The nitrogen cycle in sweet cherry

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

Nitrogen is the element most people think they already understand. In sweet cherry, however, it behaves in a way that overturns the logic of "base dressing": half of the nitrogen used in spring does not come from the soil at all, but from the previous season's reserves. Miss that, and the fertiliser will always go on at the wrong moment.

Units

Rates in this English edition are given per hectare. The Greek edition works in stremmata and in "units", where one unit is 1 kg of nutrient per stremma. One hectare equals 10 stremmata, so 3 units per stremma is 30 kg N per hectare.

50%of the spring nitrogen
comes from reserves

65.6%uptake of the
spring application

52.5%of the winter dressing
is lost

2.2–3.4%sufficiency range for
leaf nitrogen

Contents

What nitrogen does inside the tree
Spring: where the nitrogen really comes from
How much nitrogen sweet cherry actually needs
How much of the fertiliser is used, by season
Storage, where it goes and in what form
Autumn: the transfer from leaves to buds
The full cycle, season by season
What it means in practice for fertilisation
Nitrogen and fruit quality
Deficiency, excess and toxicity
The environmental side
Sources

1. What nitrogen does inside the tree

This article is an updated and expanded version of a piece published with Konstantinos Kazantzis, of the Department of Deciduous Fruit Trees at Naoussa, on the Farmacon platform [12]. The figures have been rechecked against the original sources, and one rate is corrected.

Nitrogen is among the most important elements for plants. The only elements present in greater abundance are oxygen, carbon and hydrogen, the elements of water and air.

Nitrogen compounds make up 50% of the dry matter of the protoplasm. Nitrogen is essential for the formation of amino acids, proteins, nucleic acids and chlorophyll.

It is taken up in nitrate or ammonium form. The ammonium form, however, is converted immediately to nitrate within the plant, because it is toxic.

Nitrate or ammonium, there is a difference Work on apple showed that fertilising with nitrate nitrogen gives stronger shoot growth and development but delays the onset of cropping. With ammonium nitrogen, shoot growth is more moderate and the tree comes into bearing normally [11]. In young plantings that are slow to crop, this is no small detail.

In sweet cherry, the sufficiency range for leaf nitrogen is 2.2 to 3.4%, depending on the cultivar and the rootstock [10].

2. Spring: where the nitrogen really comes from

This is the critical point, and the most misunderstood one in stone fruit fertilisation.

In apricot, sweet cherry, peach and plum, soil nitrogen and the other soil elements are not available at flowering. They become available only once sufficient leaf area has developed, so that transpiration provides the energy that draws the nutrients out of the soil solution.

Indeed, three weeks after flowering, nitrogen uptake from the soil is already declining [4].

Why stored nitrogen matters in the tree 50% of the nitrogen used in spring comes from stored nitrogen, and only the remaining 50% from the soil [2]. In effect, half the bloom and half the first flush of growth were already decided the previous September. Whatever goes on in March is too late to correct empty reserves.

Sources: 2 4

3. How much nitrogen sweet cherry actually needs

Everything above answers when. How much went unanswered for years, because the decision rested on leaf analysis and critical values, that is on an indicator of status rather than a measurement of demand. A University of California research project completed in 2023 produced the first nitrogen budget for sweet cherry, measured by excavating and fully analysing whole trees [14].

Demand splits in two. The first part is the nitrogen that leaves with the fruit and never returns. The second is the nitrogen locked permanently into perennial wood as the tree grows each year.

Cultivar	Nitrogen removed with the fruit, kg per tonne	Nitrogen for the annual growth of perennial wood, kg per hectare
Rainier	2.74	32.5
Coral	2.73	31.8
Bing	2.32	30.8
Weighted average	2.59	31.7

The source gives pounds of nitrogen per 1,000 pounds of fresh fruit and pounds per acre. The first column is a mass ratio and does not change on conversion, 2.59 lb per 1,000 lb equals 2.59 kg per tonne. The second was converted with a factor of 1.121 from pounds per acre to kilograms per hectare [14].

The figure in the first column can be put another way, which makes it easier to use. Fresh sweet cherry fruit contains about 0.26% nitrogen by weight. Because this is a composition of the fruit itself and not a property of the planting, it is also the figure that transfers most safely to other conditions.

The arithmetic for one hectare

A yield of 15 tonnes per hectare.

With the fruit: 15 × 2.59 = 39 kg N per hectare

Into perennial wood: 32 kg N per hectare

Total demand: about 71 kg N per hectare

The demand of the tree is not the fertiliser rate

Those 71 kilograms are what the tree needs, not what is applied. Between the two sit use efficiency, given in section 11 as 40 to 50% [9], the nitrogen the soil already supplies through mineralisation of organic matter, and the nitrogen in the irrigation water where that applies.

The arithmetic 71 ÷ 0.45 gives an order of magnitude of around 160 kg N per hectare before the other sources are subtracted. This calculation is ours and combines two independent pieces of work. Neither of them makes it, and the 40 to 50% efficiency was not measured on sweet cherry. It is given as a yardstick against what is applied in practice, not as a rate recommendation.

Diagram of cumulative annual nitrogen uptake in sweet cherry against days from full bloom, with four milestones and the eight weeks after harvest limit marked — Figure 1. The course of uptake through the season. The shape of the curve is what matters, not the dates: uptake starts with leaf-out, peaks in the rapid phase and is essentially over before leaf fall. Figure drawn by us from the data of the source [14].

The same work describes the timing. Uptake begins once leaf-out reaches 50% and ends at the onset of leaf senescence. Root uptake starts 20 to 30 days after full bloom, the rapid phase lasts about four months, and up to 90% of the annual uptake is complete before the end of summer [14]. From December to February canopy nitrogen stays level or falls, most likely through translocation to perennial organs [14], which agrees with what section 7 describes.

Two published statements that do not agree

Section 2 reports, on the authority of a Michigan doctoral thesis on dwarfing rootstocks, that three weeks after bloom nitrogen uptake from the soil is already reduced [4]. The Californian work, on trees on Mazzard, places the start of root uptake at exactly that point [14].

The two statements cannot be read as descriptions of the same thing. The first measures what is left of a labelled spring fertiliser, the second the total accumulation of nitrogen in the tree. What follows from both is that in the first three weeks after bloom the soil contributes almost nothing. The disagreement concerns what happens immediately afterwards, and the published work does not settle it.

Where the figures were measured and which of them transfer

Three 15-year-old commercial orchards in the San Joaquin Valley, California, cultivars Bing, Coral and Rainier on Mazzard rootstock, at a density of about 300 trees per hectare [14].

What transfers is the coefficient of 2.59 kilograms per tonne of fruit, because it is a composition of the fruit and not a property of the planting. The sequence of stages on the curve transfers too, because it is phenological rather than calendar-based.

What does not transfer is the figure of 31.7 kilograms per hectare for perennial wood. It depends on density, rootstock, age and training system. A planting on Gisela at 800 to 1,200 trees per hectare has an entirely different distribution of perennial biomass from 300 trees on Mazzard, and no corresponding Greek measurement was found published. The figure is given as an order of magnitude and not as a value for a Greek orchard.

Sources: 9 14 15

4. How much of the fertiliser is used, by season

With isotopically labelled nitrogen it is possible to measure how much of the fertiliser actually ended up in the tree. The results in sweet cherry are instructive.

Timing of application	What the measurements show
Spring	The highest uptake: 65.6%
Summer	Uptake of only 37.44%, but see the box below
Winter	52.5% is lost with the crop and with summer pruning [3]

Why the "lower percentage" does not mean lower value Less of the summer application is taken up, but the nitrogen that is taken up goes where it is needed: into the buds and the older wood, as a reserve for the following season. By contrast, much of the spring nitrogen leaves with the fruit. That is precisely why the literature highlights the importance of the post-harvest application [3]. The subject is developed in detail in the article on post-harvest nutrition in stone fruit.

Sources: 3

5. Storage, where it goes and in what form

Providing for the following season, trees store nitrogen in the flower and leaf buds, in the older wood and in the roots. Storage is in the form of proteins or amino acids.

Two different stores Nitrogen storage is one thing and storage of non-structural carbohydrates is another. The second takes place mainly in the older wood of the trunk and in the roots. Both are equally necessary for a proper start the following season [8]. A tree can have nitrogen and lack carbohydrates, or the reverse, and in either case the spring will be poor.

6. Autumn: the transfer from leaves to buds

What happens in autumn is a redistribution, not an uptake. The tree empties its leaves and fills its buds.

Measurements show a 27% rise in nitrogen concentration in the flower buds, in the spurs, and in the shoot buds, while at the same time a fall of 39 to 49% is recorded in the leaves [1].

The practical consequence The canopy must be kept alive as late into the autumn as possible. Every leaf that falls prematurely, from cherry leaf spot, from spider mite, from drought or from irrigation cut off too early, goes with its nitrogen still in it. There is no time for that nitrogen to return to the buds.

Sources: 1

7. The full cycle, season by season

Period	Where the nitrogen moves	What it means in the orchard
Flowering	Entirely from the reserves. The soil does not contribute yet, because the leaf area is missing	Fertiliser at this moment is too late
Spring	From the soil into the leaves, for amino acids, proteins and nucleic acids. At the same time into the buds and the new growth	The application is used most efficiently (65.6%), but much of it leaves with the fruit
Summer, after harvest	Storage begins gradually, into the new dormant buds and the older wood	The most underrated window. This is where the next season is built
September	The process peaks. The leaves are all but drained of their remaining nitrogen	The canopy must be healthy. Early defoliation means nitrogen lost
Spring of the following season	The stored nitrogen is remobilised for flowering and the new growth	The cycle closes. What was stored is now spent

8. What it means in practice for fertilisation

A single nitrogen application as a base dressing cannot meet the storage requirement, for two reasons:

A large part of the nitrogen will be removed with the crop and another part will be leached.
Surplus nitrogen will reduce the firmness of the flesh.

The recommended approach is therefore to split it in two:

Soil application after harvest

30 kg of nitrogen per hectare, 15 days after harvest, and only where soil analysis does not show surplus nitrogen already present.

In practical terms, 30 kg N per hectare corresponds to about 88 kg/ha of ammonium nitrate 34-0-0, or about 143 kg/ha of ammonium sulphate 21-0-0. The figures are indicative; the final rate is set after soil analysis and an on-site assessment by an agronomist.

Autumn foliar sprays with urea

Two applications. In the Michigan study they are placed in September and October; the phenological equivalent, which is the transferable one, is after harvest and before natural leaf fall, while the canopy is still active. In northern Greece that window falls later than in Michigan and is set by the condition of the canopy, not by the month.

What the autumn urea delivers

A higher concentration of stored nitrogen for the following season.
An increase of 4.25 °C in the cold hardiness of the buds [1] [5]. In a late spring frost, that is the difference between having a crop and not having one.
Work in Romania showed a 24% rise in the nitrogen content of the buds, giving greater productive leaf area per bud, better carbohydrate production and larger fruit.
In the same work, two urea applications raised yield from 7,440 to 10,780 kg per hectare [6], an increase of about 45%.

Caution with the foliar spray A foliar spray with urea, like any foliar application, can cause scorch on the foliage and marking on the fruit if fruit is still on the tree. A prior test on a limited number of trees is required, with the same product and the same rate, and a wait of 5 to 7 days before the general application. The spray is applied in the late afternoon or early in the morning, never in a heatwave and never onto foliage under water stress. Plant protection products and fertilisers are used according to the label and the approvals in force in the country concerned [13].

Sources: 1 5 6 13

9. Nitrogen and fruit quality

Here nitrogen turns against the grower, if it is overdone.

Applications of large quantities of nitrogen before harvest significantly raise the nitrogen concentration in the fruit. Those fruit, however, had:

a shorter shelf life in cold storage, and
lower flesh firmness [7].

Nitrogen use in spring calls for real care, so that fruit quality is not compromised.

The nitrogen dilemma The same kilogram of nitrogen, applied in spring, gives more growth but a softer cherry that does not hold up in cold storage. Applied after harvest, it does nothing to this year's quality and builds next year's crop. The question is not "how much nitrogen" but "when".

10. Deficiency, excess and toxicity

Cultivated soils in Greece are generally poor in nitrogen. In the trees, however, elevated levels are often found, because of indiscriminate use of nitrogen fertilisers, which is why deficiencies rarely appear.

Condition	How it shows
Deficiency	Stunted growth. Annual shoots short and thin. Reduced yield. Fruit small and intensely red. Leaves small and pale green, turning reddish at the end of the growing season [9]
Slight deficiency	Paradoxically pushes trees to form a large number of fruiting structures, with heavy bloom and set [9]
Excess	Lush growth that stays soft. Leaves dark green. Fruit watery, with poor organoleptic quality. Reduced defences in the tree and favourable conditions for pests and diseases. Fruit with reduced tolerance of transport and storage [9]
Toxicity	Not caused by excess nitrogen. Although the ammonium form is toxic, trees convert it to nitrate immediately after uptake and re-form it as ammonium when they need it [9]

The slight deficiency that gives more flowers This is one of the most counter-intuitive points in fruit growing. A tree under slight nitrogen shortage stops building growth and turns to reproduction. An over-fertilised tree makes wood. This is not a recommendation to starve trees, it is the explanation for why the neighbour who did not fertilise this year has more flowers.

Sources: 9

11. The environmental side

Nitrogen is a highly mobile element in the soil. It leaches readily, especially on sandy soils, and is also subject to denitrification and volatilisation.

The figure that ought to be uncomfortable Only 40 to 50% of the nitrogen applied is used by the crop. The rest is lost. Which is to say, more than half of the fertiliser that is paid for never reaches the tree. That is an economic problem and an environmental one at the same time.

Nitrogen fertilisers, and nitrates in particular because they are readily water-soluble, are responsible for most water pollution, groundwater above all. Judicious use is therefore required [9].

The points to take away

Half the spring nitrogen comes from the reserves. Flowering is fed by last year, not by this year's fertiliser.
At flowering the tree cannot take nitrogen from the soil, because it has no canopy yet to draw it up.
A single base dressing is not enough, the nitrogen leaves with the crop and with leaching.
30 kg N per hectare 15 days after harvest, where soil analysis allows it.
Autumn foliar urea at 3.5%, two applications, September and October, with a prior test.
Keep the canopy alive late. Every leaf that falls early takes its nitrogen with it.
Too much nitrogen in spring means a soft cherry that does not hold up in cold storage.

12. Sources

The numbers in the text refer to the list below.

[1] Ouzounis, T. and Lang, G.A. (2011). Foliar applications of urea affect nitrogen reserves and cold acclimation of sweet cherries (Prunus avium L.) on dwarfing rootstocks. HortScience 46(7): 1015–1021. Source for the autumn foliar urea rate of 3.5%, for the 27% rise in nitrogen concentration in the flower and shoot buds, for the fall of 39 to 49% in the leaves, and for the improvement of 4.25 °C in bud cold hardiness.
[2] Grassi, G., Millard, P., Wendler, R., Minotta, G. and Tagliavini, M. (2002). Measurement of xylem sap amino acid concentrations in conjunction with whole tree transpiration estimates spring N remobilization by cherry (Prunus avium L.) trees. Plant, Cell and Environment 25: 1689–1699. The foundational source for this article: 50% of the nitrogen used in spring comes from the reserves and the remaining 50% from the soil.
[3] San-Martino, L., Sozzi, G.O., San-Martino, S. and Lavado, R.S. (2010). Isotopically-labelled nitrogen uptake and partitioning in sweet cherry as influenced by timing of fertilizer application. Scientia Horticulturae 126(1): 42–49. Source for the uptake percentages by season: 65.6% for the spring application, 37.44% for the summer one, and a loss of 52.5% of the winter dressing with the crop and with summer pruning. Documents the importance of the post-harvest application.
[4] Zavaloni, C. (2004). Evaluation of nitrogen-fertilizer uptake, nitrogen-use and water-use efficiency in sweet cherry (Prunus avium L.) on dwarfing and standard rootstocks. PhD thesis, Michigan State University. Source for the finding that three weeks after flowering nitrogen uptake from the soil is already declining.
[5] Ayala, M., Bañados, P., Thielemann, M. and Toro, R. (2014). Distribution and recycling of canopy nitrogen storage reserves in sweet cherry (Prunus avium) fruiting branches following 15N-urea foliar applications after harvest. Ciencia e Investigación Agraria 41(1): 71–80. Source for the distribution and recycling of nitrogen reserves in fruiting branches after post-harvest foliar urea applications.
[6] Mitre, I., Mitre, V., Setras, A. and Setras, R. (2012). Effects of fall applications of urea in order to improve fruit sizes, weight and buds cold hardiness in sweet cherry. Bulletin UASVM Horticulture 69. Source for the 24% rise in bud nitrogen content and for the increase in yield from 7,440 to 10,780 kg per hectare with two urea applications.
[7] Swarts, N.D., Mertes, E. and Close, D.C. (2017). Role of nitrogen fertigation in sweet cherry fruit quality and consumer perception of quality: at- and postharvest. Acta Horticulturae 1161. Source for the finding that large pre-harvest quantities of nitrogen give fruit with shorter shelf life in cold storage and lower flesh firmness.
[8] Cheng, L., Ma, F. and Ranwala, D. (2004). Nitrogen storage and its interaction with carbohydrates of young apple trees in response to nitrogen supply. Tree Physiology 24: 91–98. Source for the distinction between nitrogen storage and storage of non-structural carbohydrates, and for the role of both in a proper start to the following season.
[9] Chatzicharisis, I. and Kazantzis, K. (2014). The sweet cherry and its cultivation. AgroTypos, 442 pages. In Greek. Source for the symptoms of nitrogen deficiency and excess, for the absence of toxicity, and for the point on nitrate pollution of groundwater.
[10] Stylianidis, D., Simonis, A. and Syrgiannidis, G. (2002). Nutrition and Fertilisation of Deciduous Fruit Trees, pp. 110–115. Stamoulis Publications. In Greek. Source for the sufficiency range of leaf nitrogen in sweet cherry, 2.2 to 3.4% depending on cultivar and rootstock.
[11] Manolakis, E. (1976). Die Wirkung gleichmässiger und jahreszeitlich abwechselnder Ammonium- und Nitraternährung auf Apfelbäume. PhD thesis, TU Berlin, FB15. Source for the differing effects of nitrate and ammonium nitrogen on growth and on the time of entry into bearing.
[12] Pastopoulos, S. and Kazantzis, K. (2018). The nitrogen cycle in sweet cherry (Prunus avium L.). Farmacon, Technical Articles, Nutrition and Fertilisation. In Greek. The original text on which this article is based, with the full reference list and the diagrams of the nitrogen cycle. See also Taiz, L., Zeiger, E., Møller, I.M. and Murphy, A. Plant Physiology and Development, 6th edition, pp. 385–411.
[13] Greek Ministry of Rural Development and Food, database of approved plant protection products. The only authoritative source for what is permitted on each crop in Greece. In Greek, and valid in Greece only.
[14] Brown, P., Amaral, D. and Camargo, R. (2023). Development of Nutrient Budget and Nutrient Demand Model for Nitrogen Management in Cherry. Final report, Fertilizer Research and Education Program, California Department of Food and Agriculture, project 19-0954, University of California Davis. Source for the nitrogen removal coefficients with the fruit by cultivar, for the nitrogen of the annual growth of perennial wood, for uptake beginning at 50% leaf-out, for root uptake beginning 20 to 30 days after full bloom, for 90% of the annual uptake by the end of summer, for canopy nitrogen staying level or falling from December to February, and for the recommendation that no soil application be made later than eight weeks after harvest. Full text.
[15] Optimising nitrogen management in cherry trees: new approaches to maximise yield according to the University of California. Cherry Times, 25 January 2024. Trade press that presented the results of the above project. Every figure was checked against the final report and not against this text.

Disclaimer This text is informational and educational in character. It does not replace an on-site agronomic assessment and does not constitute a prescription for the application of fertilisers or plant protection products. The rates given are indicative and are not a recommendation for application; the final rate is set after soil and leaf analysis and an on-site assessment by a licensed agronomist. Any foliar spray on trees still carrying fruit requires a prior test on a limited number of trees, with the same product and the same rate, and a wait of 5 to 7 days before the general application. The plant protection approvals referred to here are issued by the Greek Ministry of Rural Development and Food and are valid in Greece only; they do not apply in other countries. Label instructions and national approvals always take precedence. Pastopoulos Agronomics accepts no liability whatsoever for the use of the information above.