Nitrogen application rate and timing in the Imperial Valley of California.

Abstract

Growers in the Imperial Valley have adopted glyphosate resistant varieties in their sugar beet production system.  One of the advantages of the use of glyphosate resistant varieties is the reduction of the need to cultivate for weed control at layby (November).  This cultivation operation at layby was also combined with a split application of nitrogen.  The cultivation at layby required that irrigation basins be deconstructed for equipment access to the field and then rebuilt following the cultivation.  With the advent of glyphosate resistant varieties, weed control is obtained without cultivating and thus the irrigation basins do not need to be deconstructed.  This requires growers to apply their nitrogen fertilizer pre-plant instead of the former split application.  The objective of this study was to determine the effect of nitrogen rate and timing on sugar beet root yield and quality.  The study was established at four locations from 2017 to 2020.  The treatments were a factorial combination of eight nitrogen application rates (0, 40, 80, 120, 160, 200, 240, and 280 lbs. N per acre) and two application timings (pre-plant and layby).  This study suggests that delaying N application until November is not needed and that the optimum N application rate for sugar beets harvested in June and July was 220 lbs. N per acre with another 100 lbs. soil nitrate-N per acre in the surface 43 inches of soil at planting.