Meta-analysis of the effect of agronomic factors on root yield and quality of sugar beet (Beta vulgaris L.)

Different environmental and genetic factors such as variety, climate, soil and agronomic practices factors are effective in increasing root sodium content and reducing the yield and quality of sugar beet roots. Therefore, in this research, using meta-analysis, the effect of these factors has been determined and agronomic practices for reducing the sodium content of the roots and increasing the quality of produced sugar. The purpose of this meta-analysis was to determine management practices with significant effects on yield and quality of sugar beet roots in Iran.

This study was conducted on data collected from the experiments carried out at Sugar Beet Seed Institute (SBSI) in Karaj and Agricultural and Natural Resources Research and Education Center in different provinces in Iran for the period of 1997 to 2020. Data were analyzed from 33 final technical reports of research projects of the the experiment that had appropriate agronomic management treatments. The data and information of these reports were created as a database containing 450 rows in 26 columns. The corresponding data to the investigated treatments were considered from the database and then the reaction ratio, average of the reaction ratio, standard deviation and the significant effect of each factor on sugar beet root yield and quality traits were determined.

The results of meta-analysis of agronomic practices factors in the period of 23 years of research showed that lack of irrigation in the early season after crop establishment caused significant decrease in root sodium content (α=0.05). The effects of row and plant spacing, land preparation methods, crop rotation, late season moisture stress, mild and severe drought stresses, on root sodium content were not significant. Crop rotation caused significant increase in root, sugar and white sugar yields by 17.5%, 23.7% and 26.7%, respectively. Early and late season drought stresses and severe drought stress caused significant decrease in root yield by 21%, 42%, 33%, respectively. Reduction in white sugar yield were 18%, 43% and 32% under above mentioned drought stresses conditions.

The crop rotation of legumes-wheat-sugar beet compared to the conventional rotation of wheat-sugar beet increased sugar beet root yield by about 20%. The best method of soil preparation was detrmined as plowing or using sub-soiller in autumn and carrying out other operations including disc and furrower in spring. Increasing the planting row spacing to 60 cm caused significant decrease in root, raw sugar and white sugar yields by 6% to 10% due to the decrease in plant density. Changing plant spacing within rows from 20 cm to 15 cm did not have significant effect on sugar beet traits. Water deficit at the early season and after the establishment of sugar beet crop decreaseed the sodium content of sugar beet roots during the season, and also reduced root, sugar and white sugar yields, but the amount of yield reduction was lesser than drought stress at the end of season. Therefore, it is recommended to continue irrigation during the sugar beet technological ripening stage. Irrigation could be applied after 70% decrease of the soil moisture content to reduce water use without any significant reduction in root yield.