Abstract
The detrital food web plays an important role in the functioning of agro-ecosystems due to their positive effect on organic matter transformations and nutrient supply to the growing crops, however, the activities of the organisms involved are strongly influenced by agricultural practices. In NW Spain, commercial Hayward kiwifruit (Actinidia chinensis var. deliciosa) is intensively produced using conventional techniques (CONV), however, more sustainable methods, such as integrated (INT) and organic (ORG), have been increasingly adopted to decrease the negative impacts on the environment. We investigated the effects of these agricultural managements on earthworm abundance and functional diversity as well as microbial biomass and enzyme activity and evaluated the potential implications for nutrient retention and runoff in kiwifruit orchards. Our results showed that the CONV soils significantly contained fewer earthworms (ca. 80% less individuals than the INT and ORG systems), with their communities being mainly dominated by small epigeics, but a higher microbial biomass (0.53 ± 0.06 mg C g-1 dw soil compared to <0.25 mg C g-1 dw soil in INT and ORG), and 20% more activity of the enzymes involved in C (β-glucosidase) and N mineralization (urease). Consequently, more C and N was lost from these soils (on average, >37% more CO2, and five times more DIN) than from the less intensively managed soils. In contrast, the INT and ORG systems sustained a more complex and functionally diverse soil food web that lead to higher soil C and N retention. Therefore, agriculture management (i.e., intensive vs. less intensive) and its effects on the structure of the below-ground communities (i.e., microorganisms plus surface detritivores vs. deep burrowers plus geophagous forms) determine the nutrient sink/source function of these agro-ecosystems. These findings highlight the importance of including the contribution of soil biota to soil processes when optimizing fertilization loads and mitigating environmental impacts of agricultural practices.
Highlights
38% of the world’s land surface is cultivated, but this is projected to increase 30% more by 2050 to meet the food demand of a continuous growing human population (FAOSTAT, 2018)
Agricultural management had a significant effect on earthworm populations (p < 0.05), with the lowest abundances of these organisms being recorded in the conventional agricultural practices (CONV) orchard (78 and 79% less individuals than in the INT and ORG orchards, respectively)
The structure of earthworm community showed important alterations with agriculture intensification (Figure 1), and in particular, those species belonging to the anecic group were drastically reduced in the most intensive treatment (CONV), with the majority of the individuals being small epigeic worms (Figure 1)
Summary
38% of the world’s land surface is cultivated, but this is projected to increase 30% more by 2050 to meet the food demand of a continuous growing human population (FAOSTAT, 2018). Spain occupies the 11th position in the list of kiwifruit producing countries (20,884 t y−1; MAPAMA, 2018) and the Galicia region (NW of Spain) yields 53% of the total national production (11,510 t y−1; MAPAMA, 2018). In this Atlantic area, this perennial fruit tree has been traditionally grown using conventional agricultural practices (CONV). In the last 25 years, alternative techniques (integrated, INT and organic, ORG) have been slowly adopted to mitigate the harmful effects on the environment
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