Yield of ‘ Pingo de Ouro ’ Cowpea Bean Under Different Sowing Densities and Goat Manure Doses in the Region of Mossoró , Brazil

Using goat manure may substantially increase cowpea bean productivity. This study evaluated the yield of ‘pingo de ouro’ cowpea bean under different sowing densities and goat doses in the region of Mossoró, Brazil. The experiment was conducted from October to December 2016 at the Experimental Farm Rafael Fernandes, Mossoró-RN, Brazil. Treatments arranged in two-way factorial with four goat manure doses (0.0, 0.5, 1 and 2 kg m), and two sowing densities of bean (75,000 and 37,500 plants ha), with three replicates. The experiment was performed in complete randomized blocks design. We evaluated the number and length of pods per plant, number of seed per pod, weight of 100 dry grains and dry grain yield. Higher grain yield occurred using 2.0 kg m of goat manure (1,162.4 kg ha or 234 kg 2,000 m) and 75,000 plants ha (693.4 kg ha or 138.6 kg 2,000 m). High sowing density in combination with goat manure is an affective.


Introduction
The cowpea (Vigna unguiculata (L.) Walp) is one of the main food sources of tropical regions because it contains substantial lipids, sugars, calcium, iron, potassium, phosphorus and several essential amino acids (Cardoso & Ribeiro, 2006).
In the state of Rio Grande do Norte, Brazil, the cultivation of cowpea generates employment and income.The cultivation takes place in small areas, where the farmers cultive varieties adapted to the climatic conditions of the region.Brazil stands out among the bean-producing countries, occupying the third position, with an average production of 1.083 kg ha -1 (IBGE, 2017).
The rusticity, precocity and the wide adaptability allow the cultivation of cowpea in aggressive environments, an essential characteristic for the northeastern region of Brazil (Souza et al., 2013).In this region, climate is semi-arid, and string beans stand out as a significant crop that used as major source of proteins and carbohydrates, in the form of dry and green grains (Lima, 2014).The Brazilian states with the highest per capita consumption of beans are Ceará and Piauí, predominantly using cowpea (Wander, 2007).
Despite the low productivity of grains in the Northeast, the cultivation of cowpea beans can be an alternative of consumption and income through the cultivation of the 'Pingo de Ouro' variety.Many farmers in the State of Rio Grande do Norte consider the 'Pingo de Ouro' variety more productive than other local varieties, such as 'Centa de Vaca' and 'Canapu'.The use of local varieties contributes greatly to the reduction of production costs (Carpentieri-Pípolo et al., 2010).Goat manure is a source of organic matter that is easily available and can be used for fertilization.A positive effect of goat manure application was found in sunflower (Pereira et al., 2014), maize (Oliveira et al., 2016) and lettuce (Figueiredo et al., 2012).
In addition to fertilization, the definition of ideal seeding density contributes to increasing the productivity of cowpea.Therefore, proper management of the culture, balancing the production factors, is fundamental to achieve optimum productivity (Cardoso Melo & Andrade Junior, 1997).However, studies testing different seeding densities for beans of the local varieties are still scarce.
Thus, due to the importance of cowpea in the High West region of Rio Grande do Norte, this study aimed to evaluate the impact of goat manure and sowing densities on yield of cowpea Pingo of Ouro type.

Materials and Methods
The research was developed October to December 2016 in an area in the community of Alagoinha, belonging to the Federal Rural University of the Semi-arid from October to December 2016, rural area of Mossoró-RN, Brazil (5º03′37″ S, 37º23′50″ W).The climate is BSwh', dry and very hot according to the Köppen classification, with a dry season from June to January, and a rainy season from February to May (Carmo Filho & Oliveira, 1989).Average annual rainfall of 673.9 mm and average relative humidity of 68.9%.The soil was classified as Argisolic Yellow Latosol (Embrapa, 2006).
Before set up of the study, samples of soil were collected from the 0-20 cm layer.These soil samples, were air dried and sieved in a 2 mm mesh, an then analyzed at the Soil Chemistry and Fertility Laboratory of Universidade Federal Rural do Semi-Árido (UFERSA).The results from the laboratory testing at UFERSA were the following: pH (water 1:2.5) = 6.64; exchangeable cations Ca = 1.30cmol c dm -3 ; Mg = 0.60 cmol c dm -3 ; K = 34.5 mg dm -3 ; Na = 10.7 mg dm -3 ; P (Mehlich) = 34.5 mg dm -3 ; N = 0.77 g/kg and M.O = 2.48 g kg -1 .
The experiment was conducted in complete randomized blocks, in a 4 × 2 factorial design three replications.Treatments included four doses of goat manure (0.0; 0.5; 1.0 and 2.0 kg m -1 ), for the plant density of 75,000 and 35,000 plants ha -1 a the spacing of 0.4 × 1.0 m, 0.8 × 1.0 m were used respectively.The densities were choose based on the densities used by cowpea producers in the municipality of Frutuoso Gomes, RN.
Farmers from Frutuoso Gomes-RN commonly use the local variety 'Pingo de Ouro', which was used at this work.Each experimental unity consisted of 6 meters with 45 and 21 plants at the spacing of 0.4 and 0.8 m, respectively.The soil was prepared by plowing and grading.The experiment was irrigated by a drip system, with one hose per block, and emitters spaced at 0.40 m, with flow rate of 1.5 L h -1 .
The goat manure used was sourced from of the UFERSA, which are raised in an intensive system, fed with corn-based concentrate, soy bean and wheat bran, and having as bulk Canarian grass (Echinocloa polystochya), the chemical concentration manure was included: pH (water 1: 2.5) = 8.06; and the total contents of 16.5 g kg -1 of N; 6.6 g kg -1 of P; 19.0 g kg -1 of K + ; 0.849 g kg -1 of Na + ; 14.4 g kg -1 of Ca 2+ and 7.7 g kg -1 of Mg 2+ ).
Seeds used came from the farmers of Frutuoso Gomes-RN.Sowing was carried out on October 6, 2016, by placing five seeds per hole.Fifteen days after sowing two plants were removed, and remaining three plants per hole kept throughout the experiment.
Irrigation was performed twice a day for 60 minutes.Weeds were removed at every 15 days.For the control and prevention of pests, such as caterpillars, leafminer, and aphids, the NeenMax Insecticide, (Azadirachtin) was used, at the dose of 10 ml liter -1 .
Harvest of the dry pods was made manually.At the Laboratório de Pós-Colheita de Hortaliças of the Departamento de Ciências Vegetais of UFERSA, we measured the number and length of pods per plant, number of seeds per pod, weight of 100 dry grains and yield of dry grains.
The average number of pods per plant: was obtained through the sum of all pods of the plot, except for the border, divided by the number of plants.The mean length of pods per plant: was evaluated in a random sample of 15 plants of each plot, measuring all pods of the plants using a graduated ruler in centimeters.The average number of seeds: determined from a sample of 20 randomly selected pods from the useful area of each plot, expressed as seed pod -1 .The weight of 100 dry grains: was obtained using a digital scale with an accuracy of 1 g.The dry grain yield: was determined from the weight of the dry grains of the area of each plot and expressed in kg ha -1 and kg 2.000 m -2 .
Analyses of variance (ANOVA) were used to verify the effects of the manure and density of seeds on the response variables of Pingo de Ouro variety.Regressions were made to analyze the relations of the response variables with the increase in manure doses, using the software ESTAT (Kronka & Banzato, 1995).

Results and Discussion
We found a significant interaction (p < 0.05) among manure doses and the sowing densities for the weight of 100 grains and mean length of pods per plant (Table 1).In the goat manure dose, there was a significant effect (p < 0.01) on the number of pods per plant, number of seeds per pod, weight of 100 dry grains and yield of grams of cowpea be (p < 0.05) Figure 4