The aim of the paper is to evaluate the relative importance of the selected inputs for cereals yields in Poland, especially the importance of certified seed. The following data have been used in research: inputs of artificial fertilizers per hectare, consumption of pesticides per hectare, certified seeds per hectare and average soil quality. All data were calculate for provinces level for each year in the period 2000-2017. The patterns of source of productivity were investigated using two methods: interpretation of estimated parameters in Cobb-Douglas production function and analysis of squared semipartial correlations. The results from both methods applied in the research are similar. The paper argues that the least "pure impact" is connected with certified seeds, medium impact to chemical originated inputs (fertilizers and pesticides) and the largest impact - to soil quality. The findings of the study indicates that: - pure impact of "certified seeds" is 7%; - impact of chemical origin inputs is circa 30% - (influence of pesticides and artificial fertilizers are not to be separated because its strongly depend each other); - pure impact of "soil quality" - about 60%. Domination of chemical inputs in yield formation is visible. It was also stated, that interaction of four inputs constitute from 35 to 62% of total influence on cereals yield. From this perspective it can be concluded that level of all other inputs have to be adequate to soil conditions and one of most important factor is interaction between variety, soil and fertilizing.
Keywords: Cereals production in Poland, biological progress, squared semipartial correlations method.
Jel Code: D24, Q12, Q16