23 Oct 2012

Soil test values and nutrient balances from a long term fertilizer experiment

Presentation at 2012 ASA Meeting Armidale, NSW.

Robert M Norton1, Peter Howie2 and Charlie Walker3.

The Dahlen long term nitrogen and phosphorus experiment was established in 1996 and has been sown to a canola, wheat, barley and pulse rotation each year since then. The experiment has four rates of P (0, 9, 18, 36) applied at sowing, and 5 rates of N (0. 20, 40, 80, 160) either all at sowing or split 50:50 between sowing and the start of reproductive growth. Soil test values including P (total P, Colwell P) and N (total N, mineral N) contents have been tracked over the course of the experiment and provide information on the long term effects of fertilizer use in this region, including fertilizer nutrient use efficiency.

The initial Colwell value was 24 mg/kg (PBI 115) and after 16 crops, the soil test values were 17, 40, 72 and 125 mg/kg for the 0, 9, 18 and 36 kg P /ha/y rates. Soil mineral N values were 24, 36 and 34 kg N/ha (0-60 cm) and 58, 226 and 529 kg N/ha (0-150) for the 0, 80 and 160 kg N/ha rates respectively. Soil C values were not affected by N application and averaged 1.24 +/- 0.16, while soil C levels were 1.09, 1.25, 1.33 and 1.29 (LSD= 0.21 p=0.05) for the 0, 9, 18 and 36 kg P/ha/y rates respectively. Based on these data, P application rates that are similar to P removal will maintain the soil P test level and maintain soil C contents as well. Over application of N resulted in a large accumulation of N in the subsoil but had no effect on soil C.

1 International Plant Nutrition Institute, http://anz.ipni.net Email rnorton@ipni.net
2 Melbourne School of Land and Environment, Private Bag 260, Horsham, Vic 3402. www.unimelb.edu.au, Email peterwh@unimelb.edu.au
3 Incitec Pivot Fertilizers, PO Box 54, North Geelong, Vic 3214. www.incitecpivot.com.au, Email charlie.walker@incitecpivot.com.au
Dahlen Long Term Fertilizer Experiment.pdf (size: 1.77 MB)

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