Section 1 - Stand Establishment, Fertility & Water Use

Tips for Managing Soil Crusting

Heavy rains on fields not yet emerged can lead to questions of whether soil crusting will be a problem. Consider waiting at least 5 days after a crop is beginning to emerge to determine what percentage of the stand will be established. If a heavy crust does occur, a harrow or rotary hoe will be the best option once the soil starts to dry. Before deciding to rotary hoe or harrow, be sure that seedlings are unable to emerge through the crust. Harrowing can break off an emerging coleoptile or hypocotyl resulting in more damage than good. It is not advised to harrow canola, flax, mustard, or other crop seedlings which can be small and near the soil surface. If the plant is leafing out under the crust layer and the stand is poor, then breaking the crust layer is recommended. A harrow, rotary hoe or any empty press drill with disc openers has been used successfully to break up a crust. Light, spring tooth harrows should be set shallow (½ inch deep) and angled back to reduce the potential of going too deep. Harrowing at a right angle to the rows and driving as slow as possible will also reduce the injury potential to the crop that has emerged.

Water Use of Wheat

A wheat crop of about 50 bu/ac has a water requirement that is about equivalent to 10 inches. However, because water also evaporates from the soil surface, the actual amount of water needed to produce a crop is higher. Under most conditions in the Northern Plains, small grains will need between 14 and 16 inches of soil moisture per season, depending on climactic conditions and the length of the growing season.

Daily crop water use, also called evapotranspiration or ET, depends on canopy development and will generally peak between heading and early dough stage. Daily ET during this peak period can range from 0.10 to 0.30 inches, depending on air temperature and cloud cover. The table below shows estimated daily ET rates figured for spring wheat in N.D. at different stages of growth and selected maximum daily air temperature ranges. As weather is variable by location, so too will daily ET estimates vary by location. Real-time estimated daily crop ET may be observed over the Internet during the growing season at: http://ndawn.ndsu.nodak.edu and also for Minnesota: www.soils.wisc.edu/wimnext.

Water Stress in Corn

Water stress during flowering and pollination delays silking, reduces silk elongation, and inhibits embryo development after pollination. Moisture stress during this time reduces corn grain yield 3-8% for each day of stress. Moisture or heat stress interferes with synchronization between pollen shed and silk emergence. Drought stress may delay silk emergence until pollen shed is nearly or completely finished. During periods of high temperatures, low relative humidity, and inadequate soil moisture level, exposed silks may desiccate and become non-receptive to pollen germination.  Silk elongation begins near the butt of the ear and progresses up toward the tip. The tip silks are typically the last to emerge from the husk leaves. If ears are unusually long (many kernels per row), the final silks from the tip of the ear may emerge after all the pollen has been shed. Another cause of incomplete kernel set is abortion of fertilized ovules. Aborted kernels are distinguished from unfertilized ovules in that aborted kernels had actually begun development. Aborted kernels will be shrunken and mostly white.

Water stress during grain filling increases leaf dying, shortens the grain-filling period, increases lodging and lowers kernel weight. Water stress during grain filling reduces yield 2.5 to 5.8% with each day of stress. Kernels are most susceptible to abortion during the first 2 weeks following pollination, particularly kernels near the tip of the ear. Tip kernels are generally last to be fertilized, less vigorous than the rest, and are most susceptible to abortion. Once kernels have reached the dough stage of development, further yield losses will occur mainly from reductions in kernel dry weight accumulation.

Severe drought stress that continues into the early stages of kernel development (blister and milk stages) can easily abort developing kernels. Severe stress during dough and dent stages of grain fill decreases grain yield primarily due to decreased kernel weights and is often caused by premature black layer formation in the kernels. Once grain has reached physiological maturity, stress will have no further physiological effect on final yield. Stalk and ear rots, however, can continue to develop after corn has reached physiological maturity and indirectly reduce grain yield through plant lodging. Stalk rots are seen more often when ears have high kernel numbers and have been predisposed to stress, especially drought stress.

UM Research Links Iron Chlorosis to high N levels

University of Minnesota research indicates that the severity of iron deficiency chlorosis may be linked to high levels of nitrate-nitrogen in the soil that subsequently increases the concentration of nitrate N in the soybean plant. Higher concentrations of nitrate N apparently can inhibit the soybean plant’s metabolism of iron, resulting in lower concentrations of chlorophyll in the soybean plant and subsequently lower yields. Thus, management practices in soybeans need to keep concentrations of nitrate-nitrogen in the soil to a minimum. One approach would be to avoid using excessive amounts of fertilizer nitrogen for the preceding corn crop. Another approach is to use a competition crop such as oats. See research results online: www.extension.umn.edu/cropenews/2007/07MNCN03.htm.

Cool, wet weather along with soil high in pH, carbonates and salinity are ideal conditions for iron chlorosis to develop. Chlorosis associated with iron deficiency does not appear until the first trifoliate leaves appear in the plant.

The adoption by growers of more chlorosis/salt tolerant varieties has resulted in more soybean fields withstanding this stress. Warmer, drier weather helps improve chlorosis symptoms, although NDSU research suggests that even fields which recover quickly may have yield affected due to the condition.

To date, foliar applications of micronutrients or iron sprays on soybeans have not shown consistent yield increases from this condition. Some herbicides may further stress soybeans already stressed by chlorosis. See more information online at www.ag.ndsu.edu/procrop/syb/ironchlorosis.htm.

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