Response of Controlled Water Table Level and N-Fertilizer Rates on Yield of Potato.

Subirrigation used to irrigate potato in NE Florida requires significant water withdrawals from the aquifer to maintain a high watertable to irrigate the crop. High watertable level facilitates offsite movement of soluble nutrients and runoff. The objective of this study was to determine yield and fertilizer use efficiency of potato in response to N-fertilizer rates under three water table levels. Field experiments were conducted in Hastings, FL in 2014. The experimental design was a randomized complete block, evaluating N-rates at 0, 112, 224, 336 kg/ha with potato variety (‘Atlantic’ and ‘FL1867’) as the split plot factor. Each treatment was replicated three times in each of three adjacent potato fields, for a total of nine replications. Each field utilized subirrigation to maintain a different water table height, targeting averaging 40, 55, and 75 cm below the top of the raised potato row and the resulting average in season water table level was used as a covariate factor for each replicate. The effects of N-rate, potato variety and water table level on available on potato yield were quantified. There was an interaction between N-rates and watertable levels for marketable yield. Yield ranged from 4.2 to 38.0 Mg/ha with treatments receiving 336 kg/ha N having the highest yield for both varieties (p<0.001). There were no differences in yield when N rate ranged from 112 to 336 kg/hawhen a high water table level was maintained for variety ‘Atlantic’, while significant differences in N rates were observed for lower watertable level treatments. For potato receiving 336 kg/ha N, as water table level decreased marketable yields of ‘Atlantic’ and ‘FL1867’  increased by 28% and 8% respectively, however within N-rates below 224 kg/ha a similar response to water table level was not observed. The results of this study support the importance of considering water table management alongside N-fertilizer application rate to achieve optimum potato yield in NE Florida.