Print version ISSN 0100-2945
Rev. Bras. Frutic. vol.33 no.2 Jaboticabal June 2011
SOIL AND PLANT NUTRITION
Potassium fertilization for pineapple: effects on soil chemical properties and plant nutrition1
Adubação potássica em abacaxizeiro: efeitos no solo e na nutrição das plantas
Luiz Antonio Junqueira TeixeiraI; José Antonio QuaggioII; Heitor CantarellaIII; Estêvão Vicari MellisIV
IResearcher. Centro de Solos e Recursos Ambientais do Instituto Agronômico (IAC). PO Box 28, 13012-970, Campinas-SP, Brazil. firstname.lastname@example.org
IIResearcher. Centro de Solos e Recursos Ambientais do Instituto Agronômico (IAC). email@example.com
IIIResearcher. Centro de Solos e Recursos Ambientais do Instituto Agronômico (IAC). firstname.lastname@example.org
IVResearcher. Centro de Solos e Recursos Ambientais do Instituto Agronômico (IAC). email@example.com
A field experiment was carried out on an Ultisol located at the city of Agudos (22º30'S; 49º03'W), in the state of São Paulo, Brazil, in order to determine the effects of rates and sources of potassium fertilizer on nutritional status of 'Smooth Cayenne' pineapple and on some soil chemical properties. The experiment was a complete factorial design with four rates (0, 175, 350, and 700 kg ha-1 of K2O) and three combinations of K sources (100% KCl, 100% K2SO4 and 40% K2SO4 + 60% KCl). Soil samples were taken from the depths 0-20 cm, 20-40 cm and 40-60 cm at planting and 14 months after. Nutritional status of pineapple plants was assessed by means of tissue analysis. Soil K availability increased with application of K fertilizer, regardless of K sources. Soil chlorine and Cl concentration in pineapple leaves increased with application of KCl or K2SO4+KCl. Plant uptake of potassium was shaped by soil K availability and by the application rates of K fertilizer, independently of K sources.
Index terms: Plant analysis, soil analysis, potassium chloride, potassium sulphate, Ananas comosus / K.
Foi realizado um experimento de campo num Argissolo Vermelho-Amarelo, em Agudos-SP (22º30'S; 49º03'W), com o objetivo de determinar os efeitos de fontes e doses de fertilizante potássico no estado nutricional de abacaxi 'Smooth Cayenne' e em alguns atributos químicos do solo. Empregou-se um arranjo fatorial com quatro doses (0; 175; 350 e 700 kg ha-1 de K2O) e três combinações de fontes (100% KCl, 100% K2SO4 e 40% K2SO4 + 60% KCl). A amostragem de solo foi realizada nas camadas de 0 a 20 cm, 20 a 40 cm e de 40 a 60 cm na época do plantio e 14 meses depois. O estado nutricional dos abacaxizeiros foi avaliado por meio de análise foliar. A disponibilidade de K no solo aumentou em função das doses, independentemente da fonte empregada. A concentração de cloro no solo e seu teor nas folhas de abacaxizeiro cresceram com a aplicação de KCl e de K2SO4+KCl. A absorção de potássio pelo abacaxizeiro apresentou correlação significativa com as doses de K aplicadas, independentemente da fonte.
Termos para indexação: Análise de plantas / análise de solo / cloreto de potássio / sulfato de potássio / Ananas comosus / K.
Potassium is the foremost nutrient required for pineapple crop and the lack of this nutrient reduces plant growth, fruit yield and affects negatively fruit quality as pointed out by Lacoeuilhe (1978, 1984) and Spironello et al. (2004). Therefore, potassium fertilization plays an important role to pineapple yield, but high rates of potassium chloride, the most common and cheapest source of this nutrient, can negatively affect fruit size and some internal fruit characteristics, as compared with potassium sulphate (LACOEUILHE, 1978).
The choice of an appropriate source of potassium may be as important as determining the correct rate of K fertilizer for some crops (ZEHLER et al., 1986). Potassium chloride is generally the cheapest source of K, but the more expensive sources as sulphate and potassium nitrate provide other nutrients and have some advantages (HEPTON, 2003). According to Kleinhenz (1999), K2SO4 has advantages over KCl because it carries two major plant nutrients, has a lower salt index, is preferable for chloride-sensitive crops, and improves quality of many crops. Kleinhenz (1999) also mentioned that in the soil, chloride is more vulnerable to be leached than the sulphate, and in a similar manner, potassium KCl-fertilizer is more readily leached than in K2SO4-fertilizer.
Despite the importance of potassium on pineapple nutrition, there is a lack of information about the effects of K fertilizer sources on soil properties and on pineapple nutrition in Brazilian plantations. The objective of the present study was to assess the effects of rates and sources of potassium fertilizer on nutritional status of pineapple plants and on some soil chemical properties.
MATERIAL AND METHODS
The field experiment was located in Agudos (22º30'S; 49º03'W), Brazil, in a low fertility Ultisol. The soil (0 to 20 cm) chemical characteristics before experiment placement (no lime applied) were: organic matter = 17 g dm-3, Presin = 6 mg dm-3, pH in 0,01 mol L-1 CaCl2 solution = 4.1, exchangeable K, Ca, and Mg = 0.7, 3, and 2 mmolc dm-3, respectively, (H+Al) = 38 mmolc dm-3 and soil base saturation = 13%, measured according to the methods proposed by Raij et al. (2001). Three months before planting, the soil was limed. Lime requirement was calculated to increase the soil base saturation to 50 % of the CEC at pH 7.0 according to Spironello and Furlani (1997). The climate was classified as Cwa-Köppen with dry winter.
The experiment was carried out inside a commercial plantation established in June, 2003. The plots were composed of three double rows (0.5 m by 1.15 m) 8 m long (39.6 m2). Seven meters (approximately 35 plants) of central double row was considered for sampling. The plant spacing within the rows was 0.4m, resulting in a plant population of about 34,600 plants ha-1. Selected slips of the 'Smooth Cayenne' variety previously treated with fungicides and pesticides were used. .
It was applied a randomized blocks design, with four replications, using a factorial design (4x3), consisted of four rates (0, 175, 350, and 700 kg ha-1 of K2O) and three combinations of K sources (100% KCl, 100% K2SO4 and a mixture of 40% K2SO4+60% KCl). In the combined treatment, K2SO4 was applied in the first two dressings and KCl in the last two.
Phosphorus was totally applied 30 days after planting at the rate of 80 kg ha-1 of P2O5 as single superphosphate (SSP) containing 18% of P2O5 and 10% of S. Nitrogen was applied at the rate of 600 kg ha-1 of N, as ammonium nitrate together with the potassium treatments. Fertilizers were surface applied, close to the plant base, on an area of maximum root activity, according to the following application schedule: 10%, 30%, 30%, and 30% of the total rate, respectively 1, 5, 7, and 9 months after planting. These optimal N, P, and K rates and fertilizers splitting schedule were determined in recent trials conducted with pineapple in the same region by Spironello et al. (2004) and Teixeira et al. (2002).
At the beginning of flower emission (September, 2004), leaf samples were taken to determine total of nutrient concentrations. The tissue sample comprised whole D-leaves (last fully developed leaf, often the longest leaf) collected from each plot (LACOEUILHE, 1984; CUNHA and CABRAL, 1999). Samples of plant tissue were analyzed according to Bataglia et al. (1983). Composite soil samples, each one with 8 subsamples, were taken from each depth (0-20 cm, 20-40 cm and 40-60 cm) from every replication of the treatments in November 2004. Soil analyses were processed according to the methods described in Raij et al. (2001). Chlorine extraction (plant tissue and soil) for chemical analysis were done by shaking with water and Cl was measures with an ion-selective electrode (RAYMENT AND HIGGINSON, 1992).
The effects of treatments were evaluated using analysis of variance (ANOVA). Differences among sources of K were assessed with Tukey multiple range test (p<0.05) when the effects of sources were statistically significant (p<0.05 for the F test in ANOVA). For the variables significantly affected by rates of K, the quantitative effects of rates were determined adjusting regression equations. Only models (equations) statistically significant (p<0.05) were presented. When the interactions between rates and sources were significant, the equations for rates were established for each source.
RESULTS AND DISCUSSION
Among some chemical characteristics showed in Table 1, only soil S-SO4 and Cl contents were affected by sources of potassium. In general, fertilization with K2SO4 increased soil S-SO4 in comparison with KCl and soil Cl content was higher with KCl application.
The effects of K rates on the soil exchangeable K in all sampled depths was linear, independently of the K source used (Figure 1). The effect of the different sources on soil K availability was not statistically significant (p>0.05 for the F test in ANOVA). In plants with no applied K, pineapple cropping from planting to flowering caused soil K depletion of about 0.5 mmolc dm-3 at 0-20 cm depth. The minimum rate of K application necessary to maintain soil exchangeable K at the same concentration found prior to pineapple planting (0.7 mmolc dm-3) was around 290 kg ha-1 of K2O (Figure 1). According to Spironello and Furlani (1997), the rate of K recommended for pineapple in such soil conditions is 600 kg ha-1 of K2O. Comparing to soil K depletion observed, that rate of K recommended is more than enough to keep K availability found prior to pineapple planting.
The changes on soil K at the 40-60 cm depth, caused by K application, indicate that some K was lost by leaching. As showed in Figure 1, for each 100 kg ha-1 of K2O applied approximately the soil K at the 40-60 cm depth increased 0.07 mmolc dm-3. According to Cunha and Cabral (1999), at this depth there is no significant activity of the pineapple root system, stressing the need to split the rates of K in order to increase potassium fertilizers efficiency, especially in tropical soils with low cation exchange capacity, such as the one used in the experiment (CEC 44 mmolc dm-3). The downward movement of potassium was the same for all K sources (Table 1). These results did not agree with those reported by Kleinhenz (1999) who considered that K applied as potassium chloride more vulnerable to losses by leaching than K as potassium sulphate. This discrepancy might be related with differences in clay content or potassium holding capacity between the soils used in these studies.
The application of K2SO4 increased significantly soil S-SO4-2 down to 40-60 cm soil layer (Table 1 and Figure 2A). The effects were more pronounced in deep layers than in surface one, demonstrating that S-SO4 was rapidly leached and retained only in the deep layers of the soil profile. Probably it explains why despite the use of SSP as P source, soil S-SO4 did not reach the critical level of 10 mg dm-3, for surface soil layer, proposed by Raij et al. (1997).
Potassium fertilization using KCl and K2SO4+KCl caused a linear increase on soil Cl content at all sampled depths (Figure 2B). The increase of soil Cl, as consequence of KCl application, may be of concern, due to pineapple sensitivity to chloride as pointed by Teiwes and Grüneberg (1963), Zehler et al. (1986) and Kleinhenz (1999). Chlorine accumulation in soil is potentially dangerous to intolerant plants and avoiding inputs of this ion through the correct management of fertilizers may be the best choice as demonstrated by Kleinhenz (1999).
Nitrogen concentration in the D-leaf decreased with increasing K rates (Figure 3), probably due to dilution effect caused by increasing rates of K. Average values of leaf N were not affected by K sources (Table 2), and were over critical level (12 g kg-1) proposed by Teixeira et al (2009) for 'Smooth Cayenne' cropped in the state of Sao Paulo (Brazil). The effect of the different sources on K supply to pineapple was not statistically significant (p>0.05 for the F test in ANOVA). So, Leaf K increased with the application of K fertilizers, independently of K source (Figure 3). This result concurred with changes observed on soil K availability. For leaf K and soil K availability, there were no differences between K sources.
The lower limit considered adequate for leaf K is 21 g kg-1, according to Teixeira et al (2009), was reached with approximately 533 kg ha-1 of K2O (Figure 3). Those results accorded with the recommendations of Spironello and Furlani (1997) for pineapple crop in the State of São Paulo, where is prescribed the rate of 600 kg ha-1 of K2O.
Leaf K content of pineapple plants variation was associated with soil K availability (Figure 4) and quadratic function was adjusted relating soil and leaf K concentrations. According to this model, 1.2 mmolc dm3 in soil K (0-20 cm) was necessary to achieve a desired leaf K concentration for pineapple plant, around 21 g kg-1.
Increasing potassium rates reduced leaf Ca and Mg (Table 3). It may be explained by competition between ions for transport sites in the plasma membrane of the roots (MARSCHNER, 1997). Lacoeuilhe (1984) reported a strong effect of K accumulation on decreasing leaf contents of Ca and Mg. Leaf Ca and Mg were below the sufficiency limits (8 and 3 g kg-1, respectively) proposed by Lacoeuilhe (1984). As the pineapple plants presented normal development, without any symptom of Ca or Mg deficiency, it is possible that the sufficiency limits for Ca and Mg suggested by Lacoeuilhe (1984) may be too high for the Smooth Cayenne variety used.
Although single superphosphate with 11% of S was applied at planting (450 kg ha-1 of SSP), the use of K2SO4 (X) still caused a linear increase (Y= 0.72+0.000282X; R2=0.30; p<0.05) on leaf sulfur content (Y). The minimum adequate level of leaf S for pineapple is not clear in the literature: Haag et al. (1963) found that approximately 10 g kg-1 of S in the pineapple leaf may be normal and with 6.5 g kg-1 of S plants showed deficiency symptoms; differently, Cibes and Samuels (1958) stated that 2.5 g kg-1 was a normal value of leaf S concentration and 1.3 g kg-1 was a minimum. Paula et al. (1991) used ammonium sulphate as N source for pineapple up to 75 g (NH4)2SO4 per plant and found maximum leaf S content around 1.2 g kg-1. In the present experiment, besides the use of SSP, the rate of 700 kg ha-1 of K2O as K2SO4 increased leaf S to values not higher than 1.0 g kg-1. It is not clear if adequate leaf S is variety-dependent for pineapple plants but it seems that for the 'Smooth Cayenne' the 1.3 g kg-1 suggested as minimum by Cibes and Samuels (1958) may not apply. The low values of leaf S found may be attributed in some degree to the mobility of S-SO4 in the soil profile. S-SO4 is not hold in the surface layers of tropical soils but tend to accumulate in the subsurface layers where the shallow root system of pineapple plants may not efficiently take it up. In the Table 1 is possible to confirm that soil S-SO4 contents increased with soil depth.
Among micronutrients, only the effects of rates and sources of K on leaf Cl content were significant. Other micronutrients leaf contents, as B, Cu, Mn and Zn were not affected neither by rates nor by sources of K (p>0.05 for the F test in ANOVA).The application of KCl or K2SO4+KCl caused significant increase on leaf Cl content. At the rate of 700 kg ha-1 of K2O of KCl or K2SO4+KCl, leaf Cl concentration reached 4.3 g kg-1 of Cl (Figure 5B). Chapman (1973) considered values of leaf Cl from 1.1 to 4.3 g kg-1 as "intermediate range". Samuels and Díaz (1960) applied 270 kg ha-1 of K2O as KCl or K2SO4 and found that chloride-fertilized plants contained 6.1 g kg-1 of Cl as compared to 3.9 g kg-1 of Cl where potassium sulphate was applied. Py et al. (1984) stated that chlorine from KCl would not cause problems if its concentration in D-leaf is lower than 17 g kg-1 of Cl. The effects of KCl or K2SO4+KCl on leaf Cl contents were similar probably because in the combined treatment, K2SO4 was applied in the first two dressings and KCl in the last two. So, at leaf sampling, the soil Cl availability was likely to be the same for both treatments.
Leaf Cl increased linearly in response to Cl accumulation in soil (Figure 5A) and as a function of K fertilization with KCl or K2SO4+KCl (Figure 5B). Despite the relatively narrow variations in soil Cl observed for K sources (Table 1), larger differences were observed in leaf-Cl, demonstrating the pineapple sensitivity to chlorine. It seems that leaf analysis presented better capacity to diagnose Cl toxicity as compared to soil analysis, although soil sampling was done 8 months after the last split application of K fertilizers when considerable Cl leaching may had taken place.
Considering soil Cl availability and possible problems caused by Cl for pineapple nutrition, the use of KCl or K2SO4 + KCl as it was applied in this experiment may pose a risk to plants.
1-The use of KCl or K2SO4+KCl as a source of K to pineapple increased soil Cl availability and Cl contents of plant leaves in comparison to K2SO4 application.
2-Pineapple K uptake was influenced by K rates and by soil K availability, regardless of K sources.
The authors are grateful to Milton and Armando Yoshiura, pineapple growers, for their support for field activities and to Sulphate of Potash Information Board (SOPIB) and to Fundação de Apoio à Pesquisa Agrícola (FUNDAG), for financial support.
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Recebido em: 01-06-2010. Aceito para pubilcação em: 07-01-2011.
1 (Trabalho 141-10).