Hydro Potato Workshop March/April 2003 into potatoes” “Putting the

USA Work Independent research has produced this information but what is it showing us?

Something is significantly affecting tuber yield of potatoes, but what is it?

P 2 O 5 tato crops which stay phosphate rich longer produce higher yields

Tuber yield is increased by 0.6 t/ha for every extra day during which tissue phosphorus is maintained above 0.22%

Petiole phosphorus levels decline naturally as the season progresses What can be done to delay arrival at the critical P=0.22% threshold?

Rate of Petiole P decline (Phosyn Holland 1998/99) Confirmation of Westermann’s work. Slow rates of P decline are associated with higher yields

Delaying the P decline? Apply a product solution Develop a pro-active analysis system to identify the problems early

Apply more phosphorus fertilizer Potato soils are rarely deficient in phosphorus, in fact the opposite is more often the case. So will applying more phosphorus to the soil make any difference? Probably not. Plants have difficulty taking up phosphorus from the soil even when soil levels are satisfactory

Phosphorus uptake from the soil requires a well developed root system Plants only absorb phosphate from very close (less than 1mm) to the root surface (plants must “forage” for P)

A drop in soil temperature from 21 to 13 o C reduces phosphorus availability by almost 70% Cold soils reduce phosphorus availability

Use foliar applications of phosphorus Although it is considered a macro- nutrient the annual requirements are relatively small Phosphorus is readily taken up and translocated by leaves Foliar application overcomes any soil or environmental conditions which may limit uptake from the soil

Foliar phosphorus applications Foliar sprays throughout tuber bulking can help delay the natural decline in petiole phosphate and increase yield potential. Use Hydrophos (29% P 2 O 5, 4% Mg, 5%K 2 O) throughout tuber bulking.

Delaying the P decline? Apply a product solution Develop a pro-active analysis system to identify the problems early

Development of the Phosyn guideline systems Green guidelines are the Idaho program

Phosyn guideline systems Red guideline becomes a more proactive system allowing earlier, less frequent sampling

Delaying the P decline will increase yields Apply Hydrophos to supplement soil applications Use MEGALAB.net analysis to identify phosphorus problems pro-actively Thanks for your attention