Phosphorus availability for three crop species as a function of soil type and fertilizer history

Knowledge of the capacity of a soil to supply phosphorus (P), and the variation in the ability of different crops to access soil P, is critical to successfully managing P in modern cropping systems. Isotopic dilution techniques were used to examine the capacity of three contrasting soil types (Calcarosol, Vertosol and Chromosol) to supply P, and to compare the ability of three different crop species (wheat, chickpea and canola) to access P under both low and adequate P conditions. This was achieved by measuring L values of the different crops grown for 56 days in P-32-labelled soils with various combinations of history of P fertilisation (native vs. cultivated soils) and recent P addition (none vs. added P). A parallel experiment used these identical soil types/treatments without plants to determine E values. The three soils studied varied in the capacity to supply P to crops. The sandy Calcarosol, on average, had higher E values than other two soils. E-values were generally constant or slightly decreased over 42 d. Adding water-soluble P enhanced E values in all 3 soils. While chickpea absorbed more P from the P-deficient native soils, wheat was superior to either canola or chickpea in acquiring both freshly applied and residual P fertilizer across the three soils. The L values were generally constant over 56 d for all the soils and plant species, although the value was lower at Day 21 compared to later harvests for some treatments. Irrespective of soil type, plant P uptake correlated well with L and E values. Interestingly, wheat and chickpea but not canola had higher L/E ratios when grown in the P-deficient native soils than in other P treatments of Calcarosol and Vertosol. It is concluded that soil type, crop species and P history all affect P acquisition from soil and applied fertilizer, and that both L and E values are reliable indicator of predicting plant-available P in soil.