Wpływ dodatku węgla brunatnego na parametry struktury gleby rozwijającej się z gruntów pogórniczych KWB Konin

Soil structure is widely accepted as one of the most important attributes affecting its physical properties and soil humus is commonly considered as one of the most important structure-forming factors. Chemical composition of brown coal similar to that of soil humus was a premise which prompted the application of this component for soil restoration. In 1992, an experiment was established in which brown coal dust in the amount of 1000 tha-1 was applied. The experiment with brown coal comprised four combinations of mineral fertilisation: 0 NPK - without mineral fertilisation, 100 kg N.ha-1 200 kg N.ha-1 and 300 kg N.ha-1. Levels of fertilisation with phosphorus and potassium on all plots with mineral fertilisation were as follows: 40 kg P2O5.ha-1 and 80kg K2O.ha-1. The control included plots without brown coal supplementation and three fertilisation combinations: 100 kg N.ha-1, 200 kg N.ha-1 and 300 kg N.ha -1as well as potassium-phosphorus fertilisation in the amount of 40 kg P2O5.ha-1 and 80kg K2O.ha-1. In both variants winter cereals were cultivated and straw as well as post-harvest residues were ploughed under every year. Investigations of soil structures were carried out on the basis of published original methodological solutions elaborated by Rzasa and Owczarzak in which an aggregate measuring 1 cm(3) is the basis of investigations. The following parameters were determined: dynamic water resistance of soil aggregates (DW), static water resistance of soil aggregates (SW), state of secondary aggregation after dynamic and static action of water, velocity of capillary seepage (Tkmin), minimal (Vkmin) and maximal (Vkmax) capillary water capacity, aggregate compression resistance (Rc). The above-mentioned values were determined in 5 replications. Using methods commonly known and applied in soil science, texture composition, solid state density, hygroscopic capacity (H) and maximal hygroscopic capacity (MH) were also determined. The analysed samples belonged to two neighbouring texture groups sandy barns and light loams. It is evident from the performed investigations that the application of brown coal resulted in loosening of the arable soil layer. The observed increase of porosity in absolute values by approximately 15% means increase in pore numbers of about 50% in relation to the numbers of pores in the soil without brown coal supplementation. The aggregates collected from the soil without the addition of brown coal were characterised by the resistance ranging from 1.460 to 1.798 MPa. It was almost three times greater than that of aggregates with brown coal addition (0.453-0.775 MPa). The addition of coal reduced from two to five times the resistance to dynamic water action. The degree of breakdown of the analysed primary aggregates measured by the so called sum of secondary aggregates (mezo-aggregates) measuring >0.25 mm varied widely both for dynamic and static water action. The addition of brown coal worsened soil secondary aggregation. This also contributed to the increase of hygroscopic and maximal hygroscopic water capacity. The hygroscopic capacity of aggregates with the addition of brown coal was by about 50% and of maximal hygroscopic capacity - by about 100% greater in comparison with those without the addition of brown coal. Moreover, the addition of brown coal also accelerated water transfer in aggregates. Water translocation time in aggregates without the addition of brown coal was by about three times higher. Minimal capillary water capacity of soil aggregates collected from the variants without brown coal supplementation ranged from 49.3 to 55.8%, and maximal capillary water capacity - from 55.1 to 74.8%. Minimal and maximal capillary water capacity was considerably greater in aggregates collected from variants supplemented with brown coal and amounted to: from 47.4 to 83.9% and from 61.8 to 84.5%, respectively. The performed investigations revealed that the addition of brown coal loosened bulk soil in the arable soil level leading to its improved susceptibility to the action of cultivation tools. However, during periods of low total precipitation, these soils are sensitive to excessive sputtering. This was confirmed by the results associated with water resistance of soil aggregates, resistance of aggregates to compression as well as secondary aggregation following static and dynamic water action. The addition of brown coal increased possibilities of water retention but majority of this water was not easily accessible to plants as indicated by the research results concerning H and MH as well as capillary water capacity.