The Dutch sugar industry and sugar beet research institute initiated the project SUSY (Speeding Up Sugar Yield) as a reaction to decreasing beet prices in relation to the reform of the European Unions sugar regime. The project was aimed at softening the reform’s impact on growers income by improving their knowledge on raising sugar yield and identifying possible cost savings. From each sugar beet growing region in The Netherlands, 26 pairs of ‘type top’ (high yielding) and ‘type average’ (average yielding) farmers were selected, based on the average yield of the farm in 2000-2004. All measures of sugar beet cultivation, costs calculation and phytopathological, agronomical and soil characteristics were investigated from 2006 and 2007 on 75 fields of ‘type top’ and 74 fields of ‘type average’ growers
in relation to yield and quality. The factors year and grower caused most of the significant effects on yield, quality and cost variables. The ‘type top’ growers had significantly 20% higher sugar yield in each year compared to ‘type average’ growers, but the total variable costs did not differ. This makes the ‘type top’ growers more efficient in resource use. Costs for manure and fertiliser, ‘other’ and irrigation significantly increased the total variable costs. With higher fungicide costs, sugar yield significantly increased. However, there was no significant relation between the intensity of sugar beet production and sugar yield so that the observed differences in sugar yield were not caused by economical constraints. Based on this study, it can be concluded that the most profitable strategy for the growers is maximising sugar yield and optimising costs.
Heterodera schachtii and Beet necrotic yellow vein virus (BNYVV) were mainly found on clay soils. Type top growers on clay soil had significantly lower infestation levels of H. schachtii (4.4x lower, P = 0.008), BNYVV (2.7x lower, P = 0.016) and other foliar symptoms (Pseudomonas, Phoma betae and Verticillium spp. combined) (1.5x lower, P<0.001) than the type average growers, respectively. On sandy soils, infestation levels of Meloidogyne spp. (P = 0.016), Cercospora beticola (P = 0.005) and Erysiphe betae (P = 0.027) were significantly lower (5x, 1.4x and 1.8x, respectively) for the type top growers. Type top growers on clay or sand soils sowed 5 and 6 days earlier respectively, and made more fungicide applications than the type average growers. Insect pests were not observed at levels damaging for sugar yield: Insecticidal seed treatments provided sufficient control of insect pests. By multiple regression, 35% of the variance in sugar yield on clay soils was explained by H. schachtii and BNYVV infestation levels and by sowing date. On sandy soils, the infestation levels of H. betae and Aphanomyces cochlioides, number of fungicide applications and sowing date explained 71% of the variance in sugar yield.
Despite crop protection measures, the calculated yield losses due to pests and diseases were for the type top growers 30.2 and 13.1% and for type average growers 37.1 and 16.7% on sandy and on clay soils, respectively. Therefore, pest and disease infestation level partly explained the differences in sugar yield between type top and type average growers analysed. The skills and management of the grower are important to reducing damage by pests and diseases.
Mean saturated hydraulic conductivity in the subsoil (Ks) was significantly higher on fields of type top growers than of type average growers, 0.49 and 0.31 m day-1, respectively. Mean Ks was below a damage threshold level of 0.10 m day-1 on 34% of the type average growers’ fields and on 27% of the type top growers’ fields. Ks was found 0.00 m day-1 on 9% of all fields. By multiple regression analysis without the factor grower type, 15.3% of the variability of Ks was explained by a model with the terms fine sand fraction (50-105 μm) in the subsoil and depth of primary tillage (Dpt; m).
Type top growers basically made use of comparable technical equipment, but applied lower tractor tyre inflation pressure and a lower number of field operations for seedbed preparation compared with type average growers. This did not result in a significant difference in mean air-filled porosity (AP) at field capacity in the topsoil between grower types although the number of fields with an topsoil AP in the 10-15 cm layer below 10% was lower in fields of top growers (13 fields) than of average growers (18 fields).
Direct effects of soil management on AP could be established by statistical analysis without the factor grower type, but may have been influenced because both management characteristics and AP appeared to be strongly related to top soil clay content.
AP of the topsoil and Ks of the subsoil explained 24.9% of the variation in sugar yield. Therefore, under the given conditions of soil type (clay content), a better soil structure can be influenced by the grower, resulting in a higher sugar yield.
Harvest losses were measured in 2006, 2007, and 2008 on 150 sugar beet fields in the Netherlands. Losses by overtopping, root breakages, and of whole beet were on average 2.9 t ha-1 and ranged from 0.45 t ha-1 to 9.1 t ha-1. Although the type top growers had significant lower losses due to overtopping and whole beet losses, they did not have lower total harvest losses compared to the type average growers. Reducing the harvest losses is a relatively easy and efficient way to improve yield and profitability of the sugar beet crop.
Fertilization of sugar beet did not differ between the type top and type average growers in this project. No substantial effects of applied elements on sugar yield were found, since all were already in the optimal range for a high sugar yield. The amino-N content of sugar beet was found predicting the removal of total-N from the fields (R2 = 0.66). Due to the increased quality of the sugar beet during the years as a result of breeding efforts, the N demand stays on similar level.
The type top growers had significant higher plant population per hectare compared to the type average growers. The delay in emergence on type average growers’ fields can be explained by sowing quality and sowing date. Sowing quality from this project comes to seed placement in compressed (below the loose seedbed) and in humid soil (not dried by the weather), which are closely related. The type top growers place significantly more seeds in humid soil, providing more optimal circumstances for the seeds to germinate and being less dependent on rainfall after sowing. Here, the grower’s management is of major importance, for using a properly maintained sowing machine, for preparing a high quality seedbed and for checking the seed placement in the soil during sowing.
Type top growers sowed their sugar beets significantly five days earlier. This resulted in an earlier closure of canopy with positive influence on yield and reducing the effect of pathogens. The harvest date was not different for both grower types, consequently, the gain has to be set at seasons’ start.
The costs of weed control were comparable between type top and type average growers. Next, all the recorded inputs, like number of applications, type and amount of compounds used and interval of applications were similar for both type top and type average growers, except the pre-sowing and pre-emergence applications. Thus, difference in weed control between type top and type average growers is set early in the season. The yield loss due to weed competition was estimated to be about 6%. With the importance of growers’ management on the late emergence of weeds, the challenge remains whether to control weeds successfully and to avoid weed competition after canopy closure.
This study clearly shows that there is no general key issue attention should be paid to but raising sugar yield demands a continuous dedication to the crop, an optimised grower's management, and a specific guidance by new knowledge generated by scientific research.
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