Laboratory Incubations Aiming At Designing Soil Fertility Recommendations for Soils From Unharvested Sugar Beet Fields.

Laboratory incubations aiming at designing soil fertility recommendations for soils from unharvested sugar beet fields

The onset of an early 2009 October frost in the Big Horn Basin resulted in 60 percent of the sugarbeet crop unharvested. It was believed that the crop residue left on the field likely contributed large amounts of soil labile carbon (C) that tied up soil nitrogen (N). This was likely to result in changes in the timing of N release to subsequent malting-quality barley. The overall objective of this study was to investigate the effects of the leftover beet residue on soil mineral N originated from sugar beet residues and augmented with different rates of N fertilizer (0, 100, 200 lbs/acre) at different times of the growing season (early vs. mid season).  To accomplish this goal we carried out a laboratory 28-day incubation experiment to determine the timing and the amount of N and C mineralization from soils that were unharvested and contained sugar beet residues and soils that were harvested and did not contain any sugar beet residues.  Laboratory observations were later validated by seasonal field observations of soil and lysimeter studies determining mineral N, labile C, greenhouse gas (GHG) emissions, plant quality and biomass.  The laboratory incubation showed that fertilizer additions in the no residue soils produced higher levels of CO2 than the no-fertilizer control indicating microbial immobilization.  The filed results suggest that the timing of the release of N to the soil from the residue decomposition did not correspond with adequate soil N management for producing malting quality barley.  In addition, significant losses to GHG and surface water run-off occurred early in the season.  Our findings were in contrast to our hypothesis as they revealed significant quantities of residue-derived soil mineral N that does not affect malting quality under field conditions.