Long-Term Winter Wheat Cropping Influence on Soil Quality ... 67RESULTS AND DISCUSSION
Lessons Learned from a Long-Term Experiment
“Crop Rotation”
Soil Physical Properties
Soil texture at the experimental plots presented in Vučić e (1960), Belić et
al. (1986), Milošev (2000), Šeremešić (2012) was changed over a course of 50
years of experimental running. The unfertilized plots showed significant
differences that could be attributed to the omission of the fertilizers, whereas
plots with regular application of fertilizers were less changed. The slit content
in plow layer was depleted and more recent studies of the soil texture showed
decrease of a clay content and increase in the fine sand content. Additional
studies must be conducted to quantify wind erosion contribution and to
interpret changes of soil texture. Difference in soil texture was also observed
between crops. Soil texture analyses showed that clay fraction is lower after
winter wheat compared with the maize cropping systems. This could be
explained with the rainfall effects on the topsoil during the autumn-winter
season on the winter wheat plots that washout finest soil aggregates in deeper
layer. In contrary, silt fraction is higher in top soil after winter wheat
compared with the maize (Šeremešić, 2012).
The maintenance of a favorable soil structure is crucial for sustainability
of the agricultural systems, and largely depends on the stability of the
aggregates. Analyses of dry aggregate size classes (dry sieving) after winter
wheat showed similar arrangement of aggregates in different wheat-based
cropping systems. Variations between the fertilized and the unfertilized
systems were not identified suggesting that NPK addition had less effect on
dry aggregate distribution (Šeremešić et al., 2013). Soil under winter wheat
showed better arrangement of the dry aggregate soil classes compared with the
soil under maize. The topsoil of wheat monoculture has the highest
concentration of the aggregates that is considered as indicators of good
structure (0.25 to 2 mm). Vučić (1960) accessed the content of water stable
aggregate (WSA) content in the “Crop Rotation” experiment and establishes a
positive relationship of winter wheat growing and WSA, but he argues that the
value of the WSA were inversely proportional to ratio of winter wheat in the
rotation. Most recent study (Šeremešić, 2012) showed significantly higher
content of the macroaggregates on the adjacent untilled grass (77.24%)
compared to the plow layer of the soil samples from arable soils (43-57%).
This result can be explained by continuous intensive cropping that influences