Lateral Transfer of Organic Carbon and Phosphorus by Water Erosion at Hillslope Scale in Southern Spain Olive Orchards

Dissolved organic C (DOC) and dissolved reactive P (DRP) in runoff and total organic C (TOC) and total P (TP) in sediment were measured in three olive (Olea europaea L.) orchards, during a 3-yr runoff plot experiment under two soil management systems (temporary cover crop in lanes [CC]; conventional tillage [CT]). Losses of DOC (7.8-13.6 kg ha(-1) yr(-1)) were equivalent and losses of TOC (101-432 kg ha(-1) yr(-1)) were higher than those measured in other agricultural systems, so both sources of organic C, dissolved and in sediment, should not be neglected when accounting fluxes to water bodies in the region and soil organic C (SOC) balances at the hillslope scale in olive orchards. Losses of DRP (0.03-0.21 kg ha(-1) yr(-1)) were in the lower to medium range, while losses of TP (2-39 kg ha(-1) yr(-1)) were in the higher range than those reported from agricultural areas. The average annual concentration of DOC in runoff was similar for both systems (20.9-9.1 vs. 21.4-8.7 mL L-1 for CC and CT, respectively) and also for DRP (0.45-0.02 vs. 0.20-0.02 mg L-1 for CC and CT, respectively). Concentrations of TOC and TP were higher under CC, but under CC the TOC and TP fluxes were lower because of reduced sediment losses. To achieve a large reduction in TP and TOC, CC management should provide early ground cover beginning in early fall, the start of the rainy season. A conceptual model of TOC and TP losses was developed to estimate the impact of different cover crop soil conservation strategies.