Determining the optimal population density of sugarbeet crops in England

Eleven experiments were conducted at seven sites in England from 2006 to 2008 to investigate the sugarbeet yield response to plant populations resulting from different seed rates. Experiments were made on loamy sand, sandy loam, sandy clay loam and silt clay loam soils to test whether different soil types need different optimal plant populations. All experiments were harvested by machine. The various seed rates resulted in plant populations ranging from 40,000 to 180,000 per hectare although this range was not achieved in every experiment. Sugar concentration and dirt tares tended to increase as the population density increased whereas sodium, potassium and amino nitrogen concentration tended to decrease. The differences in adjusted beet yield of different plant populations were not statistically significant in six of the eleven experiments. However, a relationship was fitted to plant population density and adjusted beet weight per plant. It accounted for more than 80% of the variation in all eleven experiments. These relations were then used to estimate the optimal plant population per hectare for maximum beet yield and for maximum net economic return. The median plant population for achieving at least 97% of the maximum beet yield ranged from 80,000 to 120,000 per hectare. However, the median plant population for achieving at least 97% of the maximum net economic return at 80% seedling establishment rate, after taking the beet price and seed cost into account, varied from 70,000 to 120,000 per hectare. Among the eleven experiments, the plant population that was most likely to achieve the maximum beet yield was 100,000 per hectare (i.e. 8 out of 11 experiments), but the plant population that was most likely to achieve the maximum net economic return was 80,000 per hectare (i.e. 10 out of 11 experiments). The net economic return depended on the seedling establishment rates. The optimal plant population was not affected by soil type or yield potential of the location.