Effects of Land Management on Different Forms of Soil Carbon in Olive Groves in Mediterranean Areas

This study analyses soil organic carbon (SOC) and hot‐water extractable carbon, both measures of soil quality, under different land management—(i) conventional tillage (CT); (ii) CT plus the addition of oil mill waste alperujo (A); (iii) CT plus the addition of oil mill waste olive leaves (L); (iv) no tillage with chipped pruned branches (NT 1 ); and (v) no tillage with chipped pruned branches and weeds (NT 2 )—in a typical Mediterranean agricultural area: the olive groves of Andalusia, southern Spain. SOC values in CT, A, NT 1 and NT 2 decreased with depth, but in NT 2 , the surface horizon (0–5 cm) had higher values than the other treatments, 47% more than the average values in the other three soils. In L, SOC also decreased with depth, although there was an increase of 88·5% from the first (0–10 cm) to the second horizon (10–16 cm). Total SOC stock values were very similar under A (101·9 Mg ha −1 ), CT (101·7 Mg ha −1 ), NT 1 (105·8 Mg ha −1 ) and NT 2 (111·3 Mg ha −1 , if we consider the same depth of the others). However, SOC under L was significantly higher ( p  <  0 · 05 ) at 250·2 Mg ha −1 . Hot‐water extractable carbon decreased with depth in A, CT and NT 1 . NT 2 and L followed the same pattern as the other management types but with a higher value in the surface horizon (2·3 and 4·9 mg g −1 , respectively). Overall, our results indicate that application of oil mill waste olive leaves under CT (L) is a good management practice to improve SOC and reduce waste. Copyright © 2014 John Wiley & Sons, Ltd.