Micronutrient deficiencies are rarely observed in New England soils, especially on soils that have a history of compost or manure applications. For this reason little research has been completed calibrating soil tests for micronutrients, and there are no reliable soil test calibration data to interpret soil micronutrient levels and make recommendations for amounts of micronutrients to apply. Most New England labs offer micronutrient soil testing and present results relative to values typically observed in soils analyzed in their laboratory for comparison.
Calibration data for plant tissue analysis are also limited. When a grower suspects a micronutrient deficiency, the recommended procedure is to collect soil and plant tissue samples from areas in the field with good and poor plant growth, and have the samples analyzed using standard methods. A relative comparison of the concentrations of micronutrient in the soil and plant tissue samples will usually allow a diagnosis to be made. Foliar applications of micronutrients may alleviate nutrient deficiencies observed during the season. However, applications of micronutrients to the soil are the better long-term approach to address the rare occurrence of micronutrient deficiencies.
Micronutrient deficiencies are most likely to occur in sandy soils with low organic matter. High soil pH may also bring about micronutrient deficiencies, especially in sandy soils. It may be necessary to maintain pH between 6 and 6.5 to avoid problems in coarse-textured soils with low organic matter. Of all the micronutrients, boron (B) is most likely to be needed in New England to supplement soil levels for vegetable production. Cauliflower, broccoli, cabbage and beets are most susceptible to “hollow heart” caused by boron deficiency. Boron, copper, zinc and molybdenum have small ranges for optimum soil test values, which means the difference between deficient levels and toxic levels in the soil are small. Be careful with applications of these nutrients to avoid toxic quantities. Some vegetable crops are particularly sensitive to high levels of boron. Sensitive crops should not be planted on fields following crops that have received boron application. Table 3 lists crops according to their sensitivity to boron.
Table 3: Relative Tolerance of Vegetables to Boron
Adapted from L.V. Wilcox, Determining the quality of irrigation water, USDA Agricultural Information Bulletin 197 (1958) and information from Robert Becker, Cornell University.