Productive Potential of Nitrogen and Zinc Fertigated Sugarcane

: The relevance of sugarcane ( Saccharum o ﬃ cinarum L.) in the agribusiness is irrefutable because it not only contributes greatly to the development of countries but is also an important source of job creation and income generation. The objective of this study was to evaluate the stalk productivity (SP) and sugar and alcohol yields of plant and ratoon crops of sugarcane (variety IACSP 95-5000) under N and Zn fertigation treatments using a central pivot, in Cerrado Red Latosol soil. The experiment was conducted under ﬁeld conditions, in the municipality of Jata í , Goi á s (GO), Brazil. A randomized block design was used, with a 4 × 5 split-plot arrangement and three replications. The fertilization treatments consisted of four doses of N (0, 60, 120, and 180 kg ha − 1 ) and ﬁve doses of Zn (0, 2.5, 5.0, 7.5, and 10.0 kg ha − 1 ) in plant and ratoon crops. N fertilization treatments, in the form of urea, were divided into three applications from 60 days after planting. Zn fertilization, in the form of Zn sulfate, was applied in a single application. Sugarcane was harvested 330 days after planting. The productivity (SP) was determined by weighing the stalks present in the respective subplots. Sugar and alcohol yields were calculated from the amount of raw sugar determined in the technological analysis. The sugar and alcohol yields of sugarcane (variety IACSP 95-5000) were improved with the fertigation of 180 kg ha − 1 of N, in relation to Zn doses. Compared with the control (without N fertigation), sugarcane productivity (plant and ratoon crops) increased by 38.90% and 13.70% when treated with 180 kg ha − 1 of N at the Zn dose of 10 kg ha − 1 . Sugarcane (variety IACSP 95-5000) has productive performance, sugar and alcohol yield, optimized and maximized when fertigated with 10 kg ha − 1 of zinc and 180 kg ha − 1 of nitrogen.


Introduction
The relevance of sugarcane in the Brazilian agribusiness is irrefutable because it not only contributes greatly to the development of the country but is also an important source of job creation and income generation. Despite investments in the dissemination of technologies to improve the quality of the quality of the final product, additional scientific research may still contribute greatly to the maximization of the production process [1,2].
Such technologies include the use of irrigation to mitigate the effect of water scarcity, and the use of fertigation to increase the efficient use of nutrients in sugarcane production. Despite these technologies being interesting and viable alternatives, they are still rarely used in sugarcane producing countries. Irrigation promotes economic, social, and environmental sustainability, and is also an important tool to increase sugarcane productivity [3][4][5][6][7]. The use of fertilizers via irrigation (fertigation) reduces losses without increasing production costs, moreover, irrigation alone greatly affects the stalk, sugar, and alcohol yield variables, but fertigation usually intensifies these increases [8][9][10][11], and has thus become a relevant technique to supply the water and nutrients required by sugarcane. Due to the importance of this technique, a further understanding of the characteristics related to water and nutrient supply may contribute to significant improvements of sugarcane management systems to obtain higher yields [12].
Nitrogen (N) and zinc (Zn) have been shown to have varied effects on sugarcane (cane-plant), and significant increases in productivity and yield may or may not be associated with the use of these nutrients. Although this ambiguity and the importance of these nutrients are recognized, studies on the association of N and Zn, mainly administered via irrigation water (fertigation), remain limited [13][14][15][16].
Therefore, the objective of this study was to evaluate the stalk productivity (SP) and sugar and alcohol yields of plant and ratoon crops of sugarcane (variety IACSP 95-5000) under N and Zn fertigation treatments using a central pivot, in Cerrado Red Latosol soil.

Material and Methods
The sugarcane (Saccharum officinarum L) experiment was conducted under field conditions at an average altitude of 907 m in an area of the Raízen Mill, in the municipality of Jataí, Goiás (GO), Brazil (17°44′2.62′ S and 51°39′6.06′ W). The area is characterized, which is irregularly distributed throughout the year, by an annual rainfall of ~1800 mm, with rain from October to April and little to no rain from May to September. According to the classification described by Köppen [17], the local climate is tropical savannah with a dry winter (Aw). The minimum and maximum temperatures range from 12 to 15 °C and 35 to 37 °C, respectively. The average temperature during the experiment was 23.50 and 23.20 °C, average relative humidity was 66. 35 and 65.50%, and average rainfall was 115.60 and 103.10 mm, in plant and ratoon crops, respectively ( Figure 1). The soil in the experimental area is classified as dystrophic Red Latosol, is very clayey, and in the Cerrado phase [18]. The characteristics and classifications of the soils in the experimental area are described in Table 1.  The soil in the experimental area is classified as dystrophic Red Latosol, is very clayey, and in the Cerrado phase [18]. The characteristics and classifications of the soils in the experimental area are described in Table 1. Table 1. Physical, chemical, and hydrographic characteristics, and the textural and granulometry classifications of the soil in the experimental area, Jataí-GO. A randomized block design was used, with a 4 × 5 split-plot arrangement and three replications. The fertilization treatments consisted of four doses of N (0, 60, 120, and 180 kg ha −1 ) and five doses of Zn (0, 2.5, 5.0, 7.5, and 10.0 kg ha −1 ) in plant and ratoon crops. The size of the experimental plot was of 0.2 ha. The fertilization treatments were established considering the indication of 60 kg ha −1 of N and 5 kg ha −1 of Zn [19]. N fertilization treatments, in the form of urea, were divided into three applications from 60 days after planting (applied in phenophase of tillering). Zn fertilization, in the form of Zn sulfate, was applied in a single application (applied after planting). The urea and Zn sulfate applied by pivot. All treatments were fertilized in the furrow with P 2 O 5 (100 kg ha −1 ) in the form of triple superphosphate, K 2 O (80 kg ha −1 ) in the form of potassium chloride, and micronutrients, except Zn, according to soil analysis results and recommendations by Sousa and Lobato [19].
The variety used in the experiment was IACSP95-5000, under plant cane conditions. This variety is mainly characterized by a high agricultural production, upright position, excellent ratoon sprouting, high sucrose content, resistance to the major diseases, favorable tillering and canopy closure in medium environments, and does not flower or exhibit tumbling [20].
Soil was prepared using the conventional system, through ploughing and harrowing, followed by the opening of the planting furrows. Planting was mechanized, carried out commercially, and following the recommended number of buds per meter for the specific variety used.
Irrigation was performed by a central pivot, model PC 08-64/03-647/01-646/L4 + AC, made of galvanized steel, under low pressure, with 12 support towers. Irrigation was applied over a total area of 139.31 ha at a speed of 268 m h −1 in the last tower, applying a minimum gross blade of 1.35 mm (for one turn to 100%). The irrigation was managed using the IRRIGER ® software.
Sugarcane degree ( • ) Brix was monitored in the field in the four weeks prior to harvesting. The maturation index (MI) was determined using a portable refractometer to establish the sugarcane time of harvesting, MI classified according to Rosseto [21].
Sugarcane was harvested 330 days after planting. The stalk production (SP) was determined by weighing the stalks present in the respective subplots, quantifying the stalk weight within 2 m of the two central lines. For this, the stalks were cut as close as possible to the soil. The stalks were then spread out and the pointers were detached. The stalks were weighed on a hook-type digital scale (Soil Control) with an accuracy of 0.02 kg and a capacity of 50 kg. A total of 10 stalks were randomly sampled from each plot at harvest and sent to the laboratory of agro-industrial processes of the Raízen Plant, in Jataí, GO, for determination of sugar and alcohol yields, using to the CONSECANA system [22].
Sugar and alcohol yields were calculated from the amount of raw sugar determined in the technological analysis, following [23], using Equations (1) and (2), respectively: where RAç indicates the sugar yield (kg ha −1 ); PCC indicates the amount of raw sugar (%) contained in the stalks as determined by the laboratory; SP indicates the stalk production (t ha −1 ).
where RA indicates the alcohol yield (m 3 ha −1 ); PCC indicates the amount of raw sugar (%) contained in the stalks as determined by the laboratory; F indicates the stoichiometric transformation factor of sucrose into one molecule of glucose and one molecule of fructose, equal to 1.052; ARL indicates the free reducing sugars (%), whose values vary from 0.70% to 0.85%, (the distillery uses 0.7 for high PCC values); Fg indicates the Gay Lussac factor, equal to 0.6475; SP indicates the stalk production (t ha −1 ). The data were subjected to analysis of variance and the F test (p < 0.05). Significant findings were subjected to a regression analysis of the N and Zn fertilization levels using the SISVAR ® statistical software [24].

Results and Discussion
The productivity (SP) of plant crops in response to the N doses was adjusted using the linear model, with R 2 > 92.90% ( two central lines. For this, the stalks were cut as close as possible to the soil. The stalks were then spread out and the pointers were detached. The stalks were weighed on a hook-type digital scale (Soil Control) with an accuracy of 0.02 kg and a capacity of 50 kg. A total of 10 stalks were randomly sampled from each plot at harvest and sent to the laboratory of agro-industrial processes of the Raízen Plant, in Jataí, GO, for determination of sugar and alcohol yields, using to the CONSECANA system [22].
Sugar and alcohol yields were calculated from the amount of raw sugar determined in the technological analysis, following [23], using Equations (1) and (2), respectively: where RAç indicates the sugar yield (kg ha −1 ); PCC indicates the amount of raw sugar (%) contained in the stalks as determined by the laboratory; SP indicates the stalk production (t ha −1 ).
where RA indicates the alcohol yield (m 3 ha −1 ); PCC indicates the amount of raw sugar (%) contained in the stalks as determined by the laboratory; F indicates the stoichiometric transformation factor of sucrose into one molecule of glucose and one molecule of fructose, equal to 1.052; ARL indicates the free reducing sugars (%), whose values vary from 0.70% to 0.85%, (the distillery uses 0.7 for high PCC values); Fg indicates the Gay Lussac factor, equal to 0.6475; SP indicates the stalk production (t ha −1 ). The data were subjected to analysis of variance and the F test (p < 0.05). Significant findings were subjected to a regression analysis of the N and Zn fertilization levels using the SISVAR ® statistical software [24].

Results and Discussion
The productivity (SP) of plant crops in response to the N doses was adjusted using the linear model, with R 2 > 92.90% (  Teodoro et al. [25] reported that the marginal substitution rate of irrigation water for N is not fixed, and increases as the irrigation depth decreases, but only to a certain level. These authors also Teodoro et al. [25] reported that the marginal substitution rate of irrigation water for N is not fixed, and increases as the irrigation depth decreases, but only to a certain level. These authors also reported that the response of sugarcane to N fertilization, based on the straight line that limits the production region, increases in direct relation to the water availability of the soil. Joris [26] observed that the absorption of N from fertilizer is lower in medium textured soil than in clayey soil when applied in similar quantities and times; thus concluding that high doses of N (above 120 kg ha −1 ) can increase sugarcane SP in responsive environments. In the present study, N significantly increased the SP and sucrose content of sugarcane (plant crops), thus consequently increasing the sugar yield, under the Zn applications. In addition, a relationship exists between productivity and evapotranspiration in sugarcane, therefore, sugarcane growth and development are directly proportional to the transpired water [27,28]. These findings indicate that N and Zn fertigation can significantly improve sugarcane SP.
The application of nutrients via irrigation water promoted a significant increase in sugarcane productivity (>22%). In addition to a productivity of 152 t ha −1 , sugarcane extracts 1.4 kg ha −1 of Mn and 2.3 kg ha −1 of Zn [29,30]. This SP is similar to the results obtained in the present study in the fertigation treatment with 7.5 kg ha −1 of Zn and 180 kg ha −1 of N, and is lower than the fertigation treatment with 10.0 kg ha −1 of Zn and 180 kg ha −1 of N ( Figure 2B).
An increased nutrient supply (N and Zn) has been shown to result in vigorous sugarcane growth [31], consequently resulting in sugarcane plants with maximum height and diameters, and improved total recoverable sugar (TRS) and sugarcane SP. In the present study, the productivity of sugarcane fertigated with the highest doses of N and Zn was >160 t ha −1 . Becari [32] reported that Zn application resulted in a sugarcane SP of 157 t ha −1 , which was 21.7% higher than the productivity (of variety SP 81−3 250) obtained in the controls planted in Red Latosol with low Zn content.
Agronomy 2020, 10, x FOR PEER REVIEW 5 of 12 reported that the response of sugarcane to N fertilization, based on the straight line that limits the production region, increases in direct relation to the water availability of the soil. Joris [26] observed that the absorption of N from fertilizer is lower in medium textured soil than in clayey soil when applied in similar quantities and times; thus concluding that high doses of N (above 120 kg ha −1 ) can increase sugarcane SP in responsive environments. In the present study, N significantly increased the SP and sucrose content of sugarcane (plant crops), thus consequently increasing the sugar yield, under the Zn applications. In addition, a relationship exists between productivity and evapotranspiration in sugarcane, therefore, sugarcane growth and development are directly proportional to the transpired water [27,28]. These findings indicate that N and Zn fertigation can significantly improve sugarcane SP.
The application of nutrients via irrigation water promoted a significant increase in sugarcane productivity (>22%). In addition to a productivity of 152 t ha −1 , sugarcane extracts 1.4 kg ha −1 of Mn and 2.3 kg ha −1 of Zn [29,30]. This SP is similar to the results obtained in the present study in the fertigation treatment with 7.5 kg ha −1 of Zn and 180 kg ha −1 of N, and is lower than the fertigation treatment with 10.0 kg ha −1 of Zn and 180 kg ha −1 of N ( Figure 2B).
An increased nutrient supply (N and Zn) has been shown to result in vigorous sugarcane growth [31], consequently resulting in sugarcane plants with maximum height and diameters, and improved total recoverable sugar (TRS) and sugarcane SP. In the present study, the productivity of sugarcane fertigated with the highest doses of N and Zn was >160 t ha −1 . Becari [32] reported that Zn application resulted in a sugarcane SP of 157 t ha −1 , which was 21.7% higher than the productivity (of variety SP 81−3 250) obtained in the controls planted in Red Latosol with low Zn content.
The SP of ratoon crops in response to the N doses was adjusted using the linear model, with R 2 > 82% ( Figure 3A). Compared with the control (0 kg ha −1 of N), the SP increased by 8.70%, 6.60%, 6.90%, 6.10%, and 4.60% when treated with 60 kg ha −1 of N and increased by 26.20%, 19.80%, 20.60%, 18.30%, and 13.70% when treated with 180 kg ha −1 of N, at the Zn doses of 0, 2.5, 5.0, 7.5, and 10.0 kg ha −1 , respectively. Sugarcane SP also increased by 0.14, 0.12, 0.14, 0.13, and 0.11 t ha −1 for each 1 kg ha −1 increase in N at the Zn doses of 0, 2.5, 5.0, 7.5, and 10.0 kg ha −1 , respectively ( Figure 3A).  Orlando Filho et al. [33] evaluated the cumulative effect of increasing doses of N fertilization on the productivity of plant cane and three consecutive ratoon cycles and reported increases of 20% Agronomy 2020, 10, 1096 6 of 11 and 30% for doses of 60 and 120 kg ha −1 of N, respectively, compared to the control. The inadequate management of a sugarcane field, especially with regards to N fertilization, can result in decreases in both crop productivity and longevity [34].
Nutrient availability in the soil is one of the major factors that limits the mean productivity of sugarcane [35][36][37]. Although fertilization is used to increase the soil nutrient availability, it can have a significant impact on the production costs of sugarcane, accounting for up to 25% of these costs.
The sugar yield of plant crops in response to the N doses was adjusted using the linear model, with R 2 > 92% ( Figure 4A). Agronomy 2020, 10, x FOR PEER REVIEW 6 of 12 30% for doses of 60 and 120 kg ha −1 of N, respectively, compared to the control. The inadequate management of a sugarcane field, especially with regards to N fertilization, can result in decreases in both crop productivity and longevity [34]. The SP of ratoon crops in response to the Zn doses was adjusted using the linear model, with R 2 > 97% ( Figure 3B). The SP increased by 10.10%, 10.10%, 9.90%, and 7.90% when treated with 2.5 kg ha −1 of Zn at N doses of 0, 60, 120, and 180 kg ha −1 , respectively. Sugarcane SP also increased by 5.00, 5.30, 5.40, and 4.70 t ha −1 for each 1 kg ha −1 increase in Zn at N doses 0, 60, 120, and 180 kg ha −1 , respectively ( Figure 3B).
Nutrient availability in the soil is one of the major factors that limits the mean productivity of sugarcane [35][36][37]. Although fertilization is used to increase the soil nutrient availability, it can have a significant impact on the production costs of sugarcane, accounting for up to 25% of these costs.
The sugar yield of plant crops in response to the N doses was adjusted using the linear model, with R 2 > 92% ( Figure 4A).  Sugarcane crops fertigated with high doses of N usually presented significant increases in sugar productivity (>22 t ha −1 ), because sugarcane tends to show improved growth and development, which are normally associated with increases in the final values of alcohol and sugar production, in response to nutrient application via irrigation water [11,39].
The sugar yield of ratoon crops in response to the N doses was adjusted using the linear model, with R 2 > 84% ( Figure 5A). Compared with the control (0 kg ha −1 of N), the sugar yield increased by 10.70%, 7.90%, 7.90%, 7.30%, and 6.20% when treated with 60 kg ha −1 of N and increased by 32.  Sugarcane crops fertigated with high doses of N usually presented significant increases in sugar productivity (>22 t ha −1 ), because sugarcane tends to show improved growth and development, which are normally associated with increases in the final values of alcohol and sugar production, in response to nutrient application via irrigation water [11,39].
The alcohol yield of plant crops in response to the N doses was adjusted using the linear model, with R 2 > 92% ( Figure 6A). Compared with the control (0 kg ha −1 of N), the alcohol yield increased by 11.90%, 14.80%, 15.80%, 14.60%, and 14.20% when treated with 60 kg ha −1 of N and increased by 35.86%, 44.53%, 47.49%, 43.86%, and 42.67% when treated with 180 kg ha −1 of N, at the Zn doses of 0, 2.5, 5.0, 7.5, and 10.0 kg ha −1 , respectively. The alcohol yield of sugarcane increased by 0.04 m 3 ha −1 for each 1 kg ha −1 increase in N at the Zn dose of 10 kg ha −1 ( Figure 6A).  The maximum alcohol yield (>15 m 3 ha −1 ) was found in sugarcane fertigated with 10 kg ha −1 of Zn and 180 kg ha −1 of N. Alcohol yields 12 m 3 ha −1 have been observed in sugarcane irrigated and fertilized with N doses >100 kg m 3 ha −1 [39,41].
Chandiposha et al. [42] reported increases in plant height, stem diameter, productivity, and sugar and alcohol yields in sugarcane due to the additional availability of N and Zn. Increased N and Zn doses have been shown to increase the accumulation of stalk dry matter, total aerial dry matter, and the number and length of internodes; thus improving the growth of plants and resulting in higher sugar and alcohol yields [11,41,43].
The alcohol yield of ratoon crops in response to the N doses was adjusted using the linear model, with R 2 > 84.8% ( Figure 7A). Compared with the control (0 kg ha −1 of N), the alcohol yield increased by 10.57%, 7.82%, 7.89%, 7.21%, and 6.10% when treated with 60 kg ha −1 of N and increased by 31.70%, 23.40%, 23.70%, 21.60%, and 18.40% when treated with 180 kg ha −1 of N, at the Zn doses of 0, 2.5, 5.0, 7.5, and 10.0 kg ha −1 , respectively. The alcohol yield of sugarcane fertigated with 10 kg ha −1 of Zn indicated an increase of 0.01 m 3 ha −1 for each 1 kg ha −1 increase in N at the N dose of 180 kg ha −1 ( Figure 7A).
Chandiposha et al. [42] reported increases in plant height, stem diameter, productivity, and sugar and alcohol yields in sugarcane due to the additional availability of N and Zn. Increased N and Zn doses have been shown to increase the accumulation of stalk dry matter, total aerial dry matter, and the number and length of internodes; thus improving the growth of plants and resulting in higher sugar and alcohol yields [11,41,43].
The alcohol yield of ratoon crops in response to the N doses was adjusted using the linear model, with R 2 > 84.8% ( Figure 7A). Compared with the control (0 kg ha −1 of N), the alcohol yield increased by 10.57%, 7.82%, 7.89%, 7.21%, and 6.10% when treated with 60 kg ha −1 of N and increased by 31. Carvalho et al. [44] reported increases in the gross yield of alcohol and SP in response to an increased irrigation level. Other studies also reported increased growth, productivity, technological quality, and gross yields of alcohol and sugar in sugarcane fertigated with N [41,[45][46][47].
Azevedo [48] researched plant cane and reported a maximum gross alcohol yield of 11.50 m 3 ha −1 with a total quantity of water of 1043 mm. Cunha et al. [41] reported that the gross alcohol yield increased by 0.03 m 3 ha −1 for each 1% increase in water replacement in sugarcane. Carvalho et al. [44] reported increases in the gross yield of alcohol and SP in response to an increased irrigation level. Other studies also reported increased growth, productivity, technological quality, and gross yields of alcohol and sugar in sugarcane fertigated with N [41,[45][46][47].
Azevedo [48] researched plant cane and reported a maximum gross alcohol yield of 11.50 m 3 ha −1 with a total quantity of water of 1043 mm. Cunha et al. [41] reported that the gross alcohol yield increased by 0.03 m 3 ha −1 for each 1% increase in water replacement in sugarcane.

Conclusions
The sugar and alcohol yield of sugarcane (plant crops) in relation to zinc doses is potentiated with the use of 180 kg ha −1 nitrogen fertigation, in which the increments are significant (0.81 ton ha −1 and 0.58 m 3 ha −1 ) for each 1 kg ha −1 increase in Zn, in the other doses (0, 60, 120 kg ha −1 of N), these increases practically do not vary (0.37 ton ha −1 and 0.27 m 3 ha −1 ).
Compared with the control (without N fertigation), the sugarcane productivity (plant and ratoon crops) increased by 38.90% and 13.70% when treated with 180 kg ha −1 of N at the Zn dose of 10 kg ha −1 .
Compared with the control (without Zn fertigation), the sugarcane productivity (plant and ratoon crops) increased by 30.80% and 31.83% when treated with the maximum dose of zinc and N, respectively; the increase in sugarcane productivity is the same in plant and ratoon crops that shows the benefit of Zn fertigation.
The sugar and alcohol yields of sugarcane (variety IACSP 95-5000) were improved with the fertigation of 180 kg ha −1 of N, in relation to Zn doses. The recommended Zn dose for irrigated sugarcane or with high doses of N fertilization is 10 kg ha −1 .
The recommendation of highest doses of zinc and nitrogen in sugarcane (plant and ratoon crops) had the greatest effects on the productive potential of the crop, providing better sugar and alcohol yields. Sugarcane (variety IACSP 95-5000) has the productive performance, sugar and alcohol yield, optimized and maximized when fertigated with 10 kg ha −1 of zinc and 180 kg ha −1 of nitrogen.