ISSUE 8   July 3, 2008

VARIABLE CORN EMERGENCE – 2008

I have observed abnormally high levels of variability in the plant height of corn this spring. Much of this variability is related to differences in plant emergence timing. No doubt the cooler than normal temperatures this May were partly to blame for the magnitude of this problem. Variability in plant size is especially pronounced in fields with poorly incorporated residues from the previous crop. Plant height differences were also accentuated this year by the excessive wet conditions of early June. Plants that emerged later seem to have less access to plant nutrients because of smaller root mass, further stunting their growth. Of the common crops grown in North Dakota, corn is probably the most responsive to stand uniformity. Corn can compensate for some reductions in plant populations associated with poor seedling emergence or from poor seed drop. On the other hand, corn is quite sensitive to unevenness in plant emergence and plant height. Plants that are significantly smaller than their neighbors will be shaded and often struggle to form a cob. They will, nevertheless, still compete for light, water, and nutrients with their larger neighbors (unlike a skip). In a real sense, they become very expensive weeds that are not practical to control.

Yield losses associated with late emerging or short plants can be impacted by a number of factors including differences in size, the hybrid grown, and the percentage of the plants that emerge late (or that are significantly smaller than their neighbor). Recent research reported yield losses of between 4 and 23% depending on the percent of the plants that emerged late and the length in the delay in emergence of the late emerges. The greatest losses when emergence delays are one week occur when 50% of the plant emerge late. The longer the delay (most research looked at delays of up to 3 weeks) the greater the yield losses. See a recent article by Elmore and Abendroth (http://www.ipm.iastate.edu/ipm/icm/2006/6-12/cornheight.html) for additional details on relevant research findings. Some data suggest that hybrids may differ in their ability to compensate for stand unevenness, though there is no definitive research to elucidate characteristics that impart greater yield stability in such hybrids.

Differences in the temperature and moisture that surround the seed and seeding depth are probably the main factors impacting the timing of seedling emergence. Though we cannot alter the weather, we can to some extent alter the micro-environment in which the seed is place. The following are practices may improve stand uniformity:

Joel Ransom
Extension Agronomist for Cereal Crops
Joel.ransom@ndsu.edu

Iron is essential for plant growth. Plants can develop iron deficiency chlorosis deficiency (IDC) symptoms in the plant tissues, especially newly formed leaves, when iron in the plant is insufficient to meet the requirements. IDC will show up as unusual yellowing of the leaves in between the veins of the leaf. The veins may remain green. Iron is needed in the production of chlorophyll; the lack of leaf color is due to the failure of the chlorophyll to develop normally. Affected leaves turn brown and eventually the tissue dies resulting in weak and stunted plants.

Usually IDC is due to non-absorption rather than a lack of iron in the soil. A high soil pH (>7) can cause other elements to interfere with the absorption of iron. IDC is a common yield reducing soybean plant condition when crops are grown on high pH calcareous soils especially when salt levels are elevated. Although soybeans may grow out of the chlorosis, yields can be reduced or in severe cases the soybean plant may die.

The most important management practice is selecting chlorosis tolerant soybean varieties. The website http://www.soilsci.ndsu.nodak.edu/yellowsoybeans/ provides IDC scores for many soybean varieties grown in the region. The rating scale used by NDSU is:

Chlorosis severity differs from year to year, and it is impossible to give exact recommendations as to what level of chlorosis resistance is appropriate for a specific field. In general, the more severe the chlorosis symptoms occur in a field, the higher level of variety resistance should be selected. In Figure 1, the higher IDC scores (more severe chlorosis symptoms) within each year gave lower yield regardless of the different yield potential for each growing season.

Figure 1.  Source R.J. Goos

Different plant stresses can cause yellowing and produce chlorotic symptoms. Yellowing can be a result of wet soils, insufficient nitrogen, insects, soybean cyst nematode, root rot, or herbicide injury. Note that true iron deficiency has yellowing between the leaf veins but green veins.

Carbonates and salts are two important factors affecting potential for iron chlorosis. Carbonates are a fixed soil property, but salts can be reduced with tile drainage. Soil pH alone is not a good indicator of potential iron chlorosis, however knowing the carbonate and salt level can help growers choose soybean production fields.

Hans Kandel
Extension Agronomist, broadleaf crops
hans.kandel@ndsu.edu