Timing is key when irrigating silage corn crops

WATER WATCH A host of factors needs to be considered with creating an irrigation plan, 
but careful monitoring of available soil moisture is crucial

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You need to add just the right amount of water to get a high-yielding, top-quality silage corn crop, says an irrigation expert.

“Growers are encouraged to properly manage irrigation by regularly monitoring soil water to ensure that the availability of water does not become a limiting factor in producing a high-yielding silage corn crop,” said Alan Efetha, an irrigation management specialist with Alberta Agriculture in Lethbridge.

Applying irrigation just before the available soil water is depleted to 60 per cent and replenishing available soil water near field capacity in the appropriate root zones is key, he said. Along with achieving the desired crop response, good irrigation management will also minimize soil degradation and protect water quality. But there several factors at play, including:

  • Soil fertility, crop nutritional requirements;
  • Soil-water-plant relationships;
  • Crop type;
  • Crop sensitivity to water stress;
  • Crop growth stages;
  • Availability of a water supply;
  • Rainfall, temperature, humidity, and net radiation; and
  • Irrigation system capabilities and limitations.

These factors should be used to develop a workable, efficient, and profitable irrigation scheduling program, said Efetha.

“A workable and efficient irrigation management strategy should be crop specific, one where water is used efficiently to meet a specific crop’s water requirements for maximum water productivity.”

Generally, the goal is to ensure that water is available at germination and in early development by applying light, frequent irrigations if there is no rainfall, he said. This method promotes vigorous growth and replenishes and increases available soil water content in the entire root zone during the pre-silking growth stages.

“Such a strategy will allow modern sprinkler irrigation systems to meet crop demand during the peak water-use period, which typically occurs during the silking and fruit-formation growth stages,” he said.

Irrigation scheduling works for silage corn because it is a warm-season crop.

Silage corn uses a significant amount of water for growth and cooling purposes. Typically, silage corn requires 500 to 550 millimetres of water per growing season when grown under optimum conditions that include a crop which is well fertilized, well irrigated, seeded in suitable row spacing, pest free, and with a uniform and optimum canopy and a plant population of 30,000 to 33,000 plants per acre. When silage corn is seeded into warm soils, greater than 10°, with available water between 60 and 100 per cent of soil capacity in early May in southern Alberta, silage corn will germinate and grow rapidly. Corn will reach a peak water use of nearly eight millimetres per day during the tasselling, silking and fruit-formation growth stages Crop water use declines to two to three millimetres per day during ripening.

Typically, the roots of silage corn grow to an effective water extraction depth of 100 centimetres in a well-developed soil, said Efetha. Root distribution is concentrated near the surface so silage corn obtains more than 70 per cent of its water from the upper half of its 100-centimetre active root zone. The active root zone changes from a few millimetres at emergence to a maximum depth of 100 centimetres at the tasselling and silking growth stages.

Ideally, soil water content in the top 50 centimetres should be greater than 60 per cent of readily available water at planting, he said. If seeded in a dry seedbed (less than 60 per cent of available in the zero- to 50-centimetre depth) in early May before irrigation water is available, the first and subsequent irrigations (15 millimetres per irrigation event) should be applied as soon as irrigation water is available. If the soil is very dry in spring, irrigation is recommended before seeding.

To maximize yields and quality, available soil moisture should not be depleted to less than 60 per cent in the upper half of the 100-centimetre root zone during the vegetative through silking growth stages. To prevent this, light and frequent applications should be used once available moisture levels hit the 65 per cent mark.

Silage corn is most sensitive to dry condition during the tasselling and silking growth stages, Efetha said. Moisture stress may desiccate silks and pollen grains, and also cause poor pollination, seed set, and barren ear tips. Silage corn roots reach maximum extension at the tasselling to silking growth stages and moisture should be monitored to a depth of 50 centimetres at this time, and then increased to 100 centimetres at the blister kernel growth stage.

The timing of the last irrigation to refill the root zone for silage corn depends largely on the soil texture, prevailing weather conditions, and availability of irrigation water. The final irrigation to refill the root zone may be applied between the dough and dent growth stages, a week to 10 days before harvest.

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