At tuber initiation, an adequate supply of phosphorus ensures supplies of optimum numbers of tubers are formed. While potatoes are very responsive to fresh soil phosphate, the economic optimum rate is often very difficult to define. Rates will depend on soil type and soil test results. The example below is on Desiree potatoes, Wales.
In trials with Russet Burbank potatoes in USA, tuber yield is increased by 0.6t/ha (0.3t/ac) for every extra day during which leaf tissue phosphorus is maintained above 0.22%.
It is particularly important that phosphorus is available at tuber initiation. Where sufficient soil phosphorus is not available for growth, foliar phosphate ensures rapid availability. Applied just before tuber initiation, foliar phosphate increases total tuber number.
In addition, foliar phosphate, applied after tuber initiation, has been shown in England trials to have a positive effect on tuber yields by increasing tuber size. However, foliar phosphate is not a substitute for soil applied phosphate. Without adequate soil phosphate early season growth is sub-optimal.
Phosphate fertilizer use can influence starch quality. By increasing the tuber P content, the viscosity of the gelatinized starch is also increased and the gelatinization temperature decreased. As starch is commonly used as a thickening agent in food and other products, good phosphate nutrition can be of significant benefit.
Following tuber initiation, phosphorus is an essential component for starch synthesis, transport and storage.
Under situations of high phosphorus lockup e.g. volcanic soils or low organic matter, low P, sandy soils, it is important that fertilizer-P is placed close to the tuber.
Because phosphorus is relatively immobile in the soil, banding the fertilizer usually works better than broadcasting.
While potatoes are very responsive to fresh soil phosphate, the economic optimum rate is often very difficult to define. Rates will depend on soil type and soil test results.
|Phosphorus at potato growth stages|
|Planting||More tubers, growth and dry matter|
|Before tuber initiation hook stage||More tubers, stronger growth|
|Tuber initiation||Bigger tubers|
|Bulking||Maintain tuber growth|