Throughout the growing season, crops may exhibit unusual coloring, stunted growth and leaf damage or defoliation. Often these visual symptoms are due to nutrient deficiencies, which reduce yields, crop quality and ultimately producer profitability. By recognizing visual symptoms during the growing season and pinpointing production issues before harvest, growers can make plans for post-harvest steps that will help prevent similar issues with subsequent crops.
“Nutrient deficiency symptoms can be anything from leaf yellowing and leaf loss to twisted ears with irregular kernel rows and imperfectly developed ear tips. Even stalk lodging can be a symptom of nutrient deficiency,” explains Matias Ruffo with The Mosaic Co.
In previous years such as 2010 and 2011, yellow or purple corn in the spring was often blamed on cool, wet soils. Generally, growers could wait for warmer temperatures for the crop to recover.
“2012 has given most of the Corn Belt an unusually warm and dry spring,” says Ruffo. “That may mean less discolored corn, and may also present a better opportunity to visually scout for areas of nutrient deficiency. If corn is discolored this year, chances are it’s something other than the weather.”
Ruffo says the flipside of the benefits of a warm spring can be overconfidence. It would be tempting to look at green, apparently healthy, corn this year and automatically assume no nutrient deficiencies exist. But that assumption could prove costly in lost yield this season and in the future. Once a deficiency symptom appears, some yield, and perhaps quality, may have already been lost.
Nutrient deficiencies are widespread and scattered across the Corn Belt. In 2011, soil testing results from A&L Great Lakes Laboratories showed the most common secondary and micronutrient deficiencies were sulfur (S) and zinc (Zn), with most Midwestern states showing a high percentage of low soil test ratings for both nutrients. (Results may be viewed here under customer tools, soil test summaries.)
“Your soil test may indicate adequate N, P and K, but a deficiency of S or Zn can reduce corn’s ability to take up and utilize those nutrients,” says Ruffo. “Leaf tissue testing might even show high concentrations of P, but inadequate S or Zn could be inhibiting the corn plant’s ability to use P to produce yield potential.”
Nutrients all impact one another in the plant, which is why balanced fertility of all nutrients is so important. And why Mosaic has developed fertilizer products such as MicroEssentials SZ, in which S and Zn are added in partial layers around phosphorus-based fertilizer particles. The result is uniform, nutritionally balanced fertilizer granules, each with essential nutrients combined in precisely the correct ratio for plant health.
Trust The Test
Don’t try to outsmart the soil test. Gyles Randall, professor of soil science at the University of Minnesota, has noted that low soil test P can be particularly costly to yield when growers try to mine the soil for short-term input cost savings. Nevertheless, some growers will try to save input costs.
“There have been efforts to use leaf tissue analysis to determine a corn crop’s nutrient needs,” says Randall, “but tissue testing is a complicated method with shortcomings, so should not be used as a sole indicator of determining the amount of soil nutrients necessary compared to soil testing.”
The nutrient content of a corn leaf is highly dependent on when the leaf sample was taken — the smaller the plant, the higher the concentration. Additionally, plant growth phase and timing of fertilizer application will affect the leaf tissue results.
Randall says plants initially may not show obvious symptoms of deficiency other than slower growth. But even a mild deficiency or fertility imbalance can disrupt essential plant metabolic processes. Since deficiencies rarely occur uniformly across an entire field, crops may mature unevenly, leading to less yield, harvesting difficulties and lower quality of the harvested product.
Randall’s research has shown significant yield benefits from adding more P (25 to 50 pounds per acre) to the soil when soil tests show a low P level of seven parts per million (ppm). Very high soil P-test soils (25 ppm) showed no yield benefit (or loss) from adding additional P.
What Tissue Testing Teaches
While tissue testing is no guarantee of adequate soil fertility, it can be a good way to red-flag fields, or areas of fields, for potential nutrient deficiency problems.
Bob Deutsch with AgVise Labs notes that plant tissue tests across North Dakota, South Dakota and Minnesota showed an average of more than 25% of all corn tissue samples below the critical level for N, P, K, S and Zn. Much of that could be due to soil variability across individual fields, or to the fact that in some cases, growers requested tissue tests of plants already showing visual deficiency symptoms.
“The corn data indicates we had a significant number of fields testing low in N, P, K, S and Zn,” says Deutsch. “The large number of corn fields testing low in N may be partly due to the loss of N during above-normal precipitation events, causing leaching and denitrification.”
Wheat data indicates many of the same trends as corn. The high number of wheat fields testing below the critical level in Zn was somewhat surprising. This low number may be due to the fact that we are receiving large volumes of plant tissues from areas where Zn has never been applied.
“We need to be aware we have nutrient issues on corn and wheat in our area with the three major nutrients of N, P and K,” Deutsch continues. “We also have issues with secondary nutrients of sulfur and chloride and the micronutrients zinc and copper.” Deutsch indicates these micronutrient issues could be addressed with products like MicroEssentials.