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Abstract
Traditionally, in the southeastern United States, new peach orchards do not receive supplemental irrigation until three or four years after field planting. Thus, the only source of water comes from rainfall. However, droughts are becoming more common in the region, making supplemental irrigation more important. Fertilizer recommendations for peaches in the southeastern United States were likely created decades ago and may not reflect the peach trees’ requirements under modern cultivation practices. The objectives of this research were to investigate the effects of irrigated vs. non-irrigated trees, drip- vs. micro-sprinkler-irrigated trees, and four different fertilizer levels (25%, 50%, 100%, and 200%; with 100% = current fertilizer recommendations) on young ‘Julyprince’ trees grafted onto ‘Guardian™’ rootstock. In 2016, below average rainfall (severe drought) was recorded throughout the year. Drought negatively affected non-irrigated trees, reducing canopy volume (56%), trunk cross-sectional area (39%), photosynthetic activity (40%), and leaf and stem water potential (39%) when compared to irrigated trees. Further, non-irrigated trees had increased expression of genes related to ABA biosynthesis (ChlH and PpCYP707A3), osmoregulation (SIP1 and P5SC), and reactive oxygen species scavenger (POD); and decreased relative expression of genes related to dehydration and aquaporins (PpDhn3 and Pp-δTIP1). In 2017 and 2018, drought stress was not observed. However, the negative effects in tree growth and physiological responses of the 2016 season carried over to 2017 and 2018. Irrigated trees had 23% greater fruit yield than non-irrigated trees in 2017. Treatment effects on fruit quality were minimal and without representative trends across years. Differences between irrigation systems were not consistent; however, drip is more efficient than micro-sprinkler irrigation, with ~38% of water savings. Different fertilizer levels had no major effects on young trees’ growth and yield, fruit quality, nitrogen partitioning, and relative gene expression. Overall, irrigation since planting increased tree growth and commercial yield, especially under drought conditions. Similarly, reductions in fertilizer recommendations can be made without negative effects to plants, but with large potential economic savings.