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Cover crops decreased initial water content, sugarbeet yield and residual N- NO3 in the northern Great Plains

Sugarbeet is a valuable crop in North Dakota, but it leaves the soil uncovered after harvest, decreasing soil health. The lack of soil coverage during the winter increases soil losses due to wind erosion. In addition to that, high levels of residual deep nitrogen after cereal production can decrease sugar yield in sugarbeet. Cover crops and no-tillage provide soil coverage, preventing soil erosion, and reducing NO3-N leaching. The experiment was conducted at two locations, Prosper and Hickson, ND, in 2017. The experimental design used was a RCB with four replicates. The cover crops were radish, winter camelina, winter wheat, oat, winter rye, and a check plot (without cover crop), established into spring wheat residue in August 2017. Biomass production averaged across locations was 2.2 Mg ha-1 in both radish and oat. Soil green cover was 70% for both oat and radish while in rye it was 57%, all providing soil protection from wind. Nitrogen accumulation in the biomass was significantly higher in oat, radish, and winter rye than in winter wheat and winter camelina biomass. Soil NO3-N, in late fall was significantly higher in the check plots (25.9 kg ha-1) than in plots with a cover crop; oat (12.3 kg ha-1), winter rye (13.2 kg ha-1), and radish (16 kg ha-1) This indicates cover crops are scavenging residual NO3-N and keeping it in their biomass. In conclusion, radish, winter rye, and oat provided soil cover in the fall by protecting the soil from erosion and reduced soil residual NO3-N prone to leaching during fall which likely contributes to deep soil NO3-N accumulation.

In May 2018, a sugarbeet experiment was planted with RCBD design with a split-plot arrangement, where the main plot was cover crops (from the previous experiment) and the sub plot was nitrogen rate (0 and 112 kg ha-1). Winter camelina, winter rye, and winter wheat survived the winter and were actively growing early in the spring. Due to this, gravimetric water content was significantly lower in winter rye (21.4%) and winter camelina (23.7%) than in the no cover crop plots (26.0%). Also, the sugarbeet stand count was strongly decreased because of the lack of water in the winter hardy cover crop plots. This situation was clearly observed in Hickson, where the main plot as winter rye (48,438 plants ha-1) had lower sugarbeet stands than sugarbeet following winter camelina and winter wheat (77,239 plants ha-1). Sugarbeet density following these winter hardy cover crops were lower than when following check, oat, and radish (98,245 plants ha-1). The interaction of cover crop and  N rate was significant in sugarbeet yield at Hickson, distinguishing a low yield in winter rye cover crop plots with 0 kg ha-1  N application (56.3 Mg ha-1) in comparison with check plots with 0 kg ha-1 N (83 Mg ha-1). Similar trends were observed at Prosper but differences were not significant at this location. In conclusion, winter wheat, winter rye and winter camelina provided green soil cover in early spring and decreased gravimetric water content, which produced a decreased stand count and decreased sugarbeet yield. This situation also opens the possibility of earlier sugarbeet planting in comparison with soils with no green cover, being an opportunity in the wet springs and heavy clay soils of the northern Great Plains.

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