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

摘要

Production of high-quality sugar beets requires precise nitrogen (N) fertilizer management with N recommendations based on a measurement of residual nitrate-N to 120cm (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 x 18.3m grid cells in 1997 and 1998. Nitrogen application maps for four different grid cell sizes 18.3x 18.3m (60 x 60ft), 54.9 x 54.9m (180 x 180ft), 91.4 x 91.4m (300 x 300ft), and 128 x 128m (420 x 420ft) 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 x 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 x 54.9m, 91.4 x 91.4m, and 128 x 128m soil sampling grids were similar in 1997. The application map derivedfrom 18.3 x 18.3m 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 gridcell sizes or constant rate applications in either 1997 or 1998.