1991 Annual Report for ANC91-004
Influence of Cropping Systems on Contamination of a Shallow Aquifer in the Northern Great Plains
Summary
Rationale:
Several different farming methods are being termed "sustainable agriculture," although each
practice uses various sets of inputs to maintain similar levels of production. The purpose of this
study was to assess the environmental integrity and the economic sustainability of these
contrasting approaches.
Objectives:
1) Examine the influence a "Conventional," "Integrated Input," and "Biological" cropping system
would have on pesticide and nitrate contamination of a shallow contained aquifer.
2) Evaluate the potential of each cropping system to maintain effective long-term sustainable
crop production.
3) Determine and compare long-term economic stability of each of the cropping systems, based
on costs and returns of production and environmental integrity.
Methods:
To assess the environmental impact of each cropping system, levels of pesticides and nitrates
were measured in a shallow confined aquifer underlying each test plot. Sustainability was
evaluated by measuring the available soil nutrients, soil structure, and soil organic matter prior to
planting and following harvest each year. Economic assessment was conducted by accounting for
all external costs, yields, and price paid for each crop. A spring wheat, Triticum aestivum (1992),
sunflower, Helianthus annuus (1993), and fallow (1994) sequence was applied to each cropping
system.
Results:
In all cases, elevated nitrate concentrations in the Carrington aquifer were highly variable,
sparsely replicated, and sporadic, indicating that nitrate movement was occurring primarily as
localized preferential flow at all sites. In six pesticide sets there were no plausible detections of
pesticides under any of the treatments. Spring wheat yield and yield components were similar
across the different cropping systems except for seed protein, which was higher under the
Conventional and Integrated cropping systems. The Biological system resulted in a significantly
lower yield than the other two systems. This was probably the result of low available nitrogen,
resulting from slow decomposition and mineralization of existing organic matter. It is difficult to
draw any final conclusion from the present results because Biological cropping systems usually
take many years to reach a state of equilibrium, especially in the north, where growing seasons
are short.
Total costs of inputs applied to the soil, plus cost of the field operations vary between the
production systems for spring wheat and sunflower. The Conventional spring wheat had the
lowest cost per acre followed by the Biological. For sunflower, the Biological practices had the
lowest total cost, followed by the Conventional. The Integrated practice system had the greatest
total cost per acre for both spring wheat and sunflower.
Conventional production resulted in the greatest return to land, labor, and management for both
spring wheat and sunflower production. However, since the evaluation of these three
management practices does not include long-term costs or impacts on the environment or on the
health of the laborers, there is an opportunity for determining a trade off for short-term returns.