GROWTH RESPONSE OF WATTLE (<em>ACACIA</em> <em>MEARNSII</em>) SEEDLINGS TO PHOSPHORUS FERTILISATION AND INOCULATIONS WITH <em>GLOMUS</em> <em>DESERTICOLA</em> AND <em>RHIZOBIUM</em> SP. IN NON-STERILE SOIL

Abstract

The effect of phosphorus (P) fertilisation and inoculation with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus deserticola and Rhizobium sp. was studied in containerised seedlings of wattle (Acacia mearnsii). The non-sterile soil used was amended with tricalcium phosphate and superphosphate at the rates of 0, 50, 100, 150, 200 and 250 mg kg-1 soil. The seedlings inoculated with G. deserticola alone but receiving no P fertiliser were comparable in growth to those uninoculated seedlings which received 150 mg kg^-1 soil of tricalcium phosphate and 100 mg kg^-1 soil of superphosphate. Rhizobium inoculated wattle seedlings which received no P fertiliser were similar in size to those of uninoculated seedlings fertilised with 200 and 150 mg kg^-1 soil of tricalcium phosphate and superphosphate respectively, whereas the seedlings coinoculated with G. deserticola and Rhizobium sp. without added P fertiliser were more than equivalent in growth to uninoculated control seedlings fertilised with 250 mg kg^-1 soil of tricalcium phosphate or superphosphate. P fertilisation invariably increased tissue P concentration in the seedlings, reduced mycorrhizal root colonisation but markedly stimulated nodulation. The highest nutrient (N,P,K) concentrations in the plant tissues were recorded in the seedlings coinoculated with G. deserticola and Rhizobium sp. when compared with individual inoculations. Phosphorus utilisation efficiency decreased with increasing P fertiliser doses and inoculations with G. deserticola and Rhizobium sp.