Results and Discussion
- Possibilities for the Use of Oil Contaminated Solids for Agricultural Purposes

According to the above described method aft er site preparation (delivery of clean and contaminated soils from the area in the vicinity of the pipeline rupture location) the plant growth experiment was set up. Those treatments were were included where the changes were expected, both, in the soil (basic chemical properties, metals, oils, PAHs), and in the crops grown (chemical composition of plant material, crop establishment and yield achievment).

The data presented in this paper show slight, barely present chemical heterogeneity of the soil (Table 1). Soil reaction is low acid to neutral in all samples, and varies in the range from pH 6.42 to pH 7.13. Th ese values indicate that soil reaction values are not signifi cantly aff ected by varying quantities of hydrocarbons in the soil. However, this is not the case with the organic matter content in the soil. Th e soil taken from the site outside of the rupture location, the one which was not aff ected by oil well operations has lower organic matter content (treatments 1; 7 and 8). In all other treatments the organic matter content is higher, or it was increased consistent with the increase in the content of oil i.e. hydrocarbons in the soil. For that reason, we fi nd it not surprising that the highest organic matter content has been found in completely contaminated soil taken from the contaminated soil disposal site at the Števkovica-4. The presence of available phosphorus and potassium in the soil is high, which can be attributed to fertilization carried out in plant growth experiment.

The crops being investigated include: winter wheat (Triticum aestivum L.) which was sown on 14 October 2003 and 26 October 2005 respectively, winter barley (Hordeum vulgare L.) sown on 21 October 2004 and soybean (Glycine hyspida L.) sown on 29 June 2005 and 3 July 2006 respectively. Sowing standards applied in these investigations comply with standards for these crops sown in natural field conditions.

Crop establishment recorded, which will be probably be confi rmed by yield achieved, indicates that oil contaminated soil was crucial factor in the decrease of crop establishment, and consequently number of plants and yield reduction. By the similar results in their research reached: Gogoi et al., 2003; Maliszewska-Kordybach and Smreczak 2003; River-Espinoza and Dendooven 2004. Judging by recorded crop establishment, the diff erences in yield achieved are expected, as shown in the tables 2, 3, 4 and 5.

During the first year of research, in winter wheat crops (variety - Zlatni dukat), in the very stages of germination and emergence, diff erences in crop emergence were observed depending on the diff erent content of hydrocarbons in the soil. Emergence of plants being investigated was inversely proportional to the crude oil content of soil. In the treatments with signifi cantly more contaminated soil (treatments 2, 4, 7 and 8) emergence recorded was lower relative to the treatments with less hydrocarbon or oil contaminated soil (Table 2). It is clear that a thin oil coating is formed around the germ thus preventing oxygen infl ux and causing death of the seed and/or slower emergence of the future plant. If an optimum number of plants would have been the one recorded in the check treatment(100%), then in contaminated soil 74% plants crop establishment was recorded; in treatment 3: almost 100%; in treatment 4: 60%; in treatment 5: 88% plants; while in treatment 6, crop establishment was only 50% plants. On the two remaining treatments crop establishment were 57% and 37% plants respectively. Yield achieved on check treatment was statistically higher relative to the other treatments, but no statistically signifi cant diff erences were found between the other treatments.

During the second year of investigation winter barley (variety – Rex) was sown in pots. In the very beginning of crop emergence diff erences were observed relative to the fi rst year of research when the wheat was sown. In the second year crop emergence was rather uniform and that which trend continued throughout the growth process.

The number of plants recorded and crop establishment achieved show no diff erences that were observed during the fi rst year. Based on the established number of plants no statistically signifi cant diff erences were noticed. However, yield achieved indicates statistical diff erences, but less striking than in the fi rst year. Th e greatest diff erence was recorded between the check (treatment 1) and contaminated soil (treatment 2), while other treatments had more or less uniform yield (Table 3).

After barley was removed from the pots, soybean was sown (cultivar Sabina: 00-000 maturity group). Crop establishment and yield show very interesting changes relative to the previous year. As usual, sowing standard for all treatments and all pots was the same. However, in the early emergence stage and also during the growth cycle significant diff erences were observed in crop establishment and yield achieved. Th roughout the growth cycle the largest number of plants was recorded with the check treatment, while with other treatments the established number of plants varied (Table 5). By far the worst crop establishment was found with treatment 6, and with other treatments it was signifi cantly lower than with the check treatment. Th e highest yield was recorded with the check treatment; while with others, yield was signifi cantly lower. Although the experiment was commenced three years ago, it can be noticed that oil contamination even then had signifi cant eff ect on the number of emerged plants and, accordingly, crop establishment of soya.

In order to make a comparison with the fi rst year of research when winter wheat was sown in pots, this crop (the same variety – Zlatni dukat) was sown again in 2005. In the early emerging stage signifi cant changes could be noticed in crop establishment achieved relative to the fi rst investigation (Table 4). As in the fi rst year, around 200 viable seeds per pot were sown and wheat establishment varied from 70% with the check treatment to 50% with the soil completely contaminated with oil. During the earing up stage almost similar percentages were recorded. If establishment achieved with the check treatment is taken as optimum establishment in the earing up stage then 70% establishment achieved could be noticed with contaminated soil (treatment 2), 95% establishment with treatment 4, and with all other treatments crop establishment was around 90% of the optimum establishment achieved with the check treatment.

Knowing that in the first year of research when the same crop of the same type was in the pots, the establishment with some treatments was only 30% of the optimum establishment, the diff erences recorded this year are not considered to be statistically signifi cant, except treatment 2 where was recorded lower number of plants. In correlation with check treatment the treatment where crude fresh oil was used yield was signifi cantly smaller (Table 4). In the latest year of research presented in this paper (in autumn 2006 barley variety Rex was sown again in pots), in July 2006 the soybean was sown again, but this time another cultivar – Dora: 0-00 maturity group. In relation to 2005 when soybean type Sabina was sown in pots, this year, crop establishment (the number of emerged plants) was signifi cantly diff erent. This requires clarifi cation of the diff erence in the number of emerging plants with the check treatment in these two years when in both cases the soybean was sown in the pots. Sabina is a type of soybean which is sown with higher target plant population: 1.400.000 plants per hectare, while Dora is a type which is sown in the target plant population of 650.000 plants per hectare. This accounts for the diff erence in the number of emerged plants. However, based on recorded crop establishment, it can be assumed with a great degree of probability that these diff erences will not be great or statistically signifi cant (Table 5).

The presented results of three-year research and growth of fi ve crops indicate that incidents caused by various oil well operations result in soil changes and changes in the plant material or yield. Similar conclusion results in their research bring forth: Riser, 1998; Rhykerd et al., 1999; Maila and Cloete, 2005; King et al., 2006; Osuji and Onojake, 2006. The changes are particularly noticeable during the first year followed by the obvious decrease in changes in the following years. Similarly, the diff erences in yield and crop establishment between stubble crops and spring crops were observed. Since these are investigations of plant growth in pots, all doubts arising out of such research will be addressed in the three-year field research yet. Thanks to financial contribution of INA Exploration and Production and to an international European project “Development of Programme for Constant Monitoring of Croatian Soils Including the Pilot Project – LIFE05 TCY/ CRO/000105” a field project (near Nature Park Lonjsko polje) was set up using very similar methodology.

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