Broadcasting phosphate fertilisers produces higher yields of potatoes (Solanum tuberosum L.) than band-placement on coastal sands

The relative effectiveness of broadcasting compared with band-placement of phosphorus (P) fertilisers (0-480 kg P/ha) was compared using potatoes grown on P-deficient sandy soils over 2 seasons in Western Australia (Karrakatta sand in 1993, experiment 1; and Spearwood sand in 1996, experiment 2). The maximum yield of potatoes when P fertiliser was broadcast and incorporated to 20-25 cm before planting (broadcast) was 17 t/ha higher than when P was placed in 2 bands 5 cm to the side of and below seed piece level (banded) in experiment 1, and 13 t/ha higher in experiment 2. However, higher rates of applied P were required to reach 99% of maximum yield on the broadcast compared with the banded plots in both years (i.e. 174 v. 134 kg/ha in experiment 1, and 279 v. 125 kg/ha in experiment 2). Despite the lower levels of applied P required to achieve maximum yield in the banding treatment, banding P fertiliser for potatoes grown on Karrakatta and Spearwood sands would result in significant economic loss. The higher yield in the broadcast treatment corresponded with significantly (P<0.001) higher P concentrations (about 2-fold) in petioles of youngest fully expanded leaves from 56 to 131 days after sowing. When tubers were 10 mm long, the petiole P concentrations corresponding with 95 and 99% of maximum yield were 1.13 and 1.28%, respectively, for the broadcast P treatments in experiment 1, and 0.95 and 1.11% in experiment 2. The reduced yield in the banded treatments was assumed to be due to P fertiliser toxicity in the soil and not P toxicity in the plant tissue. Phosphorus uptake by tubers was significantly (P<0.001) higher (about 2-fold) when P was broadcast rather than banded, especially at high levels of applied P. Phosphorus recovery efficiency by tubers (P uptake by tubers/P applied, both in kg/ha) was higher when P was broadcast rather than banded, particularly at high levels of applied P (e.g. at 480 kg applied P/ha, recovery efficiency was 0.07 in the broadcast treatment compared with 0.03 in the banded treatment). These results show that, for growers to avoid significant economic loss, broadcast applications of P fertilisers should continue to be recommended for potatoes grown on the low P-fixing, sandy soils of the Swan Coastal Plain.