The effect of one-year application of vermicompost on yield and quality of sugar beet and its economic assessment

One of the solutions to increase soil organic matter levels in Iran is to use biological fertilizers such as vermicompost. The use of vermicompost in sustainable agriculture, in addition to increasing the activity of useful microorganisms including mycorrhizal fungi and phosphate soluble microorganisms, serves to provide plants with nutrients e.g. nitrogen, phosphorus, potassium, and eventually to improve crop yield (Arancon et al., 2004). Vermicompost offers numerous advantages, which include: being light and odorless, as well as being free of weed, containing beneficial microorganisms, being a rich source of nutritional elements, possessing plant-growth promoting hormones and having high water and nutrient holding capacity (Farmohammadi and Zandian, 2017).Since the combined use of vermicompost and chemical fertilizer in sugarbeet production has received less attention of researchers, this study was conducted to evaluate the possibility of partial replacement of chemical fertilizer with vermicompost in sugarbeet cultivation and its impact on yield and quality of the crop.
A field experiment was conducted based on randomized complete block design with four replications at Kermanshah Agricultural Research Center, Kermanshah, Iran during 2013-2014 growing season. An Iranian monogerm sugarbeet cultivar named Ekbatan was used in the study.Eleven experimental treatments included:1-application of 50% recommended dose of chemical fertilizers based on soil test. 2- application of 50% chemical fertilizers plus 3 tons of vermicompost 3- application of 50% chemical fertilizers plus 5 tons of vermicompost. 4-application of 50% of chemical fertilizers plus 7 tons of vermicompost. 5- application of 100% chemical fertilizers. 6- application of 3 tons of vermicompost. 7-application of 5 tons of vermicompost. 8- application of 7 tons of vermicompost. 9-application of 3 tons of vermicompost plus application of 100% chemical fertilizers minus equivalent amount of nutrients in 3 ton vermicompost. 10-application of 5tons of vermicompost plusapplication of 100% chemical fertilizers minus equivalent amount of nutrients in 5 ton vermicompost. 11-application of 7 tonsof vermicompost plus application of 100% chemical fertilizers minus equivalent amount of nutrients in 7 ton vermicompost.
The results indicated that the effect of the chemical and bio-fertilizers on sugarbeet root yield and gross and net sugar yields was significant.The highest yield of sugarbeet root (57 to 59 t/ha) was obtained from the combined use of chemical fertilizer and vermicompost, and the lowest sugarbeet root yield (42 t/ha) was in the treatment of vermicompost without the application of chemical fertilizer. Since gross and white sugar yields depend on root yield of sugarbeet, the lowest values for these two traits were associated with the treatments No. 6,7 and 8 in which verimcompost was used at the rates of 3 to 7 t/ha without any chemical fertilizers. Reports indicate that vermicompost application at rates between 2 to 7 t/ha had no significant influence on mineral nutrient content of sugarbeet root and sugar percentage, but only resulted in increased sugarbeet root yield (Kabil et al., 2015). Since sugarbeet requires a great amount of nutrients from the soil, in the treatments where no chemical fertilizer was applied (treatments No. 6,7 and 8), the least sugarbeet yields (40.6, 44 and 45 t/ha) were respectively recorded and despite the consumption of vermicompost up to 7 t/ha, it failed to provide the required nutrients for the plant. However, when the sugarbeet plant was treated with 3 to 7 t/ha of vermicompost and was also supplied with 50 % of chemical fertilizer (treatments No. 2, 3 and 4), its yield per hectare was close to the treatment No. 5 (without vermicompost but with full application of chemical fertilizer), which produced 58.3 t/ha sugarbeet yield. This shows that vermicompost and chemical fertilizer are complementary to each other.
Our study showed that to achieve long-term environmental benefits, application of 3 to 5 t/ha vermicompost plus 50% of chemical fertilizer is recommended for the sugarbeet cropping. Nevertheless, given the current price of vermicompost, and based on the economic calculations that only take farm profitability into account, it is not economically feasible to use vermicompost in the sugarbeet production. Therefore, there is a need to reduce the production cost for vermicompost.