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FieldNET Irrigation Management Advantages
There are many advantages to remote monitoring of pivots and pumps.
These include:
Flexibility for current equipment
Effective tool for professional service providers
Development and use of Knowledge:
Reduced risk and less downtime
Enhanced best practices and stewardship:
Timing the Final Irrigation Using Watermark TM Sensors
Chris Henry Ph.D., Associate Professor and Water Management Engineer Rice Research and Extension Center
P.B.
Francis Ph.D., Professor University of Arkansas at Monticello
L.
Espinoza Ph.D., Soil Scientist Crop, Soil and Environmental Science
M.
Ismanov Ph.D., Program Technician Soils, Crop, Soil and Environmental Science
Arkansas Is Our Campus
This is the last in a series of three fact sheets on Watermark Soil Moisture Sensors.
The first fact sheet provides details on "How to Prepare, Test and Install Watermark Sensors." The second fact sheet discusses "How to Use Watermark Soil Moisture Sensors." This fact sheet provides a guide to using information from soil moisture monitoring to aid in irrigation termination decisions in corn and soybean production.
Timing the final irrigation of the season can be a challenging decision for crop managers.
The last irrigation should provide the water necessary to optimize yield.
It should IMPROVE profitability.
At times, rainfall can provide the last remaining water to carry the crop to maturity.
Irrigation is unnecessary.
Extending irrigation beyond what the crop requires is inefficient.
It also is costly because late season pumping typically is the most expensive due to increasing depth to groundwater after a long pumping season.
Prolonged irrigation also can delay harvest and exacerbate pest problems, which may reduce yield and quality.
For corn, the crop-based recommendation is to monitor ear maturity by examining the starch line development on kernels from the middle of the ear.
For furrow irrigated fields, irrigation termination is recommended when starch line movement is greater than 50%, and there is adequate moisture.
The final irrigation for soybeans is recommended to occur at growth stage R6 such that there is adequate moisture at R6.5.
are helpful, but they lack precision in specifying water needs to finish the crop or how to gauge how much soil moisture is available in the root zone.
This fact sheet provides a procedure to determine the amount of water available and needed to reach crop maturity.
Information in this fact sheet provides a crisp answer to when to stop irrigating.
Background: Monitoring Soil Moisture and Determining Allowable Depletion
For irrigation termination decisions, one should determine crop stage and then gauge whether the soil has adequate plant available water or if additional water is needed via irrigation.
The calculation is simply..
= Water needed to finish the crop
Water available in the root zone effective rainfall
If the plant water need value is positive, then irrigation or rain is needed.
If it is negative, no further irrigation will provide any benefit.
Irrigation is not completely effective due to application efficiencies.
Thus the amount of water that must be applied through irrigation must be adjusted for these efficiencies.
The amount of water that should be applied through irrigation is determined by dividing the plant water need by the irrigation efficiency.
It is not necessary to perform this calculation during the season, only for the last irrigation.
Irrigation Application Depth
= Plant Water Need Irrigation Efficiency
When making soil moisture determinations, the full rooting profile should be used.
In most soil types in Arkansas, this will be 30 to 36 inches.
While visual inspection of roots can be done using soil probes or shovels, generally it is most practical to utilize changes in soil moisture sensor readings to assess the effective rooting depth.
For the last irrigation of the season for both center pivots and furrow systems, it is recommended to use either a 45% or 50% allowable depletion.
This will allow the crop to use all remaining soil water, and it will save on pumping costs.
Using an allowable depletion of up to 60% is considered acceptable for the last irrigation, SO using 50% has a factor of safety included.
Table 1.
Plant Available Water for a Given Soil Matric Potential or Tension at 50% Managed Allowable Depletion
Soil Tension Sand Sandy Loam with Pan Silt Loam Clay
0 1.77 1.51 1.01 1.83 1.38
5 1.72 1.51 1.01 1.83 1.36
10 0.74 1.00 1.01 1.65 1.09
15 0.35 0.74 1.01 1.53 0.91
20 0.14 0.58 1.01 1.41 0.78
25 0.02 0.46 0.88 1.29 0.68
30 0.37 0.79 1.19 0.60
35 0.29 0.76 1.14 0.53
40 0.23 0.72 1.00 0.47
45 0.18 0.64 0.89 0.42
50 0.14 0.57 0.80 0.37
55 0.10 0.49 0.71 0.33
60 0.06 0.45 0.63 0.30
70 0.01 0.35 0.50 0.23
80 0.25 0.39 0.18
90 0.21 0.29 0.13
100 0.13 0.22 0.09
120 0.03 0.09 0.02
Source: Lab and model data of irrigated soils sampled and grouped from Arkansas farms.
Plant available water is dependent on soil texture.
The soil in the rooting zone has an upper and lower limit of storing water available to crop plants.
Water Holding Capacity determinations have been done for groups of Arkansas soils.
Table 1 shows WHC for average Watermark readings for different generalized soil textures at a 50% allowable depletion or Managed Allowable Depletion.
Charts for 35% and 45% allowable depletions and in-season decision making is provided in the second fact sheet in this series.
These charts provide the plant available water in inches per foot for an average soil tension value.
Thus, for a one foot average reading of 45 centibars in a clay soil, there are 0.42 inches of plant available water.
For an effective rooting depth of 30 inches or 2.5 feet, there are 1.05 inches of plant available water.
Four Steps to Irrigation Termination Using Sensors
Step 1.
Determine crop stage and water needed to finish the crop.
The amount of soil water typically required for plants to reach maturity varies with production region and system.
Crop water demand for corn is provided in Table 2 based on Nebraska research, and for soybean based on research in Marianna, Arkansas.
For corn at R5 growth stage with kernel development at 3/4 milk line, the crop is approximately 7 days from maturity (black
Table 2.
Crop Water Demand for Corn
Crop Growth Stage Kernel Development Days to maturity to mature Water needed
R4 Dough 34 7.5
R4.7 Beginning dent 24 5
R5 1/4 milk line 19 3.7
R5 1/2 milk line to full dent 13 2.2
R5 3/4 milk line 7 1.0
R6 Maturity 0 0
Table 3.
Crop Water Demand for Soybeans
Crop Growth Pod and plant Days to maturity Water needed

FieldNET Irrigation Management Advantages

There are many advantages to remote monitoring of pivots and pumps.

These include:

Flexibility for current equipment

Effective tool for professional service providers

Development and use of Knowledge:

Reduced risk and less downtime

Enhanced best practices and stewardship:

Timing the Final Irrigation Using Watermark TM Sensors

Chris Henry Ph.D., Associate Professor and Water Management Engineer Rice Research and Extension Center

P.B.

Francis Ph.D., Professor University of Arkansas at Monticello

L.

Espinoza Ph.D., Soil Scientist Crop, Soil and Environmental Science

M.

Ismanov Ph.D., Program Technician Soils, Crop, Soil and Environmental Science

Arkansas Is Our Campus

This is the last in a series of three fact sheets on Watermark Soil Moisture Sensors.

The first fact sheet provides details on "How to Prepare, Test and Install Watermark Sensors." The second fact sheet discusses "How to Use Watermark Soil Moisture Sensors." This fact sheet provides a guide to using information from soil moisture monitoring to aid in irrigation termination decisions in corn and soybean production.

Timing the final irrigation of the season can be a challenging decision for crop managers.

The last irrigation should provide the water necessary to optimize yield.

It should IMPROVE profitability.

At times, rainfall can provide the last remaining water to carry the crop to maturity.

Irrigation is unnecessary.

Extending irrigation beyond what the crop requires is inefficient.

It also is costly because late season pumping typically is the most expensive due to increasing depth to groundwater after a long pumping season.

Prolonged irrigation also can delay harvest and exacerbate pest problems, which may reduce yield and quality.

For corn, the crop-based recommendation is to monitor ear maturity by examining the starch line development on kernels from the middle of the ear.

For furrow irrigated fields, irrigation termination is recommended when starch line movement is greater than 50%, and there is adequate moisture.

The final irrigation for soybeans is recommended to occur at growth stage R6 such that there is adequate moisture at R6.5.

are helpful, but they lack precision in specifying water needs to finish the crop or how to gauge how much soil moisture is available in the root zone.

This fact sheet provides a procedure to determine the amount of water available and needed to reach crop maturity.

Information in this fact sheet provides a crisp answer to when to stop irrigating.

Background: Monitoring Soil Moisture and Determining Allowable Depletion

For irrigation termination decisions, one should determine crop stage and then gauge whether the soil has adequate plant available water or if additional water is needed via irrigation.

The calculation is simply..

= Water needed to finish the crop

Water available in the root zone effective rainfall

If the plant water need value is positive, then irrigation or rain is needed.

If it is negative, no further irrigation will provide any benefit.

Irrigation is not completely effective due to application efficiencies.

Thus the amount of water that must be applied through irrigation must be adjusted for these efficiencies.

The amount of water that should be applied through irrigation is determined by dividing the plant water need by the irrigation efficiency.

It is not necessary to perform this calculation during the season, only for the last irrigation.

Irrigation Application Depth

= Plant Water Need Irrigation Efficiency

When making soil moisture determinations, the full rooting profile should be used.

In most soil types in Arkansas, this will be 30 to 36 inches.

While visual inspection of roots can be done using soil probes or shovels, generally it is most practical to utilize changes in soil moisture sensor readings to assess the effective rooting depth.

For the last irrigation of the season for both center pivots and furrow systems, it is recommended to use either a 45% or 50% allowable depletion.

This will allow the crop to use all remaining soil water, and it will save on pumping costs.

Using an allowable depletion of up to 60% is considered acceptable for the last irrigation, SO using 50% has a factor of safety included.

Table 1.

Plant Available Water for a Given Soil Matric Potential or Tension at 50% Managed Allowable Depletion

Soil Tension Sand Sandy Loam with Pan Silt Loam Clay

0 1.77 1.51 1.01 1.83 1.38

5 1.72 1.51 1.01 1.83 1.36

10 0.74 1.00 1.01 1.65 1.09

15 0.35 0.74 1.01 1.53 0.91

20 0.14 0.58 1.01 1.41 0.78

25 0.02 0.46 0.88 1.29 0.68

30 0.37 0.79 1.19 0.60

35 0.29 0.76 1.14 0.53

40 0.23 0.72 1.00 0.47

45 0.18 0.64 0.89 0.42

50 0.14 0.57 0.80 0.37

55 0.10 0.49 0.71 0.33

60 0.06 0.45 0.63 0.30

70 0.01 0.35 0.50 0.23

80 0.25 0.39 0.18

90 0.21 0.29 0.13

100 0.13 0.22 0.09

120 0.03 0.09 0.02

Source: Lab and model data of irrigated soils sampled and grouped from Arkansas farms.

Plant available water is dependent on soil texture.

The soil in the rooting zone has an upper and lower limit of storing water available to crop plants.

Water Holding Capacity determinations have been done for groups of Arkansas soils.

Table 1 shows WHC for average Watermark readings for different generalized soil textures at a 50% allowable depletion or Managed Allowable Depletion.

Charts for 35% and 45% allowable depletions and in-season decision making is provided in the second fact sheet in this series.

These charts provide the plant available water in inches per foot for an average soil tension value.

Thus, for a one foot average reading of 45 centibars in a clay soil, there are 0.42 inches of plant available water.

For an effective rooting depth of 30 inches or 2.5 feet, there are 1.05 inches of plant available water.

Four Steps to Irrigation Termination Using Sensors

Step 1.

Determine crop stage and water needed to finish the crop.

The amount of soil water typically required for plants to reach maturity varies with production region and system.

Crop water demand for corn is provided in Table 2 based on Nebraska research, and for soybean based on research in Marianna, Arkansas.

For corn at R5 growth stage with kernel development at 3/4 milk line, the crop is approximately 7 days from maturity (black

Table 2.

Crop Water Demand for Corn

Crop Growth Stage Kernel Development Days to maturity to mature Water needed

R4 Dough 34 7.5

R4.7 Beginning dent 24 5

R5 1/4 milk line 19 3.7

R5 1/2 milk line to full dent 13 2.2

R5 3/4 milk line 7 1.0

R6 Maturity 0 0

Table 3.

Crop Water Demand for Soybeans

Crop Growth Pod and plant Days to maturity Water needed