U.S. Department of Agriculture: Agricultural Research Service, Lincoln, Nebraska


Document Type


Date of this Version



Great Plains Soil Fertility Conference, March 5-6, 2002


Site specific management (SSM) has the potential to improve both economic and ecological outcomes in agriculture. Effective SSM requires strong and temporally consistent relationships between identified management zones, underlying soil physical, chemical and biological parameters defining yield potential, and crop yield. In a farm-scale (250 ha) experiment in semiarid northeastern Colorado, each of eight 31-ha fields was individually mapped for soil apparent electrical conductivity (ECa) and classified into four management zones (ranges of ECa). Soil analyses revealed a strong negative relationship between ECa zones and soil parameters associated with innate fertility (P ≤ 0.06). The objective of the present study was to further evaluate ECa as a basis for SSM by examining its relationship to actual yield using two years of yield maps for winter wheat (Triticurn aestivum L.) and corn (Zea mays L.). Within field wheat yields were strongly related to ECa, particularly when regressing mean wheat yields within ECa classes against mean ECa within ECa classes (r2 = 0.95 to 0.99). Yield response curves revealed a boundary line of maximum yield that decreased with increasing EC". In this semiarid dryland system, ECa-based management zones can be used in the SSM of wheat for: (1) yield goal determination, (2) soil sampling to assess residual fertilizer concentrations and soil attributes affecting herbicide efficacy, and (3) prescription maps for metering fertilizer, pesticide and seed inputs. Inconsistent relationships were found between ECa and corn yields indicating that, while soil factors controlled wheat yields, corn yields were more influenced by weather.