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Arthropod generalist predators can be effective natural control agents of pests and weeds in agroecosystems. Their activity and contribution to biocontrol may increase in response to more complex agricultural habitats. In this study, we investigated the effects of winter wheat-pea mixed intercropping on the biocontrol potential of generalist predators compared with the respective mono-crops. We evaluated not only the effects during the intercropping season but also the pre-crop values of the mixture for the subsequent barley crop. Furthermore, we evaluated the influence of different long-term soil organic carbon and fertility management regimes on activity and biocontrol potential of predators. Field work was conducted over two seasons in a field experiment located in Gembloux, Belgium. A set of proxies for ecosystem functions were measured using the Rapid Ecosystem Function Assessment approach.We measured attack and predation rates of sentinel prey and weed seeds artificially placed in the field. Furthermore, we assessed activity density of the main groups of generalist predators during the exposure of the baits. Our results showed that crop type affected activity and biocontrol potential of predators. Predation rates were much lower in wheat than pea and wheat-pea. The mixture wheat-pea had a positive effect on predator activity density compared to wheat mono-crop, while pea supported an intermediate activity of epigeal predators. In the second season of the field work, we found the highest biocontrol potential by predators in barley plots cultivated after pea. Finally, our results failed to find any differences in biocontrol potential of predators between long-term soil organic carbon and fertilisation management strategies. These results suggest that crop type has a major relevance in influencing the activity of generalist predators, and the mixed intercropping wheat-pea may represent a valid strategy to enhance biological pest control in comparison to wheat cultivated as mono-crop. Furthermore, we show that the cultivation of pea as monocrop may have an important pre-crop value within the rotation increasing the provision of ecosystem services such as biocontrol.

1. Although organic farming was originally promoted as an alternative farming system to address agronomic, environmental and ecological issues, its conventionalisation has led to an intensification and specialisation of production. In the light of this, several studies have questioned the environmental benefits of organic farming as well as its agronomic viability. Thus, there is a need to improve organic vegetable systems to reduce their environmental impact without affecting their productivity.To tackle this challenge, European farmers and researchers have recently started to focus on agroecological service crops (ASCs). However, few studies have simultaneously evaluated the agronomic, environmental and ecological aspects of ASC management under different European pedo-climatic conditions.2. We evaluated effects of the ASC management strategies-no-till roller crimping (NT-RC) and green manuring (T-GM) on cropping system performance using agronomic, environmental and ecological indicators-to exemplify the need for | 1027

A sustainable supply of phosphorus (P) to agricultural soils should maintain soil fertility without jeopardizing the environment. This study analyzed the change in the soil P as a function of the net soil P mass balance, i.e. the input minus removal by the harvested crop. The P available for crops was estimated by the P extracted by ammonium lactate at pH 3.75 (P-AL). First, laboratory and pot-trial data showed that the net change in soil P-AL was only 68% of the change in total soil P, either when P had been added to soil or when P had been mined by plants for 1-2 years, indicating removal to or release from the non-extractable pool depending on the balance. Secondly, data were collated from field trials in Europe with a wide range of cumulative soil P balances (-1200 to +2500 kg P ha -1 ) in time spans ranging from 3-51 years. The average change in P-AL across the negative and positive balance was only 27% (95% confidence interval 25-30%) of the net balance. The change in P-AL was larger as the net balance increased and as the initial P-AL decreased. The slope of the change versus the balance was smaller as time increased and initial P-AL decreased. The other soil characteristics did not affect these changes, and the model developed was not different for negative or positive P balances. Our results suggest that a steady state P-AL concentration at optimal P supply for crops is obtained at a net P balance of about 1-10 kg P ha -1 . The P mass balance of a 51 year-old trial showed that the aqua regia soluble P of the 0-90 cm layer accounted for only 64% of the net P balances at the surface. This still incomplete P balance could be related to upward P transport by plant uptake from >90 cm soil layers, lateral P movement in the field, and changes in the soil P fraction that could not be extracted with aqua regia. This study quantified the long-term dynamics of P-AL, which is useful for agronomic and environmental purposes and policy, and pointed out the importance of non-extractable P and vertical P movement.