Crop Load Treatments Research Articles

Zonal Chemical Signal Pathways Mediating Floral Induction in Apple.

Phytohormones that trigger or repress flower meristem development in apple buds are thought to be locally emitted from adjacent plant tissues, including leaves and fruitlets. The presence of fruitlets is known to inhibit adjacent buds from forming flowers and thus fruits. The resulting absence of fruitlets the following season restores flower-promoting signalling to the new buds. The cycle can lead to a biennial bearing behaviour of alternating crop loads in a branch or tree. The hormonal stimuli that elicit flowering is typically referred to as the floral induction (FI) phase in bud meristem development. To determine the metabolic pathways activated in FI, young trees of the cultivar 'Ruby Matilda' were subjected to zonal crop load treatments imposed to two leaders of bi-axis trees in the 2020/2021 season. Buds were collected over the expected FI phase, which is within 60 DAFB. Metabolomics profiling was undertaken to determine the differentially expressed pathways and key signalling molecules associated with FI in the leader and at tree level. Pronounced metabolic differences were observed in trees and leaders with high return bloom with significant increases in compounds belonging to the cytokinin, abscisic acid (ABA), phenylpropanoid and flavanol chemical classes. The presence of cytokinins, namely adenosine, inosine and related derivatives, as well as ABA phytohormones, provides further insight into the chemical intervention opportunities for future crop load management strategies via plant growth regulators.

The Effects of Different Crop Loads on Yield, Quality, and Sugar Fractions in Early Sweet (Vitis vinifera L) Table Grape

The quality of the grapes taken from the vines varies depending on many factors. Grape quality is one of the critical determining factors in the crop load left on the vine. The aim of this study was to investigate the effects of three different crop load levels (36 (T1), 75 (T2), and 105 (T3) bud vine-1) on yield, quality, and sugar fractions of Early Sweet (Vitis vinifera L.) table grape variety grown in Alaşehir district of Manisa/Türkiye. As two years average, the heaviest clusters, berry weight, and soluble solid content (733.0g, 4.41g, 18.05%) were determined in T1 crop load level while the lowest weight clusters and berry weight (580.7g, 388g, 17.42%) were obtained from T3 crop load level. The opposite of these findings was observed in titratable acidity values. In the research; the highest amount of table grapes per vine was obtained at T2 treatment in both years. The mean total glucose values for both years varied between 45.70% (T1), 45% (T2), and 37.90% (T3), respectively. Fructose content ranged between 41.50% (T1) and 41% (T3), and sorbitol content was 2.17% (T1), 2.05% (T2), and 2.17% (T3). Galactose content was negligible in all crop load treatments and ranged between 0.54% and 0.56%. The result is also T2 treatment (75 bud vine-1) can be recommended to ‘Early Sweet’ grape growers as the most effective treatment that provides the highest amount of marketable grapes in terms of yield-quality balance.

Fruitlet Thinning Improves Juice Quality in Seven High-tannin Cider Cultivars

Over 3 years (2016–18), tree productivity, biennial bearing, return bloom, and fruit quality were evaluated for seven high-tannin cider apple (Malus ×domestica Borkh.) cultivars. Five treatments were evaluated on each of the seven cultivars: hand-thinned of all fruit (a zero crop load treatment); hand-thinned to crop densities of three, six, or nine fruit/cm2 trunk cross-sectional area (TCSA); or left unthinned. In this paper, we report on the fruit maturity and juice quality properties that were analyzed for the three nonzero crop load treatments and the unthinned control. The effects of crop load on fruit maturity, as measured by starch pattern index and preharvest drop, were cultivar dependent. Crop density (fruit/cm2 TCSA) had a significant effect on all fruit maturity and juice quality variables, although effects were weakest in the “off” year (2017) for the whole planting when initial fruit set was low. As crop density increased, total poly phenols, titratable acidity, soluble solids, and primary amino nitrogen decreased in the juice of all seven cultivars. A partial budget analysis indicated that the reduced costs of nitrogen supplements due to increased primary amino nitrogen concentration alone would not justify cost of chemical or hand-thinning. By extrapolating the spring flowering density in the fourth year to potential fruit yields at harvest, we found that reducing crop load was projected to increase cumulative total polyphenol yields per tree over the long term. For the cultivars in this experiment, a target crop density of nine fruit/cm2 was found to adequately decrease biennial bearing while also not diminishing juice quality for hard cider production. High-tannin cider apple growers should consider juice quality, particularly tannin production, when making crop load management decisions.

Relationship between crop load and fruit quality in low-chill peaches and nectarines

ABSTRACT Fruits from low-chill peach and nectarine cultivars have lower quality in comparison with traditional varieties. One of the factors that most affect both fruit quality and fruit yield is the crop load (CL). The objective of the present work was to evaluate the relationship between CL and the external and internal fruit quality of low-chill peaches in a temperate-subtropical transition zone of the central-east region of Santa Fe province (Argentina). Fruit diameter (mm), total soluble solids (°Brix), titratable acidity (%), juiciness (%), skin red over-colour (%) and the Commission Internationale de l'Elcairage (CIE) colour parameters, and fruit yield efficiency (kg cm−2 trunk cross-sectional area; TCSA) were evaluated in nine low-chill peach cultivars under three CL treatments: 1.0 (low), 1.5 (medium) and 2.0 (high) fruit cm−2 TCSA. Increasing from low to medium CL did not affect the internal or external fruit quality attributes of any of the nine low-chill cultivars studied but increased fruit yield from 20% to 44% according to the genotype. In some cultivars, such as ‘Don Agustín’ and ‘Lara’, it was possible to increase the CL to 2 fruit cm−2 TCSA without affecting fruit quality.

Crop Load and Thinning Methods Impact Yield, Nutrient Content, Fruit Quality, and Physiological Disorders in ‘Scilate’ Apples

Most apple cultivars produce too many flowers to enable consistent yields of high-quality fruit, thus, crop load management (thinning) is an integral part of orchard management in modern apple cultivation. Crop load is managed by thinning excess flowers and/or fruit from a tree, however ideal targets vary between cultivars. In this two-year study, the effect of thinning methods at different levels of crop load on fruit quality and production, post-harvest storability and physiological disorders, and fruit and leaf nutrient content in ‘Scilate’ apples were investigated in southern Tasmania, Australia. Two thinning methods, artificial bud extinction (ABE) and hand thinning (HT), were compared at three levels of crop load: 3, 6, or 12 fruit cm−2 limb cross-sectional area (LCSA), described as low, medium, and high, respectively. During the second season, all the ABE and HT treatments received additional chemical thinning (CT). The results demonstrated that ABE consistently outperformed HT in terms of improved fruit set, return bloom, and fruit weight. The fruit quality parameters, such as flesh firmness, total soluble solids, dry matter content, malic acid content, and fruit shape, were also improved under the ABE regime, with these positive effects being the clearest in the second season. In general, high-quality fruits were obtained from the low and medium crop loads, while the fruit quality was poor for the high crop load trees, but the low crop load fruit had a slightly higher incidence of internal flesh browning (predominantly radial) and fruit softening after regular atmosphere storage. The crop load also impacted on the fruit and leaf mineral nutrient content, where fruit N, Ca, Mn, and Zn, and leaf N, Fe, Zn, and Cu content increased while fruit and leaf K declined with a higher crop load. High crop load, irrespective of the thinning regime, and HT with a medium crop load, induced severe biennial bearing, whereas, the fruit yield was relatively consistent with ABE, even with a medium crop load. We conclude that ABE with a medium crop load (around six fruit cm−2 LCSA) is an effective method of managing crop load and optimizing the fruit quality in ‘Scilate’ apples.

Metabolic Pathways for Observed Impacts of Crop Load on Floral Induction in Apple.

The triggers of biennial bearing are thought to coincide with embryonic development in apple and occurs within the first 70 days after full bloom (DAFB). Strong evidence suggests hormonal signals are perceived by vegetative apple spur buds to induce flowering. The hormonal response is typically referred to as the floral induction (FI) phase in bud meristem development. To determine the metabolic pathways activated in FI, young trees of the biennial bearing cultivar ‘Nicoter’ and the less susceptible cultivar ‘Rosy Glow’ were forced into an alternate cropping cycle over five years and an inverse relationship of crop load and return bloom was established. Buds were collected over a four-week duration within 70 DAFB from trees that had maintained a four-year biennial bearing cycle. Metabolomics profiling was undertaken to determine the differentially expressed pathways and key signalling molecules associated with biennial bearing. Marked metabolic differences were observed in trees with high and low crop load treatments. Significant effects were detected in members of the phenylpropanoid pathway comprising hydroxycinnamates, salicylates, salicylic acid biosynthetic pathway intermediates and flavanols. This study identifies plant hormones associated with FI in apples using functional metabolomics analysis.

Effect of crop load on fruit nutritional and nutraceutical traits of greenhouse tomato

ABSTRACT This study aimed to evaluate the effect of crop load on the fruit quality traits especially nutritional and nutraceutical properties of two cultivars of greenhouse tomato (Solanum lycopersicum L.) i.e. ‘Grandella’ and ‘Isabella’. The crop load treatments were: saving one fruit per truss (1F), two fruits per truss (2F), three fruits per truss (3F), and no fruit thinning (control). The results showed that decreasing crop load increased the dry matter content, glucose, fructose, and sucrose concentrations of fruits because of less competition between fruits of each truss and higher relative expression level of tomato hexose transporter genes (LeHTs). Higher transport of sugars toward fruits of 1F resulted in high secondary metabolites concentration. The high secondary metabolites concentration with high fruit load in control that has low soluble sugar availability may result from the opportunity to take advantage of the excess pool of carbon to build cost-free carbon-based secondary metabolites. A reduced crop load would be a recommended management strategy to improve greenhouse tomato quality.

Occurrence of physiological browning disorders in stored ‘Braeburn’ apples as influenced by orchard and weather conditions

Physiological storage disorders continue to cause sizable economic losses in a range of commercially important pomefruit cultivars. Given similar storage regimes, the incidence and severity of browning disorders in the apple cultivar ‘Braeburn’ can vary in different years in a way that can be explained by the interaction of preharvest seasonal and orchard factors. Over a three-year period (2016–2019) at the Kompetenzzentrum Obstbau Bodensee (KOB) in Southwest Germany a range of orchard and storage treatments were conducted for: air temperature during cell division for three weeks post petalfall or during four weeks preharvest, and crop load. Following controlled atmosphere (CA) storage, the disorder incidence for internal browning and cavity formation varied markedly over the three different growing seasons. Crop load treatments strongly influenced the expression of browning disorders in all years. Differences in air temperatures (△ +/- 2 °C compared to ambient) during the cell division period showed little effect on browning incidence. Warm night temperatures (>10 °C) prior to harvest can reduce internal browning in ‘Braeburn’ apples during CA storage and shelf-life.

Leaf Photosynthesis and Carbon Metabolism Adapt to Crop Load in ‘Gala’ Apple Trees

It is widely accepted that a tight coordination between carbon (C) utilization in the sink and C assimilation and metabolism in the source exists in higher plants. However, much of our current understanding is based on research from herbaceous plants, where the source and sink interaction is less sophisticated compared to woody perennials with a significant sink presence. Apple (Malus x domestica Borkh.) is a good representative of the latter category, and its production and transport of sorbitol, in addition to sucrose, adds complexity to C regulation. In this study, four-year-old “Gala”/”M.26” apple trees were subjected to crop load levels at 2.5, 7.5, and 15 fruits/cm2 trunk cross-sectional area. Low crop load trees exhibited reduced leaf C assimilation and extra accumulation of non-structural carbohydrates (NSC). This was primarily a result of reduced activity of Rubisco and increased activities of key enzymes that synthesize starch, sucrose, and sorbitol. Among the NSC, leaf starch was found to be most sensitive to crop load and could function as a leading indicator for source–sink balance in apple. However, even the high crop load trees still retained a significant amount of NSC in leaves at dawn, demonstrating that apple is fundamentally different from herbaceous plants in the way it balances leaf carbon inventories at dawn with carbon export at night for sink growth.

Auswirkungen von Substrat und Fruchtbehang auf Ertrag und Mineralstoff-Versorgung der Rebsorte ‘Early Sweet‘

The study was conducted to determine optimum substrate type and crop load in soilless grape culture. ’Early Sweet’ table grapes were used as the plant material. Grapevines were grown under plastic cover with nutrient solutions. Three different substrates (Cocopeat, mixture of Perlite and Peat (2:1, v:v) and Basaltic Pumice) and two different level of crop loads (10 and 15 clusters per grapevine) were experimented. To determine the effects of applications, in the first year, some shoot parameters and in the second year, grape yield, cluster, berry and must characteristics and leaf nutrients were examined. The highest grape yield (38 t ha−1) was obtained from Perlite:Peat medium and 15-cluster crop load treatment. Average cluster weights varied between 263.87 g (Cocopeat) and 346.18 g (Perlite:Peat). For all treatments, nitrogen, phosphorus, potassium, calcium, iron and zinc concentrations of the leaves sampled at veraison were lower but, magnesium concentrations were higher than the optimum limits reported the previous literature. So, sufficient yield and quality levels were achieved, Perlite:Peat medium and 15 clusters vine−1 crop load treatments were recommended for ’Early Sweet’ cultivar to cultivate in soilless culture under plastic house. However, because it was a locally available and cheap material, Basaltic Pumice with close yield levels to the other growth media was also recommended for soilless grape culture.

Fruit canopy position and crop load influence on watercore severity in ‘Fuji’ apples

Watercore (WC) is a physiological disorder related to carbohydrate metabolism in apple fruit. Late season WC typically develops as 'Fuji' fruit mature on the tree. WC affected fruit develop water-soaked tissue around the vascular bundles and/or fruit core when the intercellular spaces are filled with fluid. While mild symptoms dissipate in storage, severe WC can develop into internal browning with alcoholic off-flavours under controlled atmosphere storage conditions. Fruit position on the tree and crop load are factors associated with WC incidence. In 2015, at the KOB experimental orchard in southwest Germany, late-harvest 'Fuji' apples with a high incidence of WC (93%) were harvested in a single pick from three different positions within the tree canopy (top/middle/bottom) and from trees with two different crop loads (high = full crop but not over cropped or low = ~54% thinned at 67 d before harvest). At-harvest, the fruit weight, fruit density and severity of WC (scale 0 to 5; 0 = no WC to 5 = severe) were determined for all apples per tree. Fruit from low crop load trees showed higher WC compared to high crop load trees. Fruit from the top of high crop load treatment showed a trend to higher WC when compared with fruit from the bottom. Sorbitol was higher in fruit from the low crop load treatment. Comparing the leaf area per fruit with the WC severity suggests, WC development is regulated by other factors in addition to the assimilate supply.

Limitations to photosynthesis of leaves of apple (Malus domestica) trees across the growing season prior to and after harvest

Photosynthetic responses to CO2 were followed on leaves of Malus domestica cv. Cox's Orange trees growing in orchard conditions, before and after harvest. Rates of photosynthesis, at ambient and CO2 saturated concentrations, were stable across the growing season, except for minor decreases at harvest although rates recovered and remained high thereafter. Stomatal conductance increased over the growing season but declined transiently just before harvest and recovered for most of the season. Rates of ribulose-1,5-bisphosphate (RuBP) carboxylation declined before harvest, however, rates of RuBP regeneration mirrored assimilation. After harvest, rates of RuBP regeneration increased whereas rates of carboxylation increased but remained low, limiting photosynthesis. Lack of change in photosynthesis after harvest was at odds with the literature where photosynthesis of high crop load trees declined soon after, suggesting crop load was not as demanding on the Cox's Orange trees as in other studies.

Effects of the percentage of terminal flowering on postharvest fruit quality in mango (Mangifera indica) ‘Calypso’™

The objective of this study was to investigate the relationship between the percentage of flowering terminals, crop load and postharvest fruit quality in the mango cultivar 'Calypso'™ (B74) grown at Dimbulah in North Queensland. The percentage of flowering terminals was manipulated experimentally by removing flowers at anthesis to give eight treatments in which trees had 5, 10, 20, 30, 40, 60, 70 or 80% of their terminals with flowers. Fruit were sampled at harvest, ripened at 23°C and, at eating ripe, were assessed for fruit number and yields per tree and fruit quality parameters including: fruit size (length, width and depth), fruit weight, background skin colour, blush colour, flesh colour, total soluble solids (TSS), dry matter and internal physiological disorders (jelly-seed, soft nose). The 5% crop load treatment (removing 95% of inflorescences from terminals) significantly reduced the average fruit yield per tree. Average fruit weights were highest in trees with 5 and 10% of terminals flowering, followed by trees with 20% of terminals flowering. There was no difference in average fruit weight between trees with 30, 40, 60, 70 or 80% of terminals flowering. Average fruit length increased significantly in trees with 5, 10 and 20% of terminals flowering compared with those with larger numbers of flowering terminals, with the longest in the 5% treatment. Fruit length was similar in treatments with 30% or more terminals flowering. Similar trends were observed for fruit width, with the widest (89.35 mm) and deepest (80.53 mm) fruit found in the 5% treatment. Although the comparative results between treatments confirmed that the highest values of fruit TSS, dry matter and percentage of blush colour occurred in fruit from trees with only 5% of terminals flowering, observations did not differ significantly among treatments.

Root and aerial growth in early-maturing peach trees under two crop load treatments

The objectives of the paper were to study the pattern of root growth (measured by minirhizotrons) in relation to trunk, fruit and shoot growth and the effects of crop load on tree growth and yield in peach trees. Two crop load (commercial and low) treatments were applied in a mature early-maturing peach tree orchard growing in Mediterranean conditions. Root growth dynamics were measured using minirhizotrons during one growing season. Shoot, trunk and fruit growth were also measured. At harvest, all fruits were weighed, counted and sized. Roots grew throughout the year but at lower rates during the active fruit growth phase. Root growth was asynchronous with shoot growth, while root and trunk growth rates were highest after harvest, when the canopy was big enough to allocate the photo-assimilates to organs that would ensure the following season’s yield. Shoot and fruit growth was greater in the low crop load treatment and was accompanied by a non-significant increase in root growth. High level of fruit thinning decreased the current yield but the fruits were more marketable because of their greater size.

A 3D digitizing tool to determine fruit quality distribution within the canopy

The Slender Spindle, one of the most used training systems for apple, was compared with the Bi-axis, an innovative training system, to determine their effect on fruit quality and fruit distribution within the canopy on 'Gala' cultivar. Two levels of crop loads were also introduced to observe their effects through chemical and manual thinning. Fruit position in the canopy was monitored during summer using different software to draw in 3D the tree architecture. Also, fruits were monitored during the growing season for their growth and maturation. At the end of the season, fruits were harvested, graded and analyzed for their quality traits. Fruit position had a strong influence on fruit quality. The fruits in the layers were significantly different. In the upper part of the tree, fruits had a higher percentage of over color and bigger fruit size compared to the middle and the lower part of the canopy. No significant differences were found between the two training systems. Crop load influenced fruit quality in both training systems in the same way on fruit size and over color. The lowest crop load treatment had a higher percentage of over color and bigger fruit size compared to the higher crop load.

Effects of different leaf-fruit ratios on uptake and partitioning of N and K in 'Uenishiwase' persimmon trees

To supply appropriate amount of nutrients to persimmon trees with high crop load is critically important for the stable production year after year. This study was conducted to determine absorption and partitioning of nitrogen (N) and potassium (K) in 13-year-old ‘Uenishiwase' persimmon trees with different crop loads. The leaf-fruit (L/F) ratio was adjusted to 20 (high) and 10 (low) by fruit thinning on July 2 after the June drop. The trees were harvested in early spring and late autumn, and increases of dry weight (DW) and N and K in different tree parts during the growing season were calculated. As the L/F ratio decreased from 20 to 10, total fruit DW increased from 4.3 to 7.6kg per tree. Of the total DW increase in a season, fruit accounted for 14% in a high and 24% in a low L/F tree. DW in older than 1-year-old woods accounted for 44% in a high and 41% in a low L/F tree. Different L/F ratios did not significantly affect the increase of tree total DW. Upon decreasing the L/F ratio, the amount of fruit N increased by 1.7-fold where N partitioning to fruit increased from 10% to 17% of the tree total, whereas fruit K increased by 2-fold, increasing its partitioning from 25% to 44%. It was noted that N and K increases were lower in aerial woods of the low L/F trees. Total N per tree increased by about 170g in both the high and low L/F trees, but the total K increases were 175g and 202g in a high and low L/F tree, respectively. The results suggested that a fertilization program for high crop-load trees should take two points into consideration, namely, the magnitude of nutrients removed from the tree by fruit harvest and the reduced nutrients in woody organs essential for tree development the next season.

Crop Load Density Affects ‘York’ Apple Juice and Hard Cider Quality

To assess the impact crop load has on hard cider chemistry, ‘York’ apple (Malus ×domestica Borkh.) trees were hand thinned to three different crop loads: low [two apples per cm2 branch cross-sectional area (BCSA)], medium (four apples per BCSA), and high (six apples per BCSA). Higher crop loads produced smaller, less acidic fruit that were slightly more mature. In juice made from fruit from these treatments, the total polyphenol content did not differ at harvest, but, after fermentation, the medium crop load had 27% and the high crop load had 37% greater total polyphenol content than the low crop load. Yeast assimilable nitrogen (YAN) concentration in juice made from fruit from the low crop load treatment had 18% and 22% greater than the medium and high crop load, respectively. YAN concentrations in juice from the medium and high crop load treatments were similar. Our results provide apple growers and hard cider producers with a better understanding of how apple crop load impacts YAN concentrations in juice and total polyphenol concentrations in juice and cider.

Consequences of Deficit Irrigation and Crop Load Reduction on Plant Water Relations, Yield, and Quality of ‘Ambrosia’ Apple

Uncertain water supplies resulting from changing climatic conditions in western North America led to this investigation of the role of crop load reduction in maintaining performance of high-density ‘Ambrosia’ apple (Malus ×domestica) on M.9 rootstock. A split-plot experimental design was imposed for three growing seasons (2007–09) with six replicates of four main plot irrigation treatments and three crop load subplots comprised of three trees. Four season-long irrigation (Irr) treatments were applied through 2 × 4 L·h−1 drip emitters per tree and included Irr1) control [100% evapotranspiration (ET) replacement], Irr2) 50% ET replacement, Irr3) 50% ET replacement to half the emitters, and Irr4) an increasingly severe treatment commencing at 50% ET replacement (once every 2 days) in 2007 and progressing to 25% and 18% ET replacement, 2008–09. Three target crop loads were established annually, 4–5 weeks after bloom as low (2.5, 3, and 3.75), medium (4.5, 6, and 7.5), and high (9, 12, and 15) fruit/cm2 trunk cross-sectional area (TCSA) 2007–09, respectively, by hand thinning around 4 weeks after bloom. Volumetric soil moisture contents generally reflected the amount of water applied and ranged from 20% for control (Irr1) to <10% for Irr4. Both irrigation and crop load treatments affected midday stem water potential more than leaf photosynthesis and stomatal conductance (gS). By the 2nd and 3rd year stem potential values for irrigation treatments ranged from a maximum of −1.0 to −1.3 MPa for Irr1 to minimums ≤-2.0 MPa for Irr4. gS decreased as midday stem potential decreased, but at any given stem potential value was greater at high crop loads, presumably in response to an increased demand for photosynthates. Fruit size decreased as crop load increased, but as irrigation deficits became more severe, fruit size was more closely correlated with stem water potential than gS. Consequently, fruit size was controlled by two mechanisms, competition for photosynthates and the effects of plant water status on gS. Negative linear relationships between crop load and average fruit size were used to determine the crop load required to produce an average fruit size of 200 g at different irrigation deficits. It was not possible to achieve adequate fruit size when applications were very low, as at 18% to 25% ET in Irr4. Crop load reduction around mid-June had no negative consequences for fruit quality, enhancing fruit color, and soluble solids concentration (SSC) and did not affect the incidence of sunburn, internal breakdown or bitter pit at harvest.

Interaction of Crop Load and Irrigation on Yield, Fruit Size, Color and Stem-end Splitting Ratio of Apple c.v. ‘Gala, Galaxy’

In this study, the interaction between crop load and irrigation level on yield, fruit size, skin color and stem-end splitting fruit ratio in the apple cultivar ‘Gala, Galaxy’ grafted on rootstock M9 were investigated. Six irrigation programs were applied during the whole growth season: deficit irrigation (rates of 0.25 kc, 0.50 kc, 0.75 kc), full irrigation (rate of 1.00 kc), excess irrigation (rate of 1.25 kc) and non-irrigation (rates of 0.00 kc of “Class A” pan evaporation coefficient). Four crop loads in each irrigation application were performed by hand thinning after the June drop as a- a low crop load (3 fruits cm−2 TCA), b- a medium crop load (5 fruits cm−2 TCA), c- a heavy crop load (7 fruits cm−2 TCA), and d- an un-thinned crop load (> 7 fruits cm−2 TCA). The total tree yield increased with crop load and irrigation levels. Fruit size was significantly increased by the low crop load. Irrigation increased the fruit size compared to non-irrigation treatment. Further 0.75 kc, 1.00 kc and 1.25 kc irrigation treatments significantly increased the fruit length. Irrigation reduced the fruit flesh firmness. While the low crop load increased the skin red color, it decreased the fruit skin brightness. The yellowness of skin decreased with increasing in the irrigation amount. Irrigation reduced the skin brightness and yellowness, but it increased red color. Crop load and irrigation significantly affected the stem-end splitting fruit ratio. While the splitting fruit ratio increased with a decrease in the crop load, it decreased with an increase in irrigation amount, relatively. Consequently, the low and medium crop load treatments would be beneficial to increase the ratio of marketable fruits without any significant losses in yield for ‘Gala’ apple, especially under 0.75 kc deficit irrigation treatment.

The Effect of Deficit Irrigation and Crop Load on Leaf and Fruit Nutrition of Fertigated ‘Ambrosia’/‘M.9’ Apple

Mature, fruiting ‘Ambrosia’/‘M.9’ apple [Malus ×sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] trees were subjected over three growing seasons to a split-plot experimental design involving four irrigation main plot treatments and three subplot crop load treatments with six replicates. This semiarid production region is traditionally irrigated 01 May to 01 Oct. during which time an average of ≈ 15 cm of precipitation occurs. Irrigation treatments were applied through 2 × 4 L⋅h−1 emitters per tree and included I1: daily application of 100% evapotranspiration (ET); or I2: 50% daily ET; or I3: 50% ET applied to one side; and I4: 50%, 25%, or 18% ET-application, applied every second day, 2007–09, respectively. Crop load treatments were imposed annually ≈4 to 5 weeks after full bloom to create low (2.5, 3, and 3.75 fruits/cm2 trunk cross-sectional area (TCSA), medium (4.5, 6, and 7.5 fruits/cm2 TCSA), and high crop loads (9, 12, and 15 fruits/cm2 TCSA), 2007–09, respectively. Leaf and fruit nutrient concentration was affected more by crop load than by any deficit irrigation strategy. Increased crop load increased concentrations of leaf nitrogen (N), calcium (Ca), and fruit Ca in 2 of 3 years and consistently decreased concentrations of leaf and fruit phosphorus (P) and potassium (K) and, in 2 of 3 years, fruit boron (B). Reductions in seasonal water applications (as with I4) reduced leaf P in 2 of 3 years. But, when significant, (usually only 1 of 3 year) increased fruit Ca, magnesium (Mg), P, K, and B concentrations. Crop load also had a dominant effect on fruit nutrient removal rates expressed as kilograms per hectare. High crop load increased removal of all measured nutrients in most years. In contrast, imposition of deficit irrigation strategies often (2 of 3 years) reduced fruit P, Mg, and B removal rates but had little effect on N, Ca, and K. Cumulative evidence suggests that deficit irrigation applied to N, P, K, and B fertigated high density ‘Ambrosia’ apple orchards in combination with crop load reduction to maintain fruit size should usually not create additional nutrient problems. However, low fruit Ca concentrations may occur if the crop is very low. Fertigation of 20 g K/tree/year was insufficient for older trees because inadequate K occurred in all treatments by the third year.