Strawberry Fertilizer

5.1 Nutrients uptake and removal

Strawberry Flower - Haifa Fertilization Program

The purpose of fertilizing any agricultural crop is to supply it with all the nutrients needed for the normal development of the plants. For this, naturally, one needs to know the amounts of nutrients that the plant needs, in order to:

grow the vegetative mass,
maintain plants' current activity, and
build up the fruit mass that will eventually be removed from the field. In cases where the field serves multiple crops, growers indicate a minimal amount to be returned to the field, in order to compensate the field for the fertility that was used for the production of the exported fruit.

These crucial data are summarized in the following table.

Table 5.1: Uptake and removal of macro-nutrients by open-field or protected strawberry crop

Sources: La Malfa, 1992, and Haifa NutriNet™

		N	P₂O₅	K₂O	CaO	MgO
Removal (kg/MT fruits)		6 – 10	2.5 – 4.0	10 – 15	3.7-4.9	1.1
Yield level	Uptake & removal by yield levels (kg/ha)
8 MT/ha	Plants uptake	49	21	83	29	6
	Yield removal	15	5	26	9	2
	Total recommended application rate	59	68	108	15	6
16 MT/ha	Plants uptake	81	34	138	48	9
	Yield removal	30	10	51	18	3
	Total recommended application rate	97	83	179	24	9
25 MT/ha	Plants uptake	118	48	200	68	13
	Yield removal	47	15	80	27	5
	Total recommended application rate	142	100	260	34	13
30 MT/ha	Plants uptake	129	51	218	75	14
	Yield removal	57	18	96	33	6
	Total recommended application rate	155	104	283	38	14
35 MT/ha	Plants uptake	147	59	250	85	16
	Yield removal	66	21	112	38	7
	Total recommended application rate	176	113	325	43	16

Factors to be taken into account for efficient application:

Strawberries' root system is rather shallow with ~70 % in the upper 7 cm (3") of the soil, and even shallower, just below the surface in mulched crops.
The plant suffers from EC level higher than 2 dS/m and from brackish water and/ or soil.
Floral bud differentiation, which determine the yield, occurs early and depends on the nutrient reserves of the plant
Nutrient absorption is at its maximum during flowering.

5.2 Fertilization methods

Commercial cultivation of strawberries normally takes one of the following fertilization schemes:

Base dressing + a few side dressings throughout the growth cycle of the crop. This method is common among growers who are not equipped with a nutrigation (fertigation) setup.
Base dressing + many side-dressing sessions throughout the growth cycle of the crop. "Many" can take the form of once weekly, once daily, or even- many daily applications, carried out by nutrigation (fertigation).
Usage of controlled release fertilizers. Special paragraph 6.2 of this publication is devoted to this advanced method.
A combination of the above-mentioned methods, according to the grower's capability and preferences.
Foliar feeding. This method serves normally as a complementary treatment to assist the application when encountering problems of soil uptake, and when fast correction results are needed.

5.2.1 Soil preparation and base dressing

Soil preparation should start 4–5 months before planting. So, for an autumn- planting of fresh runners, soil preparation that will include tilling, fumigation and weed control, should start by early summer.

Organic matter

As strawberries respond well to high organic matter in the soil, one or more of the following options is recommended:

Well-composted animal manure such as poultry manure, applied at 8–10 MT/ha, several weeks before sowing of most green-manure crops.
Sowing of green-manure crops, several months before planting. Green-manure crops like cowpeas, oats and forage sorghum can be grown for 2–4 months and incorporated into the soil before they mature. Sufficient time must be allowed for the crop to completely break down in the soil before fumigation and bed formation takes place.

Well-composted manure is advocated, while application of fresh manures such as fresh horse-, cow- or chicken- manure, just before planting, must be avoided, as these can burn and damage the delicate strawberry plants.

pH amendment

If the soil pH is below pH 6.0 apply either agricultural lime or dolomite at least 6 months before planting. Dolomite is best used if soil magnesium is low. The lower the pH value, the higher the rate of lime or dolomite that should be applied. The rate also depends on the planned life-span of the crop. About 5 MT/ha (2 ST/A) of ground limestone per expected year, will keep the soil at a relatively stable pH.

The lime or dolomite should be worked into the soil to a depth of 30 cm, which is the effective root region of strawberries.

Fertility

It is best to apply and incorporate all major nutrients into the soil, to ensure that young transplants will encounter a good mineral background for their establishment phase. It is preferable to apply the potassium and the phosphorus as low-solubility formulae such as potassium sulfate and triple-superphosphate, respectively, to support the plants throughout their growth cycle. The composition of this application may be as follows:

N	P₂O₅	K₂O	CaO	MgO
(kg / ha)
150	150	240	120	60

Additionally, it is best to apply a small dose of N-P-K soluble fertilizer, a week or two before transplanting. Its N-P-K ratio should be 1-2-1 or 1-3-1, such as 5-10-5 or 8-24-8. It should be worked into the upper 8 cm to 20 cm (3 inches to 8 inches) of the soil, at a rate of 120 kg / ha (110 pounds / acre).

When soil zinc level is low, applications of zinc sulfate at 17 to 22 kg / ha (15 to 20 pounds / acre) prior to planting are recommended.

Table 5.2: Desirable pre-plant pH, organic matter, and soil fertility for strawberries, strawberry ph

Soil parameter	Optimal values
pH	5.8 to 6.5
Organic matter	2% to 3%
Phosphorus	67 – 90 (available kg / ha)	60 – 80 (available pounds / A)
Potassium	315 – 360 (exchangeable kg / ha)	280 to 320 (exchangeable pounds / A)
Magnesium	280 (exchangeable kg / ha)	250 (exchangeable pounds / A)
Zinc	11.2 – 13.5 (available kg / ha)	10 – 12 (available pounds / A)
Boron	1.7 – 2.25 (available kg / ha)	1.5 – 2.0 (available pounds / A)

5.2.2 Side dressings in open-fields

It is beneficial to apply fertilizers by multiple sessions during the life-cycle of a strawberry field, especially on lighter soils (that tend to leach nitrogen more easily than medium and heavier soil), as follows:

Table 5.3: Side / top dressings for open-field strawberries

Plant type	Timing	Product	Rate
Kg / ha	Pounds / Acre
All	Early spring, just before planting	8-24-8	120	110
All	Spring, 4 to 6 weeks after planting	20-20-20	80	70
All	Early August	20-20-20	60	54
Day-neutral and everbearing	After first harvest	20-20-20	60	54
June-bearing	Field renewal when plants are completely dry	20-20-20	60	54

Sufficient watering should be applied after each topdressing session to bring the fertilizer to the roots of the growing plants.

Hence, maximum annual application of 40 kg / ha of N for June-bearers and a maximum annual application of 80 kg / ha N for ever-bearers should be observed if applied as a base or top dressing.

Table 5.4: Recommendation for soil-solution composition of main nutrients, at peak demand, for field-grown strawberries in Israel

	Nitrogen	Phosphorus	Potassium
Application rate	1.5 to 2.5 kg / ha / day
Soil solution	Nitrate-N: 20 to 30 ppm at all times	P kept at 20 to 30 ppm (Olsen)	K kept at 1 to 2 meq / liter

With a plant density of 35,000 plants / ha, and an expected yield of 35 to 40 MT / ha, the recommended rate of nutrients for outdoor grown strawberries are as follows:

N	P₂O₅	K₂O
(kg / ha)
150 to 200	110 to 130	230 to 250

5.2.3 Nutrigation™ (fertigation) in open fields

This is an effective way to apply fertilizers to already established plants. The technique supplies soluble fertilizers to crops through the irrigation system, whether they are under the plastic mulch in the field, or in tunnels or greenhouses, using soil or soilless cultivation methods.

Strawberry Nutrigation™ (fertigation) in open fields

The use of compensated, no-leak drip irrigation allows for highly accurate application of both water and plant nutrients directly to the plants' root zone. This allows for precise feeding of the plants, according to their specific growth stage, and as a preparation for forecast stresses, or as a quick correction of plant nutrient imbalance during both the growing and fruiting stage of the plant.

To take advantage of this method, the fertilizers should be dissolved in high-quality irrigation water. Avoid using water with high carbonate levels (hard water), which may react with soluble fertilizers high in phosphate, sulfate, or calcium that can cause precipitation and block drippers. A soluble fertilizer mix is best applied after plants are established and at different intervals, as detailed above. The nutrigation mix needs to change depending on crop need and seasonal conditions. It is best to start injecting the dissolved fertilizer stock solution after about 20% of the irrigation water has been delivered, and complete the injection session after about 80% of the irrigation water has been delivered, to assist the movement of nutrients down into the roots zone.

Apply at least 0.5 to 1 liter of irrigation water per plant, depending on soil type. Some of the more common soluble fertilizers used in strawberries are shown in Table 5.5. Some can be in combination with others with no restriction, but care should be taken to never mix phosphate- or sulfatic fertilizers with calcium fertilizers in the same dissolving tank. Separating them between two dissolving tanks prevents the precipitation of calcium phosphate or calcium sulfate, in the tank or in the pipeline. Figure 5.1 describes a common method to safely prepare fertilizer combinations.

Table 5.5: Some common fertilizers used in nutrigation, their solubility, nutrient content, and soil reaction

Product	Analysis	Solubility(g / L) at 20⁰C	Reaction
Urea	46% N	1,070	Neutral

Ammonium nitrate	34% N	1,952	Acidic
Ammonium sulfate	21% N + 24% S	754	Acidic
Mono-ammonium phosphate (MAP)	12.5% N + 61% P2O5	370	Acidic
Phosphoric acid	61% P2O5	Already liquid	Very acidic
Mono-potassium phosphate (MKP)	52% P2O5 + 34% K2O	230	Acidic
Potassium nitrate	13% N + 46% K2O	320	Basic
Potassium sulfate	40% K2O + 16% S	110	Neutral
Calcium nitrate	15.5% N + 26% CaO	1,200	Basic
Magnesium nitrate	11% N + 16% MgO	2,250	Slightly acidic

Other soluble fertilizers include zinc sulfate, iron chelate, boric acid, manganese sulfate, and sodium molybdate. These trace elements are best applied if soil or leaf analysis indicates a need for them, or when plants show field deficiency symptoms.

Figure 5.1: Recommended combinations of fertilizers to be dissolved in Tank A and Tank B for the preparation of stock solutions

When a heavy pre-plant fertilization is applied, such as:

Nitrogen at 100 kg / ha
Phosphorus at 100 kg / ha of P₂O₅
Potassium at 200 kg / ha of K₂O

It is enough to leave for the side-dressing applications by nutrigation, a rate of 50 to 100 kg / ha of nitrogen + 50–100 kg / ha of K₂O.

It has been found that for the 'Chandler' cultivar grown under plastic mulch on sandy soils, nitrogen at about 135 kg / ha is optimum for reduced vegetative growth and firmer fruit without compromising marketable yield.

The optimum N rate varies among soils, and may be even lower for heavier-textured soils. The recommended rate for K2O under these conditions is 135 kg / ha.

Table 5.6: Recommended N-P-K-Ca-Mg concentrations in nutrigation water during strawberries' main growth stages in the field

Source: Abdal-Razak, Israel, 2004

Dates	Growth stage	N	P	K	Ca	Mg
(mg / L = ppm)
Oct. to Jan. 10	Establishment and vegetative growth	30 – 50	20 – 25	45 – 60	40 – 50	40 – 45
Jan. 11 to Jan. 15	1^st wave fruit-set	70 – 85		60 – 80	70 – 90
Jan. 16 to Feb. 28	1^st wave fruit growth	80 – 85			80 – 90
March 1 to Apr. 15	2^nd – 3^rd waves fruit-set & fruit growth	80 – 85			80 – 90
March 16 to end of May	4^th wave fruit-set & fruit growth	55 – 60		55 – 60	70 – 80

As a result of the A/M application rates, the desirable N, P, and K levels in sampled soil solutions should be the following:

Nitrate-N: 20 to 30 ppm; P: 20 to 30 ppm (Olsen); K: 40 to 80 ppm.

5.2.4 Nutrigation™ (fertigation) in soilless culture

Table 5.7: Suggested nutrient composition for a two-stage growth cycle of cv. Elsanta*.

Source: Atwood et al, 2005, and Fennimore et al, UC Davis

Nutrient	Starter (mg/L)	Fruiting (mg/L)
NH₄-N	14	14
NO₃-N	100	120
P	46	46
K	175	250
Ca	140	125
Mg	20	30
Fe	1.5	1.5
Mn	0.8	0.8
Zn	0.5	0.5
B	0.15	0.15
Cu	0.05	0.15
Mo	0.05	0.05

* Cultivars like: Diamante, Jubilee, andEverest can tolerate somewhat higher nutrient concentrations

Nutrient irrigation-water conductivity

Starter: 1.0 -1.6 dS / m, but increase rapidly on overwintered crops
Fruiting: ~ 1.8 dS / m in normal conditions; 1.6 dS / m in hot / dry conditions; 2.0 dS / m in damp, overcast conditions.
Ever-bearers can go over 2.0 dS / m
Run-off should be up to 0.2 dS / m above the irrigation water

Table 5.8: Recommended macro- and secondary nutrient solution composition by growth phase in greenhouse soilless culture of strawberries in Israel

Growth phase
	Mg / L (ppm)
Transplanting	55 – 60	20– 25	45 – 60	60 – 70	35 – 40	35
Anthesis** & 1^st wave of fruits	70 – 85	20 – 25	70 – 90	100	45	50
2^nd wave of fruits	80 – 85	25 – 30	80 – 90	100	45	55
3^rd wave of fruits	80 – 85	25 – 30	80 – 90	100	45	55
4^th wave of fruits	55 – 60	20 – 25	55 – 60	80	35	50

* The ratio Nitrate-N / ammonium N should be in the range of 7 to 11 throughout the growth cycle.

** Flower opening

Fe	B	Mn	Zn	Cu	Mo
mg / L (ppm)
2.8	0.6	0.4	0.2	0.1	0.03

Final irrigation water parameters

pH: ~ 6.0 to 6.2

EC: ~ 1.4 to 1.6 dS / m

Crops grown in soilless substrates and intensively nutrigated require regular monitoring of irrigation and nutrition. It is advisable to monitor the levels of feed being applied to the substrates as well as those draining through the system. Such monitoring should be used in conjunction with foliar analysis, to avoid excessive use of nutrient feeds and drainage of high concentration feeds into the soil beneath the bags, troughs, or other containers into which the crop has been planted.

Table 5.10: Liquid feed schemes for peat-bag and soil-grown strawberries in the UK. Source: Strawberry Production Under Protection, supplies for small-holders

Crop stage	N	P₂O₅	K₂O	MgO	EC (dS / m)
(mg / L)
Bud break to flowering (peat)	120	100	200	25	1.6 – 1.8
Flowering to end of harvest (peat)	120	100	300	30	1.8 – 2.0
Soil grown	120	60	240	20	1.4 – 1.6

Table 5.11: Recommended nutrient composition of soilless-grown strawberries in Poland

Developmental phase	N	P₂O₅	K₂O	MgO
(mg / L)
Vigorous growth	120	66	150	25
Fruiting phase	100	50	200	30

Table 5.12: Recommended nutrient concentrations in the irrigation water of soilless-grown strawberries, in their fruiting phase, in South Korea

Parameter	Value
NO₃	1.9 m mol/L	118 ppm
NH₄⁺	0.1 m mol/L	2 ppm
P	0.40 m mol/L	12 ppm
K⁺	0.7 m mol/L	27 ppm
Ca²⁺	0.9 m mol/L	36 ppm
Mg²⁺	0.6 m mol/L	15 ppm
SO₄^2-	0.5 m mol/L	48 ppm
HCO₃^-	<0.2 m mol/L	<12 ppm
Si⁴⁺	0.30 m mol/L	8 ppm
Fe	5.8 μ mol/L	0.32 ppm
Mn	0.7 μ mol/L	0.04 ppm
Zn	0.3 μ mol/L	0.02 ppm
B	23 μ mol/L	0.25 ppm
Cu	<0.2 μ mol/L	<0.01 ppm
Mo	<0.2 μ mol/L	<0.02 ppm
Cl^-	<0.2 m mol/L	<7 ppm
Na⁺	<0.8 m mol/L	<18 ppm
pH	5.6
EC	0.5 dS/m

Crops grown in soilless substrates and intensively nutrigated require regular monitoring of irrigation and nutrition. It is advisable to monitor the nutrient levels being applied to the substrates, as well as those draining through the system. Such monitoring should be used to determine the need for foliar feeding, to avoid excessive use of nutrient feeds and drainage of high concentration feeds into the soil beneath the bags, troughs, or other containers into which the crop has been planted.

5.2.5 Soluble compound fertilizers

Many fertilizer companies sell ready-to-use N-P-K blends in a variety of nutrient combinations and ratios that comply with the ratios needed by strawberry growers.

Compound fertilizers for nutrigation are generally composed of a mixture of solid products, mostly in crystalline form, containing any of the above mentioned N-P-K products, with or without soluble magnesium, and with or without micronutrients. They are generally physical blends, in which care has been taken to avoid interactions that would result in precipitation, caking, and to secure full solubility, free flow and high concentration of the nutrients. It is very important that no cheap components, such as potassium chloride, are included, to avoid salinity effects, as elaborated upon in Chapter 3, Salinity. It is the growers' responsibility to make sure they get high-quality components only.

Based on their N / P/ K ratios, there are several main families of products:

The 1-1-1 group, such as 18-18-18; 19-19-19 and 20-20-20. The fertilizers belonging to this group are considered the formula for crop growth and vegetative development.
The 2-1-1 group, such as 24-12-12 has a higher proportion of nitrogen, yet is easier to produce and the price per nutrient unit is somewhat lower.
The "V" type fertilizers are formulae supplying the best nutrient ratios for flowering and fruit-set phenological growth stages. Characteristic examples for these NPKs are 2-1-2; 3-1-3 and 4-1-4, e.g., 20-9-20; 24-8-24.
In situations of high potash requirements at the maturation stages of crops rich in sugar or oil, formulae of 10-5-35, or 16-8-24 are common.
The "^" type fertilizers, e.g., 1-2-1 or 1-3-1, such as 15-30-15 or 10-30-10, are rich in phosphorus, and are used for the early stages of seed and transplant establishment, after planting.

Haifa produces and markets a large variety of N-P-K fertilizers complying with "Nutrigation™ grade" and "Greenhouse grade" standards. (The latter is more demanding in terms of purity, solubility, and reduced insoluble matter rates.) The products included in these groups are highly soluble, low in insoluble ingredients, practically free of deleterious ingredients, such as chloride, sodium, heavy metals, and perchlorates. Some of these products are enriched with magnesium, and some with organic compounds to satisfy specific requirements put forward by growers worldwide.

Haifa's compound products, specially developed for nutrigation of fruit trees and open-field vegetables, are grouped under the Poly-Feed™ Drip line.

Poly-Feed™ Drip formulae are enriched with magnesium and micronutrients. The wide range of products enable complete plant nutrition scheme, throughout the growth cycle. Poly-Feed™ Drip is easily identified by the light-blue color of both the bag and the product.

The advantages of Poly-Feed™ Drip

♦ Fully water soluble.

♦ Made of high quality ingredients, exclusively.

♦ Consists of 100% plant nutrients.

♦ Virtually free of chloride, sodium and other detrimental elements for plants.

♦ Provides balanced, complete plant nutrition.

♦ Available in a wide range of formulae.

Micronutrients included in Poly-Feed™ Drip^™ formulae: 1000 ppm iron (Fe), 500 ppm manganese (Mn), 200 ppm boron (B), 150 ppm zinc (Zn), 110 ppm copper (Cu), 70 ppm molybdenum (Mo).

Table 5.13: Haifa's Poly-Feed™ Drip: Fully soluble and chloride-free N-P-K compound fertilizers that supply all strawberry growers needs for nutrigation

Growth stage	N:P₂O₅:K₂O	Formula	N-NH₂ (%)	N-NO₃ (%)	N-NH₄ (%)	SO₃ (%)
Establishment	1-4-1	11-44-11	-	3	8	-
	1-3-1	13-36-13	-	3.7	9.3	-
	1-2-1	15-30-15	4.8	4.3	5.9	3.9
Vegetative development	1-1-1	19-19-19+1MgO	9.9	5.5	3.6	1.9
	1-1-1	20-20-20	10	6	4	-
	1-1-1	18-18-18+2MgO	9	5	4	3.9
	2-1-1	26-12-12+2MgO	20	3.5	2.5	3.9
	2-1-2	21-11-21+2MgO	13	6	2	3.9
Fruit set and fruit development	2-1-3	14-7-21+2MgO	-	6	8	25.2
	2-1-3	18-9-27+2MgO	8.6	7.6	1.8	3.9
	2-1-4	14-7-28+2MgO	-	8	6	16
	2-1-4	16-8-32+2MgO	5.5	9	1.5	3.5
	3-1-3	23-7-23+2MgO	15	6.5	1.5	1.9
	High K	12-5-40+2MgO	-	11	1	3.9

5.2.4 Foliar sprays

The purpose of foliar feeding is not to replace soil fertilization. Supplying a plant’s major nutrient needs (nitrogen, phosphorus, and potassium) is most effective and economical via soil application. However, foliar application has proven to be an excellent method of supplying plant requirements for secondary nutrients (calcium, magnesium, sulfur) and micronutrients (zinc, manganese, iron, copper, boron, and molybdenum), while supplementing N-P-K needs for short and / or critical growth stage periods.

Strawberries respond to foliar nutrients with increased vegetative development and improved flower numbers, their fruit-set rate, and higher yields, as well as by higher flavor and sugar content. See Table 5.14 and Table 5.15. Treated berries are firmer, hold up better, and show increased resistance to fungus attacks in the field and post harvest.

Table 5.14: Main results obtained by foliar-fed Zn and Fe on "Chandler" strawberries

Source: Chaturvedi et al, 2005

Plant & fruit parameters	Control	ZnSO₄ (0.4%)	FeSO₄(0.2%)
Plant height (cm)	15.5	18.9 (+22%)	18.3 (+18%)
Number of leaves/plant	19.2	24.9 (+30%)	23.2 (+21%)
Number of runners / plant	1.95	2.10 (+7.7%)	1.90 (-2.5%)
Number of flowers / plant	2.22	3.22 (+45%)	3.33 (+50%)
Number of fruit-set/plant	1.77	2.60 (+47%)	2.8 (+58%)
Number of fruits/plant	11.2	16.1 (+44%)	16.9 (+51%)
Plant fruit yield (g/plant)	86.4	133.9 (+55%)	140.5 (+63%)
Mean fruit mass (g/fruit)	6.85	7.85 (+15%)	7.98 (+16%)
Ascorbic acid (mg/ 100g pulp)	65.5	66.1 (+1%)	65.94 (+1%)
Fruit acidity	0.962	0.968 (+0.6%)	0.967 (+0.5%)
TSS contents (⁰Brix)	8.70	9.32 (+7.1%)	9.42 (+8.3%)
Shelf life in ambient temp. (days)	2.45	2.71 (+11%)	2.71 (+11%)

Table 5.15: Results (expressed as % change over control) obtained by pre-harvest foliar-feeding with Ca and B on "Chandler" strawberries

Source: Singh, et al, 2007

Fruit parameters	Control	CaCl₂ (2kg/ha)+ Boric acid (0.15 kg / ha)	Boric acid(0.15 kg / ha)
Incidence of fruit albinism	15.1 a	6.5 b (-57%)	14.8 a (-2%)
Incidence of fruit grey mold (%)	8.4 b	1.9 a (-78%)	8.1 b (-4%)
Incidence of fruit mal-formation	12.4 a	3.1 b (-75%)	3.4 b (-73%)
Marketable fruit yield (g/plant)	149.3 a	179.2 c (+20%)	161.3 b (+8%)
Fruits firmness after 5 shelf days	0.91 a	1.33 b (+46%)	1.01 a (+11%)
Ascorbic acid content (mg / 100g pulp)	39.1 a	45.0 b (+15%)	40.2 a (+3%)
TSS content (mg/ 100g pulp)	8.5 a	7.8 b (-8%)	8.2 a (-3%)
Acidity content	0.91 a	1.07 b (+18%)	0.95 a (+4%)

The initial application at the first sign of bloom is made to promote plant growth, early season fruiting and improved set.

A second application two weeks later helps to prolong plant vigor and fruiting, as a further aid to increasing total yield and quality.

Additional applications are recommended at 14- to 20-day intervals.

An application in the first half of September aids in the development of fruiting buds for the following spring.

Additionally, foliar feeding is intended to delay natural senescence processes shortly after the end of reproductive growth stages. Foliar feeding targets the growth stages where declining rates of photosynthesis and leveling off of root growth and nutrient absorption occur, in attempts to aid translocation of nutrients into seed, fruit, tuber, or vegetative production. Also, foliar feeding is an effective management tool to favorably influence pre-reproductive growth stages by compensating for environmentally induced stresses of adverse growing conditions and / or poor nutrient availability. Early foliar applications can make an already good crop better, either by stimulating more vigorous regrowth or maximizing the yield potential growth stage period.

Foliar fertilizer sprays can be used on established plants to quickly correct deficiencies identified by leaf analysis or by field symptoms. There are several commercial blends of complete foliar fertilizers suitable for strawberries. They contain a wide range of essential nutrients that are readily absorbed through the leaves. Plants under stress, for example during early fruit set and fruit development, can benefit from a foliar fertilizer spray program. Most foliar fertilizer sprays can be tank-mixed with pesticides; however, check the labels of both products before mixing.

Micronutrients should be applied according to need as determined by a tissue test, and should always be applied along with nitrogen in the solution. Combinations of certain nutrients may pose solution solubility problems, especially where nutrient solutions are combined with fungicides and pesticides. Potassium nitrate is compatible with most pesticides, exceptions being lime and sulfur. Magnesium sulfate is not compatible with arsenicals or copper sprays. Dormancy zinc sprays are not compatible with oil. Manganese solutions should not be mixed with phosphate, iron sulfate, or with nabam.

Buffering agents should be added to the foliar fertilizer solution to stabilize the pH of the solution (preferably between 5.0 and 6.0) and provide for quick and uniform coverage of the spray.

Biuret-free urea and compound nutrient sprays are commonly applied to large acreages of strawberries in the northern USA during the fruiting period to maintain fruit size. Here again, spraying is combined with the application of insecticides and fungicides. Sprays are performed during the late spring and early summer. The materials are added to the spray tank and applied along with insecticides and fungicides.

Table 5.16: Foliar spray program for maintaining highly fertile strawberry plants (nutrient-specific recommendations for addressing deficiency situations were suggested in Chapter 4).

Growth stages

P₂O₅

K₂O

Application rate (kg / ha)

For annual fields

First sign of bloom

2.8 - 3.9

0.6 - 1.1

0.9 - 1.4

1.1 - 1.7

0.6 - 1.1

0.3

Two weeks later

2 to 3 weeks later

For perennial fields

Early spring at 15-20 cm new growth

1.7 - 2.8

0.35 - 0.6

0.45 - 0.9

Early September (fall)

Need more information about growing strawberries? You can always return to the strawberry fertilizer & strawberry crop guide table of contents

Crop Guide: Strawberry Fertilizer Recommendations

5.1 Nutrients uptake and removal

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5.1 Nutrients uptake and removal

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