Use of Senna uniflora as Organic Fertilizer in the Production of Lettuce in the Brazilian Semiarid

The use of plant resources available on the farm, and of great relevance to the family farmers of the Northeastern semi-arid region, Brazil. The experiment was carried in the experimental area of the agricultural science center, Universidade Federal Rural do Semi-árido (UFERSA), Mossoró, Brazil, with the objective of evaluating use of Senna uniflora as organic fertilizer in the production of lettuce in the Brazilian semiarid, from October 2014 to February 2015. The experimental design of randomized complete blocks with the treatments arranged in 4 × 4 factorial scheme, with three replicates. The first factor consisted of amounts S. uniflora (0, 1.8, 3.6, and 5.4 kg m of dry matter) with four incorporation times into the soil (0; 28; 56 and 84 days before transplanting lettuce). The transplanted lettuce cultivar went was the “Elba”. The evaluated characteristics were the following: plant height, diameter plant, number of leaves per plant, green mass production and dry mass production. The best agronomic efficiency was obtained with soil incorporation of 5.4 kg m in the incorporation period of 56 days after transplanting, with phytomass production of 235.2 g plant. S. uniflora becomes a viable option to be used as an organic fertilizer in lettuce production.


Introduction
Soil degradation with chemical fertilization causes a decrease in the productive capacity, altering the structure and its soil fauna, besides provoking an entire erosive process, leading to losses of soil and nutrients Sustainable agriculture is the basis of agroecological production, a system of production without the use of chemical inputs. In the semi-arid region of the Brazilian Northeast, family farmers potentiate their production with the use of animal fertilizers, cattle manure and goat. However, because it is a resource with little availability among farmers, it contributes to increasing production costs (Linhares et al., 2014).
According to Linhares (2013) the practice of incorporating or leaving the organic residue in cover brings benefits to the soil-plant system. In addition, it guarantees the producer success in the production and optimization of the resources used. The organic fertilization with spontaneous Caatinga species is an alternative for small farmers in the semi-arid region. Aiming an agroecological production, many researchers and farmers seek for sustainable and diversified agricultural systems with low chemical inputs (Altieri, 2012).
Given the importance of the use of Northeastern semiarid species as organic fertilizer in the production of vegetables, the following research hypothesis was presented: The yield of lettuce depends on the greater amount and period of incorporation of S. uniflora. Therefore, it was aimed, to study organic fertilization with Use of S. uniflora as organic fertilizer in the production of lettuce in the Brazilian semiarid.

Study Area
The study area was located at the Rafael Fernandes experimental farm, in the period from October 2014 to February 2015, in the district of Alagoinha (5º03′37″ S, 37º23′50″ W), northwest of Mossoró, State of Rio Grande do Norte, Brazil, which has approximately 400 hectares (Rêgo et al., 2016). The production system is located in the semi-arid region of Brazil.

Characterization of Soil and Climate
The soil of the experimental area was classified as Eutrophic Red Yellow Argissolo, Caatinga hyperxerophilic phase and flat relief (Embrapa, 2018). According to Kottek et al. (2006) and the classification of Köppen, the local climate is BSwh', dry and very hot, the dry season being normally from June to January, and a rainy season being from February to May. The average annual rainfall is 673.9 mm and the average relative humidity is 68.9%.

Experimental Design and Treatments
The experimental design of randomized complete blocks with the treatments arranged in 4 × 4 factorial scheme, with three replicates. The first factor consisted of different amounts of S. uniflora incorporated into the soil (0.0, 1.8, 3.6 and 5.4 kg m -2 ) the second factor to the times of incorporation into the soil (0.0, 28, 56 and 84 days before the transplanting of lettuce).
The propagation of the lettuce seedlings was done in expanded polyethylene trays of 128 cells, containing vermiculite substrate. The seedlings were grown in a greenhouse for 15 days with 50% shading until they reached about 10 cm in height. Each plot had a total area of 1.96 m 2 (1.40 m × 1.40 m) containing 49 lettuce plants spaced of 0.20 m × 0.20 m. The harvest area of each plot was 1.0 m 2 (1.00 m × 1.00 m) containing 25 lettuce plants.

Nutrient Content of S. uniflora
S. uniflora was harvested in June 2014, in an area of semi-arid shrub vegetation in the flowering period. Soon after being harvested the material was crushed and dried in the sun, being packed in raffia bags to be used as an organic fertilizer. The material was sent to the soil fertility and nutrition laboratory at the UFERSA Agricultural Sciences Center, with a chemical concentration of 16.5 g/kg of N; 870 g/kg of OM; 402 g/kg of organic carbon (C); 24/1 C/N ratio; 0.68 g/kg of P; 5.87 g/kg of K; 1.45 g/kg of Na; 0.23 g/kg of Ca and 0.05 g/kg of Mg.

Evaluation of the Characteristics Studied
After harvesting, plants were transported to the Post-Harvest of Vegetables Laboratory at the Department of Agronomic and Forestry Sciences at UFERSA where they were analyzed.
The characteristics evaluated were as follows: plant height (was measured from twenty plants of the useful area, using millimeter rule, being expressed in cm/plant), diameter plant (was estimated through the distance between the opposing edges of the leaf disc, measured with a ruler and expressed in centimeter of twenty plants), number of leaves per plant (was measured with a sample of twenty plants, with result expressed in leaves/plant), green mass production (was obtained by removal all plants of the useful area, weighed in a precision scale of 1.0 g, expressed in g/plant) and dry mass production (measured by determining the dry matter content of lettuce in g/kg, multiplied by green mass production in m 2 , expressed in g/plant).

Statistics Analysis
Analyses of variance were conducted for the evaluated characteristics using the ESTAT software (Kronka & Banzato, 1995). Response curve adjustment for the quantitative factor was performed using the Table Curve software (Systat Software Inc., 2002). The response functions were evaluated based on the following criteria: biological rationale, significance of the mean square of the regression (QMRr), high coefficient of determination (R 2 ), significance of the regression parameters, using the t test at p < 0.01 probability).

Analysis of Variance
There was interaction between the amounts and periods of incorporation of the S. uniflora in the characteristics of the diameter of the plant and green mass of lettuce. However, there was an isolated effect at the level of probability (p < 0.01) in the different amounts of S. uniflora for plant height, number of leaves/plant and dry mass. In relation to the incorporation periods, there was a difference in the level of probability (p < 0.01) for height and number of leaves per plant and dry mass (Table 1). Note. ** = P < 0.01, statistical significance at 1% probability, * = P < 0.05, statistical significance at 5% probability and ns = not significant.

Plant Eight, Leaves per Plant and Diameter
There was an increase in height and number of leaves per plant, with the addition of S. uniflora, reaching maximum values of 25.02 cm/plant and 28.8 leaves/plant, in the amount of 3.6 kg/m 2 , occurring decrease up to the amount of 5.4 kg/m 2 ( Figures 1A and 1B). For the periods of incorporation, 54 days before planting promoted the greatest increase in plant height and leaves, with maximum values of 23.65 cm/plant and 31.46 leaves/plant (Figures 2A and 2B). jas.ccsenet.
F Figure 2 The