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This work studied the efffect of P omission on the P uptake and on the rootlength of eight maize genotypes of known P-efficiency response patterns. Two experimentswere carried out in growth chambers. In the first one, the seedlings were transplanted to 1.5 Lplastic pots with full strength Steimberg’s nutrient solution for seven days. After this period Pwas omitted in half of the treatments for 3 days, when the kinectic studies were then initiated bytaking 10 ml aliquots every 30 minutes during 8 hours. The second experiment followed the same methodology, except where the P omission was for 6 days. After this period the roots ofall treatments were harvested to measure their lengths.These results showed that the omissionof P for 3 days increased the Vmax and the P influx of all the P-efficient genotypes and two ofP-inefficient genotypes. The Km values changed in two genotypes only. This may indicate thatincreases in Vmax and P influx are mechanisms of response to low P concentration , but theyshould not be used as parameters to establish differential P response patterns between genotypes.After 6 days of P omission , the root length incresed in 3 of the four P efficient genotypes. Thispattern was not observed with the P-inefficient genotypes, thus suggesting that the differentialroot growth may be one of the possible mechanisms of P use efficiency in maize.