Productivity of Lettuce Under Organic Fertilization

Organic fertilizersare a viable alternative to reduce the expenses associated with synthetic fertilizers, besides improving the chemical, physical and biological attributes of the soil and promoting the increase of productivity in the cultivation of vegetables. The aim of this research was to evaluate the effect of goat manure applicatiosn on lettuce yield, cv. Cristina. The experiment was conducted at the Center for Agri-Food Science and Technology, Federal University of Campina Grande in the municipality of Pombal, PB, Brazil. The experiment was conducted in randomized blocks with treatments composed of five goat manure percentages (0, 25, 50, 75 and 100%), considering 100% of the recommended dose being 36.50 ton/ha de goat manure, in five replications, using a spacing of 0.25 × 0.25 m between plants. Harvesting was performed 30 days after transplanting the seedlings. The following parameters were analyzed: aerial part height, plant diameter, number of leaves, aerial fresh weight, root fresh weight, total fresh weight, aerial dry weight, root dry weight, total dry weight, root volume and productivity. The data were submitted to polynomial regression analysis. When the lettuce plants cv. Cristina were fertilized with 75% of the N ratio required for maximum production, the goat manure application produced the greatest development and increase productivity.


Introduction
The consumption of leafy vegetables, such as lettuce, is widely recommended, since these foods provide innumerable benefits to the body, such as organic development and regulation of the body, due to its high content of vitamins and minerals (Martins et al., 2008).The lettuce (Lactuca sativa L.), belonging to the Asteraceae family, stands out among the leafy vegetables, being the most consumed by the Brazilian population, besides being widely cultivated in all countries (Silva, Pinheiro, Paula, & Prigol, 2015).In Brazil, its cultivation is traditionally carried out at family farms, a factor that adds value to the field and increasing the labor which has potential sociological benefits.
Due to the large demand for lettuce, it is important in improve the production practices that will increase its availability.Mineral fertilization, despite its advantages, brings with it significant negative environmental impacts, such as increasing soil salinity, decreasing long term fertility, decreasing organic matter, and the accumulation of agrochemicals in soils (Pedrotti et al., 2015).
Organic fertilization appears to be a good option for reducing mineral fertilizers expenditures, due to the greater availability of nutrients, especially nitrogen, phosphorus, sulfur and micronutrients, increasing the pH, as well as the indirect benefits to the soil's physical, chemical and biological properties, and, thereby, increasing crop productivity (Kiehl et al., 1999;Santos et al., 1999;Santi et al., 2010).
Among the many sources of organic fertiliziers, we highlight the use of animal manure, the indirect effects that manure produce, due to its high organic matter content, and as a mean to improve a soil's physical, chemical and biological characteristics.In this context, goat manure is potentiallybeneficial because its lower carbon/nitrogen (C/N) ratio when compared to other manures (Souto et al., 2005).The lower C/N ratio results in a higher mineralization speed of nutrients, an essential characteristic in the fertilization leafy vegetables, due to the rapid cycle of these crops.
The nutrient amounts excreted in the goat feces was evaluated by Orrico et al. (2007), where they obtained a dry matter mean of 1.39% N; 0.62% P and 0.29% K, They also found an increase in nutrient concentrations in feces, as the animals approached the adult stage and were fed diets rich in concentrate.
Studies that provide information on the management of organic fertilization by the application of goat manure in the lettuce crop are extremely important for the construction of technical subsidies that aim at raising productivity rates, reducing fertilizer costs, and greater profitability to the producer.However, there are few studies that have investigated the application of goat manure in lettuce these are examples, Figueiredo et al. (2012);Batista et al. (2012);Peixoto Filho et al. (2013).
The use of this type of organic fertilizer is seen as a useful and economical practical for producers, especially vegetable producers, since it offers innumerable benefits, increasing fertility and soil conservation and thus providing organic nitrogen accumulation in the soil, increasing its potential of mineralization and its availability to plants.However, higher or lower application rates will depend on the soil type, texture, structure and organic matter content, since each manure type is unique characteristics and therefore must be studied in a singular way (Santos & Trindade, 2010).
Thus, it is necessary to know the application rates of organic fertilizer that promotes the greatest crop production, because this factor directly relates with lettuce productivity indexes.Therefore, the objective of this work was to study the proportion of goat manure that will provide the maximum yield of lettuce, cv.Cristina.

Material and Methods
The researchwas conducted at the Center for Agri-Food Science and Technology, Federal University of Campina Grande, in the municipality of Pombal, Paraíba, Brazil from June 18 to August 18, 2016.The municipality climate, according to Koopen classification adapted to Brazil (Coelho & Soncin, 1982), is of type BS h', which represents hot and dry climate with summer/fall rains, with an average precipitation of 750 mL by year.The experimental area soil was classified as Luvissolo Crômico Órtico typical (MAPA, 1972;Santos et al., 2013).

Production of Lettuce Seedlings
The lettuce seedlings cv.Cristina were produced in 200-cell expanded polystyrene trays, filled with commercial Hortplant® substrate, and allocated two seeds per cell.Ten days after emergence thye seedlings were thinned to one plant per cell.The seedlings were transplanted to the field beds on July 18, 2016, 30 days after sowing, when the majority seedlings had four leaves.

Treatments and Experimental Design
The experiment was a randomized complete block design and five goat manure treatments (0, 25, 50, 75 and 100%), which were determined by the nitrogen (N) recommendation for the crop.Prior to incorporating the manure, dry samples of the material were collected to determinethe chemical attributes according to the methodology of (Donagema et al., 2011).The analyzes were done at the Laboratory of Analyzes of Soil, Water and Plants of the Federal Institute of Paraíba-Campus Sousa (Table 1).
7.7 93.73 9.5 1.68 3.66 After the determination of the nitrogenin the goat manure sample (Table 1), five ratios of goat manure (0, 25, 50, 75 and 100%) were determined based on the fertilization recommendation of Raij et al. (1997), with 100% (36.50 ton/ha) as the manure dose calculated based on the goat manure nitrogen content and the amount of N required for the crop.

Installation and Conduction of the Experiment
The experimental area was cleared and all undesirable materials were removed prior to cultivation The soil was then plowed whith plow of large discor, to depth of 20 cm using and the beds were raised, 0.30 m high.Each experimental plot was 1.2 m long by 1.2 m wide, resulting in 1.44 m² per plot.
The pre-established proportions of the goat manure treatments, in kg/ha, were distributed and incorporated into the 0-15 cm layer of the plot using, applying 40% of the total recommended manure 15 days before transplanting and 60% of the recommended dose one day before transplanting the lettuce seedlings.The amount of goat manure was calculated according to Furtini Neto, Vale, Resende, Guilherme, and Guedes (2001), using the following expression: Where, X = amount of organic fertilizer to be applied, kg/ha; A = dose of N required by the crop for a given yield, kg/ha (Raij, Cantarella, Quaggio, & Furlani, 1997); B = dry matter content of organic fertilizer, %; C = N content in dry matter of organic fertilizer, %; D = conversion index of N from the organic form to the mineral form, 50% (Furtini Neto et al., 2001).
The weeds were manually harvested from the emergence of weeds in order to avoid competition for water, light and nutrients.The irrigation system used in the area was of the micro sprinkler type with an emitter flow of 80 mL/h.Irrigation was done twice a day, with a duration of approximately 15 min each.

Characteristics Evaluated
The four center plants were used for data collection while the other plants were used as border plants.The day before the lettuce was harvested the plant heights and head diameters were measured, with values expressed in cm per plant.
On August 18, 30 days after transplanting, the lettuce plants, both the above gound plant and the roots, were harvested and then transported to the plant breeding laboratory of the Center for Agri-Food Science and Technology, Federal University of Campina Grande.The harvested plants were then washed and separated into the above ground plant material and the roots for evaluation.The number of leaves was obtained by counting all fully expanded leaves.The fresh weight of the aerial portion and the root were determined separately with the values expressed in grams per plant.The total fresh weight was the sum of the aerial portion and the roots expressed in grams per plant.
The separate plant portions were placed in paper bags for drying in a oven using forced air circulation at a 65 °C until a constant weight was obtained (determined by oven drying during 72 h and reweighing).The total plant dry weight is the sum of the dry weight of the aerial portion and roots expressed in grams per plant.
Root volume was determined by placing the fresh roots in a 1,000 mL beaker, containing a known volume of water (500 mL), by the difference, the direct root volume response was obtained by the equivalence of units (1 mL = 1 cm 3 ), according to the methodology described by Basso (1999).
Productivity was obtained by multiplying the total fresh mass of the lettuce by the population of plants extrapolated to 7,500 m², considering the useful area of one hectare, expressed in ton/ha.

Statistical Analysis
The data were submitted to analysis of variance through the software SISVAR, version 5.6, according Ferreira (2011).The averages were adjusted in the linear and quadratic models through the simple polynomial regression analysis.

Results and Discussion
For aerial part height (Figure 1A), there is a positive response to the increasing use of goat manure doses, obtaining a higher performance of the variable when applied to the 100% dose (36.50 ton/ha of goat manure) resulting, according to the derivative of the equation, in a maximum average of 23.95 cm per plant, showing the significant effect of the availability of nutrients through manure.The various benefits of organic fertilization occur as a result of the release of nutrients as the organic waste is decomposed into the soil, thereby providing a higher production of plants.
Positive results in relation to the use of goat manure were found in experiments carried out with lettuce submitted to manure (bovine and goat) and nutrient concentration by Silva et al. (2011) goat manure provided greater efficiency in lettuce growth and yield.

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Figure 4. T