Response of Grafted Tomato to Nitrogen

Grafting tomatoes (Solanum lycopersicum) onto disease resistant rootstocks is a proven method for managing numerous soil-borne diseases. Recent studies have demonstrated the ability for rootstocks to enhance scion vigor in the form of increased vegetative growth and yield. One theory explaining this increased vigor is that these vigorous rootstocks can more efficiently uptake nitrogen. To investigate this theory, a two-year study was conducted at the Sandhills Research Station in Jackson Springs, NC, to determine how open-field grown grafted tomatoes respond to different levels of nitrogen fertilizer. The tomato cultivar ‘Tibute’ was utilized as the non-grafted control and scion for two commercially available rootstocks (‘Maxifort’ and ‘RST-106’). Five nitrogen rates (0, 50, 100, 150, and 200 lbs/acre) were imposed on the non-grafted and grafted treatments through drip irrigation under a traditional plasticulture system. Plant height data was collected weekly for seven weeks in both 2013 and 2014. Mature fruit at the breaker stage was harvested for three and five weeks in 2013 and 2014, respectively.  Fruit were graded by size as regular (between 1-28/32” and 2-28/32”), jumbo (> 2-28/32”), and culls (< 1-28/32” or damaged due to pest or disease). No significant variety × fertilizer treatment was observed in plant height or yield data. The main effect of variety was significant on yield in both years. Plants grafted on ‘Maxifort’ rootstocks yielded 15% and 30% more marketable fruit than non-grafted treatments in 2013 and 2014, respectively. No significant difference was observed in marketable yield between plants grafted onto ‘RST-106’ rootstocks and non-grafted plants in 2013. However, in 2014 marketable yield was significantly higher (23% more) in ‘RST-106’-grafted plants compared to the non-grafted controls. Our results suggest, depending on rootstock variety, grafting may significantly increase marketable yields for open-field grown tomatoes in North Carolina under conditions lacking severe soil-borne disease pressure