Insert your DGT P value here: Calculate Your RY%

Recommendations

0 – 75 µg/L: High likelihood of a response to applied P fertiliser

Things to consider:
  • Potato crops grown in soils with DGT-P concentrations less than 75 µg/L are likely to suffer a moderate to substantial yield penalty if no P fertiliser is applied.
  • Soils that fall within this zone may have a high affinity to tie up phosphorous fertiliser; use the Phosphorous Buffering Index soil test to assess the soils’ ability to tie up phosphorous.
  • Project research sites with DGT-P <75 µg/L that were responsive to fertiliser P application were either Ferrosols (acidic and rich in iron) or Vertosols (alkaline and rich in calcium) with corresponding PBI values ranging from 154 – 239 (moderate).
    • These sites suffered yield penalties between 30 and 70% when no P fertiliser was applied.
    • Yield results from these sites indicated that the P application rates (broadcast pre-plant) required to obtain >90% relative yield were in the range 90 – 140 kg/ha.
    • Consider banding fertiliser rather than broadcasting in such soil types to enhance fertiliser efficiency and to reduce application rates.
  • Discuss soil test results with your agronomist or advisor to determine appropriate fertiliser application rates for your soil type and situation.
75 – 310 µg/L: Moderate likelihood of a small response to applied P fertiliser

Things to consider:
  • Potato crops grown in soils with DGT-P concentration between 75 and 310 µg/L have a moderate likelihood of achieving a small yield increase when P fertiliser is applied.
  • Research sites that fell within this zone had Phosphorous Buffering Index (PBI) values ranging from 18 - 53 (low) and therefore have a low affinity to tie up phosphorous fertiliser; use the PBI soil test to assess the soils’ ability to tie up phosphorous.
  • Despite two of our sites falling within this zone, they did not respond to applied P fertiliser, which can happen in this zone of marginal deficiency.
  • The range 75 – 310 µg/L needs to be further refined with results from additional research sites.
  • Discuss soil test results with your agronomist or advisor to determine appropriate fertiliser application rates for your soil type and situation.
    • Consider conducting P application rate trials for your soil type and situation to identify ideal rates if your soil falls within zone.
>310 µg/L: Very low likelihood of a response to applied P fertiliser

Things to consider:
  • Potato crops grown in soils with a DGT P concentrations >310 µg/L have a very low likelihood of achieving a yield increase when P fertiliser is applied. There are two options in this case:
    • Apply no P fertiliser, acknowledging that soil P reserves will be mined.
    • Target P fertiliser applications at replacement rates only (see table below).
  • Project research sites that fell within this zone were predominately shallow to deep sands with Phosphorous Buffering Index (PBI) values ranging from 4 - 32 (extremely low) and therefore have an extremely low affinity to tie up phosphorous fertiliser; hence, P that is present in the soil is freely available for plant uptake.
  • Project results indicated that eight of the nine sites that fell within this zone were not responsive to P application i.e. they contained sufficient phosphorous to meet crop needs.
  • Results of the Colwell, Olsen and Bray 2 soil tests showed starting P concentrations in the soil well in excess of previously determined critical values (see results section).
  • Discuss soil test results with your agronomist or advisor to determine appropriate fertiliser application rates for your soil type and situation.
Target tuber yield (t/ha) P removed (kg)*
20 11
25 14
30 17
35 20
40 22
45 25
50 28
55 31
60 34
65 36
70 39

*Based on removal rates quoted by Maier, N. A. Potocky-Pacay, K.A. Jacka, J.M. Williams, C.M.J. (1989). Effect of phosphorous fertiliser on yield of potato tubers (Solanum tuberosum L.) and the prediction of tuber yield response by soil analysis. Australian Journal of Experimental Agriculture. CSIRO, Volume 29, 419-32.

Download the DGT Fact Sheet for potatoes


Project Partners

Potatoes South Australia PIRSA RSSA National Landcare Programme The University of Adelaide premiumgreen-logo