Growth and Production of Millet Irrigated With Dilutions of Treated Gray Water

The present work aimed to analyze the effects of the application of dilutions of treated gray water (TGW) in well water (WW) on growth and production of millet cv. Ceará (Pennisetum glaucum). The experiment was carried out in a greenhouse, on the department of agronomic and forestry sciences, at the Federal Rural University of the Semi-Arid (UFERSA), Mossoró, RN, Brazil. The experimental design was randomized blocks with five treatments and six replications, totaling thirty plots. The experiment was carried out in vases with volume of 25L containing four plants per vase. The treatments consisted in five dilutions of TGW in WW: T1—100% WW plus 0% TGW; T2—75% WW plus 25% TGW; T3—50% WW plus 50% TGW; T4—25% WW plus 75% TGW and T5—0% WW plus 100% TGW. During the experiment it was analyzed the attributes of plant height, number of tillers, number of leaves, stem diameter and total fresh and dry matters. With the results, it was observed that the exclusive irrigation with TGW (T5) promoted better millet development. As the concentrations of TGW increased in dilutions, also increased plant height, number of leaves and tillers. The rise in the number of leaves is associated to the rise in height and tillers, and those are associated to the rise in stem diameter and fresh matter, resulting in better accumulations of dry matter and showing the viability of gray water use to improve forage production and increasing potable water availability to multiple uses.


Introduction
The way to increase availability of sources of water to irrigation is to rationalize its use (Santos Júnior et al., 2013), as well as to reuse water from different activities (Medeiros et al., 2010).The reuse of wastewater on forage production comes as a strategy to sustainable management of water, to reduce future problems of water scarcity.Beyond preventing water sources eutrophication, this technic when used correctly can improve food production because it has nutrients that allow to substitute in part or totally mineral fertilization to cultures, promoting benefits both economic and environmental.
Millet (Pennisetum glaucum) is an easy installing culture when compared to other because it requires less inputs due to its deep and vigorous roots, being efficient on water and nutrients use.According to Silva et al. (2015), millet has high productive potential in areas with low rainfall, being used in adverse conditions, showing to be a good alternative of forage in semiarid regions.
Residual water is being studies in many areas of reuse, presenting promising results (Santos et al., 2016;Alves et al., 2014;Deon et al., 2010).A study carried out in Campinas, SP, with treated domestic wastewater proved that its use promotes water and nutrients to fertilize soil and improve mays productivity (Javarez Júnior et al., 2010).Another study carried out in Apodi, RN, shown that treated domestic wastewater use to irrigate red rice promoted rise on some nutrients tax, such as nitrogen (Brito et al., 2014).
According to Baracuhy et al. (2015), water reuse is a way to reduce environmental pollution, providing water availability to forage irrigation, improving economic development on semiarid region.Among different sources of wastewater, it can be named the gray water, generated from urban and rural residences that come from showers, washbasins, kitchen sinks, tanks and washing machines.In its compositions there are elements from soaps and cleaning products, being free from toilet effluents (Feitosa et al., 2011).It has been studying mainly by architecture and civil engineering branches to be reused with non-potable purposes (Guerra, 2016).Rapoport (2004) states that gray water from kitchen sinks have oil, fat and human food particles in its composition.
In the long run, the use of wastewater can promote salts and heavy metals accumulation in soil to a harmful level to crops development and production (Rusan et al., 2007).Gray water dilutions in well water are done aiming to reduce salts concentration so water's electrical conductivity remain within standards stablished on COEMA's resolution n.2/2017 (Ceará, 2017) for agricultural and forestry purposes.A study carried out in Mossoró, RN, evaluated the effects of cotton irrigation with different dilutions of domestic sewage in two kinds of soil.It was observed that both soils presented increase in sodium content, which is harmful to soil's structure, dissipating soil particles and reducing its permeability (Andrade Filho et al., 2013).
There are reports about wastewater reuse on forage production, for instance, studies developed with water from coffee processing (Fia et al., 2010) and livestock (Piccolo et al., 2013;Saraiva & Konig, 2013).On literature, studies point to wastewater reuse on forage production (Erthal et al., 2010;Andrade et al., 2014;Homem et al., 2016), however it is scarce studies on gray water reuse on millet development and production.
Thus, this work aimed to analyze the effects of application of treated gray water dilutions in well water on millet's cv.Ceará (Pennisetum glaucum) production and development.

Method
The experiment was carried out on greenhouse, on the department of agronomic and forestry sciences at the Federal Rural University of the Semi-Arid (UFERSA), Mossoró, RN, State Of Rio Grande do Norte, Brazil (05°12′03.9″S; 37°19′98″ W).According to Köppen climate classification, the region's climate is classified as BSh, which is a country climate, semiarid, warm and dry, with low altitude and latitude, morphoclimatic domain caatinga, average annual rainfall lower than 650 mm and average annual temperature higher than 265 °C (Alvares et al., 2013).In this region the average annual rainfall is 673.9 mm, humidity of 65.9% (Dias et al., 2010) and average speed of wind is 3.32 m s -1 (Morais et al., 2014).
The experimental design used was randomizes blocks with five treatments and six replications, totaling thirty plots.The experiment was carried out in vases with volume of 25 L containing four plants per vase.The treatments consisted in five dilutions of TGW in WW: T1-100% WW plus 0% TGW; T2-75% WW plus 25% TGW; T3-50% WW plus 50% TGW; T4-25% WW plus 75% TGW and T5-0% WW plus 100% TGW.Gray water dilutions are recommended to reduce salt concentration and to identify the most adequate dilution to culture development (Brito, 2014;Medeiros et al., 2015).
Gray water was collected from a treatment station located on Monte Alegre I settlement (5°3′13.06″S; 37°27′23.27″W) in Upanema, state of Rio Grande do Norte, Brazil.The gray water produced in the residence is composed by shower, bathroom sink and laundry tanks.The house is inhabited by two people and they have three visitors on weekends, producing average of 80 L of gray water per day.The applications of gray water dilutions in well water was carried out through an irrigation system of microtubes with a PVC reservoir (60 L), an circulating pump Metalcorte/Eberle, self-ventilated, EBD250076 model, lateral lines of 16 mm and microtubes with average flow of 8.5 L h -1 .The irrigation system applied, daily, the needed volume of dilutions to increase soil humidity until its maximum water retention capacity.
Non-destructive evaluations of growth were weekly done through the variables: plant height, number of leaves, number of tillers and number of panicles.At the end of the cycle, it was evaluated development characteristics: height, number of leaves and tillers, stem diameter, number and length of panicles, fresh and dry matter.
The material was collected manually on October 16 th of 2017, 65 days after sowing.Plants were cut 0.05 m above the soil taking all its leaves.The fresh matter of the forage was obtained after cutting, when the material was putted in paper bags and weighted.Then, the material was sent to hothouse with forced air circulation on 65 °C until it gets to constant weight and then it was weighted again to obtain dry matter.Later the material was milled in Willey Mill and kept in plastic bags to go to laboratory analysis.
Data of millet development and production were submitted to analysis of variance, using test F with 5% of probability.The means were compared though Tukey test with 5% of probability.Regression models were chosen based on determination coefficient values and regression equation coefficients, using test F with 5% of probability.Statistical analysis of data was carried out with aid of SISVAR program developed by Ferreira (2011).

Results and Discussion
It was observed that while increase TGW proportion on treatments, plants acquired higher amount of biomass with increase in height, number of leaves and tillers.For height, it was observed no significant difference on the first four weeks and after that plants started to express treatment effects with 5% of significance and 1% of significance from fifth week on (Table 4).The better treatment was the one with 100% of TGW (T1), which presented average height of 112.87 cm while treatment T1 presented average height of 92.04 cm (Figure 2A).Note.*, **: significant at 5% and 1% of probability, respectively, for F test. ns: non-significant for F test.DAS: days after sowing.
The tillers started to show from the beginning of dilutions application, showing significant difference of 1% on treatments from the 31 th day after sowing (Table 5).The treatment with 100% of TGW presenter better number of tillers, promoting higher biomass with average of 11.5 tillers while the treatment T1 obtained average of 1.5 tiller (Figure 2C).Note.*, **: significant at 5% and 1% of probability, respectively, for F test. ns: non-significant for F test.DAS: days after sowing.
The number of leaves on the main stem were not significant during part of the experiment, being significantly different from the 7 th week (Table 6).On average, the number of leaves on the main stem was bigger in the treatment T1 (7 leaves) and smaller on treatment T5 (3.4 leaves) (Figure 2E).Note.*, **: significant at 5% and 1% of probability, respectively, for F test. ns: non-significant for F test.DAS: days after sowing.
Despite the number of leaves on main stem do not present big difference during the experiment, the difference can be noticed on the number of total leaves per plant, that increased as increased the number of tillers.This variable presented significant difference of 1% from the 3 rd week after sowing (Table 7) with bigger number of leaves on treatment T5 with average of 53.67 leaves per plant, while on treatment T1 there were 14.09 leaves (Figure 2D).Note.*, **: significant at 5% and 1% of probability, respectively, for F test. ns: non-significant for F test.DAS: days after sowing.
Panicles started to emerge from the 5 th week.With the rise in tiller, more panicles emerged, showing significant difference of 1% from the 6 th week after sowing (table 8) with greater number of panicles the treatment T5 with mean of 8.46 panicles while treatment T1 had 1.3 panicles per plant (Figure 2B). jas.ccsenet.

Table 2 .
Physico-chemical characteristics of treated gray water (TGW) and well water (WW) and its related average (A) and standard deviation (SD)

Table 3 .
Volume in liters of treated gray water (TGW) dilutions in well water (WW) and applied during the experimental period

Table 4 .
Summary of analysis of variance to height during miller experiment produced with treated gray water

Table 5 .
Summary of variance analysis for the number of tillers during millet experiment produced with treated gray water

Table 6 .
Summary of variance analysis for the number of leaves on the main stem during millet experiment produced with treated gray water

Table 7 .
Summary of variance analysis for the number of total leaves during millet experiment produced with treated gray water