Effect of Soil Sample Density on Nitrogen Application Maps and Sugar Beet Root Yield and Quality

Abstract

Production of high‐quality sugar beets requires precise nitrogen (N) fertilizer management with N recommendations based on a measurement of residual nitrate‐N to 120 cm (4 ft) soil depth. The objective of this study was to determine the agronomic and economic aspects of using different grid cell sizes for sampling soil nitrate‐N. A 5‐ha field (12.4 acre) was soil sampled for nitrate‐N using 18.3×18.3 m grid cells in 1997 and 1998. Nitrogen application maps for four different grid cell sizes 18.3×18.3 m (60×60 ft), 54.9×54.9 m (180×180 ft), 91.4×91.4 m (300×300 ft), and 128×128 m (420×420 ft) were developed from these soil samples and compared with a conventional average for each field. The five nitrogen fertilizer treatments adjusted for grid cell size were applied with a fertilizer truck equipped with a variable rate applicator in two replicates of 274‐m long strips. Sugar beet quality was determined on root samples taken immediately before root harvest on a 18.3×18.3 grid. Root yield was determined with a conventional harvester equipped with a yield monitor. The nitrogen fertilizer application maps derived from the 54.9×54.9 m, 91.4×91.4 m, and 128×128 m soil sampling grids were similar in 1997. The application map derived from 18.3×18.3 m grid cell size was different from the application maps derived from larger grid cell sizes. Although there were differences in N application maps, there were no differences in root yield, root quality, or recoverable sucrose among grid cell sizes or constant rate applications in either 1997 or 1998.

Keywords:

• Site specific
• soil test
• soil nitrate‐N

Acknowledgments

We thank the following for their help with this project: The Sugarbeet Research and Education Board of Minnesota and North Dakota for partial funding; Steve Freese, sugar beet farmer, for his cooperation and permission to use the land and sugar beet harvester; Darin Johnson for his assistance with transferring the yield data from the yield monitor; and Larry Sax for the preparation of the N application maps.