09 Sep Visual symptoms tell nutrient deficiency story
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 pin-pointing 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 Dan Froehlich, agronomist with The Mosaic Company. “We’ve seen deficiency symptoms across the board in 2010. Also, fields with marginal fertility that might not show the deficiency under good growing season conditions are showing it this year because the soil conditions have made nutrients slightly less available and because the roots of the crop are not as active to compensate for the reduction in nutrient availability.”
To help growers diagnose potential nutrient deficiencies, The Mosaic Company offers an on-line photo library illustrating visual symptoms of nutrient deficiency in 19 major crops. The library is found at http://www.Back-to-Basics.net.
Here are some of the deficiency symptoms for primary plant nutrients.
Phosphorus deficiency symptoms
Phosphorus (P)-deficient plants are smaller and grow more slowly than do plants with adequate phosphorus. Phosphorus deficiency is usually visible on young corn plants because the nutrient readily mobilizes and translocates in the plant. Affected plants are dark green with reddish-purplish leaf tips and margins on older leaves. Newly emerging leaves will not show the coloration.
In addition, deficiency symptoms nearly always disappear when plants grow to three feet or taller. Detecting phosphorus deficiency can sometimes be difficult, because some corn hybrids tend to show purple colors at early stages of growth even though phosphorus nutrition is adequate, yet other hybrids do not show the color symptoms even though inadequate phosphorus severely limits yields.
Phosphorus deficiency is common in cold soils that are too wet or too dry; when P is applied where plant roots cannot absorb it; where restricted root growth is caused by compacted soils; and where roots have been injured by insects, herbicides, fertilizers, or cultivation.
Potassium deficiency symptoms
Plants absorb potassium as the potassium ion (K+). Potassium is a highly mobile element in the plant and is translocated from the older to younger tissue. Consequently, potassium deficiency symptoms usually occur first on the lower leaves of the plant and progress toward the top as the severity of the deficiency increases. One of the most common signs of potassium deficiency is the yellow scorching or firing (chlorosis) along the leaf margin while the midrib stays green. In severe cases of potassium deficiency the fired margin of the leaf may fall out.
Potassium deficient crops grow slowly and have poorly developed root systems. Stalks are weak and lodging of cereal crops such as corn and small grain is common. In alfalfa, potassium deficiency creates small dots on the margins of the upper leaflets of alfalfa. When severely deficient, the size and number of spots increase, the leaves become yellow and dry, and the lower leaves drop. Poor root development, defective nodal tissues, unfilled, chaffy ears and stalk lodging are other symptoms in corn.
In soybeans, K deficiency also appears as firing or scorching on the outer edge of the leaf. When leaf tissue dies, leaf edges become broken and ragged. Delayed maturity and slow defoliation as well as shriveled and less uniform beans are also symptoms.
Sulfur deficiency symptoms
Adequate sulfur (S) is necessary for high-yield cropping systems and optimum plant use of nitrogen and potassium. Plants encountering inadequate S will exhibit a slow growth rate and poor response to nitrogen. New leaf growth will be pale green in color and the protein levels of the soybean will be low. However, other soil/crop conditions, such as soil texture, can influence crop need and use of nutrients such as S. Sulfur is a mobile nutrient in the soil and the nutrient reservoir is smaller for coarse textured soils.
The functions of S and its influence on plant growth show why S is a full season nutrient. It promotes plant growth from the seedling stage until the crop reaches physiological maturity. Sulfate S is very mobile in soil solution, but considered non-mobile within the plant. Elemental S must be converted to the sulfate form in the soil before taken up by the plant. A severe shortage of S often develops visible deficiency symptoms on new growth.
The preferred method of S application is to use a combination of the sulfate form for immediate uptake and elemental sulfur for mid- to late-season uptake. This provides season-long S supply while minimizing potential leaching losses. MicroEssentials is a phosphorus-based fertilizer that offers both forms of sulfur in addition to P and N in one uniform granule.
Zinc deficiency symptoms
Zinc (Zn) deficiency in corn causes interveinal, light striping or a whitish band beginning at the base of the leaf and extending towards the tip. The margins of the leaf, the midrib area and the leaf tip usually remain green. Plants are stunted during the first few weeks because internodes are shortened. Deficiency appears later with beans as flower buds shed or with cotton as growth and fruiting are delayed.
Thus, most crops need a readily available supply of Zn for both early and late season growth and yield development. Zinc deficiency is favored by high soil pH; low organic matter soils with high soil pH; and cool, wet soil.
Because Zn is often needed at a rate of only a few pounds per acre, uniformly distributing Zn in a traditional fertilizer blend can be difficult because of product segregation. MicroEssentials SZ, which includes the correct ratio of P, N, S and Zn in one uniform granule, allows uniform distribution of nutrients to each plant across the field.