Water and nutrient management are essential to achieve high yield and desirable quality attributes in processing tomato (Lycopersicon esculentum Mill.). A 4‐yr field study (2006–2009) was conducted to assess effects of contrasting water management (drip‐irrigation vs. nonirrigation), fertilizer P (0, 30, 60, and 90 kg P ha−1), and K (0, 200, 400, and 600 kg K ha−1) on yields and quality of processing tomato when the optimum N rate of 270 kg N ha−1 was applied. Compared with nonirrigation, drip irrigation increased marketable fruit yield by 127%, total fruit yield by 66%, and fruit size by 32%, while it decreased soluble solids content (SSC) by 19% and lycopene content by 8%, with no effects on dry biomass of stems and leaves (DBSL). Phosphorus addition had no effects on marketable yield and SSC, but increased the DBSL and lycopene content to maximum values at 60 kg P ha−1. Fertilize K rate affected all examined variables but the lycopene content. Increasing K rates from 0 to 200 kg K ha−1 increased marketable fruit yield by 10% and total fruit yield by 9%, but fruit size declined by 3%. Increasing K rates from 200 to 600 kg K ha−1, however, had no effects on yield and fruit size. Fertilizer K rate had no effects on SSC with nonirrigation, but resulted in a linear increase in SSC with drip‐irrigation. The results suggested that, with optimum N supply, K application is required to increase fruit yield and quality of drip irrigated processing tomato.