Effects of agricultural management on chemical and biochemical properties of a semiarid soil from central Spain

• SOM sequestration reached a steady state after 15 years of conservation tillage.
• Vertical gradients of most soil properties increased as tillage intensity decreased.
• No effects of tillage systems on soil δ 13C were found.
• Soil δ 15N showed that N cycling under fallow is more closed than in tilled soils.

Long-term agricultural management may change soil C sequestration and alter soil C and N dynamics. The objective of this study was to investigate the impact of several tillage regimes with different intensity on C and N stocks in a Calcic Haploxeralf with a leguminous/cereal rotation under semiarid conditions after 15, 18 and 21 years of management. Seven chemical and biochemical properties (total C, total N, δ 13C, δ 15N, FDA hydrolysis, β-glucosidase and urease activities) were measured in a soil (0–5 cm, 5–10 cm, 10–20 cm, 20–30 cm) under the following agricultural management: fallow (F), no-tillage (NT), zone-tillage subsoiling with a paraplow (ZT), conventional tillage with mouldboard plow (CT), minimum tillage with chisel plow after NT (MTN) or CT (MTC). The results showed that soil reached a steady state of organic matter sequestration 15 years after starting the experiment and that C and N stocks varied greatly with agricultural management, particularly in the top 0–10 cm, and followed the order: F ≈ NT ≈ ZT > MTN ≈ MTC > CT. Fallow and less intensively cultivated soils (NT, ZT) exhibited strong vertical gradients of most properties analyzed (total C, total N, FDA hydrolysis, urease and β-glucosidase activities) with values decreasing with depth, followed by minimum tillage treatments (MTN, MTC) whereas similar values along soil profile were observed in CT treatment. No significant differences in soil δ 13C values were detected among plots with different land use or tillage systems; however, the δ 15N values suggested that, although tillage system did not affect significantly N-cycling processes, a change from “open” to “closed” N cycling occurred when cultivated soils were set aside.