A 2-year field experiment was carried out in Central Italy on processing tomato (Lycopersicon esculentum Mill., cv. PS1296) to assess the effect of fertigation–irrigation frequency on crop N uptake and yield. The crop was grown with three N-fertiliser rates (0, 100 and 300kgNha−1: N0, N100 and N300, respectively) applied at three different fertigation–irrigation weekly schedules: one fertigation (F1) for the fertilised treatments, or one irrigation (I1) for the unfertilised control; three fertigations (F3) for the fertilised treatments, or three irrigations (I3) for the unfertilised control; one fertigation+two irrigations (F1+I2) for the fertilised treatments. The N rates and fertigation–irrigation schedules were combined to realise a total of eight treatments: N0I1, N0I3, N100F1, N100F3, N100F1+I2, N300F1, N300F3, and N300F1+I2 (Table 1). All treatments received the same weekly water volume based on crop ETc estimated by the Penman–Monteith equation. We performed fortnightly measurements of crop growth and N accumulation, weekly measurements of NO3-N concentration in soil solution taken from suction lysimeters at depth of 0.6m, and a post-harvest measurement of soil mineral N content. At the highest N rate, a high frequency of fertigation and/or irrigation increased the uptake of fertiliser-N, guaranteed optimal crop N nutritional status even in the early stages and promoted crop growth but did not significantly affect fruit yield. Compared to fertigation frequency, irrigation frequency seems to be the main factor affecting N recovery at high fertiliser-N rate. Thus, high fertigation and/or irrigation frequency may represent a strategy to increase N uptake efficiency in processing tomato fed with very high N and water supply, which is often the case in intensive processing tomato production.
