Effect of Fertilizer Source and Grafting on Quality of High Tunnel-grown Tomato

Tomato is a major vegetable crop world-wide, and is grown in high tunnels in most regions. This study compared two fertilizer sources and the use of grafted plants on the quality of tomato fruit grown in high tunnels in northwest Washington in 2015. The two fertilizer sources were commercial conventional fertilizer [monoammonium phosphate (11-52-0), potassium sulfate (0-0-50), and urea (46-0-0)] applied at 112 N, 168 P₂O₅, and 56 K₂O kg^.ha^-1, and an integrated fertility treatment [poultry manure (2242 kg^.ha^-1) plus 90 kg^.ha^-1 urea (46-0-0)] where poultry manure application was limited by P content. The experimental design was a split plot where the main plot treatment was fertilizer and the subplot treatment was grafting: ‘Panzer’ grafted on ‘Estamino’, Maxifort’, ‘DRO138TX’, and non-grafted ‘Panzer’ (control). Fruit were harvested once a week, when fruit reached the 75% red stage, and the quality of marketable fruit were evaluated for juice content, fruit firmness, soluble solid content (SSC), pH and titratable acidity. There were no significant differences due to fertilizer source on any of fruit quality parameters measured in this study. Overall mean juice content was 93.4% for both the commercial fertilizer and the integrated fertility treatments. Overall mean firmness of tomato fruit was 2.5 N for commercial fertilizer and 2.4 N for the integrated fertility treatment. Overall mean SSC (^oBrix) of tomato fruit was 5.1, and overall mean pH was 4.3 for both fertilizer treatments, while overall mean titratable acidity (% CA eq.) was 0.36 and 0.33 for the commercial and integrated fertilizer treatments, respectively. On the other hand, fruit from grafted plants had higher juice content than non-grafted plants on 10 and 17 Aug. (93.6% and 93.2% overall average, respectively). Additionally, fruit from plants grafted with ‘Estamino’ rootstock had a higher pH on 10 Aug. than other grafting treatments (4.4 and 4.3, respectively). There were no differences in fruit firmness, SSC, or titratable acidity due to grafting.