| Summary: | The paper considers the application of the studies of nutrient cycling on the determination of phosphorus requirements in sugarcane plantations. The work was performed in a 4.5 ha experimental plot located in the valley of Yaracuy river in central, Venezuela. The plot was planted with the varieties Puerto Rico (PR) 1028 and Venezuela (V) 58-4. The principal flows of phosphorus, as well the quantities of this element in the soil-plant components were measured throughout the growing cycle of the crop (second ratoon). The inputs through precipitation (wet and dry) were high, that was associated with the intense agricultural (prescribed burning of sugarcane plantation) and industrial activities occurring in the area. The annual balance for both varieties was negative (-17 and - 23.3 kg.ha-1 for V 58-4 and PR 1028, respectively). The negative budget is mainly due to the important amounts of P that are exported with the cane stems. The losses must be compensated though fertilisation, nonetheless, preliminary results indicated no response to P dressing, suggesting that in the studied mollisol the internal processes e.g. Po mineralization and P solubilization, efficiently operate generating important available P levels. It was also found that the burning of the sugar cane plantation plays an important role in the recycling of phosphorus, since 25-30% of the P requirements of the varieties are reincorporated into the soil from the ashes.
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