Researchers conducted trials on rice-wheat cropping systems to determine the best frequency of phosphorus application for optimal productivity. Applying 90 kg of P2O5 per hectare to both rainy and winter crops each year resulted in the highest system productivity. However, farmers may achieve greater net returns by applying 60 kg of P2O5 per hectare to winter crops at one location, while applying the same amount to both rainy and winter crops at another location yielded higher returns. Alternating the application of 60 kg of P2O5 per hectare to winter crops every other year led to the highest net returns at a third location.