The 2011 ASHS Annual Conference

Efficient use of nitrogen (N) is important to reduce production costs, conserve natural resources, and minimize negative environmental effects of crop production. Field trials were conducted to evaluate the need for new N fertilizer rate recommendations for processing tomatoes. Tomato cultivars ‘111’ and ‘9704’ were grown at N rates from 0 to 240 lbs/acre in a replicated trial on sandy loam soil in a corn-soybean-vegetable rotation. N was supplied from urea either before transplanting, or both before and 35 days after transplanting (DAT). Seedlings were transplanted on June 11, 2010, at a density of 9,680 plants per acre, and harvested Sept. 7-10. For ‘111’ yield of red and turning fruit (yield) was significantly greater at 180 lbs/acre N than at 0 lb/acre N (26.4 vs. 22.3 tons/acre, respectively). For ‘9704’, yield was significantly greater at 90 lbs/acre N than at 180 lbs or 0 lb/acre N (24.9 vs. 18.4 and 20.6 tons/acre, respectively). Other treatments were not significantly different. Bacterial spot and high temperatures during bloom may have limited yield. Aboveground dry weight (DW) of ‘111’ showed a positive linear response to N rate at 95 DAT. DW of ‘9704’ showed a curvilinear response: increasing up to about 120 lbs/acre N and then leveling off. For both cultivars, the percentage of DW in fruit decreased from 70% to 65% as N rate increased from 0 to 240 lbs/acre. Total N uptake at 95 DAT showed a linear response to N rate for both cultivars, increasing from 85 to 138 lbs/acre as N rate increased from 0 to 180 lbs/acre. For ‘9704’, N uptake per ton of yield increased linearly from 3.87 to 7.85 lbs as N rate increased from 0 to 180 lbs/acre. For ‘111’ N uptake per ton of yield was not correlated with N rate, and ranged from 4.16 to 5.00 for 0 to 180 lbs/acre N. Leaf N concentration was greater than the published sufficiency range of 2.5–4% on all dates tested. Available soil N from 0 to 24 inches averaged 112 lbs/acre before planting and fertilization. On Oct. 13 available N to 24 inches increased from 34 to 249 lbs/acre as N rate increased from 0 to 240 lbs/acre. A post-harvest soil N test may be useful to assess whether fields have excess N and to guide future N fertilization plans. A second year of research is planned to identify repeatable results.