A Comparison of Controlled-release and Certain Soluble N Fertilizers on Yield and Maturity in Spring-grown Head Lettuce

Comparisons were made between urea, NH 4 NO 3 , (NH 4 ) 2 SO 4 and several controlled-release N (CRN) fertilizers on spring-grown lettuce ( Lactuca sativa L.). In 1980 and 1981, single applications of CRN fertilizers produced high yields of excellent quality lettuce. In 1980, the largest yield with the most 2-dozen and fewest 2½-dozen size heads (24 and 30 heads/carton, respectively) came from lettuce receiving methylene urea (MU) F2950 at 168 kg N/ha preplant plus 84 kg N/ha as urea at folding stage. However, the yields from lettuce fertilized with this combination were not significantly different from those of lettuce fertilized with a single application of sulfur-coated urea (SCU) F9999 at either 252 kg N/ha preplant or 168 kg N/ha at thinning stage. Lettuce fertilized with urea applied at 168 kg N/ha preplant produced relatively low yields. Lettuce fertilized with urea at 168 kg N/ha in 3 applications of 56 kg N/ha each produced significantly higher yields than when the crop received urea at 168 kg N/ha preplant, but the extra applications were costly and time consuming. In 1981, lettuce fertilized with CRN sources at 224 kg N/ha preplant was earlier maturing than when fertilized with any common soluble N material at the same rate. The data show that CRN fertilizers could be helpful in reducing fertilizer application costs and keeping crop production profitable.