study of soil fertility and plant nutrition of proteas cultivated under subtropical conditions

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Study of Soil Fertility and PlantNutrition of Proteas Cultivatedunder Subtropical ConditionsMercedes Hernández a , Marino Fernández‐Falcón a

& Carlos E. Alvarez aa Departamento de Agrobiología y Medio Ambiente ,Instituto de Productos Naturales y Agrobiología –CSIC , La Laguna, Tenerife, SpainPublished online: 26 Aug 2008.

To cite this article: Mercedes Hernández , Marino Fernández‐Falcón & Carlos E.Alvarez (2008) Study of Soil Fertility and Plant Nutrition of Proteas Cultivated underSubtropical Conditions, Communications in Soil Science and Plant Analysis, 39:13-14,2146-2168, DOI: 10.1080/00103620802135427

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Study of Soil Fertility and Plant Nutrition of ProteasCultivated under Subtropical Conditions

Mercedes Hernandez, Marino Fernandez-Falcon, and Carlos E. Alvarez

Departamento de Agrobiologıa y Medio Ambiente, Instituto de Productos

Naturales y Agrobiologıa – CSIC, La Laguna, Tenerife, Spain

Abstract: A study of soil physicochemical characteristics and mineral nutrition of

four cultivars of Leucospermum cordifolium (‘Scarlett Ribbon,’ ‘High Gold,’

‘Veldifre,’ ‘Sunrise’) and Leucospermum patersonii species was carried out along 2

years in commercial protea plantations, distributed throughout a subtropical

region (La Palma Island, Canarian Archipelago). Soils presented a slightly acid

pH range, whereas organic matter showed suitable values. Generally, available

soil phosphorus (P) contents were less than 25 mg kg21, with high available

potassium (K) and calcium (Ca) levels, though the ratio of Ca of the sum of

available cations was usually appropriate. Despite the high electrical conductivity

(EC) levels (4.31–8.87 dS m21) determined in some soils, no salinity symptoms

were ever detected. Distribution and behavior of foliar nutrients nitrogen (N), P,

K, Ca, magnesium (Mg), and sodium (Na) along time showed that nutritional

needs varied in some cases among cultivars and species. L. patersonii presented

the least N concentration, whereas ‘High Gold’ and ‘Veldfire’ had the greatest

levels. Data denoted that P requirements were larger in younger plants, during the

recovery after pruning, and while new buds developed. ‘Sunrise’ cultivar stood

out for its large foliar levels of P, whereas ‘Scarlett Ribbon’ and ‘Veldfire’ had the

least K contents. As a general pattern, K decreased in winter samplings. L.

patersonii species and the cultivar ‘Sunrise’ exhibited the highest Ca values, and

the same was true for Mg only in the species. A special need for Na appeared in

all the cultivars and species studied. L. patersonii and the cultivar ‘Sunrise’

showed the greatest Na levels. A general stabilization of nutrient concentrations

Received 27 February 2007, Accepted 22 October 2007

Address correspondence to Carlos E. Alvarez, Departamento de Agrobiologıa

y Medio Ambiente, Instituto de Productos Naturales y Agrobiologıa – CSIC,

Apartado de correos, s/n, 38200 La Laguna, Tenerife, Spain. E-mail: carlose@

ipna.csic.es

Communications in Soil Science and Plant Analysis, 39: 2146–2168, 2008

Copyright # Taylor & Francis Group, LLC

ISSN 0010-3624 print/1532-2416 online

DOI: 10.1080/00103620802135427

2146

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was observed in the fourth, fifth, and/or sixth samplings, so that November is

recommended for taking samples for current foliar analysis. In this context, foliar

ranges for the studied nutrients are suggested.

Keywords: Nutrient foliar ranges, nutrition, protea, sampling time, soil fertility

INTRODUCTION

Proteas grow normally on leached, acidic soils, which are poor in availableminerals (Thomas 1974; Meynhardt 1976; Silber, Neumann, and Ben-

Jaacov 1998). Soil texture plays an important role in protea development.

Vogts (1979) and Claassens (1981) indicated that clay soils should be

avoided, because they tend to become waterlogged as a result of their low

permeability. Montarone (2001) stressed that the preferred soils for these

crops are sandy with less than 20 g kg21 clay and less than 40 g kg21 silt.

Regarding pH, Thomas (1974) reported that many protea plants

prefer acid soils. On the other hand, Claassens (1981) stated that manyprotea cultivars prosper on a wide pH range, with most species growing

well between 5.5 and 7.0. This author also reported that proteas are

occasionally found on calcareous soils with a considerably higher pH.

Silber, Mitchnick, and Ben-Jaacov (2001) stressed that pH affects root

development and indirectly affects nutrient availability and ion uptake.

As far as organic matter is concerned, Witkowski (1989) reported

levels around 8.7 mg kg21, both in the field and in greenhouses, lowerthan the normal levels of horticultural crops (Maier and Robinson 1996).

The requirements of phosphorus (P) differs depending on species and

genera of family Proteaceae (Thomas 1980; Handreck 1991; Montarone

and Ziegler 1996), as well as their sensitivity to high P concentration in

the soil (Buining and Cresswell 1993). Phosphorus concentration in the

rhizosphere affects development of the root system (Silber, Neumann, and

Ben-Jaacov 1998), involving the formation of proteoid roots that, inaccordance with Jeffrey (1967), is the response of the plant to the low level

of P. Contrarily, Lamont (1972) reported that an increase in P nutrition is

accompanied by an increase in the production of proteoid roots. Toxicity

symptoms, such as growth reduction and leaf necrosis in the presence of

high P concentration, have been described in numerous plants of the

Proteaceae (Goodwin 1983; Prasad and Dennis 1986). Nichols (1983)

classified Leucospermum cordifolium as highly susceptible to P, indicating

toxicity values based on concentrations of available P greater than 15 mgkg21, although Parvin (1986) gave values of up to 25 mg kg21. In Israel,

protea cultivation has been restricted to soils with less than 15 mg kg21 of P

(Silber, Neumann, and Ben-Jaacov 1998). Jamienson (1985) recommended

a maximum level of P of 30 mg kg21 for proteas, with the exception of

Soil Fertility and Nutrition of Proteas 2147

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Leucadendron ‘Safari Sunset,’ which can withstand concentrations up to

45 mg kg21. However, Maier et al. (1995) found that large concentrations

of P (up to 64 mg kg21) could not be related to low production.

Usually proteas are tolerant to low N levels in soils (Van Standen

1967), and some species prefer ammonia (NH3)–nitrogen (N) (Claassens

1986). As far as available cations are concerned, Jamienson (1985)

recommended soil calcium (Ca) values less than 6.2 cmol kg21 and

potassium (K) levels less than 1.0 cmol kg21, whereas concentrations of

magnesium (Mg) should be less than 1.2 cmol kg21. Parvin (1986)

reported K values between 1.4 and 2.5 cmol kg21 for Banksia, 1.2 cmol/

kg for Leucospermum, and between 0.9 and 2.7 cmol kg21 for Protea. In

this regard, Cecil et al. (1995) and Maier et al. (1995) confirmed small K

requirements for optimum growth of protea plants.

As far as salts are concerned, Vogts (1982) considered proteas to be

glycophytic (salt-sensitive) because protea plants absorb salts to a

harmful degree. In contrast, Walters, Jooste, and Raitt (1991) stated

that several species thrive in soils with similar sodium (Na) contents to

those observed in halophytic (salt-tolerant) plants. Claassens (1981)

suggested that many species of proteas can tolerate relatively high salt

concentrations, providing that the levels of nutrients such as nitrates and

phosphates are not overly great. Rodrıguez Perez, Fernandez Falcon, and

Socorro Monzon (2000) reported that Protea obtusifolia is moderately

tolerant to salts, indicating that the thresholds for electrical conductivity

of irrigation water and saturated soil extract for dry-matter production

were 2.7 and 6.0 dS m21, respectively, and that Leucospermum

cordifolium can be considered to be moderately sensitive to salinity,

establishing thresholds in this regard at 1.5 and 1.9 dS m21 (Rodrıguez

Perez, Fernandez Falcon, and Socorro Monzon 2001).

Large differences in nutrient content between genera as well as

between cultivars and species within genera have been reported (Classens

1986; Montarone 2001). Montarone et al. (2003) studied the nutritional

requirements of the genera Protea and Leucospermum and found that the

genus Leucospermum absorbs twice as many minerals as the genus

Protea. ‘High Gold’ and ‘Succession’ cultivars demanded much K, with a

K/N ratio of 1.6, whereas in Protea this ratio was near to 1. The genus

Leucospermum, and specifically L. candicans, withstands greater P levels

than genera Banksia, Leucadendron, Protea, and Telopea (Thomas 1980).

On the other hand, several authors have reported P toxicities (Nichols

1983; Prasad and Dennis 1986). Prasad and Dennis (1986) and

Montarone (2001) have emphasized the limited information that exists

on nutrition requirements of these plants.

The development of this culture in a subtropical region (La Palma

Island, Canarian Archipelago) is mainly based on the genus

Leucospermum. Among them, L. cordifolium (‘Scarlett Ribbon,’ ‘High

2148 M. Hernandez et al.

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Gold,’ ‘Veldifre,’ ‘Sunrise’) and the species L. patersonii are some of the

most promising. The objective of this article is to study macronutrient

distribution in soils and leaves of those cultivars and species along time,

grown in commercial plantations, as well as to suggest foliar ranges and

sampling time for the studied nutrients.

MATERIALS AND METHODS

The study of the cultivars ‘Scarlett Ribbon,’ ‘High Gold,’ ‘Veldfire,’ and

‘Sunrise’ of Leucospermum cordifolium, and of the species L. patersonii,

was carried out in commercial plantations located in eight municipalities

of La Palma (Canary Islands), distributed around the island. Soils were

Inceptisols Andepts and an Ultisol Udult.

Soil Sampling and Analysis

Soil samples were collected in May and November, 2002 and 2003, at a

depth of 0 to 20 cm with an Eijkelkamp soil sampler. These sample times

coincided with the vegetative growth period beginning after pruning and

the beginning of blossom. Three replications were taken from every farm

sampled, each one consisting of a composite sample of five subsamples.

The samples were air dried and passed through a 2-mm mesh. The pH

was measured in water in a ratio of 2:5, shaken, and allowed to settle for

10 min. Organic matter was determined by the Walkley and Black

method as modified by the Comision de Metodos Analıticos del Instituto

de Edafologıa y Agrobiologıa ‘‘Jose M. Albareda’’ (1973).

Available cations were extracted with an ammonium acetate 1 M

solution at pH 7 and determined by inductively coupled plasma (ICP;

Perkin-Elmer, Waltham, Mass.). Available phosphorus (P) was extracted

by the Olsen et al. (1954) method and determined by the Watanabe and

Olsen (1965) method.

Electrical conductivity (EC) was measured in the saturated soil

extract, and texture was determined by the Bouyoucos method (Lopez

and Lopez 1990).

Plant Samplings and Analysis

Five foliar samplings were carried out along the cultivation cycle (12

months long) during 2 years. The first one was in May 2003, which

coincided with the beginning of the vegetative growth period of the plants (2

months after pruning). The sampled leaves were the last fully developed


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ones (Jones, Wolf, and Mills 1991), which usually matched with the fourth

or fifth leaf counting from the apex. Three replications were taken from

every cultivar and species in each plantation. Each replication consisted of a

composite sample of leaves from 15 plants that were chosen at random.

The samples were washed in distilled water and dried in an oven at 80 uC,

after which they were ground to powder. One gram of the powder was ashed

in an oven at 480 uC and then mineralized by dry ashing with 6 M hydrochloric

acid (Chapman and Pratt 1961). The levels of Ca, Mg, Na, and K cations were

determined by ICP. Phosphorous was determined by colorimetry according to

the vanadate–molybdate method (Chapman and Pratt 1961). Nitrogen was

determined by the Kjeldahl method (Cottenie 1980).

Statistical Analysis

Data were subjected to one-way variance analysis, correlation, linear

regression, time series analysis, and chi-square test by Statgraphics Sgwin

4.0 software (Statgraphics, 1999). Foliar reference levels consisted of a

range determined by adding and subtracting the standard deviation to the

mean of each nutrient concentration.

RESULTS AND DISCUSSION

Soils

Data of the physical analysis of soils are shown in Table 1, and the

chemical properties are reported in Tables 2 to 7.

Texture

Several plantations had compensated soil texture (sandy clay loam), but

some soils showed high clay contents (Table 1) that are not recommended

for proteas (Vogts 1979; Claassens 1981; Montarone 2001). Nevertheless,

good growth and productions were observed in most plantations,

probably due to their organic-matter content, which improved protea

growth conditions.

pH

Most soils presented slightly acid pH range (Tables 2–6), which is in

agreement with pH reported by other authors (Witkowski 1989; Cecil

et al. 1995; Maier et al. 1995). According to Claassen (1981) and

Montarone (2001), proteas adapt easily to this pH range.


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Organic Matter

The values of organic matter (OM) were acceptable (between 20 and

50 g kg21) in the greater part of the soils where ‘Scarlett Ribbon,’

‘High Gold,’ and ‘Sunrise’ were cultivated. Farms with less than 20 g

Table 1. Texture of the soils of the plantations where the studied proteas were

grown

‘Scarlett

Ribbon’ ‘High Gold’ ‘Veldfire’ ‘Patersonii’ ‘Sunrise’

Farm Texture Farm Texture Farm Texture Farm Texture Farm Texture

1 Sandy

clay

loam

2 Sandy

clay

loam

3 Sandy

clay

loam

4 Sandy

clay

loam

9 Clay

9 Clay 4 Sandy

clay

loam

4 Sandy

clay

loam

6 Sandy

clay

11 Clay

12 Clay 8 Clay 5 Sandy

clay

loam

7 Sandy

clay

loam

16 Sandy

clay

loam

13 Clay 9 Clay 15 Clay 10 Sandy

clay

loam

17 Clay

14 Clay 13 Clay 19 Sandy

loam

19 Sandy

clay

loam

18 Clay

15 Clay 15 Clay 21 Clay 20 Sandy

clay

loam

— —

Table 2. Cultivar ‘Scarlett Ribbon’ and chemical characteristics of the soils of

the different plantations

Farm pH OM (g kg21) P (mg kg21)

Available cations (cmol kg21)

K Ca Mg Na

1 6.48a 57.6a 3.5c 2.44 a 12.05 ab 3.31 bc 0.56 a

9 6.30a 33.5c 7.0bc 2.41 ab 10.57 ab 4.04 b 0.19 c

12 6.60a 35.8bc 23.0b 1.18 c 13.26 a 7.54 a 0.48 a

13 5.42b 36.8bc 52.4a 2.38 a 10.40 b 2.67 c 0.32 bc

14 6.22a 31.6c 42.8a 1.53 bc 13.70 a 3.31 bc 0.41 ab

15 5.33b 40.9b 0.9d 1.54bc 5.31 c 3.12 bc 0.43 ab

Note. Data of the columns followed by different letters are statistically

significant at the p 5 0.05 level.


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Table 3. Cultivar ‘High Gold’ and Chemical characteristics of the soils of the

different plantations

Farm pH

OM

(g kg21)

P

(mg kg21)


K Ca Mg Na

2 6.17 c 72.4 a 4.4 d 1.62 bc 10.75 c 4.42 b 0.64 a

4 6.56 a 51.8 b 21.1 bc 3.07 a 17.11 a 5.57 a 0.71 a

8 6.45 ab 30.0 e 41.9 ab 3.03 a 13.75 b 3.95 b 0.35 b

9 6.27 bc 34.1 de 7.0 cd 2.36 ab 10.73 c 4.15 b 0.39 b

13 5.42 d 36.8 cd 52.4 a 2.38 ab 10.40 c 2.67 c 0. 32 b

15 5.33 d 40.9 c 0.9 d 1.54 c 5.31 d 3.12 c 0.43 b



Table 4. Cultivar ‘Veldfire’ and Chemical characteristics of the soils of the


Farm pH

OM

(g kg21)

P

(mg kg21)


K Ca Mg Na

3 6.05 c 91.5 a 3.5 d 1.18 c 10.02 c 1.25 a 0.50 b

4 6.56 b 51.6 b 21.0 b 3.07 a 17.11 b 0.99 ab 0.71 ab

5 6.57 b 98.1 a 12.2 c 1.58 bc 22.18 a 1.11 ab 0.54 b

15 5.51 d 19.3 c 0.9 d 1.44 c 5.55 d 0.84 b 0.48 b

19 6.89 a 17.0 c 11.4 c 2.28 b 11.87 c 1.20 ab 0.52 b

21 6.59 b 33.8 bc 37.1 a 1.92 bc 11.11 c 1.26 a 0.90 a



Table 5. Species Leucospermum patersonii and chemical characteristics of the

soils of the different plantations

Farm pH

OM

(g kg21)

P

(mg kg21)


K Ca Mg Na

4 6.56 b 51.8 b 21.0 b 3.07 a 17.11 c 5.57 b 0.71 ab

6 6.51 b 19.4 d 19.7 b 2.58 ab 17.96 c 8.99 a 0.77 ab

7 6.62 ab 83.4 a 79.9 a 1.30 c 22.17 b 3.11 c 0.33 b

10 6.92 a 28.0 cd 62.9 a 3.03 a 27.93 a 3.79 c 0.62 ab

19 6.46 b 31.1 c 13.5 b 1.64 bc 12.62 d 5.58 b 0.86 ab

20 6.36 b 50.8 b 26.6 b 2.74 a 19.27 bc 5.32 b 1.22 a




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kg21 OM should be complemented with this material (Sana, Carles,

and Cohı 1996). In contrast, levels of 70 g kg21 of organic matter have

been quoted by several authors as being too high for some crops,

possibly interfering with micronutrient absorption (Witkowski 1989;

Cecil et al. 1995; Maier and Robinson 1996; Pique, Alvarez, and

Fernandez 1996).

Phosphorus

Soil P levels were low for crops in general, but considering that protea

requirements of this element are small (Prasad and Dennis 1986;

Heinsohn and Pammenter 1986; Maier et al. 1995; Cecil et al. 1995),

such values may prove to be acceptable for this crop, perhaps with the

exceptions of plantations 1, 2, 3, and 15, in which concentrations of P are

significantly less than in the remainning ones.

Potassium

Available K levels were mostly high in the soils of the different cultivars

(concentrations greater than 2 cmol kg21), taking into account that

several authors (Heinsohn and Pammenter 1986; Cecil et al. 1995; Maier

et al. 1995) reported that proteas have small requirements for K, which is

in agreement with the data referred by Jamienson (1985), who

recommended K levels less than 1.02 cmol kg21 for these plants.

Parvin (1986), on the other hand, cited values of 1.24 cmol kg21 for

Leucospermum, and Fernandez Falcon, et al. (2006) indicated concentra-

tions of 0.57 to 1.36 cmol kg21 for the same genus. However, taking into

account the sum of available cations (Sana, Carles, and Cohı 1996), the

proportion of available K is acceptable in some soils, although it remains

high in a considerable number of them.

Table 6. Cultivar ‘Sunrise’ and Chemical characteristics of the soils of the


Farm pH

OM

(g kg21)

P

(mg kg21)


K Ca Mg Na

9 6.05 ab 31.0 bc 5.7 c 3.13 a 10.94 bc 4.86 b 0.40 b

11 6.39 a 38.4 b 73.8 a 1.58 cd 14.08 ab 5.79 a 0.45 b

16 6.30 ab 65.2 a 4.8 c 0.91 d 15.73 a 1.97 d 0.33 b

17 5.91 b 23.9 c 20.5 b 2.12 bc 9.10 c 3.25 c 0.45 b

18 6.14 ab 34.0 b 14.4 bc 2.48 ab 11.72 bc 3.52 c 0.64 a




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Calcium

Most concentrations of available Ca in the soils were high (10.02 cmol

kg21 to 19.27 cmol kg21), with the exception of farm 15 of cultivars

‘Scarlett Ribbon’ and ‘Veldfire,’ where their values did not reach the 6.24

cmol kg21 recommended by Jamienson (1985). It should be stressed that

the soils in which L. patersonii was cultivated showed the greatest

contents, reaching a value of 27.93 cmol kg21 (farm 10). When the sum of

cations was considered (Lopez and Lopez 1990), the values of Ca were

quite acceptable in the greater part of the farms studied, irrespectively of

the variety being cultivated.

Table 7. Electrical conductivity of the soils of the cultivars along the different

samplings

Farm Sampling

EC (dS/m)

‘Scarlett

Ribbon’

‘High

Gold’ ‘Veldfire’

L.

patersonii ‘Sunrise’

A 1 1.37 bc 1.32 1.19 b 2.38 b 1.49

2 1.71 b 1.50 2.29 a 8.87 a 1.45

3 0.97 c 1.22 1.47 b 1.38 b 1.33

4 2.46 a 1.73 1.59 b 6.75 a 1.71

B 1 1.84 a 2.37 b 2.31 b 1.01 ab 0.95

2 1.97 a 8.87 a 8.77 a 1.24 a 1.26

3 1.09 b 1.38 b 1.48 b 0.86 b 1.25

4 1.63 a 6.75 a 6.80 a 1.21 b 1.16

C 1 0.86 1.12 1.78 — 1.16 c

2 1.19 1.22 2.02 3.35 a 5.98 a

3 0.82 1.68 1.97 2.10 b 3.84 b

4 0.81 2.84 2.74 2.65 b 3.87 b

D 1 1.47 ab 1.84 a 0.90 a — 0.76

2 1.89 a 1.97 a 0.88 a 6.36 a 0.70

3 1.20 b 1.09 b 0.61 b 6.80 a 0.84

4 1.12 b 1.63 a 0.61 b 1.27 b 0.79

E 1 0.87 1.47 ab 0.85 b 2.33 1.22

2 0.85 1.89 a 2.11 ab 3.09 1.34

3 0.76 1.20 b 1.69 ab 3.90 1.36

4 1.04 1.12 b 4.31 a 5.67 1.22

F 1 0.89 a 0.89 a 0.98 b 2.81 ab

2 1.11 a 1.11 a 1.87 a 1.47 b

3 0.92 a 0.61 b 1.20 b 3.37 a

4 0.59 b 0.61 b 0.95 b 1.81 ab

Note. Farms A, B, C, D, E, and F correspond respectively to the first, second, third,

fourth, fifth, and sixth farms chosen to be sampled for each cultivar and the species.

Data of the columns followed by different letters are statistically significant at

the p 5 0.05 level.


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Magnesium

The values of available Mg (normally between 1.97 cmol kg21 and 5.79

cmol kg21) greatly exceeded the recommendation by Jamienson (1985)

for these plants (1.23 cmol kg21), with the exception of four soils where

‘Veldfire’ was cultivated, with mean values that were less than this limit.

However, when the proportion of Mg in the sum of the cations was taken

into account, this proportion proved to be acceptable (Sana, Carles, and

Cohı 1996) in the majority of the soils of the ‘Veldfire’ cultivar and can be

applied to the remaining crops and species.

Sodium

The detected concentrations of Na were low in general (under 1 cmol kg21),

both when the proportion of cations was taken into account and when

absolute values were considered (Rodrıguez Perez, Fernandez Falcon, and

Socorro Monzon 2001), and they did not negatively affect protea plant

development. However, it must be taken into account that available Na levels

were normal when compared to soils from other crops, because no references

to the content of this element in protea soils have been found in the literature.

Electrical Conductivity

A large percentage of the soils of the different cultivars (Table 7) showed

salinity indexes within acceptable ranges (less than 2 dS/m), taking into

account that Rodrıguez Perez, Fernandez Falcon, and Socorro Monzon

(2001) concluded that Leucospermum cordifolium is considered to be

moderately sensitive to salinity, with a threshold for electrical con-

ductivity of 1.9 dS m21. On the other hand, and referring to proteas in

general, several authors (Vogts 1979, 1982; Claassens 1981; Maier et al.

1995) reported suitable values of electrical conductivity (EC) as being

between 1.0 and 2.0 dS m21. Although very high values of EC appear

occasionally in the ‘High Gold,’ ‘Veldfire,’ and ‘Sunrise’ cultivars, they

were observed in 63.6% of the soils of L. patersonii species, attaining

values up to 8.87 dS m21. These high values are considered to be harmful

to the majority of crops, and to proteas in particular, which, according to

Vogts (1979), are sensitive to salts. Nevertheless, no salinity symptoms

were detected in any of the cultivars.

Plant Nutrition

Tables 8 to 11 and Figures 1 to 6 show foliar nutrient composition and

variation along time of the studied protea plants.


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Nitrogen

The ranges of our data (between 9.1 and 13.4 g kg21) were in accordance

with the value (11 g kg21) pointed out by Parvin (1986) for L. cordifolium.

In genus Protea, Haigh, Parks, and Cresswell (1997) determined ranges

from 3.5 to 28.3 g kg21, meanwhile Nichols (1988) had reported levels

from 8 to 15 g kg21, and Maier et al. (1995) detected values from 7.7 to

Table 8. Mean foliar levels of N, P, and K (g kg21) in the different cultivars and

species in both years of sampling

Cultivars and

species Years

Mean

N P K

‘Scalett

Ribbon’

1 11.8 1.3 a 4.1

2 12.2 0.9 b 4.3

‘High Gold’ 1 9.1 b 1.3 a 6.1

2 13.4 a 0.8 b 5.6

‘Veldifre’ 1 12.4 1.4 a 5.1

2 12.5 0.8 b 5.5

L. patersonii 1 13.4 1.6 a 6.1

2 12.0 0.9 b 6.3

‘Sunrise’ 1 12.6 1.6 a 7.6

2 11.2 1.2 b 6.6

Note. Data of each cultivar and species in the different years followed by

different letters denote a statistical significant difference at the p 5 0.001 level.

Table 9. Mean foliar levels of Ca, Mg, and Na (g kg21) in the different cultivars

and species in both years of sampling

Cultivars and

species Years

Mean

Ca Mg Na

‘Scalett

Ribbon’

1 6.3 b 2.0 b 5.9 b

2 15.4 a 9.2 a 14.0 a

‘High Gold’ 1 10.0 b 3.3 b 8.7 b

2 13.1 a 5.7 a 11.5 a

‘Veldifre’ 1 10.2 b 2.5 b 5.3 b

2 21.1 a 10.7 a 14.9 a

L. patersonii 1 11.4 b 5.7 b 5.3 b

2 24.7 a 21.4 a 14.9 a

‘Sunrise’ 1 10.8 b 3.8 b 8.5 b

2 27.3 a 16.4 a 20.8 a

Note. Data of each cultivar and species in the different years followed by

different letters denote a statistical significant difference at the p 5 0.001 level.


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8.6 g kg21. In Leucadendron, Ran et al. (2001) obtained concentrations

between 15 and 20 g kg21, and Cecil et al. (1995) reported concentrations

of 3.9 to 6.8 g kg21.

The larger values of the first sampling (with the exception of cultivars

‘Scarlett Ribbon’ and ‘Veldfire’ in the first year), shown in Figure 1, could

be due to a greater N requirement of the plants to recover from the

current winter pruning. Nitrogen fluctuated in the other samplings, which

agreed with Parvin’s (1986) observations.

Most N percentages remained stable between the fourth and fifth

samplings (months of November and January) in both years, with the

exception of cultivar ‘High Gold,’ and Sunrise in the second one. This

fact suggests that these months could be chosen for sampling leaves to

determine the standard N levels.

Phosphorus

Mean concentrations obtained in this study (0.8 to 1.6 g kg21) were

similar to those reported by Parvin (1986) for Leucospermum cordifolium.

Values observed in other protea plants (Nichols 1988; Cresswell 1991;

Maier et al. 1995; Haigh, Parks, and Cresswell 1997) ranged between 0.5

Table 10. Means comparison of foliar macronutrient (g kg21) among the

different cultivars and species, fourth sampling (November) of the second year

Nutrient ‘Scarlett R.’ ‘High Gold’ ‘Veldfire’ ‘Patersonii’ ‘Sunrise’

N 12.3 ab 13.2 a 13.0 a 11.4 b 12.5 ab

P 0.9 b 0.8 b 1.0 b 1.0 b 1.5 a

K 3.9 c 7.5 a 5.8 b 6.5 ab 6.8 ab

Ca 18.6 c 10.5 d 30.5 b 34.7 a 36.6 a

Mg 11.3 d 4.1 e 14.2 c 30.3 a 23.4 b

Na 12.9 b 13.0 b 13.7 b 23.0 a 20.4 a

Note. Data of the same file followed by different letters are statistically


Table 11. Foliar macronutrient ranges (g kg21) among the different cultivars

and species, fourth sampling (November) of the second year

Nutrient ‘Scarlett R.’ ‘High Gold’ ‘Veldfire’ ‘Patersonii’ ‘Sunrise’

N 10.1–14.5 11.0–15.4 11.1–14.9 10.1–12.7 9.2–15.8

P 0.6–1.2 0.5–1.1 0.7–1.3 0.6–1.4 0.7–2.3

K 3.2–4.5 5.3–9.7 4.5–7.1 4.0–9.0 5.2–8.4

Ca 15.8–21.4 8.6–12.4 22.1–38.9 28.9–40.5 31.3–41.9

Mg 9.9–12.7 3.3–4.9 11.6–16.8 26.2–34.4 19.9–26.9

Na 11.2–14.6 7.4–15.5 11.1–16.3 18.4–27.6 18.3–22.5


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and 3.2 g kg21 for proteas in general, whereas Ran et al. (2001) in

Leucadendron quoted values from 0.6 to 1.2 g kg21. Besides, opposed to

the generalized opinion and confirmed by our results, it is outstanding

that Silber et al. (1998, 2001) reported that these plants are not

susceptible to high P levels, because they obtained high concentrations

in leaves (up to 3.4 g kg21) without the plants showing any toxicity

symptoms.

Phosphorus foliar levels were significantly greater in the first year.

Because at the beginning of this study the sampled plants had an age less

Figure 1. Nitrogen evolution along time during sampling cycle of the two years

of assay. Data within the same line with different letters are significantly different

at p 5 0.05.


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than 2 years, these data seem to point to a greater need of P in younger

plants. This hypothesis suggests that the levels of P for obtaining the

standard foliar levels are those of the second year of the assay, because in

this year most plants had reached their maturity.

The high values of P observed in the first sampling (spring) of most

cultivars in both years (Figure 2) could be due to higher P nutritional

requirements along the stage after general pruning and new bud

development (February to March). Maier et al. (1995) and Cecil et al.

(1995) observed also higher concentrations of P in spring than the

remainder of the year.

Figure 2. Phosphorous evolution along time during sampling cycle of the two

years of assay. Data within the same line with different letters are significantly

different at p 5 0.05.


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On the other hand, P values of both years stabilized in the summer–

autumn samplings (July, September, and November), in accordance with

Maier et al., (1995) findings in Australia working with genus Protea. It isinteresting to point out that in cultivars ‘Scarlett Ribbon,’ ‘High Gold,’

and ‘Veldfire’ and the species L. patersonii, the plants that grew in farms

with soils of low P levels did not present significant differences in the

foliar concentrations of this element when they were compared to plants

Figure 3. Potassium evolution along time during sampling cycle of the two




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growing in farms with high levels of P in their soils. This suggests that a

low P presence in the soil is enough to supply the P requirement of these

plants, a fact that has been observed by other researchers in different

protea cultivars (Nichols 1988; Cresswell 1991). Nevertheless, cultivar

‘Sunrise’ had the greatest foliar contents of P when grown in soils richerin this element, which suggests that its requirements are greater than

those of the other cultivars and species studied. On the other hand, the

absence of P toxicities in the plants developed in soils with the highest P

levels suggest that these plants can resist high soil P concentrations

Figure 4. Calcium evolution along time during sampling cycle of the two years


at p 5 0.05.


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(means up to 183 mg kg21) without damage (Fernandez Falcon et al.,

2006). These observations are in contradiction with the statements of

other authors (Jamienson 1985; Heinsohn and Pammenter 1986; Maier et

al. 1995; Cecil et al. 1995).

Potassium

The mean of foliar K pointed out by Parvin (1986) for Leucospermum

cordifolium (4.4 g kg21) was less than the ones (4.1 to 6.6 g kg21) detected

in this assay. In the genus Protea, variations within the range of 1.8 to

4.1 g kg21 have reported by different authors (Price 1986; Nichols 1988;

Haigh, Parks, and Cresswell 1997; Maier et al. 1995). Cecil et al. (1995)

pointed out much smaller values (0.8 to 2.2 g kg21) in Leucadendron, andthe opposite was obtained (5 to 8 g kg21) by Ran et al. (2001). Potassium

concentration decreased in all the cultivars and species in the last

samplings of the 2 years (Figure 3), a trend that Cecil et al. (1995) and

Maier et al. (1995) observed in Leucadendron and Protea, respectively. In

general, K levels stabilized in the third and fourth samplings (September

and November) in both years.

Calcium

Foliar levels (6.3 to 27.3 g kg21) were greater than those (6.7 g kg21)

reported by Parvin (1986) in Leucospermum cordifolium and the ones (3.5

to 13 g kg21) observed by Price (1986), Maier et al. (1995), and Haigh,

Figure 5. Magnesium evolution along time during sampling cycle of the two




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Parks, and Cresswell (1997) in genus Protea. Cecil et al. (1995) in

Leucadendron pointed out lower values (2.4 to 3.9 g kg21).

In contrast to K, the lower levels of Ca appeared always in the first

and second samplings (May and July) of each year (Figure 4); meanwhile,

it usually increased significantly in the two last sampling of both years,

especially in the last one (winter time). This behavior coincides with thatobserved by Maier et al. (1995) in the Protea genus.

In general, Ca level stabilization differed according to the studied

year, though it was observed more consistently in the second (July) and

fourth (November) samplings.

Figure 6. Sodium evolution along time during sampling cycle of the two years


at p 5 0.05.


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Magnesium

Magnesium concentrations (2.0 g kg21 up to 21.4 g kg21) were greater

than the mean (2.4 g kg21) observed by Parvin (1986) in L. cordifolium, as

well as those (1 to 4 g kg21) reported by Nichols (1988) and Haigh, Parks,

and Cresswell (1997) in Protea genus and the range (1.6 to 2.5 g kg21)

detected by Cecil et al. (1995) in Leucadendron. Maier et al. (1995)

reported in genus Protea a gradual increase of this element along time, a

behavior that was also observed in the present study.

Magnesium concentrations also behaved in such a way that

November (fourth sampling) was the most appropriate month to sample

the plants for setting the standard foliar Mg levels (Figure 5).

Sodium

Rodrıguez Perez, Fernandez Falcon, and Socorro Monzon (2000, 2001),

working with genera Leucospermum and Protea, detected an Na range

similar to the one observed in this assay (5.3 to 20.8 g kg21). Although

Nichols (1988) mentioned that concentrations up to 2 g kg21 seem to be

normal, he considered that many proteas can tolerate greater levels.

Haigh et al. (1997) and Maier et al. (1995) in genus Protea, and Cecil et

al. (1995) in Leucadendron, found smaller concentrations than in this

study. Taking into account the low level of Na in the soils of La Palma,

the high concentrations of this nutrient in the different cultivars and

species are surprising. This suggests that these plants have a special

eagerness for Na.

Foliar Na levels of the first sampling (May) of each cultivar and the

species, in both years, showed a trend to be the least (Figure 6). This

could be due to a smaller presence of soil soluble Na in this time because

of the leaching caused by winter rains. The sampling of November

appears with sufficient frequency in the zones of Na level stabilization as

to consider it as suitable for a standard sampling for foliar Na

determination.

Foliar Standard Levels

As it was mentioned previously, a generalized stabilization of nutrient

concentrations is observed in the fourth sampling (November). The

plants of some studied plantations had not yet reached maturity age in

the first year of sampling, so data that belonged to the fourth

(November) sampling of the second year has been considered more

convenient for determining the reference values. These data are shown in

Tables 10 and 11.


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Nitrogen

L. patersonii presented the lowest average concentration, with statistical

differences from cultivars ‘High Gold’ and ‘Veldfire,’ which had the

highest values, that could be due to a greater demand of this element by

these cultivars. On the other hand, the species showed the shortest

standard range.

Phosphorus

When the foliar P levels among cultivars and the species were compared,

‘Sunrise’ differed significantly from the rest, which suggests that this

cultivar has a greater need of this nutrient. The standard range is also

more ample than that of the other protea plants.

Potassium

The contents of K were statistically lower in the cultivar ‘Scarlett

Ribbon,’ followed by ‘Veldfire,’ though the last one is significantly

different only to ‘High Gold.’ The greater limit of the standard variation

range of ‘Scarlett Ribbon’ (0.45 g kg21) is of the same order as the lower

one of the other cultivars and species.

Calcium

The cultivar ‘Sunrise’ and L. patersonii showed significantly higher Ca

levels than the other cultivars, specially ‘High Gold.’ Although average

Ca concentration of ‘Veldfire’ occupies an intermediate position, the

suggested range of variation is the widest of all.

Magnesium

The content of this element in L. patersonii has a behavior similar to that

of Ca, and ‘High Gold’ also presented the lowest levels of Mg. It is

interesting to emphasize that the minimum value of the standard interval

recommended for L. patersonii is higher than the maximum found in

most of the cultivars.

Sodium

The species L. patersonii and the cultivar ‘Sunrise’ had Na levels

significantly higher than the other cultivars. Both exhibit standard

ranges whose minimums are higher than the maximum of the other

cultivars.


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ACKNOWLEDGMENT

We acknowledge Enrique Huertas (technician of the Government

of La Palma Island) and Francisco N. Molina (technician of the

Association of Protea Growers) for their important collaboration. We

acknowledge the Cabildo Insular de La Palma for the funds to carry out

these essays.

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study of soil fertility and plant nutrition of proteas cultivated under subtropical conditions

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