EN
Deficiencies of boron occur in much wider range of crops and climatic conditions than the deficiencies of any other micronutrients. The recent estimation of the micronutrient abundance in Polish soils showed the soluble boron deficiency on the level of 79% on the basis of analyzed 101521 soil samples from arable horizon Deficiency of 1 mole HCl · dm⁻³ soluble boron in soil is usually not fully reflected. by its concentration in crops, also boron application in such cases is of ten ineffective. On the other hand, plants adequately supplied with boron, of ten positively response to boron application. The results prompted us to verify the threshold values estimating soil boron extractable in 1 mole HCl · dm⁻³ , used in Poland since 1986. New calibration of the test hitherto used was elaborated using stepwise multiple regression computation, on the basis of analytical data on soil and plants of sugar beet from 235 fields. Sugar beet is an adequate indicator crop of boron supply level. Investigations on boron supply on large farms, carried out in 1988-1994, covered 561 fields of different crops. It was stated that increased boron content in soil and plants usually affected the yielding proving the yieldforming role of this element. Positive response to the boron application from both, crops of high and low requirements, was shown in strict experiments. Thus, not only high but also lower nutritive needs of that last group of crops, appear not to be covered by natural soil B resources. In such cases boron application usually brouth in measurable effects. Increased yield of sugar beet roots up to 15,8% and biological sugar yield up to 0,95 t per ha under boron application were obtained in field experiments. At boron application the yields of winter and spring rapeseeds rose by 8-18% and maize green matter yields increased by 11 to 30% both at low and adequate level of available B in soil. Yields of cereal grain increased by 8-12%, and in case of oat, as much as by 20%. No symptoms of boron harmfulness were stated when applied in higher doses. The results induce to verify the prevailing opinion on boron ineffectiveness for cereal crops. Needs of further research on the improvement of boron supply to crops are also justified by the results of latest American investigations that showed negative consequences of this element scarcities in human and animal organisms.