Exam 1 Soils 456.   Take home test. Due in class on March 10 Bring hard copy and floppy disk. No class on March 8 to work on examination.

 

1.     Explain under what conditions you would use sprinkler vs a flood vs a drip irrigation system to irrigate a soccer field in Las Cruces. Explain the advantages and disadvantages of each type of system and explain the reasoning behind your final choice of irrigation system.  The field is located on the east side of Burns Lake. Please look up the soil type and incorporate that knowledge in your answer. Points 15

 

Soil classified as beldon clay to Glendale clay loam Gf  

 

 

If the field is already dead level and the available water is a high enough flow q so that a high flow turn out can be used. Install an underground valve and risers with alfalfa values on them. Use 15 inch alfalfa valves and design supply field to be able to irrigate the entire soccer individual field without any boarders in the middle of the field. Flood irrigations would result in not being able to use field for 4 days after irrigation. Low infiltration might cause problem of drowning out grass.

Surface irrigation advantages

·        Low cost of operation

·        Low understanding of system to operate

·        Can be used on crops that are boarder or furrow irrigated

Disadvantages

·        Can not be automate easily

·        Can cause damage to crops if infiltration process takes more than 15 hr on heavy soils

·        Uniformity can be low if not used with high turnouts

·        Application efficiency can be low if not used with high turnouts

·        Fertilizer application in water may not be uniformly applied

 

The sprinkler system must be run at night and frequently so that the water supply must be sufficient to irrigate the field in 12 hrs. when the wind speed are low. Would install this system.

 

Sprinkler advantages-

 

Disadvantages

If the field has a lot of use then the sprinkler system may make the soil two wet to play on following a night irrigation and installing a buried system would be the best way.

 

Buried Surface irrigation advantages

·        Low cost of operation

·        Low understanding of system to operate

·        Can be used on crops that are boarder or furrow irrigated

Disadvantages

·        Can not be automate easily

·        Can cause damage to crops if infiltration process takes more than 15 hr on heavy soils

·        Uniformity can be low if not used with high turnouts

·        Application efficiency can be low if not used with high turnouts

·        Fertilizer application in water may not be uniformly applied

 

Buried Drip irrigation advantages

·        Can apply light frequent application daily or even more frequently

·        Can increase yield by preventing drying and wetting cycle

·        Can be automated

·        Can have fertilizer injected into system for furtigation

·        Low evaporation loss

Disadvantages

·        High cost

·        Long learning curve to operate requires trained operators

·        Maintenance is higher than flood or sprinkler

 

 

 



 

 

 

 

2. The feel method is used to determine the soil type and the moisture content for scheduling when to irrigate. A technician went to the Chile field located at a field located 5 miles north of Las Cruces and reported to you that he found the following information.


      Sample depth   1ft     soil stays in a ball when squeezed and makes a strong ribbon and does not feel gritty or very smooth

 

Answer soil is a clay.  1.51inches/ft

 

      Sample depth    2 ft    soil stays in a ball when squeezed and does not form a ribbon. The second foot shows subsurface horizon development with a gypsum layer

 

Answer soil is a loamy sand    0.99 inches/ft

 

      Sample depth 3 ft      soil does not stays in a ball when squeezed and does not form a ribbon, but the soil moisture content is the correct amount for analysis. 

 

Answer soil is a sand.  0.89 inches/ft

 

What are the soil textures with depth and what is the total available water holding capacity of the 3 ft root zone. Use the Saxton  calculator  to calculate  the water-holding capacity of different textured soils. Show all calculations. Also what is the soil order?  Show all calculations.  Points 15 

 

 

Total water holding capacity  3.39inches

 

2.     The water use of a lawn in April is 0.2 inches per day.  A sprinkler irrigation system with an application rate of 0.45 inch /hr was turned on for 1.5 hrs every three days  to irrigated a lawn located at a residence on Telsore Blvd. The front lawn had a slope of 15 percent and after the system ran for 40 minutes, runoff started to occur. The soil was a clay loam soil with a saturated hydrologic conductivity of 0.05 inch/hr.  Explain physically what was happing to the water applied by the sprinkler system and why the runoff started to occur after 40 minutes but not before that time.  A water samples was take and the soil was high in sodium with an Sodium Absorption Ratio of  7 .Explain what impact a high SAR had on the runoff problem and what you would do to fix the runoff problem?  Show all calculations.  Points 15
 

 

Answer   At the beginning of the infiltration process the main driving force is capillary force between the wet front and the dry soil below. As time occurs and the wetting front depth increases this force is decreased as the capillary force act over a long distance. Gravity then starts to be the main force cause water to move through the soil . The larger the pores in the soil the higher the infiltration rate. Sand has the highest infiltration rate.

 

 

High Sodium  or high SAR in the irrigation water will replace Ca and cause the clay particles in the soil to disperse decreasing the pore sizes and decreasing the infiltration rate causing runoff to occur sooner

 

 

 

 

 

 

 

 

 

4.  If a field that has a  loam soil was planted to cotton on May 1 2001 at the Leyendecker science center.  On what dates should the field be irrigated to prevent any reduction in yield due to moisture stress. The irrigation system is furrow and the runs are short so a flow of 1800gpm is applied to the 6 ac field and the time to irrigate the field is 5 hr. Please attach the excel spreadsheet to show your calculations. What is the irrigation efficiency of the furrow system? Show calculations for irrigation efficiency.  Points 25


qt=ad

q= 4.02 cfs

a= 6 ac

t=5 hr

d= 3.35 inches

 

 

 

see spreadsheet for answer

 

 

 

 

 

5. The city of Alamogordo gets its water from a Lake in the mountains with the surface of the lake located at 4720ft. The bottom of the lake is at 4600 ft. A pipe runs from the bottom of the lake to the city distribution site at 4220 ft. What is the water pressure at the distribution site? If you have a house that is located a mile away at an elevation of 4500ft and the friction loss is ignored what is the pressure at your water meter.  Points 10

 

Difference in hight between lake surface and distribution point.    4720-4220= 500ft /2.31= 216 lb/inch^2

 

House difference in elevation   4720-4500= 220/2.31= 95 lb/inch^2

 

 

 

 

 

 

 

 

 

 

6. A cotton field is flood irrigated with a high flow turnout that discharged 6750 gmp into the field. The boarder in the field is 600 ft long and 120 ft wide. The irrigation-scheduling model determined that a irrigation was due on May 20 and a 3.5 inch irrigation was need to fill the root zone which would result in 2.8 inches of water being stored in the root zone. The farmer tells the irrigator to go and turn water into the field until the water reaches 75% of the way to the end of the field and then shut the water off. The irrigator does this and reports to the farmer that it took 30 minutes to irrigate that boarder. The field contains 6 boarders and the irrigator was through irrigating after 3 hr. 

 

 

What was the depth of water the irrigator applied to the field? What was the target efficiency and what was the final irrigation efficiency that the farmer calculated that occurred using the rule of thumb to shut the water off when it reaches ¾ of the length of the field and let it cost the rest of the way.. Point 15

 

Qt=ad

6750 /448= 15 cfs

area= 600* 120/43560= 1.65 ac

 

t=.5 hr

 

d= qt/a

d= 4.45 inches applied

 

Target efficiency 2.8/3.5=80%

Irrigation efficiency  2.8/4.45= 63%. 

 

7. Explain the different type of irrigation scheduling methods and the advantages and disadvantages of each and which method you would use to schedule irrigation for a large park. There were eight method presented at the Chile conference talk by Dr. Sammis  Points 20

 

•Condition of crop

advantage easy requires no measurement but when the crop shows stress it is two late.

 

 

•Soil moisture feel

Minimal equipment-soil auger requires educated hand hard to learn, also time consuming requires three samples in different locations in field.

 

•Soil moisture sensing device

Easy to use if calibrated for your soil, cost time and money to install. Must be monitored and data plotted or connected to data logger and data down loaded.

 

 

•Calendar scheduling

easy to use but has not relationship to the needs of the crop. Over irrigate at the beginning and end of the season when using fix time interval.

 

 

•Scheduling by irrigation district

Works find if the irrigation district will publish data in the paper or on a web site and you are using drip or sprinkler irrigation. Does not do the water balance for flood irrigation

 

 

•Commercial scheduling service

Best method but highest cost

 

 

• Media reports

Does not have water balance ok for trickle or flood but may not be timely. Must be published every day by the paper. They skip days on the weekend when no one gives them the data

 

•Computer models

Complex to use and may not be accurate if inputs are not correct.