Nutrient Management Research Database

A survey of 78 commercial iceberg and romaine lettuce (Lactuca sativa L.) fields
in the coastal valleys of central California was conducted in 2004–2005. Whole leaf
samples were collected at early heading and again within 1 week of harvest. Diagnosis
and Recommendation Integrated System (DRIS) leaf concentration norms were calculated
for N, P, K, Ca, Mg, S, B, Zn, Mn, Fe, and Cu. Iceberg and romaine lettuce had
sufficiently similar leaf nutrient concentrations that the data were combined in the DRIS
calculations. Optimum leaf nutrient ranges were developed using data from high-yield
fields in which all nutrients were in balance according to the DRIS approach. The DRIS derived optimum ranges for K and Ca were substantially lower than previously
published leaf sufficiency ranges, whereas for the other nutrients, the DRIS optimum
ranges were in close agreement. Cu was the nutrient most frequently below the optimum
range in low-yield fields. Comparison of leaf nutrient concentrations with soil nutrient
availability and grower fertilization practices suggested that significant improvement in
fertilizer management was possible.

• Study took place in 2004 and 2005 on 35 commercial fields of iceberg and 43 fields of romaine lettuce
• Composite soil samples of the top 30cm were collected in each field at the start of the season and assessed for soil pH, organic matter content, texture, soil P availability, soil-exchangeable K, Ca, and Mg, extractable Zn, Mn, Fe, and Cu. 
• Whole leaf samples were collected at the early heading stage and within 1 week of harvest and assessed for total leaf N, K, Zn, Mn, Fe, Cu, P, S, Ca, Mg, an B concentrations
• Growers reported seasonal fertilization rates and commercial yield for each field, as well as crop quality and noted fields where economic conditions, disease or insect damage reflected yield.
• Fields were divided into high yielding (2220 cartons/ha for iceberg and 2470 cartons/ha for romaine) and low yielding (1970 cartons/ha for iceberg and 2220 cartons/ha for romaine) fields and data from fields of intermediate yield or fields where non-nutrient related factors affected yields were eliminated.
• Industry average mass per carton is 22 and 17 kg for iceberg and romaine lettuce, respectively.
• Diagnosis and Recommendation Integrated System (DRIS, an evaluation of nutrient balance in a plant that uses relationships between pairs of nutrients to rank nutrient levels from deficient to excessive) analysis was performed on the combined iceberg and romaine data for each growth stage

• Fertilizer applications averaged 184, 19 and 26 kg/ha N, P and K, respectively.
• There were 29 high-yield and 25 low-yield fields.
• All nutrients were in balance in 12 and 13 high-yield fields at early heading and preharvest stages, respectively
• Resulting optimum ranges for K and Ca were substantially lower than previously published leaf sufficiency ranges.
• Cu appeared to be the most commonly limiting nutrient.
• Results indicate that an overall reduction in N application and increased use of soil testing to help adjust P and K fertilization could be warranted.

study took place in the coastal valleys of central CA with iceberg and romaine lettuce varieties