A Pond-and-Field Nutrient Loop, Closed by Arithmetic or Not at All: A Full Nitrogen and Phosphorus Budget for a 0.2 ha Fish Pond Serving 0.5 ha of Crops

SIMULATED, NOT MEASURED. A full annual nitrogen and phosphorus budget for a stated integrated unit (0.20 ha fish pond, 0.50 ha crops, 960 kg feed/yr, 680 kg fish/yr), computed from an accompanying script. The loop supplies 19.2% of crop nitrogen demand and 57.7% of phosphorus demand, leaves $69.56/yr of external fertiliser still required, and turns into a pollution source at 1,700 kg feed/yr, set by phosphorus.