ISSUE 14   August 16, 2007

CORN WATER USE AND PRODUCTIVITY

Conditions for corn growth in most of North Dakota have been quite good this season. Nevertheless, water requirements for optimal crop development are highest for corn during early grain filling and drought stress is becoming a concern in parts of the state. Corn is a very efficient user of water (produces more bushels per unit of water than most crops) but has high water requirements. In fact, a corn crop can use in excess of a third of an inch of water per day during this time of the year. The accumulated water use by corn in just the past 10 days has ranged from 2.3 inches in the southwest to 1.1 inches in the northeast. When crop water demand exceeds that available from rainfall and the soil, the plant becomes stressed, the rate of photosynthesis is slowed and yield is reduced. Information on the difference between corn crop water use and the amount of rainfall received is readily available for any given period of the growing season from NDAWN (http://ndawn.ndsu.nodak.edu/) by selecting "Corn Crop Water Deficit" within the "Applications" portion of the website. Data for the last 10 days reveal a range in corn crop water deficits from 2.13 inches (the corn crop used 2.13 inches more water than was available from rainfall during that period) in Beach to -1.66 inches (there was 1.66 inches more rainfall than the crop used) in Michigan. The amount of water available from the soil to fill any deficit depends on the soil texture, rooting depth, and soil moisture content. A fully charged silty-clay loam soil can hold 5.4 inches of available water in the top three feet, enough for about three weeks of water use by a corn crop under conditions similar to those experienced in southwestern ND during the past 10 days.

When water stress is severe, leaves wilt, leaf margins curl inward, and leaves appear onion-like. The following table provides general guidelines as to the amount of yield loss associated with drought stress during different developmental stages. If water stress is not so severe that leaf tissue actually "fires" and dies, leaves can recover from drought once additional moisture is received.

Effect of four days of visible wilting at different development stages on corn yield.

Stage of development

% yield reduction

Early vegetative

5-10

Tassel emergence

10-25

Silk emergence, pollen shedding

40-50

Blister

30-40

Dough

20-30

Adapted from Classen, M.M. and R.H. Shaw. 1970. Water deficit effects on corn. II. Grain components. Agron. J. 62:652.

As indicated in the accompanying table, corn is most sensitive to drought stress during pollination and early grain filling. Fortunately, most corn in North Dakota is now well into grain filling and is more tolerant to drought stress than just after pollination. One reason that the corn plant tolerates stress during late grain filling is that kernels have gained sufficient mass that they are able to draw stored carbohydrates from the stem. These carbohydrates play an important role in the health of the stem. It is, therefore, common for corn plants that have been subject to drought stress during late grain filling to have weak stems, to develop stem rots and to experience greater lodging than unstressed plants. Harvest severely stressed fields in a timely manner to avoid harvest losses that are associated with lodging.

drought stress during vegetative development
Drought stress during vegetative development of corn

severe drought stress
Beginning of severe drought stress during grain-filling of corn

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

 

AFTER HARVEST ….. PREPARATION FOR THE FUTURE

The small grain, canola, and field pea crop harvest is nearing completion and preparation and planning will take place for next year’s crop. The cool-season crops which were planted early tended to have the highest yield potential this year. During some parts of the 2007 growing season there were many fields with saturated soil conditions, which delayed planting or caused crop injury in lower parts of the fields.

Water management is an important factor in crop production and many producers already have surface drainage ditches in their fields. The next management step is to consider if the subsurface moisture can be managed as well. Water management is the use of surface ditches, subsurface permeable pipes, or both, to remove standing or excess water from poorly drained fields.

During the late 1800s, European settlers in the Upper Midwest began digging drainage ditches to remove excess water from the wet areas of their fields to nearby streams and rivers. Later, producers in what is now the "corn belt," increased drainage by installing subsurface drainage pipes generally at a depth of around three feet. Until the 1970s, most subsurface drainage pipes were made from short, cylindrical sections of concrete or clay called "tile." Terms like tile, tile drainage, and tiling are still used, even though most drainage pipe now is perforated polyethylene tubing.

When installing a subsurface drainage system, pipes are either strategically placed in a field to remove water from isolated wet areas or installed in a pattern to drain an entire field. Many soils in North Dakota have poor natural internal drainage and remain waterlogged for several days after excess rain. This prolonged wetness prevents timely fieldwork and causes stress to growing crops because saturated soils do not provide sufficient aeration for crop root development. The roots of most crops grown in North Dakota cannot tolerate excessively wet conditions for more than a few days.

Farmers must make a significant financial investment when installing an agricultural sub-surface drainage system. This investment is often made for the following major reasons:

1) Tile drainage usually increases crop yields (and potential quality) on poorly drained soils by providing a better environment for plants to grow, especially during years with wet periods.

2) The systems generally help improve field conditions for timely tillage, planting, spraying, and harvesting.

3) The drainage systems are long term improvements in the farming operation and tax laws allow writing off tile drainage costs (see your accountant).

Agricultural engineers have developed depth and spacing guidelines for installing drainage pipes. The newest and most comprehensive system available is controlled drainage, which has become recognized as an effective practice. This practice involves placing simple water control structures at various locations in the tile system to control the water table in the soil based on the management decision of the producer.

It takes time to design a tile drainage system for a field and to obtain the necessary permits. The best period to tile a piece of land is after cool season crops have been harvested. Tiling can be done till the soil freezes.

Information about tile drainage in our region (and the source for this article), can be found at:

http://d-outlet.coafes.umn.edu/.

Installing a tile drainage system
Installing a tile drainage system

Hans Kandel
NDSU Extension Agronomist
hans.kandel@ndsu.edu


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