Tuberization and yield of sweet potato as affected by planting date in a subtropical climate

The objective of this study was to assess the effect of planting dates on tuber initiation (TI) and yield of sweet potato in a subtropical climate. A field experiment was carried out at Santa Maria, RS, Brazil, with four planting dates (08/25/2011; 11/21/2011; 01/03/2012 and 02/13/2012), to obtain plants growing in different environmental conditions, especially temperature and photoperiod. The variety Princesa was planted at a density of 25.000 plants ha(-1). The experiment was a complete randomized block design with four replications. Two weeks after planting four plants were collected every two days for determining the TI. Harvesting of all planting dates took place at 05/15/2012. The duration of phases between planting to tuber initiation (PL-TI) and tuber initiation to harvest (TI-HA) was expressed in calendar days and thermal time (degrees C day). The conditions of temperature and photoperiod modified PL-TI duration in each planting date, indicating that short photoperiods and higher temperatures accelerate TI. The potato yield was higher when planting was done in late winter (08/25/2011) due to increased TI-HA duration, which coincided with periods of high solar radiation and temperatures favorable to the growth and development of sweet potato.