PHOSPHORUS FERTILIZER TIMING FOR RUSSET BURBANK POTATO GROWN IN CALCAREOUS SOIL

Potato (Solanum tuberosum L.) has surface roots with enhanced activity upon canopy closure that should allow application of phosphorus (P) via fertigation. Fertilizer trials were conducted in 2005–2006 with four pre-plant broadcast (0, 112, 224, or 336 kg P2O5 ha−1) and two split applied in-season fertigation (0 or 56 kg P2O5 ha−1) rates. Total and undersized tuber yield had a quadratic relationship with pre-plant P, increasing and then declining as pre-plant P fertilizer rate increased, with predicted yield peaks at 246 and 167 kg P2O5 ha−1, respectively. Marketable and US No. 1 yields increased linearly with increasing pre-plant P fertilizer rate. A trend for an increase in total yield as a function of in-season P fertilization was also measured. The P rate for maximum yield did not decline with in-season application, suggesting that this practice does not enhance P fertilizer use efficiency.