Exam 1 Soils 456  Take home test. Due in class on March 7 Bring hard copy and floppy disk. No class on March 4 to work on examination.

 

  1. List the different type of irrigation systems and explain the advantages and disadvantages of each one. Get information about system from class notes and from internet. Do a search on the Internet for the different systems. Points 15

  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 Pecan field at Stalman’s farm located 5 miles south 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 medium ribbon and does not feel gritty

      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

      Sample depth 3 ft      soil does not stays in a ball when squeezed and does not form a ribbon.

 

What are the soil textures with depth and what is the total available water holding capacity of the 3 ft root zone. Use table 6.3 in your book for the water-holding capacity of different textured soils. Show all calculations. Also what is the soil order?  Points 15

 

  1. Explain what controls the infiltration process and why the infiltration rate starts out high and the decrease to the final infiltration rate close to the hydraulic conductivity of the soil. Explain what impact water high in sodium might have on the infiltration rate and why?  Points 15

  2. If the final infiltration rate of a silt loam soil in 0.40 inches/ hr and the application rate of a sprinkler system is 0.5 inches/hr and the land is rolling have a 15 to 20 % slope what will happen to the irrigation water.  Points 10

  3. If a field that has a clay loam soil was planted to cotton on May 1 2000 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


  4. The city of Alamogordo gets its water from a Lake in the mountains with the surface of the lake located at 6000ft. The bottom of the lake is at 5900 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

 

7. New Mexico State University needs to install a flood irrigation system using underground pipe and alfalfa valves to irrigate an alfalfa field. The turnout from the irrigation ditch  is 4 cfs of flow when the value is fully opened. The width of the field is 500 ft and an alfalfa valve is located every 100ft. The last alfalfa valve is located 450 ft from the turnout.. The field is divided into boarders that are 100 ft wide and 400ft long and one alfalfa valve is open at a time to irrigate each of the five boarders. The head of the water needed at the alfalfa valve located on the surface of the land is 1 ft in order to discharge 4cfs and the head of water at the inlet turnout is 5 ft. Ignore the friction loss through the turn out and alfalfa valve. What size inside diameter pipe must be installed to have sufficient head at the last alfalfa valve? The pipe is pvc with a C coefficient of 150.  Pipe size for large pipe is either 6 inch, 8 inch, 10 inch, 12 inches  in diameter. The inside diameters are 5.988, 7.958, 9.948, 11.938.  Show all calculations.  Points 10