Effects of Different Fertilizer Doses and Variations in Grafted and Ungrafted Tomato Plants on Yield, Plant Nutrition, and Soil Properties

Optimization of nitrogen (N), phosphorus (P), and potassium (K) fertilization is important for tomato yield, nutrition status, and sustainable soil fertility. The use of grafted tomato seedlings has become quite widespread in greenhouse cultivation. Since tomato grafting changes the nutrient requirements, it is necessary to determine the appropriate amounts of fertilizer to apply. For this purpose, three different chemical fertilizer doses (F1: 50% less than the recommended NPK, F2: the recommended NPK, and F3: 50% more than the recommended NPK) were applied to two scions (P1: Anıt, P2: Bestona) and four rootstock scion combinations (P3: Anıt/Vividfort, P4: Anıt/Beaufort, P5: Bestona/Vividfort, P6: Bestona/Beaufort). After the 16-week growing period, soil electrical conductivity (EC), total nitrogen (TN), available phosphorus (av-P), exchangeable potassium (ex-K), calcium (ex-Ca), and magnesium (ex-Mg) concentrations increased with increasing NPK dose, whereas soil available iron (av-Fe) and copper (av-Cu) concentrations were not affected. Soil reaction (pH), av-P, zinc (av-Zn), and manganese (av-Mn) concentrations were altered by tomato rootstock/scion combinations. Fruit yield was not affected by grafting but increased with fertilization, particularly at the F2 and F3 doses. Grafting consistently increased leaf N concentration relative to ungrafted plants. Increases in leaf P, Mg, Fe, Mn, and Cu were not uniform across all graft combinations but were most pronounced in the Bestona/Vividfort combination, indicating that these nutritional benefits were largely rootstock/scion-specific rather than a general grafting effect. Grafting might be a useful tool for increasing plant nutrition status, but did not translate into a significant yield benefit during the 16-week growing period. F2 (3.52 kg plant−1) and F3 (3.44 kg plant−1) doses produced comparable yields while F3 markedly reduced partial factor productivity and increased soil EC. Results indicated that the recommended NPK dose (F2) remained appropriate for tomato production regardless of graft status, and did not need to be modified.