Around the world and throughout history, slugs are one of the most enduring and pervasive pests that plague plant cultivation. Slugs cause damages not only to crops, but to pastures, gardens, and, in some regions, even fruit tree plantations, resulting in around 60 million dollars in yearly damages in the United States alone. In the UK, that number ascends to 100 million sterling pounds, and with the potential expansion of the Spanish slug (Arion vulgaris) and other invasive slug species threatening the world's agriculture, those numbers could go much higher. To make things worse, the methods used until now to reduce slug damage have increased soil degradation, ultimately working against growers' best interests. A chapter of the Handbook of Vegetables Pests, published by Academic Press in 2001, recommends for example a finely textured or compacted soil, regular tillage, and the lack of residual organic matter (i.e. mulch) as means to prevent an expansion of the slug problem; all of the methods that also produce soil exposition to environmental degradation. The discovery of a biological means of control for slugs was, consequently, a major advantage for agriculture. Phasmarhabditis hermaphrodita, the main agent for biological control of slugs. Enter the humble nematode Phasmarhabditis hermaphrodita, only adequately studied in the 1990s, and now commercialized around the world as a safe and effective tool for slug control. Phasmarhabditis hermaphrodita is a tiny nematode of barely less than two millimeters long (often visible only with a microscope) that enters into the bodies of slugs and parasites them, producing between 200 to 300 other nematodes in the process. Between the introduction of the first nematode into the body of the slug and its ultimate death, a period of 4 to 21 days follows in which the slug will feed gradually less, and at the end of which it will crawl into a secluded space before dying. The nematodes keep acting and reproducing throughout wet or dry weather, as long as slugs are active (especially when they are active, in fact!). These biological control agents such as pesticides and insecticides also fulfill one of the main conditions to qualify as such at a large scale, which is not becoming an invasive pest itself. Fortunately enough for growers, Phasmarhabditis hermaphrodite has also evolved to target only molluscs, and as such does not attack earthworms, insects, birds, spiders or humans. AGENT PROFILE Common name(s): Phasmarhabditis hermaphrodita, commercialized under the name Nemaslug® . Often-used species: Only the mentioned above. Type of predator: Not predatorial, parasitic. Potential damaging effects: Against non-damaging or beneficial freshwater snails; as such it should not be used near bodies of fresh water. Interesting literature on its usage: A general review on its usage and effects (2009), a brief study of the species in the scientific journal Nematology (2019), on the possibility of similarly useful species existing (2019), a case study on its effectivity on two slug species (2002).

Trichoderma fungi are an efficient, cost-effective, and selective means for the biological control of fungal diseases, bacterial diseases, and even nematodes, as through their own growth they outcompete, parasite, and create resistance in plants against damaging pathogens. Rather than being an agent of biocontrol, they conform a genus out of which around 25 species serve as agents individually or in distinct combinations, and all of the 25 species are used around the world as a weapon against the over 10,000 species of fungi that produce economically significant damage in crops. Together, Trichoderma fungi species constitute around 90% of the fungal species known to serve as anti-fungal agents in agriculture, and they form the basis for around 60% of the fungicides of biological origins currently available in the market. Trichoderma harzianum, one of the most widely used species of Trichoderma fungi, seen growing from spores under the microscope. Possibly the greatest strengths of Trichoderma fungi are both their capability to establish themselves permanently in an agricultural setting that is capable of sustaining fungal life (outlining once more the importance of integrating conservation techniques of biological control into the whole equation) and their incredibly wide range of techniques to combat fungal and bacterial plagues as well as nematodes. Trichoderma fungi act either directly against pathogens by mycoparasitism (parasitism of one fungus on another), aggressive competition and generation of antibiotics, or indirectly by improving the health of the plants that serve as their hosts, thus making them more resistant to pathogens (weakened as well through the more direct action of Trichoderma fungi). All of this makes them incredibly useful, dual-purpose creatures that at the same time increase yield, vigor and nutrient absorption as they combat disease and ensure a better overall health of the crops. Trichoderma fungi are also mycorrhizal fungi, and as such they present all the benefits of mycorrhizae. Above, a comparison between root systems not inoculated and inoculated with Trichoderma harzianum. AGENT PROFILE Common name(s): Trichoderma fungi. Often-used species: Depending on the region, species used are often non-native. Type of predator: Non-predatorial (parasitic at most). Potential damaging effects: On crops of edible fungi, such as Agaricus bisporus. Interesting literature on its usage: A general but very detailed overview on these fungi and their usage (2020), a general review of their usage alongside other fungi (2020), a review of their biocontrol mechanisms (2004), a study of their working alongside mycorrhizae and other fungi against nematodes (2020), divulgation material on their usage (2016).

The crown jewel of biological pest control, Bacillus thuringiensis is a species of bacteria that has become one of the most frequently used (if not the most frequently used) biological insecticides around the world. Its insecticide properties appear when this bacterium (bacteria is the plural) enters the phase of its life called sporulation, in which bacteria turn into something similar to spores by dividing within their own cellular walls, with one part of those who have divided consuming the rest and entering into a dormant state. This behavior is triggered by environmental factors like drought or a lack of nutrients available, which is often the case when Bacillus thuringiensis is applied artificially on a field. As part of that process of sporulation, these bacteria produce a certain type of protein that interacts with the gut of insects who have consumed leaves or stalks that were inoculated with Bacillus thuringiensis: the insects eventually have their whole digestive systems disrupted, eventually stopping eating and dying of hunger. This can happen as soon as a few hours after having consumed the inoculated plants, or take as long as a few weeks, according to an estimate of the National Pesticide Information Center of the US. These little creatures have saved millions of people from famine, among other achievements. Bacillus thuringiensis is an absolute juggernaut of biological pest control, targeting pests as diverse as moths (tent caterpillars, tomato hornworm, date moth, flour moth), nematodes, beetles (such as the Western corn rootworm, Diabrotica virgifera virgifera), mosquitoes, and fungus gnats. Furthermore, it does all of this while respecting beneficial insects such as bees, butterflies, or other biological control agents such as lacewings or predatory wasps (because none of these consumes enough plant matter to contract a Bacillus thuringiensis infection), as well as being safe for human beings. AGENT PROFILE Common name(s): Bacillus thuringiensis. Often-used species: Single species, with subspecies used to target specific pests (such as Bacillus thuringiensis israelensis for mosquitoes). Type of predator: Non-predatorial (parasitic). Potential damaging effects: No significant ones registered to date. Interesting literature on its usage: A fact sheet on Bacillus thuringiensis, from pages 109 to 113 (2020), use against mosquitoes (2020), use against nematodes (2003), against fungus gnats (2001), a detailed paper on how the bacterium functions and its derivative use in non-organic, transgenic agriculture (1998).

In past articles of this series we have covered with certain detail the thirteen micro and macronutrients that all plants need to survive and grow, as well as some traditional (inorganic and organic) methods of adding nutrition to the soil. The only question that remains for now is: how can the availability of these nutrients be assured? That is, how can growers ensure that, should they be unable to fertilize their fields for one growing season (let’s say), the land will not become a barren, inhospitable, infertile space? The answer to this lies in taking notice of other factors behind the measurable presence of nutrients in the soil. If a landscape is always in need of repeated fertilization to remain productive it is already in a very precarious state, in which most of the fertilizers are probably consumed during a growing season and the soil is, otherwise, inhospitable if not intensively managed. The only way to responsibly address this is to start building the soil, and here we will focus especially in two aspects of this: soil pH, and water content. All of the nutrients that we have talked about becoming more or less available according to the acidity or alkalinity of a soil. Soils that are more acidic have less availability of calcium (Ca) and magnesium (Mg), because these chemical compounds become less mobile and plants have more difficulty absorbing them. At the same time, iron (Fe), manganese (Mn), and zinc (Zn) become far more mobile and available to plants, while phosphorus (P) becomes more available at first and later is almost completely immobilized. An increase in alkalinity (that is, an increase in pH levels) reverses these processes. This is why the pH of the soil is a critical condition to be balanced and preferably adjusted to the requirements of most crops (6.0 to 7.0, but it may vary depending on the species). Here's a full pH scale, so we can contextualize that: And here's a table depicting the availability of most nutrients and micronutrients according to soil pH, courtesy of Wikimedia Commons: The water content of the soil is another major component, simply because it makes every chemical substance within the soil more soluble. Even though plants use water for other purposes as well beyond nutrient absorption, if we focus only on soil fertility it is, by itself, evident that constant presence of ideal water levels is essential for plants to actually be able to access the nutrients present in the soil. Same as with pH levels, the thirteen micronutrients and macronutrients may all be present in perfect amounts, but these two conditions deeply affect whether these nutrients are in a state that is actually useful for plants and, consequently, their keepers. Water content is measured in the percentage of water out of the total weight of a sample of soil, with results that may look like these excellent diagrams from the North Carolina Extension Gardener Handbook: Improving these two conditions passes as well through managing other chemical, physical and biological conditions of the soil, so keep an eye in our blog for future articles on those subjects. In the meantime, happy growing!

Out of all the water in the world, only 3.5% is freshwater, and around 70% of it is currently trapped in the form of permanent ice. This basically means that only around 1% of the existing water (1.05%, to be exact) is available for all sorts of things we humans need it for; from drinking, to showering, to watering the fields that keep supermarkets stocked and the food chain running. If that percentage weren’t small enough for the myriad uses of water, climate change and pollution are reducing it even further, with the contamination of freshwater bodies and more frequent droughts making it doubly essential to find ways to conserve water as much as possible in agricultural settings. Otherwise, the consequences for farming could be dire. Former agricultural land in Oklahoma, where incorrect techniques of soil management and a strong drought joined forces to create an ecological disaster. With this in mind, the ATTRA National Sustainable Agriculture Information Service, located in the US and managed jointly by the National Centre for Appropriate Technology (NCAT) and the United States Department of Agriculture, produced a report underlying the simple principles that land stewardship should follow to maximize water conservation and soil penetration and reduce unnecessary water usage. In the report (which is certainly worth a read by itself) five main principles stand out, in particular, as the basis of water-friendly agriculture. These can be summarized as: Protecting the soil surface: a basic principle that involves not leaving soil uncovered; mulching or covering crops should always fill the space left after a harvest. Bare soil will grow weeds, erode, be exposed to faster temperature changes, and, above all, gradually lose all the water it contains through simple evaporation. Minimize soil disturbance of all kinds: another often-heard recommendation, as tillage that is performed frequently, will grind soil to a powder, resulting in sandy soil that is unable to hold water and is prone to wind erosion. A dust bowl, anybody? Plant diversity: a much less frequent recommendation, but very important. Not only a variety of plants’ roots can reach different depths and thus different water levels, making the complete death of all life on your soil-less likely in the event of a drought, but different plants also produce different root exudates and host different bacterial communities. This leads to healthier soil, with better structure and greater capacity to hold water. Continual live roots in the soil: a corollary of the first principle, specifically requiring live plants to remain present in the soil so that microbial strains communities can continue to exist. Livestock integration: another rarely-heard one, but essential for organically managing land. Instead of importing bio-manure all the time, why not have the animals that produce it? In the ATTRA’s words: “…thoughtful integration of livestock onto cropping land can reduce weed pressure, herbicide use, and livestock waste associated with confinement, thereby improving water quality and addressing nutrient-management concerns.” All of this might sound complicated, but consider: is it more complicated than facing an unexpected drought? Is it more expensive than the losses in water that less efficient systems entail? As the ATTRA says: "Investments, such as adding organic amendments, practicing no- or reduced tillage, leaving crop residue, planting cover crops, and diverse crop rotations, will help the soil efficiently cycle both water and nutrients, sustain plant and animal productivity, and maintain or improve water quality. The return on soil health investments will pay off year after year after year." Here we say: yes, indeed.

One of the beautiful aspects of organic agriculture (and regenerative agriculture in particular) is that it’s not magic: it’s a comprehensive, widely different approach to growing food that’s based on the central pillar of organic fertilization. It’s backed by hundreds of thousands of studies in the fields of biology, chemistry, ecology, economics, management, and even history (to document traditional knowledge in techniques as useful as forest gardening). And, at the root of organic fertilization, composting lies as probably the most widespread method of using and reusing nutrients within an agricultural system. That’s precisely why it’s important to understand a key concept in composting: the carbon-to-nitrogen ratio, expressed in parts of carbon per parts of nitrogen, or C: N. So, to make things clear 10:1 means ten units of carbon per unit of nitrogen, and 850,000:1 means eight hundred and fifty thousand units of carbon per unit of nitrogen, and so on (this last one is pure madness, but you get the point). The importance of all of this lies simply in the fact that the bodies of soil microbes are themselves made of carbon and nitrogen in a ratio of 8:1. Microbes need to eat carbon and nitrogen from the environment to maintain this ratio (since they lose carbon as CO2 through respiration), and in this process of eating they decompose the organic matter that they find: this process is the process of composting. The liberation of heat is a sign that compost is teeming with bacterial activity, as heat is generated by the bacteria as a byproduct of their catabolic processes (their eating, basically). Healthy compost should be warm and stay warm even in colder climatic conditions. The C: N ideal rate for microbes is 24:1; they need that level so that there’s always enough carbon to maintain the amount already existing in the body (8 units of carbon), plus something to eat and gain energy to move and reproduce (another 16 units of carbon, give or take). So, the whole point of this is that material that has a higher C: N ratio than 24:1 will take longer to decompose (up to months or even years), while material that has a lesser C:N ratio will take less to decompose. This is why fruits and vegetables seem to rot away relatively quickly, even on a cupboard or fridge, while straw or dry leaves can stay on a field for several weeks and just appear to look even dryer or slightly decomposed. Fruits and vegetables tend to have a lesser C:N ratio, while dry leaves or stalks of plants tend to have a higher C:N ratio. Because of these general guidelines, organic matter with lower C:N ratio than 24:1 is often called in the composting business ‘green’ matter, while organic matter with higher C:N ratio is called ‘brown’ matter. Don’t let the color alone fool you, of course: a brown banana might look brown, but it’s really a ‘green’ material for composting. A compost pile that keeps a healthy balance of 'greens' and 'browns', trying to approach the 24:1 carbon-to-nitrogen ratio. Notice the cardboard, straw, and dry leaves ('brown' materials), and the fresh leaves, flowers, and occasional pea pod ('green' materials). Why does this matter for organic farming, in the end? Put simply, it’s as we said above: producing any sort of finished compost or other organic fertilizer can take a drastically longer time with a C: N ratio of over 24:1. It can also force microbes to take nitrogen-fixing bacteria from the soil to cover for all the carbon they're eating so that the natural balance in their diet is and body composition is not disrupting, and this could even lead to an actual decrease in the nitrogen available for crops themselves. What’s the best way to prevent this? Looking into the several materials that are being composted, and ensuring that the overall mix approaches the 24:1 rate as closely as possible. The Department of Agriculture of the United States has even made a useful leaflet explaining how that works in more detail. Why not take a look at it here?

As a part of the collective efforts of the agricultural industry for finding ways of dealing with microscopic agents of disease, there has been an important amount of research devoted to identifying equally microscopic agents for the prevention of disease. Among these, a collection of the most effective bacteria for the prevention and combat of plagues in crops have been termed the 'plant probiotics', for these aforementioned capabilities of building resistance to disease in the plants that host them. Plant growth-promoting rhizobacteria, or PGPR, belong to this group of little creatures. Pseudomonas putida, one of the most commonly used plant growth-promoting rhizobacteria. PGPR are bacteria that have co-evolved alongside the plants that host them across a timespan of millions of years, and as such, they have developed an astounding capability for mutual influence. Apart from their straightforwardly positive benefits as stimulants of plant growth, from which they derive their names, and apart from their passive increase of plant disease resistance by augmenting the strength of plants themselves and by out-competing other bacteria, these microorganisms actively perform work as biological control agents on two levels: 1) Producing compounds used by the bacteria to stifle the growth of competing, pathogenic microbes. This is done through the production of a variety of compounds, which a team of Canadian and Chinese researchers has narrowed down to antibiotics, antimicrobial peptides, bacteriocins metabolites, siderophores, toxins, and other microbial blends. These compounds have effects on dangerous microorganisms that go from inhibiting the synthesis of their cell walls (antibiotics) to depriving them of iron (siderophores). 2) Promoting the development of immune responses by the plant. PGPR are capable of triggering, in their host plants, systemic immune responses to disease that have long-lasting endurance and that do not even require the PGPR to interact with a pathogen in the first place! This (discussed here, with more bibliography provided in the source) means that plants do not need to actually get sick in order to develop immunity to broad groups of pathogens, with the PGPR functioning as a sort of plant vaccine. The common positive (both passive and active) effects of PGPR, as well as their diversity and its consequently large span of possible plant hosts and possible pathogens to target, make them a necessary option to consider (and to explore in more depth) for the implementation of any modern biological control scheme. AGENT PROFILE Common name(s): Plant growth-promoting bacteria, PGPR. Often-used species: A wide array, from an equally wide array of genera. Type of predator: Non-predatorial (mutualist relation with host plants). Potential damaging effects: Only registered in sugar beets. Interesting literature on its usage: A general review of the role of PGPR in agricultural sustainability (2016), use against diseases in tomato plants (2020), use against nematodes (2018).

Everywhere around the world, but more so in the developing countries, vast deserts spring up from the ground and begin to cover formerly forested areas of their nations. These deserts, however, are different from the Sahara or the Gobi Desert: from a large distance, they look green and lush. On closer look, however, they are vast extensions of a single cultivated species, almost completely devoid of any significant interrelationships between other species within them. Monocultural oil palm plantations in Indonesia. Palm oil plantations are some of the most striking examples of biodiverse 'green deserts' (© CEphoto, Uwe Aranas). These green deserts (a term originally coined in Brazil to refer to the ever-enlarging eucalyptus plantations in the 1960s) seem rich in life, but their apparent stability and fertility are fictitious: any interruption in the flow of enormous human effort and care that go into their maintenance could turn them into barren landscapes in less than one growing season. That, or any new disease that could spread like wildfire, as happened in the 1950s with destruction the global banana production, in the 19th century with the French vineyard collapse, or as is happening now with the pathogens that threaten the world production of potatoes, soybean, and wheat today, in 2021. Organic agriculture can help to fight this trend. All of the existing data to the moment shows that spaces where organic agriculture is practiced have 30% more species (even in organic monoculture!) than non-organic agricultural land. This trend is also especially significant in what regards some of the most useful creatures for agriculture: earthworms, beneficial bacteria, mycorrhizal fungi, and butterflies alongside other pollinators have all much higher concentrations and a higher diversity of species in organic farms. As organic agriculture builds soil fertilizers, this fertile new soil is increasingly populated by a diversity of microorganisms that create a resilient balance, thus making organic agriculture a much more solid contributor to food security than inorganic agriculture. Biodiversity brings major economic benefits, too. It is widely acknowledged that the economic benefits of not-so-well-known aspects of how an ecosystem works can’t be accounted for, so we do not know by how much agricultural profit margins rise with a 30% increase in biodiversity. We do have a clue, however, thanks to the UN-affiliated TEEB: a nearly US$ 800 billion market across pharmaceuticals, biotechnology, personal products, and agriculture depends entirely on biodiversity.

In the struggle to transition to a greener, healthier world, every single victory is a victory for the planet as a whole. Efforts of supranational organizations such as those of the European Union and the FAO are inspiring, but there’s yet nothing quite like a victory to prove that transitioning to better models of agriculture can be done on a large scale. Such is the case of the Indian state of Sikkim, sitting on the slopes of the Himalayas. The Prime Minister of India, Narendra Modi, and Sikkim's Chief Minister Pawan Kumar, review the state's agricultural products in 2016, one year after it declared its complete transition to organic agriculture. Since the year 2003, and under the then Chief Minister Pawan Kumar Chamling, the state began implementing an energetic policy of doing everything in its power to pursue an ambitious goal: completely switching to organic agriculture. In that year, and after its inaugural speech for the program given in the State’s Legislative Assembly, the government took drastic first steps by directly banning the import and export of synthetic fertilizers and pesticides, at the same time it reduced gradually the state’s subsidies for their production within Sikkim itself. This was accompanied in 2010 by the formation of the Sikkim Organic Mission (SOM), which became the governmental office dedicated exclusively to the implementation of organic policies state-wide. By the early 2010s (2010-2014), the government implemented a full ban on the use of synthetic fertilizers and pesticides, which is coupled with massive investments into the production of organic fertilizers at a community level, and the creation of cooperatives to organize the commercialization of the farmers produces. Among its policies, the government also began widespread training programs and intensive awareness campaigns of the new official agricultural stance of the State. Tea-producing slopes in the district of Namchi, South Sikkim. The state has seen a substantial increase in agrotourism and the services industry since its transition to organic agriculture. Though there have been challenges to the implementation of 100% organic farming (and there still are), the complete commitment of the government to the organic transition proved fertile, when Sikkim has officially declared a completely organic state in 2015. By 2018, three years later, the claims were corroborated by the Food and Agriculture Organization of the United Nations, officially confirming the success of the programs. The lesson from Sikkim’s policymakers to the world, independently of each nation and region’s special circumstances for the implementation of organic policy (Sikkim had it easier due to its relatively low usage of synthetic fertilizers and pesticides in the first place, but not so easy if we consider the resources available for one of India’s smallest-GDP states), would seem to be that a consistent and continuous stance of complete government support is essential for a massive transition to a greener world. A greener and a richer world too, as Sikkim expects no less than sixty-six thousand families to reap economic benefits from their transition to organic agriculture.

According to the most recent data on the subject, no less than a quarter of all the world’s greenhouse gas emissions come from agriculture, and from the food chain that brings its produces to the consumers. Considering that such a large impact comes from just one sector of the economy, making whatever changes seem sustainable (and not only in the sense of being environmentally sustainable but economically sustainable too), is essential to act against climate change across the world. Unlike in other highly-emitting sectors such as energy production, however, the ways to decarbonize agriculture are less clear and rely less on the invention of new technologies. Instead, they are more about the adoption of new techniques and the implementation of many strategies dedicated to reduce food waste and change consumption habits, for example. A comparison (courtesy of the Rodale Institute) between soil cultivated using traditional (left) and organic techniques (right). The darker color of organic soil implies a higher carbon content, as a result of better carbon conservation and sequestration practices. Organic agriculture is key for achieving these goals, bringing a whole new set of practices that decrease the environmental impact of agriculture. Such were the findings of a 2018 study by researchers from the universities of Harvard and Sharjah, in the UAE. In their study, the researchers used data from the United States in the period 1997-2010 to assess the difference in emissions between conventional and organic agriculture. Their conclusions were steadfast in their support of organic agriculture’s reduced emissions: "Organic farming practices are by design sustainable in the role they play in maintaining optimal soil health, increasing carbon sequestration, and reducing GHG [greenhouse gas] emissions". They also address clearly the frequently repeated concerns that organic agriculture might in fact be unsustainable, by being based on speculation, questionable, inadequate or non-existing evidence. In contrast, the researcher's state clearly: "After accounting for other sources of emissions and potentially influential observations, we find that one percent increase in organic farming acreage could decrease GHG emissions by 0.049%". According to these calculations, a net increase of 100% in the organic cultivated area could lead to a 4.9% fall in greenhouse gas emissions. That might not sound like much, but to put this in context, however, the United States currently has only 0.6% of its land under organic cultivation. An increase of this to the level of some European states such as Austria, where that figure stands at 25%, could mean an incredible amount of reduced greenhouse gas emissions, potentially turning agriculture into a carbon-capturing industry. The future will decide if this happens, but one thing is clear: there’s potential in organic agriculture to change the world, one hectare (or acre) at a time.