Effects of Italian ryegrass and date of plow-in on soil mineral nitrogen and sugarbeet yield and quality

Winter cover crops can reduce N losses from cropping systems; however, they can affect subsequent crops. Two field experiments were conducted in Slovenia to determine the effects of the Italian ryegrass (Lolium multiflorum Lam.) as a cover crop and the date of spring plow-in on the soil mineral N (N-min) content before winter and in spring, and on subsequent productivity of sugarbeet (Beta vulgaris L.). In Exp. I (2004-2005), summer seeded Italian ryegrass was fertilized with 60 kg N ha(-1) (IRF) or not (IRO); the control (C) was without cover crop or fertilization. In Exp. II (2005 -2006), oil radish [Rapbanus sativus L. spp. oleiferus (DC.) Metzg.] (OR) and white mustard (Sinapis alba L.) (W.M) were added as additional treatments. In Exp. I, the top growth of cover crops was removed in autumn from the field. Differences between IRF and IRO were not significant, neither in soil N-min content, nor in sugarbeet yield in any of the experiments. The IRF and IRO treatments significantly reduced soil Nmin content in spring. Early plow-in (EP; 17 d before sugarbeet seeding), resulted in higher soil N-min content at seeding than did late plow-in (LP; 4 d before seeding). In Exp. I, fresh beet yield was higher for C than for IRF and IRO, and was higher in EP than in LP. In Exp. 11, fresh beet yields were higher in control treatments C, OR, and WM than in IRF and IRO, and was higher in EP than in LP. The IRF and IRO did not affect sugar concentration, nonsugar impurities (K, Na, alpha-amino N) concentrations, or white sugar yield, whereas EP increased Na concentration in Exp. I, and alpha-amino N concentration in Exp. II Results suggest that Italian ryegrass as a winter cover crop can efficiently reduce soil N-min content during autumn and winter. Results also indicated a negative effect of Italian ryegrass on succeeding sugarbeet fresh yield, although the effect on white sugar yield was not significant at P <= 0.05.