2018 ASHS Annual Conference

Phosphorus is relatively immobile in soil under moderate soil pH. As a result of long-term P applications in potato production area, the soils are high in P on average of 351 mg/kg Mehlich-3 P (range 81 to 599). This average P level is almost 8 times greater than the UF/IFAS recommendation for zero P application. However, potato growers keep applying 112 kg/ha every growing season because they can have 5% to 10% tuber yield response which is just their profit margins. To help growers optimize their phosphate management, on-farm trials with six P levels (0, 45, 90, 135, 179, and 224 kg/ha P2O5) were conducted at HAEC, Hastings, FL from 2015 thru 2017. Plot size was 49.55 square meters (12.2 m × 4.1 m). Randomized Complete Block Design was used with four replicates. Potato cultivar was ‘Atlantic’. The results showed that zero P application had significantly lower tuber yield than 45 kg/ha P application. The yield difference was 7% or 17%. The soil pH was as low as 4.8 in the growing season. The soil had 563 kg/ha aluminum and 131 kg/ha iron. The P in soil was tied up with active aluminum and iron. Phosphate fractionation showed that approximately two thirds of P were locked out by the metal ions. The data show that 45 kg/ha P is sufficient for potato production in the Hastings area in Florida.