Influence of Sowing and Harvest Dates on Sugar Beet Yield

The influence of early and late sowing and of early and late harvest on the yield and quality of sugar beet was monitored at six locations in Czech beet-growing areas for the time of 4 years. Three locations had different levels of infestation by beet cyst nematode Heterodera schachtii L. and that is why rhizomania-tolerant variety and rhizomania-and-nematode-tolerant variant were monitored. The interval between early and late sowing was 13 days and between early and late harvest it was 33 days on average. Early sowing (compared to late sowing) has much greater impact on the increase in sugar beet weight than on the sugar content; in the case of late harvest, the increase in sugar yield is significantly affected by increased sugar content. At locations without nematode infestation, the average annual sugar yields are very similar for sensitive as well as for tolerant varieties with the same vegetation period. The decrease in sugar yield due to late sowing (about 13 days) is about 1.7 t/ha sugar; the increase in yield due to longer vegetation period in fall (33 days) was 2-2.5 t/ha sugar. By converting these numbers to 1 day of the vegetation period it is clear that spring increase is about twice as high. At locations with beet cyst nematode infestation, the yields of sensitive varieties are significantly lower in both cases - compared to non-infested locations and to tolerant varieties. The decrease in yield of sensitive varieties due to nematodes grows with the length of the vegetation period: it is 7.4% for late sowing and early harvest and 15% for early sowing and late harvest. The increase in yield in sensitive varieties at infested locations falls by 0.9 t/ha sugar for late harvest. If the varieties are chosen correctly, i.e. sensitive variations at non-infested locations and tolerant varieties at infested locations, the decrease in yield due to late sowing (13 days) is 0.8-1 t/ha standard (converted) beet per one day of delay. The increase in yield in the case of late harvest (33 days) is 0.4-0.5 t/ha standard beet per one day of vegetation extension. The discussion now concentrates on the possibilities to accelerate sowing and move the beginning of sugar campaigns to later dates.