Modulating effect of water and nitrogen factors on root yield and sucrose content of sugarbeet

Drip irrigation has been applied to sugarbeet cultivation in Xinjiang currently, while there are presently very few reports concerning optimal irrigation amounts and nitrogen application quantities in the cultivation of drip irrigated sugarbeet in Xinjiang, China. This study provides a theoretical basis for economically rational irrigation and nitrogen application programmes enabling the standardized cultivation of sugarbeet. Field tests were performed in conjunction with a two-factor quadratic saturation D optimum design scheme involving moisture and nitrogen to establish a binary quadratic polynomial mathematical model with moisture and nitrogen as independent variables and root yield and sugar concentration as target functions. Analysis and optimization using the model yielded the optimal irrigation and nitrogen application amounts. Results showed that there was a significant interaction between moisture and nitrogen with regard to root yield and sucrose content. Moisture is the chief factor affecting beet root weight and sugar content, followed by nitrogen. Moisture and nitrogen have a significant interactive promoting effect on root yield, but also have a significant interactive inhibiting effect on sucrose concentration. Under low levels of irrigation and nitrogen application, root yield increases with irrigation amount and the nitrogen application rate. However, after certain levels are reached, increases in root yield are not significant. Sucrose content first decreases then increases with irrigation amount and nitrogen application rate. Under the experimental conditions employed in this study, irrigation amounts and nitrogen application rates of 6417-8100 m(3)/ha and 166.5-292.8 kg/ha, respectively, achieved root yields exceeding 80 t/ha.