Effect of the nitrogenada fertilization on the production of the Mamona irrigated with water and effluent of treated domestic sewer

A mamona (Ricinus communis L.), pode ser considerada uma cultura com muitas utilidades, dentre elas a de utilizar o seu Ãleo para produÃÃo de um biodiesel, combustÃvel considerado ecologicamente limpo, ou seja, pouco ou nÃo poluidor do ambiente. AlÃm de trazer benefÃcios ambientais, a exploraÃÃo da mamona possibilita, tambÃm, a geraÃÃo de emprego. No presente estudo, conduzido em um Argissolo Acinzentado eutrÃfico, no municÃpio de Aquiraz (CE), foram investigadas as respostas da mamona (variedade BRS-149, Nordestina) a crescentes doses de nitrogÃnio (0, 30, 50, 70 e 90 kg N ha-1), usando-se duas diferentes fontes de Ãgua para irrigaÃÃo: Ãgua tratada e Ãgua de poÃo oriunda de estaÃÃo de tratamento de esgoto domÃstico (efluente). O experimento foi instalado e conduzido em condiÃÃes de campo na estaÃÃo experimental da CAGECE/PROSAB/CT-UFC no municÃpio de Aquiraz-CE. A Ãrea foi dividida em duas parcelas, sendo uma irrigada com Efluente de Esgoto Tratado e a outra irrigada com Ãgua de PoÃo. O espaÃamento utilizado foi de 1m entre plantas e 3 m entre filas. O delineamento experimental utilizado foi o de parcelas subdivididas com 3 repetiÃÃes. Foram avaliados componentes de produÃÃo e de crescimento. Foram obtidas produtividades de sementes de atà 2250 kg N ha-1 na parcela com Efluente de Esgoto e 2240 kg N ha-1 na parcela irrigada com Ãgua de PoÃo. As doses que promoveram maior produtividades de sementes foram: 70 e 90kg N ha-1, para o Efluente de Esgoto Tratado e 50kg N ha-1, para a parcela irrigada com Ãgua de PoÃo. Doses crescentes de nitrogÃnio (UrÃia), provocaram efeitos diferentes nas parcelas irrigadas com Efluente de Esgoto DomÃstico e Ãgua de PoÃo.The castor bean (Ricinus communis L.) can be considered as a commercial crop with multiple utilities, among them, the use of its seed oil for biodiesel production, a motor fuel considered ecologically clean. The present study was conducted under field conditions, in an Argissolo Acinzentado eutrophic soil, and had the objective to evaluate the castor bean yield (cultivar Nordestina BRS-149) response to nitrogen fertilization. The experimental design consisted of a split-plot model. One plot was irrigated with treated sewage effluent and the other with well water. Each plot was fertilized with five N rates in a form of Urea (T1=0, T2=30, T3=50, T4=70, T5=90 kgha-1 N), control treatment and three replications. The following parameters were evaluated: number of racemes/plant, first raceme length, 100 seed weight, kg of seed per hectare, first raceme height and stem diameter. The number of racemes/plant was significantly higher in the plot irrigated with treated sewage effluent than in the plot irrigated with well water. The type of irrigation did not cause differences in the first racemes lengths; however, differences occurred inside each plot as function of the N rate. The seed highest productivity was 2250 kgha-1 (rate of 90 kg Nha-1) for the plot irrigated with treated effluent, while was 2240 kgha-1 (rate of 50 kg Nha-1) for the plot irrigated with well water. The higher pH of the effluent may caused higher N volatilization, what may explain the higher N rate to reach maximum productivity in the effluent irrigated plot. The nitrogen fertilization caused significant increases in all parameters evaluated, except for 100 seed weight