Sunday, May 08, 2016

Biological Agriculture for Roboticists, Part 1

This is the first post in what I expect will become a series. As such, it makes no attempt to be comprehensive, but rather is intended to be a gentle introduction to the subject, which I have chosen to call "biological agriculture" for an audience composed of roboticists and robotics enthusiasts. This choice of names is somewhat arbitrary, but I think it will serve well enough, the idea being that methods based in biology and the manipulation of organisms should be used in preference to methods based in chemistry, even biochemistry. By this I do not mean that there is no place for chemistry, far from it, but that, in the sense/think/act paradigm common in robotics, chemistry properly belongs primarily to sensory input.

I also expect to do a series on Robotics for Gardeners and Farmers, as time and clarity allow.

Let's begin with a few definitions.

Cultivation has two primary meanings, one of which is specific to a class of tillage operations in which the soil is disturbed, usually lightly, to kill or suppress the development of weeds. The other meaning of cultivation is more general, roughly equivalent to the term husbandry, and may or may not include tillage as a practice. This more general meaning is what I had in mind in naming my blog Cultibotics. Cultivation without tillage is frequently referred to as a 'no-till' regime.

Soil is more than dirt. It is a complex ecosystem generally including a mineral component, but even that mineral component isn't static. The clay in soil is constantly in flux, trapping nutrients as it forms and releasing them again as it dissolves. It also contributes to the ability of soil to absorb and retain water. Decomposing organic matter in soil is collectively referred to as humus, which also contributes to water retention, as well as providing both nutrients for plants and food for the many living organisms found below the surface. Besides a bewildering array of bacteria and fungi, these also include worms, insects, and higher animals like moles and mice. Some microorganisms live in symbiosis with the roots of plants, receiving energy from them and providing a valuable service in return, for example nitrogen fixation. Living soil is also partly gaseous, with a continuous network of tiny pockets and channels throughout. In the absence of tillage or other disturbance, soil develops structure driven by the many simultaneous processes happening within it.

Anything that provides substances needed by plants for growth and maturation can be considered a fertilizer, from the dung of passing herds of ungulates to composted feedlot waste, to slurry from urban sewage, to ground minerals, to industrially produced ammonium nitrate. Fertilizers are usually applied for the purpose of increasing yields, but may also be used to improve the nutritional quality and/or marketability of crops produced.

You may have heard of Glyphosate. It is one prominent example of herbicides, compounds marketed for the purpose of killing or suppressing the development of weeds that compete with crops, and has become a hot topic of debate in part because crop varieties which are relatively tolerant of this substance have been developed to broaden its applicability to crops that would otherwise be damaged or killed by it as much as the weeds it's meant to control. This is because it is a 'broad-spectrum' herbicide. Some herbicides are more specific, killing or stunting the growth of problematic species more selectively.

Generally the term pesticide is applied to substances which kill or suppress the development of multicellular animals, usually arthropods (insects, spiders, crustaceans) but commonly also tiny worms called nematodes and gastropods (slugs). Some of these substances are produced by and refined from organisms, or synthesized based on naturally produced compounds, while others are entirely synthetic. Depending on the metabolic pathway they target, pesticides may also be highly toxic to humans, and the use of those that are has already been prohibited or is tightly regulated, with limits established for residues in food sold for human consumption.

Fungicides are much like pesticides, except that they target fungi, such as ergot, which infects cereal crops like wheat and rye.

Biological Control
A prime example of biological control is one used by many gardeners, the release of ladybird beetles (ladybugs) to control aphids. Others include distribution of praying mantis egg cases and encouragement of parasitic wasps, which lay their eggs in or on the larvae of a variety of insects, such as the tomato hornworm. Biological controls tend to be more specific than synthesized products and are far less likely to present any danger to humans, but they also tend to be more management intensive, meaning that, for a given effect, they tend to require more time and attention from the gardener or farmer.

Plants are seldom found in uniform, single-species stands in nature, there is nearly always a mixture of species, forming plant communities, which in turn constitute the most visible aspect of ecosystems. Polyculture attempts to mimic this by combining plants that play well together into mixed plantings, simultaneously, sequentially, or both. One popular approach which arguably qualifies as polyculture is planting different crops in alternating rows in the same field. This practice may help keep populations of beneficial insects from crashing, by spreading out the season during which resources are available to them.

Crop Rotation
A compromise solution which achieves some of the benefits of polyculture without the complication of combining multiple types of plant together in the same field at the same time is crop rotation. Rotations can often be expressed as a simple, repeating sequence of crops, such as clover followed by maize followed by wheat.

Think vineyards and orchards, although some herbaceous crops are also perennial. Even though vines and trees eventually die, they live for years and may be replaced by young plants of the same type, perpetuating the continuity of the ecosystem which develops around them. Permacultures may also be polycultures, and may include annual crops in the mix, but the presence of perennials constrains the use of highly disruptive techniques, like plowing, to the space between them, discouraging the use of such techniques at all.

That's enough for a decent beginning. Stay tuned for Part 2, and for the series on Robotics for Gardeners and Farmers.

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