Di-ammonium phosphate and mono-ammonium phosphate improve canola growth when banded in a P-fixing soil compared with triple superphosphate

Abstract

Banding of fertiliser may restrict fixation of P by soils and thus improve P fertiliser use efficiency. Using pots that allow soil to be sectioned, we examined the effect of banding triple superphosphate (TSP), mono-ammonium phosphate (MAP), and di-ammonium phosphate (DAP) on canola (Brassica napus L. cv. 'Karoo') growth and nutrition in P-fixing soils and the pattern of nutrient distribution from these bands. After 28 days, growth of canola fertilised with MAP or DAP was greater than that of canola fertilised with TSP. Nutrient analysis of the shoots indicated that these differences in growth were most likely the result of differences in nitrogen nutrition. Movement of P was greatest from the DAP band. This was attributed to less fixation of P as a result of an increase in the pH surrounding the DAP band that reduced the fixation of P as Al or Fe phosphate. This study showed that canola grew better when fertilised with DAP or MAP; given the greater movement and availability of P and N from the DAP compared with MAP band, the DAP fertiliser would result in the best canola production in this P-fixing soil.