Crop diversification represents a key lever to support the development of sustainable agri-food systems. Knowledge on trade-offs and carry over effects from different crop diversification strategies is essential to inform agricultural stakeholders of potential costs and benefits. This knowledge is limited by existing data and performance measures predominantly focused on single crops, rather than complete rotations. Moreover, sustainability performance indicators are often used for assessment purposes, rather than supporting stakeholder learning and actions. A new set of 32 indicators was developed to address these needs, and used to evaluate the environmental, economic and social sustainability of the diversified agricultural systems highlighted in the case studies, which are often characterized by data availability constraints. This approach was tested in France, Germany and Italy to determine a critical ex-post diagnosis of the existing systems, and for the assessment of ex-ante innovative scenarios. The results will be used to support these case studies in the identification and design of more sustainable agricultural systems. Although the framework is based on feasible and proxy indicators, the assessment outcomes have allowed local actors to reflect on the effects generated by the implemented crop diversification strategies. Key issues include trade-offs occurring between optimizing economic and environmental performance.
Background
Sustainable agriculture seeks to optimize the application of nitrogen (N) fertilizers to reduce adverse economic and ecological effects. Crop diversification has been proposed to increase the efficiency of N fertilization. An open question is how the soil microbiome responds to these beneficial practices.
Methods
In a field study we investigated the effects of mineral N fertilizer with a 0-control, a conventional amount of 150 kg N ha−1 and an excessive application of 250 kg N ha−1 on the soil microbiome within a diversified cropping system with oil radish and undersown ryegrass over a period of 2.5 years and a non-diversified control, both in rotation of potato, winter rye and maize.
Results
N-fertilizations and crop rotations altered the pH, but differences were less pronounced with the diversified system. Compared to the crop species and season, N fertilization and crop diversification had less influence on the abundance of soil bacteria, archaea and fungi. The crop diversification showed a much stronger effect on archaeal than on bacterial or fungal abundances, while the microbial carbon use efficiency correlated strongly with bacterial abundance. At the end of the growing seasons, crop diversification increased prokaryotic richness and Shannon diversity in response to N addition, with a greater increase in the conventional N. At conventional N supply, prokaryotic co-occurrence networks revealed a much denser and complex structure in the diversified system.
Conclusions
The diversified cropping system under conventional N application rates showed positive effects on the prokaryotic soil microbiome by increasing their richness, Shannon diversity, and promoting a more elaborated network structure.
In agroecosystems, crop diversification plays a fundamental role in maintaining and regenerating biodiversity and ecosystem services, such as natural pest control. Temporal diversification of cropping systems can affect the presence and activity of natural enemies by providing alternative hosts and prey, food, and refuges for overwintering. However, we still lack studies on the effects of temporal diversification on generalist predators and their biocontrol potential conducted at field scale in commercial agricultural settings. Here, we measured proxies of ecosystem functions related with biological pest control in 29 commercial agricultural fields characterized by cereal-based cropping system in Lower-Saxony, northern Germany. The fields differed in the number of crops and cover crops cultivated during the previous 12 years. Using the Rapid Ecosystem Function Assessment approach, we measured invertebrate predation, seed predation and activity density of generalist predators. We aimed at testing whether the differences in the crop rotations from the previous years would affect activity of predators and their predation rates in the current growing season. We found that the length of the crop rotation had neutral effects on the proxies measured. Furthermore, predation rates were generally lower if the rotation comprised a higher number of cover crops compared to rotation with less cover crops. The activity density of respective taxa of predatory arthropods responded differently to the number of cover crops in the crop rotation. Our results suggest that temporal crop diversity may not benefit the activity and efficiency of generalist predators when diversification strategies involve crops of very similar functional traits. Adding different resources and traits to the agroecosystems through a wider range of cultivated crops and the integration of semi-natural habitats are aspects that need to be considered when developing more diverse cropping systems aiming to provide a more efficient natural pest control.
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