Effect of Fertilizer Source and Grafting on Tomato Growth, Leaf Nitrogen, and Fruit Yield in High Tunnels

This study investigates fertilizer source and the use of grafted plants for season extension and fruit yield of tomato grown in high tunnels in northwest Washington in 2015. An integrated fertilizer [poultry manure (2242 kg^.ha^-1) plus 90 kg^.ha^-1 urea (46-0-0)] was compared with commercial chemical 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 plant growth and fruit yield were measured. Additionally, grafting was tested to see if it affects leaf petiole nitrogen, early marketable yield, and season extension. Grafting treatments were ‘Panzer’ tomato grafted on ‘Estamino’, ‘Maxifort’, ‘DRO138TX’, and non-grafted ‘Panzer’ (control). Plant height and number of leaves were measured at transplanting and every 3 weeks thereafter. Height was greater for plants grown with commercial fertilizer than with integrated fertility on 21 May and 11 June, but there was no effect due to grafting with the three rootstocks. Plants grown with commercial fertilizer had more leaves than plants grown with integrated fertility on 30 Apr., 21 May and 11 June, but there was no difference among the three rootstocks. Plants were pruned once per week from 30 Apr. to 24 Aug., and pruning biomass was greater with commercial fertilizer than for the integrated fertility treatment early in the season (4 and 11 June), and due to rootstocks later in the season (21 July, 10 and 24 Aug.). Nitrate-N was measured in both leaf tissue and fresh petiole sap of fifth or sixth youngest fully mature leaf (from the plant top) at 5, 7, 9 and 11 weeks after transplanting. There was no effect of fertilizer source on nitrate-N of either leaf tissue or fresh petiole sap; however, plants grafted on ‘Estamino’ had significantly more nitrate-N in fresh petiole sap on 1 June. Fruit were harvested once a week at 75% red stage, and harvest did not occur significantly earlier or later in the high tunnel due to the use of grafted plants. Marketable fruit number was greater for non-grafted plants on 21 Jul, for plants grafted with ‘Estamino’ on 14 Sep, and with the integrated fertility treatment on 28 Sep. Total mean marketable fruit weight was 6.3 kg per plant and did not differ due to fertilizer source or rootstock. Fertility management with 100% mineral fertilizer or an integrated fertility treatment can have equal fruit yield, and grafting did not affect harvest window or yield.