Phosphorus fertiliser placement for lupins in southern New South Wales

Abstract

Research in Western Australia and South Australia indicated that fertiliser phosphorus (P) banded below the seed of narrow leaf lupin (Lupinus angustifolius L.) at sowing was a more effective method of applying P fertiliser than the usual placement of P with the seed. This technology has not been investigated in southern New South Wales where lupins have been known to be unresponsive to fertiliser P.

We conducted 4 field experiments to examine the effect on lupin yield of applying 6 rates of P (0, 5, 10, 15, 20 and 40 kg/ha) either by placement with or below the seed. To further test responsiveness to P, an additional set of treatments was used; applying P at 40 kg/ha before sowing and then placing additional P below the seed at the 6 rates of application. The grain yield of lupin was increased by P application at all sites, despite the medium to high P status of 3 of the 4 sites used in these experiments. However, the technique of banding P fertiliser below the seed depth rather than placing it in direct seed contact had only a small advantage in grain yield responsiveness to applied fertiliser P (P = 0.09). Fitted response curves indicated that when P was applied at 15 kg/ha, grain yield increased by 60 kg/ha at one site and 30 kg/ha at the other 3 sites, if P was deep-placed rather than applied in seed contact. This advantage of deep placement of P fertiliser was much smaller than has been reported in Western Australia.

Placement of P below the seed of lupin when sown on the red earth and red-brown earth soils of southern New South Wales slightly enhanced the availability of fertiliser P. This applied even when sowing was quite shallow (2–3 cm), provided recommended rates of P fertiliser were used at conventional row spacing (17 cm). Separation of seed and fertiliser to avoid reduced germination may be an advantage when using double row spacing and higher P application rates.