Nutrient Management Research Database

https://www.cdfa.ca.gov/is/ffldrs/frep/pdfs/completedprojects/03-0650Hartz2007.pdf

A survey of commercial lettuce and cauliflower fields in the Salinas and Santa Maria production regions was conducted in 2004-2005 to refine the use of soil and plant tissue testing as nutrient management tools. More than 100 fields were surveyed, with roughly equal numbers of head lettuce, romaine lettuce and cauliflower fields sampled. The specific objectives were to: 1) develop broadly applicable tissue macro- and micronutrient sufficiency ranges for lettuce and cauliflower. 2) quantify the sources of variability in tissue sampling and handling to standardize practices and improve interpretation of results. 3) document the relationship between soil nutrient availability and tissue nutrient levels In each field samples of soil and plant tissue were collected at three growth stages (early vegetative growth, midseason, and preharvest), and the status of both macro- and micronutrients was determine using established laboratory techniques. Cooperating growers provided information on fertilizer rate and commercial yield and quality for each field. Whole leaf nutrient concentrations were evaluated using the Diagnosis and Recommendation Integrated System (DRIS) approach to develop a set of nutrient sufficiency ranges for each crop and growth stage. DRIS analysis involves a mathematical comparison of leaf nutrient concentrations, and nutrient ratios, between high-yield and low-yield fields. Leaf sufficiency ranges were calculated for N, P, K, Ca, Mg, S, Zn, Fe, Mn, Cu, and B. Additionally, leaf Na, Cl and Mo concentrations were determined, and deficiency or toxicity effects evaluated. Midrib sufficiency ranges for NO3-N, PO4-P and K were also calculated using data from high-yield fields found to be ‘nutritionally balanced’, based on DRIS analysis. Head and romaine lettuce had very similar leaf nutrient concentrations, and were combined for the DRIS analysis. In comparison to existing recommendations from commonly used reference sources, the DRIS-derived leaf macronutrient sufficiency ranges were generally higher for N and lower for K. The only serious discrepancy between the DRIS midrib sufficiency ranges and existing references was for PO4-P, with the DRIS values being significantly lower. The DRIS leaf micronutrient ranges were in general agreement with existing references with the exception of Ca, which we found to be in lower concentrations in both crops than the existing references suggest is desirable. Cu was the nutrient most frequently present in concentrations below the DRIS sufficiency range, with nearly half of low-yield fields of both crops having low leaf Cu. Low leaf Cu was most common in fields with DTPA-extractable soil Cu < 2 PPM. Low leaf Mo (≤ 0.2 PPM) was also common with lettuce. Additional research to determine whether soil Cu or Mo supply actually limits commercial yield should be pursued. A negative linear correlation was found between yield and leaf concentration of Na (both crops) or Cl (cauliflower only), emphasizing the importance of irrigation water quality and adequate soil leaching in minimizing the detrimental effects of these elements on crop productivity. Leaf and midrib nutrient concentrations were similar across a range of varieties, confirming that the nutrient sufficiency ranges should be readily applicable across varieties. Neither time of day of sampling, nor post-sampling handling practices significantly affected midrib nutrient concentrations. However, midrib NO3-N was highly variable over time, sometimes changing as much as 50% over the course of just several days. This variability was in large part due to the effects of field environment. There was a strong negative, linear correlation between midrib NO3-N and reference evapotranspiration (ETo) in the two days prior to sampling; warm, high sunlight conditions apparently hastened the conversion of NO3-N to organic N compounds in the leaf. These environmental effects confounded the relationship between midrib NO3-N and concurrently measured soil NO3-N, casting serious doubt on the value of midrib testing as a fertilizer management tool. Comparison of grower fertilization practices with soil and leaf nutrient levels provided some useful insights into how fertilizer management can be improved. Seasonal N fertilization varied among fields from 27 - 392 lb/acre for lettuce, and from 116 - 459 lb/acre for cauliflower. However, there was no correlation between fertilizer rate and either yield or leaf N concentration, suggesting that over-fertilization was common. Similarly, there was no relationship between P fertilization rate and soil test P level. Indeed, many of the cooperating growers simply fertilized on a ‘recipe’ basis, with all fields of a given crop receiving the same fertilizer, regardless of soil characteristics or soil test levels. While the net effect of this approach to fertilization was wasteful application of N and P, there was evidence that ‘recipe’ fertilization resulted in inadequate K fertilization in a number of fields.

• This study surveyed over 100 fields to develop sufficiency ranges for N, P, K, Ca, Mg, S, Zn, Fe, Mn, Cu, and B. The sufficiency ranges are included with the report.
• Sources of potential variability were identified in order to standardize practices and ensure accurate interpretation of results.
• The relationship between plant tissue nutrient levels and soil nutrient availability was investigated.