Chemical and technological characteristics of sugarcane as a function of pelletized organomineral fertilizer with filter cake or sewage sludge sources

Sugarcane is one of the major alternatives for the biofuel sector and its large production has considerable environmental impacts. Organomineral fertilizers formulated with environmental liabilities such as filter cake and sewage sludge positively affect parameters of plant growth and development. The objective of this study was to evaluate the chemical and technological characteristics of sugarcane fertilized with pelletized organomineral fertilizers based on filter cake and sewage sludge. Eight field treatments were studied, being three levels of organomineral (50, 100, 150%) of two organic matter sources (filter cake, sewage sludge), plus a control with 100% of the recommended fertilization via mineral fertilizer and no fertilization control (0%). Sugarcane was evaluated during two consecutive harvest, and the amount of stalks per hectare (ton ha−1), the sugarcane productivity (ton ha−1), the quantity of sugar per hectare (TSH, ton ha−1), and the chemical and technological analysis of the sugarcane juice: pol (%), brix (%), purity (%) and fiber (%) were evaluated. None of the organomineral sources or doses differed from the exclusive mineral fertilization. The analysis of both harvests indicated that the first cut was the most productive since the responses of the first harvest were superior or similar to the second harvest. The recommended organomineral dose to obtaining maximum quantitative and qualitative sugarcane results was between 102 and 109% of the regular recommendation for mineral fertilization, regardless of the organic source in the first sugarcane harvest. In the second sugarcane harvest, sewage sludge source increase by 4.68 and 4.19% the total amount of sugar per hectare and the quantity of sugarcane compared to the sugarcane filter cake source. Sewage sludge and sugarcane filter cake as sources for organominerals are viable alternatives and advantageous in economic and environmental terms for the cultivation of sugarcane.


Introduction
Organomineral fertilizers have distinctive characteristics; for example, phosphorus 114 derived from these fertilizers was more rapidly available than from the mineral source (triple 115 superphosphate) [15]. The organomineral fertilizers also provided a higher content of 116 exchangeable potassium in the superficial soil layers in sugarcane cultivation, and are more 117 efficient in all evaluated concentrations compared to exclusive mineral fertilization, which 118 may replace the mineral fertilizers and provide up to 15% more efficiency in the production of 119 sugarcane stalks [16]. 120 In the case of sugarcane, the high productivity of stalks must be accompanied by 121 physical-chemical parameters favorable to industry to guarantee high yields in the production 122 of sugar and alcohol. However, the research still has much to contribute, justifying 123 economically, environmentally and technically the use of organomineral fertilizers. Therefore, 124 the objective of this study was to evaluate the chemical and technological characteristics of   [18]. 139 The experiment was installed upstream of a hill in a soil classified as Dystrophic 140 Yellow Latosol (Oxisol) [19]. The soil is characterized as sandy soil, with 72% of sand, 141 18.5% of clay and 9.5% of silt. Soil sampling was performed at 0-0.2 and at 0.2-0.4 m depths 142 and their chemical analyses are described in Table 1.  [20].

150
The soil of the experimental area received 2.4 t ha -1 of dolomitic lime, 1. polymer to produce the organomineral pellets. The organomineral pellets were about 3.9 mm 182 diameter by 9.1 mm length.

183
The chemical characteristics of the sewage sludge and sugarcane filter cake usedare 184 presented in Table 2.        The quantity of stalks per hectare (ton ha -1 ), the sugarcane productivity (ton ha -1 ), and 232 the quantity of sugar per hectare (ton ha -1 ) were estimated for each experimental plot. The 233 processing was carried out according to the methodology based on sucrose content. After the 234 disintegration and homogenization of the sugarcane stalks, an aliquot of 0.5 kg was subjected 235 to a hydraulic press to extract the juice, which was used for the determinations chemical-236 technological [24]. The variables evaluated were:   The software SPSS Statistics® was also used to evaluate the ANOVA presumptions: 249 Shapiro-Wilk's [26] normality of residue distribution and Levene's [27] homogeneity of 250 variances, both at p > 0.01 probability.

251
After attendance of the ANOVA presumptions, the data were subjected to ANOVA (F 252 test) to detect interactions between the factors (organic sources × doses) and differences 253 among the levels in each factor (p < 0.05) [28]. When differences were detected appropriated 254 comparisons were performed.

255
The additional treatments (mineral fertilization and no-fertilization) were compared to 256 the factorial by the bilateral Dunnett's test [29] (p < 0.05) using the software Assistat®.

257
The means of the factorial were compared by the Tukey's test [30] (organic sources) at  The sugarcane crop yield variables between de first (366 days after planting in 2015) 263 and second (376 days after the first harvest in 2016) sugarcane harvest were compared via a 264 joint-analyses by the Tukey's test [30].

268
The application of organomineral fertilizer based on sewage sludge at a dose of 100% 269 (SS100) of the recommendation of fertilizer (100% mineral fertilizer), presented stalk 270 production per hectare (SH) higher in the first year (Table 3).

271
The absence of fertilization (negative control) resulted in lower production of 272 sugarcane per hectare and production of sugarcane than the positive control in both cycles.

273
The application of SS100 reflected in a greater quantity of sugar produced per hectare (SH) in 274 the second cycle, being 31.5% higher than that obtained in the negative control. Also, the  (Table 3), while in the second cycle, only 278 the sugarcane juice purity was reduced in the negative control. In the first cycle, there was a significant interaction between the organic matter source used in the formulation of the organomineral fertilizers and the dose applied for sugarcane productivity. Only the sewage sludge source presented a significant (p<0.05) polynomial model for yield (Fig 1A), indicating that the highest yield (159.3 ton ha -1 ) observed was for a dose of 83.4% of referred organomineral fertilizer. The filter cake source (no polynomial adjustment detected) resulted in sugarcane productivity of 159.4 ton ha -1 for the 150% (FK150) dose of the recommendation of mineral fertilizer.
In the second cutting cycle, there was no interaction between sources and doses for sugarcane productivity; thus, the effect of the doses is independent of the organic matter source used (Fig 1B). The largest sugarcane production observed was 154.8 ton ha -1 , obtained at a dose of 108.3% of organomineral fertilizer. The use of sewage sludge in the first cycle resulted in 17% savings in fertilization, with a contribution of 2.8% to the productivity compared to the second cut. The highest yield in the first cut was observed when 50% of the recommended dose was used via organomineral fertilizer based on sugarcane filter cake (162.8 ton ha -1 ), and was approximately 7.73% higher than the negative control (151.1 ton ha -1 ). In this same dose, the organomineral fertilizer based on sugarcane filter cake resulted in high fiber production in the first cut (13.9%), compared to the fiber in the negative control (13.1%) ( Table 3).
The greatest stalk productivity per hectare observed in the first cut was 86.7 ton ha -1 obtained at a dose of 110.2% of organomineral fertilizer -regardless of the source of the organic matter used in the formulation of the organomineral. In the second cut, the greatest stalk productivity was 83.1 ton ha -1 at a dose of 108.7% of organomineral fertilizer (Fig 2). It is noticeable that the need for organomineral to express maximum stalk productivity was close between cuts, despite higher productivity (4.3% superior) in the first cut. In the first cut, when the sewage sludge was the base for the organomineral fertilizer, the percentage of apparent sucrose (pol) was 2.16% higher than the pol observed when sugarcane filter cake was the base for the organomineral (Table 3). Similarly, in the second cut, when sewage sludge source was used, the quantity of sugarcane produced and the total amount of sugar per hectare was 4.19 and 4.68% higher than the sugarcane filter cake source, respectively (Table 4). Table 4. Average of apparent sucrose (pol), sugarcane productivity and total of sugar produced for fertilization treatments including organominerals.  The largest percentage of apparent sucrose (pol) presented in the first and second cut, were 15.5 and 14.3%, respectively, for the doses of 104.1 and 102.1%, regardless of which of the sources was used in the fertilizer organomineral (Fig 3). The percentage of soluble solids (brix) greatly varied with the organomineral fertilizer dose in both cycles, independently of the source of organic matter used. The largest percentage of soluble solids was 20.8% in the first cut and 19.2% in the second cut, respectively, for the doses of 104.3 and 96% of organominerals (Fig 4). In the first cut, the highest sugarcane juice purity (89.3%) was found for the organomineral fertilized dose of 91.6%, using sewage sludge or sugarcane filter cake. In the second cut, for each kilogram of organomineral fertilizer applied, using sewage sludge or sugarcane filter cake, there was an increase of 0.0182% in the purity of the sugarcane juice (Fig 5). In the first cut, the highest fiber content observed was with the sewage sludge source (13.6%) obtained for the organomineral fertilized dose of 79.7% (Fig 6). There was no significant effect of doses and sources on fiber (%) in the second cut, being the average fiber found of 12.86%. The largest quantity of sugar produced per hectare was 24.3 ton ha -1 in the first cut and 21.9 ton ha -1 in the second cut, respectively, for the doses of 102.3 and 106.5% of organominerals -using sewage sludge or sugarcane filter cake as organic sources (Fig 7). The joint analysis between the first and second cuts indicated that the first harvest presented results greater than, or equal, to the second harvest, but never lower (Tables 5 and  6).  Treat.: treatments applied to sugarcane crop. SS: organomineral fertilizer based on sewage sludge. FK: organomineral fertilizer based on sugarcane filter cake. SH: tonnes of sugarcane stalk per hectare (ton ha -1 ). TSH: total of sugar produced per hectare (ton ha -1 ). Prod: sugarcane productivity (ton ha -1 ). TRS: total of recovered sugar (kg ton -1 ). 1 Averages followed by the same capital letter in line indicate similar results between the sugarcane cuts by the Tukey test (p < 0.05). MSD: minimum significant difference. S.W.: statistics of Shapiro-Wilk for error normality (all are normal, p > 0.01). L.: statistics of Levene for homogeneity of variances (all are homogeneous, p > 0.01).

Discussion
The soil fertilization carried exclusively via mineral or via organomineral fertilizers did not diverge for the majority of the variables analyzed, indicating that organomineral fertilizers are a viable way of fertilizing sugarcane crop. The alternatives proposed in the present study, minimize the impacts arising from the successive application of mineral fertilizer sources, which are associated with the loss of soil biodiversity and the long-term dependence on external inputs [31,32]. The positive environmental aspect of the use of sanitized sewage sludge and filter cake in organominerals in agriculture is safe and appropriate, according to the pre-treatment required for each source.
The organic fraction of organomineral fertilizer is an important aspect of these fertilizers. This fraction causes beneficial modifications that alter the dynamics of nutrient cycling in the soil-plant system [33]. Several studies also indicate organomineral fertilizers as viable substitutes for mineral fertilizers in many crops [8,[34][35][36][37][38]. Regarding the soil dynamics of C and N, long-term field report demonstrated reductions in soil stocks of these nutrients in deep soil layers after the applications of large quantities of synthetic mineral fertilizers, which did not occur when the fertilizer source was an organomineral [39]. Organomineral fertilizers also reduce nitrogen (N-NH 3 ) volatilization when compared to exclusively mineral sources [40].
Sugarcane filter cake also has considerable fractions of phosphorus, a critical element for agriculture in the Cerrado due to their low natural availability in the soils of this biome [41]. In addition to providing essential nutrients, organomineral fertilizers potentially increase the soil chemical quality due to the increase of the soil's negative charges, extending the cation exchange capacity (CEC) and reducing the concentration of exchangeable aluminum (Al 3+ ) [42][43][44]. The soil organic matter correlated with the regular applications of N and P, and with high soil CEC when sewage sludge was used as the source for organomineral fertilizer [45]. The monitoring of the environmental conditions and the orientation of farmers of this raw material (sewage sludge) on public policies is also essential to avoid heavy metals and biological contaminants during the reuse and management of this environmental liability [45].
Organomineral fertilizers based on sanitized sewage sludge can replace the mineral fertilization efficiently on maize [46] and sorghum [47] while improving soil fertility even in reduced doses and without heavy metal contamination. In soybean, reduced doses (25% less compared to mineral fertilizer) of pelletized organomineral fertilizer formulated with sanitized sewage sludge or sugarcane filter cake resulted in increments in plant height and stem diameter [9; 48]. In sewage sludge compost, the level of P present depends on the chemicals used in the process of the residue treatment to improve P concentration [49]. The release of nutrients to the environment occurs gradually in organomineral fertilizers, improving fertilizer efficiency [50]; thus, the P derived from organic residues constitutes a complementary strategy of supply of labile P to weathered soils [51].
The nitrogen:phosphorus (N:P) ratio of the organomineral with sewage sludge as the organic source is typically greater than that required by plants. In soils that receive sewage sludge organomineral plants accumulate more P than plants grown with only mineral fertilizers; the rate of P accumulation by the plants is influenced by the dynamics between climate and soil characteristics, especially in terms of the properties which determine the relationship between the proportion of adsorption and desorption of P from the soil [52]. The gradual P release is determined by the soil microbiota biodiversity and population present [53,54,4], and also by the residual effect of the fertilizer -organomineral fertilizers based on sugarcane filter cake can last for 4 years after its application [55,56].
The soil P concentrations in a study with maize [36] increased from 6 mg kg -1 (without fertilizer) to 24 mg kg -1 with the use of mineral fertilizer, and to 56 mg kg -1 with the use of organomineral fertilizer. The results found in that maize study were similar to what was found in the present study, in which the sugarcane production with organomineral fertilizer formulated with filter cake was comparable to the production where mineral fertilizer was applied. The root performance is also correlated to the effect of P in plant metabolism, being the presence of P fundamental for good rooting and sugarcane tillering, with a direct effect on final yield and sugar production [8]. Also, increments of P improve the apparent percentage of sucrose, the initial plant development and the P leaf content [57,58]. In wheat, the application of filter cake also presented positive results, increasing grain yield with a tendency to interrupt the yield increase at doses greater than 60 ton ha -1 [59].
The organic fraction present in sanitized sewage sludge and in sugarcane filter cake organominerals contributes to improving soil aggregation, density, porosity, aeration, infiltration and the capacity of water retention [60]. Such factors are essential in the cultivation of sugarcane in months with low rainfall and in cultivations without irrigation [38,61]. In eucalyptus, sewage sludge compost increased the dry matter of the plants with a gain of 50% compared to the mineral fertilizer, indicating that this source of OM can replace the mineral fertilization [62]. The organomineral fertilizers have also the potential to significantly reduce the dependence on imports of mineral fertilizer sources of N, P and K. The reduction of costs of importation of P by a combination of features allows to increase economic productivity due to better use of energy and water [63], which increases the competitiveness of the agricultural sector. For example, the P obtained from sewage waste can recover the equivalent to 15 to 20% of the world demand phosphate rock [64].
The supplementation of the organic fraction with mineral elements can influence the use of both resources, with lower environmental impact and higher agronomic efficiency. Greater sugarcane yield was observed in the combination of 15 t ha -1 of filter cake and 350 kg ha -1 of NPK fertilizer [65,66]. The effect of organic fertilizers in sugarcane using different organic sources (chicken bed, sugarcane filter cake, vinasse) associated with basic NPK fertilizer indicated that sugarcane filter cake provided the greatest amount of roots, which positively reflects in great productivity in the first and second cuts [60]. On the other hand, following the present study, no substantial increase in the production was found from the first to the second cut [38]. However, a study indicated a tendency of maintaining and even increase the productivity of stalks was regularly observed, since 13 clones, out of 25 clones, showed higher productivity with the application of organominerals [67].
The values observed for brix in the present study were higher than 18% for both harvests. The optimal value of brix is 18%, and it is an important variable for sugarcane yield since brix has a direct relationship with the sugar content and corresponds to 18 to 25% of the total of sugar [68]. The apparent percentage of sucrose (pol, %) is also important for the sugar industry which has an expectation of optimal value above 14% [69]. The values of sugarcane pol below 14% were observed in the treatment without fertilizer (negative control) in the first cut. The purity of the sugarcane juice represents the quality of the juice to recover its sugar, and the organomineral fertilizers (sewage sludge or filter cake) were similar to the mineral fertilizer, and all above 85% in both harvests. This value exceeds the ideal value estimated by the sugar industry [69], since the industry may refuse the receipt of shipments with purity below 75% [24]. Similarly, the fiber content (12 to 13%) in the first cut was within the ideal range considered adequate (10 to 13%) [69,70], highlighting the efficiency of organominerals to provide nutrients to sugarcane crop adequately.
Favorable responses to the sugarcane cultivation have been observed at 120% of the fertilizer recommendation as organomineral, not differing from the 100% dose [71], a result that is similar to what was observed in this study. However, in consonance with the present study, little effect of the fertilization with organomineral in qualitative parameters is observed in the literature [72,73,5], highlighting the organominerals as efficient alternatives in the cultivation of sugarcane. The analysis of both harvests -the first and second harvests after the sugarcane planting -indicated what was expected for this crop culture, that the first cut is usually the most productive [74] since the responses of the first harvest were superior or similar to the second harvest.
This study allowed the observation that organomineral fertilizers can replace the exclusively mineral fertilization in sugarcane crop around the world, without negatively interfering in the quantity and quality of the attributes evaluated. The type of organic sources (sewage sludge or sugarcane filter cake) had little influence on the results observed; however, proper care must be taken on the collection, management and treatment of any organic source. In this way, a renewable resource, whose improper disposal can cause environmental impacts, generate favorable effects when added to the soil prepared for sugarcane

Conclusions
The recommended organomineral dose to obtaining maximum quantitative and qualitative sugarcane results was between 102 and 109% of the regular recommendation, regardless of the organic source in the first sugarcane harvest.
In the second sugarcane harvest, sanitized sewage sludge source increase by 4.68 and 4.19% the total amount of sugar per hectare and the quantity of sugarcane produced compared to the sugarcane filter cake source.
Sanitized sewage sludge and sugarcane filter cake as sources for organominerals are viable alternatives and advantageous in economic and environmental terms for the cultivation of sugarcane.