• The Effect of Nitrogen Fertilization Rates on Head Lettuce Yields: A Preliminary Report

      Carling, D.E.; Michaelson, G.J.; Ping, C.L. (Agricultural and Forestry Experiment Station, School of Agriculture and Land Resources Management, University of Alaska-Fairbanks, 1987-06)
      Quantities of nitrogen (N) traditionally applied to lettuce fields by commercial growers range from lows of 80 to 120 lbs N/A (commonly 800 to 1200 lbs of 8-32-16 or 10-20-20) to rates as high as 250 lbs N/A. The higher rates are attained by supplementing the principal application of N-P-K with ammonium nitrate. Fertilization response research conducted elsewhere suggests that the higher rates are well beyond quantities of N required for maximum yields; however grower experience indicates that the additional N indeed does increase head size and yields, especially in late season plantings when cooler soil temperatures may reduce N uptake. Optimal rates of N to be applied can differ depending upon application rate during the previous year and carryover of N in the soil. Questions remain as to what soil N concentration is required for optimal yield under Alaskan conditions. The field experiment reported here was conducted to assess the effects of increasing rates of N fertilization on lettuce yields and soil N concentrations. Although preliminary, these data may be helpful to growers deciding N application rates.
    • Effects of Residual Soil Nitrogen and Applied Nitrogen on Yields of Head Lettuce

      Carling, D.E.; Michaelson, G.J.; Ping, C.L.; Walworth, J.L. (Agricultural and Forestry Experiment Station, School of Agriculture and Land Resources Management, University of Alaska Fairbanks, 1990-02)
      Field studies previously conducted in the Matanuska Valley have determined that head lettuce production can be optimized by applying approximately 100 lbs per acre of nitrogen (N) as a fertilizer supplement when residual soil N levels are low (Carling et al., 1987 and 1988). However, conditions in grower's fields often are such that significant quantities of residual N fertilizer may remain in the soil from one growing season to the next. Maximizing the utilization of residual N makes sense both economically as this N has substantial value as a plant nutrient, and ecologically as N may contribute to groundwater contamination if permitted to leach from the soil profile. A field study was conducted during the 1988 growing season to examine the effects of residual soil N in combination with various levels of spring-applied N fertilizer on head lettuce yields. Residual soil N is defined as N present in the soil and detected by a soil test prior to the application of fertilizer in the spring. This study had two primary objectives: to promote maximum utilization of N through accurate interpretation of soil test results and to evaluate interactions between residual and spring-applied N. The results of the first year of this study were reported by Michaelson etal. (1989). The experiment was repeated during the 1989 growing season and the results of that study are contained in this report.