Apricot nutrition

Savvas Pastopoulos, Agronomist MSc, Pastopoulos Agronomics, Neos Mylotopos, Pella, Greece

Apricot nutrition is decided within a few specific windows of the growing season, and each nutrient has one of its own. The instrument that checks them, leaf analysis, has a window of a few weeks itself: a sample taken outside it compares to no published range. Nitrogen is judged not by a window but by a level, since above a certain point fertilisation raises yield while it lowers fruit firmness and accelerates the darkening of the dried product in storage. Potassium, the element removed in the greatest quantity with the fruit, is demanded while that fruit is enlarging. Calcium has the narrowest window of all, accumulating almost entirely within four weeks of fruit set, beyond which no intervention raises it appreciably. What follows, for each of these, is the measured evidence, the period in which it is decided, and the quantities as set by the regulations of the countries that have binding limits for the crop.

1. Leaf analysis: sampling period and sufficiency ranges

The leaf sampling period in apricot is narrow, and it is the single point on which all sources converge independently of one another.

The Californian source quantifies the deviation: for August or September samples, 0.2 percentage points are subtracted from nitrogen and 0.2 from potassium before any comparison [7]. That correction exceeds the difference between two adjacent sufficiency classes, so a sample taken outside the period cannot be evaluated, whatever the quality of the laboratory analysis.

Eight of the nine protocols specify the leaf, and all but one call for a leaf from the middle of a current-season shoot. The exception is California, which calls for a leaf from a non-fruiting spur [7]. Since the Greek protocol belongs to the first group [1], the Californian ranges do not correspond to a Greek sample.

Seasonal variation of leaf concentrations

The July period has until now been supported by the convergence of protocols rather than by a published curve. A Turkish study at Isparta determined the variation with fifteen samplings at fourteen-day intervals, from full bloom on 27 April to leaf fall on 9 November, on twelve-year-old trees of the cultivar Ismail Aga on seedling rootstock, on a soil of pH 7.75 with 10 per cent carbonates, at an altitude of 950 m [22]. Fruit at that site ripened in the second week of July.

The values document the position of the sampling period. From full bloom to early July leaf nitrogen decreases from 4.66 to 2.51 per cent, that is by 46 per cent in ten weeks. From 5 July to 31 August it changes from 2.51 to 2.20, and calcium from 1.94 to 1.93. Potassium has already passed its maximum, recorded on 21 June at 4.18 per cent, and remains at about 3.9. A summer sample therefore corresponds to the section of minimum slope of all three curves, while a May or October sample corresponds to a section of steep change. The same follows independently from the other two series of measurements: at Erzincan the variation was minimal from twenty days before harvest until harvest [21], and in Serbia the most suitable moment was determined at 120 days after full bloom [23].

Sufficiency ranges

The apricot sufficiency ranges in circulation in Greece [1] come from foreign manuals, chiefly a German plant nutrition handbook of 1988 [3] and an American review of 1980 [4]. No Greek calibration has been made. There is, however, one Greek measurement, covering 24 commercial orchards in Chalkidiki of the cultivar Tirynthos, sampled in early July, which gives the ranges found in orchards yielding 5 to 20 t/ha [2]:

These ranges concern an early cultivar in one district and do not constitute thresholds. Their usefulness is limited to the order of magnitude within which Greek orchards of normal production operate.

A fourth source of ranges, the Australian one, is used as the reference point by both the Turkish and the Serbian studies, and is the only one of the four that states explicitly which leaf it corresponds to [20]:

The table, as published, leaves a gap for calcium between 3.5 and 4.1. On comparison with it, the Greek medians place nitrogen, calcium, copper and manganese in the normal class, zinc at its lower limit, phosphorus, potassium and iron in the low class and magnesium in the high class. The comparison is indicative, since the Greek study does not specify the type of leaf sampled.

The outcome of applying foreign reference values on a different soil is documented in a five-year Serbian study in a young orchard of the cultivar Roxana, in which six fertilisation schemes were compared, from cattle manure and compound fertiliser to urea and natural zeolite, alongside an unfertilised control. At 120 days after full bloom, and using the deviation from optimum percentage index with the Australian values as reference, all six schemes and the control were placed below the optimum for nitrogen, potassium, calcium, magnesium, iron, zinc and boron, and above it for phosphorus alone [24].

The finding carries two qualifications. The index compares against a single reference value, so a negative sign does not in itself establish deficiency, but a value below the Australian reference. The soil was also acidic, with pH from 4.33 to 4.86, of opposite properties to Greek soils, and the authors attribute part of the result to the soil and to inadequate fertilisation. The essential point remains: the foreign reference value returned the same negative sign for seven elements at once, in the fertilised treatments and in the control alike, and therefore did not discriminate between treatments.

A second Serbian study quantifies the effect of a factor unrelated to fertilisation. In the same orchard, in the same cultivar Vera, on the same date and in the same year, with seven different plum interstocks, leaf nitrogen ranged from 1.25 to 1.70 per cent and calcium from 1.61 to 2.26 [23]. The difference of 0.45 points of nitrogen is comparable to the width of an entire sufficiency class, which for low nitrogen amounts to 0.6 points.

The variation between years follows from the Turkish survey of twenty orchards at Erzincan, with the same cultivar and the same sampling period in two consecutive years: leaf nitrogen ranged from 1.02 to 2.04 per cent in 1991 and from 1.76 to 3.26 in 1992 [21]. Comparing an orchard against itself remains the only safe method, but it requires a run of years and not two measurements.

Sources: 1 2 3 4 5 6 7 20 21 22 23 24

2. Nitrogen: rate, distribution and effect on quality

Three published series of nitrogen rates in apricot exist, in three countries and three cultivars, and their results do not coincide in all respects. The widest in its range of rates was conducted in South Australia, on twelve-year-old trees of the cultivar Moorpark, on a sandy soil, over three years [8][9]. The rates were 0, 250, 500, 750, 1,000 and 1,250 g of nitrogen per tree per year, split 30 per cent at budburst, 30 per cent six weeks later and 40 per cent after harvest.

Fresh yield was maximised at 1,000 g per tree in the second and third years [8]. The quality attributes changed in the opposite direction: firmness decreased as the rate rose, uniform ripening of the flesh was recorded only at 0 and 250 g, and the rate of darkening of the dried fruit in storage increased with nitrogen in all three years. The authors recommend below 500 and ideally below 250 g per tree [9].

Low fertilisation has its own cost, and it is not omitted: at 0 and 250 g, total soluble solids were lower than at 750 and 1,250 g [9], a finding not confirmed by the other two studies and examined below. Maturity was also delayed by four to eight days at the higher rates [8]. Choosing between the two ends is a commercial decision that depends on where the fruit is going.

The French study on the cultivar Bergeron

In the Rhone valley, in a Bergeron orchard on GF 305 planted in 1989, three nitrogen levels were tested for seven years, nil, 25 and 150 kg per hectare, in all combinations with two potassium levels, 25 and 150 kg per hectare [25]. The high rate was 75 kg per hectare in the first two years and 150 from the third year onwards. Nitrogen was applied twice in spring, in March and in May, to a 2 m strip along the tree line.

Yield increased with nitrogen, but most of the increase was attributable to the first step of the scale: the difference from nil to 25 kg per hectare exceeded the difference from 25 to 150 [25]. Pitburn, the browning of the flesh around the stone, followed the high rate exclusively. Averaged over four years, affected fruit stood at 23 per cent with no nitrogen, 26 per cent at 25 kg per hectare and 58 per cent at 150. The difference between the first two levels was not statistically significant in any year except the first.

The authors conclude that, of the levels tested, 25 kg of nitrogen per hectare was the most commercially suitable, with yield only slightly below that at 150 and with the incidence of the disorder at less than half [25]. That figure is lower than every rate imposed or recommended by the regulations in section 5.

The Moroccan study: rate and distribution of nitrogen

Near Marrakech, in a Canino orchard planted in 1980, a full factorial design of sixteen treatments was applied: nitrogen at 80 and 150 kg per hectare, phosphorus at 30 and 90, potassium at 60 and 120, and two schemes for distributing the nitrogen, one third in February with two thirds in April, or the reverse [26].

At 150 kg per hectare the fruit was heavier by 6.7 g, against a mean weight of 49.3 g, but lower in sugars: fruit from the 80 kg treatment showed at least 8 per cent higher mean sugar concentration than all other treatments, and the refractometric index changed in the same direction. Potassium acted in the opposite direction to nitrogen, raising both sugars and the refractometric index on moving from 60 to 120 kg per hectare. Phosphorus did not emerge as a significant factor [26].

The Greek survey

In those same 24 orchards, where nitrogen was applied to all of them at the same rate, 200 kg per hectare in a single February application, leaf nitrogen showed no relationship with yield. Across its entire range, from 2.30 to 3.10 per cent, yield moved by 0.7 t/ha, one sixth of a standard deviation, and downwards [2]. This is an observation rather than a controlled trial, but it establishes that nitrogen fertilisation was not the factor that differentiated yield across those orchards.

How the applications are split across the year

• In the Australian study nitrogen was distributed 30 per cent at budburst, 30 per cent six weeks later and 40 per cent after harvest [8]. Because apricot flowers before the leaves emerge, no dose fell before bloom.
• A French study on the cultivar Bergeron showed that shifting application from before to after harvest did not change yield, though it tended to lower soluble solids and colouring [10].
• The Moroccan study compared two distribution schemes directly, one third in February with two thirds in April and the reverse. The distribution was not a neutral factor: at the same total rate, the two schemes gave different fruit weight, different accumulation of phenolic compounds and a different content of organic acids. The strongest interaction in the whole design was that between nitrogen and potassium [26].
• Emilia-Romagna prohibits any nitrogen, mineral or organic, before the start of flowering and after 15 October, and does not allow more than 60 kg per hectare in a single dose [12]. Piedmont prohibits nitrogen from leaf fall until the end of February [13].
• Campania places demand in three windows, from flowering to fruit set, during fruit enlargement, and during summer flower bud differentiation, and requires the production nitrogen to be split across them [18].

Common to all the sources is splitting. The whole annual dose in one application, and before bloom at that, is recommended by none. In the one case where the distribution was compared directly, at a constant total rate, the result in the fruit differed.

Sources: 2 8 9 10 12 13 18 25 26

3. Potassium and calcium

An Italian study followed calcium accumulation in the apricot fruit alongside the transpiration of the fruit itself, and established that calcium accumulates linearly and reaches 80 per cent of its final content within the first four weeks of fruit development, rising slowly thereafter to about 6 mg per fruit at harvest [11].

The mechanism is documented in the same study. Fruit transpiration is maximised immediately after fruit set, at 0.55 plus or minus 0.03 mmol per square metre per second six days after it, and over the following three weeks decreases by 43 per cent, settling close to 0.3. Calcium accumulation correlates linearly with transpiration, with a coefficient of determination of 0.81 [11]. The cultivar was Tirynthos, the same one as in the 24 Greek orchards. Calcium moves only with the transpiration stream and is not redistributed within the plant as nitrogen and potassium are, so when the stream to the fruit stops, its supply stops with it.

Fruit calcium is also linked to the browning of the flesh around the stone. A French study on the cultivar Bergeron established that high nitrogen increased vegetative growth, yield and mean fruit weight, and at the same time aggravated the incidence of the disorder, with fruit nitrogen positively correlated with it at every evaluation time [10]. Increased potassium, by contrast, improved soluble solids and colouring without affecting the disorder.

The seven-year French study examined potassium alongside nitrogen, at two levels, 25 and 150 kg per hectare. Potassium affected neither vegetative growth nor yield nor fruit weight. It did increase total soluble solids, to 16.8 against 14.6 per cent in the final year, as well as colouring [25].

The relationship between nitrogen, calcium and pitburn is quantified in the same study. As the nitrogen rate increased, fruit nitrogen rose from 1.0 to 1.5 per cent of dry weight and fruit calcium fell from 0.9 to 0.7 parts per thousand. The correlation coefficient of pitburn with fruit nitrogen was 0.822 and with calcium minus 0.857 [25]. Fruit potassium did not change with fertilisation in either of the two years measured.

An interaction was also recorded that precludes a single-factor reading: heavy potassium fertilisation increased pitburn in the absence of nitrogen and reduced it at the low nitrogen rate [25]. Potassium is therefore not assessed independently, but in relation to the accompanying nitrogen. The same follows from the Moroccan factorial design, where the strongest of all interactions was the one between these two elements [26].

In the Greek survey of 24 orchards, leaf potassium and calcium were the only two of the ten elements that emerged as statistically significant predictors of yield. From the lower to the upper end of the potassium range yield moves by 6 t/ha, and across calcium by 4.3 [2].

For at least one cultivar an upper limit on potassium is also recorded. The Greek manual states that in Bebecou heavy potassium fertilisation overturns the potassium to calcium ratio and causes spotting at the apex of the fruit [1]. The observation is not supported by any published study and is recorded as a recommendation of that source, but it is consistent with the findings of the Italian study on calcium.

Foliar potassium

An Egyptian study examined five potassium sources as a foliar application at 0.2 per cent, three times within the season, on Canino trees, over two seasons [27]. All the solutions improved yield, colouring, fruit weight and firmness, and reduced lipid peroxidation, with a corresponding improvement in behaviour during storage. Of the five sources, potassium nitrate gave the highest values both for yield and for keeping quality. The study was conducted in the Nubaria region, in a climate warmer than the Greek one, on a cultivar with a chilling requirement of about 550 hours. No equivalent study exists under Greek conditions, and the values do not transfer as they stand.

Sources: 1 2 10 11 25 26 27

4. Micronutrients on calcareous soils

Greek soils are as a rule calcareous and alkaline, and the behaviour of micronutrients in them differs from that on the acidic soils against which northern European and American manuals are calibrated. Two sets of measurements on soils of similar properties quantify the difference.

At Erzincan, across twenty orchards with soil pH from 7.50 to 8.40 and organic matter from 0.77 to 3.16 per cent, available soil manganese was adequate in every one of them, above 1 ppm, while leaf manganese was determined to be low. The authors attribute the finding explicitly to restricted uptake rather than to a lack of reserves [21]. Available soil iron was low in 60 to 70 per cent of the orchards.

The Greek survey records the same picture from the side of the leaf. Iron had a median of 88.3 ppm, below the lower limit of the normal class in the Australian ranges, which is 100 ppm, and zinc a median of 21.0 ppm, at the lower limit of the same class [2][20]. Manganese ranged across the widest span of any element, from 39.5 to 272.0 ppm, that is from the edge of the low class to the high one, within a single district and a single cultivar.

Micronutrients require stricter observance of the sampling period than macronutrients do. In the Turkish series of fifteen samplings, leaf zinc decreased from 55.8 ppm at full bloom to 14.8 ppm on 19 July and to 7.07 ppm in late October [22]. The same tree therefore traverses the entire scale within one season, from the high class to deficiency, without any change in fertilisation. Copper follows a comparable course, from 15.4 to 5.28 ppm. For these two elements the sampling date determines the result more than nutrition does.

In the nursery, where the medium is under control, the picture differs. An Indian study on apricot seedlings showed that inoculating the soil with arbuscular mycorrhizal fungi, combined with 5 mg of zinc per kilogram of soil, raised leaf zinc by 82.4 per cent and leaf manganese by 87.5 per cent relative to the uninoculated control [28]. The finding concerns seedlings in a controlled medium rather than bearing trees in the field, and does not transfer as an orchard practice.

Sources: 2 20 21 22 28

5. Quantities: what leaves with the fruit and what is applied

Piedmont publishes removal coefficients specifically for apricot: 6.0 kg nitrogen, 2.0 kg P₂O₅ and 7.0 kg K₂O per tonne of fruit, covering the fruit only [13]. The Spanish guide gives whole-tree figures, that is fruit plus leaves, branches, trunk and roots, of 5.1 kg nitrogen per tonne in total and 3.7 kg net, with 1.32 P₂O₅ and 5.68 K₂O [15]. An Italian regional document gives the two bases separately: fruit only about 0.9 nitrogen, 0.5 P₂O₅ and 3.6 K₂O per tonne, whole plant about 5.5, 1.3 and 5.3 [16].

What is constant across every source is that potassium leaves in greater quantity than nitrogen, and always in a multiple of the phosphorus. At a yield of 20 t/ha, the highest of these coefficients gives a removal of about 120 kg of nitrogen and 140 kg of K₂O per hectare.

The rates set by regulation

The French rule is a formula rather than a fixed figure: nitrogen equals 90 kg per hectare plus 1.2 kg for every tonne of expected yield per hectare, from the fourth leaf year onwards [14]. The Spanish guide uses the same structure with a lower constant term, 50 kg per hectare plus 1.2 kg per tonne [15]. The two countries agree on the variable part and disagree on the fixed one.

For the scale of the crop: according to the Annual Agricultural Statistical Survey of the Hellenic Statistical Authority for the reference year 2023, the Greek apricot area was 9,410 hectares and production was 155,600 tonnes, up 17.8 per cent on 2022 [19].

Sources: 2 12 13 14 15 16 17 19

6. Sources

The numbers in the text refer to the list below.

• [1] Ministry of Productive Reconstruction, Environment and Energy and ELGO Dimitra, Institute of Plant Breeding and Genetic Resources, Department of Deciduous Fruit Trees of Naoussa (2015). Fertilisation Manual for Deciduous Fruit Trees (in Greek). Scientific editor Dr T. Sotiropoulos. Source for the apricot sampling protocol, for the sufficiency ranges in circulation in Greece, and for the warning about potassium in Bebecou. Read in full, with the tables taken from a photograph of the printed pages, because within the file they are images.
• [2] Almaliotis, D., Velemis, D., Bladenopoulou, S. and Karapetsas, N. (2006). Apricot yield in relation to leaf nutrient levels in northern Greece. Acta Horticulturae 701:669-673. Soil Science Institute, N.AG.RE.F., Thermi, Thessaloniki. Source for the 24 orchards in Chalkidiki, the cultivar Tirynthos, the early July sampling, the rate of 200 kg N per hectare in February, the ranges and medians of the ten elements, the effect of each element on yield, the significance of potassium and calcium, and the range of soil properties. The full paper was read, with all tables.
• [3] Bergmann, W. (1988). Ernährungsstörungen bei Kulturpflanzen. Gustav Fischer Verlag, Stuttgart, 762 pp. Source for the German apricot sufficiency ranges against which the authors of the Greek study compare their measurements. The book was not obtained; the values were read as quoted verbatim in the Greek study.
• [4] Shear, C.B. and Faust, M. (1980). Nutritional ranges in deciduous tree fruits and nuts. Horticultural Reviews 2:142-163. Source for the American apricot sufficiency ranges against which the authors of the Greek study compare their measurements. The review was not obtained; the values were read as quoted verbatim in the Greek study.
• [5] Roussos, P.A., Karabi, A., Anastasiou, L., Assimakopoulou, A. and Gasparatos, D. (2023). Apricot Tree Nutrient Uptake, Fruit Quality and Phytochemical Attributes, and Soil Fertility under Organic and Integrated Management. Applied Sciences 13(4):2596. Source for the mid-July sampling protocol in Bebecou and Diamantopoulou orchards in Argolida. The full text was read; the table of per-element concentrations is an image within the page and was not read, so no concentration figure is taken from it.
• [6] Kuster, T., Eicher, O., Leumann, L., Müller, U., Poulet, J. and Rutishauser, R. (2017). Fertilisation en arboriculture, chapter 13 of the Principes de fertilisation des cultures agricoles en Suisse. Recherche Agronomique Suisse 8(6). Source for the Swiss sampling protocol at 75 to 105 days after full bloom. The full chapter was read.
• [7] Beutel, J., Uriu, K. and Lilleland, O. Leaf Analysis for California Deciduous Fruits. In: Soil and Plant Tissue Testing in California, University of California, Division of Agricultural Sciences, Bulletin 1879. Source for the July sampling of non-fruiting spur leaves and for the instruction to subtract 0.2 percentage points of nitrogen and potassium from August and September samples. Read in full.
• [8] Rettke, M.A., Pitt, T.R., Maier, N.A. and Jones, J.A. (2006). Growth and yield responses of apricot (cv. Moorpark) to soil-applied nitrogen. Australian Journal of Experimental Agriculture 46(1):115-122. Source for the six nitrogen rates, the split, the yield peak at 1,000 g per tree, the delay in maturity and the fall of topsoil pH to 4.7. The publisher's full abstract was read; the full text is behind a paywall.
• [9] Rettke, M.A., Pitt, T.R., Maier, N.A. and Jones, J.A. (2006). Quality of fresh and dried fruit of apricot (cv. Moorpark) in response to soil-applied nitrogen. Australian Journal of Experimental Agriculture 46(1):123-129. Source for the loss of firmness, the uniform ripening only at the two lowest rates, the darkening of dried fruit, the lower soluble solids at low rates, and the recommendation below 500 and ideally below 250 g per tree. The publisher's full abstract was read.
• [10] Bussi, C., Besset, J. and Girard, T. (2003). Effects of fertilizer rates and dates of application on apricot (cv. Bergeron) cropping and pitburn. Scientia Horticulturae 98(2):139-147. Source for the finding that application before or after harvest did not change yield, for the aggravation of pitburn incidence by high nitrogen, for the positive correlation with fruit nitrogen, and for the improvement in soluble solids and colouring from potassium. The publisher's abstract was read.
• [11] Montanaro, G., Tataranni, G., Mazzeo, M. and Dichio, B. (2010). Transpiration and calcium accumulation in apricot fruit. Acta Horticulturae 862:429-432. Source for the linear accumulation of calcium to 80 per cent of its final content within the first four weeks of fruit development, for the roughly 6 mg per fruit at harvest, and for the peak of fruit transpiration immediately after fruit set. The publisher's abstract was read. The work concerns apricot only.
• [12] Regione Emilia-Romagna, Direzione Generale Agricoltura, Caccia e Pesca. Disciplinari di Produzione Integrata 2024, Norme tecniche di coltura, ALBICOCCO. Source for the binding nitrogen, phosphorus and potassium rates for apricot by yield class and soil endowment, and for the timing restrictions on nitrogen. The full sheet was read and verified as identical to the 2022 edition.
• [13] Regione Piemonte. Disciplinari Produzione Integrata, Allegato I, Fertilizzazione, 2019. Source for the apricot removal coefficients of 0.6 nitrogen, 0.2 P2O5 and 0.7 K2O per 100 kg of fruit, for the statement that they cover the fruit only, and for the maximum permitted 135 kg N per hectare. The full annex was read; the conversion to kilograms per tonne is ours.
• [14] Ministere de l'Agriculture, Bureau Qualite (2024). Exportations par les productions vegetales, table de reference pour le calcul de l'item Bilan azote de la Haute Valeur Environnementale. Source for the French nitrogen formula for apricot from the fourth leaf year onwards. The full table was read.
• [15] Espada Carbo, J.L. Abonado de los frutales caducifolios, chapter 25 of the Guia Practica de la Fertilizacion Racional de los Cultivos en Espana. Source for the whole-tree removals of 5.1 and 3.7 kg nitrogen, 1.32 P2O5 and 5.68 K2O per tonne, and for the nitrogen calculation formula. The full chapter was read.
• [16] Servizio Agrometeorologico Regionale AMAP, Regione Marche. Calcolo del bilancio azotato, vite, olivo e fruttiferi. Source for the separate apricot coefficients on a fruit-only and on a fruit, wood and leaves basis. Read in full; the assignment of the two sets of coefficients to the two bases follows from the document's own explanatory note, and the conversion to kilograms per tonne is ours.
• [17] Bertschinger et al. (2003), Swiss orchard fertilisation principles. Source for the recommended rates in a mature apricot orchard at three yield levels. The original was not located; the values were read as reproduced, with a full citation, in a thesis that quotes them.
• [18] Regione Campania, Assessorato Agricoltura. Disciplinari di Produzione Integrata, Tecniche Agronomiche, 2026 update, ALBICOCCO sheet. Source for the three windows of nutrient demand within the growing season. The full sheet was read; it contains neither quantities nor leaf sufficiency ranges.
• [19] Hellenic Statistical Authority (2025). Annual Agricultural Statistical Survey, reference year 2023, press release of 26 June 2025. Source for the area of 9,410 hectares and the production of 155,600 tonnes. The full release was read; it contains no breakdown by regional unit.
• [20] Leece, D.R. and van den Ende, B. (1975). Diagnostic leaf analysis for stone fruit. 6. Apricot. Australian Journal of Experimental Agriculture and Animal Husbandry 15:123-128. Source for the Australian sufficiency ranges for apricot and for the leaf they refer to. The original was not obtained. The table of ranges was read exactly as reproduced in Table 2 of the Turkish paper [21], and the sampling protocol as explicitly described by the two Serbian papers [23] and [24], that is, mid-shoot leaves at 120 days after full bloom. The original work was carried out on the cultivar Trevatt.
• [21] Guleryuz, M., Bolat, I., Pirlak, L., Esitken, A. and Ercisli, S. (1996). Investigations on determination of nutritional status of apricot (cv. Hasanbey) grown in Erzincan. Turkish Journal of Agriculture and Forestry 20(6):479-487. Source for the window of twenty days before harvest, for the leaf nitrogen ranges in the two years, for the soil pH of 7.50 to 8.40 and organic matter of 0.77 to 3.16 per cent, and for the finding that manganese was adequate in the soil and low in the leaf. Read in full, with the tables. The main text is in Turkish, with an English abstract.
• [22] Ucgun, K., Bayav, A., Altindal, M. and Kocal, H. (2019). Seasonal variation of nutrients and nutrient ratios in apricot leaves. Ziraat Fakultesi Dergisi 14(1):1-10. Source for the series of fifteen samplings at fourteen-day intervals, for the table of macronutrients by date, for the fall in zinc and copper through the season, and for the soil conditions at Isparta. Read in full, with Tables 1 and 2. The values in the table in this article are taken verbatim from Table 1 of that paper.
• [23] Milosevic, T. and Milosevic, N. (2011). Diagnose apricot nutritional status according to foliar analysis. Plant, Soil and Environment 57(7):301-306. Source for the protocol of 120 days after full bloom on leaves from the middle of bearing shoots, and for the variation in leaf nitrogen and calcium with the interstock, in the same cultivar on the same date. Read in full, with Table 1.
• [24] Milosevic, T., Milosevic, N. and Glisic, I. (2013). Tree growth, yield, fruit quality attributes and leaf nutrient content of Roxana apricot as influenced by natural zeolite, organic and inorganic fertilisers. Scientia Horticulturae 156:131-139. Source for the finding that all eight fertilisation schemes, together with the unfertilised control, came out simultaneously with excess phosphorus and insufficiency in seven other elements when judged against the Australian ranges. The soil of that study was acidic. Read in full.
• [25] Bussi, C. and Amiot, M.J. (1998). Effects of nitrogen and potassium fertilization on the growth, yield and pitburn of apricot (cv. Bergeron). Journal of Horticultural Science and Biotechnology 73(3):387-392. Source for the three nitrogen levels and two potassium levels, for the pitburn percentages of 23, 26 and 58 per cent, for fruit nitrogen and calcium, for the correlation coefficients of 0.822 and minus 0.857, for soluble solids by treatment, and for the nitrogen by potassium interaction. Read in full, with Tables I, II and III. Some databases record the second author as M.A.L. Smith. The byline given here is the one carried by the published text itself.
• [26] Radi, M., Mahrouz, M., Jaouad, A. and Amiot, M.J. (2003). Influence of mineral fertilization (NPK) on the quality of apricot fruit (cv. Canino). The effect of the mode of nitrogen supply. Agronomie 23(8):737-745. Source for the factorial design of sixteen treatments, for the two modes of splitting nitrogen, for the fruit weight difference of 6.7 g, for the 8 per cent difference in sugars, and for the finding that the strongest interaction was nitrogen by potassium. Read in full, with Tables I to VI. The paper gives rates as kg of nitrogen, phosphorus and potassium per hectare without specifying whether phosphorus and potassium are expressed as the element or as the oxide.
• [27] Okba, S.K., Mazrou, Y., Elmenofy, H.M., Ezzat, A. and Salama, A.-M. (2021). New insights of potassium sources impacts as foliar application on Canino apricot fruit yield, fruit anatomy, quality and storability. Plants 10(6):1163. Source for the foliar application of five potassium sources at 0.2 per cent, three times per season, and for the results in yield, colouring, firmness and storage. The study was conducted in the Nubaria region of Egypt. Read in full.
• [28] Dutt, S., Sharma, S.D. and Kumar, P. (2013). Arbuscular mycorrhizas and Zn fertilization modify growth and physiological behavior of apricot (Prunus armeniaca L.). Scientia Horticulturae 155:97-104. Source for the increase in leaf zinc and manganese in apricot seedlings following inoculation with mycorrhizal fungi and zinc addition. It concerns a nursery and not a bearing orchard. Read in full.