After planting fertilising
Post-plant, apply a total of 250–300kg/ha N and K if pre-plant soil N and K are low, depending on soil type, with higher rates for more sandy soils. On sandy soils, divide the total amount into weekly applications and on heavier soils into three-weekly applications.
On processing potatoes, apply K as sulphate or nitrate because muriate of potash has been shown to lower the specific gravity (dry matter %) of tubers compared with other forms of fertiliser potassium.
Apply some nitrogen as calcium nitrate to supply up to 75kg Ca/ha post-planting, in addition to any calcium applied before or at planting. For example, 394kg calcium nitrate per hectare (19% Ca and 15% N) applies 75kg Ca and 60kg N.
Seed crops often require less fertiliser N than non-seed crops, as they may grow for a shorter period, especially if the plan is to maximise the yield of small round seed. Tuber size in some varieties, such as Atlantic, is very sensitive to applied N and high rates may result in low yields of small round seed and high yields of oversize tubers. Excess N may also increase tuber disorders such as hollow heart in sensitive varieties.
Monitoring fertiliser program with plant testing
Monitor the effectiveness of your fertiliser program by using plant (petiole) tissue testing. For the trace elements Cu, Zn, Mo, Mn and B, petiole testing is much more accurate than soil testing as there are very few standards for deficiency or adequacy for WA soils.
Collect 20 to 30 petioles per test area of the crop and note the crop stage by measuring the length of the longest tuber in millimetres.
| Nutrient and symbol | % or mg/kg | At S2 (10mm tuber stage) |
|---|---|---|
| Nitrogen (N) | % | 4.5-5.5 |
| Nitrate-N (NO3-N | % | 2.6-3.5 |
| Phosphorus (P) | % | 0.8-1.0 |
| Potassium (K) | % | 10-16 |
| Calcium (Ca) | % | 0.5-1.5 |
| Magnesium (Mg) | % | 0.3-0.75 |
| Sulphur (S) | % | 0.2-0.35 |
| Boron (B) | mg/kg | 20-40 |
| Copper (Cu) | mg/kg | 5-16 |
| Iron (Fe) | mg/kg | 230 |
| Manganese (Mn) | mg/kg | 20-100 |
| Molybdenum (Mo) | mg/kg | 0.1-1.5 |
| Zinc (Zn) | mg/kg | 30-110 |
Use the results of the petiole test and other relevant agronomic information to adjust the fertiliser program to account for nutrient inadequacies or excesses if they arise.
Acknowledgements
Much information on this page is based on results from a number of potato research and development projects funded by Horticulture Australia Limited with voluntary contributions from APC Potato Producers Committee, matched by the Australian Government, and with in-kind contributions from and managed by the Department of Agriculture and Food, Western Australia.