The impact of intercropping, tillage and fertilizer type on soil and crop yield in fruit orchards under Mediterranean conditions: A meta-analysis of field studies

A meta-analysis specially based on tree crops was conducted to evaluate the changes in soil organic carbon (SOC), soil N and P, and crop yield in a Mediterranean climate, which are affected by: (i) management practices (crop diversification, tillage, fertilization); (ii) environmental characteristics, such as soil clay and climatic variables; and (iii) study length. The aim of this study was to assess the benefits of crop diversification, conservation tillage (minimum tillage/no-tillage) and organic fertilization as alternatives to intensive conventional mono-cropping in field studies. All the diversified systems and conservation tillage systems and the use of organic fertilizers induced positive effects on SOC. The highest response in SOC was achieved by the growth of permanent crops in the alleys. Soil N showed a similar trend to that of SOC, but the effect of no-tillage was not significant compared to conventional tillage. No significant effect was observed in soil P except for the cultivation of permanent crops in the alleys, which had a negative effect. No effect was observed in tree crop yield due to the growth of alley crops, conservation tillage or organic fertilization. However, the response of crop yield was related to the specific climatic conditions of each region, with possible negative effects in warm and dry areas. Overall, the use of intercropping, conservation tillage and organic fertilization led to improvements in soil quality and fertility and maintenance of a ground cover that can protect soil. However, to avoid possible negative effects on soil P and N availability, the growth of annual alley crops with minimum tillage is suggested instead of permanent crops with no-tillage, especially in dry and warm areas. Our results also suggested that the soil properties evaluated were not the main drivers of long-term yield variability.