrick H. Brown, Roger A. Duncan, and Steven A. Weinbaum
Almond [Prunus dulcis (Mill.) D.A. Webb] yields have increased substantially since the 1961 publication of the Univ. of California (UC) guidelines for leaf potassium (K). Numerous growers and reputable analytical laboratories are concerned that the recommendations for leaf K are inadequate. A highly productive almond orchard with low leaf K was selected to reassess the leaf K critical value of 1.1% to1.4% and determine the relative sensitivity of various yield determinants to inadequate K availability. Baseline yields for 100 individual trees were measured in 1998 and four rates of potassium sulfate were applied under drip irrigation emitters to establish a range of July leaf K concentrations between 0.5% and 2.1%. No relationship was observed between leaf K and post-treatment yield measurements made in 1999. We also monitored individual limb units on trees from the treatment extremes for effects of low K availability on flower number, percentage fruit set, fruit size, spur mortality, and vegetative growth (potential fruiting sites in subsequent years). Those measurements indicated that although current-year yield determinants (percentage fruit set and fruit size) were not influenced by K deficiency, components of future yield were impacted negatively by low K availability: mortality of existing fruiting spurs was increased by K deficiency and growth of fruiting wood was reduced.
Daniel S. Kirschbaum, Kirk D. Larson, Steven A. Weinbaum, and Theodore M. DeJong
The pattern of total nonstructural carbohydrate [starch and soluble sugars (TNC)] accumulation in strawberry (Fragaria ×ananassa Duch.) nursery runner plants, cv. Camarosa, was determined for three growing seasons. A similar study was conducted on `Selva', but for only one year. Growth, development and fruit production patterns of plants transplanted to growth chambers (GC) or fruiting fields were also evaluated. The experiments were carried out on plants propagated in high latitude (41°50' N) nurseries in California (Siskiyou County). Plants were sampled beginning late summer through early autumn and analyzed for dry mass (DM) and TNC. Plants from different digging dates were established in GC or fruit evaluation plots in Irvine, Calif. (33°39'N). Initial TNC concentration in storage tissues at the time of nursery digging increased steadily from the second week of September to the third week of October. Crown and root TNC concentration and content were correlated positively with the accumulation of chilling units (CU = hours ≤7.2 °C) in the nursery. Root TNC concentration consistently increased from 6% to 10% DM in `Camarosa' (a short-day cultivar), and from ∼4% to 14% DM in `Selva' (a day-neutral cultivar) from mid-September to the first week of October. The root TNC content increased ∼2.5 times in `Camarosa' and ∼3.7 times in `Selva' during the same period. Transplant growth, development, and fruiting pattern were affected by digging date. Root TNC concentration and content were more sensitive to CU accumulation than crown TNC concentration and content. Therefore, root sampling appeared to be more appropriate than crown sampling for assessing the carbohydrate status and optimal digging dates of strawberry nursery runner plants early in the fall.
Timothy Spann, Robert H. Beede, Steven A. Weinbaum, and Theodore M. DeJong
Rootstock significantly alters the pattern of shoot growth of pistachio (Pistacia vera) cv. Kerman. Trees grown on P. atlantica typically produce a single flush of spring growth, whereas trees on P. integerrima selection PGI and P. atlantica × P. integerrima selection UCB-1 can produce multiple flushes during the season. We have shown that the spring flush is entirely preformed in the dormant bud for all three rootstocks, but later flushes are neoformed, that is, nodes are initiated and extended during the same season. Shoots producing both preformed and neoformed growth have lower yield efficiency than those producing only preformed growth. Additionally, yield components of the crop from shoots with both preformed and neoformed growth was different than for shoots producing only preformed growth. However, these differences do not appear to be significant at the whole tree level. These data suggest that neoformed growth can both compete with fruit growth for available resources (lower yield efficiency) and act as an additional source (altered yield components), depending on the factor being measured. Controlling neoformed growth may potentially increase pistachio yield through a shift to the more efficient preformed shoots while at the same time lowering orchard maintenance costs by reducing required pruning. We have data to indicate that regulated deficit irrigation and new pruning techniques may be viable methods for controlling neoformed growth in pistachio without affecting yield.
Timothy M. Spann*, Robert H. Beede, Steven A. Weinbaum, and Theodore M. DeJong
Rootstock significantly alters the pattern of shoot growth of pistachio (Pistacia vera) cv. Kerman. Trees on P. atlantica typically produce a single flush of spring growth whereas trees on P. integerrima selection PGI and P. atlantica × P. integerrima selection UCB-1 can produce multiple flushes during the season. Terminal buds of shoots on all three rootstocks were dissected during the dormant season to determine the number of preformed nodes. Data indicate that there are 8-9 nodes preformed in the dormant terminal bud of shoots from Kerman trees and that this number is independent of rootstock, canopy location, crop load, and shoot carbohydrate concentration, suggesting genetic control. This number corresponds with the number of nodes typically found on a shoot at the end of the spring growth flush. Unlike the spring flush which is preformed in the dormant bud, later flushes are neoformed, that is, nodes are initiated and extended during the same season. Neoformed growth depends on current season photosynthates and may compete with fruit growth for available resources. Neoformed growth is sensitive to water stress and trees on all three rootstocks grown under two levels of regulated deficit irrigation showed a reduction in both the number and length of neoformed shoots. Preformed shoot growth did not appear to be reduced under water stress conditions, supporting the hypothesis that preformed shoots are more dependent on environmental conditions during the season they are initiated than during the season they are extended. Additionally, preformed shoots on well irrigated trees were similar in length for all rootstocks, further supporting the idea that preformed shoots are under genetic control and are not easily manipulated.