In a system approach, a field with the plants cultivated in it may be considered a single system. It is, therefore, necessary to consider the meteorological factors in conjunction with the soil quality and the changing plant cover. In the paper the author gives an example of assessment of the value ranges of meteorological factors, favourable for crop yields, during various stages of plane development. The results for spring barley cultivated on light and medium heavy soils are presented in Table 1. The effect of excessively high and low precipitation, as well as optimum precipitation, during the period from emergence to earing on medium heavy soils is presented in Table 2, and on light soils - in Table 3. The results provided in the Tables confirm the view that soil quality has a differentiating effect on the influence of certain levels of precipitation on the productivity of plants.
The aim of the respective investigations was to prove the possibility of productivity increase of arable sandy soils. Fifty three communes with a great prevalence of sandy soils were selected. The agricultural production of private peasant farms in the communes under study and in the whole country in the period 1980-1982 was characterized (Tables 1, 2). The same is done in relation to selected communes of higher productivity of soils as compared with average (Tables 3, 4). A growth of the NPK fertilization, of the share of barley, cereal mixtures, sugar beets and fodder root crops in sowings has been found in the selected communes in relation to remaining ones. Also a distinct differentiation of the structure of sowings and of livestock depending on increasing share of grasslands has been proved. It has been concluded that one of the basic conditions of arable sandy soil productivity increase would be a suitable adaptation of the structure of sowings and of livestock to natural conditions.