Statistics for Spatial Data.

Increasing nutrient inputs into terrestrial ecosystems affect not only plant communities but also associated soil microbial communities. Studies carried out in predominantly unmanaged ecosystems have found that increasing nitrogen (N) inputs generally decrease soil microbial biomass; less is known about long-term impacts in managed systems such as agroecosystems. The objective of this paper was to analyze the responses of soil microorganisms to mineral fertilizer using data from long-term fertilization trials in cropping systems. A meta-analysis based on 107 datasets from 64 long-term trials from around the world revealed that mineral fertilizer application led to a 15.1% increase in the microbial biomass (Cmic) above levels in unfertilized control treatments. Mineral fertilization also increased soil organic carbon (Corg) content and our results suggest that Corg is a major factor contributing to the overall increase in Cmic with mineral fertilization. The magnitude of the effect of fertilization on Cmic was pH dependent. While fertilization tended to reduce Cmic in soils with a pH below 5 in the fertilized treatment, it had a significantly positive effect at higher soil pH values. Duration of the trial also affected the response of Cmic to fertilization, with increases in Cmic most pronounced in studies with a duration of at least 20 years. The input of N per se does not seem to negatively affect Cmic in cropping systems. The application of urea and ammonia fertilizers, however, can temporarily increase pH, osmotic potential and ammonia concentrations to levels inhibitory to microbial communities. Even though impacts of fertilizers are spatially limited, they may strongly affect soil microbial biomass and community composition in the short term. Long-term repeated mineral N applications may alter microbial community composition even when pH changes are small. How specific microbial groups respond to repeated applications of mineral fertilizers, however, varies considerably and seems to depend on environmental and crop management related factors.

Long-term effects of mineral fertilizers on soil microorganisms – A review

Tens of thousands of species are threatened with extinction as a result of human activities. Here we explore how the extinction risks of terrestrial mammals and birds might change in the next 50 years. Future population growth and economic development are forecasted to impose unprecedented levels of extinction risk on many more species worldwide, especially the large mammals of tropical Africa, Asia and South America. Yet these threats are not inevitable. Proactive international efforts to increase crop yields, minimize land clearing and habitat fragmentation, and protect natural lands could increase food security in developing nations and preserve much of Earth's remaining biodiversity.

Future threats to biodiversity and pathways to their prevention

Soil structure as an indicator of soil functions: A review

Allelopathy is a common biological phenomenon by which one organism produces biochemicals that influence the growth, survival, development, and reproduction of other organisms. These biochemicals are known as allelochemicals and have beneficial or detrimental effects on target organisms. Plant allelopathy is one of the modes of interaction between receptor and donor plants and may exert either positive effects (e.g., for agricultural management, such as weed control, crop protection, or crop re-establishment) or negative effects (e.g., autotoxicity, soil sickness, or biological invasion). To ensure sustainable agricultural development, it is important to exploit cultivation systems that take advantage of the stimulatory/inhibitory influence of allelopathic plants to regulate plant growth and development and to avoid allelopathic autotoxicity. Allelochemicals can potentially be used as growth regulators, herbicides, insecticides, and antimicrobial crop protection products. Here, we reviewed the plant allelopathy management practices applied in agriculture and the underlying allelopathic mechanisms described in the literature. The major points addressed are as follows: (1) Description of management practices related to allelopathy and allelochemicals in agriculture. (2) Discussion of the progress regarding the mode of action of allelochemicals and the physiological mechanisms of allelopathy, consisting of the influence on cell micro- and ultra-structure, cell division and elongation, membrane permeability, oxidative and antioxidant systems, growth regulation systems, respiration, enzyme synthesis and metabolism, photosynthesis, mineral ion uptake, protein and nucleic acid synthesis. (3) Evaluation of the effect of ecological mechanisms exerted by allelopathy on microorganisms and the ecological environment. (4) Discussion of existing problems and proposal for future research directions in this field to provide a useful reference for future studies on plant allelopathy.

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Research Progress on the use of Plant Allelopathy in Agriculture and the Physiological and Ecological Mechanisms of Allelopathy

The forecasted 9.1 billion population in 2050 will require an increase in food production for an additional two billion people. There is thus an active debate on new farming practices that could produce more food in a sustainable way. Here, we list agroecological cropping practices in temperate areas. We classify practices according to efficiency, substitution, and redesign. We analyse their advantages and drawbacks with emphasis on diversification. We evaluate the potential use of the practices for future agriculture. Our major findings are: (1) we distinguish 15 categories of agroecological practices (7 practices involve increasing efficiency or substitution, and 8 practices need a redesign often based on diversification). (2) The following agroecological practices are so far poorly integrated in actual agriculture: biofertilisers; natural pesticides; crop choice and rotations; intercropping and relay intercropping; agroforestry with timber, fruit, or nut trees; allelopathic plants; direct seeding into living cover crops or mulch; and integration of semi-natural landscape elements at field and farm or their management at landscape scale. These agroecological practices have only a moderate potential to be broadly implemented in the next decade. (3) By contrast, the following practices are already well integrated: organic fertilisation, split fertilisation, reduced tillage, drip irrigation, biological pest control, and cultivar choice.

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Agroecological practices for sustainable agriculture. A review

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Intercropping with legume for agroecological cropping systems: Complementarity and facilitation processes and the importance of soil microorganisms. A review

It has become commonplace to consider ploughing as an agricultural practice that destroys soil fertility Organic farmers have traditionally used the plough to till their soil and control weeds However, there is a growing interest in adopting tillage practices without ploughing to preserve long-term soil fertility and in the hope, subsequently, of increasing crop yields The aim of this paper is to assess if conservation tillage treatments in organic farming did in fact improve long-term soil fertility, wheat rooting and yield in a long term field experiment (2004–2015) We compared the effects of conservation tillage treatments (superficial tillage – ST- with chisel at 15 cm depth and very superficial tillage – VST- at 5–7 cm depth) and conventional tillage treatments (traditional mouldboard ploughing- MP at 30 cm depth and shallow mouldboard ploughing – SMP- at 18 cm depth without skim coulter) during 10 years on a sandy loam soil in France To assess soil fertility, physical (soil penetration resistance, visual soil profile observation), chemical (organic carbon – Corg, total nitrogen – Ntot and available phosphorus – OlsenP) and biotic (earthworms biomass, density and diversity) soil properties were measured in 2004-5 and 2015 The effect of soil fertility on wheat roots and crop growth was also measured in 2015 VST, and to a lesser extent ST, increased Corg, Ntot and OlsenP in the upper soil layer (from 0 to 15 cm) compared to ploughing treatments On the contrary, soil compaction increased using conservation tillage treatments (VST and ST) during the 10 years of experiment, especially in the layers between 15 and 30 cm depth in comparison with ploughing treatments This effect is not offset by an increase in earthworm abundance and activities in conservation treatments Earthworm biomass and endogeic abundance were even higher in SMP compared to ST Soil compaction limits roots, with less roots in depth with VST (from 12 to 30 cm and 48 to 70 cm) and ST (from 24 to 30 cm) compared to ploughing treatments Conservation tillage treatments had positive effects on soil chemical components in the upper soil layer and contributed to the increase of wheat biomass until tillering stage However, no wheat yield difference was found between treatments Physical and biotic soil properties had not significantly improved after 10 years of conservation tillage This could be due either to the insufficient duration of the experiment to foster a positive earthworm effect on soil porosity, or to the sandy soil, too sensitive to soil compaction in this organic cropping system (intensive mechanical weeding) and unfavourable for the development of the earthworm population

Soil fertility after 10 years of conservation tillage in organic farming

Soil sampling based on field spatial variability of soil microbial indicators.

In France, agronomists have studied the effects of cropping systems on soil structure using a field method based on a morphological description of soil structure. In this method, called “profil cultural” or soil profile in English, the soil structure of the tilled layer is observed on a vertical face of a pit. Subsoil and more especially the transition layer between topsoil and subsoil have not always been given specific consideration. However, these layers undergo the effect of cropping systems through soil compaction or smoothing/smearing. A more accurate quantification of earthworm macropores and cracks in the transition layer would enable a more precise evaluation of the agronomical potential of the soil, manifest in root development or water retention. Thus, the aim of this paper is to present the profil cultural method in detail, along with the improvements we have made to quantify the ability of roots to penetrate compacted zones in the transition layer. We propose two indicators: (i) number of earthworm burrows per m 2 counted on a horizontal surface at the bottom of the transition layer in the soil pit (ii) cracking quantified by taking a 50-mm × 50-mm × 100-mm sample of soil from the transition layer and examining the number of cracks. Results from experiments on different tillage treatments are used to demonstrate why it is worthwhile to take into account cracks and earthworm activity. Soil profiles were examined in mouldboard ploughed and no tillage fields, and described using the profil cultural method and the new indicators. Root maps were also traced to observe the effect of soil structure on root growth. Preliminary results show that the classification of cracking and the quantification of the number of earthworm burrows per m 2 can explain observed root development in subsoil. This first approach towards a better observation of subsoil structure and the effect it has on roots needs to be confirmed through further research, and especially via quantification and scoring of soil structure impact on roots.

Jean-François Vian

Papers

Agroecological practices for sustainable agriculture. A review

Intercropping with legume for agroecological cropping systems: Complementarity and facilitation processes and the importance of soil microorganisms. A review

Soil fertility after 10 years of conservation tillage in organic farming

Soil sampling based on field spatial variability of soil microbial indicators.

Assessment of soil structure in the transition layer between topsoil and subsoil using the profil cultural method