Aggregate composition and stability of structural aggregates in humus horizons of forest, pasture and arable field rendzinas

Abstract

The present study includes the results of comparative investigations of aggregate composition and water stability of structural aggregates in humus horizons of calcareous rendzina, Estern Serbia, under native forest and pasture vegetations and the same rendzina utilized long-term as arable field. The results show that aggregate composition and water stability of structural aggregates in the cultivated calcareous rendzina are significantly impaired due to a long-term anthropogenization. In the cultivated rendzina, the content of agronomically most valuable aggregates (0.25-10 mm) is decreased, while the percentage of cloddy aggregates (>10 mm) is increased about 1.5 to 2 times in comparison with the forest and pasture. The forest and the permanent pasture calcareous rendzina had a greater aggregate water stability than the cultivated rendzina in humus horizon. The lowest water stability is found in aggregates >3 mm. The largest mean weight diameters (MWD) of dry aggregates were found in forest calcareous rendzina (4.48 mm, vs. 4.23 mm in pasture and 3.98 mm in arable field). MWD of water stable agregates was higher in pasture (1.32 mm) and forest (1.12 mm) than in cultivated calcareous rendzina (0.54 mm). The structure coefficient of cultivated calcareous rendzina was lower than in forest and meadow. .

U ovom radu je izvršeno uporedno istraživanje agregatnog sastava i vodootpornosti strukturnih agregata u humusnom horizontu karbonatnih, skeletno praškasto-glinovito ilovastih do glinovito ilovastih rendzina na laporcu i laporovitim krečnjacima, pod prirodnom šumskom i pašnjačkom vegetacijom, i istih rendzina koje se dugotrajno (stolećima) koriste kao njivska zemljišta u istočnoj Srbiji. Rezultati istraživanja pokazuju da su agregatni sastav i vodootpornost strukturnih agregata u humusnom, tj. oraničnom horizontu njivskih rendzina znatno pogoršani usled dugotrajne antropogenizacije. Međutim, i pored toga, prema klasifikaciji koju navode ŠEIN et al. (2001), njihov agregatni sastav je još uvek dobar. U njivskim rendzinama sadržaj agronomski najpovoljnijih agregata (prečnika 0.25-10 mm) je znatno smanjen, dok je udeo (prosek 20.55%) grudvastih agregata (prečnika >10 mm) povećan za 1.5 do 2 puta u poređenju sa šumom (13.49%) i pašnjakom (11.84%). U humusnom horizontu istraženih karbonatnih rendzina pod šumom i pašnjakom utvrđena je znatno veća vodootpornost strukturnih agregata nego u njivskoj rendzini. Najmanju vodootpornost pokazali su strukturni agregati prečnika >3 mm. Najveći prosečni prečnik strukturnih agregata (MWD) u suvom stanju utvrđen je u zemljištu pod šumom (4.48 mm), 4.23 mm pod pašnjakom i 3.98 mm u njivskoj rendzini. MWD vodootpornih strukturnih agregata veći je za oko 2 puta u zemljištu pod pašnjakom (1.32 mm) i pod šumom (1.12 mm) nego u njivskoj (0.54 mm) karbonatnoj rendzini. Koeficijent strukturnosti u njivskoj redndzini znatno je manji nego pod šumom i pašnjakom. .