Heat and Drought on Young Corn
June 07, 2012 by Steven Heightchew
A corn field rolling in the heat of the day is not an uncommon sight in the Central Corn belt. What is uncommon is to see this in the middle of May. 2012 has been a unique weather year to say the least. Planting progressed at a record pace due to the dry, warm winter and spring, and this same weather pattern has continued. Producers are now observing their corn fields suffering from heat and drought stress at a very young age. This raises a lot of questions in regard to how negatively the drought will impact the growing crop.
The “Old Timers” always say that dry weather early in the season makes corn root deeper, allowing it to reach subsoil moisture later in the season. This statement does have some merit, but soil moisture is needed for nodal roots to grow to their full potential. A corn plant relies very heavily upon its nodal root system for water and nutrient uptake. Nodal roots are the thick, white roots that extend out of the crown at a 45 degree angle. Growth of these roots occurs at the tip. This root tip has to be in contact with soil water for growth to occur, so issues can arise when nodal roots are not in moisture. Without adequate moisture the growth of these roots stops, and an underdeveloped root system results. Timely rainfall becomes crucial for a small root system.
Hot, dry weather after planting can complicate seed furrow issues. Planter disc openers that were drug through high moisture soils can slice the sidewall open creating a resistance layer in the seed furrow. Warm, dry conditions follow and “bake” this sidewall tight. Nodal roots fail to penetrate the sidewall and can’t establish themselves as the anchor for the corn plant. This results in roots only traveling down the sidewall instead of the preferred 45 degree angle. Under severe circumstances, the furrow gets so hot and dry that the nodal roots don’t have any moisture to grow, and the root tips are burned off. The plant then has zero nodal root development and can fall over at the 4-5 collar growth stage. This phenomenon is sometimes called “floppy” or “rootless” corn syndrome. Rainfall is needed to get the roots growing again.
Compaction layers caused by secondary tillage applications have been very evident as well this spring. Fields that appeared to have been worked very dry are now showing signs that more soil moisture was present than was accounted for. A hard layer can be found where field cultivator sweeps and disc blades were ran in less than ideal situations. This layer has become very hard and impenetrable to nodal root systems. Compaction is present almost every year, but rainfall typically softens up this layer and lets the nodal roots go through. Several growers haven’t had this luxury in 2012, and root systems are extremely constricted.
Barring any rooting complications, corn can still be found rolling during the day and the topic of yield reduction starts being discussed. Leaf rolling is a defense mechanism of the plant to help limit transpiration of water from the plant when soil moisture is not adequate in the root zone. The negative side to leaf rolling is photosynthesis is often limited. Several days of limited photosynthesis can impact the overall accumulation of dry matter resulting in shorter plants and smaller leaves. The size of the plant typically has no effect on yield if conditions are conducive to good yields during grain fill. Unfortunately, if moisture remains short and plants continue to endure stress after pollination, smaller plants and leaves will reduce the plant’s photosynthetic rates and ultimately grain yield.
Corn starts determining the number of kernel rows at V6 (6 collars) and will continue to do so through V12. This factor is heavily influenced by plant genetics rather than environmental factors. This means that a plant can be somewhat stressed early in the season and not sacrifice too much yield. However, extreme stress during the V5 to V7 growth stage can restrict kernel row formation.
On the other hand, the potential kernels per row, or ear length, are strongly influenced by environmental factors. This process starts at V12 and is complete around the V17 leaf stage. Stress during this timeframe can greatly restrict yield potential by shortening the ear. Some of the March planted corn will be nearing this growth stage soon and a timely rainfall will be crucial in maximizing ear potential.
Drought has its biggest impact when corn nears its reproductive stages, starts pollinating and begins filling kernels. As the above chart indicates, the corn crop begins using much more water during these growth stages, and the need for rainfall becomes much more prudent as the crop continues to age. The longer fields undergo drought conditions, the less subsoil moisture there will be to work off of once the crop heads into these critical growth stages. Couple this with underdeveloped root systems, and timely rainfall becomes critical in holding onto yield potential. A good corn crop can still be harvested, but dependence on future moisture is essential.
Source: Irrigation Management for Corn. University of Nebraska – Lincoln Extension. Kranz, Irmak, van
Donk, Yonts and Martin, May 2008
Source: Hot & Dy: Toll on Young Corn? Purdue Cooperative Extension Service – Pest & Crop Issue 9.
Nielsen, May 25, 2012