Petiole Sap Nitrate Sufficiency Values for Fresh Market Tomato Production*

Two tomato (Lycopersicon esculentum Mill.) cultivars, Mtn. Spring and Jet Star, were grown on black polyethylene-mulched beds of a loam soil with an organic matter content of 2.4% for two seasons, 1996 and 1997, to evaluate preplant N rate effects on fruit yield and leaf blade total nitrogen (N) and petiole sap NO3-N concentration. Four rates of N fertilizer (0 to 136 kg ha−1), as urea, were rotovated into the bed prior to laying the plastic mulch. Samples of the most recently matured leaves were taken every two weeks for N and NO3-N content. Fruit yield and quality were associated with early season, 4 and 6 week, petiole sap NO3-N concentration. Mtn. Spring required 1050 ppm sap NO3-N compared with 900 ppm for the Jet Star cultivar. In 1996, Mtn. Spring achieved maximum yield at 31 kg N ha−1 whereas Jet Star required 67 kg N ha−1. Maximum yield occurred at 67 kg N ha−1 for both cultivars in 1997. Nitrogen rates above the optimum decreased early yields in 1996, but not in 1997. Soil N mineralization data showed > 112 kg N ha−1 by mid-July in the top 30 cm of the soil profile. On the prairie soils of the upper Midwest soil N management should be similar for both determinate and indeterminate fresh market tomatoes.