Studies on leaf nutrient concentration in mango have been focused on variations due to age, leaf position (Koo & Young, 1972; Pathak & Pandey, 1976), soil type, cultivar effect, and differences between terminal shoots with and without fructification (Samra, Chadha, & Thakur, 1978; Young & Koo, 1971). In addition, the results have varied according to the vegetative flush, sampling season (Rajput, Chadha, & Thakur, 1985) and phenological stage in which the leaf sampling is carried out (Ponchner, Rojas, & Bornemisza, 1993).
Avilán (1971) described two critical phases of the concentration of nutrients in 'Kent' mango grown in Venezuela. In the first, an increase in the leaf nutrient concentration begins with the end of the harvest period and extends until flowering; in the second, there is a decrease in the amount of nutrients, which coincides with the formation of the fruit and is the most critical. However, Castro-López, Salazar-García, González-Durán, Medina-Torres, and González-Valdivia (2012) found different results in the cv. Ataúlfo, Kent and Tommy Atkins in Mexico since the concentration of nutrients in leaves of the spring vegetative flush (SpVF) was more affected by the later stages of flower development (cauliflower stage before anthesis), while in summer (SuVF) or autumn vegetative flush (AVF) leaves, nutrient changes occurred to a greater extent due to fruit growth (Castro-López et al., 2012). However, there must be a period of minimum variation in the concentration of most nutrients, which would be adequate to perform leaf sampling for nutrient diagnosis purposes (Salazar-García, González-Durán, & Ibarra-Estrada, 2015).
The main criterion for determining the appropriate time for leaf sampling is that the nutrient concentration is stable. However, this is obtained from descriptive graphs, so the identification of the period of least nutrient variation is visual (Quiñones, Soler, & Legaz, 2013). This makes it difficult to determine the exact stage of stability, since only the dates in which leaf nutrient analysis was performed are given, and generally the interval between samplings is very broad (Benítez-Pardo, Hernández-Montoya, Osuna-Enciso, Valenzuela-López, & Galván-Piña, 2003; Young & Koo, 1971).
The use of mathematical functions and their respective derivatives have been useful in determining the appropriate leaf sampling period (ALSP) since they help identify the stage in which the least variation in nutrient concentration occurs during the life of the leaf. This procedure was used to establish the ALSP in 'Hass' avocado (Salazar-García et al., 2015). However, no information in this regard was found for mango.
In the state of Nayarit, Mexico, leaf analyses are increasingly used to diagnose the nutrient status of mango orchards. However, the dates to collect the leaves are determined a priori, without considering the age of the leaves or the vegetative flush they come from, or extrapolated from other regions. Therefore, the aim of this research was to identify the appropriate period for leaf sampling of rainfed 'Ataúlfo', 'Kent' and 'Tommy Atkins' mangos for the purpose of nutrient diagnosis.
Materials and methods
The research was conducted during 2006 and 2007 in seven rainfed commercial orchards of the cvs. Ataúlfo (two orchards), Kent (three orchards) and Tommy Atkins (two orchards) established at 8 x 8 m in the municipalities of Acaponeta (northern zone), San Blas and Tepic (central zone) and Compostela (southern zone) in Nayarit (Table 1). In this region, the climate is sub-humid warm (García, 1998), and the maximum and minimum average temperatures are 28 and 18 °C, respectively. Rainfall occurs from June to October (1,089 to 1,324 mm) and the precipitation of the driest month is less than 50 mm.
|Cultivar||Location, municipality||Coordinates||Elevation (masl)||Age (years)||Soil classification|
|Ataúlfo||Atonalisco, Tepic||NL 21° 36’ 46.9’’ WL 104° 49’ 43.6’’||601||12||Chromic luvisol|
|Chacala, Compostela||NL 21° 10’ 20.3’’ WL 105° 10’ 32.7’’||42||11||Eutric cambisol|
|Kent||Buenavista, Acaponeta||NL 22° 27’ 44’’ WL 105° 26’ 55.8’’||11||10||Eutric cambisol|
|Las Palmas, San Blas||NL 21° 37’ 05.0’’ WL 105° 09’ 30.1’’||139||20||Humic acrisol|
|Chacala, Compostela||NL 21° 10’ 05.2’’ WL 105° 10’ 31.5’’||54||17||Eutric cambisol|
|Tommy Atkins||Buenavista, Acaponeta||NL 22° 27’ 44’’ WL 105° 26’ 55.8’’||14||18||Eutric cambisol|
|Chacala, Compostela||NL 21° 10’ 14.3’’ WL 105° 09’ 52.2’’||38||17||Eutric cambisol|
At the beginning of the study (May 2006), 10 trees were randomly selected in each orchard and from each one a sample composed of four subsamples (one for each cardinal point) was obtained from the tree’s drip zone, from 0-30 cm deep, since it is where there is the greatest abundance of fine roots (Salazar-García, Ramírez-Murillo, & Gómez-Aguilar, 1993). From the 40 sub-samples, a composite sample was obtained and analyzed for its physical and chemical characteristics in a laboratory accredited by the North American Proficiency Testing (NAPT) program of the Soil Science Society of America. Soil properties determined were: texture; pH (1:2 water) (McLean, 1982); organic matter by the method of Walkley and Black (Nelson & Sommers, 1982); N-inorganic (Dahnke, 1990); P-Bray (Bray & Kurtz, 1945); K, Ca, Mg and Na extracted with ammonium acetate (Doll & Lucas, 1973); Fe, Zn, Cu and Mn by the DTPA method (Lindsay & Norvell, 1978), and B by the hot water method and Azometina-H (Bingham, 1982). Nutrients were quantified with an atomic absorption spectrophotometer (Thermo Series S, Madison, Wisconsin, USA), with the exception of P and B, which were determined in a spectrophotometer (Genesys™ 20, Thermo Scientific, Madison, Wisconsin, USA).
In each orchard, trees were identified that, according to the grower, had an annual production ≥ 100 kg, which surpasses the current average (11 t·ha-1) of mango in the region (Servicio de Información Agroalimentaria y Pesquera [SIAP], 2016). Of these trees, 20 were randomly selected and in each one 20 shoots of each vegetative flush were tagged in a bud-breaking stage (zero day). In each mango cultivar, two vegetative flushes were studied. Their starting dates were: January 5 for the SpVF (Ataúlfo, Kent and Tommy Atkins), June 22 for the SuVF (Ataúlfo and Kent) and September 21 for the AVF (Tommy Atkins). Once the zero day was established, the days after leaf sprouting (DALS) were counted until abscission.
Monthly leaf samplings were made for each vegetative flush, alternating between odd- and even-numbered trees (10 trees per sampling date), which started when the leaf was ≥ 5 cm long and ended when senescence and abscission occurred. To avoid contamination of the leaves by the soil, they were attached from the petiole, with a cotton thread, to the shoot that held them. In each sampling, 20 healthy, complete (lamina + petiole) leaves were collected per tree from the six and seven basipetal positions. In total, 15 leaf samplings of the SpVF were performed in the three mango cultivars (from February 2006 to April 2007), 12 samplings from the Ataúlfo and Kent cultivars of the SuVF (from August 2006 to July 2007) and 12 samplings from the Tommy Atkins cultivar of the AVF (October 2006 to September 2007). Additionally, in each sampling the length of the lamina of 10 leaves from each tree was measured.
The leaves were washed and dried in a forced-air oven at 65 °C for 48 h. Subsequently, they were ground in a stainless-steel mill (MF10, IKA®), sieved in mesh no. 1.0 (35 holes·cm-2) and sent to the aforementioned laboratory to determine the concentrations of N-total, NO3, P, K, Ca, Mg, S, Fe, Cu, Mn, Zn and B. N-total was determined by the semi-microKjeldahl method (Alcántar-González, & Sandoval-Villa, 1999; Bremner & Mulvaney, 1982), which is based on the wet oxidation of organic matter using sulfuric acid and a catalyst, while for NO3 the nitration method with salicylic acid was used (Alcántar-González, & Sandoval-Villa, 1999; Etchevers et al., 2000). The K was extracted with distilled water and quantified in an atomic absorption spectrophotometer (ICE 3000™, Thermo Scientific) (Alcántar-González, & Sandoval-Villa, 1999; Etchevers et al., 2000). The P and S were determined using the vanadate-yellow molybdate and turbidimetry methods, respectively. The B was determined by the azomethine-H calcination method (Enríquez, 1989) with a spectrophotometer (Genesys™ 20, Thermo Scientific, Madison, Wisconsin, USA). For Ca, Mg, Cu, Fe, Mn and Zn, the HNO3+HCl microwave digestion method was used (Alcántar-González, & Sandoval-Villa, 1999; Etchevers et al., 2000). These last nutrients were quantified by atomic absorption in a spectrophotometer (ICAP 7200™, Thermo Scientific).
Determination of appropriate leaf sampling period
In this determination, the procedure described by Salazar-García et al. (2015) was used. For each orchard and vegetative flush, mathematical functions were generated using DALS as an independent variable and the concentrations of each nutrient as dependent variables. The general equation was: Nutrient = β0 + β1D + β2D2 + β3D3 + β4D4 + β5D5; where D are the days after sprouting and β the mathematical coefficients. Subsequently, for each nutrient, the best mathematical function was selected by order of response (from the first to the sixth order) with the "Stepwise" procedure of the Statistical Analysis System (SAS Institute, 2009). The criteria for choosing the best functions were: 1) highest R2 value, 2) lowest mean squared error (MSE) and 3) Mallows's Cp value (Draper & Smith, 1981; Neter, Li, & Kutner, 1985). Once the best functions were identified, their mathematical coefficients (β0,…, βn) were calculated by the REG procedure (SAS Institute, 2009). The predicted values for each day of the nutrient evolution were calculated by substituting the DALS value in the general equation.
Once the best mathematical functions of each nutrient were selected, the derivatives for each day were calculated. The values obtained were plotted in SigmaPlot (Systat Software Inc., 2006) to identify the periods of least variation, referred to here as having greater stability, of each nutrient. The values can be positive or negative, and as they approach zero the rate of change in the concentration of each nutrient is lower; therefore, the criterion to determine the ALSP was that the result of the derivative was equal or close to zero (Granville, Smith, & Longley, 1963). Then, for each mango cultivar, a table was prepared with the periods of greatest stability for macro and micronutrients, as well as the ALSP for each vegetative flush.
Results and discussion
There were some differences in the soil characteristics of the mango orchards where the study was carried out (Table 2). The Chacala and Atonalisco orchards had the most clayey textures. Soil pH varied from 4.7 in Chacala to 6.7 in Las Palmas, and in the 'Tommy Atkins' and 'Kent' (Buenavista) orchards it was within the limits in which mango thrives (5.0 to 6.5) (Chávez-Contreras, Vega-Piña, Tapia-Vargas, & Miranda-Salcedo, 2001). On the other hand, in the 'Ataúlfo' orchards, the most acidic pH values were recorded (4.7 to 4.9); this type of soil tends to favor leaf nutrient deficiencies, mainly Ca and Mg (Salazar-García, 2002). No salinity problems were detected. As for organic matter, only in the Buenavista orchards was the content very low. Additionally, low and very low concentrations of Ca, Mg, Zn and B were evident, and that of Mn was classified as moderately high to very high.
|pH (1:2)||4.9 SA||4.7 SA||5.1 SA||6.6 MoAc||6.7 N||6.4 MoAc||5.5 SA|
|O.M. (%)||3.0 MoH||3.4MoH||1.2 MoL||4.7 VeH||3.6 H||1.4 MoL||3.7 H|
|CEC (meq(100 g-1)||7.59||7.47||4.9||15.0||18.9||5.86||9.90|
|N-Inorganic||11.4 M||15.6 M||81.4 VeH||17.7 M||8.94 MoL||6.23 MoL||12.2 M|
|P-Bray||23.4 MoH||25.2 MoH||62.1 VeH||10.8 MoL||6.98 L||9.2 MoL||13.1 M|
|K||357 M||108 L||384 M||218 MoL||346 M||227 MoL||225 MoL|
|Ca||572 L||687 L||572 L||2404 MoH||2432 MoH||858 L||1230 MoL|
|Mg||174 L||160 L||56 VeL||280 MoL||323 M||71 VeL||332 M|
|Na||68 L||34 VeL||33 VeL||38 VeL||41 VeL||31 VeL||36 VeL|
|Fe||18.6 M||17.4 M||53.4 H||8.56 MoL||7.14 MoL||56.8 H||25.9 MoH|
|Zn||0.78 L||0.42 L||0.40 L||0.44 L||0.53 L||0.75 L||0.84 MoL|
|Mn||29 MoH||73.1 VeH||47.9 H||23.8 MoH||28.9 MoH||60.5 VeH||98.4 VeH|
|Cu||0.43 MoL||2.42 H||1.63 MoH||2.05 MoH||1.26 MoH||1.45 MoH||1.47 MoH|
|B||0.42 MoL||0.63 M||0.55 MoL||0.81 M||0.63 M||0.61 M||0.78 M|
Appropriate leaf sampling period
As the results of leaf analysis vary with vegetative flush and sampling time, Rajput et al. (1985) suggest establishing an adequate sampling period for each flush to avoid erroneous results. In the present work, the periods of leaf nutrient stability (PLNS) showed differences among the mango cultivars, as well as among their corresponding vegetative flushes (Table 3).
|N, P, K, Ca, Mg, S||249-331||October 8-December 2||276-331|
|Fe, Cu, Mn, Zn, B||276-336||276-331|
|N, P, K, Ca, Mg, S||94-170||September 30- November 29||100-160|
|Fe, Cu, Mn, Zn, B||100-160||100-160|
|N, P, K, Ca, Mg, S||241-316||September 3-November 17||241-316|
|Fe, Cu, Mn, Zn, B||215-318||241-316|
|N, P, K, Ca, Mg, S||96-150||September 27- November 19||96-150|
|Fe, Cu, Mn, Zn, B||75-157||96-150|
‘Ataúlfo’. In the SpVF, the PLNS for N, P, K, Ca and Mg was from 249 to 331 DALS (Table 3; Figure 1A), and for S from 175 to 226 DALS. In the case of micronutrients, PLNS occurred between 276 and 236 DALS (Table 3; Figure 1B). Although the Mn concentration did not present stability, this period applies to this nutrient. Therefore, for both macro and micronutrients, the ALSP was delimited from October 8 to December 2 (276 to 331 DALS).
For the SuVF, macronutrients stabilized between 94 and 170 DALS (Table 3; Figure 1C) and micronutrients between 100 and 160 DALS (Table 3; Figure 1D). In both cases, the ALSP was from September 30 to November 29 (100 to 160 DALS; Table 3). In this case, as in the SpVF, the PLNS of the micronutrients was fitted to Mn even though in this nutrient there was not a period of stability.
For the 'Manila' mango grown in Veracruz, Mexico, leaf sampling is recommended in June-July or August-September, when the spring leaves are four to seven months old (Mosqueda-Vázquez et al., 1996). When comparing these results with those obtained from cv. Ataúlfo no coincidence was found, since in 'Ataúlfo' the ALSP for the SpVF was when the leaves were from nine to eleven months of age. The foregoing evidences the need to obtain specific information for each mango cultivar and cultivation condition.
‘Kent’. In this cultivar, the PLNS in the SpVF for macronutrients was from 241 to 316 DALS (Table 3; Figure 2A) and for micronutrients between 215 and 318 DALS (Table 3; Figure 2B). As in 'Ataúlfo', S did not show a PLNS that coincided with the other macronutrients; however, between 241 and 316 DALS the value of its derivative showed a lower change rate. The instability of S could be caused by the frequent chemical sprayings that contain this element to control diseases such as anthracnose and powdery mildew (Espinoza-Aburto et al., 2006).
In the SuVF, the PLNS for macro and micronutrients was between 96 and 150 DALS and 75 to 157 DALS, respectively (Table 3; Figures 2D and 2C). According to the above, the ALSP was from September 26 to November 19 (96 to 150 DALS) (Table 3). Leaf samplings are appropriate with leaf ages between eight to ten months (spring leaves) and three to five months (summer leaves). These results do not coincide with those reported by Benítez-Pardo et al. (2003), who for the same mango cultivar, but in the state of Sinaloa (located north of Nayarit), recommend analyzing leaves from two to four months of age, although they did not specify the type of vegetative flush studied; in addition, this sampling period was proposed with a visual (graphic) criterion, not a mathematical one.
‘Tommy Atkins’. The PLNS of the SpVF for macronutrients occurred from 195 to 370 DALS and from 261 to 365 DALS for micronutrients (Table 4; Figures 3A and 3B). For the AVF, the PLNS for macro and micronutrients was from 256 to 282 DALS and 258 to 284 DALS, respectively (Table 4; Figures 3C and 3D). Accordingly, the ALSP of the SpVF was from September 23 to January 5 (261 to 365 DALS) and from June 6 to 30 (258 to 282 DALS) for the AVF (Table 4). This last result differs from that mentioned by Rajput et al. (1985), since they suggest that in subtropical climates the month for sampling AVF leaves is October (April in the northern hemisphere).
|N, P, K, Ca, Mg, S||195-370||September 23-January 5||261-365|
|Fe, Cu, Mn, Zn, B||261-365||261-365|
|N, P, K, Ca, Mg, S||256-282||June 6-30||258-282|
|Fe, Cu, Mn, Zn, B||258-284||258-282|
No information was found available on sampling periods for mango SuVF leaves, probably because the SpVF, which occurs after flowering, is the most important in most mango-producing regions.
The periods of greatest stability of the leaf nutrient concentration differed among the three mango cultivars studied, their vegetative flushes and the nutrient in question. The mathematical procedure used in this research was adequate to identify the appropriate period to perform leaf samplings for the analysis of the majority of nutrients in the three main mango cultivars (Ataulfo, Kent and Tommy Atkins) in Nayarit, Mexico.