Studies on technological quality of sugar beets and soil parameters in relation to method of soil fertilization
Abstract
The aim of the studies was to determine suitability of effluent from methane digestion of organic wastes generated during processing of sugar beets for soil application at sugar beet plantations. In the paper parameters of technological value of sugar beet roots harvested from plots with standard values (i.e. optimal values for processing) which were defined by the Institute are discussed. It was shown that effluent from digestion of sugar beet pulp can be utilized as soil amendment on sugar beet plantations without any restrictions bearing in mind content of heavy metals and harmful microorganisms. Nutrients contained in studied effluent from gasifier are available for sugar beet plants at the same level as nutrients from mineral fertilizers. Determination of heavy metals in soil samples taken before and after effluent application did not reveal accumulation of harmful elements in the soil in the result of waste utilization.
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Introduction
Root of sugar beet for processing purposes should show good health status, natural colour and shape, cannot be wilted, frozen or lignified. Technological value of sugar beet is described in the literature as a complex of biological, physical and chemical properties of root which determines positive effects of processing on effectiveness of white sugar gain. The essential roots‟ traits affecting quality of sugar beets are as follows: Biological- shape of root determining content of mineral impurities; resistance to diseases; resistance to bolters production; suitability for storage; chemical -content of sucrose; content of marc; content of α
– amino acid nitrogen and amide nitrogen; content of sodium and potassium; content of invert sugar; content of conductometric ash, content of dry matter, Physical - resistance to outer effects; resistance to outer effects; resilience module; coefficient of diffusion; mean root weight; in tissue compliance to slicing (Malec et al. 2007).
At the high extend quality of feedstock determines the proper course of processing as well as losses of sucrose and efficiency of white sugar gain. In modern sugar factories processing of sugar beet roots into white sugar does not create any technical problems if factory receives roots directly form plantations or after relatively short time storage.
Anyway during campaign of sugar beet processing weather creates lot of problems which result in serious technological problems and final effects are financial losses. The basic factor which often has deterioration effect on status of stored sugar beet roots is temperature. Too low temperatures cause freezing of roots whereas too high temperature results in starting of biochemical processes and development of moulds what degrades quality of roots (Gajewnik 2015).
It is widely known that sugar beets have high requirements concerning soil quality. The medium structured soils are optimal (optimal are medium loams and sandy clay) however high yields can be gained also on heavy clay.
The main parameters of soil for growing sugar beets are as follows: deep plough layer; high content of humic substances; soil reaction close to pH 7.0; good texture; balanced water properties; resistance to sliming and clodding.
The main factor determining sugar beet yield as well as its technological quality is fertilization. Deficits of nutrients in the soil result in yield reduction and their excess is also unfavourable because can considerably affect quality of roots. Sugar beet is one of crops most susceptible to nutrients imbalance in the soil because natural soil fertility cannot cover high crop demands and application of synthetic fertilizers and organic amendments is necessary (Malec et al. 2007).
During the processing of sugar beet roots into white sugar a high amount of beet pulp is generated which has been used as a feed for ruminants. High water content of the pulp which directly increases transportation and storage cost was a prerequisite to searching of new option of effective application of this by-product. The second prerequisite is connected with sharp decrease of cattle number and specialisation in agricultural sector, farm which grows sugar beets often does not run animal production and therefore does not need sugar pulp.
According to EU regulations in Poland share of energy from renewable sources should reach 14% in 2020 (Witek 2008). At the moment biomass is considered as a main source of renewable energy in Poland and is produced on arable lands from short-rotation coppice willow plantations where Salix viminalis and some other willow hybrids are grown (Berruto et al. 2013, Szczukowski et al. 2003).
Option of nutrients recycling by application of organic amendment i.e., effluent from methane digestion of beet pulp can be treated as environmentally friendly closing of nutrients turnover cycle what is desirable for sustainability of agricultural system (Bachmann et al. 2014, Chen 2012).
At the moment in Poland the problem of management of effluent from gasifiers processing different organic feedstocks is difficult because certificate for soil application is necessary if company does not receive this certificate the only alternative is incineration what because of high cost (700 PLN ~ 170 € Mg-1 ) makes investment in gasifier unprofitable.
It is known that soil application of effluent from methane digestion at plantation of Salix viminalis is currently under studies and first obtained results are promising (Urban 2011, Zając 2011).
So far no publication about application of sugar beet effluent at plantations of sugar beets was found. Therefore our studies were undertaken to determine suitability of application of effluent from methane digestion of beet pulp and other organic wastes as an organic amendment on sugar beet plantation.
Conclusion
Effluent after digestion of sugar beet pulp can be applied to the soil bearing in mind content of heavy metals and microbes.It cannot be stated which method of fertilization (mineral fertilizer or digestion effluent) with rate of 120 kg N ha-1 was better in terms of technological quality of feedstock for sugar factory.
Evaluation of technological quality of sugar beet roots harvested from experimental field performed on the base of quality criteria has shown that sugar beet roots from both treatments fulfilled those criteria.
In the soil analysed after sugar beet harvesting high concentration of essential nutrients was found what indicated that soil was not depleted and maintained high fertility.
Nutrients from digestion effluent were available for sugar beet plants in the same level as from mineral fertilizers. Soil after growing sugar beets was enriched of calcium and phosphorus irrespectively of fertilization treatment.
Determination of heavy metals in experimental soil before sugar beet planting and after harvesting did not show any accumulation of cadmium, nickel and mercury and in case of lead, chromium, copper and zinc their elevated level cannot cause any threats for crops and the environment..