Pasture Irrigation. Irrigated Pastures l Maximum production from irrigated pastures requires timely...
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Transcript of Pasture Irrigation. Irrigated Pastures l Maximum production from irrigated pastures requires timely...
Pasture Irrigation
Irrigated Pastures
Maximum production from irrigated pastures requires timely irrigation and the exclusion of livestock when the soils are wet.
What effects irrigation?
Type of soil– How much and how long to apply
Plant water use - (ET or Consumptive use)– how much and how often to apply
Soil properties
Plant growth depends on the soil– depth– texture– Limiting factors (i.e... hardpans)
Irrigation also depends on the soil– Infiltration– Water holding capacity– Limiting factors (i.e... hardpans)
Soil Types
Infiltration
Infiltration is define as how long the water takes to move through the soil– this effects the length of an irrigation – also runoff and deep percolation
What is water holding capacity?
The soil is made up of solids and voids or pore space
Pore space is made of a water and an air component
The soil is limited to how much water it can hold, thus water holding capacity
Water holding capacity very dependent on soil texture
What happens if too much water is applied?
Fills all the pore space - saturation– wetlands
Drainage downward - Deep percolation– water unavailable for plants– loss of nutrients
Is all the water in the soil available for the plants?
NO Available water is between field capacity
and wilting point. These are measured as pressure required to extract the water
To reduce plant stress keep water extraction to about 50% of the available water
How does a plant extract water?
Most of the roots, soil micro-organisms and available plant foods are concentrated in the upper one or two feet of the soil
From the preceding slide we can see that Seventy percent or more of the water used by grasses and legumes is taken from that area also.
What determines how fast the plant uses water?
Growth stage Location Climate
– wind, temperature, humidity, Solar radiation, ground temperature
Consumptive use
Various methods have been determined to predict crop water use
Most are not direct measurements but use empirical methods
Where can this information be obtained?– Local NRCS offices– State department of Water Resources– Internet
Irrigation Frequency
We know how much water the soil holds We know how much and how fast the plant
uses the water We can estimate how often and how much
water to apply
What is the Goal?
Maximum production If the interval between irrigation is too long
the grasses go dormant and production and quality are lost
Current research shows that alfalfa-grass on deep medium-textured soils decline occurs after 15 days. Clover is approximately 7 days
The goal of Irrigation
Replace used water with as little waste as possible (runoff and deep percolation)
Runoff carries pollutants in to other water bodies, has a bad public perception
Deep percolation - not visible, but can create temporary water tables, drive out soil air and can leach plant foods
Too much water can also reduce yields as shown in the following graph
Irrigation Frequency and
Grazing Schedules Optimum irrigation frequencies as well as
the amount of water to be applied each irrigation has been determined for most crops and soils
It must be correlated with the grazing schedules to be used effectively
Dry out time
Each irrigation must be scheduled to allow adequate dry-out time before stock are admitted.
Dry-out periods of 3 to 4 days are adequate for most soils
Without dry-out time compaction and damage to the plants
The dry-out period plus the number of days each pasture is to be grazed (grazing period) within the rotation cycle plus one day to irrigate should be equal or less than the planned irrigation frequency
Formula No. 1
Dry - out period + Grazing period +1= Irrigation frequency
or
Irrigation frequency - Dry out period -1= Grazing period
Formula No. 2
Number of pastures =Regrowth period(days)
Grazing period(days)1
Formula No. 3
Grazing cycle= grazing period number of pastures
Formula No. 4
Irrigation Interval (days) numberof irrigations = grazing cycle
Once Irrigation cycle equals grazing cycle– Don’t adjust irrigation interval to meet seasonal
water needs. – In cooler months that require less water - just
apply the water for shorter time periods instead of adjusting the irrigation interval
Studies show...
1. Shortening the irrigation interval requires an increase in the number of pastures and a reduction in the grazing interval
2. That 2 or more pastures can be watered at a time when there are an even number of pastures or when the grazing period is a multiple of the irrigation interval. Works good for when water is delivered on a rotational basis.
3. That a different pasture is watered each time for odd number of pastures unless the grazing period is a multiple of the irrigation interval. Works best with sprinklers or water delivered on a demand basis.
4. That flexibility in irrigation intervals and grazing periods increases as the number of pastures are increased.
Example
DetailsGiven: 40 acres, deep medium textured soil
Grass clover pasture, Water use 0.20in/d
Soil water 2 in/ft, root depth 3ft flow rate 100 inches, Soil intake .3in/hr
Find: Irrigation frequency, Grazing period,
number of pastures, grazing cycle, and
irrigation cycle, irrigation set times
Step 1. Find irrigation frequency
Soil water x root depth= total water2in/ft x 3ft =6in
Use 50% of total water 6in x .5 = 3in3in available water
available waterwater use /day
3020
15inin d
days. /
Irrigation frequency = 15days
Solution:
Step 2. From Tech note select a dry out period of 3 days grazing period = 15days - 1 day - 3days = 11 days
Step 3. From tech note select regrowth period
Step 4. Calculate the grazing cycle
grazing period x number of pastures = 3x11 = 33 days
Doesn’t quite match
Number of pastures =regrowth period
grazing period 1
22
111 3
adjust drying time to 4 days and regrowth time to 20 days. this gives a grazing period of 10 daysand a grazing cycle of 30 days
irrigation interval 2grazing cycle
15 230
1
Good !!
P1
P2
P3
Irri
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on
Irri
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Irri
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on
Irri
gati
on
Irri
gati
on
Irri
gati
on
Irri
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on
Irri
gati
on
Irri
gati
on
10 days
20 days
14 days
20 days 20 days
20 days20 days
14 days
14 days14 days
14 days14 days
10 days
10 days
10 days
Step 5. Calculate set times
set time=inches applied
intake rate in/hr3inches.3in/hr
hrs 10
If you are sprinkling that’s fairly good. Use a 12 hour set.If you are flood irrigating then you need to add theadvance time for the water to get from the head of the field to the end. 2 hours just might do it, so 12hours set would probalby work for both.
Now let’s check efficiencies
40 acre field3 pastures/field
ac / pasture
100 miner inches = 2 cfs
13.33 ac 3 in = 40 ac-in = 3.33ac-ft needed
1333.
2 cfs = 4 ac-ft/day so 3.33ac-ft needed4ac-ft applied
083.
or 83% water each pasture in two sets 12hrs each
Summary Irrigation frequency 15 days Dry- out period 4 days Grazing period 10 days Regrowth period 20 days Grazing cycle 30 days 3 pastures 13 acres 2 set per pasture 12 hours per set 3 inches of water replaced at 83% efficiency
Questions