Vulnerability of olive orchards under the current CAP (Common Agricultural Policy) regulations on soil erosion: a study case in Southern Spain

Abstract

To measure the erosive processes taking place under conditions close to those experienced by farmers and land managers; analyses on spatial units adapted to the size of the farm must be carried out; in a non-isolated way in the case of conventional plots. The objective of this study was to describe and understand the current state – in terms of high soil losses and degradation risk – of a commercial olive farm following the CAP agro-environmental requirements as well as the interaction between soil management decisions and rainfall variability. In this work, rainfall and runoff soil loss for 6.4 hydrological years (2005–2011) were monitored in the outlet of an olive orchard microcatchment of 6.7ha. The equipment used was a flume with an ultrasonic sensor to measure flow height, a rainfall gauge and a sediment sampler. Management systems and olive yields were described for the study period. Different management operations (no-tillage, conventional tillage, no herbicides with tillage and mulch) were applied in the field as a result of the farmer adapting to yearly conditions and to recommendations on good agricultural practice.Our results indicate that the interaction between the factors of annual climatological features and management determined the hydrology, soil loss and olive yield. On the annual scale, cumulative rainfall and rainfall erosivity varied between 600 and 1000mm and 600 and 1500MJMmha−1h−1, respectively. The average annual runoff coefficient was equal to 15±10%, while total sediment loss ranged from <1tha−1year−1 to >20tha−1year−1. Olive yield ranged between 5000kgha−1year−1 and 10,000kgha−1year−1. Above average annual rainfall values were associated with both high yields and soil losses >10tha−1year−1.For the study period, frequent events with a low return period resulted in soil losses >10tha−1, despite the use of different soil management techniques and the compliance of CAP agro environmental regulations. The high risk of soil degradation evaluated might mean that the criterion based on slopes >10% is not suitable for the application of agro-environmental requirements of CAP. On the other hand, further research on conservation technologies such as a more efficient use of cover crops, mulches and plant barriers, controlled traffic farming and/or changes in land use is needed.