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The aim of the paper is to evaluate the relative importance of the selected inputs for cereals yields in Poland. The official statistics of the Central Statistical Office of Poland is used for the analysis. The following data types have been used for the study: inputs of artificial fertilisers per hectare, consumption of pesticides per hectare, certified seed inputs per hectare and average soil quality. All data were collected on the province level for the period from 1991 to 2007. The patterns of the source of productivity were investigated using two methods: interpretation of estimated parameters in Cobb-Douglas production function, and the analysis of squared semi partial correlations. The results applied in the research are similar from both methods. The paper argues that the least "pure impact" is connected with certified seeds, medium impact on chemical originated inputs (fertilisers and pesticides), and the largest impact - to soil quality. The findings of the study indicate that:pure impact of "certified seeds" is below 10%,-- impact of chemical origin inputs is ca. 30% - (influence of pesticides and artificial fertilisers are not to be -- separated (as they strongly depend on each other),pure impact of "soil quality" -- about 60%.-- The era with governing biological progress for the increase of has not yet begun in Polish agriculture. The inputs fertilisers and pesticides are still more important for the growth of productivity. Similar situation was observed in the developed countries as the USA or Germany in the 1970s. [ABSTRACT FROM AUTHOR]