During the last two decades agriculture has been subjected to many strains and stresses- social, economic, physical, and biological. Infestations of noxious weeds and insect pests have in some instances necessitated changes in crops grown and in farming practices. Changes in precipitation have induced alternate expansion and contraction of cultivated acreage in certain areas. Improved machinery has reduced the demand for farm labor, caused shifts in crops grown and in farm population. Changes in dietary habits have increased the demand for some farm commodities and decreased the demand for others, while wide fluctuations in farm prices have wrought rapid changes in the economic well-being of rural people. Relatively low precipitation in wes...