PERFORMANCE OF TIFTON 85 GRASS UNDER FERTIRRIGATION WITH SLAUGHTERHOUSE WASTEWATER

The aim of this study was to evaluate the performance of Tifton 85 grass cultivated in soil columns and fertilized with different wastewater doses of swine slaughterhouse. The experiment was conducted in the Environmental Engineering Center and Sanitary of UFLA/MG in PVC columns filled with Dark Red Latosol (Oxisol) and randomly distributed. The treatments applied with nitrogen based load (300 kg ha de N years) consisted of four doses of SW and AQT0 control at random. Three cuts were performed, at 60, 90 and 120 days after planting. The highest yields were 10.06, 16.82 and 20.39 t ha in AQT0, AAT4 and AAT3 treatments, respectively. With the increase of nutrients by N rates and root development of Tifton 85 grass, we observed higher extractions of N, P and K in the second and third cut, with maximum extraction of 384 and 10.3 kg ha of N and P in the higher dose treatments (AAT4), while the maximum extraction of the potassium was 117.7 kg ha in the AAT3 treatment. There was productivity restriction in the third cut due to the reduction of availability of essential nutrients and losses by leaching.


INTRODUCTION
Due to the scarcity of water resources and the growing demand for good quality water, several studies have been conducted over the years in order to search for viable alternatives to irrigation using lower quality water.Thus, Silva et al. (2011) argue that the reuse of wastewater for irrigation purposes contributes to the controlling of environmental pollution, saving water and fertilizers, recycling nutrients and increasing agricultural production.
High nutritional content and organic matter, coming from production process, characterize the wastewater from slaughterhouse; therefore, prior treatment is necessary before its final destination (Mees et al., 2009;Tocchi et al., 2013).According to Cabral et al. (2011), the disposal of wastewater in the soil, as an alternative of final destination, in addition to water source, promotes the nutritional increment for the development of cultivars, reducing production costs.
The fertirrigation with wastewater offers socioeconomic and environmental benefits, mainly the reduction of effluent release in the bodies of water and the recovery of nutrients (Rodríguez-Liébana et al., 2014), allowing to reduce the use of chemical fertilizers (Gil & Ulloa, 1997).However, depending on the origin and quality of the effluent, there are risks of soil and crops contamination by pathogens (Palese et al., 2009), as well as promoting salt accumulation, pH alteration and a decrease in soil infiltration rate (Bedbabis et al., 2014).On the other hand, in comparison to surface waters and/or groundwater, the use of wastewater in irrigation increases biomass production and improves crop productivity (Jang et al., 2012;Mojid et al., 2012).Therefore, finding a balance between the uses of these waters in conjunction with mineral fertilization is of great necessity, reducing fertilizer costs, in addition to providing a noble destination for these waters, increasing production, reducing fertilizer costs and increasing profitability of the producer.
Among the tropical pastures, Tifton 85 grass belonging to the Cynodon genus has been widely used in animal feed due to its higher production, nutritional content and good resistance to seasonality in relation to other genera, with a lower basal temperature of 12 ºC (Corrêa & Santos, 2006).Some studies point to significant productivities of fertirrigated grasses with wastewater, such as Prior et al. (2015) studying the association of swine wastewater and mineral fertilization in maize crop; and Fia et al. (2010) evaluating forage performance in flooded water treatment systems for coffee processing.
The aim of this study was to evaluate the performance of Tifton 85 grass cultivated in soil columns and fertirrigated with different doses of wastewater from swine slaughterhouse.

MATERIAL AND METHODS
The experiment was carried out at the Federal University of Lavras, Lavras, Minas Gerais, latitude 21°13'45"S, longitude 44°58'31"W, average altitude of 918 m and Cwa climate, (mesothermal or tropical altitude), with dry winter and rainy summer, according to the Köppen classification (Sá Junior et al., 2012).
The soil used in the experiment was classified as Dark Red Latosol (EMBRAPA, 2013).The chemical and physical characteristics of the soil are presented in Table 1, before the application of the treatments.
The experimental system consisted of 15 soil columns constructed of PVC with a diameter of 0.30 m (area of 0.07 m 2 ) and 1.20 m of height.The columns were filled from the base with 0.05 m of nº zero gravel, 0.05 m of thick washed sand and 1.05 m of Dark Red Latosol.The soil columns were cultivated with Tifton 85 grass (Cynodon spp.) as shown in Figure 1.Soil liming was carried out to fill the 0.30 m surface of all 15 columns with the use of calcium carbonate PA (CaCO3).The different treatments included the application of the Swine Slaughterhouse Wastewater (SW) from an agro-industry of Lavras-MG, in four different loads, and another with conventional chemical fertilization (AQT0) characterized as standard treatment.The applications of the treatments occurred monthly, between August and December 2015, following the recommendation of 300 kg ha -1 year -1 of nitrogen proposed by the Soil Fertility Commission of the State of Minas Gerais (Ribeiro et al., 1999) for pasture.Adopting the AQT0 standard as the recommended dosage of N, N dosages were tested via wastewater at the following dosages: 100, 200, 300 and 400% of the recommendation.
The SW characterizations were performed monthly in the Laboratory of Analysis of Wastewater of the Nucleus of Environmental and Sanitary Engineering of the Engineering Department of UFLA, following the methodology proposed by APHA; AWWA and WEF (2012).The results are shown in Table 2.During the growth cycles of Tifton 85 grass, some of the required water was supplied by SW application and another part came from irrigation management with water from the UFLA supply system.The climatic data, necessary for the estimation of the reference evapotranspiration (ETo) by the Penman-Monteith equation (Allen et al., 2006;Carvalho et al., 2011), were obtained at the Conventional Weather Station installed on the UFLA campus under monitoring of the National Institute of Meteorology.A kc of 0.8 proposed by Drumond et al. (2006) was adopted.The variations of temperature and relative humidity occurred during the experiment are shown in Figure 2. The water level applied to the soil columns was determined based on the water deficit obtained by the difference between ETc, precipitation and wastewater level applied (Figure 3).Three cuts of the Tifton 85 grass were made at 60, 90 and 120 days after transplanting to the soil columns.The cuts were carried out after each beginning of flowering at 5 cm of height.
After the collections, the Tifton 85 grass was sent to a greenhouse with forced air circulation at 65 °C for 72 h, followed by grinding in a Wiley type mill to quantify the dry matter yield and analyses of nutrient content of nitrogen, phosphorus, potassium, calcium, magnesium and sodium, according to Silva (2009) methodology.
The experiment was set up in a completely randomized design (CRD) with three replicates.Soil data were submitted to analysis of variance using the F-Test at 0.05.In the statistical analysis, the computer program Sisvar 5.1 was used (Ferreira, 2011).

Tifton 85 Grass Productivity
The dry matter yields of Tifton 85 grass are shown in Table 3.The control treatment AQT0, at the dosage of 30 kg ha -1 of N, 110 kg ha -1 of PT and 40 kg ha -1 of K, provided a dry matter yield of 10.06 t ha -1 , being 277% higher than the yield of 3.62 t ha -1 obtained in the AAT1 treatment.This result may be related to the greater easiness of NPK assimilation by Tifton 85 grass in its initial stage.In the second cut, there was no statistical difference between the data, although maximum yields of 20.39 (AAT3) were observed, however after 116 days of monitoring, the highest SW dosage increased the yield of 19.26 06 t ha -1 ( AAT4).
According to Fontaneli et al. (2012), the dry matter yield of Tifton 85 grass can range from 8 to 20 t ha -1 year -1 , depending on the level of fertility that is submitted.Matos et al. (2010) evaluated plant extractive capacity in constructed flooded systems and found an increase in dry matter productivity of Tifton 85 grass of 14.9 t ha -1 after receiving rates of 570 kg ha -1 d -1 of BOD from dairy wastewater.
The SW dosages applied, based on the nitrogen recommendation (Ribeiro et al., 1999), provided high concentrations of soluble salts in the soil solution, such as sodium, and the lower availability of essential nutrients such as phosphorus interfered in the productivities of the three cuts.

Extraction of nutrients by Tifton 85 grass
Tables 4, 5 and 6 show the average values of nitrogen, total phosphorus, potassium, sodium, calcium and magnesium extraction, based on the productivity and concentration of the dry matter of Tifton 85 grass in the three cuts.
The extraction of macronutrients and sodium by Tifton 85 grass was influenced by the interaction between the different dosages of SW and the cuts.After the first cut, 60 days after planting, a statistical difference was observed between SW dosages and conventional chemical fertilization (AQT0), as seen in Table 4.The maximum extractions were obtained with the conventional chemical fertilization treatment (AQT0), being 169.16 kg ha -1 of TKN, 3.45 kg ha -1 of PT, 17.65 kg ha -1 of K, 27, 79 kg ha -1 of Ca + Mg and 2.68 kg ha -1 of Na.
With the increase of nutrients by N rates and root development of Tifton 85 grass, higher extractions of N, P and K were observed in the second and third cuts, with maximum values of 384 and 10.3 kg ha -1 of N and P (AAT4), while the maximum potassium extraction was 117.7 kg ha -1 in the AAT3 treatment.According to Matos et al. (2009), the results of phosphorus and potassium extracted in this study are considered low, since the wastewater supply in the treatments was carried out based on the nitrogen nutritional need.Therefore, essential nutrients, such as phosphorus, may have been applied in doses lower than the necessary for the crop.Table 7 shows the equations of adjustment of the N, P and K extractions for each cut as a function of the doses.

FIGURE 1 .
FIGURE 1. Schematic configuration of the soil column profile used in the experiment.

FIGURE 2 .
FIGURE 2. Temperature and humidity variation that occurred during the experiment.

FIGURE 3 .
FIGURE 3. Distribution of rainfall and irrigation level that occurred during the experiment.

FIGURE 4 .
FIGURE 4. The total content of nitrogen (A), phosphorus (B) and potassium (C) in Tifton 85 grass taken from the three cycles of production in relation to the applied nitrogen doses by slaughterhouse wastewater (SW).

TABLE 1 .
Physical and chemical characterization of the soil used in filling columns.

TABLE 2 .
Characterization of slaughterhouse wastewater (SW) applied during the experimental period.

TABLE 3 .
Average productivity estimate, by cutting the Tifton 85 grass subjected to treatment with SW and AQT0.Averages followed by the same letter in the columns do not differ from each other by Tukey test at 5% probability. * Averages followed by the same letter in the columns do not differ from each other by Tukey test at 5% probability.
Averages followed by the same letter in the columns not differ from each other by Tukey test at 5% probability.

TABLE 7 .
Adjustment equations of total extraction of nitrogen (N), phosphorus (P) and potassium (K) according to the doses of nitrogen applied via slaughterhouse wastewater (SW) for the three cuts made.