By Lowella Fin

Corn uses less water than rice. It can be grown on a wide range of soil types, and can adapt to various planting methods. There are also plenty of hybrid varieties to choose from, and there is a steadily-growing market for feeds. Corn grains are durable (in contrast to perishable fruits and vegetables), so immediate transfer of grains to end-users is not an issue after proper drying and storage. In short, who would not want to plant corn continuously?

With these factors, even Ilocos and Central Luzon growers (corn-after-rice) would want to plant corn all-year long, if not for the severe monsoon rains, which occur annually from July to September that can surely submerge their low-lying fields. In the Visayas and Bicol regions, they make sure to plant only on well-drained soils or on rolling fields.

There is indeed an economic advantage for growing corn non-stop, but we should be aware that we also put some strain or stress on the farm we till.

Corn.

To address this, here are the best practices for corn-after-corn production, with emphasis on hybrid selection, high-crop residue challenges related to diseases, soil fertility, and weed management.

Hybrid selection

Selecting the right hybrid is an integral part of a successful corn-after-corn production. A corn grower should always ensure to:
• select hybrids with proven performance under different environments and stresses (as their field may possibly encounter);
• select hybrids with above-average drought tolerance. Under the corn-after-corn system, the root mass may be reduced, and such may not prepare the corn plant for limited water conditions;
• select the right hybrid maturities that match corn planting dates and climatic conditions forecast;
• choose the highest-performing genetics with the defensive traits required for this production system.

For better understanding of these traits and products, seek the assistance of your Pioneer agronomist or field technician in selecting hybrids for corn-after-corn.

Crop residue and diseases 

In cropping systems where great amounts of residue are left in the soil surface, corn diseases may become an issue. Pathogens or microbes survive in corn residue and disease builds up over time. This is especially true in the disease-prone areas of Mindanao, Panay, and Bicol. Sometimes, planting too early on a high-residue seedbed can increase the chances of corn seedling diseases such as the seedling blight. This can be avoided through strip tillage or removal of the residues from the rows.

Leaf diseases such as gray leaf spot, northern leaf blight, and diplodia leaf blight are known to have increased in Mindanao due to long-term, high-residue farming. This could also be possible in the cool areas of Panay and Bicol where corn-after-corn have become an acceptable farming practice. Stalk and ear rots such as Gibberella, Diplodia, Fusarium, and Aspergillus also survive in crop residue and increase in high-residue systems. Burying (or plowing under) crop residue by tillage may be an option, but all growers should select hybrids with good disease resistance and standability. Oftentimes, stalk rots accompany leaf diseases, so monitoring stalk quality and timely harvest is helpful when leaf diseases occur. The practice of manual ear-picking here in the Philippines becomes more expensive on fields with severe lodging brought about by diseases.

If ear rots are found, late-season scouting can help growers make informed decisions about harvest timing, postharvest grain handling, and storage and utilization. For example, grains with significant ear rot symptoms from the field should be dried quickly to 15 percent moisture content or less at high temperature. The lower the moisture content in storage, the lower the risk of mycotoxin (amag) development.

Soil fertility and nitrogen

In corn-after-corn, many farmers are not aware of the value of thorough soil testing and the availability of local nutrient recommendations coming from LGUs and seed companies. Soil tests are needed to measure soil pH (acidity or alkalinity, not lower than pH5.5), organic matter content (nitrogen), phosphorus (P), and potassium (K). A balanced level of P and K applied as basal can improve efficiency in nutrient uptake.

Unlike legumes (or beans), corn residues tie up much more nitrogren as they decompose in the soil. This is why using the same level of N fertilizer in the succeeding season of corn-after-corn system does not really bring any additional yield; not unless growers increase their N rates by 40 kg to 50 kg N/ha. It really pays to have a soil test or obtain local recommendations. However, recent US studies revealed that regardless of N levels, corn-after-corn never equalled to that of a corn rotated to soybeans.

Weed management

Watching out for weeds is a more important issue among corn-after-corn systems as compared to corn-after-rice. In Central Luzon, farmers have attested that weeds are more problematic in their off-season crop than corn following their rice crop in the wet season. Hence, growers should monitor fields for any increase in specific weed pressure and employ proper management especially among glyphosate-ready (RR corn) fields. Alternating the use of herbicide and the use of mixtures will help ensure long term success of weed management and prevent weed shifts or weed resistance. Watch out for volunteer plants also. These are plants that have emerged from ears or grains left in the field after harvest. Farmers should then strive to reduce stalk breakage and ear drop.

Rotation effect and stress 

The so-called “rotation effect” is an unexplained benefit that results in better yields with crop rotation, even though the limiting factors are being addressed in continuous cropping. Where yield potential is low, yield reductions become greater for corn-after-corn versus rotated corn cycle. Such observations led to the idea that generally, crop rotation renders the corn more tolerant to yield-limiting stresses such as moisture extremes, in particular. Experts implicate the root system as the most likely source of the problem. In corn-after-corn systems, soil compaction can be a likely cause, however, it could also likely be on the neglect on the part of the grower. Most of our growers do not have access to soil testing, or simply unaware that it is absolutely necessary for the sustainability of their valuable resource.

Management suggestions for corn-after-corn

• Choose fields that are best suited for corn-after-corn system. Fields should have good drainage, medium-textured soil with ample water holding capacity, and adequate P and K levels.
• Manage corn borers using Pioneer products. Your local Pioneer agronomists and sales representatives will gladly assist you in choosing which is bestsuited in your area.
• Select hybrids with appropriate maturities to suit your needs. Early-maturing hybrids will always have an advantage.
• Manage nitrogen (N) carefully. A combination of N during basal and sidedress applications may help limit effects of N losses due to leaching and denitrification in wet periods.
• Walk in the field regularly to monitor and identify any problems early on. Look for stand count issues, nitrogen shortages, insect build ups, disease outbreaks, weed problems, and moisture stress effects.
• Monitor the fields for leaf diseases and stalk and ear rots. They can be controlled by managing residues properly and selecting the resistant or tolerant hybrids.
• Be diligent to prevent soil compaction on corn-after-corn fields.

This appeared in Agriculture Monthly’s October 2018 issue.