Importance of Nutrient Management
- Nutrient management is one of the important considerations in successful corn production. Improper nutrient management has various implications on growth and yield performance of the corn plant.
- Grain yield is enhanced with better nourishment throughout the growing period, especially during the critical development stages of the corn plant.
- To attain yield potential of most corn varieties, they should get the optimum amount of nutrients they need.
- Nutrient requirements may be adjusted depending on the desired yield level for a particular variety.
- The quantities removed by the corn plants set the minimum amounts of nutrients to be provided.
- The final amount of fertilizer to be applied is determined by the nutrient supply from the soil. When the amount of available nutrient is low, fertilizer is added to the soil.
Soil Sampling and Analysis
Correct soil sampling and accurate soil analysis will help in determining the type and right amount of fertilizer to be applied in order to have a good yield.
Things to Remember in Soil Sampling and Analysis
- Collect soil samples right after harvest or before fertilizer application.
- Avoid sampling directly in the crop row or in the fertilized band.
- It is much easier to collect samples when the soil is moist.
- Conduct soil sampling and analysis of your cornfield every 3-5 years.
Steps in Soil Sampling and Analysis
Step 1.
Prepare the following: spade or shovel, pail, plastic bags, weighing scale and marking pen.
Step 2.
Divide your field into several sampling areas. Each sampling area should have similar cropping history, past fertilizer or lime treatment, slope, degree of erosion, soil texture (sandy, loamy, or clayey) and color. One sampling area may represent up to five hectares of field.
Collect 5-15 spot soil samples from several locations within each sampling area.
Step 3.
Before digging, brush away stones, rubbish and vegetation from the surface area.
With a spade or shovel, dig at a depth of about 30 cm and take a slice of soil about 2 cm thick and 5 cm wide (see illustration at right). This represents one spot soil sample. Put the sample in a clean pail.
Follow Step 3 until the total number of spots per sampling area is completed.
Step 4.
After completing the spot sampling of a particular sampling area, pulverize the soil, remove the stones and fresh plant parts and mix the samples thoroughly in the pail.
Step 5.
Airdry the soil with care and keep it away from foreign materials.
Step 6.
Take a composite sample of one kilo and place it in a clean plastic bag with a proper label that includes the name of the farm owner, farm location and sample number.
Step 7.
The soil is now ready for analysis. You can use a soil test kit (STK) or send the samples to the nearest soil testing laboratory in your area.
Types of Fertilizers
Fertilizers are materials that supply nutrients to plants. They may be inorganic or organic fertilizers.
Inorganic fertilizers.
Inorganic fertilizers are synthesized fertilizers, like urea (46-0-0) and ammonium sulfate (21-0-0) that supply nitrogen (N), complete fertilizers (14-14-14) that supplies N, phosphorus (P) and potassium (K) and ammonium phosphate (16-20-0) that supplies N and P.
Inorganic fertilizers release great quantities of nutrient elements that can be easily absorbed by the corn plants. You can see the result of application within a few days.
The nutrients commonly supplied by inorganic fertilizers are N, P and K, singly or in combination. Their percentages are alluded to in a chemical formulation such as 14-14-14 which refer, respectively, to percentages of N, P and K in a bag of fertilizer.
Organic fertilizers.
Organic fertilizers, on the other hand, are those derived from decomposed plant parts or residues, animal manures, green manures (legumes like mongo or sitao) and domestic refuse. They may also come from natural deposits (guano, phosphate rocks) and biological nitrogen fixers.
There is slow availability of nutrients with this type of fertilizers. The organic materials require microbial action to transform the nutrients in their available form for plants to absorb them.
However, when organic materials are fully decomposed and applied in large quantities, they improve soil fertility and soil aeration and promote good physical conditioning of the soil.
What are Essential Plant Nutrients?
It is now common knowledge that certain elements are essential for plant growth and that each element must be present in a specific concentration range for optimum plant growth.
If concentration of a given element in the plant root zone is low, a deficiency of that element occurs and plant growth is restricted.
Likewise, if the root zone concentration of a given element is too high, toxicity occurs and plant growth is similarly limited.
Only in a specific middle range concentration is optimum plant growth attained. One principal concern, therefore, of corn farmers is how to maintain concentrations of each essential element in this middle range.
Macro-nutrients and Micro-nutrients
Some 17 elements have been found to be universally essential for plant growth. Three of them come from air and water and 14 from soil solids.
Six of the 14 are used in relatively large amounts and are called macro-nutrients. while the other eight, needed in only very small amounts, are called micro-nutrients.
Three of the six macro-nutrients: nitrogen (N), phosphorus (P) and potassium (K) are absorbed by plants in sufficiently large quantities, taxing the ability of most soils to supply the plant's need and are normally supplemented by fertilizer application.
NPK Requirements of Corn
For corn, especially for hybrids, 27 kg of nitrogen (N), 7.5 kg of phosphorus and 20 kg of potassium (K) are needed to produce a metric ton (1,000 kg) of corn grain per hectare.
This means that a 5-ton grain yield target will need about 135 kg of N, 37.5 kg of P and 100 kg of K per hectare.
Nitrogen
Nitrogen (N) is needed to assure adequate growth of the plant, ensuring its leaves dark green and promoting full development of the ear and grains.
Nitrogen-deficient leaves turn pale green or yellowish in color with thin or spindly stems and small ears with unfilled tips.
Phosphorus
Phosphorus (P) is vital in growth processes like the use of sugar and starches. It stimulates good root systems and flowering and helps in seed formation. It counterbalances the effect of nitrogen by strengthening the stem and hastening plant maturity or the ripening of grains.
When phosphorus is deficient in the plant, the tips and margins of the young leaves turn purple. The plant grows slowly and the stem remains thin. This leads to poor grain formation on one side of the ear, causing uneven rows and curving of the cob.
Potassium
Potassium (K) is essential in the production of carbohydrates, formation of proteins and translocation of sugar. It promotes appropriate cell processes to strengthen the stem, improves the quality of ears and minimizes the susceptibility of the plant to certain diseases like stalk rots and pests.
When potassium is lacking, the plant appears squat due to shortened inter-nodes. The leaf margins of the older leaves turn yellow, then brown and finally die. The tip of the ear (or cob) has a sharpened look due to the poor grain filling. The grains are light and fluffy.
Fertilizer Calculation
The rate of fertilizer to be applied should be based on the results of soil analysis. Basing on the results of soil analysis, you can now compute the correct amounts of fertilizer to be applied.
So in computing the amount of fertilizer to be applied, you must know the fertilizer recommended rate based on the results of soil analysis and the fertilizer grade which will serve as sources of the nutrients to be applied.
Recommended rate is expressed in kilograms N, P and K per hectare, respectively.
For example, the recommended rate 80-40-20 means that 80 kg N, 40 kg P and 20 kg K are needed per hectare
Fertilizer grade refers to the minimum guarantee of the nutrient content in terms of percent N, P and K available.
For example, if ammonium sulfate is 21% N, it means that 21 kg of every 100 kg of the material is available N.
Fertilizer Application
Fertilizer Calculation
You can use the following formulas to calculate the amount of fertilizer needed to satisfy a given recommended rate (RR):
Formula 1:
Weight of fertilizer material (FM) = __RR x Area
% nutrient in FM
Formula 2:
Number of fertilizer bags = Weight of nutrient
Weight of nutrient per bag
Example of Fertilizer Calculation
Calculate how many kilograms of N, P and K are needed to satisfy the recommended rate of 90-60-30 kg of NPK per hectare given the following fertilizer materials: ammonium sulfate (21-0-0), solophos (0-20-0) and muriate of potash (0-0-60).
Weight of ammonium sulfate = 90 kg N/ha x 1 ha x 100 = 429 kg
21%N
Weight of solophos = 60 kg P/ha x 1 ha x 100 = 300 kg
20%P
Weight of muriate of potash = 30 kg K/ha x 1 ha x 100 = 50 kg
60%K
You will need 429 kg N, 300 kg P and 50 kg K to satisfy the recommended rate of 90-60-30 kg NPK per hectare.
General Fertilizer Recommendation in the Absence of Soil Analysis
As previously stated, the rate of fertilizer to be applied should be based on the results of soil analysis.
However, in the absence of soil analysis, use the following general recommendation:
- Use four bags of complete fertilizer (14-14-14) per hectare as basal application in the furrows and cover the fertilizer with a thin layer of soil, about 2 cm thick.
- After 25-30 days of planting, side dress with four bags of ammonium sulfate or two bags of urea. Cover the fertilizer immediately by shallow hilling-up.
Fertilizer Application During the Wet Season
- Split application of nitrogen (N) fertilizer is recommended.
- Apply all the needed phosphorus and potassium and half of the recommended amount of N in the furrows before planting.
- Side dress the other half of N at least 4-5 cm away from the base of the plant 20-24 days after emergence or immediately before hilling-up when there is right soil moisture.
- To attain higher yields, apply animal manures and crop residues just before land preparation.
Fertilizer Application During the Dry Season
- Due to the possibility of drought during the dry season, apply all the recommended amount of fertilizer in the furrows just before planting to provide the crop all the nutrients it needs.
- However, if supplemental irrigation is available, follow the application of fertilizer for the wet season.
- Cover the fertilizer with 2-4 cm soil to prevent seed injury.
- Organic fertilizer or compost may be applied in addition to the recommended inorganic fertilizer.
Liming
Soil acidity is a common problem in areas where precipitation is high enough to leach appreciable amount of calcium and magnesium from the surface of the soil.
Leaching. Draining away of minerals or chemicals from the soil when dissolved in rainwater.
It also arises from a variety of factors, such as the type of clay, presence of iron and aluminum oxides and free acids from continuous application of large amounts of acid-forming fertilizers like ammonium sulfate, ammonium phosphate and ammonium nitrate.
Soil acidity reduces corn yields because less nutrients are available in acidic soils. Corn yields are greatly reduced in soils having a pH (degree of soil acidity or sourness) much lower than 5.3. For better yields, liming is normally practiced for acidic soils.
Benefits of Liming
- As soil pH approaches neutrality, most soil nutrients become available for plant use.
- Indirectly, improved structure is also encouraged when an acidic soil is limed.
- Lime stimulates activities of many soil organisms favoring formation of humus and encouraging elimination of by-products that are toxic to plants.
Lime Application
The agricultural lime commonly available in the Philippines is calcitic limestone or calcium carbonate.
A usual rate of 3 tons per hectare is recommended but this varies depending on the magnitude and nature of soil acidity.
Do the following procedures in applying lime:
- Pulverize the limestone before applying to the soil. Finer lime materials act at a faster rate in neutralizing soil acidity.
- Plow in the lime a week before planting for better incorporation in the soil.
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