Kenneth J. Nicol

Models and projected results of soil loss restraints for environmental improvement through U.S. agriculture

Abstract Resource use and production patterns in agriculture which relate to enviromental quality are closely related to the stage of economic development in the sector. Purely subsistence agriculture forms nearly a “closed” system in the use of inputs and outputs. Highly developed agriculture is an “open” or “interdependent” system with other sectors. Resource prices and productivities cause it to import and intensively use heavy dosages of capital materials. Accordingly, it increasingly exports a greater proportion not only, of its product but also of its inputs. Resource prices also favor larger and more specialized units which in turn favor row cropping or monoculture and specialized feed lots. The resulting increase in soil erosion or sedimentation and concentration of animal wastes both provides increased environmental contaminants and a greater vehicle for transport of unassimilated nitrates, phosphates and pesticides. These tendencies have progressed far under the stage of development in U.S. agriculture. Accordingly, legislation is being posed or enacted to limit levels of chemical use, soil erosion and concentration and export of animal wastes. To evaluate the economic, spatial, national and regional impacts of these environmental restraints in agriculture, we have built a set of models which incorporate the entirety of U.S. agriculture and the detail of the regions as well. Impacts can be measured at the national, regional, individual resource, or commodity level. The models include 223 regions, 1 891 land resource groups, 51 water regions and 30 consuming or market regions. They are composed of 3 500 equations and 37 800 variables. They include equations for each land resource group, water supplies, crop supplies, livestock supplies, commodity demands, transport services, nitrogen balances and soil loss restraints. They have been applied to U.S. agriculture to evaluate agricultural production possibilities when soil loss and nitrogen sources are limited under different export levels. When soil loss is restrained, annual national soil loos is estimated to be 727 million tons, as compared to 2 677 million tons in the absence of restrictions. The models select among land use technologies for each of the 1 891 land resource groups under an imposed 5-ton per acre soil loss. They indicate the need for halving of straight row farming and its elimination entirely on certain land classes, a ten-fold increase in terracing and a tripling of contour practices under conventional tillage. They specify infinite relative increases in contouring, terracing and strip cropping under reduced tillage farming methods. Greatest changes are indicated for South Atlantic and South Central states where rainfall is abundant. The least amount of change is indicated for the Great Plains, North West and South West states with limited rainfall and greater expanses of level land. Even with imposition of a national limit on soil loss, the flexibility and capacity of U.S. agriculture is great. Domestic and export demand projected to the year 2000 could be met with only modest increases in supply prices as changes in farming technology and land and water use are implied through soil loss limits. Weighted farm level commodity prices would increase by somewhat less than 10% under the imposition of soil loss restraints at the 5-ton level.

NATIONAL MARKETS AND THE IMPACTS OF STATE LAND USE AND ENVIRONMENTAL PROGRAMS

Environmental and resource quality recently have become special public concerns. A few states have already enacted legislation posing land use-environmental restrictions. Vermont, Hawaii, Colorado, Maine, Massachusetts and New York, passed land use laws. Illinois formed a Pollution Control Board to quantify nutrients and sediment polluting streams and suggest action. In 1971, the Iowa Legislature passed the “Conservancy District Act,” creating soil conservancy districts “to preserve and protect public interest in soil and water resources for future generations.” Legislation centers on soil erosion and sedimentation. Erosion is declared a nuisance if it results in siltation damage. The law sets allowable soil loss limits on land at one to five tons per acre per year, depending on soil type.

Economic trade-offs to limit nonpoint sources of agricultural pollution

A national model has been built which allows analysis of physical and economic trade-offs as soil loss per acre is limited to specified levels in each major land group of the nation. Crop variables with their associated conservation practices are developed for each of 1891 land groups in 223 agricultural producing regions and 51 water supply regions. The regions and soil groups are made interdependent through regional commodity demands and a transportation submodel. Hence, changes in cropping systems and erosion control practices in one region are simultaneously expressed in effects on other regions. Soil loss limits are set at 10, 5, and 3 t per acre. The 10 t limit does not have a large impact on interregional production patterns and farm comodity prices. However, the 5 and 3 t limits, either singularly or in combination with different export levels, cause rather marked increases in commodity prices. Also at limits of 5 and 3 t, considerable shifts take place among regions in the crops grown and the erosion control methods used. Regions with erosive soils sacrificed in reduced income; regions with level soils can crop more intensely and gain greater income. Conservation practices such as reduced tillage increase the amount of pesticides needed in some regions and pose special environmental problems. The South Atlantic region is affected most by soil loss limits to control nonpoint pollution. The Great Plains regions with more level land and limited rainfall are affected least.