Irregular Bearing Research Articles

Studies on the Influence Age of Rootstocks and Season on Grafting Success in Manila Tamarind (Pithecellobium dulce Roxb.)

Background: Manila tamarind (Pithecellobium dulce (Roxb.) Benth) belongs to the family Fabaceae and sub-family Mimosoideae. This tree have multiple uses; fruit, firewood, honey, fodder, soap oil, tannin, hedges and shade. Naturally this plant species can be multiplied by seeds. Apart from genetic variability, the seedling progenies may take long time to first bearing and sometimes irregular bearing also noticed due to its genetic makeup. In order to overcome these drawbacks, vegetative propagation is the only alternate way to get genetically uniform, early bearing and high yielding characters. The age of rootstocks and season of grafting influences the success of the grafts and performance of the grafted plants. With this background, studies on age of rootstocks and season on grafting success in Manila Tamarind was carried out. Methods: An experiment was conducted to assess the effect of season and age of the rootstocks in Manila Tamarind (Pithecellobium dulce). The experiment was laid out in factorial randomized block design with 15 treatment combinations and four replications. In this study, three rootstocks of different age viz., 6, 9 and 12 months old were grafted during June, July, August, September and October. Result: The main and interaction effects on age of rootstocks and season of grafting had a significant influence on survival percentage, number of days taken to first sprouting, number of leaves per plant and chlorophyll content of manila tamarind under controlled conditions. The softwood grafting performed on nine month old rootstocks during September recorded the highest survival percentage and it was significantly different from all other treatments. The same treatment i.e., nine months old rootstock grafted in September was also recorded the less number of days taken to first sprouting with highest number of leaves per plant and chlorophyll content.

Economics of Mango Production, Marketing System and Constraints Faced by Growers in Lucknow District of Uttar Pradesh

Background: Mango is an important commercially grown fruit crop and it is very popular due to its wide range of adaptability and high nutritive value. The present study was conducted in Lucknow district of Uttar Pradesh to know the economics of mango production, marketing system and constraints faced by growers in production and marketing.Methods: The study was based on primary data collected from 200 respondents with the help of personal interview using a pre-tested questionnaire, semi-structured interview schedule and open discussion method. Estimate the cost and return of mango cultivation by using simple cost and return equation. The marketing system of mango involved market channels, margin, cost, price spread, producer share in consumer’s rupee and marketing efficiency was worked out by tabular analysis. The Garrett’s ranking technique was adopted to rank the constraints faced by the growers in production and marketing of mango.Result: The total cost of mango cultivation was found Rs.23450.67/ha. Out of which, the variable cost was constituted Rs.18316.39/ha (78.11%) and fixed cost was Rs.5134.28/ha (21.89%). The net return over the cost of cultivation was found to be highest as Rs. 62811.59/ha at the 4th growing stage of orchard. It was observed that net price received by growers, per cent share in consumer’s rupees and market efficiency was highest in channel-III followed by channel-II and III, where the numbers of marketing intermediaries were involved lesser. The market margin, cost and price spread were highest in channel-I followed by Channel-II and III. The channel-III was found to be most efficient and profitable for farmers in the study area. Among the production and marketing constraints faced by mango growers, the shattering of flowers and premature fruit drop were cited as the most serious constraints. While alternate and irregular bearing creates glut with excess production in one year and results in low production in the next year was reported as second major constraint. Usually, contractors were not paying money to the orchard owner in the lump sum amount and at the appropriate time. Thus, the second major constraint was delayed and irregular payments to producers.

Hormones and carbohydrates are both involved in the negative effects of reproduction on vegetative bud outgrowth in the mango tree: consequences for irregular bearing.

The negative effects of fruit production during one cycle on reproduction during the following cycle are generally explained by two complementary processes: hormone synthesis and carbohydrate mobilization. Our study focused on mango (Mangifera indica L.) for which it has been shown that reproduction decreases and delays vegetative bud outgrowth. This, in turn, affects flowering and fruiting in the following cycle. Vegetative growth therefore plays a pivotal role in irregular fruit production patterns across consecutive years. Our aim was to decipher the respective roles of hormones and carbohydrates on the negative effects of reproduction on vegetative growth. We analyzed the changes in various hormone (auxin, cytokinin, abscisic acid) and carbohydrate (glucose, sucrose, starch) concentrations in terminal axes with vegetative and reproductive fates of two mango cultivars, Cogshall and José, characterized by different bearing patterns, across consecutive phenological periods during a growing cycle. Auxin concentrations were high in inflorescences, fruit peduncles and axes bearing inflorescences or fruit, suggesting auxin-induced inhibition of vegetative bud outgrowth in the flowering and fruiting axes. Moreover, growing fruits, which are strong sink organs, depleted carbohydrates from non-fruiting axes. During vegetative growth, this starch depletion probably contributed to decreasing the probability of and to delaying vegetative bud outgrowth of reproductive axes for Cogshall, and of reproductive and nonreproductive axes for José. Starch dynamics in quiescent and flowering growth units during early fruit growth and their starch concentrations at fruit maturity differed between the two cultivars, presumably in relation to the observed contrasted crop loads and/or to differences in photosynthetic capacity or carbohydrate allocation. These differences between the two cultivars in terms of starch concentration in terminal axes during vegetative growth could partly explain their different bearing patterns.

A Complex Gene Network Mediated by Ethylene Signal Transduction TFs Defines the Flower Induction and Differentiation in Olea europaea L.

The olive tree (Olea europaea L.) is a typical Mediterranean crop, important for olive and oil production. The high tendency to bear fruits in an uneven manner, defined as irregular or alternate bearing, results in a significant economic impact for the high losses in olives and oil production. Buds from heavy loaded (‘ON’) and unloaded (‘OFF’) branches of a unique olive tree were collected in July and the next March to compare the transcriptomic profiles and get deep insight into the molecular mechanisms regulating floral induction and differentiation. A wide set of DEGs related to ethylene TFs and to hormonal, sugar, and phenylpropanoid pathways was identified in buds collected from ‘OFF’ branches. These genes could directly and indirectly modulate different pathways, suggesting their key role during the lateral bud transition to flowering stage. Interestingly, several genes related to the flowering process appeared as over-expressed in buds from March ‘OFF’ branches and they could address the buds towards flower differentiation. By this approach, interesting candidate genes related to the switch from vegetative to reproductive stages were detected and analyzed. The functional analysis of these genes will provide tools for developing breeding programs to obtain olive trees characterized by more constant productivity over the years.

Differential expression of genes in olive leaves and buds of ON- versus OFF-crop trees

Alternate bearing (AB) refers to the tendency of trees to have an irregular crop load from 1 year (ON) to the next year (OFF). Despite its economic importance, it is not fully understood how gene networks and their related metabolic pathways may influence the irregular bearing in olive trees. To unravel molecular mechanisms of this phenomenon in olive (cv. Conservalia), the whole transcriptome of leaves and buds from ON and OFF-trees was sequenced using Illumina next generation sequencing approach. The results indicated that expressed transcripts were involved in metabolism of carbohydrates, polyamins, phytohormones and polyphenol oxidase (POD) related to antioxidant system. Expression of POD was increased in leaf samples of ON- versus OFF-trees. The expression pattern of the greater number of genes was changed more in buds than in leaves. Up-regulation of gene homologues to the majority of enzymes that were involved in photorespiration metabolism pathway in buds of ON-trees was remarkable that may support the hypotheses of an increase in photorespiratory metabolism in these samples. The results indicated changes in expression pattern of homologous to those taking part of abscisic acid and cytokinin synthesis which are connected to photorespiration. Our data did not confirm expression of homologue (s) to those of chlorogenic acid metabolism, which has been addressed earlier that have a probable role in biennial bearing in olive. Current findings provide new candidate genes for further functional analysis, gene cloning and exploring of molecular basses of AB in olive.

Effect of CSL on the characteristics of six-pocket hybrid irregular journal bearing

This article examines the effect of couple stress lubricant on the characteristics of six-pocket hybrid irregular journal bearing system. Various shapes of irregular journals viz. barrel, bell-mouth, and undulated journal are considered in the analysis. To model the behavior of the flow of couple stress lubricant in bearing clearance space, the modified form of Reynolds equation is derived by using Stokes theory. The unknown pressure field in Reynolds equation is determined by using Galerkin's method. To illustrate the effect of couple stress lubricant on bearing system, the results for characteristics parameters of journal bearing system are presented. The results noticeably reveal that the presence of different geometrical irregularities in journal may ominously influence the performance of bearing system. Further, the use of couple stress lubricant instead of Newtonian lubricant offers a significant improvement in the value of bearing characteristic parameters of geometrically irregular hybrid journal bearing system viz. [Formula: see text], [Formula: see text] and [Formula: see text].

Relationships between yield and pollen concentrations in Chilean hazelnut orchards

Abstract Chilean hazelnut (Corylus avellana L.) industry has been recently experiencing a solid development and nut production is consistently increasing. Corylus avellana is subjected to strong inter-annual yield fluctuations, which raise the issue of price predictability. In alternate bearing, a high fruit load hinders flower initiation thus leading to a smaller fruits production in the following year. This suggests the use of pollen airborne concentration as a proxy for flowers number to predict hazelnut irregular bearing. We addressed this question using high-resolution yield and pollen data collected on four hazelnut plantations located in Central Chile, and three hazelnut cultivars. Pollen parameters were calculated from modelled and non-modelled pollen seasons, after selecting the best modelling approach. An alternate bearing index was calculated to characterize hazelnut biennial bearing and to select plots with high yield variability. The calculated pollen parameters were then correlated with yield data. Significant correlations were found between pollen parameters and nut yields, with stronger relationship when alternate bearing was higher. The modelled peak of the pollen season presented the highest variability (average CV = 81 %) and its positive correlation with crop production (ρ = 0.45) was consistent across sites and cultivars. Our results support the integration of airborne pollen data in hazelnut yield prediction systems, as predictors of alternate bearing and to forecast annual yield.

Nitrogen and carbon management in Australian mango orchards to improve productivity and reduce greenhouse gas emissions

Australian mango orchards, particularly of the 'Kensington Pride' cultivar, are often characterized by low yields and irregular bearing. Improved nutrition management techniques which increase total soil carbon sequestration and reduce nitrogen losses (nitrous oxide) may improve productivity and also reduce greenhouse gas emissions. A factorial trial was established in a 'Kensington Pride' mango orchard at Mareeba, Australia to assess the benefits of applying organic hay mulch to tree rows in combination with three nitrogen fertiliser treatments including two controlled-release fertiliser products. Three years after the initiation of treatments it was found that mango tree growth and fruit productivity was significantly improved when mulching was used to increase soil organic matter. Mulched soils had improved soil water holding capacity, less temperature variability, increased root biomass in the top soil, greater canopy leaf area and higher plant tissue potassium levels. Average fruit weights were increased by 10% and mango fruit yields per tree increased by 11%. Fruit quality was not affected when standard fungicide management treatments were used, although disease levels were higher with no post-harvest fungicide treatment. The nitrogen fertiliser products investigated did not have a significant influence on mango growth or final productivity. Trial results suggest that the adoption of mulching practices in mango orchards is a management practice which can increase orchard productivity and the sequestration of soil organic carbon, without detrimental effects on fruit quality.

Linking vegetative growth, reproduction and irregular bearing in the mango tree

Irregular bearing is a major agronomic issue with economic consequences for many temperate and tropical fruit species. In particular, the mango tree, characterized by terminal flowering, is prone to irregular bearing, with a clear cultivar effect. Mango trees within a monoclonal orchard exhibit contrasting patterns of bearing, suggesting that, for a given cultivar, irregularity is triggered and/or maintained by endogenous architectural and physiological factors and not only by environmental factors. In several species, architectural traits of shoots can affect flowering. In this paper we summarize and discuss the results obtained in different studies on the reciprocal interactions between vegetative development and flowering and fruiting at different scales in the mango tree, namely the terminal growth unit, the scaffold branch and the whole tree. The topology, morphology and phenology of the mango terminal growth units affect their probability of flowering and fruiting, indicating that structural and temporal vegetative traits are clearly involved in reproduction. Conversely, the reproductive fate of a terminal growth unit affects the occurrence, intensity and phenology of its subsequent vegetative growth, which represents the potential flowering points for the following cycle. These results show that, at the mango growth unit scale, irregular bearing results from the effects of the flowering and fruiting behavior during a cycle on the reproductive behavior during the following cycle, these effects being partly mediated by vegetative growth occurring between the two reproductive events. We discuss the three following points: what are the physiological mechanisms underlying these relationships at the growth unit scale? what happens at larger scales, i.e., at the scaffold branch and the whole tree scales? and what could be the effects of climate change and cultivation practices on these relationships?

The costs of reproduction in plants: a novel approach to study irregular bearing of fruit crops

Irregular bearing is a major issue limiting productivity of temperate and tropical fruit crops. It is generally studied through the effects of fruit production in one year on flowering and fruit production in the following year, involving classical nutritional and/or hormonal hypotheses. As shown in various species, especially in the apple, there are strong reciprocal relationships between vegetative and reproductive growth, not only in a same year but also from one year to the other. These relationships are then a key point to understand irregular bearing. The effects of flowering and fruiting on the subsequent vegetative growth were investigated during two growing cycles on two irregular mango cultivars. Vegetative growth was quantified by the biomass and leaf area of new axes, assessed by allometric relationships. Negative relationships between fruit production and the subsequent vegetative growth were evidenced at the tree, scaffold branch and growth unit levels, with differences between the two cultivars. On the basis of these results, a novel approach is presented to study in a more comprehensive way the mechanisms involved in irregular bearing. It relies on the conceptual framework of the costs of reproduction in plants, originally developed in evolutionary ecology. The hypothesis is that compromises are necessary to allocate plant resources among three vital functions, namely growth, reproduction and defence, in order to maximize the reproductive success during the whole life span, and not during only one production cycle. We discuss the interest of this concept to study irregular bearing. (Resume d'auteur)

Deciphering the Costs of Reproduction in Mango - Vegetative Growth Matters.

Irregular fruit production across successive years is a major issue that limits the profitability of most temperate and tropical fruit crops. It is particularly affected by the reciprocal relationships between vegetative and reproductive growth. The concept of the costs of reproduction is defined in terms of losses in the potential future reproductive success caused by current investment in reproduction. This concept, developed in ecology and evolutionary biology, could provide a methodological framework to analyze irregular bearing in fruit crops, especially in relation to the spatial scale at which studies are done. The objective of this study was to investigate the direct effects of reproduction during a growing cycle on reproduction during the following growing cycle and the indirect effects through vegetative growth between these two reproductive events, for four mango cultivars and during two growing cycles. Two spatial scales were considered: the growth unit (GU) and the scaffold branch. Costs of reproduction were detected between two successive reproductive events and between reproduction and vegetative growth. These costs were scale-dependent, generally detected at the GU scale and infrequently at the scaffold branch scale, suggesting partial branch autonomy with respect to processes underlying the effects of reproduction on vegetative growth. In contrast, the relationships between vegetative growth and reproduction were positive at the GU scale and at the scaffold branch scale in most cases, suggesting branch autonomy for the processes, mainly local, underlying flowering and fruiting. The negative effect of reproduction on vegetative growth prevailed over the positive effect of vegetative growth on the subsequent reproduction. The costs of reproduction were also cultivar-dependent. Those revealed at the GU scale were related to the bearing behavior of each cultivar. Our results put forward the crucial role of vegetative growth occurring between two reproductive events. They are discussed in the context of irregular bearing considering both the spatial scale and the various bearing habits of the mango cultivars, in order to formulate new hypotheses about this issue.

Fruit yield of common orange varieties in south-east Australia: Initial evaluation versus long term performance

Fruit yield of 12 common orange varieties on either ‘sweet orange’ rootstock or ‘Carrizo citrange’ rootstock growing on light textured soil in south-east Australia were measured from 2000 to 2012. The varieties covered the range from early maturing (April) through to late hanging (March), and the trial was conducted to identify suitable varieties to ensure continuity of common orange supply to service the Australian fresh orange juice market. Based on the initial four seasons’ yield data, ‘Hamlin’ would have been selected for the June–August period, and ‘Salustiana’, which cropped relatively poorly in the initial four years, would have been rejected. Subsequent yields of fruit by ‘Salustiana’ trees meant that its overall cropping levels were similar to ‘Hamlin’, calling into question the adequacy of recommending a variety based on only an initial four years of observation. Although all varieties demonstrated some degree of irregular cropping, only three varieties could confidently be called biennial bearers. The tendency to irregular bearing (biennial or otherwise) was unrelated to a selection's seasonality, suggesting an inadequacy in our current understanding of the importance of the presence of fruit in determining the size of the return crop.

New insights for estimating the genetic value of segregating apple progenies for irregular bearing during the first years of tree production

Because irregular bearing generates major agronomic issues in fruit-tree species, particularly in apple, the selection of regular cultivars is desirable. Here, we aimed to define methods and descriptors allowing a diagnostic for bearing behaviour during the first years of tree maturity, when tree production is increasing. Flowering occurrences were collected at whole-tree and (annual) shoot scales on a segregating apple population. At both scales, the number of inflorescences over the years was modelled. Two descriptors were derived from model residuals: a new biennial bearing index, based on deviation around yield trend over years and an autoregressive coefficient, which represents dependency between consecutive yields. At the shoot scale, entropy was also considered to represent the within-tree flowering synchronicity. Clusters of genotypes with similar bearing behaviours were built. Both descriptors at the whole-tree and shoot scales were consistent for most genotypes and were used to discriminate regular from biennial and irregular genotypes. Quantitative trait loci were detected for the new biennial bearing index at both scales. Combining descriptors at a local scale with entropy showed that regular bearing at the tree scale may result from different strategies of synchronization in flowering at the local scale. The proposed methods and indices open an avenue to quantify bearing behaviour during the first years of tree maturity and to capture genetic variations. Their extension to other progenies and species, possible variants of descriptors, and their use in breeding programmes considering a limited number of years or fruit yields are discussed.

QTL mapping of flowering and fruiting traits in olive.

One of the challenge fruit growers are facing is to balance between tree production and vegetative growth from year to year. To investigate the existence of genetic determinism for reproductive behaviour in olive tree, we studied an olive segregating population derived from a cross between ‘Olivière’ and ‘Arbequina’ cultivars. Our strategy was based on (i) an annual assessment of individual trees yield, and (ii) a decomposition of adult growth units at the crown periphery into quantitative variables related to both flowering and fruiting process in relation to their growth and branching. Genetic models, including the year, genotype effects and their interactions, were built with variance function and correlation structure of residuals when necessary. Among the progeny, trees were either ‘ON’ or ‘OFF’ for a given year and patterns of regular vs. irregular bearing were revealed. Genotype effect was significant on yield but not for flowering traits at growth unit (GU) scale, whereas the interaction between genotype and year was significant for both traits. A strong genetic effect was found for all fruiting traits without interaction with the year. Based on the new constructed genetic map, QTLs with small effects were detected, revealing multigenic control of the studied traits. Many were associated to alleles from ‘Arbequina’. Genetic correlations were found between Yield and Fruit set at GU scale suggesting a common genetic control, even though QTL co-localisations were in spe`cific years only. Most QTL were associated to flowering traits in specific years, even though reproductive traits at GU scale did not capture the bearing status of the trees in a given year. Results were also interpreted with respect to ontogenetic changes of growth and branching, and an alternative sampling strategy was proposed for capturing tree fruiting behaviour. Regular bearing progenies were identified and could constitute innovative material for selection programs.

Paclobutrazol Soil Drenching Suppresses Vegetative Growth, Reduces Malformation, and Increases Production in Mango

Emergence of unproductive vegetative shoots/flushes is considered to be a main cause of low yield, irregular bearing, and malformation of inflorescences in mango. Selected mango trees of the cultivars ‘Chaunsa’, ‘Dushehare’, and ‘Anwar Ratool’ growing in the subtropical region of Khanewal (30°18′0N, 71°56′0E), a district of Pakistan, were characterized as having excessive vegetative growth, erratic flowering, and fruiting with declining productivity due to malformation of inflorescences. Paclobutrazol soil drenching was evaluated as a method to suppress excessive vegetative growth and to increase the number of reproductive shoots even during the ‘off’ season. Different rates of paclobutrazol was applied at rates of (0, 2, 4, 6, 8, 10, and 12 g a.i.) in September through soil drenching. Results showed that soil drenching with paclobutrazol at the highest rates (12, 10, and 8 g a.i.) was significantly effective in suppressing vegetative growth, reducing the increase in canopy volume, and flush length as compared to control trees in all treated cultivars of mango. Statistically significant differences were recorded in treated trees as compared to control regarding the emergence of reproductive shoots, fruit setting, panicle length, fruit drop, intensity of emergence of malformed panicles, and yield. Response of selected cultivars of mango to paclobutrazol was statistically different regarding various vegetative and reproductive growth characteristics. Paclobutrazol was more useful in ‘Seasonal Chaunsa’ as compared to ‘Dushehare’ and ‘Anwar Ratool’ for improving various vegetative and reproductive parameters studied in this research.

EFFECTS OF GIRDLING AND DEFOLIATION ON HORMONAL CHANGES DURING FLOWER INDUCTION IN LONGAN (DIMOCARPUS LONGAN LOUR.)

The discovery of potassium chlorate (KClO 3 ) as flower inducing agent in longan (Dimocarpus longan Lour.) has overcome the problem of irregular bearing and enables farmers to produce this fruit crop in off-season. However, the underlying physiological mechanism of how this chemical triggers flower induction (FI) remains unclear. A possible explanation might be the timely hormonal changes in longan leaves during the transitional growth stage from vegetative to floral buds following KClO 3 application. The experiment consisted of a control treatment and four treatments with KClO 3 application; (1) no shoot girdling and no defoliation, (2) shoot girdling and removal of all leaves and petioles above the girdle, (3) shoot girdling without defoliation above the girdle and (4) apical defoliation without girdling. All shoot treatments were applied to each of twenty mature trees. KClO 3 was applied as soil drench at mature leaf stage in September 2007. The girdle was 2 mm wide and applied at about 10 cm below the shoot tip. Leaf samples for analysis of diffusible and extractable plant hormones were collected 8 times at 1- to 3-day intervals until 28 days after treatment (DAT). The concentration of endogenous hormones such as indole-3-acetic acid (IAA), gibberellins (GA 1, 3,20 measured as GA 3 equivalents), and the cytokinins isopentenyladenin/isopentenyladenosin (iP/ [9R] iP) and trans-zeatin/t-zeatin riboside (Z/ [9R] Z) were determined in leaves. The results show that IAA concentrations in leaves of all treatments were slightly reduced between 4 to 13 days following KClO 3 application but values remained rather constant thereafter. In general, leaves above the girdle had significantly higher concentrations of iP/[9R]iP but less Z/[9R]Z whereas the export of diffusible iP/[9R]iP from upper leaves of non-girdled shoots increased from 10 to 13 days after application.

A Comparison of Return Bloom and Nonstructural Carbohydrates, Nitrogen, and Potassium Concentrations in Moderate and Severe Alternate-bearing Pecan Cultivars

The most significant horticultural problem facing pecan producers is alternate bearing. Four pecan [Carya illinoinensis (Wangenh.) C. Koch] cultivars were chosen, two with low to moderate and two with severe alternate-bearing tendencies, to compare selected characteristics related to irregular bearing. The cultivars were Colby and Peruque (low to medium alternate-bearing tendency) and Osage and Giles (high alternate-bearing tendency). Vegetative shoots and fruit-bearing shoots in the terminal and lateral position on 1-year-old branches were tagged in October, and flowering was determined the next spring. Shoot and root samples were collected while dormant and then analyzed for organically bound nitrogen (N), potassium (K), and nonstructural carbohydrate concentrations. As expected, ‘Colby’ and ‘Peruque’ had a lower alternate-bearing tendency than ‘Giles’ and ‘Osage’. Cultivars with a low alternate-bearing tendency had a larger return bloom on the bearing shoots in the terminal position than the other shoot types. Cultivars with a high alternate-bearing tendency had a lower return bloom on bearing terminal shoots than vegetative shoots. Bearing shoots in the lateral position usually had a lower return bloom than the other shoot types regardless of cultivar. Neither root nor shoot N, K, or nonstructural carbohydrate concentrations appeared to be closely related to the alternate-bearing characteristics of the four cultivars. The unique characteristic identified for low alternate-bearing cultivars was their ability to produce as many or more flowers and flowering shoots the next year on previously bearing terminal shoots compared with previously vegetative shoots. In high alternate-bearing cultivars, return bloom of bearing terminal shoots was suppressed relative to their vegetative shoots.

(328) Effect of Supplemental Nitrogen Applicationat Selected Times on Pecan

Supplemental nitrogen applications were tested to reduce irregular bearing and improve yield on drip-irrigated pecan (Caryaillinoinensis Wangenh. C. Koch. cv. Mohawk) trees planted in 1989. Treatments were: 1) no N fertilization; 2) 75 kg·ha-1 N in March; 3) 75 kg·ha-1 N in March plus 50 kg·ha-1 N in August; and 4) 75 kg·ha-1 N in March plus 50 kg·ha-1 N in October. Withholding N did not reduce July leaf N concentration compared to the other treatments until the sixth year of the study. Trees receiving N had similar July leaf N concentrations regardless of treatment throughout the study. October leaf N concentrations were unaffected by treatment, except in 2002, when withholding N suppressed leaf N compared to other treatments. The percentage of fruiting shoots was lower when supplemental N was applied in October compared to August during 2 of 6 years. Otherwise, the percentage of fruiting shoots was unaffected by treatment. Weight per nut and kernel percentage were not affected by treatment, except kernel percentage was lower during 1 year when supplemental N was applied in August compared to October. Kernel grade was usually not affected by treatment.

Potassium nitrate and urea sprays affect flowering and yields of ‘Tommy Atkins’ (Mangifera indica) mango in Ethiopia

The effects of leaf applications of potassium nitrate (KNO3), alone and in combination with urea at different concentrations on flowering, fruit set and fruit quality of Tommy Atkins' mango grown in the rift valley of Ethiopia were evaluated. The trees were characterised by erratic flowering, continuous and high intensity of vegetative growth as well as irregular bearing. Uniform trees were selected for a randomised complete block design experiment with three replications and three trees per plot. Spraying was conducted initially on the immature postharvest flushes and then repeated after the flushes had matured and had dark green leaves. Potassium nitrate concentrations especially in combination with urea (5 litre solution of 4% KNO3+0.5 g urea tree−1 and 5 litres of 4% KNO3+I g urea tree−1) produced better results for most of the flowering and yield parameters. There was a non-significant difference for the qualitative parameters between the treated and non-treated trees. The supplementation of nitrogen through the spraying of KNO3 and urea is believed to be the reason for the observed greater flowering and yield results of the sprayed relative to the unsprayed trees.

Response of Pecan to Nitrogen Rate and Nitrogen Application Time

Nitrogen was applied between 1996 and 2002 to grafted `Mohawk' pecan (Carya illinoinensis Wangenh. C. Koch.) trees at 75 or 150 kg·ha-1 either as a single application in March or as a split application with 60% applied in March and 40% the first week of June. In 1997 and 2001, a spring freeze damaged developing shoots and buds, resulting in a small, noncommercial crop and the June portion of the N application was withheld. Nitrogen was also applied during the first week in October at 0 or 50 kg·ha-1 N if the crop load before fruit thinning in August was ≥40% fruiting shoots. There were few differences in the percentage of fruiting shoots or cluster size associated with N rate or applying N as a single or split application. Leaf N concentrations were either not affected by treatment or the results were inconsistent. Omitting the June application when a crop failure occurred did not affect the percentage of fruiting shoots the following year. October N application either did not affect or reduced the percentage of fruiting shoots the following year, and had no influence on leaf N concentration in July or October. These results indicate that the only advantage of a split N application is the option of withholding the second portion in the event of a crop failure. However, the added expense associated with splitting the N application versus the risk of crop failure must be assessed for each situation to determine if this is a sound economic practice. These data do not support an October N application when the crop is ≥40% fruiting shoots to reduce irregular bearing.