Determination of available phosphorous for plants using different sources and 33P as a tracer

In an experiment with flower-pots we compared for three different types of soil the amount of phosphorus available to rice and barley from commercial phosphorus sources. We used 33P to label the soil and based on the specific activity of the plants growing in flower pots, in the presence and absence of commercial phosphorus sources, the available amount of phosphorus for the plant was calculated. This was done for every source in TSP whits for each soil type. It was found that available phosphorus for the plant in the three soil types were TSP >> Thomas and Reno >> Roca Salto y Pesca > Roca Huila