Agronomic performance and industrial yield of sugarcane under water-saving irrigation in cerrado soil

The objective of this study was to evaluate the growth and gross yield of sugar and ethanol of first-year sugarcane with water-saving irrigation via hose-drawn traveller using a line of sprinklers. The experimental design was randomized blocks, analyzed in a split plot scheme with four replications. The factors evaluated in the plots consisted of five levels water-saving irrigation applied after planting (0, 30, 45, 60 and 75 mm). The subplots were represented by four evaluation periods (90, 170, 250 and 330 days after planting DAP). The sugar yield and gross alcohol yield were evaluated punctually at the end of the cycle to 330 DAP. In the central lines of the subplots, the morphological characteristics relative to plant height, culm diameter, internodes length, number of sugarcane plants, number of leaves, leaf area, leaf length and leaf width, were evaluated. The gross yields of sugar and alcohol were calculated using the raw sugar value determined by technological analysis of the broth from a sample with 12 culms per experimental unit. Water-saving irrigation provides a positive effect on leaf length, leaf area, plant height and number of sugarcane plants. Water-saving irrigation of 75 mm definitely promotes an increase of 30% in gross sugar and alcohol yield.


INTRODUCTION
Currently, increases in productivity of sugarcane have been achieved combined with a higher quality and gross yield of sugar and alcohol from sugarcane raw material, in large part due to the use of irrigation (Simões et al., 2015).
The use of irrigation in the culture of sugarcane is essential for growth, development and increased crop productivity (Souza et al., 2015).Irrigation provides productivity expectation well above the minimum required for renewal of the area favoring much greater potential of longevity of sugarcane (Silva et al., 2014).
There is a strong correlation between levels irrigation and the variables that define the quality of the raw material of sugarcane, mainly the content of total recoverable sugars, the total soluble solids (Brix o ), the pol, the purity and the pol percent cane (PCC) increased in proportion with the irrigation water levels (Farias et al., 2009).
In the sugarcane culture, different types of irrigation are used, including irrigation by mechanized spraying, selfpropelled, center pivot and subsurface drip irrigation (Quintana, 2010).
In self-propelled irrigation systems currently available in the domestic market, there are two distinct forms of water spray for crops: Irrigation bar or hydraulic cylinder (Prado, 2008).The use of self-propelled spraying with an irrigation bar is highlighted.The irrigation bar can replace the cylinder spray in lower slope areas, with the advantage of a more uniform distribution of water and droplets with a smaller diameter (Marouelli et al., 2013).
From the different investments aiming to increase the yield of sugarcane, water-saving irrigation should be highlighted, as it may result in an increased production without expanding the agricultural area (Dalri et al., 2008;Dalri andCruz, 2002, 2008;Quintana, 2010).Thus, water-saving irrigation of sugarcane is one of the technological alternatives that pursue the increase in production in areas previously marginalized by water deficit (Teixeira et al., 2012).
Throughout its growth, sugarcane needs good soil moisture conditions to express all its productive potential (Silva et al., 2008).Consequently, the yield and the production of sugar and ethanol from irrigated sugarcane depend on the amount of water applied and on the irrigation management (Dantas Neto et al., 2006).Therefore, the hypothesis is that water-saving irrigation promotes a greater efficiency in the culture of sugarcane.
The objective of this study was to evaluate the growth and gross yield of sugar and ethanol of first-year sugarcane with water-saving irrigation via hose-drawn traveller using a line of sprinklers.

MATERIALS AND METHODS
The experiment was carried out in July 2013, during the crop cycle of the cane plant of the variety SP83-5073 in the Boa Vista mill located in the municipality of Quirinópolis -GO, which has a soil classified as distroferric Red Latosol cerrado phase, according to Embrapa (2013).The climate is () classified according to Köppen and Geiger (1928) climate classification as tropical savanna with dry winter and rainy summer (Aw), with an annual rainfall between 1430 and 1650 mm, and drought period well defined between May and October.
The experimental design was randomized blocks, analyzed in a split plot scheme with four replications.The factors evaluated in the plots consisted of five levels water-saving irrigation (WSI) applied after planting (0, 30, 45, 60 and 75 mm).The subplots were represented by four evaluation periods (90, 170, 250 and 330 days after planting -DAP).
The experimental plots, in virtue of the proportion of the area wetted by the irrigation equipment, were 50.0 m long and 50.0 m wide (33 crop lines with 1.5 m spacing), with a total area of 2500.0 m 2 .The subplots were composed of 5.0 m of 2 lines, located in the center of the plot.
The application process was made according to the management adopted in every area of commercial cultivation of the mill.During soil preparation, spread fertilization was carried out with incorporation by average grade for the layer 15 cm deep.The planting fertilizer used was according to the soil analysis (Table 1) in accordance with the recommendations of Sousa and Lobato (2004).The recommendation was 200 kg ha -1 of P2O5 in the form of simple superphosphate.As for the K and N sources, the concentrated stillage enriched with urea, totaling 180 kg ha -1 K2O and 100 kg ha -1 nitrogen was used.For micronutrients, the dose of 100 kg ha -1 in the form of granulated Fritted Trace Elements (FTE), being 4 kg ha -1 zinc, 2 kg ha -1 boron and 2 kg ha -1 copper was used.The nitrogen coverage fertilization was performed 60 days after planting, where 120 kg ha -1 N (urea) were applied on both sides of the lines.
Water-saving irrigation was carried out by a self-propelled reel winder, model 140/GSV/350-4RII, coupled to an irrigation bar, model 48/54; MDPE tube with 140 mm outer diameter and length of 350 m; wall thickness of 10.3 mm, with lattices 24.5 m long on each side, totaling 49.0 m of adjustable structure, allowing the irrigation of sugarcane to 4.0 m high, with height compensation system through telescopic wheels installed along the lattices, the central car of the bar was operated with 3.0 m width.The emitters spaced at 1.85 m were used, totaling 26 emitters; the working pressure in the bomb was 10 Kgf cm -2 and in the reel was 5 Kgf cm -2 ; the reel was operated with an average wind speed of 14.5 m s -1 .The application of the water volume was located between the lines of the varieties of sugarcane, but the wetness of the experimental area was total.
During the crop cycle, variety SP83-5073, weather data were collected daily, obtained by the meteorological station of the mill; being the reference evapotranspiration (ET0) calculated according to the equation of Penman-Monteith-FAO/56 (Allen et al., 1998) (Table 2).
The number of leaves was determined by counting the fully expanded leaves with a minimum of 20% of green area, counted from the +1 leaf; the leaf area was determined by counting the number of green leaves (fully expanded leaf with minimum of 20% green area, counted from the +1 leaf) and the measurements on +3 leaves, being obtained the leaf length and width in the middle portion, according to the methodology described by Hermann and Câmara (1999): Where, L = length of the +3 leaf; W = width of the +3 leaf; 0.75 = correction factor for the leaf area of the culture; NF = number of expanded leaves with at least 20% green area.
The number of sugarcane plants was determined by counting all plants in the parcel containing more than six fully expanded leaves.The sugar yield and gross alcohol yield were evaluated punctually at the end of the cycle to 330 DAP.

--------------g cm
Where: Ay = gross alcohol yield in liters per ton of sugarcane in m 3 ha -1 ; PCC = percentage of raw sugar contained in the culms and determined in the laboratory; F = stoichiometric conversion factor of glucose to a sucrose molecule plus another fructose molecule, equal to 1.052; ARL = percentage of free reducing sugars, whose values range from 0.7 to 0.85% (the distillery uses 0.7 for a high PCC); GLf = Gay Lussac factor of 0.6475; PC = culms production in t ha -1 .
The data were submitted to analysis of variance by F test at 5% probability, and in cases of significance, regression analysis was performed to the water-saving irrigation depths and the evaluation dates, using the statistical software SISVAR (Ferreira, 2011).

RESULTS AND DISCUSSION
In the summary of analysis of variance, it is observed that there was a significant interaction between the factors water-saving irrigation (WSI) and days after planting (DAP) for the variable leaf length, and there was a significant isolated effect for leaf area regarding WSI and DAP.Concerning the number of leaves and leaf width, there was a significance only for DAP (Table 3).Silva et al. (2015) also found that there were no significant effects of irrigation on number of leaves in the early stage of sugarcane, while for leaf area they found an effect of irrigation at all stages of sugarcane.Farias et al. (2007) also noted that there was a great influence of irrigation on leaf area index during the growing season.
The number of leaves of sugarcane plants at every 80 days had an increase of 9.1% (Figure 1A).The maximum leaf width sugarcane plants was observed at 225 days after planting (approximately five leaves), which is 21.7, 3.6, 0.72 and 12.9% higher than that observed at 90, 170, 250 and 330 DAP, respectively (Figure 1B).Silva et al. (2012) observed that the maximum area of individual leaves respond to the length of the leaves as soon as the width tends to stabilize.
Leaf length and leaf area adapted to linear growth in function of water-saving irrigation in sugarcane plants.According to the regression equation obtained, there was an increase of 4.9 and 3.2% for each 15 mm increase for leaf length (at 90 DAP) and leaf area of sugarcane by using water-saving irrigation (Figure 2A and C).The leaf area had an increase of 14.7% every 80 days in function of days after planting (Figure 2D).
The water-saving irrigation in general, provided a major growth of leaves, mainly in length; when compared the treatments with and without water-saving irrigation it was verified accented differences in relation to the size of the leaves, resulting in lower leaf area which occurred preferentially in the initial stages.For better productivity, yields of sugar and alcohol to sugarcane needs a shoot well-developed, for this is very important that the differences in leaf size (initial stages) with respect to the maximum leaf growth will be smaller, the longest time possible, thus obtaining a major rate development of shoot.
The culture yield of sugarcane and the expansion of its leaf area are directly related because rapid growth of leaf area maximizes the interception of solar radiation and accumulation of biomass, increasing the yield of sugarcane (Inman-Bamber, 1994;Hanauer, 2011).
The water-saving irrigation in sugarcane plants was significant at 1% probability for plant height and number of sugarcane plants, as well as days after planting.There was a significant effect at 1% probability in relation to DAP for internode length and culm diameter (Table 4).Souza et al. (2015) found a significant effect of irrigation on plants' growth in height and on culm phytomass of sugarcane (variety SP 79-1011).Silva et al. (2009) found in this variety that the sugarcane growth parameters values, related to the number of culms, culm length, culm diameter, number of internodes and culm weight, responded significantly to irrigation.
The number of sugarcane plants and plant height with water-saving irrigation indicated a total increase of 19.8 and 18.7% compared to 0 and 75 mm water-saving irrigation (Figure 3A and C).Farias et al. (2008) verified lower values of plant height (1.53 m) and increase of only  4 cm in plant height compared with cultivation rainfed.The number of plants and plant height in function of days after planting in sugarcane plants adapted to a linear model, indicating an increase of 11.4 and 24.2% every 80 days (Figure 3B and D).
The internode length increased by 6.4% every 80 days.Thus, a total increase of 19.3% between 90 and 330 days after planting can be seen (Figure 4A).Culm diameter in function of days after planting adapted to a quadratic model with R 2 = 98.8%.There was an increase in culm   diameter up to 256 DAP.In this period, a culm diameter of approximately 28.4 mm was reached.The maximum culm diameter verified at 256 DAP was 10.2, 2.7 and 2% larger than the culm diameter observed at 90, 170 and 330 DAP, respectively (Figure 4B).Silva (2007) and Oliveira et al. (2010) observed culm diameter of approximately 27 mm in the RB867515 and RB72454 varieties.
With water-saving irrigation, it was verified a major number of sugarcane plants.Water-saving irrigation did not influence the culm diameter; however, it should be highlight that the plant height has a major effect on   productivity and yield of sugar and alcohol of sugarcane than the culm diameter, being responsible for increments quite considerable consequently verified that plants of sugarcane with water-saving irrigation demonstrated best performance in this variable.The water-saving irrigation was significant at 5% probability for gross sugar yield and gross alcohol yield in sugarcane plants (Table 5).Carvalho et al. (2009) also observed a significant influence of irrigation on yield of sugar and alcohol.
The regression analysis showed a linear behavior for gross sugar and alcohol yield in function of water-saving irrigation (R 2 > 91%) for first-year sugarcane plants.Consequently, the maximum gross yield of sugar and alcohol was obtained with a 75 mm water-saving irrigation, indicating a difference of 30% in average yield in relation to absence of water-saving irrigation (Figure 5A and B).Campos et al. (2014), evaluating varieties of sugarcane submitted to water-saving irrigation in the Cerrado of Goiás, concluded that water-saving irrigation of sugarcane in the Cerrado proved to be generally highly practicable, with a great response by most varieties, verified increases in average productivity of culms.
The gross sugar yield found in 60 and 75 mm watersaving irrigation was 17.2 and 18.3 t ha -1 .The gross sugar yield, according to the regression equation, obtained a 6.1% increase for each 15 mm increase of water-saving irrigation, thus demonstrating an increase in gross sugar yield of 0.07 t ha -1 for every 1 mm increase in water-saving irrigation in sugarcane plants (Figure 5A).
The gross alcohol yield observed in the 60 and 75 mm water-saving irrigation was 12.2 and 12.98 m 3 ha -1 , soon verifying an increase of 6%, due to the 15 mm increase, which shows an increase in gross alcohol yield of approximately 0.05 m 3 ha -1 for each 1 mm increase in water-saving irrigation in sugarcane plants (Figure 5B).Carvalho et al. (2009) noted that the increase in irrigation levels resulted in increases in the production of culm, the gross income of sugar and alcohol in gross income.

Conclusion
Water-saving irrigation provides a positive effect on leaf length, leaf area, plant height and number of sugarcane plants.Water-saving irrigation of 75 mm definitely promotes an increase of 30% in gross sugar and alcohol Water-saving irrigation (mm)

Figure 1 .
Figure 1.Number of leaves (A) and leaf width (B) of sugarcane in function of days after planting, Quirinópolis -GO, 2013/14.** and * , significant at 1 and 5% probability, respectively by F test at 5% probability.

Figure 2 .
Figure 2. Leaf length and leaf area of sugarcane in function of water-saving irrigation (A and C) and of days after planting (B and D), Quirinópolis -GO, 2013/14.** and * , significant at 1 and 5% probability, respectively by F test at 5% probability.

Figure 3 .
Figure 3. Number of sugarcane plants and plant height in function of water-saving irrigation (A and C) and of days after planting (B and D) of sugarcane, Quirinópolis -GO, 2013/14.** and * , significant at 1 and 5% probability, respectively by F test at 5% probability.

Table 1 .
Physical, water and chemical characteristics of the soil in the experiment area.

Table 2 .
Monthly data of temperature (maximum, minimum and average), relative humidity, Rainfall and reference evapotranspiration.

Table 3 .
Summary of ANOVA of number of leaves (NL), leaf length (LL), leaf width (LW) and leaf area (LA) of sugarcane in different times of evaluation with water-saving irrigation, Quirinópolis -GO, 2013/14.Days after planting (DAP).Source of variation (SV), Degree of freedom (DF), mean square (MS) and coefficient of variation (CV).** and * -significant at 1 and 5% probability, respectively; ns not significant by F test at 5% probability.

Table 4 .
Summary of ANOVA of plant height (PHe), internode length (IL), culm diameter (CD) and number of sugarcane plants (NSP) in different times of evaluation with water-saving irrigation, Quirinópolis -GO, 2013/14.DAP, days after planting; SV, source of variation; DF, degree of freedom; MS, mean square; CV, coefficient of variation ().** and * -significant at 1 and 5% probability, respectively; ns not significant by F test at 5% probability.