Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/30/2002
Publication Date: 1/15/2003
Citation: JOHNSON, C.K., MORTENSEN, D.A., WIENHOLD, B.J., SHANAHAN, J.F., DORAN, J.W. SITE-SPECIFIC MANAGEMENT ZONES BASED ON SOIL ELECTRICAL CONDUCTIVITY IN A SEMI-ARID CROPPING SYSTEM. AGRONOMY JOURNAL 95:303-315. 2003. Interpretive Summary: Increasing costs of agricultural inputs (fertilizer and pesticides) and environmental concerns associated with their inappropriate use (leaching and runoff, acidification, compaction, and toxin accumulation) raise questions about the efficiency of uniform farm management across a field. Site-specific management (SSM) applies production inputs to within-field zones of varying soil characteristics according to their yield potentials. However, cost- effective methods for identifying management zones are lacking. In a two-year on-farm experiment in semiarid northeastern CO, a section of farmland (610 ac) in a no-till winter wheat-corn-proso millet-fallow rotation was mapped for electrical conductivity (EC) using a commercially available EC meter. Wheat and corn yields were mapped with a yield monitor. Management zones based on ranges of EC (low, medium low, medium high and high) effectively partitioned wheat yields across fields. Average and maximum wheat yields decreased with increasing EC. Management zones based on EC can be used for the SSM of wheat to: (1) determine yield goals, (2) assess residual fertilizer concentrations, and (3) meter fertilizer, pesticide and seed inputs. Corn yields were not consistently related to EC, probably due to weather influences.
Technical Abstract: Site specific management (SSM) has the potential to improve both economic and ecological outcomes in agriculture. Effective SSM requires a strong and temporally consistent relationship between identified management zones and underlying soil physical, chemical, and biological parameters defining yield potential. The objective of this study was to examine the relationships between apparent electrical conductivity (ECa) and two years of winter wheat (Triticum aestivum L.) and corn (Zea mays L.) yield maps as a basis for SSM. In a 250-ha farm-scale experiment, eight fields were individually partitioned into four management zones (ranges of ECa) using two different methods, unsupervised and equal-size classification; yield variances within ECa zones were not significantly different between methods. Within fields, 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). No consistent associations between these parameters were found for corn. Yield response curves relating maximum wheat yields and ECa revealed a boundary line of maximum yield that decreased with increasing ECa. 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.