Utilização nitrato de sódio em viveiros de camarão marinho

Abstract

The fertilizers based on urea and ammonia as nitrogen source is more used in aquaculture, mainly for their low cost. However it should be pointed out that those fertilizers in high doses could cause ammonia toxicity. On the other hand, fertilizers based on nitrates, even with superior costs, present advantages over those based on ammonia, because nitrate is not toxic and it is totally oxidized in the cultivation atmosphere. It was aimed at with the present work to test the use of sodium nitrate in ponds of sea shrimp. It was considered two treatments: NS (sodium nitrate enriched with phosphate, silicate, boron, magnesium, sulfur and potassium) and SNS (urea, triple super phosphate and sodium silicate). Sampling and analyses of the water were accomplished, being weekly performed for the plankton and for the soil in the beginning and in the end of the cultivation cycle. The application of sodium nitrate was initially in the soil and later in the water. For statistical analysis it was used T test (P <0,05). Yield data for the cultivate (mean weigh to the first forty days of cultivation, mean final weight, time of cultivation, survival, productivity and feed conversion) in the Atlantis and Cana Brava farms, showed no present significant difference among the treatments. In thephytoplankton groups, diatoms (12.554 and 5.833 céls/ml) in the Atlantis farm and cyanobacteria (146.052 and 34.250 céls/ml) in the Cana Brava farm, significant differences were observed among the treatments (NS and SNS), respectively. The zooplankton groups (cladoceran, copepod and rotifers) in the Atlantis and Cana Brave farms did not present significant difference, among the treatments. In the chemical variables of the water, silicate (2.3508 and 3.4787 mg/L) and orthophosphate (0.0158 and 0.0068 mg/L) in the Atlantis farm, significant differences were observed, among the treatments (NS and SNS), respectively. The oxidation of the organic matter in the Atlantis farm (36,2 and 20%) and in the Cana Brava farm (6,5 and 0,2%), presented significant difference, among the treatments (NS and SNS), respectively. The treatment NS provided higher diatoms densities in the Atlantis farm and higher cyanobacteria densities in the Cana Brava farm. The treatment NS provided better concentrations of the chemical variables silicate and orthophosphate in the Atlantis farm, and a higher oxidation of the soil organic matter.