abstract: The paper contains results of statistic and geostatistic analysis as well as an estimation of spatial distribution of selected soil physical and chemical properties on an area of three individual fields and on a whole commune.
Trzebieszów commune was selected as an investigation object. It has an area of 140 km2 and is located in Łukowska Plain, being one of mesoregions of Południowopodlaska Lowland. The commune is of typical agricultural character with 62.3% of arable land, 18.2% of meadows and pastures, and only 13.5% of forestations. The whole commune area is flat, mostly built from outwash material, with loose sands to low clayey sandy soils.
Soil samples were collected from two soil layers (0-10 and 30-40 cm) in 464 points. On the commune area 214 sampling points in random network were located and remaining points in regular networks within three fields. One of these fields (1.8 ha; 150 points) was a mixed cropland (wheat, barley and oats), the second (1 ha; 50 points) was a rye crop and the third (0.25 ha; 50 points) was an idle land. For each point granulometric composition (sedimentation), organic matter content (dichromate wet combustion), pH in KCl and H2O (potentiometry), cation exchange capacity (titration of soil homoionic hydrogen forms) were determined in both soil layers. Moreover, for the cultivated fields soil bulk density in 0-10 cm layer was measured in early spring and late summer, and grain yield of rye and mixed corn (in a set of 1 m2 squares) was determined. Separately for all objects examined basic statistical parameters of the studied soil physical and chemical properties were calculated and analysis of spatial dependence and distribution within the objects was performed using geostatistical methods. Mathematical functions were fitted to the experimentally derived semivariograms that were used further for mapping of soil properties and plant yield applying kriging method.
Soil granulometric composition, low organic matter content and soil chemical properties were characteristic for sandy soils. The average content of the soil granulometric fractions was 55% sand, 32% silt and 13% clay, and 0.7% of organic matter. The soil reaction was acidic to neutral (average pH was around 4.4) and the average CEC was 10 cmol kg-1. However, despite similar proportions and ranges of the values, the above parameters markedly varied within the studied areas. The largest differentiation of values were observed in the sand content, and the smallest in clay content, and higher dispersion was noted in the commune than in particular fields. As a rule, the sand content was greater in top than in lower depth layer and the opposite were found for clay. The organic matter content in all studied object was over 2 times higher in the top layer, the pH was slightly higher in lower layer and the CEC was higher in top layer. The spatial dependence was observed for all soil parameters studied, for both soil layers, and for each of the studied areas. The exponential character of the spatial dependences prevailed for the data description for the commune area and the spherical one for the field areas. Ranges of the spatial dependences were connected mainly with the scale of the object, and with the studied parameters, as well.
The studies performed may have not only theoretical but also practical importance. The general state of the basic soil chemical and physical properties in the commune area was recognized, the parameters describing their spatial variability were determined and the spatial distribution of soil features was mapped. The knowledge on spatial variability of soil properties and plant yield in agricultural fields allowed for determination of the realistic conditions of plant development that may constitute a base for selection of the areas requesting changes in agricultural measures as liming or fertilization, as well as may serve for elaboration of detailed agrotechnical instructions for optimization of the cropping system.