Interference of white clover with the growth and yield of sugar beet

Abstract

Interference between sugar beet (Beta vulgaris L. cv. Amazon) and white clover (Trifolium repens L. cv. Huia) was examined in a field experiment based on the DeWit replacement series model. The object of this study was to test the extent to which the growth of sugar beet is suppressed by white clover. Eight treatment combinations were replicated four times in a randomised complete block design. In all treatments 16 plants per m² were maintained in proportions (1:0; 0.75:0.25; 0.50:0.50; 0.25:0.75; and 0:1) of sugar beet and white clover. Both in-row and between-row planting arrangements were included in the experimental design. Three harvests were taken at six weekly intervals from 187 days after sowing. The competitive ability of the two species was examined mostly by using the concept of relative yield total (RYT).

A lack of competitive suppression of sugar beet and a severe reduction of white clover yield in mixture with sugar beet was observed in this study. When grown with white clover in a 0.75:0.25 mixture and between-row arrangement, sugar beet had a total dry matter yield 18% higher than that in pure stands at the final harvest. On the other hand, pure stands of white clover produced a significantly higher total dry matter yield than the average of the mixed populations. However, the 75:25 SB:WC mixture produced greater relative yield (RY) ratio and thus the corresponding RYT for the total dry matter was greater than 1.0. This was due to higher economic yield (root + crown) of sugar beet in the 75:25 SB:WC mixture.

The RYT of root dry weight was consistently greater than 1.0 with 75:25 SB:WC treatment when grown in between row arrangement. Nevertheless, the highest RYT of 1.37 was finally achieved by the 25:75 SB:WC association in the in-row arrangement.

At the final harvest, pure stands of sugar beet had 20% higher shoot dry weight, 19% higher leaf dry weight, and 9% larger leaf area than the average in the 75:25 SB:WC mixture.

The 75:25 and 25:75 SB:WC mixtures have given conflicting RYT values for root dry weight, presumably reflecting the larger relative leaf area and thus bigger root size of individual plants in the low density sugar beet population.

It was observed that severe shading by sugar beet leaves reduced the light energy available to white clover plants considerably and markedly suppressed their growth and development, particularly the stolon production. Consequently, white clover, a light-demanding plant, was less effective in competition with sugar beet. Therefore, no detrimental effects of white clover as a weed could be demonstrated in the present experiment. However, it is suggested that white clover may enhance the growth and yield of sugar beet in mixture.