Submitted to: International Conference on Precision Agriculture Abstracts & Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/15/2000
Publication Date: 7/16/2000
Citation: Franzen, D.W., Halvorson, A.D., Hofman, V.L. 2000. Management zones for soil n and p levels in the northern great plains. International Conference on Precision Agriculture Abstracts & Proceedings. CD-ROM.
Interpretive Summary: A field study was conducted near Mandan, ND from 1995 to 1998 to determine the relationship between soil fertility levels, N and P, determined from grid soil sampling patterns and topographic soil sampling patterns in a dryland, winter wheat-sunflower-spring wheat rotation. Soil fertility patterns from topographic sampling were highly correlated with the intensive grid sampling. By zone sampling based on topography, the number of samples required to describe the field soil fertility pattern was reduced while maintaining a high or higher level of information than with a 66 m grid sampling. Variable-rate fertilizer application was profitable with sunflower when the range of NO3-N values was sufficient to provide a meaningful change of N rate. Soil NO3-N levels were lowest and least variable following sunflower. Water stress limited wheat yields and response to N some years. Variability of soil N in this study was too low in most wheat years for variable-rate fertilizer application to be profitable.
Technical Abstract: A study was conducted near Mandan, ND in a winter wheat, sunflower, spring wheat rotation to determine the relationship of soil fertility levels between grid sampling and topographic sampling. Grid sampling from these fields revealed that fertility patterns were related to topography. The nutrients included in this relationship were NO3-N and Olsen P. By zone sampling based on topography, the number of samples required to describe the field soil N and P levels was reduced while maintaining a high or higher level of information than a 66 mm grid estimate. Variable-rate application of fertilizer was profitable in sunflower when the range of NO3-N values was sufficient to provide for meaningful change of N rate and when the range was in a category where changes of N rate were possible. Variability of soil N was too low in most wheat years for variable-rate application to be profitable.