No abstract

There is an urgent need for novel agronomic improvements capable of boosting crop yields while alleviating environmental impacts. One such approach is the use of optimized crop rotations. However, a set of measurements that can serve as guiding principles for the design of crop rotations is lacking. Crop rotations take advantage of niche complementarity, enabling the optimization of nutrient use and the reduction of pests and specialist pathogen loads. However, despite the recognized importance of plant-soil microbial interactions and feedbacks for crop yield and soil health, this is ignored in the selection and management of crops for rotation systems. We review the literature and propose criteria for the design of crop rotations focusing on the roles of soil biota and feedback on crop productivity and soil health. We consider that identifying specific key organisms or consortia capable of influencing plant productivity is more important as a predictor of soil health and crop productivity than assessing the overall soil microbial diversity per se. As such, we propose that setting up soil feedback studies and applying genetic sequencing tools towards the development of soil biotic community databases has a strong potential to enable the establishment of improved soil health indicators for optimized crop rotations.

Summary1. Atmospheric ammonia (NH 3 ) is one of the main drivers for ecosystem changes world-wide, including biodiversity loss. Modelling its deposition to evaluate its impact on ecosystems has been the focus of many studies. For that, universal indicators are needed to determine and compare the early effects of NH 3 across ecosystems. 2. We evaluate the effects of atmospheric NH 3 in ecosystems using lichens, which are one of the most sensitive communities at the ecosystem level. Rather than measuring total diversity, we use a functional diversity approach because this is potentially a more universal tool. 3. We evaluated the spatial and temporal patterns of atmospheric NH 3 concentrations ([NH 3 ] atm ) emitted from a point-source over a 1-year period in a cork oak Mediterranean woodland. We observed a temporal pattern of [NH 3 ] atm , with maximum concentrations during autumn. 4. The distribution of lichen species was c. 90% explained by [NH 3 ] atm . The tolerance of lichen species to atmospheric NH 3 , based on expert knowledge from literature, was tested for the first time against direct measurements of atmospheric NH 3 . Most species were well classified, with the exception of Lecanora albella and Chrysothrix candelaris, which were more tolerant than expected. Our updated lichen classification can be used to establish lichen functional groups that respond to atmospheric NH 3 , and these can be used in other Mediterranean countries. 5. Increasing [NH 3 ] atm led to a complete replacement of oligotrophic by nitrophytic species within 65 m of the NH 3 source. The geostatistical analysis of functional diversity variables yielded a spatial model with low non-spatial variance, indicating that these variables can cope robustly with high spatial variation in NH 3 . 6. Synthesis and applications. Our results support the use of functional diversity variables, such as a lichen diversity value, as accurate and robust indicators of the effects of atmospheric NH 3 on ecosystems. The spatial modelling of these indicators can provide information with high spatial resolution about the effects of atmospheric NH 3 around point-and diffuse sources. As this methodology is based on functional groups, it can be applied to monitor both the impact of atmospheric NH 3 and the success of mitigation strategies.

No abstract

RESUMO -A presente pesquisa objetivou estudar os efeitos dos períodos de controle e de convivência de uma comunidade infestante sobre as características produtivas da soja nos sistemas de semeadura direta (SSD) . Tolerando cinco por cento de perda na produtividade da cultura, constatou-se que os períodos críticos de prevenção da interferência foram dos 33 aos 66 DAE para o cultivar CD 201 no SSD e dos 34 aos 76 DAE para o cultivar M-SOY-6101 no SSC. A interferência das plantas daninhas durante todo o ciclo da cultura reduziu, em média, 46% (SSD) e 32% (SSC) a produtividade de grãos da soja. Não houve efeito das plantas daninhas na estatura das plantas, na altura de inserção da primeira vagem e no número de vagens por planta.Palavras-chave: competição, Glycine max, períodos de controle. ABSTRACT -This work aimed to determine the interference of weed communities in crop yield INTRODUÇÃOA cultura da soja const itui-se na mais importante oleaginosa cultivada no mundo. No âmbito mundial, o Brasil é o segundo maior produtor e um dos principais exportadores dos grãos. A soja está sujeita a uma série de fatores que podem influenciar o seu desenvolvimento e a produção. As plantas daninhas acarretam perda s na produtiv idade devido, principalmente, à competição por luz, nutrientes e água, além de dificultarem a colheita. Atuam também