Figure 1. Example of a Watermark sensor reading from 3 ft deep on a datalogger.
View crop water use from around the Nebraska at the Nebraska Ag Water Mgnt Network.
Location 1: 2 miles west of Hooper, rainfed no-till corn after soybeans on Moody Silty Clay Loam soil (about 2.2″ of available water per foot)
July 22 – July 29
Weekly Rainfall & Crop Water Use for July 22 – July 29:
Rainfall = 0.0″
ET Reference Reading = 1.5
Corn Water Use (R3 milk stage) = 1.65″
Soil Water Depleted at Depth (Sensor Reading) on July 29:
1 ft = 0.61″ (72)
2 ft = 0.63″ (74)
3 ft = 0.00″ (32)
Total water depleted = 1.24″
Total available soil water for use before crop stress (50% of soil water depleted in top three feet) occurs: 2.06″
Seasonal Summary (view previous weekly crop water use at NE Ag Water Mgnt Network):
June 10 – July 29 Rainfall: 9.2″
June 10 – July 29 Corn Water Use: 8.3″
Total June 10 – July 29 (Rainfall – Crop Water Use) Surplus: 0.9″
Check out the Nebraska Drought Monitor Map too, new map release on Thursdays each week.
Location 2: 5 miles east of Winslow, irrigated soybeans after corn on Belfore Silty Clay Loam soil (about 2.0″ of available water per foot)
July 22 – July 29
Weekly Rainfall & Crop Water Use for July 22 – July 29:
Rainfall = 0.1″
Irrigation = 0.0″
ET Reference Reading = 1.3
Soybean Water Use (R3 beginning pod stage) =1.43″
Soil Water Depleted at Depth (Sensor Reading) on July 29:
1 ft = 0.51″ (60)
2 ft = 0.45″ (53)
3 ft = 0.43″ (51)
Total water depleted = 1.38″
Total available soil water for use before irrigation should start (trigger point to start pivot is 35% of soil water depleted in the top three feet): 0.70″ or about 3-4 days from now.
Seasonal Summary:
June 23 – July 29 Rainfall: 5.3″
June 23 – July 29 Soybean Water Use: 6.6″
Total June 23 – July 29 (Rainfall – Crop Water Use) Deficit: 1.3″
June 23 – July 29 Irrigation: 0.0″
Location 3: 2 miles north of Arlington, irrigated no-till corn after soybeans on Belfore Silty Clay Loam Terrace soil (about 2.0″ of available water per foot)
July 22 – July 29
Weekly Rainfall & Crop Water Use for July 22 – July 29:
Rainfall = 0.0″
Irrigation = 0.8″
ET Reference Reading = 1.3
Corn Water Use (R3 milk stage) = 1.43″
Soil Water Depleted at Depth (Sensor Reading) on July 29:
1 ft = 0.46″ (54)
2 ft = 0.49″ (57)
3 ft = 0.75″ (95)
Total water depleted = 1.69″
Total available soil water for use before irrigation should start (trigger point to start pivot is 35% of soil water depleted in the top three feet): 0.48″ or about 2 days from now.
Seasonal Summary:
July 1 – July 29 Rainfall: 2.6″
July 1 – July 29 Corn Water Use: 6.0″
Total July 1 – July 29 (Rainfall – Crop Water Use) Deficit: 3.4″
Total July 1 – July 29 Irrigation: 0.8″
Frequently asked questions (FAQ):
Why are we letting the soil dry down or get depleted when we have irrigation? The goal of irrigating corn and soybeans in this area is to ensure we don’t cause any water stress (50% of soil water depleted) yet provide some storage capacity for future rainfall events. Because it can take about 3 days to irrigate a field, we want to leave about 4 days worth of crop water use stored in the soil above the point of causing water stress on the crop. Therefore we can deplete about 2″ of soil moisture in the top 3 feet in a silty clay loam soil in this area before we need to start the pivot. If we apply 1″ with the pivot, that still leaves room in the soil to store another 1″ from a rainfall event in the near-term.
