Agronomy for Sustainable Development

Effective Microorganisms (EM®) is a “biofertiliser” soil inoculant, marketed as a crop yield enhancer. However, the literature has neither comprehensively reviewed its purported effects on harvests across multiple species nor investigated its effects on plant herbivore defence other than this group’s previous research on tomatoes. Here a meta-analysis of 39 journal articles and a greenhouse experiment with nine crop species afforded a nuanced assessment of Effective Microorganisms’ effects on plant growth and yield. Overall, in line with predictions, Effective Microorganisms showed significant positive effect on yield and growth (0.03 effect sizes increase) in the meta-analysis, and increased growth 16 % in the greenhouse, but with strong, and at times negative, species-specific responses. An additional potential benefit of Effective Microorganisms includes increased defence against herbivore attack, but inoculated corn (Zea mays) in a field and a greenhouse experiment exhibited decreased defences. Specifically, the field experiment demonstrated that Effective Microorganisms treatment corresponded to a 26 % reduction in predatory insect diversity on corn plants, while not improving growth or yield but did increase water uptake. A subsequent greenhouse experiment suggested likely physiological mechanisms behind the loss of predator diversity. When non-inoculated control corn plants were set upon by caterpillars of the herbivorous insect Spodoptera littoralis, the plants increased production of defensive volatile organic compounds (VOCs) by 272 %. Surprisingly, inoculation with Effective Microorganisms rendered greenhouse corn plants 51 % more palatable to S. littoralis. Further localised studies are, therefore, needed to efficiently incorporate Effective Microorganisms with either conventional or sustainable agricultural management systems.

Validation of models for plant disease management is a crucial part in the development of decision support systems in plant protection. Bespoke field trials are usually conducted to determine the performance of a model under practical conditions. However, field trials are very resource-demanding, and the use of already existing field trial data could significantly reduce costs for model validation. In this study, we took this novel approach to verify the performance of models for determining the need of fungicide applications against leaf blotch diseases in wheat by utilising historical weather data and yield data available from fungicide efficacy field trials. Two models based on humidity factors were used in the study. To estimate how specific humidity settings in the two models affect the number of recommended fungicide treatments per season, historical weather data from a 5-year period from weather stations in Denmark, Sweden, Norway, Finland, and Lithuania was used. The model output shows major differences between seasons and regions, typically recommending between one and three treatments per season. To determine the prediction potential of the models, data on yield gains from either one or two fungicide applications in fungicide efficacy trials conducted in wheat over a 5-year period in the five countries was utilised. The yield responses from fungicide treatments in the efficacy trials varied considerably between years and countries, as did the proportion of predictions of profitable treatments. In general, there was a tendency for the models to overestimate the need to apply fungicides (low specificity), but they rarely failed to recommend an application that was needed (high sensitivity). Despite the importance of having specific trials across regions in order to adjust models to local cropping and weather conditions, our study shows that historical weather data and existing field trial data have the potential to be used in model validation.

Urban agriculture is characterized by fast rotation of cropping cycles and high inputs and outputs on relatively small areas of land. Depletion of soil organic carbon and low nutrient use efficiency are severe agricultural constraints in the sandy soils of West Africa. We hypothesized that such an intensive system would provide ideal preconditions for the use of biochar, that biochar would enhance yields in urban horticulture, and that farmers would be able to produce biochar for on-farm use in Tamale, Ghana. Therefore, we studied the opportunities and challenges of biochar using a semi-participatory research approach. Working with 12 participant farmers, we defined research questions which were relevant to their livelihoods and collected qualitative and observational data, which determined the selection of variables to measure quantitatively. Different quality parameters such as leaf color and stiffness of lettuce were important to farmers and marketers when assessing the agronomic benefits of biochar. By adding biochar to their normal agricultural practice farmers were able to increase lettuce yields by 93%. This remarkable increase might be partially caused by farmers’ improved management of biochar plots: they concentrated their resources where they expected to yield the largest returns. Using a simple top-lit updraft gasifier, a special chimney for rice husk carbonization, it was relatively simple for farmers to produce biochar in the field, with an efficiency of 15–33%. These stoves’ payback times were between 1 and 2 months. Yet, rather than the efficiency of the carbonization technology, often emphasized in biochar research, the availability of feedstock and labor considerations determine the technology selected by farmers for biochar production. This is a novel approach to considering the economic realities of farmers in a semi-participatory appraisal where farmers both produce and apply biochar. This is crucial in order to understand and identify meaningful and economically viable uses of biochar.

Gray mold, caused by Botrytis cinerea, is a common threat for greenhouse production of tomatoes. Control of this disease can be difficult even with chemical treatments, and alternative methods are needed. Nitrogen (N) fertilization is known to modify the impact of pathogens on plants. However, there is scarce knowledge about the effect of fertilization on the efficacy of biocontrol. Here, we studied the effect of N fertilization on biocontrol agents Trichoderma atroviride and Microdochium dimerum that protect tomato against B. cinerea. Plants were grown for 2 months in a greenhouse with a soil-less drip irrigation system. Differential N fertilization (five concentrations of nitrate) was applied for the last 4 weeks prior to leaf pruning, biocontrol agent application, and B. cinerea inoculation. Results show that increasing N fertilization up to 10 mmol/L reduced disease by half for controls. High N fertilization also increased biocontrol, with a protection index rising from nearly 0 to up to 100 % depending on the biocontrol agent and the pressure of the pathogen. Indeed, high N fertilization delayed stem symptoms and slowed lesion expansion. To our knowledge, this is the first report of an effect of N fertilization on the efficacy of biocontrol against an airborne disease. Therefore, adapting N fertilization is a promising technique to protect greenhouse tomato.

The intensive use of inorganic fertilizers and pesticides in the agricultural field has globally destroyed soil fertility, killed beneficial microorganisms, and also decreased natural resistance in crops, thereby making them more vulnerable to diseases besides affecting human health and the environment. To overcome these problems, it is very important to shift our attention towards eco-friendly alternatives like vermicompost and vermicompost tea which not only can increase crop growth and yield, suppress diseases and pests sustainably but can also protect human health and the environment. Vermicompost with its rich nutrient content, plant growth promoters like auxins, gibberellins, cytokinins, and beneficial microbes not only improves the growth and yield of crops but also increases the diversity and activity of antagonistic microbes and nematodes, which helps to suppress pests and diseases caused by soil-borne phytopathogens. Vermicompost tea also has a tremendous potential to protect plants from diseases and its application to plants can coat leaf surfaces and reduce available sites for pathogen infection or increases microbial diversity that can kill harmful pathogens. Here, we review recent scientific achievements towards the management of crop diseases and pests by these organic amendments and the major points are the following: (1) production of vermicompost and vermicompost tea, (2) management of crop pests and diseases by vermicompost and vermicompost tea, and (3) the possible mechanisms and some important factors involved in the suppression of diseases and pests. Finally, we conclude that by using these eco-friendly organic amendments as a replacement to inorganic pesticides and fungicides, diseases and pests can be managed successfully without affecting human health and the environment and chemical-free food can be provided to humankind in the future.