Drought Stress in Shallow Rooted Corn

Shallow Rooted CornWet conditions in spring can cause shallow rooted corn, which may lead problems later in the season. When roots develop in wet soils, the majority of the root mass can end up in the top 2 to 4 inches of the soil and deep penetrating roots can have poor establishment (Figures 1 and 2). Shallow rooted corn may be prone to root lodging and may not be able to pull in the nutrients that a growing plant needs. If dry conditions occur, shallow rooted corn may also show symptoms of drought stress.

Shallow Roots

Wet, saturated soils have lower levels of oxygen and can also have lower soil temperatures. These conditions can reduce root growth and cause shallow roots. If conditions surrounding the shallow root zone become dry, corn plants may experience stress.

 
 

Drought Stress

 
Because the soil surface dries first and deeper soils hold moisture longer, corn fields that have shallow roots may experience drought stress earlier than corn roots at a normal depth. Drought stress prior to pollination may reduce ear length and reduce the number of potential kernels. Heat and moisture stress during pollination and the period immediately following can cause significant reductions in yield potential and possibly complete barrenness. The level of yield reduction is dependent on severity of drought, field environment, and hybrid. Table 1 shows potential yield reductions due to stress at different growth stages.
 

 

 

Potential Corn EvapotranspirationSilks are approximately 95% water; therefore, when there is dry weather in combination with high temperatures of >90° F, a delay in silk emergence is common. Corn pollen shed typically lasts five to seven days with silk emergence beginning one to two days after tassel emergence. In drought, pollen shed is often reduced to two to three days and silk emergence delayed four to five days, resulting in a reduction in viable pollen to fertilize the silks. Temperatures above 95° F often reduce pollen viability. Continuation of dry and hot weather in late July and early August can cause post-pollination kernel and ear abortion. Kernels are most susceptible to abortion in the days immediately following pollination. Kernel abortion begins at the ear tip and works its way down the ear. Shallow root systems, high plant populations, nutrient deficiencies, and individual hybrid genetics can impact the severity of kernel and ear abortion. Water use in the plant is highest from silking to milk stage of development. This is when the largest reductions in yield can occur.

 
 

Management

 
Preventative management to reduce the chance for shallow rooted corn includes practices that can help minimize compaction and hybrid selection. Corn hybrid performance can vary greatly. Early hybrids may be favored in drought due to earlier flowering and grain fill in more favorable moisture conditions. However, if the weather turns cool and rain is received, then later hybrids may be favored because of the timing of flowering and grain fill better coinciding with rainfall. Leaf rolling in corn is a way for the plant to respond when it is stressed. Leaf rolling results in a reduction of photosynthesis within the plant. Under normal conditions a plant can take in water during the nighttime hours which provides the plant with moisture for daytime photosynthesis; however, in drought, this may not be possible. Leaf rolling does not always indicate yield performance at harvest but can indicate root development throughout a field. Shallow rooted, poorly developed root systems, or root injury from corn rootworm larvae often result in leaf rolling due to an inability to take in water.
 

 

Estimating Pre-Harvest Corn Yield

​Corn hybrids with good drought tolerance have a better ability to handle the lack of water. However, drought tolerant hybrids can still experience yield reductions due to drought stress. Monsanto intends to launch DroughtGard™ Hybrids, its newest technology, as part of the Genuity® family of traits in 2013. They are part of a system offering farmers improved genetics and agronomic practice recommendations together with the new drought trait to help farmers manage the risk of yield loss caused by drought. DroughtGard™ Hybrids are fully approved in the U.S. but certain key international approvals are still pending.

 

In addition to planting DroughtGard™ Hybrids, planting corn with a biotech trait to help protect against corn rootworm injury can also help provide some protection from drought stress. Genuity® DroughtGard™ Hybrids will be available with Genuity® VT Triple PRO® corn, Genuity® VT Double PRO® RIB Complete™ blend, and Roundup Ready® Corn 2 products.

 
 

Harvest

 
Corn may have the ability to recover from drought stress. Therefore, harvesting a crop for silage instead of grain should be delayed until the situation has been assessed. Table 2 gives an example of how to estimate yield potential. If corn has reached tassel, has leaves that do not unroll at night, and the tips start to brown, it will probably not recover. If half the leaves are dead or dying, the field may be a candidate for silage. If the decision to harvest the crop for silage is made, the next step is deciding when to harvest the silage. As browning of the corn plant continues, forage quality decreases. Therefore, delaying silage harvest will reduce yield and quality and may reduce the chance for planting a second crop. Corn moisture should be checked prior to harvest. If the moisture is greater than 75-80%, harvest should be delayed to avoid seepage and loss of silage quality.
 

 

 

 

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