Doctoral Dissertations

Date of Award

8-1981

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Agricultural Economics

Major Professor

Luther Keller

Committee Members

Cuskaden, Brown, Klindt, Safley

Abstract

The purpose of this study was to develop a method for determining the size of manure storage structure which would minimize the cost of operating a liquid manure and commercial fertilizer application system on any given dairy farm.

An earthen manure storage structure of 193,646 gallons (6 months storage) was determined to be optimum for a synthetic 60 milking cow dairy farm. An earthen manure storage structure capable of storing manure for 8.5 months (500,000 gallons) was optimum for a synthetic 100 milking cow dairy farm, utilizing pasture. An earthen manure storage structure of 630,000 gallons (9 months storage) was shown to be optimum for a synthetic 100 milking cow dairy farm, utilizing a drylot. Manure storage structures, fabricated from metal or concrete staves, were inferior to structures fabricated from earth on a cost basis as long as manure was maintainable at a moisture content of less than 92 percent in the earthen structure.

The optimum manure storage structure size depended upon a number of factors. The size of and distance to fields utilized for corn silage greatly influenced the optimum amount of manure storage. Increasing the price of commercial fertilizer by 50 percent increased the optimum amount of manure storage on a synthetic 60 milking cow dairy farm from 193,646 gallons to 320,000 gallons.

Injecting manure, rather than surface applying it, normally reduced the optimum amount of manure storage and the cost of operating a liquid manure and commercial fertilizer application system. The cost of meeting the plant nutrient requirements of an acre of corn silage was reduced from $101.43 with surface application to $77.83 with manure injection.

The linear programming model, utilized in the study, was tested for validity by varying the value assumed for key parameters. The analysis did not uncover any erratic or implausible results; however, model validity was shown to depend upon explicit knowledge of the moisture content of manure prior to land application and upon the nutrient composition of manure as it is produced.

The model showed little sensitivity to the value assumed for the plant nutrient loss rate from field applied manure over a range from 1.5 percent to 2.5 percent per month. Varying the amount of manure input to the liquid manure system and varying the time required for the surface application of manure produced very small changes in the cost of operating the system and in the optimum manure storage structure size.

A hand-held programmable calculator program was developed which is capable of determining the optimum manure storage structure size for any given dairy farm. The calculator program utilized a branch and bound type algorithm and produced results generally comparable to those obtained with the linear programming model.

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