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The success and profitability of growing crops depends significantly on the fertility of the soil, i.e. the amount of required fertilizers. On the other hand, the reduction of humus content is among the most significant indicators of soil degradation in Croatia. For this reason, 1, 000 composite soil samples on a depth of 0-30 cm in eastern Croatia were collected firstly in 2005 and 2006 (500 samples each year), and then again from the same locations after 15 years, i.e. in 2020 and 2021. In total, 2, 000 samples from 1, 000 different production plots were collected and this paper presents an analysis of changes in soil organic matter content on 780 plots under crops production. In the initial set of samples (2005 and 2006), an average of 2.25% soil organic matter (SOM) was determined, and after 15 years, an average of 1.99% SOM was determined, i.e. 9.89% less SOM. The decrease in SOM was determined on three quarters of analyzed arable soils in Croatia which indicates a very serious degradation of soil fertility. An average of 21.7 t/ha of SOM was lost (9.9% of initial SOM content) in these soils over a period of 15 years (1.45 t/ha per year), which represents a significant loss of nitrogen pool of 1.086 kg/ha, i.e. an annual loss of 72.43 kg/ha. The decrease in humus content results in a decrease of the mineralization potential by an average of 18.7%, but in 43% of the soils the mineralization potential is reduced by more than 20%. The determined reduction of the N pool over 15 years indicates that more than 1% of the initial amount of nitrogen has been mineralized per year, and therefore models that predict mineralization of more than 1.5% of nitrogen in the conditions of continental Croatia should be used. The result of humus degradation is also reflected in the fact that more than 195 kg/ha of N is needed for corn fertilization on more than three quarters of the analyzed soils, and 15 years ago this was needed on half of the soils. The losses of the nitrogen pool and the consequent higher need for fertilization show how important it is to stop the degradation of the humus content in soils, even if only the direct reduction of the N content is taken into account. |
