In recent years there has been a shortage of organic fertilizers. This can be explained by the economic crisis and the lack of incentives in the livestock sector as well as increased health requirements for livestock breeding, in accordance with European Directives. As a negative result, the number of breeding animals and poultry fell sharply. On the other hand the increase of subsidies for development of organic farming, farmers’ interest to this program has steadily risen. This requires necessity to create and implement new organic products that serve as enhancers fertilizers in agricultural sector.
Biogas production through anaerobic digestion (fermentation) is a method where the solid and liquid fractions of manure as well as wide range of organic wastes and energy crops are converted into renewable energy and organic fertilizer, suitable for application in agriculture (Seadi et al., 2009; Simeonov et al., 2012(a); 2012(b)). So, the benefits of biogas are twofold: on one hand, the production of cheap energy and other biomass fermentation, called secondary (digestate), are priceless organic fertilizers rich in macro and micronutrients. Compression to natural manure the digestate shows many advantages: easy and quick utilization because of the homogeneous structure, higher content of nutrients, a balanced C / N ratio; minimum odors, etc. Depending on the type of feedstock, the purity of the compost (digestate) can be controlled by maintaining a suitable temperature for fermentation, pasteurization or sterilization to inactivate the pathogens, weed seeds, etc. (Marinova et al, 2012; Seadi et al., 2009; Simeonov et al., 2012(a); 2012(b);)
The aim of this study is to establish the feasibility of digestate as fertilizer, on the growth and quality of leafy vegetables such as parsley.
Materials and methods
The experiment was conducted in the greenhouse of ISSAPP “N. Poushkarov” under controlled conditions. The plants were grown in 1kg pots. Each treatment consisted of four replications. To establish efficacy of digestate and as an indicative culture is used parsley (Petroselinum hortense var. Foliosum), grown as a secondary culture after lettuce (Lactuca sativa). In every pot were sowed 20 seeds of parsley. During the vegetation the parsley has been mowed twice. In both experiments as a test crops were used leafy vegetables. It is well known that leaf vegetables are especially appropriate as indicators to test specific factors (Dinev and Mitova, 2011; Dinev and Mitova, 2013; Mengel and Kirkby, 1982).
Two soil types were selected for the study – Smolnitsa and Alluvial meadow soil, which are classified according to the Bulgarian soil classification (Penkov et al., 1992). For achievement of equivalent interpretation and clear presentation of scientific results, the information on soil types, requires parallel correlation with international classifications (Ivanov, 2010, 2011). In this regard, the soils types are classified according to the World Reference Base for Soil Resources (IUSS Working Group WRB, 2006) as follows: Smolnitsa – Vertisols; Alluvial meadow soils – Fluvisols.
The experiment on both soil types contains the following variants:
- Control- without fertilizers;
- N300P300K300-mineral fertilization
- 5% — digestate to the soil weight;
- 15% — digestate to the soil weight;
- 25% — digestate to the soil weight;
- 35% — digestate to the soil weight;
Variant — 2, where fertilization with mineral fertilizers in quantities of 300 mg.kg-1 applied as NH4NO3, Са (Н2РО4)2.2Н2О and KCl also serves such a controls of the tests with digestate.
Used digestate was produced in a pilot biogas installation from anaerobic digestion from a mixture of pig manure and fruit and vegetable waste in a ratio 70/30 % (Simeonov et al., 2012 9(a)). Chemical and agrochemical characteristics of digestate and soil, used in the experiments, were published in our previous study (Simeonov et al., 2012(b)) and are presented in Tablе – 1.
Chemical and agrochemical characteristics of the digestate (with a ratio of 70% SM and 30 % FVW) and the soils.
|Water %||98.90||Total N %||0.21||0.64|
|Dry matter %||1.10||Total P %||0.14||0.28|
|Organic C %||24.88||MobileNH4+-N mg.kg-1||11.8||8.2|
|Total P %||7.67||MobileNO3—— N mg.kg-1||7.10||5.8|
|Total N %||10.80||Mobile Р2О5 mg.100g-1||29.10||0.22|
|Total K %||9.02||Mobile К2О mg.100g-1||21.80||36.9|
|Mobile NH4+-N %||5.48|
|Mobile NO3— N %||0.53|
|Mobile Р2О5 %||0.54|
|Mobile К2О %||1.25|
|Heavy metals mg.kg-1||Heavy metals mg.kg-1|
|As||< 5.0||As||< 1.0||< 1.0|
|Cd||< 1.0||Cd||< 1.0||< 1.0|
The results of soil analysis (Table-1) showed that alluvial-meadow soils are characterized with low mineral nitrogen content (18, 9 mg.kg-1) with available ammonium form-11, 8 mg.kg-1. Soils are well supply with available phosphorus (29, 1 mg Р2О5.100g-1) and available potassium (21.8 mg К2О.100g-1). The total amount of heavy metals in soil is below permissible concentrations. Haplic Vertisol also has low content of mineral nitrogen-14.0 mg.kg-1 and available ammonium form is 8, 2 mg kg-1. This soil possess very poorly reserve of available phosphorus 0, 22 mg-1 Р2О5.100g-1 and very well reserve of available potassium 36, 92 mg К2О.100g-1). The heavy metals content is below permissible concentrations (Table-1).
Top of Form
- The content of macro and microelements and some heavy metals in soil were determined by standard methods (Arinushkina, 1970);
- The total nitrogen – according to the method of Kjeldahl;
- Ammonium and nitrate nitrogen colorimetrically;
- Available forms of phosphorus and potassium by method of P. Ivanov, 1984; Available forms of microelements (heavy metals) — EDTA-method;
- Total heavy metals content by method with «aqua regia» ISO 11466;
- pH potentiometrically in water solution and a solution of potassium chloride.
In plant tissue the total nitrogen content was determined by the Kjeldahl method by decomposition with concentrated Н2SO4 and 30% Н2O2. The other macro and micronutrients were determined by «dry» burning in muffle furnaces and subsequently dissolved in 20% HCl accounting with atomic-absorption spectrophotometer.
In greenhouse experiment fresh weight of plants was determined by weight in grams per pot. The content of plastid pigments in fresh mass — (mg.g-1) was determined by the method of Vernon, 1960. From plant samples after drying at 65 0С with prior fixation is determined dry matter (ACB %) – by weight. The content of total sugars was determined refractmetrically — (%) (Digital refractometer — 32145). The nitrate content is determined on device RQ flex plus 10 Merck.
Results and Discussion
After harvesting lettuce, the soil samples were taken from all variants for analysis. They are used as a source for background information in conducted experiment with parsley. Table-2 is presenting the values of available forms of nitrogen, phosphorus and potassium in the variants; it appears that all fertilized variants after ending the experiment with lettuce have high residual concentration in all three macroelements.
The values of mineral nitrogen in Fluvisols are between 5.03 and 6.02 times higher compared to the initial control soil without any treatments. Loading of Vertisols whit mineral nitrogen is even greater, between 8.12 and 16.16 times higher than the initial soil content. Similar trends are observed regarding the available forms of phosphorus and potassium. In Fluvisols residual available phosphorus content is between 1.12 and 2.63 and for Vertisols are between 14.23 and 300.6 times higher than the control. For K2O values in Fluvisols are 1.51 to 2.07 times higher than the control, and for Vertisols they are in the skope 1.25 to 2.74. It is noteworthy that the residual mineral nitrogen contents (Zlatareva et al., 2012 (a); (b)) in both soils were significantly higher than the available forms of phosphorus and potassium (in the exception of P2O5 in the variant of mineral fertilization in Vertisols).
The obtained values for the reserves of both soil types, regarding the available forms of N, P and K, which are initial for the experiment whit parsley, show high storages (especially on leaching Vertisols) for the all three macronutrients (Table-2).
Vegetative mass of parsley, depending of digestate percentage content in soil, soil type and sampling point.
|1.Control- without fertilizers||7,45||7,39||0,364||3,57||3,15||0,912||3,96||3,88||0,460||3,01||2,96||0,402|
- Influence of fertilization on parsley biomass accumulation.
Biomass yields of test culture from two mows were showed (Table-3).
Agrochemical characteristics in Fluvisols and Vertisols before seeding parsley
|1.Control- without fertilizers||5.8||12,7||21.2||18.4||6.1||9,6||0.20||29,8|
The differences in biomass accumulation between two soil types are more significant in the first mow. On Fluvisols the average yields of parsley is higher than in Vertisols. In first mow average biomass of all variants on Fluvisols is 60.7% and in second is 28.7% higher compared with Vertisols. It is known that parsley is growing well on light and aerated soils (Rankov and Boteva, 1995; Dinev and Mitova 2013). This is proved by yields from control variants. Compared with Vertisols, in both mows yields are higher in Fluvisols with 108.7 % in the the first mow and 31.6% in the second. The yield data showed that in both soil types in both mows, the higher produced biomass were observed in variants with 25% digestate. On Fluvisols statistically proven differences were estimated between plants with mineral fertilizer and variants with 25% digestate, while in Vertisols those differences were not observed. Increasing percentage shares of digestate in soil after testing five variants exerted strongly depressive effect on plant development. Plant biomass in the variant with 35% digestate fell with 20.2 % in first mow and 32.97% in the second, compared to treatment with 25% digestate. In comparison with the yield in variants with 25% digestate, in Fluvisols yields decreased in variants with 35% digestate whth 84.8% in the first mow and 90.95% in the second. Depressed plant growth in variants with 35% digestate, is visually expressed in lessening and yellowing of the leaves and intrauterine growth of the root system. This picture appears most strongly depression in the first mow in Vertisols. Probable cause of depression in development and production of parsley, for variants with more than 25% added digestate is not only an imbalance in the receipt and utilization of nutrients from plants, but also degradation of physical and mechanical composition in soil.
- Content and export of nutrients with parsley biomass.
Data about total nitrogen content in plant biomass in both soils and both mowing are approximately the same: between 1.7 and 2.7 % in the first mow and 1.2 and 2.7% in the second (Table-4).
Nutrient content in parsley vegetative mass (%)
|1-st mow||2-nd mow|
|Total N||Р2О5||К2О||Total N||Р2О5||К2О|
|1. Control- without fertilizers||1,7||0,17||3,8||1,2||0,36||3,8|
|3. 5%- digestate||1,8||0,19||4,0||2,0||0,39||4,2|
|4. 15%- digestate||1,9||0,20||3,8||1,9||0,33||3,9|
|5. 25%- digestate||2,1||0,19||5,0||1,7||0,32||4,1|
|6. 35%- digestate||2,0||0,19||5,1||2,1||0,33||4,3|
|1-st mow||2-nd mow|
|Total N||Р2О5||К2О||Total N||Р2О5||К2О|
|1. Control- without fertilizers||2,0||0,16||5,8||1,7||0,19||4,6|
|3. 5%- digestate||2,0||0,21||5,3||1,9||0,25||4,4|
|4. 15%- digestate||2,1||0,17||5,2||1,8||0,32||5,3|
|5. 25%- digestate||2,4||0,19||6,1||2,7||0,32||4,1|
|6. 35%- digestate||2,3||0,19||6,0||1,8||0,23||5,3|
The values of total nitrogen in Vertisols from the first mow are higher, compared to the second measurements. In Fluvisols similar pattern is not observed. In the variants with 25% digestate in both soils highest content of total N in parsley was measured: in Fluvisols -2, 1%, and the Haplic Vertisols 2.7%. Plants with mineral fertilization on both soils type have similar values of total nitrogen compared to those with 25% digestate application.
The Р2О5 content in plant biomass (Table-4) in both soils types varies between 0.16 and 0.28% for the first mow and 0.19 to 0.43% in the second. In both soils the phosphorus content in the biomass of the second mow is much higher than in the first. In Fluvisols, the variant with mineral fertilization has highest content of phosphorus, 0.28% in the first mow and 0.43% in the second. In Vertisols pattern it wasn’t observed in accumulation of phosphorus in plants tissues. The first mow in the variants with 5% digestate highest phosphorus content in plant (0.21%) was onbserved, while in the second mow with application 15 and 25% digestate 0.32% phosphorus was found.
The content of K2O in plant tissue (Table-4) is between 3.8 and 6.1 %in the first mow and between 3.8 and 5.3 % in the second. Like the nitrogen, content of potassium in the first mow in Vertisols is greater than the second. High potassium content in the first mow were found in the 5 and 6 variants with values 5 and 5.1% for Fluvisols and 6.1 and 6.0 for Vertisols. With these values we could explain the high yields in the variants with 25% digestate but not a depression of plants for variant 6 with — 35% digestate. In the second mow similar pattern was not observed.
The measured content of macronutrients (total N, P2O5 and K2O) were comparable to the results obtained in other studies (Rankov and Botev, 1995).
Export of nutrients with parsley vegetative mass (g.pot).
|1-st mow||2-d mow||1-st mow+ 2-dmow|
|Total N||Р2О5||К2О||Total N||Р2О5||К2О||Total N||Р2О5||К2О|
|1.Control- without fertilizers||0,35||0,04||0,79||0,25||0,08||0,79||0,60||0,12||1,58|
|3. 5%- digestate||0,36||0,04||0,79||0,40||0,08||0,84||0,76||0,12||1,63|
|4. 15%- digestate||0,39||0,04||0,78||0,38||0,07||0,79||0,77||0,11||1,57|
|5. 25%- digestate||0,44||0,04||1,05||0,34||0,06||0,82||0,78||0,10||1,87|
|6. 35%- digestate||0,43||0,04||1,10||0,43||0,07||0,88||0,86||0,11||1,98|
|1-st mow||2-d mow||1-st mow+ 2-d mow|
|Total N||Р2О5||К2О||Total N||Р2О5||К2О||Total N||Р2О5||К2О|
|1.Control- without fertilizers||0,37||0,03||0,94||0,33||0,04||0,90||0,70||0,07||1,84|
|3. 5%- digestate||0,36||0,04||0,95||0,38||0,05||0,88||0,74||0,09||1,83|
|4. 15%- digestate||0,41||0,03||1,00||0,35||0,06||1,03||0,76||0,09||2,03|
|5. 25%- digestate||0,54||0,04||1,22||0,54||0,06||0,81||1,08||0,10||2,03|
|6. 35%- digestate||0,40||0,03||1,05||0,37||0,05||1,09||0,77||0,09||2,14|
Results in Table-5 showed the exported quantities by the crop from the soil of total nitrogen, phosphorus and potassium by both mows of the parsley and exported. In Fluvisol, with highest total exported N, P2O5 and K2O distinguished the variant with full mineral fertilization. From the variants with digestate fertilization the hihgest export of the three macronutrients is observed were 35% digestate were added. On Vertisols the total amounts of N and P2O5 were exported in the variants with the highest yield (with 25% digestate application). Plants with mineral fertilization exerted the highest export of K2O in Vertisols. In variants with organic fertilization, the highest K2O export in plants suffering from excessive rates of organic fertilizer were estimated (35%. Digestate).
As a summary we can say that parsley, as other crops that is preferably potassium dependent (Mitova and Dinev, 2011), exports largest amounts of K2O with biomass, followed by total N and P2O5.
III. Influence of fertilization on some physiological parameters in parsley.
Table-6 presents obtained results for the plastid pigments content. Their content depends on many conditions: type, variety, development stage, temperature, lighting conditions, nutrition, etc. The chlorophyll (Chl) content can serve as an indirect index characterizing growth conditions. The chlorophyll «a» is more sensitive to external influences than chlorophyll «b» (Petrova, 2010). In both mows chlorophyll content in Vertisols is higher than in Fluvisols. The Chl «a» values for Fluvisols in the first mow ranges from 6, 23 to 8, 32 mg.g-1 and for Vertisols from 7, 08 to 10, 95 mg.g-1. For the second mow, values are between 5, 02 and 7, 5 mg.g-1 for light soil and between 7, 0 and 9, 06 for Vertisols. Chl «b» values in the Fluvisols for the first date varies from 3, 38 to 4, 73 mg.g-1 and from 3, 90 to 5, 08 mg.g-1 – for Vertisols. In second mow, results from 3, 47 to 3, 94 mg.g-1 on Fluvisols and from 3, 56 to 4, 29 mg.g-1 in Vertisols were observed. The highest chlorophyll content in both soil types for both mows were observed in the variants with 25% digestate, which seems to be an optimal variant. The ratio between Chl «a»/Chl «b» is in the lower range (2 to 3/1) according to obtained results for plant development (Berova et al, 2007). In first mow of Vertisols, the ratio between Chl «a» / Chl «b» is closest to those referred in literature.
Content of plastid pigments in parsley leaf, depending on soil type and sampling point (mg%)
|1-st mow||2-d mow|
|1.Control- without fertilizers||6,23||4,09||1,52||5,02||3,47||1,45|
|3. 5%- digestate||7,48||4,06||1,84||6,80||3,57||1,90|
|4. 15%- digestate||7,93||4,52||1,75||6,95||3,77||1,84|
|5. 25%- digestate||8,32||4,73||1,76||7,51||3,94||1,91|
|6. 35%- digestate||6,98||3,38||2,07||6,03||3,65||1,65|
|1-st mow||2-d mow|
|1.Control- without fertilizers||7,08||4,57||1,55||7,00||4,17||1,68|
|3. 5%- digestate||8,34||4,25||1,96||6,72||3,70||1,82|
|4. 15%- digestate||9,34||4,58||2,04||7,50||3,92||1,91|
|5. 25%- digestate||10,95||5,08||2,16||9,06||4,29||2,11|
|6. 35%- digestate||7,82||3,90||2,01||7,00||3,64||1,92|
Despite the fact that other indicators in variants with mineral fertilization shows good results in both used soils, in terms of pigment content they defer to variant with 25% digestate.
Values of biochemical parameters characterizing the quality of production were presented /Table-7; Fig.1; Fig.2/.
Effects of fertilization, soil type and time of sampling on the quality indicators in the parsley
|1-st mow||2-d mow||1-st mow||2-d mow|
|3. 5%- digestate||352,7||129,5||318,6||82,6|
|4. 15%- digestate||397,2||163,7||352,6||194,4|
|5. 25%- digestate||1695,6||278,0||361,3||372,7|
|6. 35%- digestate||1745,8||1080,3||300,0||276,0|
Dry matter (Manuelyan, 1982; Stancheva, 2008) expressed values of components of vegetable production. Its qualitative composition is genetically determined, but the quantitative aspect of this indicator is influenced by a number of environmental conditions. In the experiment tendency was observed /Fig.1/ that absolute values of plant dry matter (ADM) on Fluvisol for both mows are higher than those on Vertisols. For the Fluvisol from the first mow values are between 19, 75 and 21, 99%, while in Vertisols they are between 17, 44 and 20, 01%. In the second mow they varied between 20, 07 to 20, 86% for Fluvisol, while for Vertisols they are between 19, 44 and 21, 03%. The plants from variants with mineral fertilization have the most ADM content in both mows on Vertisols, but only in the first mow on Fluvisol. A similar pattern was observed in previous experiments with organic and mineral fertilization growing other crops (Mitova and Kancheva, 2010; Mitova and Dinev, 2011, Stancheva, 2004).
Carbohydrates are one of the main indicators determining the biochemical activity of plants. As a product of photosynthesis they are an indicator for carbon assimilation activity, energy source and substrate for metabolic transformations of hydrocarbonates (Mengel and Kirkby, 1982; Petrova, 2010, Stancheva, 2008). The measured total sugar content in this study was indicators for those processes. In terms of total sugars (Fig.2) in the first mow highest value have plants with mineral fertilization-15, 2% in the alluvial soil and 13, 3% in Vertisols. In plants with organic fertilizer the variants with 25% digestate have the most sugars content in mows, alluvial 14, 1% and 12.9% on Vertisols. In second mow the highest content of total sugars in the alluvial soil, have plants fertilized with 25% digestate followed by variants with mineral fertilization. In Vertisols with 15% digestate the highest content of total sugars were observed. The reported average values of total sugars in both mows on alluvial-meadow soils are higher than those obtained on leaching-Vertisols.
The measured nitrate content in parsley biomass (Table-7) showed a sharp drop in the second mow. The nitrate content in parsley grown on alluvial soil is considerably higher than those grown on Vertisols. In the first mow the differences are very large. Average nitrate content in the fresh mass of plants on alluvial soil is more than 3, 3 times higher that on Vertisols (alluvial soil 1203, 1 mg.kg-1 fresh weight and leaching- Vertisols 358, 9 mg.kg -1 fresh weight). In the second mow those differences remained, the nitrate in plants on alluvial soil were 2, 4 times higher than those on Vertisols.
In the conducting experiment the highest nitrate content of the plants are in variants with mineral fertilizer grown on both soils in both mows. In the first mow from alluvial soils most plant nitrates are observed in variant fertilized with 35% digestate -1745, 8 mg.kg-1 fresh weight. In the second mow the trend remains and the highest nitrate content is in he same variants -1080, 3 mg NO3.kg-1 fresh weight. However on Vertisols in both mows in the variants with 25% digestate more nitrates were found than the variants with 35% digestate. This is probably due to depression and abnormal metabolism in the cells of plants fertilized with 35% digestate.
1. The experiment established a positive effect of fertilization with digestate on the parsley development. On both soil types in both mows the highest biomass and the highest chlorophyll content measured in variants fertilized with 25% digestate. In Fluvisols higher quantity of vegetative mass was obtained as compared to Vertisols. In the first mow, the average biomass on Fluvisols is 60, 7% and in the second 28, 7% greater than that obtained in Vertisols.
- The highest export of total N, P2O5 and K2O in plants grown on Fluvisol is observed when mineral fertilization was applied, while on Vertisols highest export of macro elements is observed in variants with 25% digestate.
- The amount of dry matter and total sugars content in plants grown on Fluvisol in both mows were higher than those in Vertisols. Plants with mineral fertilization have the highest content of dry matter and total sugars in the first mow on both soils types. In second mow of plants grown on Fluvisols the highest content of total sugars was found in the variant with 25% digestate and on Vertisols with 15% digestate.
- Parsley biomass grown on Fluvisols contains more nitrates than plants on Vertisols. The high levels of nitrate have plants with mineral fertilization for both mows. In variants with organic fertilization on Fluvisols, the highest nitrate content have plants with 35% digestate in both mows while in Vertisols highest nitrate content was measured in plants fertilized with 25% digestate.
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- Zlatareva E., S. Marinova, H. Pchelarova, R. Tontcheva, A. Katsarova, S. Mihailova. 2012. (a) Changes in soil properties as a result of fertilization with compost produced in biogas production. Environmental engineering and environment, (2): 5-11.[schema type=»book» name=»POSSIBILITY FOR USING DIGESTATE TO PRODUCE A QUALITY PLANT PRODUCTION» description=»The experiment was conducted on two soil types in the greenhouse of ISSAPP “N. Poushkarov” under controlled conditions. In two harvested of parsley were determinate the influence of mineral and organic fertilizer (digestate) on biomass development, absorption of nutrients and some indicators characterizing the quality of the experimental culture. It was found that parsley plants developed on Fluvisol and Vertisols, in both mows, the biggest biomass is forming in variant fertilized with 25% digestate, in this variant also is measured the highest chlorophyll content. The biggest vegetative mass, dry matter, total sugars and nitrate is established on Fluvisols compared to Vertisols. The export of nutrients, dry matter and total sugar content in first mow is biggest in Fluvisols with mineral fertilization, but these plants in both mows as with biggest nitrates accumulation. In Vertisols biggest export of macro elements is reported in versions with 25% digestate. In the second mow in Fluvisols with the highest content of total sugars outlines options with 25% digestate and leaching on Vertisols one with 15% digestate.» author=»Ivanka Mitova, Vera Petrova, Elena Zlatareva» publisher=»БАСАРАНОВИЧ ЕКАТЕРИНА» pubdate=»2016-12-20″ edition=»euroasia-science_28.04.2016_4(25)» ebook=»yes» ]