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SUGARBEET

Effects of Italian Ryegrass and Date of Plow-In on Soil Mineral Nitrogen and Sugarbeet Yield and Quality

Univ. of Maribor, Faculty of Agriculture, Vrbanska cesta 30, 2000 Maribor, Slovenia

^* Corresponding author (branko.kramberger{at}uni-mb.si).

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 (IR0); the control (C) was without cover crop or fertilization. In Exp. II (2005–2006), oil radish [Raphanus sativus L. spp. oleiferus (DC.) Metzg.] (OR) and white mustard (Sinapis alba L.) (WM) 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 IR0 were not significant, neither in soil N_min content, nor in sugarbeet yield in any of the experiments. The IRF and IR0 treatments significantly reduced soil N_min 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 IR0, and was higher in EP than in LP. In Exp. II, fresh beet yields were higher in control treatments C, OR, and WM than in IRF and IR0, and was higher in EP than in LP. The IRF and IR0 did not affect sugar concentration, nonsugar impurities (K, Na, -amino N) concentrations, or white sugar yield, whereas EP increased Na concentration in Exp. I, and -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.

Abbreviations: BDMY, biomass dry matter yield • C, control • DMY, dry matter yield • EP, early plow-in • Exp., experiment • IRF, fertilized Italian ryegrass • IR0, nonfertilized Italian ryegrass • LP, late plow-in • N_min, soil NH₄–N and NO₃–N • OR, oil radish • WM, white mustard

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Received for publication September 20, 2007.