Scientia Horticulturae 106 (2005) 70–75 www.elsevier.com/locate/scihorti
Foliar treatment of Mn deficient ‘Washington navel’ orange trees with two Mn sources I.E. Papadakis a,*, E. Protopapadakis b, I.N. Therios a, V. Tsirakoglou a a
Laboratory of Pomology, School of Agriculture, Aristotle University, 541 24 Thessaloniki, Greece b N.AG.RE.F., Institute of Olive Trees and Subtropical Plants, 73100 Chania, Greece
Received 7 November 2004; received in revised form 16 February 2005; accepted 23 February 2005
Abstract The objective of this study was the comparison of the effect of two Mn sources (MnSO4H2O, MnEDTA) which were applied at various concentrations (0, 200, 400, 800, and 1200 mg Mn l 1) to the leaves of ‘Washington navel’ orange trees in order to correct Mn deficiency. One hundred and seventy days after the foliar application of Mn solutions, the mean Mn concentrations in the leaves treated with MnSO4H2O (200, 400, 800 or 1200 mg Mn l 1) or MnEDTA (400, 800 or 1200 mg Mn l 1) were significantly higher than those of the control leaves. Manganese sulfate (MnSO4H2O) was more effective than MnEDTA regarding the improvement of the leaf Mn concentrations of the trees, when applied at equal Mn concentrations. Finally, the leaf Mn concentrations were in the sufficiency range (>25 mg kg 1 d.w.), only after the application of 800 or 1200 mg Mn l 1 as MnSO4H2O. # 2005 Elsevier B.V. All rights reserved. Keywords: Mn sulfate; Mn chelate; Foliar fertilizers; Citrus; Mn deficiency; Foliar spray
* Corresponding author. Tel.: +30 2310 998603; fax: +30 2310 402705. E-mail address:
[email protected] (I.E. Papadakis). 0304-4238/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.scienta.2005.02.015
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1. Introduction Two chemical forms are mostly used for the correction of Mn deficiency of fruit trees. The one is inorganic (MnSO4H2O) and the other is organic (MnEDTA). The organic source (MnEDTA) is inefficient after its soil application since Mn is rapidly substituted in the chelate by Fe, Cu or Zn. The result of this process is the immobilization of Mn and therefore the decrease of its availability to the plants. The effectiveness of Mn sulfate is extremely variable since it depends on many soil physical and chemical parameters. However, not only the chelate Mn (MnEDTA) but also the inorganic one (Mn sulfate) can be applied to the plants by foliar sprays (Murphy and Walsh, 1972; Walter, 1988; Reuter et al., 1988; Bergmann, 1992; Marschner, 1995). According to Bergmann (1992), the most rapid and efficient way for prevention and/or correction of Mn deficiency is the foliar application of solutions containing MnSO4 or MnEDTA. It is worth mentioning that no comparative studies have been published concerning the foliar application of these two Mn compounds to the citrus plants. However, such studies were reported for other plants like lupins (Brennan, 1996), sugar beets (Last and Bean, 1991), wheat (Modaihsh, 1997) and apples (Thalheimer and Paoli, 2002). The objective of this study was the comparison of the effectiveness of two Mn sources (MnSO4H2O, MnEDTA), applied foliarly in ‘Washington navel’ orange trees.
2. Materials and methods 2.1. Plant material and growth conditions Forty-five 23-year-old trees of ‘Washington navel’ (Citrus sinensis L.) orange grown in an orchard located in the ‘Agia’ village of Chania (Crete, Greece), grafted on sour orange (C. aurantium L.) rootstock and presenting visible symptoms of Mn deficiency, were used in this study. Generally, all the experimental trees were grown under uniform cultural and management practices and were planted at a spacing of 5 m 5 m. For many years each tree was annually supplied with the following fertilizers: (a) soil application of 1.5 kg calcium nitrate (15.5% N, 19.5% Ca) at the end of February and (b) fertigation with 1.5 kg potassium nitrate (13.8% N, 36.5% K), divided in three doses of 0.5 kg, during the period between 15 of each July and 15 of each August. 2.2. Leaf and soil samplings At the beginning of April, leaf and soil samples were taken in order to determine the precise Mn status of the each tree as well as the physical and chemical properties of the soil. A composite soil sample was collected at a depth of 0.05–0.45 m. It was air dried, crushed, and tested for pH, electrical conductivity, organic matter, free CaCO3, exchangeable Ca and Mg (EDTA), available P by the Olsen procedure, available K after extraction with ammonium acetate, and the micronutrients Mn, Zn and Fe after extraction with DTPA.
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Concerning the leaf sampling, 30–40 leaves per tree, representative of the different leaf ages, were collected. Afterwards, the leaves were washed initially with tap water in order to replace the Mn fixed in the negative sites of the leaf free space by the calcium and magnesium salts contained in the water (Epstein, 1972). Then, the leaves were also washed twice with deionized water, oven-dried at 75 8C for 3 days and milled to a fine powder to pass a 30-mesh screen. For the determination of Mn, 0.5 g of each sample was dry ashed for 6 h at 550 8C, dissolved in 3 ml of 6 N HCl and diluted up to 50 ml with deionized water. The leaf Mn concentration was determined by atomic absorption spectroscopy (PerkinElmer 2340). 2.3. Treatments Based on the leaf Mn concentrations of trees (derived from the inorganic analysis of leaf samples collected at the beginning of April), the trees were separated into nine uniform groups. Each group consisted of five trees (replications), which were randomly distributed in the orchard. The average Mn concentrations in the leaves of various tree-groups ranged between 6.0 and 8.6 mg kg 1 d.w. (Fig. 1). Eight days after the first leaf sampling (shortly before the beginning of spring vegetation flush), the trees were sprayed with solutions of MnSO4H2O (32% Mn) and MnEDTA (13% Mn) at the concentrations of 200, 400, 800 and 1200 mg Mn l 1. For preparation of the spraying solutions, good quality (EC: 0.25 mmhos cm 1, pH: 7.14) tap water was used. The control trees were sprayed with tap water (0 mg Mn l 1). About 10 l of spray solution was applied per tree. One hundred and seventy days after the Mn treatments, another leaf sampling was carried out in order to determine again the Mn nutritional status of the trees. The leaf sampling method and analysis were the same as mentioned above.
Fig. 1. Concentrations of Mn in the leaves of ‘Washington navel’ orange trees, 8 days before Mn foliar spray treatments (8 DBT) and 170 days after them (170 DAT). The control trees were sprayed with tap water (0 mg Mn l 1), while the rest eight tree groups were treated with 200, 400, 800 or 1200 mg Mn l 1 in the form of MnSO4H2O or MnEDTA (n = 5); the means of same sampling (8 DBT or 170 DAT) that are marked with the same letter do not differ with statistical significance from each other (Duncan’s multiple range test, P 0.05).
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2.4. Statistics The data were analyzed with the SPSS 11.0.1 for Windows statistical package (SPSS Inc., Chicago, USA). They were subjected to analysis of variance (ANOVA) and the mean leaf Mn concentrations were compared by the Duncan’s multiple range test for the probability level less than 5% (P 0.05).
3. Results and discussion 3.1. Soil analysis The main physical and chemical parameters of the soil are presented in Table 1. Based on the relative percentages of the three major soil particles (sand, silt, clay), the soil was classified as silty clay loam. The high percentage of organic matter (4.4%) exerts a positive effect on soil properties. Soil pH (7.55) was slightly above the optimum range for citrus trees, which lies between 5.5 and 7.0 (Davies and Albrigo, 1994). It can therefore be assumed that the availability of Mn for the orange roots was negatively affected. According to Maas (1993), citrus productivity decreases by 13% for each unit of increase of electrical conductivity (EC) of the soil solution above the 1.4 dS cm 1 level. In the experimental orchard, EC was 1.3 dS cm 1. Therefore, no negative effects would be expected regarding the growth of ‘Washington navel’ trees. 3.2. Concentration of Mn in the leaves At the first sampling, which was carried out one week before the application of the Mn foliar sprays, the mean leaf Mn concentrations of ‘Washington navel’ orange trees were extremely low (6.0–8.6 mg kg 1 d.w.) (Fig. 1). These concentrations were much lower than the 18 mg kg 1 d.w., value which was suggested by Smith (1966) as the critical concentration for Mn deficiency in citrus. In addition, the leaves presented intensive symptoms of Mn deficiency. According to Kabata-Pendias and Pendias (2001), the Mn Table 1 Physical and chemical properties of the soil Texture
SCL
pH (H2O:Soil, 1:1) EC (dS m 1) Organic matter (%) Free CaCO3 (%) P (mg kg 1) K exchangeable (mg kg 1) Ca exchangeable (mg kg 1) Mg exchangeable (mg kg 1) Fe (mg kg 1) Mn (mg kg 1) Zn (mg kg 1)
7.55 1.3 4.4 4.0 28 210 658 53 19 14 4.6
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deficiency in citrus is more probable to be recorded in soils contained only 1–5 mg Mn kg 1 (extracted with DTPA). In the present study, the DTPA-extracted soil Mn was relatively high (14 mg kg 1). Thus, the extremely low leaf Mn (6.0–8.6 mg kg 1 d.w.) could be ascribed to factors that reduce the Mn availability in the root zone. One hundred and seventy days after application, leaf Mn concentration was significantly higher in all treatments as compared to the control trees. At equal Mn concentrations, the MnEDTA treatments led to significantly lower leaf Mn concentrations than the MnSO4H2O sprays (Fig. 1). Furthermore, the leaf Mn concentration was in the sufficiency range (>25 mg kg 1 d.w.), only after the foliage application of 800 or 1200 mg Mn l 1 as MnSO4H2O. To our knowledge no data exist concerning the relative effectiveness of foliar sprays of MnEDTA and MnSO4H2O on citrus trees. Thalheimer and Paoli (2002) found that foliar fertilization of apple trees with manganese sulfate was more effective than manganese chelate. According to Brennan (1996), the two sources of Mn (MnSO4H2O and MnEDTA) proved to be equally effective (per kg of Mn), when they were applied to the lupins. Last and Bean (1991) further reported that MnSO4H2O in sugar beets was more effective than MnEDTA, as well as several other Mn sources. Finally, manganese sulfate had also better effects than the Mn chelate when both were sprayed on wheat plants (Modaihsh, 1997). The rate by which a chemical substance passes through the cuticle, and more generally the epidermal tissues of the leaves, depends on the following factors: (a) the concentration and the physical and chemical properties of the sprayed substance, (b) the plant species and its nutritional status and (c) the environmental conditions (Marschner, 1995; Scho¨ nherr, 2001; Scho¨ nherr and Luber, 2001). Since the environmental conditions, the scion rootstock combination and the nutritional status of the trees were the same for all treatments, the differences that were observed between MnEDTA and MnSO4H2O have to be ascribed to differences existing between these two Mn sources concerning their physical and chemical properties. It has been reported that the properties of a chemical substance that play an important role are the following: (a) the size of its molecule, (b) its solubility in water and (c) its point of deliquescence, which is a physical constant of a given chemical compound (Marschner, 1995; Scho¨ nherr, 2001; Scho¨ nherr and Luber, 2001). Certain essential differences exist between Mn chelate and Mn sulfate that increase the comparative advantage of MnSO4H2O relatively to MnEDTA. The Mn content of MnEDTA is 13%, while that of MnSO4H2O is 32%. Hence the quantity of MnEDTA required for the preparation of a spray solution with equal Mn concentration is 2.46 times greater than that of MnSO4H2O. Furthermore, the commercial price of MnEDTA, per unit of weight, is much higher than the price of MnSO4H2O. Therefore, MnSO4H2O is the preferable form for prevention or correction of Mn deficiency of ‘Washington navel’ orange plants.
4. Conclusion Manganese sulfate (MnSO4H2O) was more effective than MnEDTA in increasing leaf Mn concentrations of the ‘Washington navel’ orange trees, when both were applied as sprays containing 400–1200 mg Mn l 1. In addition to the agronomic advantages,
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MnSO4H2O is much more convenient than MnEDTA also from a commercial point of view.
Acknowledgment We thank the Greek State Scholarship Foundation (IKY) for supporting this work. We also thank Sofia Kuti and Vassiliki Tsakiridou for their assistance.
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