Nutritional status of three sugarcane varieties grown in the northeast region of Brazil

1 Centro de Ciências Agrárias, Universidade Federal de Alagoas, BR 104, Km 85, s/n, 57100-000. Rio Largo, Alagoas, Brazil. 2 Instituto Federal de Pernambuco, Campus Vitoria de Santo Antão, Propriedade Terra Preta, S/N, 55602-970, Vitória de Santo Antão, Pernanbuco, Brazil. 3 Centro de Energia Nuclear na Agricultura, Universidade de São Paulo, Av. Centenário, 303 São Dimas CEP: 13416000 Piracicaba (SP), Brazil.


INTRODUCTION
The evaluation of plant nutritional status is a tool to improve crop fertilization and thus ensure better productivity.The nutritional status of sugarcane influences the photosynthetic rate and metabolism of sucrose, consequently affecting yield, juice quality, longevity, and profitability of sugarcane plantations (Malavolta et al., 1997;Raij, 2011).Leaf analysis is widely used because leaves have high metabolic activity and exhibit the changes occurring in plant nutritional status.In Brazil, the use of leaf analysis to diagnose the nutritional status of sugarcane began in the 1960s.Gallo et al. (1968) conducted some of the first studies on the nutritional status of sugarcane in the state of São Paulo, Brazil.
Leaf nutrient contents vary according to the part of the plant and sampling time due to crop growth rates (Rozane et al., 2008).Several studies use leaf +1, the first leaf of the stem, to assess plant nutritional status (Ferreira et al., 2015;Garcia et al., 2018).However, several authors recommend the use of leaf +3 collected during the stage of maximum growth of the crop to assess the nutritional status of sugarcane (Orlando Filho, 1983;Malavolta et al., 1997;Raij, 2011;Benett et al., 2016;Oliveira et al., 2018;Rhodes et al., 2018).
The type of soil and plant variety also influences leaf nutrient contents (Faroni et al., 2009;Silva et al., 2018b).Therefore, correctly interpreting the results of leaf analysis leads to more efficient use of inputs.In the literature, adequate ranges of leaf nutrient content are found for sugarcane.Macronutrient contents of N, P, K, Ca, Mg and S range from 16 to 21, 1.5 to 3.5, 6 to 16, 2 to 10, 1.0to 3.6 and 1.3 to 3.0 g kg -1 , respectively.Micronutrient contents of Cu, Fe, Mn and Zn range from 6 to 50, 8 to 17, 40 to 500, 25 to 250 and 10 to 50 mg kg -1 , respectively (Orlando Filho, 1983;Malavolta et al., 1997;Raij, 2011).
The studies that determined these value ranges were conducted with old varieties, which are practically no longer grown.This makes it difficult to use leaf analysis to identify and correct nutritional deficiencies and imbalances (Silva et al., 2017).Research using more recent varieties shows great variation in leaf nutrient contents (Oliveira, 2014;Silva et al., 2017).Sugarcane varieties have morphophysiological differences that influence nutrient uptake kinetics and consequently nutritional status.Therefore, studies that evaluate the nutritional status of modern varieties are essential.In this respect, the aim of this study was to assess the nutritional status of three sugarcane varieties in the plantcane and first regrowth cycles in the Northeast of Brazil.

Study area and implantation of the experiment
The study was carried out in the city of Anadia (Figure 1), state of Alagoas (AL) (09°41'04''S and 36°18'15"W).The study period was from August 2011 to January 2014, which comprises the plant-cane and first regrowth cycles.The climate is tropical with autumn-winter rains (As) and a well-defined dry season, according to Köppen climate classification.Average annual precipitation is 1500 mm (Figure 2) and average annual temperature of 29°C.The relief varies from flat to gently undulating.
The soil of the experimental area was classified as Latossolo Amarelo Distrófico (Embrapa, 2018) and Oxisol (USDA Soil Taxonomy).Prior to the installation of the study, soil chemical analysis was carried out at depths of 0-20 and 20-40 cm.The results (Table 1) were used to calculate the amounts of limestone and gypsum to increase base saturation by 60% in topsoil and reduce aluminium saturation in subsurface soil, as proposed by Oliveira et al. (2018) and Raij (2011).After applying dolomitic limestone and gypsum (3:1 ratio) (Raij, 2011;Oliveira et al., 2018), the soil was plowed, harrowed and then furrowed.
Planting was carried out in August, 2011.At the bottom of the planting furrow, 500 kg ha -1 of fertilizer 09-14-22 was applied.Three sugarcane varieties were planted (RB92579, RB961552 and RB98710) and treatments were arranged in randomized complete block design with five replicates.RB92579 was chosen as the study  reference because it is the most planted in the state of Alagoas (34% of the planted area) and the third most planted in Brazil (12% of the planted area).RB961552 and RB98710 are new varieties and there is little information in the literature.
The plots consisted of 7 furrows (8 m long) at a spacing of 1.0 m, totaling an area of 56 m 2 (30 m 2 of useful area).Planting density ranged from 15 to 18 buds per meter of furrow (Silveira et al., 2007;Oliveira et al., 2018).The buds were collected in the primary nursery area of Usina Triunfo.Fertilization of the first regrowth cane was carried out after the harvest of the plant-cane.500 kg ha -1 of fertilizer 20-05-25 was applied by hand.Weed and pest management used in the first regrowth cycle was the same as that used in the plant-cane cycle.
Plant nutritional status was evaluated at the maximum growth phase of the crop (8 months after planting and 6 months after the first harvest).Twenty (20) leaves were randomly collected in the useful area of the plot.The leaves were washed in deionized water.Then, the middle third of the leaf (minus the midrib) was separated for chemical analysis.The samples were dried in an oven with forced circulation at 65°C until reaching constant weight and ground in Wiley mill.Leaf contents of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), boron (B), copper (Fe), manganese (Mn) and zinc (Zn) were determined according to the methods described by Malavolta et al. (1997).N was extracted by digestion with sulfuric acid and determined by the Kjeldahl method.B was extracted by dry digestion in a muffle Table 2. Average macronutrient contents in leaf +3 of three sugarcane varieties at the maximum growth phase in the plantcane (PC) and first regrowth (FR) cycles.

Variety
Nitrogen (g kg furnace and determined by colorimetry.The other nutrients were extracted through nitric-perchloric digestion.P was determined by colorimetry through the development of blue color by the reduction of phosphomolybdenum complex and K by flame photometry.Ca, Mg, Cu, Mn, Zn and Fe were determined by atomic absorption spectrophotometry and S by turbidimetry (Malavolta et al., 1997;Silva and Queiroz 2002).Average nutrient contents in leaves were submitted to analysis of variance by the F test and the means compared by the Scott-Knott test at 5%.These analyses were carried out using the Sisvar software (Ferreira, 2011).

RESULTS AND DISCUSSION
There was significant difference in leaf N contents in the two crop cycles evaluated in this study (Table 2).N is a component of amino acids, proteins and enzymes, in addition to being essential for adequate plant growth and development (Taiz et al., 2017).In the plant-cane cycle, RB961552 had the highest leaf N content (34.07 g kg -1 ), which was 11 and 25% higher than N contents in leaf +3 of RB92579 and RB98710, respectively.However, in the first regrowth cycle, RB92579 had the highest leaf N content (21.44 g kg -1 ), which was 10% higher than the other varieties (Table 2).In comparing leaf N contents of the three varieties with those reported by Orlando Filho (1983), Malavolta et al. (1997) and Raij (2011), RB98710 showed adequate N contents in the plant-cane cycle, while RB92579 and RB961552 contents exceeded those considered adequate.Nutrient contents higher than those required for the plant may characterize luxury consumption, or another factor may have limited growth (Faroni et al., 2009).In the first regrowth cycle, all varieties had adequate contents according to the authors mentioned earlier.
Higher leaf N content in the plant-cane cycle is due to the higher efficiency of nitrate uptake by the crop at this stage when compared with the first regrowth cycle (Table 2) (Silva et al., 2017).Soil preparation (plowing and harrowing) and correction (lime and gypsum application) in sugarcane renovation areas stimulates microbial activity.This results in higher mineralization rate of soil organic matter and increased nitrate content available to plants (Oliveira et al., 2011a;Ferreira et al., 2015).Furthermore, N uptake and translocation is influenced by endogenous availability of P (Magalhães, 1996).Higher endogenous P availability results in lower Km (Michaelis-Menten constant) and higher N uptake, thus, fertilization results in increased P availability in soil, which favors increased N uptake.
Leaf P content differed significantly only in the first regrowth cycle (Table 2).P is essential for cell division and plant energy metabolism.It influences the uptake of several various nutrients (including N), tillering and initial growth of sugarcane, in addition to improving juice quality for industrialization (Taiz et al., 2017;Garcia et al., 2018;Oliveira et al., 2018).In the plant-cane cycle, the average P content for the three varieties was 1.33 g kg -1 (Table 2), which is considered inadequate according to Orlando Filho (1983), Malavolta et al. (1997) and Raij (2011).However, plants did not show any deficiency symptoms even if leaf P content was below the recommended level.Oliveira et al. (2018) stresses that nutrient content in leaf +3 cannot be related to nutrient accumulation in shoot biomass, because plant growth is a result of dry matter accumulation, with a dilution of elements in biomass.This phenomenon is known as the "dilution effect".As stalk yield in the plant-cane cycle was 44% higher than in the first regrowth cycle, there was dilution effect for phosphorus in the plant-cane cycle (Oliveira et al., 2017).Silva et al. (2017) reported the occurrence of this phenomenon for N and P contents in varieties SP813250, RB867515, RB92579 and VAT90212 grown in Anadia (AL).
In the first regrowth cycle (Table 2), all varieties had adequate leaf P contents according to Raij (2011), but lower than those recommended by Orlando Filho (1983) and Malavolta et al. (1997).RB98710 had the highest leaf P content, which was 25% higher than RB92579 and RB961552.Oliveira et al (2017) found that RB98710 had higher inorganic phosphorus content in juice than RB92579.
The varieties did not present significant difference for leaf K contents in any of the crop cycles (Table 2).Average K contents in leaf +3 in the plant-cane and first regrowth cycles were 9.92 and 14.36 g kg -1 , respectively (Table 2).These values are 10.89 and 36.21%higher than those found in the study of Silva et al. (2017) which were 8.84 and 9.1 g kg -1 in the plant-cane and first regrowth cycles.K is the nutrient that sugarcane most absorbs and accumulates (Oliveira et al., 2018;Silva et al., 2018a).It plays a key role in stomatal movement and as an enzyme activator, which is essential for the growth of sugarcane (Taiz et al., 2017).All varieties had adequate leaf K contents in both crop cycles, according to Orlando Filho (1983), Malavolta et al. (1997) and Raij (2011).
There was a significant effect in leaf Ca contents among the varieties only in the first regrowth cycle (Table 2).In the plant-cane cycle, average Ca content of the three varieties was 3.01 g kg -1 , which is considered adequate by Raij (2011).In the first regrowth cycle, Ca content did not differ between RB92579 and RB98710 (2.38 g kg -1 ) (Table 2).Ca content in RB961552 was 1.68 g kg -1 , which was considered low by Orlando Filho (1983), Malavolta et al. (1997) and Raij (2011).
Sugarcane varieties did not exhibit significant difference in Mg content in both the plant-cane and the first regrowth cycles (Table 2).The average leaf Mg content of the three varieties was 1.31 g kg -1 in the plantcane cycle and 1.62 g kg -1 in the first regrowth cycle.In both crop cycles, Mg content was considered adequate by Orlando Filho (1983) and Raij et al. (2011), and inadequate according to Malavolta et al. (1997).In regard to S contents in leaf +3, there was a significant effect among the varieties in both crop cycles (Table 2).
RB92579 and RB98710 have similar content in the plantcane cycle of 1.48 g kg -1 , which is considered adequate by Orlando Filho (1983).S deficiency was found in RB961552, which had S content of 1.24 g kg -1 . S is a component of three amino acids (methionine, cysteine and cystine), and its deficiency is initially observed in younger leaves (Malavolta et al., 1997;Taiz et al., 2017).In the first regrowth cycle, RB98710 had the highest leaf S content of 1.40 g kg -1 , which was considered adequate by Orlando Filho (1983).RB92579 and RB961552 were similar to each other and showed an average content of 1.12 g kg -1 , which was below the reference value.Ca and S deficiency was not expected, as limestone and gypsum were applied in the study area to increase base saturation to 60% (Malavolta et al., 1997;Raij 2011;Oliveira et al., 2018).However, the fact that RB961552 was deficient in both nutrients leads us to speculate that it has different nutrient uptake kinetics from the other varieties, which resulted in lower uptake.
The results showed a varietal effect for leaf B contents only in the first regrowth cycle (Table 3).In the plant-cane cycle, the average leaf B content was 13.91 mg kg -1 .In the first regrowth cycle, RB98710 and RB92579 showed an average B content of 14.37 mg kg -1 , which is 27% higher than RB961552.All three varieties had leaf B contents considered adequate in both crop cycles.
Leaf Fe contents exhibited a varietal effect only in the plant-cane cycle (Table 3), in which RB98710 had the highest Fe contents in leaf +3, while RB92579 and RB961552 did not differ from each other (97.2 mg kg -1 , on average).In the first regrowth cycle, leaf Fe content was similar for all three varieties.The high Fe content in the plant-cane cycle is a result of precipitation distribution in 2011 and 2012 (Figure 2), which promoted increased Fe solubility and uptake (Kirkiby and Römheld, 2007).According to Orlando Filho (1983), plants had adequate Fe contents in both cycles.
There was no significant effect among the varieties for leaf Cu and Mn contents (Table 3).The average leaf Cu content of the three varieties was 3.2 and 4.27 mg kg -1 in the plant-cane and first regrowth cycles, respectively, while average Mn content was 16.2 and 17.53 mg kg -1 , respectively (Table 3).Plants exhibited inadequate leaf contents for both nutrients according to Orlando Filho (1983), Malavolta et al. (1997) and Raij (2011).According to Oliveira et al. (2011b), the soils located between the Northeast of the state of Minas Gerais and Rio Grande do Norte are commonly deficient in these nutrients.Oliveira et al. (2014) and Silva et al. (2017) have also reported Cu and Mn deficiency in sugarcane plantations in the state of Alagoas.
Cu and Mn act as components and activators of several enzymes, including polyphenol oxidase, which is involved in the synthesis of lignin from phenolic compounds (Kirkiby and Römheld, 2007).Reduced lignin synthesis as a result of the deficiency of these metals causes accumulation of phenols that negatively influence the color of the juice and hinders the manufacturing process of sugar and alcohol.Moreover, Cu and Mn deficiency results in lower photosynthetic rates because these elements are components of enzymes responsible for electron transport and water splitting in photosynthesis (Kirkiby and Römheld, 2007;Taiz et al., 2017).Thus, adequate supply of these nutrients to plants is important.In evaluating the application of steel slag in sugarcane cultivars, Madeiros et al. (2009) reported an increase in Mn leaf contents.Benett et al. (2016) evaluated different sources and doses of Mn in RB851552 and found that the application of Mn linearly influences leaf Zn contents.
There was a varietal effect for Zn contents in leaf +3 in the plant-cane and first regrowth cycles (Table 3).In the plant-cane, RB98710 had the highest leaf content.However, it did not differ from RB961552 in the first regrowth cycle and presented an average content of 13.6 mg kg -1 .RB92579 had the lowest Zn content in both crop cycles, and it did not differ from RB961552 in the plantcane cycle.The three varieties presented leaf Zn contents in both cycles considered adequate by Raij et al. (2011) but low by Malavolta et al. (1997).Silva et al. (2017) found Zn contents in leaf +3 of four sugarcane varieties of 14.3 and 13.4 mg kg -1 in the plant-cane and first regrowth cycles, respectively.These results were similar to those found in this study in the plant-cane cycle and 5% higher in the first regrowth cycle.
In general, the liming, gypsuming in the implantation of the sugarcane field and the fertilization used in the two cycles of cultivation was sufficient to adequately supply the need for most nutrients.However, it is necessary to fertilize with Cu and Mn to increase productivity.

Conclusion
There was a varietal effect for macronutrient and micronutrient contents in both crop cycles.RB961552 was the only variety to present Ca deficiency in the first regrowth cycle, and S deficiency in both crop cycles, which indicates that it has different uptake kinetics from the other varieties evaluated in this study.All three varieties presented Cu and Mn deficiency, which is one of the limiting factors of sugarcane production.

Figure 1 .
Figure 1.Location of the city of Anadia, state of Alagoas (AL), Brazil.

Figure 2 .
Figure 2. Average monthly precipitation in the study area.

Table 1 .
Soil chemical analysis at 0-20 cm and 20-40 cm of the experimental area.

Table 3 .
Average micronutrient contents in leaf +3 of three sugarcane varieties at the maximum growth phase in the plant-cane (PC) and first regrowth (FR) cycles.
Averages followed by the same letter in the column do not differ statistically from one another by the Scott-Knott test at 5%.