2.6. Nutrients budget
A preliminary budget of nutrient was developed utilizing field records of amounts of commercial feed and fertilizers added to tanks, yields of shrimp and tomatoes, volume of tanks, and evaporation rates. Inputs of nitrogen and phosphorus through atmospheric precipitation, rainfall, nitrification, and nitrogen fixation by blue-green algae were considered negligible. Concentrations of nitrogen and phosphorus were multiplied by water flows to determine the mass load in irrigation water, return water, discharged water, and input water (groundwater). Harvest biomass of shrimp and tomato plants, and sludge quantified in the final of cycle were considered utilizing their correspondent nitrogen and phosphorus concentrations. Pruning of plants were included also within losses of nitrogen and phosphorus.