Sugar beet (beta vulgaris L.) favourite sowing date, nitrogen and phosphorus rates, and plant population in Northern State of Sudan

Two field experiments were carried out at Dongloa Research Station Farm in Northern State of Sudan (22 and 16 deg N; 32 and 25 deg E) in the winters of 2005/2006 and 2006/2007 to determine sugar beet (Beta vulgaris 1.) favourite sowing date, nitrogen and phosphorus rates (Experiment 1) and plant population (Experiment 2) through studying its fresh root weight, tops and root yields, sucrose content and sugar yield. In Experiment 1, split - split plot design was adopted where three sowing dates (15 November, 15 December and 15 January), three nitrogen rates (0, 86 and 172 kg N ha-1) and three phosphorus rates (0, 43 and 86 kg P20S ha-1) were assigned to main plots, sub - plots and sub - sub plots, respectively. All studied characters responded significantly to sowing date with 15 November sowing out yielding the other sowing dates. Root weight, tops yield, root yield and sugar yield obtained at 15 November sowing gradually decreased through 15 December to 15 January sowings. ccordingly, the combined average root yield of 60.8, 44.2 and 30.4 t ha-1 were realized for the 15 November, 15 December and 15 January sowings with the corresponding sugar yields of 10.1, 7.4 and 4.4 t ha-I . All studied characters, with exception of sucrose content, significantly increased with increase in nitrogen rate. This was illustrated via combined analysis where root yields of 31.4, 47.5 and 56.5 t ha-I was achieved with application of 0, 86 and 172 kg N ha-1, respectively. The corresponding sugar yield values were 5, 7.9 and 9 t ha-I. However, the difference between 86 and 172 kg N ha-1 was relatively small, being only 19 and 14 percent for the combined root and sugar yields in that order. The highest sucrose content (%) was observed at 86 kg N ha-1. However, the combined analysis showed no significance difference in sucrose content among the nitrogen levels. In both seasons, application of phosphorus at 43.81 kg P2O5 ha-l surpassed 86 kg P2O5 ha-l via increasing tops yield, root yield, sucrose content and sugar yield. Combined analysis showed that root yields of 43.5, 46.8 and 45.2 t ha-1 were obtained from application of 0, 43 and 86 kg P2O5 ha-1, in that order. The corresponding values of sugar yield were 7, 7.7 and 7.2 t ha-l. All studied characters responded significantly to the varying levels of interactions: Sowing date x nitrogen rate, sowing date x phosphorus rate, nitrogen rate x phosphorus rate and sowing date x nitrogen rate x phosphorus rate. Considering the three - way interaction, the highest root and sugar yields were obtained when sugar beet was sown on 15 November and at the same time applying 86 - 172 kg N ha-l in combination with 43 kg P2O5 ha-l. In Experiment 2 four levels of plant population, 55 556, 66 667, 83 333 and 111 111 plants ha-l, were tested in RCBD. The highest root and sugar yields were recorded under 55,556 and 83,333 plants ha-l in 2005/06 and 2006/07 respectively. The combined analysis showed root yield of 55.1, 48.7, 52 and 43 for 55 556, 66 667, 83 333 and 111 111 plants ha-1 in that order. The corresponding values for sugar yields were 7.7, 6.8, 7.9 and 6.1 t ha-l. Accordingly the optimum plant population for both root and sugar yields was 55,556 - 83,333 plants ha-1. Based on this study, it is recommended that the sugar beet production package in Northern State should include the following components: (1) Sowing on 15 November, (2) Nitrogen rate of 86 - 172 kg N ha-1 (3) Phosphorus rate of 43 kg P2O5 ha-l and (4) Plant population of 55,556 - 83,333 plant ha-1