Efficient nitrogen (N) management in perennial fruit orchards is constrained by species-specific differences in N demand and fruit N removal, which can result in distinct soil N uptake patterns even under similar fertilization regimes. This study assessed whether apple (Malus domestica Borkh.) and sweet cherry (Prunus avium L.) orchards differ in soil mineral nitrogen (Nmin) composition by analyzing nitrate (NO3-) and ammonium (NH4+) stocks in topsoil (0-20 cm). Soil samples were collected in spring from a long-term orchard experiment over two consecutive years and from a commercial orchard on two sampling dates in Germany. In apple orchards, Nmin was dominated by NO3- (83%), whereas cherry orchards showed a more balanced composition (42% NO3- and 58% NH4+). These patterns were consistent across years, sites, fertilization types (mineral or organic), and key soil properties, including total organic carbon and total nitrogen, but were not explained by these factors. The elevated NH4+ proportion in cherry soils suggests a species-associated pattern in soil N dynamics. Overall, the results highlight species-associated differences in soil Nmin composition between apple and sweet cherry orchards. Accounting for tree species differences may therefore improve N management and enhance N use efficiency in apple and sweet cherry production.

Blueberry (Vaccinium corymbosum L.) stands out among fruit in terms of three open physiological questions about its climacteric character, CO2 uptake, and the absence or presence of stomata on its floral organs. The objective of the present study was to examine the structures of blueberry flowers and fruit to explain their contribution to CO2 exchange and transpiration in order to clarify these discrepancies. Blueberries were dewaxed and the sepals/corolla removed for stomata counts, and their micromorphology was studied via LT-SEM. The fruit has stomata, contrary to beliefs in the literature, possibly because the stomata are occluded by the dense wax cover or ‘bloom’ and hidden on the distal part of the ovary in between and underneath the corolla. However, stomata were located on the distal part of the fruit surrounded by the sepals (calyx) and found predominantly on the abaxial sepals, while the adaxial side of the sepals and the proximal part of the ovary lacked stomata. The petals were devoid of stomata, trichomes, and chlorophyll and abscised after anthesis. In contrast, the sepals remained until maturity, contributing 5–7% to the berry surface but contributing to the majority of fruit stomata and chlorophyll. With 59–71% of the fruit’s chlorophyll, sepals were a significant source of the CO2 uptake. Similarly, with 95% of the berry stomata, sepals were a significant source of water loss, measured via porometry of fruit with and without sepals. Overall, this study identified the ovary as a minor source and sepals as the dominant source of CO2 and H2O exchange in blueberries.

The international apple trade requires apples with diameters of over 70 mm. Left untouched, apple trees tend to produce many apples of small diameter. To increase apple size, the number of blossoms can be reduced in their early growth stage, leaving fewer apples which will grow larger because of access to a greater portion of nutrients. Over the past few decades this has been mainly accomplished through chemical means, but recent demand for sustainable fruit production with fewer chemicals requires means of blossom thinning using e.g. mechanical methods, i.e. a machine with rotors and brushes. The goal of this project was to perform kinematic analysis on such a mechanical thinning machine to model the motion and behavior, both mathematically and graphically, as well as offer recommendations of operating parameters to maximize the machine’s efficiency. The project involved creating and assembling a three dimensional model of the machine in Pro/ENGINEER, performing kinematic analysis on the model, using the output to produce a mathematical formula, and using that formula to both analyze and predict the operation of the machine. The mathematical model was verified successfully against field test data. It was then used to provide tractor and rotor speeds for a range of desired percentage of blossoms removed. It also accomplished the reverse, predicting the percentage of blossoms removed for a series of chosen tractor and rotor speeds.

Zusammenfassung Ziel der Untersuchungen war es, den Einfluss einer Verschmutzung von Reflexionsfolien, die zur Verbesserung der Fruchtfarbe eingesetzt werden, hinsichtlich ihres Reflexionsverhaltens zu untersuchen, was sich auf ihre Nutzungsdauer bzw. Wiederverwendbarkeit auswirkt. Dazu wurden zwei Reflexionsfolien, eine silberne Alufolie und eine weiße Polypropylen Gewebefolie (Lumilys™, Beaulieu, Belgien) – wie nach einem Herbststurm – unterschiedlich stark verschmutzt; saubere Folien dienten als Kontrolle. Mit einem Spektrometer der Firma StellarNet (Tampa, FL, USA) wurden die senkrecht nach oben gerichtete (0°) und die diffuse Reflexion (45°) im Wellenlängenbereich 500–850 nm im Labor gemessen. Bei diesen Labormessungen reflektierte die Alufolie senkrecht nach oben („gerichtet“) mehr Licht als Lumilys, aber umgekehrt war die diffuse Reflexion (45°) dieser Gewebefolie höher als bei der Alufolie, d. h. dass die Gewebefolie in alle Richtungen reflektierte. Dagegen reflektierte die verschmutzte Alufolie – senkrecht nach oben gerichtet (0°) – zwar ebenfalls weniger, aber bei 45° (diffus) überraschenderweise viel mehr Licht als die saubere Alufolie. Bei beiden Folien lagen die Reflexionsmaxima bei 625–640 nm, ohne dass die Verschmutzung mit braunem Boden die Reflexionsspektren veränderte. Bei Feldmessungen wurde die Lichtreflexion im sichtbaren Bereich (PAR, 400–700 nm) im August bei einem Sonnenstandswinkel von 49° in Klein-Altendorf (50°N) mit einem tragbaren Lichtsensor TRP‑3 (Fa. PP-Systems, Amesbury, MA, USA) in 50 cm und 1 m Messhöhe an sonnigen und bewölkten Tagen bestimmt. Bei diesen Feldmessungen reflektierten sowohl die weiße Gewebefolie (Lumilys™) als auch die Alufolie beide überraschenderweise bei leichter bis mittlerer Verschmutzung und beiden Reflexionswinkeln (0° und 45°) am stärksten; die Lichtreflexion nahm erst wieder bei der starken Verschmutzung ab. Beide Folien reflektierten mehr Licht als das Gras der Fahrgasse oder offener Boden im Baumstreifen einer Obstanlage. Die Reflexion von UV-B-Strahlen (280–315 nm) wurde parallel mit einem Optometer X1 (Fa. Gigahertz-Optik, Türkenfels, Deutschland) gemessen, weil sie zusammen mit PAR und kalten Temperaturen die rote Farbbildung bzw. Anthozyansynthese der Fruchtschale fördern. Die senkrecht nach oben gerichtete (0°) UV‑B Reflexion der Alufolie überstieg sowohl an wolkenlosen als auch bedeckten Herbsttagen die der Gewebefolie (Lumilys™). Wie erwartet, nahm die direkte (0°) UV-B-Reflexion von Aluminiumfolie mit der Verschmutzung des Bodens bis zu einem gewissen Grad ab, während die Reflexion von Gewebefolien mit der Verschmutzung des Bodens unerwartet zunahm. Die Oberflächenrauheit der Reflexionsfolien wurde – in Abhängigkeit vom Verschmutzungsgrad – mit einem Profilometer vom Typ VR-5200 (Fa. Keyence, Osaka, Japan) untersucht. Der aus Falschfarbenbildern abgeleitete Rauheitsindex Sa stieg von 22 µm der sauberen auf 28 µm bei der verschmutzten Gewebefolie Lumilys™, aber von 2 µm bei der sauberen auf 11 µm der verschmutzten Alufolie und erklärte somit den Reflexionsanstieg bei leichter und mittlerer Verschmutzung. Zusammenfassend lässt sich sagen, dass eine leichte (2–3 g Boden/m 2 ) und mittlere (4–12 g Boden/m 2 ) Verschmutzung die diffuse Reflexion von PAR (400–700 nm) und UV‑B (280–315 nm) Strahlung der Gewebefolie (Lumilys™) sowie der Alufolie sogar erhöhen kann, sodass z. B. die Gewebefolie auch bei leichter Verschmutzung nochmals verwendet werden kann, während erst die starke Verschmutzung (24–51 g Boden/m 2 ) die Lichtreflexion mindert.

Zusammenfassung Ziel der Arbeit war, Möglichkeiten zur Verbesserung der Fruchtqualität und Fruchtfarbe bei zweifarbigen Apfelsorten zu untersuchen. Daher wurde der Einfluss einer Reflexionsfolie (Typ Lumilys® Typ WH110, Beaulieu, Belgien), eines Biostimulans (Stimplex®, Arcadian Seaplants, Kanada), des Sommerschnitts sowie der Entlaubung mit oder ohne Triebspitzen (simulierte Maschinenentlaubung) vier Wochen vor der Ernte im Rahmen einer Bachelorarbeit untersucht – unbehandelte Bäume dienten als Kontrolle. Dazu wurden am Campus Klein-Altendorf der Universität Bonn (50° N) 80 neunjährige Apfelbäume (Baumhöhe ca. 2,5 m) der gestreift roten Sorte ‚Braeburn Hillwell‘ auf der Unterlage M9 in N‑S-Pflanzung unter grauem Hagelnetz ausgewählt. Die Reflexionsfolie wurde am 1. September in den Fahrgassen ausgelegt, die Entblätterung erfolgte am 17. September und die Ernte am 19. Oktober 2020. Es wurden 1800 Farbmessungen am Baum bzw. im Feld jeweils an der Außen‑, Innen- bzw. Sonnen- und Schattenseite am Fruchtäquator sowie der Fruchtunterseite durchgeführt. Diese Farbmessungen erfolgten im wöchentlichen Abstand an den gleichen markierten 120 Früchten (5 unten, 5 in der Baummitte jeweils auf der Ost- und Westseite) und die Qualitätssortierung mit folgenden Ergebnissen: 1) Die beste Deckfarbe in einem Jahr guter Farbausprägung erzielte die ca. sechs Wochen vor der Ernte im Grassteifen ausgelegte Reflexionsfolie an Früchten im unteren Kronenbereich, d. h. nahe der Folie. 2) Äpfel im mittleren Kronenbereich – nach Entlaubung mit und ohne (simulierte Maschinenentlaubung) Triebspitzen – färbten besser als die der anderen Behandlungen. 3) Der späte, moderate Sommerschnitt verbesserte die Deckfarbe der Früchte vor allem auf der Westseite im mittleren Kronenbereich – dem Bereich mit der besten Sonneneinstrahlung. 4) Im unteren Kronenbereich verbesserten die Reflexionsfolie Lumilys® WH110 und die Biostimulanz Stimplex® die Deckfarbe stärker auf der Schatten- und Unterseite als auf der Sonnenseite der Früchte. 5) Äpfel der Sorte ‚Braeburn Hillwell‘ mit der Biostimulanz (Stimplex® 2 × @ 4 L/ha) reiften etwas früher und entwickelten damit ihre Deckfarbe früher unabhängig von der Position an der Frucht und in der Baumkrone 6) Bäume mit Reflexionsfolie (Lumilys® WH110) und Biostimulanz (Stimplex®) wiesen mehr Früchte in beiden guten Farbkategorien (> 50 % und > 75 % Deckfarbe) auf als die Kontrolle. 7) Die beste Farbausprägung auf der Fruchtunterseite erzielte die Reflexionsfolie Lumilys® WH110. 8) Mit der Entblätterung wurden ca. 3 g (12 %) (ohne Triebspitzen) bzw. 4,6 g (18 %) (mit Triebspitzen) und beim Sommerschnitt ca. 7,2 g (29 %) Blatt-Kohlenhydrate pro Baum entfernt. 9) Es bestanden keine Unterschiede bei der Blütenbonitur im April des Folgejahres 2021. Die Folie Lumilys® WH110 führte zur besten Farbausprägung. Die Biostimulanz Stimplex® war durch die geringen Kosten die wirtschaftlichste Variante gefolgt vom Sommerschnitt, Entblätterung ohne Triebspitzen (simulierte Maschinenentlaubung), Reflexionsfolie Lumilys® WH110 und Entblätterung einschl. der Triebspitzen.

Temperate fruit trees are widely cultivated across the world’s temperate regions. These trees are well-adapted to cold-winter climates through their ability to synchronize their phenology with the seasons. In autumn, they enter a dormant state, which allows them to survive the low winter temperatures and lasts until they resume growth in early spring. We analyzed the agroclimatic requirements (chill accumulation in Chill Portions, CP, and heat accumulation in Growing Degree Hours, GDH) for blooming in three sweet cherry cultivars (‘Samba’, ‘Burlat’, and ‘Sylvia’) grown in distinct climatic settings in Bonn (Germany) and Zaragoza (Spain). We used Partial Least Squares (PLS) regression analysis to relate bloom dates of the three cultivars grown in both locations to local temperatures. In Bonn, the colder location, trees experienced a long period of chill exposure (87-105 CP), which allowed a rapid growth response to warm temperatures (3233-4343 GDH). The flowering dates were mainly driven by conditions during the forcing period. In contrast, in the warmer climate of Zaragoza, chill exposure of the trees was relatively short (48-59 CP). The buds required a long exposure to warm conditions (5444-6988 GDH) to subsequently bloom. In this case, flowering dates were influenced more by exposure to chilling than by conditions during the heat accumulation period. Global warming caused opposite effects on flowering dates depending on location. While in Bonn flowering dates have advanced between 3 and 5 days per decade, bloom dates in Zaragoza did not show such a trend, except for minor flowering delays in ‘Sylvia’, the late-flowering cultivar. Our results show that the response of the flowering dates to temperature appeared to depend on specific local climatic conditions. Although we applied current methodologies to determine the agroclimatic requirements of these cultivars, our methods were unable to derive consistent estimates of agroclimatic needs across the two locations.

The use of plastics in horticulture is reviewed with respect to its sustainability based on the traditional criteria of triple Rs (reduce, reuse, and recycling) plus a re-place strategy, taking into account possible alternatives. Hail (and insect) nets made of HD-PE, with their long-term use mostly on apple and polytunnels of LD-PE for cherry and strawberry as well as solarisation mulches (reuse), were found to be relatively sustainable solutions for their needs and are currently without alternatives. In contrast, standard black mulch, with its largest share among horticultural plastics, had the widest range of sustainable alternatives, ranging from biodegradable to spray mulch; few sustainable alternatives are available for fleeces and reflective mulches. For the third sustainable option, pilot recycling schemes were examined, such as PolieCoTM (Italy), MAPLATM (Spain), and ERDETM (Germany); they collect 30–50% of the agricultural plastics used in their respective areas, with a successful retrieval growth rate of ca. 20% per year in the case of ERDETM. For the fourth new R option (replace), future sustainability perspectives for the predominant black mulch are research into and development of better, biodegradable, non-fossilbased plastics, sprayable mulch; microbes for the digestion of deployed polyolefins and, for a certain limited range (on shade tolerant crops or in high-light intensity environment), hail nets and polytunnels that are equipped/substituted by/with solar panels (“agri pv”) for the concomitant sustainable production of green renewable energy.

The objective of the present work is to investigate possibilities of enriching soil organic carbon (SOC) and humus in fruit orchards as an ecosystem service. Results are presented from a 50-year long-term fertiliser trial at Klein-Altendorf near Bonn, Germany. The location (50 degrees N) is exposed to westerly Atlantic winds buffered by the mild Rhine valley. The temperate zone climate is characterised by ca. 600mm annual precipitation and 9.6 degrees C annual temperature. The soil is a fertile luvisol with 90 (out of 100) soil fertility points on loess currently planted with cherry cv. 'Kordia' on GiSelA 5. The grass mulch from the alleyways and the cuttings/prunings remain in the orchard. The four (out of eight) selected treatments, comprising 40 trees each, for this contribution were (1) control trees without additional fertilisation; (2) lime (1t CaO/ha and 10 years to stabilise the pH near the optimum for stone fruit; (3) lime as above plus organic fertiliser; and (4) lime with inorganic NPK-all applied to the tree herbicide strip only-with the following results: (1) control trees without any additional fertilisation grew well without any nutrient deficiency symptoms or yield depression, (2) occasional lime (1t CaO/ha in 10 years) over 50+ years increased soil pH from pH 6.3 to pH 6.7 within the optimum soil pH for stone fruit orchard, whereas the pH in the unfertilised plot dropped to pH 5.7-5.9, thereby confirming the slow soil acidification in the herbicide strip proposed in the literature, (3) lime as above plus organic fertiliser (in the form of pig manure at 3t dry matter/ha) in the first year and then green compost (average 10t DM/ha and year) in the last 12 years increased humus 2.5-fold from 1.8% in 1968 to 4.3% in 2021, equivalent to a 0.03% increase in soil humus content per year, (4) similarly, SOC more than doubled from 1% to 2.5% doubling with 37.5 t CO2/ha carbon sequestration over 50+ years or 0.7 t CO2/ha and year in the plot with organic fertiliser, (5) lime as above plus inorganic NPK fertiliser (40kg N/ha and year) increased both pH and soil nutrient content. These results are discussed with respect to a dual-purpose use of fruit orchards. Under the Bonn soil and climate conditions, humus enrichment in the soil, carbon sequestration and increase in SOC were only achieved with frequent supply of organic matter.

The objective of the present work was to study the effects of contamination on the reflective properties of groundcovers used for enhancing fruit colouration in the orchard. Contamination also affects longevity and possible sustainable re-use of materials. A white, woven textile (polypropylene Lumilys (TM)) and silver aluminium foil were experimentally contaminated with soil, similar to the situation after an autumn storm in a fruit orchard. Clean material served as control. Using a spectrophotometer (StellarNet; Tampa, FL, USA), vertically directed (0 degrees) and diffuse (45 degrees) light reflection in the range of 500-850 nm was compared from clean and contaminated groundcover in the laboratory. Reflection from vertically directed aluminium foil exceeded that of Lumilys (TM); however, the highest reflection in all spectral measurements was at 45 degrees (diffuse) from the clean woven textile, i.e., in all directions, and exceeded that of aluminium foil. In contrast, the contaminated vertically directed (0 degrees) aluminium foil reflected less light than the clear foil but, surprisingly, reflected much more light at 45 degrees than the clean foil. Both materials showed reflection peaks at 625-640 nm; light spectra and peaks remained unchanged irrespective of soil contamination. Light reflection in the visible range (PAR, 400-700 nm) was concomitantly measured in the field at CKA Klein-Altendorf near Bonn (50 degrees N), Germany, at 0.5 m and 1 m height using a portable TRP-3 light sensor (PP-Systems, Amesbury, MA, USA) on sunny and cloudy days at a solar angle of 49 degrees. Surprisingly, in these field measurements, Lumilys and aluminium foil reflected most light in both directions (0 degrees and 45 degrees) when slightly to moderately contaminated. Only with heavy contamination did the reflection decrease. Both groundcovers reflected more light than the grass in alleyways of fruit orchards or open soil under the trees. UV-B reflection (280-315 nm) was examined in parallel in the field using an X1 optometer (Gigahertz Optik, Turkenfels, Deutschland), as it enhances anthocyanin biosynthesis and red fruit colouration in combination with PAR and low temperature. Straight (0 & DEG;) UV-B reflection from aluminium foil exceeded that from white woven textile (Lumilys (TM)) on both clear and overcast autumn days. As expected, straight (0 degrees) UV-B reflection from aluminium foil decreased with soil contamination to a certain extent, but it unexpectedly increased from the woven textile with soil contamination. Surface roughness in dependence of contamination was measured non-destructively by a profilometer type VR5200 (Keyence, Osaka, Japan). The roughness index, Sa, increased from 22 to 28 mu m with soil contamination of the woven textile and from to 2 to 11 mu m with aluminium foil, possibly explaining differences in the observed reflectivity. Overall, the expected severe decline in light reflection (PAR and UV-B) was not seen. In contrast, light (2-3 g soil/m(2)) and moderate (4-12 g soil/m(2)) contamination improved light reflection of PAR (400-700 nm) and UV-B (280-315 nm) by woven textile (Lumilys (TM)) and aluminum foil. Thus, with slight contamination the materials can be reused, whereas severe contamination (24-51 g soil/m(2)) reduces light reflection.

This work aimed to compare the methods for improving the fruit quality and particularly fruit colour in bi-coloured apple cultivars. The influence of a reflective film (type Lumilys (R) WH110, Beaulieu, Belgium), a biostimulant (Stimplex (R), Arcadian Seaplants, Canada), summer pruning as well as defoliation with and without retaining the shoot tips was investigated four weeks before harvest as part of this bachelor thesis. The treatments were divided into six plots, including untreated trees, which were used as control trees. The reflective film was laid out in the grass alleyways on 1st September about six weeks before harvest. Trees were defoliated on 17th September and harvested 19th October 2020.Eighty nine-year-old apple trees (ca. 2.5 m) of the cultivar 'Braeburn Hillwell' on M9 rootstock under grey hail net were planted in N-S orientation at the University of Bonn Campus Klein-Altendorf (50 & DEG; N). In total, 1800 colour measurements were made on the tree in the field on the inside, outside, sunny side, and shady side at the fruit equator as well as on the fruit underside. These non-invasive colour measurements were done at weekly intervals on the same 120 marked apples. In each plot, ten apples were measured on the east and west side (five apples from the centre and five from the lower tree canopy). The measurements were also done during the quality grading with the following results:1) Apples in the lower tree canopy above the reflective film developed the best skin colour compared to the middle canopy (1.0-1.8 m height).2) Apples in the middle canopy after defoliation with and without retaining the shoot tips coloured better than those of the other treatments (reflective film, biostimulant and control).3) Late summer pruning improved fruit skin colour especially on the west side in the mid-canopy-the area with the best sun exposure.4) In the lower canopy, the reflective film Lumilys (R) WH110 and the biostimulant Stimplex (R) improved the skin colour more on the shaded inner and underside of the apples compared to the sun-exposed side of the fruit.5) 'Braeburn Hillwell' apples with the biostimulant (Stimplex (R) @ 4 L/ha) ripened earlier and had improved skin colour regardless of the position on the fruit and in the tree canopy.6) The greatest percentage of well-coloured apples in the categories > 50% and > 75% red skin colour was over the reflective film (Lumilys (R) WH110) and with the biostimulant (Stimplex (R)).7) The best red colouration on the bottom of the fruit was achieved with the reflective film (Lumilys (R) WH110).8) Defoliation removed about 3 g (12%) (excluding the shoot tip) and about 4.6 g (18%) (including the shoot tip) as well as about 7.2 g (29%) (summer pruning) of leaf carbohydrates per tree.9) There was no treatment effect, particularly defoliation, on return bloom in April 2021.Overall, the biostimulant Stimplex (R) gave the best economic returns followed by the reflective film Lumilys (R) WH110, light summer pruning and partial defoliation with or without retaining the shoot tip.

Incidents of flooding in tropical and subtropical fruit trees have increased as a result of climate change. Because of flooding, the anaerobic conditions of the rhizosphere increase the conditions for phytotoxicity and infection by pathogenic fungi and bacteria. Due to oxygen depletion in waterlogged soils, growth, functions of the roots and of the entire plant are impaired. The decrease in the photosynthetic rate is considerable because of the reduced functional leaf area because of chlorosis, necrosis, leaf drop and stomatal closure, as well as chlorophyll degradation. Plants have developed different morphological, physiological, and biochemical adaptations to survive hypoxic stress. Some fruit trees form an aerenchyma in roots for the diffusion of oxygen from the aerial parts. Induced aerenchyma-containing adventitious roots, rapidly elongate stems into deeply flooded soils; or they form hypertrophied lenticels, like some mango varieties. Measures for better adaptations and tolerance of tropical fruit trees to climatic impact include the following: adaptations of the cultivated terrain, selection of varieties, rootstocks more tolerant to hypoxic stress, pruning to reestablish the balance of the aerial part/roots, and foliar applications (e.g., of glycine betaine or hydrogen peroxide (H2O2)). Mycorrhizal colonization of roots can increase tolerance to waterlogging, while the application of fertilizers, such as CaO or MgO, can improve the redox potential of flooded soils. We present results of studies on this problem for the following fruits: yellow passion fruit (Passiflora edulis f. flavicarpa) and purple passion fruit (P. edulis f. edulis), cape gooseberry (Physalis peruviana), lulo or naranjilla (Solanum quitoense), tree tomato (Solanum betaceum), citrus (Citrus spp.), guava (Psidium guajava), papaya (Carica papaya), and mango (Mangifera indica).

In the past, chemical thinning dominated in fruit orchards. This paper for the special issue outlines alternatives to chemical thinning for crop load management (CLM) and its effect on fruit size, firmness, sugar, starch, and weight, indicating ripeness and fruit quality, yield, and alternate bearing. A total of 450 apple trees (Malus domestica Borkh., cv. ‘Roter Boskoop’; six years old) on M9 rootstock were used at the Klein-Altendorf experimental station (50° N) of the University of Bonn, Germany. As the first alternatives, trees were mechanically blossom-thinned at the balloon stage (BBCH 59) with a rotor speed of 320 rpm or 380 rpm at 5 km/h tractor speed or were chemically thinned at the full bloom stage (BBCH 65) with ammonium thiosulfate (ATS), ethephon (ETH), and/or 6-benzyladenine (BA) at 10–12 mm fruit size (BBCH 71) after applying ATS/ETH. Flower clusters and/or cluster leaves (source) were manually removed to determine the optimum sink-source ratio to achieve different ratios of fruitlets (sink) relative to the leaves (source) at fruit set (BBCH 67–69). Un-thinned, adjacent trees served as the control. The majority of CLM methods improved fruit size and weight. Removing cluster leaves at fruit set increased fruit size and weight of the remaining fruit, which has not been observed before. The most effective treatment for fruit size and weight and return bloom was the 75% flower cluster and complete cluster leaf removal. Removal of more than 50% of flower clusters successfully improved return bloom, indicative of alternate bearing. The mechanical blossom thinning had a positive effect on fruit size and weight with a return bloom similar to that of removal of 50% flower clusters.

Zusammenfassung Um die Möglichkeit der Humusanreicherung und CO 2 -Speicherung („carbon sequestration“) in Obstanlagen zu untersuchen, wurden Bodenanalysen aus dem 1968 angelegten Dauerdüngungsversuch auf dem Campus Klein-Altendorf der Universität Bonn ausgewertet. Das Klima ist dort mild atlantisch geprägt mit 600 mm Jahresniederschlag bei einer Durchschnittstemperatur von 9,6 °C. Die fruchtbare Parabraunerde auf mehreren Metern alluvialem Löß hat eine Bodenzahl von ca. 90 und ist zur Zeit mit Kirschen auf Gisela-Unterlage bepflanzt – mit Grasmulchwirtschaft; Schnittholz verbleibt in der Anlage. Die 4 ausgewählten Düngevarianten mit je 40 Bäumen sind 1) Kontrolle ohne Düngung, 2) Kalken (1 t/ha CaO alle 10 Jahre) – zur pH-Stabilisierung, 3) Kalken und organische Düngung (anfangs mit Stallmist, dann Grünkompost) und 4) Kalken mit anorganischer NPK-Düngung (40 kg N/ha und Jahr); alle Behandlungen erfolgten ausschließlich auf den Baumstreifen mit folgenden Ergebnissen: 1) Auf diesem fruchtbaren Boden entwickelten sich die Obstkulturen auch ohne zusätzliche Düngung gut. Die Kontrollbäume wiesen weder Nährstoffmangel noch Ertragsdepressionen auf und profitierten von der Grasmulchwirtschaft und geschreddertem Schnittholz. 2) Gelegentliche Kalkung über 50 Jahre erhöhte den pH-Wert von 6,3 auf 6,7 ins pH-Optimum für Steinobst und Verfügbarkeit der meisten Nährstoffe; in der ungedüngten Kontrolle sank der pH-Wert auf 5,7–5,9 und bestätigt damit die in der Literatur beschriebene langsame Versauerung des Bodens bei langjährigem Herbizideinsatz. 3) Kalken und organische Düngung – in Form von Stallmist (ca. 3 t TM/ha und Jahr) in den ersten 30 und Grünkompost mit ø 10 t TM/ha und Jahr in den letzten 10 Jahren – erhöhte den Humusgehalt um das 2,5fache von 1,8 % in 1968 auf 4,3 % Humus in 2021; dies entspricht einer Humusanreicherung von ø 0,03 % Humus pro Jahr. 4) Die Verdoppelung des organischen Kohlenstoffs (SOC) von ca. 1 % auf ca. 2,5 % entspricht etwa einer Speicherung von 37,5 t CO 2 /ha über 53 Jahre im Boden bzw. ca. 0,7 t CO 2 /ha und Jahr bei ausschließlich organischer Düngung und Kalkung. 5) Kalken und anorganische NPK-Düngung erhöhten den pH-Wert und Nährstoffgehalt des Bodens. Die Ergebnisse werden diskutiert bezüglich der Möglichkeit einer Doppelnutzung von Obstproduktion und Klimawirkung als Kohlenstoffspeicher; diese wurde unter den Meckenheimer Klima- und Bodenbedingungen jedoch nur dann erreicht, wenn langfristig und regelmäßig organischer Dünger und Kalk zur Erhaltung des pH-Werts verabreicht wurde – und nicht bei ausschließlichem Kalken oder anorganischer NPK-Düngung, wobei überhöhte Nährstoff- und Humusgehalte negative Folgen auf die Kultur haben können.

Russet is a brown necrotic appearance or physiological peel disorder of pome fruit. The objective of the present work was to identify russet in-situ on the fruit peel using new non-invasive technology. Colorimetry, spectrometry, 3D profilometry, and a luster sensor were employed on green 'Conference' and red 'Williams Christ' pears. Non-invasive true and false color images at 40x magnification with a 3D-profilometer type VR-3000 (Keyence) allowed identification of russet on 'Conference' pear with a larger roughness Ra 3.3 mu m (SE 0.4) compared with Ra 2.5 mu m (SE 0.3) on russet-devoid fruit peel. The contactless russet detection using the luster sensor CZ-H72 failed to detect a significant difference (8 a.u.) in glossiness between russet (54.5 a.u.) and non-russet (62.5 a.u.) on 'Conference' (green) in contrast to red 'Williams Christ' with a ca.2-fold statistically significant difference between russet (38.4 a.u) and non-russet (67.5. a.u.) surface. The situation reversed with colorimetry: For the red pears of 'Williams Christ', differentiation between russet (66.8 degrees hue) and russet-devoid peel (62.4 degrees hue) was impossible when using contactless colorimetry. Russet could be successfully detected for all cultivars examined using portable contactless spectrometry (190-1100 nm). A new spectral russet index (SRI) was proposed relating the two peaks of light reflection (550-600 nm and 775-785 nm) to the trough (667-685 nm). Russeted peel (e.g., 3.6) exhibited ca. 25% smaller SRI values than russet-devoid peel (4.8) of both cultivars 'Conference' (green) and 'Sweet Sensation'(red). Overall, both portable non-invasive techniques, 3D-profilometer and spectral light reflection with the novel russet index, proved suitable for real-time, in-situ russet detection in pears. In particular, the study has identified colorimetry as a suitable measure for russet detection for green and luster sensors for red pear cultivars, which offers new possibilities for contactless russet detection in the field or on a grading line.

Tree fruit species and cultivars have discrete thresholds of chill and heat, quantified with environmental models that relate temperature accumulation over time to tree fruit development. The accumulation of heat in the spring progressively leads to the deacclimation and development of reproductive buds of Prunus sp. Phenology scales have historically been used to estimate and relate this developmental progression with lethal temperatures to facilitate orchard management practices. For sour cherry, however, ecodormancy release is accompanied by an approximate 20 degrees C loss of hardiness before clearly distinguishable changes in external bud phenology occur. For this reason, we aimed to characterize the physiological changes of 'Montmorency' sour cherry floral buds during their transition from endo- and eco-dormancy through growth resumption to determine how well phenology relates to shifts in critical survival temperature of buds. We present a developmental timeline of the first preanthesis changes in floral buds as they relate to lethal temperature (LT50) changes. A simple Growing Degree Hour (GDH) model predicted freeze sensitivity explaining 93% of the variation in LT50 where overlapping phenological changes were difficult to separate. Our results can aid producers to manage frost protection and enable a better prediction of freeze susceptibility.