EFFECTS OF APPLICATION OF COMPOST PRODUCED FROM ORGANIC WASTES ON SOME SOIL PROPERTIES AND CHEMICAL COMPOSITION OF LEACHATES

Andrzej Klasa, Anna Nogalska
Department of Agricultural Chemistry and Environmental Protection, University of Warmia and Mazury in Olsztyn, Poland

ABSTRACT

There is a report concerning effects of compost application on some basic soil properties as well as chemical composition of leaching waters examined in a lysimeter experiment. Compost samples were produced from municipal solid wastes of the industrial city of Katowice and of Suwałki city in a relatively unpolluted region of Poland north-eastern by Macrum-Dano technology and from sewage sludge from municipal water treatment plant in city of Zambrów by vermicomposting. Composts were mixed with Cambizols and leaching with distilled water started. Experiment lasted 128 days. Leachates were collected and analysed for concentration of nutrients. Comparison of physicochemical properties of the soil before and after leaching showed that pH values were increased and Hh values were reduced in the course of the experiment. Electroconductivity of soil were reduced particularly in Zambrów treatment. Among the studied macronutrients, magnesium content decreased in the most pronounced way whereas the increase of available phosphorus content was found. Nitrates were leached in a relatively short period and only content of NO₃-N in the first leachate from Zambrów treatment was higher than threshold values for drinking water.

Key words: MSW composts, vermicompost, leachates, soil properties.

INTRODUCTION

Composting of organic wastes has long lasting history but nowadays such a traditional method currently has gained new meanings because it is perceived not only as a method of soil amendment and supplying crops with considerable amount of nutrients but it is advocated as a simple solution of many environmental problems [7].

Evanylo et al. [6] recommended compost as a valuable soil amendment suitable in organic vegetable cropping system. Farell and Jones [8] gave special attention to the environmental benefits of high rates of compost applied for remediation of heavy metals contaminated soils.

Compost application to the soil is considered as an environmentally safe practice and obviously it should not resulted in any pollution of groundwater by nutrients. A particular concern is given to leaching of nitrates and phosphates. If municipal solid wastes and sewage sludge from modern water treatment plants are turned into composts the new risks of heavy metals pollution arise [15]. Considerable uncertainty exists about the long-term fate of polluting trace elements. One observed phenomenon is the stabilisation leading to their immobilisation into insoluble or precipitated forms but the other is opposite i.e. increasing of plant availability through process of mineralization of organic substances in the soil [14].

In Poland municipal solid wastes (MSW) composting facilities usually process mixed municipal wastes because of the fact that wastes separation at source is rather unusual in Polish municipalities. The main reasons are organization and social limitations as well as lack of political and law pressure on local authorities to launch effective system of wastes separation with obtaining biodegradable wet organic fraction. Therefore composts produced from MSW in Poland in compost facilities are biased with the load of some pollutants including trace metals [2, 4-5] and their application potentially can contribute to pollution of groundwater.

Problems with sewage sludge management is not only limited to Poland and it seems to be one of the most important global environmental issue. What is typical for Poland that in our country sludge is not perceived in public opinion as a source of nutrients for agricultural crops but only as a waste and therefore its effective recycling occurs in a very limited extent. Under such circumstances city of Zambrów is an exemption because a whole production of sewage sludge in municipal water treatment plants is turned into vermicompost by red Californian earthworms (Eisenia fetida) [personal communication; 21]. Frederickson et. al [12] pointed out that vermicomposting has a great potential to create a sustainable system of organic waste management. Vermicompost obtained in small experimental installations as well as process of vermicomposting were studied by some authors [2-3, 10-12, 17, 20, 22]. From mentioned above reports it can be concluded that vermicomposting is a biotechnological method of wastes processing which can be widely used to obtain compost of good quality providing that raw material to process (i.e. sewage sludge) does not contain considerable amounts of trace elements.

The aim of the studies was to show if application of relatively high compost rates can cause any risk of groundwater pollution and if there is any difference in potential of compost produced from MSW and sewage sludge.

2. METHODS

2.1. Origin of composts used in the experiment
In Poland the most common method of municipal solid waste (MSW) composting is modified Danish technology Macrum-Dano. This method is used for aerobic composting of mixed MSW and the core element of this technology is the reactor called "biostabiliser" where composting process starts and the most of inert fraction is separated. In biostabiliser composting mass is kept for 24-48 hours and after sieving off so called "hard fraction" (mainly metals, glass and mineral debris) compost is matured for 16-20 months in windrows. Compost produced in two Macrum-Dano installations – one located in the capital of industrial region of Upper Silesia in south-western of Poland – city of Katowice and the second in city of Suwałki in the north-eastern part of Poland which is considered as one of the cleanest cities in Poland. The third studied was vermicompost originated from city of Zambrów small city in Podlasie region [21].

Compost samples and soil before and after leaching procedure were analysed by routine methods used in at centres of soil testing for agriculture and scope of analyses was as follows: pH, conductivity, hydrolytical acidity (in sodium acetate extracts), organic carbon by Lichetefeld's modified by Alten chromium method; available phosphorus and potassium by Engner – Riehm's in calcium lactate extracts, magnesium in CaCl₂ extract by ASA [13].

2.2. Leaching experiment procedures of chemical analyses
Experiment was conducted in cold greenhouse owned by Warmia and Mazury University in Olsztyn. Tested soil Cambisols originated from clay sand (soil showed slight acid reaction pH = 5.02; Hh of 3.2 mmol(+) kg^-1; low level of available phosphorus and magnesium and medium level of available potassium 4.2; 3.50 and 12.50 mg kg^-1 of soil, soil was poor in organic matter 8.5 g kg^-1) and soil was thoroughly mixed with studied organic substances next placed in laboratory lysimeters (diameter = 0.22 m, height = 0.75 m,  total weight of soil mixture = 30.2 kg). Tap was mounted ant the bottom of each lysimeter to collect leachates.

The following experimental treatments (in four replications) with organic substances were tested:

Rates of studied substances were calculated on organic carbon basis at rates equivalent to organic matter in 200 Mg ha^-1 of farmyard manure of good quality.

Soil moisture in lysimeters was adjusted to full field capacity by distilled water and 30 days after start of experiment first leachate was obtained, and then water losses were supplemented by distilled water. Then leachates were sampled in weekly intervals during a period of 128 days and the following parameters in leachates were determined:

All results were processed by Statistica® software and presented as mean values with standard error.

3. RESULTS AND DISCUSSION

Chemical characteristics of composts and commercial pot medium are reported in Table 1. All possible efforts were undertaken to exclude inert substances from two samples of MSW composts (Katowice and Suwałki) before chemical analyses, but it appeared to be impossible to make it and therefore dry matter of two MSW compost was higher but carbon content was lower than in vermicompost from Suwałki. MSW composts were limed what was reflected in higher pH value as well as Ca content comparing to vermicompost.

Addition of MSW composts and vermicompost to the soil resulted in increase of soil pH and reduction of hydrolytical acidity of the soil (Hh) (Table 2). The highest effects were observed in the case of MSW composts comparing to vermicompost because of the fact that liming of MSW composts in Macrum-Dano technology is a standard practice. Similar effects of MSW composts were found also in other studies [1-2, 9-11].

The pronounced effect on reduction of Hh value was observed in treatments with MSW composts application comparing to control and vermicompost. In Suwałki treatment the highest reduction was found.

Composts application resulted in distinct increase of electrocoductivity of soil comparing to control. The higher increase was found in the case of MSW composts application comparing to vermicompost and similar effect indicating the introduction of considerable amount of easily soluble inorganic compounds, as also reported by Licznar et al. [18].

Concentration of available phosphates in the soil was considerably increased only with the  application of vermicompost, in accordance with results reported by Baran et al. [2]. Application of vermicompost from Suwałki resulted also in pronounced increase of magnesium.

Content of organic carbon in the soil (analysed one month after compost application) was positively affected only in the case of treatment with MSW compost from Katowice whereas in the treatments with other two composts the reduction of organic carbon content was noted likely as the result of intense process of mineralization of organic compounds what could indicate incomplete compost maturity, similar effects were observed by Filipek-Mazur and Gondek [9].

Available potassium content was increased by treatment of soil by both MSW composts, whereas in the case of vermicompost produced from sewage sludge a lower concentration of potassium as compared to control was found, in accordance with results of other studies [2]. Nitrates concentration in the soil was the highest in case of treatment with vermicompost comparing to the other treatments and the abundance nitrates with vermicompost fertilization was also reported by another Authors [9, 11, 16, 20].

Soil analytical procedures repeated after completing of leaching showed some modifications of the soil parameters. In all studied soil samples increase of pH in KCl was found as compared with the results in the first series of studies (Table 3). This increase indicated that basic cations were leached at relatively small rates and it was more pronounced in treatments with composts than in the control thus indicating also decrease of Hh values in soil after leaching in all compost treatments. As it was expected electroconductivity of leachates in all treatments was decreased in the course of experiment and the highest reduction was found in the Suwałki treatment and the lowest in control. Changes of electroconductivity were less intensive in control soil thus indicating that composts were sources of easily soluble inorganic salts, as also noted by Łabętowicz and Ożarowski [19]. Content of available phosphorus in soil increased in all compost treatments and decreased in control what clearly showed that this compound occurred in composts in a forms which can be mobilized under the effect of leaching. Organic carbon concentration in soil of Suwałki treatment was unaffected by process of leaching whereas in other treatments mineralization of organic matter was more intense.

Analysis of some chemical properties of leachates collected during the course of the experiment showed that they were related to experimental treatments (Table 3 and 4). It was particularly obvious when nitrates content is taken into account. Addition of vermicopost from Zambrów resulted in intense leaching of nitrates in the two first dates of sampling (day 46 and 52). It is worth to mention that on any sampling date concentration of nitrates in leachates from compost treatments was higher than in the control but threshold value for drinking and groundwater (i.e. 50 mg NO₃-N l^-1) was exceeded only in leachate collected on 46th day from Zambrów treatment. In any other treatment threshold level exceeded the level of 3 mg NO₃-N l^-1.

Phosphates were not leached as quickly as nitrates form studied soils but in Zambrów treatment it was found the highest concentration of this compounds (from 66th to 110th day of leaching) in the experiment. Leaching of phosphates from MSW compost treated soils was on the level of control soils. When threshold limit of PO₄-P of 2.22 mg l^-1 is taken into account it is evident that composts applied in a such relatively high rates as in described experiment cannot cause any environmental hazard for groundwater.

CONCLUSIONS

1. Applied compost samples affected properties of the soil increasing its pH values and electroconductivity and phosphates level increased.
2. During long-time leaching of compost amended soil nitrates level in leachates was enhanced but only in the case of one compost on first sampling date its level exceeded permissible level for drinking water and groundwater and then nitrates were leached in a low amounts.

Accepted for print: 28.06.2013

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