Effects of grassing on orchard ecosystem services: a global meta-analysis

Smallholder-run orchards are often managed using clear cultivation, that is, removing grass cover to remove competition for water and nutrient with fruit trees. This business-as-usual intensification has caused severe ecological and environmental issues related to soil desiccation, soil erosion, low soil organic C (SOC) sequestration, and the excessive use of chemical fertilizers. Sod culture in orchards is an advanced soil management system because of its ecological benefits, such as regulating the ecosystem services of orchards and ameliorating the soil micro-environment; as well as its economic benefits, such as improving the productivity of orchards, thus providing income for farmers. To date, there is a lack of comprehensive and quantitative research evaluating the ecosystem service function of sod culture in orchards. The objective of this study was to quantify the effects of sod culture on orchard ecosystem services to provide a scientific basis for orchard soil management and sod culture technology promotion and application. A total of 1387 pairs of data were collected from 118 peer-reviewed research papers published between 1996 and 2020. The meta-analysis method was used to quantitatively study the impact of sod culture on ecosystem service functions in orchards in terms of provisioning service (fruit yield and quality), regulating services (soil moisture, soil temperature, and SOC), and supporting services (soil total N). The heterogeneity of the influence of sod culture in orchards on ecosystem service functions was elaborated from four aspects: altitude, climate, grass species, and orchard types. The results showed that compared with clear tillage orchards, the grassing system significantly increased the provisioning service (fruit yield and soluble solid matter), regulating services (SOC and soil moisture), and supporting services (soil total N). The average increasing rate for these five indicators was 20.7% (95% confidence interval CI: 17.4%−24.2%), 5.1% (95% CI: 2.3%−8.6%), 24.7% (95% CI: 20.9%−27.8%), 8.1% (95% CI: 6.9%−9.3%), and 15.6% (95% CI: 6.80%−9.49%) respectively. Grassing had a negative effect on titratable acid content of fruits and soil temperature, which was 10.8% (95% CI: −14.5% to −6.9%) and 10.6% (95% CI: −12% to −9.2%) lower than that in clear-cultivated orchards, respectively. However, this negative effect actually helps improve the quality of fresh fruit and avoid the damage of high temperature to fruit trees, and thus is conducive to improving the provisioning and regulating services of orchard ecosystems. Furthermore, sod culture had a positive effect on fruit yield, but its influence and extent of its effect on fruit quality varied among orchard types, climate, and altitude. Different orchard types, grass species, and climate had positive effects on regulating services (soil moisture and SOC) and supporting services (soil total N). Overall, the study showed that the sod culture in orchards greatly increased fruits yield and soil carbon, and improved the climate in orchards, thereby improving the provisioning, regulating, and supporting services of orchards. Our findings provide insights into the development of science-based orchard management practices and have great significance for ensuring the quality, efficiency, and sustainable development of orchards globally.