Selective breeding refers to the deliberate human practice of choosing which plants or animals to breed together, based on specific characteristics, in order to selectively enhance these characteristics (and their genetic basis) in their offspring.

Sensitivity and uncertainty analysis are an integral part of any modelling process. Sensitivity analysis varies the possible values of input variables to a model in order to understand the difference that these assumptions make to results and conclusions that can be drawn. Uncertainty analysis investigates the potential effects of lack of knowledge or potential errors in the model design.

Sentience is the ability to experience sensations and feelings (particularly positive and negative feelings like pain and pleasure). It is often seen as a prerequisite for moral consideration in debates on animal welfare and ethics.

Silting refers to the transport and deposition of sediment on the riverbed, which changes the dynamics of the water flow and can affect aquatic ecosystems.

See soil health.

Soil health refers to the state of the soil with regards to its capacity to support plant growth; in this sense, it is a synonym for the narrower term soil fertility. However it is also used to refer to the soil's capacity to provide other ecosystem services, such as contributing to carbon sequestration or flood management, and the role soil plays in a wider set of relationships in an ecosystem. In practice, soil health in agronomy is mostly a function of its contents of plant macronutrients (particularly nitrogen, phosphorus and potassium, NPK) and micronutrients, its proportion of organic carbon, and the microbial communities living within it. Soil in poor health might be soil lacking in some key nutrients, with a very low content of organic carbon, or with a limited or unbalanced microbial ecosystem.

The Brazilian Soy Moratorium (SoyM) is a multi-stakeholder initiative set up in 2006 by Greenpeace, the Brazilian Association of Vegetable Oil Industries (ABIOVE), and the National Association of Grain Exporters (ANEC). It was later joined by many other companies, civil society organisations, and the Brazilian government. Signatories to the moratorium take on the voluntary commitment not to buy soybeans grown on land in the Amazon that was deforested after 22 July 2008. The soy moratorium was initially renewed annually but extended in 2019 for an indefinite period. The moratorium has caused deforestation in the Amazon to decline to about one half to one third of the rate before the moratorium. Recent years, however, have seen an increase in deforestation in the Amazon. Deforestation levels were particularly high in the summer of 2019 due to an exceptional increase in forest fires. Only a small amount of the soy exported from the Brazilian Amazon is handled by traders who did not sign the Moratorium.

A specialist species is a plant or animal species that is able to thrive in only a limited variety of environmental conditions, or that has a limited diet. Unlike endemic species, populations of the same specialist species may be present at different geographical locations around the world.

Structural Adjustment Programs (SAPS) were introduced by the International Monetary Fund and World Bank in the 1980s in response to a series of economic crises in the global South. During this era, these institutions made access to loans by poor countries conditional on a set of economic policies that aimed to reduce state spending and open up their economies to international trade. Proponents of SAPs claimed that they would encourage economic growth; however they have been heavily criticised for undermining national sovereignty, deepening social inequality and further marginalising many poorer countries in the global economy.

Stunting is a medical condition where childhood growth and development is impaired as a result of inadequate nutrition, repeated infection, and inadequate psychosocial stimulation. Children are defined as stunted if their height for their age is abnormally low. Its effects can lead to an underdeveloped brain, poor cognition and educational attainment, as well as a higher risk of nutrition-related chronic diseases later in life.

Subsistence farming refers to rearing animals and growing crops only for your own consumption, without having any surplus to take to market as a source of cash income.

The substitution effect in economics refers to the idea that as prices increase or as a product becomes scarce, people will replace such items with substitutes that are cheaper or easier to access. In the context of diets, substitution effects refer to the changes in the environmental footprint of a person's diet, according to the relative impact of foods that are substituted for one another.

Sustainable intensification is a recently developed concept that is understood in different ways by its critics and supporters. A common understanding is that it denotes the principle of increasing or maintaining the productivity of agriculture on existing farmland while at the same time, reducing its environmental impacts. Understood in this way, SI designates a goal for the development of agricultural systems but does not, a priori, favour any particular agronomic route to achieve it. It may involve the intensification of different types of agricultural inputs (e.g. of knowledge, biotechnologies, labour, machinery) and apply these to different forms of agriculture (e.g. livestock or arable; agroecological or conventional). Forms of intensification that can be called sustainable intensification must lower environmental impacts and land use, relative to yields. However, for some, to merit the term ‘sustainable’ social, economic, and ethical criteria must also be considered.

A symbiotic relationship, or symbiosis, is any type of a close and long-term biological interaction between two biological organisms of different species, termed symbionts. There are three main types…

• Parasitism: symbiosis where one species benefits, and the other is harmed. Examples include both internal (e.g., worms) and external (e.g., ticks) parasites found on livestock like cattle, sheep, goats, and pigs. Some of these can be zoonotic (passed on to humans).
• Commensalism: symbiosis where one species benefits, and the other is neither harmed nor helped. An example is birds, such as cattle egrets, perching on or near grazing cattle and eating insects stirred up while they graze.
• Mutualism: symbiosis where both species benefit. Examples include pollination of flowering plants by animals, mycorrhizal interactions between a plant’s roots and fungi, and the relationship between leguminous plants and nitrogen-fixating bacteria.

System boundaries are subjective boundaries that define what is included within the system under analysis (and so counted) and what is external to the system (and so not counted). System boundaries have multiple dimensions, including what stages are focused on (e.g. production, distribution), what inputs and outputs are measured (e.g. land, greenhouse gases), what geographic locations are included, and more.