Soil structure after 18 years of long-term different tillage systems and fertilisation in Haplic Luvisol

Soil structure is a key determinant of many soil environmental processes and is essential for supporting terrestrial ecosystem productivity. Management of arable soils plays a significant role in forming and maintaining their structure. Between 1994 and 2011, we studied the influence of soil tillage and fertilisation regimes on the stability of soil structure of loamy Haplic Luvisol in a replicated long-term field experiment in the Dolná Malanta locality (Slovakia). Soil samples were repeatedly collected from plots exposed to the following treatments: conventional tillage (CT) and minimum tillage (MT) combined with conventional (NPK) and crop residue-enhanced fertilisation (CR+NPK). MT resulted in an increase of critical soil organic matter content (St) by 7% in comparison with CT. Addition of crop residues and NPK fertilisers significantly increased St values (by 7%) in comparison with NPK-only treatments. Soil tillage and fertilisation did not have any significant impact on other parameters of soil structure such as dry sieving mean weight diameters (MWD), mean weight diameter of water-stable aggregates (MWDWSA), vulnerability coefficient (Kv), stability index of water-stable aggregates (Sw), index of crusting (Ic), contents of water-stable macro- (WSAma) and micro-aggregates (WSAmi). Ic was correlated with organic matter content in all combinations of treatments. Surprisingly, humus quality did not interact with soil management practices to affect soil structure parameters. Higher sums of base cations, CEC and base saturation (Bs) were linked to higher Sw values, however higher values of hydrolytic acidity (Ha) resulted in lower aggregate stability in CT treatments. Higher content of K+ was responsible for higher values of MWDWSA and MWD in CT. In MT, contents of Ca2+, Mg2+ and Na+ were significantly correlated with contents of WSAmi and WSAma. Higher contents of Na+ negatively affected St values and positive correlations were detected between Ca2+, Mg2+ and Na+ and Ic in NPK treatments.