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Monitoring Crop Water Use (06/18/20)

The recent hot and windy weather has had me thinking about crop water use and the potential for drought stress in the state if we don’t get some rain.

The recent hot and windy weather has had me thinking about crop water use and the potential for drought stress in the state if we don’t get some rain. One way to monitor crop water status is to use the crop water use app in NDAWN. Daily water use by a crop is dependent on the crop, its stage (greater leaf area means greater water use), temperature, relative humidity and wind speed. Figure 1 charts the daily water use with this app at the Hettinger Research Extension center. Because of its greater leaf area, wheat is currently using more than twice the water of corn. Additionally, from these data one can see the impact of daily weather on water use. For example, the water use by wheat on June 13th was more than twice that recorded on June 9th.

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This app also can be used to monitor the relationship between water use and the amount of rainfall received. Currently, the crop water deficits (transpiration minus rainfall) for wheat are large with the greatest deficits (the larger the number the larger the deficit) in the southwest (Figure 2). For corn the scenario is more positive (Figure 3), with many stations reporting slight surpluses of water (more rainfall than crop use resulting in negative deficits).

The fact that water deficits are positive, does not necessarily mean that the crop has suffered from drought stress, as these calculations do not consider the amount of water available in the soil. The plentiful rainfall last fall and the snow melt this spring filled the soil profile in many regions of the state. Soils can provide 1 to 2 inches of water per foot of depth (depending on its texture), meeting the water use requirements of the crop for many days before the crop experiences drought stress. When soil moisture is depleted and the plant becomes “stressed”, it will reduce transpiration by closing the stomata. While this reduces water loss from the plant, it also reduces the amount of CO2 available to the plant for photosynthesis. Reduced photosynthesis means reduced plant growth which in turn translates into reduced plant size and reduced yield potential. Leaves soon wilt especially during the heat of the day. with severe moisture stress, plant tissues desiccate and eventually die when the stress is significant enough.

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Joel Ransom

Extension Agronomist, Cereal Crops

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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