Responses of Field-grown Tomatoes to Nitrogen Sources

Abstract

Although the effect of various N fertilizers on tomato yield and quality has been previously examined, much of this research was conducted in hydroponic or green-house studies. The objective of this research was to examine the effect of N fertilizer sources (ammonium nitrate (NH4NO3), potassium nitrate (KNO3), urea (CO(NH2)2), urea ammonium nitrate (UAN), and calcium nitrate (Ca(NO3)2) on tomato (Lycopersicon esculentum Mill.) growth, yield, and fruit quality. The 2-year experiment was conducted using black plastic mulch covered raised beds with drip fertigation. A total of 180 lb acre (202 Kg·ha−1) N was applied with each N source, with 25% applied preplant and premulch and remaining N applied as 10 weekly applications of 13.5 lb/acre (15.2 kg·ha−1). If an N source contained Ca or K, that amount was applied to all other N sources (preplant and fertigated) as potassium chloride (KCl) or calcium chloride (CaCl2). Collected data included plant height, leaf N concentration, and yield. Different N sources had varying and inconsistent effects on fruit yield and quality. Although plant height and stem diameter from UAN treatments were always smaller than those from other N sources, this effect did not extrapolate to decreased total marketable yield. Differences in N concentration of tomato leaf tissue were not consistent with N source and were not related to differences in tomato yield. There were few differences in yield and quality of nonmarketable fruit due to N source. In this one-site, 2-year study, it appears that any of the N sources studied would be suitable for tomato production, if price of N fertilizer materials are the same.