Scheduling Last Irrigation Cycle Holt Boyd Podcast

Scheduling Last Irrigation Cycle - September 1, 2022 - Amy Timmerman, Extension Educator

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• [0:00] This week’s Extension update is with Extension Educator Amy Timmerman.
• [0:05] With pumping costs ranging from $6-15/acre-inch this year, an opportunity to save money
• [0:12] by cutting back irrigation as early as possible sounds like a good strategy.
• [0:16] Correctly timing the last few irrigations of the season offers an excellent
• [0:20] opportunity to save some water and money.
• [0:24] Factors such as the amount of water a soil can hold, the amount of water
• [0:28] a crop will use until it reaches maturity, and the maximum allowable soil water depletion
• [0:33] should be considered when deciding the last few irrigations of the season.
• [0:37] In addition to water and dollar savings, another benefit of leaving the fields as
• [0:42] dry as possible without lowering yields is the potential to reduce issues with
• [0:46] nutrient leaching and increase the amount of precipitation stored
• [0:50] during the offseason.
• [0:52] The amount of water used by the plants during the tail end of the growing
• [0:56] season changes from crop to crop.
• [0:58] With different crops, it is important to know how
• [1:00] weather conditions affect crop water use.
• [1:03] For instance, weather conditions will affect the water use of the soybeans
• [1:07] because they tend to mature based on daylength, as opposed to
• [1:11] corn and sorghum that mature based on growing degree days.
• [1:15] Thus, for corn and sorghum, hotter conditions will result
• [1:19] in more water use per day but will also mature the crop sooner.
• [1:23] On the other hand, soybeans may use more water during hotter weather conditions
• [1:28] but won’t mature quicker, resulting in greater total water use.
• [1:32] How much water corn and soybean will need until they reach maturity
• [1:36] based on each growth stage is critical to know.
• [1:40] This is the baseline information needed when it comes to deciding
• [1:43] the last irrigation of the season.
• [1:46] Corn at dough stage has approximately 34 days to maturity and
• [1:50] will require 7.5 inches of water to maturity.
• [1:54] Beginning dent has approximately 24 days to maturity
• [1:58] and will required 5 inches of water.
• [2:01] ¼ milk line is approximately 19 days to maturity and will need an
• [2:05] additional 3.75 inches of water.
• [2:09] ½ milk line is approximately 13 days to maturity and will need an
• [2:12] additional 2.25 inches of water.
• [2:16] And finally ¾ milk line is approximately 7 days to maturity and will need
• [2:20] an additional 1 inch of water.
• [2:22] Soybeans at growth stage R4 is approximately 37 days to
• [2:26] maturity and will require 9 inches of water to reach that stage.
• [2:31] R5 are approximately 29 days from maturity and will require 6.5 inches of water.
• [2:38] R6 soybean are approximately 18 days from maturity
• [2:41] and will require 3.5 inches of water.
• [2:44] Soybeans at grow stage R6.5 where the leaves are beginning
• [2:48] to turn yellow are approximately 10 days from maturity and will still require 1.9 inches of water.
• [2:56] We should always keep adequate soil moisture levels to maximize
• [2:59] yield on irrigated fields if we have the water.
• [3:03] During peak water use, UNL recommends maintaining soil water storage levels
• [3:07] above 50% of plant available water in the top three feet of soil.
• [3:11] As plants approach the end of the cropping season,
• [3:14] the days are getting shorter and cooler and their leaves begin to lose
• [3:18] the ability to transpire water, which opens an opportunity
• [3:22] to let the soil dry to a lower water content without affecting yield.
• [3:26] The UNL recommendation is to lower the soil water content
• [3:30] to 40% of plant available water to a four-foot depth after the dough
• [3:34] stage in corn and R4 or end of pod elongation in soybean.
• [3:39] Another factor besides knowing how much water the crops will use between now
• [3:43] and maturity is determining the amount of water stored in the soil.
• [3:47] A fine sand soil, for example, holds about one inch per foot of soil or
• [3:52] four inches on the top four feet of soil.
• [3:54] A silt loam soil, on the other hand, holds two inches per foot of soil or
• [3:59] eight inches on the top four feet of soil.
• [4:03] Assuming both soils are at field capacity,
• [4:06] the maximum amount of water that can be used is 2.4 inches which is 60% of four inches
• [4:12] for the fine sand soil and 4.8 inches (60% of eight inches) for the silt loam soil.
• [4:19] The last piece of information needed is the expected rainfall amounts
• [4:23] between today and the date the crop maturity.
• [4:27] While many parts of the state are very dry this year,
• [4:29] one should still keep in mind the long-term average rainfall in
• [4:33] determining that last irrigation cycle.
• [4:36] This has been Amy Timmerman with Nebraska Extension.