Corn : Other Essential Nutrient Elements
Farmer education remains a key component in addressing the current situation. With the meager resources you have, it is best that you maximize the fertilizers you buy. Eliminate inefficient application methods and other causes of nutrient loss.
Much had been discussed already about the “Big 3″ elements, namely, nitrogen (N), phosphorus (P), and potassium (K). From a crop production standpoint, NPK are “managed” by the addition of fertilizers into the soil. Farmers can easily buy them, and they can also easily relate to NPK. Somehow, they can tell the deficiency symptoms associated with the lack of it in their corn plants.
When I went around Isabela and Cagayan, I saw a lot of pale green corn fields mostly in their vegetative stages. My impression is that it’s a bad indication of many growers cutting their rates of fertilizers. An ordinary farmer will tell the same thing because they have known what N deficiency is for such a long time. It lacks fertilizer that’s why it’s pale green in appearance, ears are small and characterized by poor grain-filling, and light in terms of grain weight. At this stage, it is easy to tell whether our corn output for the season will go up or down versus last year.
But again, we need to know the “other” elements required by our plants. The “others” are just as important and they could likewise spell crop losses once deficient or absent. Since they are not as popular as NPK, let’s try to be more familiar with some of them.
PRIMARY AND SECONDARY ESSENTIAL NUTRIENTS
There are 16 essential nutrient elements required by plants, 3 of which are organic (carbon, hydrogen and oxygen) and are absorbed from the atmosphere. The remaining 13 are usually applied into the soil - the major points for discussion in this article.
By definition, all essential nutrients are required for plant growth and completion of its life cycle from seed to seed. Some are absorbed or needed in larger quantities (macronutrients), while the others in much smaller quantities (micronutrients). Macronutrients include nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S). On the other hand, chlorine (CI), iron (Fe), boron (B), manganese (Mn), zinc (Zn), copper (Cu), molybdenum (Mo), and nickel (Ni) are classified as micronutrients. N, P, and K are easily managed, while Ca, Mg, and S are oftentimes found in sufficient levels in most soils, and amendments are rarely done.
From a management point of view, the primary nutrients are N, P, and K because they are often limiting and easily depleted from the soil. All of the other remaining macronutrient elements are secondary nutrients because they are rarely limiting and rarely added into the soil as fertilizers.
THE LAW OF THE MINIMUM
This is one thing that many growers have failed to recognize when it comes to nutrient management. Whether a macronutrient, or whether a primary or secondary nutrient, this Law of the Minimum is applicable. It states that yield is proportional to the amount of the most limiting nutrient, which are common among soils that contain calcium carbonate, can severely affect plant growth even with sufficient N, P, and K.
Hence, it is important that growers are aware of what may be lacking in their soils. Sometimes ago, it was declared that around 500,000 hectares of wetland rice in the Philippines are zinc-deficient. With the magnitude of the problem, the government engaged in an awareness campaign because of the lack of appreciation of many farmers for nutrients other than NPK. Rice agronomists will have to work harder with their farmers because yield will definitely be limited simply because of the Law of the Minimum.
A LOOK AT THE OTHER NUTRIENTS
As mentioned earlier, growers should also try to be familiar with secondary nutrients or what I wrote as the “others”. Being rarely a problem, it does not mean that it won’t pose a serious problem now or in the near future. The ability of the soil to supply secondary nutrients to plants indefinitely is dependent on nutrient cycling and conservation of matter or managing residues. Continuous crop removal of Ca, Mg, and S requires replenishment in the same manner as the primary nutrients, but most likely less frequently. However, once deficient, it can be difficult to recognize.
Calcium and magnesium are most of the time supplied by mineral weathering, either of agricultural limes (added to correct acidity) or of natural soil materials. Sulfur, on the other hand, comes either as atmospheric deposition (associated with air pollution) or as impurities in fertilizers.
Let’s read about some of these nutrients and their role in the plant.
Calcium. The function of most plant calcium is structural, a very important component of the cell walls of shoots and roots. Hence, minor fluctuations in Ca levels in the cellular level form part of the signaling mechanisms for environmental stress. If deficient, leaf tips stick to the next lower lead, giving a ladder-like appearance. Popular sources of Ca are calcium carbonate or calcium magnesium carbonate, as agricultural lime. Gypsum and calcium nitrate are also good source. Ca is removed from the field by crop removal and leaching.
Magnesium. The most familiar function of magnesium, being a component of the chlorophyll in the leaves, is related to plant enzyme activation. It is present in the cell wall. Deficiency is first seen as yellow to white interveinal striping of the lower corn leaves. Sometimes, dead round spots follow. Older leaves become reddish purple and tips/edges become necrotic under severe conditions indicating that Mg is mobile in the plant. Sources for Mg include dolomitic agricultural lime and magnesium sulfate.
Sulfur. When deficient in sulfur, plant growth is reduced or stunted and maturity is prolonged. Sulfur (S) is very important in the formation of proteins (amino acids) such that yellowing of the corn plant can be observed under severe conditions. With a striking similarity to N deficiency, yellowing is normally more pronounced in the young leaves indicating that it is moderately mobile. The problem is favored by acid sandy soils, low soil organic matter, and cold dry soils. S is removed from the field by crop removal and leaching. Popular local source of S is ammonium sulphate (24%).
Zinc. Among micronutrients, Zn is the most likely deficient in corn. Zn deficiency causes interveinal, light striping or a whitish band starting from the base of the leaves and extends up to the tips. The leaf margins, the midrib area, and the leaf tip would usually remain green. With shortened nodes, corn would appear stunted. Being relatively immobile, Zn-deficient plants may produce “white buds” or new leaves that are nearly white. Most plants usually outgrow this problem but not in very severe cases. Soils with high pH and low in organic matter content normally had this problem coupled with frequently wet and cool conditions. Zinc sulfate is a popular fertilizer source to manage deficiency.
Iron. Corn requires very little iron (Fe) but severe deficiency, especially in high pH soils, can result in pale green to nearly white interveinal area of the upper leaves. Even under very sufficient N, P, and K levels, Fe deficiency can severely impair yield performance.
to be continued…
