The Fe, P and Zn relationship in Cowpea was studied on a Typic ustipsamtnents soil. The P/Zn ratio increased in root and shoot with P application due to decreased mobility of Zn. iron also checked the translocation of Zn from root to shoot. The ratio (P/Zn) varied from 42 to 149 in the presence of P and from 200 to 917 when no P was added. P/Zn ratio of 200 and 40 for shoot and root, respectively was critical. The P/Fe ratio in P treated shoots was several fold higher than the untreated ones. Application of Zn in the presence of P and Fe increased the P/Fe ratio whereas the mobility ratio of P and Fe decreased. Critical P/Fe ratio for shoot was found to be 20 for shoot whereas in root no definite pattern was noticed. With the application of P, the Fe/Zn ratio became wider due to dilution effect. Application of Zn at all levels of Fe and P decreased the Fe/Zn ratio. The mobility of Fe increased with Fe application when P was also applied but the mobility of Zn was unaffected with Fe and P application. Under optimum levels of P, the Fe/Zn critical ratio was 10 and 50 for shoot and root, respectively.
