Introduction
Trace elements, as the name suggests, are only required in very small amounts but deficiency can lead to considerable yield loss. Trace elements are required by the plant for many important functions such as photosynthesis, general metabolism, growth and nitrogen use.
Western Australian coastal sands are naturally deficient in almost all trace elements. To achieve maximum yield, potatoes require adequate applications of boron (B), copper (Cu), manganese (Mn), molybdenum (Mo), zinc (Zn) and sometimes iron (Fe).
Soil conditions and soil tests
Soil tests and associated recommendations for trace element fertiliser applications are available from commercial laboratory services within and outside Western Australia. If using Australian services, ensure the laboratory is NATA (National Association of Testing Authorities) accredited as this guarantees the tests meet minimum quality standards. Accurate soil tests allow accurate fertiliser recommendations which are important in correcting trace element deficiency, avoiding toxicity and maximising profit.
On alkaline soils, iron, manganese, copper and zinc may be poorly available while molybdenum may be poorly available on acid soils.
In both situations, factors such as waterlogging, nutrient interactions and environmental conditions may induce nutrient deficiency, even though the trace elements have been applied before planting. Deficiency may be alleviated by post-planting foliar applications.
Trace element programs
Pre-planting program
Suggested pre-planting programs for old and new land on coastal sands are given in Table 1.
| Element (symbol) | Fertiliser and % of element | New land kg/ha fertiliser (kg/ha element) | Old land kg/ha fertiliser (kg/ha element) |
|---|---|---|---|
| Boron (B) | Sodium tetraborate (11%) | 34 (3.7) | 18 (2.0) |
| Copper (Cu) | Copper sulphate (20%) | 34 (8.5) | 18 (4.5) |
| Iron (Fe) | Iron sulphate (20%) | 34 (6.8) | 18 (3.6) |
| Manganese (Mn) | Manganese sulphate (26%) | 50 (13) | 25 (6.5) |
| Molybdenum (Mo) | Sodium molybdate (44%) | 22 (1.0) | 2.0 (0.9) |
| Zinc (Zn) | Zinc sulphate (36%) | 28 (10) | 16 (5.8) |
The fertilisers listed are examples only as many commercial fertilisers contain trace elements in the same or other forms. For fertilisers other than those listed, use the nutrient concentration of the element (percentage) to determine the rate of fertiliser needed to provide an equivalent amount of the trace element, which is given in brackets as kg/ha.
Before planting, trace elements should be broadcast and incorporated using a rotary hoe with other pre-planting fertilisers such as phosphorus, potassium and magnesium. More information on fertiliser for potatoes can be found at Fertiliser management for fresh market potatoes grown on coastal sands.
Post-planting program
Suggested rates and frequencies for post-planting foliar applications of trace elements are provided in Table 2. These are general guidelines only and should be used in conjunction with petiole testing to confirm the need for post-planting applications.
| Element | Fertiliser | g/100L | Frequency |
|---|---|---|---|
| Boron | Borax | 300-500 | 1-2 times |
| Copper | Copper sulphate | 200 | 1-2 times |
| Iron | Iron sulphate or chelate | 200 100-150 | weekly |
| Manganese | Manganese sulphate | 800 | 1-2 times |
| Molybdenum | Sodium molybdate | 100-200 | 1-2 times |
| Zinc | Zinc sulphate or chelate | 400 100 | weekly |
Petiole testing
The adequacy of trace element programs should be monitored using chemical analysis of petioles. Petiole monitoring is also important to avoid over-applying trace elements, which can easily occur as they are only needed in small amounts. Excess application can lead to toxicity and yield loss. Further information on the concentrations of trace elements expected in the petioles of adequately fertilised potatoes grown on sands can be found at Petiole analysis for fertiliser management of potatoes on sands.
Acknowledgements
This information is based on work carried out in a project on fertiliser and irrigation management of potatoes funded by Horticulture Innovation Australia and the Department of Agriculture and Food, Western Australia.