Complete Identification of Crop Nutrient Deficiencies

• Micronutrients are of increasing focus to maximize genetic potential.
• Complete identification of nutrient deficiency symptoms often requires both tissue and soil sampling.
• Nutrient deficiencies can be caused by the growing environment, soil pH, true soil deficiency or root damage.
• The first step to a reliable tissue diagnosis of nutrient deficiencies is getting a good representative sample of affected and unaffected plants and timely transportation to a lab.
• Severe soil deficiencies are best and most economically corrected using dry sources of soil applied nutrients.

Thanks to higher yielding hybrids and cultivars, farmers are increasingly interested maximizing the crop's genetic potential, including addressing micronutrient deficiencies. As with macro nutrients, increasing crop yields generally lead to greater micronutrient removal rates in grain and other harvested products. Other agronomic factors are valid reasons to explore if a micronutrient is limiting crop yield.

• Soil erosion and long-term cropping may have resulted in the removal of micronutrients from soils.
• Widespread replacement of micronutrient-rich manures with mineral fertilizers has reduced micronutrient addition from fertilizer sources.
• Soils may be poor in organic matter.

While global soil fertility studies[i],[ii] indicate micronutrient deficiency is widespread in major crop production areas, growers should take field-by-field assessments to determine the necessity of micronutrient application.

Complete identification of crop nutrient deficiencies requires time, patience and attention to detail. Symptoms of nutrient deficiencies, outside of the major crop nutrients of N, P and K, can often resemble one another, as shown in Image 1 below. And to further complicate, symptoms of major crop nutrient deficiencies can be confused with those caused by non-nutrient factors such as environment, chemical injury, infectious diseases and more. Accurate nutrient deficiency diagnosis becomes even more difficult when multiple deficiencies overlap and they share common symptoms - such is the case with zinc and magnesium.

Complete deficiency diagnosis should include plant tissue samples paired with soil samples taken from the same areas. Failure to take soil samples when doing tissue sampling only provides half the necessary information needed to diagnose why the deficiency occurred. Soil pH, compaction, root damage, lack of soil moisture and low soil test levels can individually or in combination affect nutrient amount, availability, and accessibility.

Attention to field details and the condition of the samples received by the laboratory will determine the reliability and usefulness of the results. Poor sample collection, preservation, packaging or shipping will skew the end results. When collecting samples, follow the list below to obtain reliable results:

• Sample both affected and unaffected areas of the field.
• One sample should be taken for each 20 acres of affected area and paired with a sample of an unaffected area nearby.
• Affected and unaffected paired samples should be collected from areas with similar soil textures and elevation.
• Sampled areas should have the same hybrid.
• Avoid damaged or excessively dirty plant tissues. Plant tissue contains very small amounts of nutrients while soil contains much higher quantities.
• Package samples in breathable paper packages to prevent spoilage during shipping.
• Avoid leaving samples in a hot environment prior to shipping.
• Ship samples during business days early in the week.
• Interpret results using Land Grant University guidelines for the State where the lab doing your analysis is located and matching the part of the plant sampled.

Complete correction of severe nutrient deficiencies caused by low soil test levels or pH imbalances can be difficult in-season. Severe deficiencies may require several foliar applications and even then, not completely solve the problem due to the low amounts of such nutrients found in commercial products. Low soil test results are best treated using broadcast or banded dry fertilizer products because they provide higher contents of crop nutrients compared to foliar products.

Soil pH nutrient deficiencies are fairly common. Most mineral based soils contain more than enough micronutrients to supply to the crop across a range of yields (Table 1). One notable micronutrient of exception to this statement is boron. Naturally occurring soil boron comes from ancient ocean deposits that occur in western states. Soil pH outside the range of maximum nutrient availability can often be the culprit of nutrient deficiencies (Table 2). Nutrient availability for a corn-soybean rotation is best when soil pH is maintained between 6.0-6.5, while nitrogen fixation is best when alfalfa is in the rotation at a pH of 6.8. Correcting low pH issues involves lime application if pH is below 6 or banding of the deficient crop nutrient(s) to prevent nutrient tie-up by the soil. In the case of too high of a pH (typically ≥ 7.0), nutrient band application is the only economical solution to prevent unavailability.

Controlled strips trials are recommended to further confirm factors that indicate deficiencies and will give you data of the economic yield responses. Trials are particularly useful since sensitivity to a particular element varies by crop, and a crop's response to micronutrients are affected by soil characteristics, such as soil pH, organic matter, soil texture, and soil P level.

Your local Southern States Cooperative crop specialist can help with complete diagnosis of crop growth irregularities. They are well trained in plant tissue sampling and skilled in diagnosing crop nutrient deficiencies with access to the NutriCrop RX tool to help track the specific deficiencies in your fields. Through the MiField Applied Research program, your Southern States Cooperative crop specialist can help you evaluate micronutrient applications by structuring and implementing an on-farm trial in suspect fields. Southern States Cooperatives offers a number of micronutrient formulations for your crop and fields' needs.

[i] Monreal, C.M.; DeRosa, M.; Mallubhotla, S.C.; Bindraban, P.S.; Dimkpa, C. Nanotechnologies for increasing the crop use efficiency of fertilizer-micronutrients. Biol. Fertil. Soils 2016, 52, 423–437.

[ii] Oliver, M.A.; Gregory, P. Soil, food security and human health: A review. Eur. J. Soil Sci. 2015, 66, 257–276.