Dahlen Long-term Nitrogen and Phosphorus Recovery Experiment

Established in 1996, this long-term site at Dahlen, 10 km west of Horsham, has had five rates of N (0, 20, 40, 80, 160 kg as urea) and four rates of P (0, 9, 18, 36 kg as triple superphosphate) applied annually over the past 16 years. The site has been direct drilled and no stubble has been removed or burned. In 2011, the site was sown to oats in mid-May as a hay crop and the standing crop cut on 20 September when the plants were still in the flag leaf growth stage.

The site mean yield was around 6 t/ha of dry matter and the effect of added P was clear with the first 9 kg of P giving a 77% increase in dry matter. Increasing P from 9 to 18 kg gave an additional 24% in dry matter. The higher hay yield was of a lower quality, with lower crude protein, higher fibre content and a lower metabolizable energy content. Despite this, total yield of both energy and protein rose significantly as more P was added. For example, the 9 kg P/ha rate increased the yield of protein and energy by 60%. Like P, applied N had a significant effect on the quality of fodder produced, with the extra N increasing crude protein content from 8.4% (nil N) to 13.1% (80 N). Balancing N and P meant that the yield gains due to the added P also maintained quality by keeping N supply up. The nil effect of applied N on hay yields was surprising, as there was only 26 kg N/ha in the top 60 cm at sowing on the nil N plots and total N demand was around 90 kg by the crop. It seems there was extra N beyond 60 cm, a remnant of the previous applications, leached down with the past two relatively wet years in the Wimmera. ANZ-08