The effect of plant population on the growth and yield of fodder beet and sugar beet

In a field experiment at Lincoln College, Canterbury, fodder beet (Beta vulgaris) and sugar beet (Beta vulgaris) were tested at plant populations,75, 150, 225, and 300 thousand plants ha⁻¹. Nine harvests were taken at three weekly intervals, starting on December 21, approximately three months after sowing. Leaf number, leaf area, and dry matter of leaves, crown and root were determined. Sugar content of the crown and root was determined from February 23 onwards to final harvest on June 10. Leaf production was higher in fodder beet than in sugar beet until March 16, while area per leaf was consistently higher in sugar beet than in fodder beet. Leaf area index (LAI) reached a maximum of 3.7 in fodder beet on February 23, and 4.0 on March 16 in sugar beet; thereafter, sugar beet maintained its superiority largely because of a greater leaf death rate in fodder beet. In both crops, the decline in leaf area later in the season was attributed more to the smaller size of the leaves than to reduction in leaf number. Leaf number per plant and area per leaf were considerably increased at the lower plant population (75,000 plants ha⁻¹). Plant populations were not significantly different in LAI from February 23 onwards, but the lower plant populations (75,000 and 150,000 plants ha⁻¹) showed a greater decrease at the final sample on June 10. Both crops did not differ in leaf and total root (root + crown) dry matter until February 23, after which sugar beet showed greater yields. Leaf dry matter reached a maximum of 295 gm⁻² in fodder beet on February 23, and 305.6 gm⁻² in sugar beet on March 16; thereafter, it decreased to a minimum of 99.3 and 252 gm⁻² in fodder beet and sugar beet respectively on June 10. The pattern of total root dry matter production was similar in both crops. Increases in the total root dry matter production .were greater from December 21 until March 16, and markedly depressed thereafter. The total root dry matter increased until May 18, and reached a maximum of 1332 and 1550 g m in fodder beet and sugar beet respectively. Plant populations did not significantly affect the leaf dry matter from February 23 onwards, but the lower plant populations (75,000 and 150, 000 plants ha⁻¹ showed greater decrease after May 18. Total root dry matter was significantly higher (1553 gm⁻²) at the lower population (75,000 plants ha⁻¹) than at 225,000 and 300,000 plants ha⁻¹ (1332 - 13380 gm⁻² ) on. May 18, probably associated with differential effects of water stress which the crop experienced in the early part of the growing season. Sugar percentage, on a fresh weight basis, in the crown and root was higher in sugar beet than in the fodder beet. In root tissue, it varied from 12.37 to 13.46% in fodder beet, and from 14.43 to 16.60% in sugar beet. The sugar percentage in the crown was lower than in the root by 2.5 to 3.0% in fodder beet and by 3.7 to 4.2% in sugar beet during the season. Sugar as a percentage of total root dry weight was higher in fodder beet than in the sugar beet. It reached a maximum of 84.4% in fodder beet and 79.2% in sugar beet on June 10. The lower sugar percentage on a fresh weight basis in the fodder beet than in the sugar beet was due solely to the higher moisture content in the fodder beet. Fresh weight sugar percentage in the crown and root increased with increasing plant population, but sugar percentage of total root dry weight was not affected. The increase in sugar percentage on a fresh weight basis with increasing population was due only to the low moisture content. Sugar yield in fodder beet increased from 603 gm⁻² on February 23 to 1120 gm⁻² on June 10, and in sugar beet it increased from 597 to 1209 gm⁻² at the same time. Sugar yield in March and June decreased with increasing plant population. In June it decreased from 1300 gm⁻² at 75,000 plants ha⁻¹ to 1106 gm⁻² at 300,000 Plant ha⁻¹.