KINETICS OF PHOSPHORUS UPTAKE AND ROOT MORPHOLOGY IN ROOTSTOCKS BELONGING TO CITRUS AND PONCIRUS GENERA

Kinetics of P uptake and root morphology was studied during 1988 in the rootstocks of Citrus and Poncirus genera and the scion of coorg mandarin (Citrus reticulata Blanco). Rootstocks of citrumelo (Poncirus trifoliata x Citrus grandis), trifoliate orange (Poncirus trifoliata Rafin) and cleopatra mandarin (C. reshni Hort. ex. Tanaka) had smaller root radius than of troyer citrange (Poncirus trifoliata x Citrus sinensis), rough lemon (C. jambhiri Lush), rangpur lime (C. limonia Osbeck) and the scion of the coorg mandarin. Rough lemon and trifoliate orange had greater root length/plant/unit shoot weight and specific root length than the other root stocks and the scion of coorg mandarin. Cleopatra mandarin and troyer citrange had greater P-inflow rate, root-demand coefficient and a moderate affinity for P, which was reflected in a higher rate of P absorption and total P uptake from the solution. In these rootstocks P inflow was linear in a greater concentration range. Rough lemon roots had high affinity for P and very low concentration of P in the equilibrium (C(min)), indicating that rough lemon can have substantial P inflow even at low concentrations, usually found in arable soils.