Study of Soil Fertility and Plant Nutrition of Proteas Cultivated under Subtropical Conditions

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  • This article was downloaded by: [Temple University Libraries]On: 23 November 2014, At: 18:59Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH,UK

    Communications in Soil Scienceand Plant AnalysisPublication details, including instructions forauthors and subscription information:http://www.tandfonline.com/loi/lcss20

    Study of Soil Fertility and PlantNutrition of Proteas Cultivatedunder Subtropical ConditionsMercedes Hernndez a , Marino FernndezFalcn a

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

    To cite this article: Mercedes Hernndez , Marino FernndezFalcn & 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 Agrobiologa y Medio Ambiente, Instituto de Productos

    Naturales y Agrobiologa 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 (4.318.87 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 Agrobiologa

    y Medio Ambiente, Instituto de Productos Naturales y Agrobiologa 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: 21462168, 2008

    Copyright # Taylor & Francis Group, LLCISSN 0010-3624 print/1532-2416 online

    DOI: 10.1080/00103620802135427

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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. Rodrguez 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 (Rodrguez

    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 Analticos del Instituto

    de Edafologa y Agrobiologa 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

    Soil Fertility and Nutrition of Proteas 2149

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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 hydrochloricacid (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 vanadatemolybdate 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 26), 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.

    2150 M. Hernandez et al.

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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 weregrown

    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 ofthe 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 p5 0.05 level.

    Soil Fertility and Nutrition of Proteas 2151

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  • Table 3. Cultivar High Gold and Chemical characteristics of the soils of thedifferent plantations

    Farm pH

    OM

    (g kg21)

    P

    (mg kg21)

    Available cations (cmol 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

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

    significant at the p5 0.05 level.

    Table 4. Cultivar Veldfire and Chemical characteristics of the soils of thedifferent plantations

    Farm pH

    OM

    (g kg21)

    P

    (mg kg21)

    Available cations (cmol 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

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

    significant at the p5 0.05 level.

    Table 5. Species Leucospermum patersonii and chemical characteristics of thesoils of the different plantations

    Farm pH

    OM

    (g kg21)

    P

    (mg kg21)

    Available cations (cmol 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

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

    significant at the p5 0.05 level.

    2152 M. Hernandez et al.

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

    and Coh 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 Coh 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 thedifferent plantations

    Farm pH

    OM

    (g kg21)

    P

    (mg kg21)

    Available cations (cmol 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

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

    significant at the p5 0.05 level.

    Soil Fertility and Nutrition of Proteas 2153

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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 differentsamplings

    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 p5 0.05 level.

    2154 M. Hernandez et al.

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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

    Coh 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 (Rodrguez 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 Rodrguez 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, attainingvalues 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 andspecies 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 p5 0.001 level.

    Table 9. Mean foliar levels of Ca, Mg, and Na (g kg21) in the different cultivarsand 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 p5 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 Parvins (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 thedifferent 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

    significant at the p5 0.05 level.

    Table 11. Foliar macronutrient ranges (g kg21) among the different cultivarsand species, fourth sampling (November) of the second year

    Nutrient Scarlett R. High Gold Veldfire Patersonii Sunrise

    N 10.114.5 11.015.4 11.114.9 10.112.7 9.215.8

    P 0.61.2 0.51.1 0.71.3 0.61.4 0.72.3

    K 3.24.5 5.39.7 4.57.1 4.09.0 5.28.4

    Ca 15.821.4 8.612.4 22.138.9 28.940.5 31.341.9

    Mg 9.912.7 3.34.9 11.616.8 26.234.4 19.926.9

    Na 11.214.6 7.415.5 11.116.3 18.427.6 18.322.5

    Soil Fertility and Nutrition of Proteas 2157

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

    at p5 0.05.

    2158 M. Hernandez et al.

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

    different at p5 0.05.

    Soil Fertility and Nutrition of Proteas 2159

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

    different at p5 0.05.

    2160 M. Hernandez et al.

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

    at p5 0.05.

    Soil Fertility and Nutrition of Proteas 2161

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

    different at p5 0.05.

    2162 M. Hernandez et al.

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

    at p5 0.05.

    Soil Fertility and Nutrition of Proteas 2163

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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

    Rodrguez 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.

    2164 M. Hernandez et al.

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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.

    Soil Fertility and Nutrition of Proteas 2165

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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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