'Agricultural engineering' is the discipline of engineering in agricultural, food, and biological systems. Agricultural engineers design agricultural machinery and equipment and agricultural structures. Some specialties include power system and machinery design; structures and environment; and food and bioprocess engineering. They develop way to conserve soil and water and to improve the processing of agricultural products. Agricultural engineers work in research and development, production, sales, or management.

*Biosystems engineering *Ergonomics, Safety and Health *Emerging Areas *Information and Electrical Technologies which includes Remote sensing *Food and Process Engineering *Forest Engineering *Power and Machinery, which includes Machine design *Soil and water, which includes Irrigation, Drainage, stormwater management and erosion control. *Structures and environment, which includes designing livestock housing as well as structures such as grain elevators and greenhouses

'Grain elevators' are buildings or complexes of buildings for storage and shipment of grain. The term became common in the late 19th century, at which time bucket elevators for lifting grain first came into use. Bucket elevators lift grain to a distribution point, where it can flow by gravity into one of a number of bins, which are then unloaded by gravity. The bins and their unloading chutes are often sited in such a way that rail cars or barges can be filled from them directly.

Prior to the advent of the grain elevator, grain was handled in bags rather than in bulk.

Grain elevators are a constant sight in the grain-growing areas of the world, such as the North American prairies. Larger terminal elevators are found at distribution centers, such as Chicago and Thunder Bay, Ontario, where grain is sent for processing, or loaded aboard trains or ships to go further afield.

Originally each small town had its own small grain elevator that would serve the local farmers. The classic grain elevator was made of wood and had 12 rectangular bins arranged in a 3x4 pattern. In more recent times with improved transportation, centralized and much larger elevators serve many farms. Two elevators in Kansas (one in Hutchinson and one in Wichita) are half a mile long. The loss of the grain elevators from small towns is often considered a great change in their identity and there are efforts to preserve them as heritage structures. At the same time, many larger grain farms have their own grain handling facilities for storage and loading onto trucks.

Grain elevator operators buy grain from farmers, either for cash or at a contracted price, and then sell futures contracts for the same quantity of grain, usually each day. They profit through the narrowing 'basis', that is, the difference between the local cash price, and the futures price, that occurs at certain times of the year.

Before economical truck transportation was available, grain elevator operators would sometimes use their purchasing power to control prices. This was especially easy since farmers often had only one elevator that was within a reasonable distance of their farm. This has led some governments to take over the administration of grain elevators. Many elevators were purchased by cooperatives.

'Fertilizers' or 'fertilisers' are compounds given to plants with the intention of promoting growth; they are usually applied either via the soil, for uptake by plant roots, or by foliar spraying, for uptake through leaves. They can be naturally-occurring compounds such as peat or mineral deposits, or manufactured through natural processes (such as composting) or chemical processes (such as the Haber process).

Fertilizers typically provide, in varying proportions, the three major plant nutrients (nitrogen, phosphorus, and potassium), the secondary plant nutrients (calcium, sulfur, magnesium), and sometimes trace elements (or micronutrients) with a role in plant nutrition: boron, manganese, iron, zinc, copper and molybdenum.

* Examples of naturally-occurring inorganic fertilizers include diatomaceous earth and limestone. * Examples of manufactured or chemically-synthesized inorganic fertilisers include ammonium nitrate, potassium sulfate, and superphosphate, or triple super phosphate.

Synthesized materials are also called 'artifical fertilizers', and may be described as 'straight', where the product predominantly contains the three primary ingredients of nitrogen (N), phosphorous (P) and potassium/potash (K), often described as 'NPK fertilizers'. They are named or labelled according to the content of these three elements, thus a 5-10-5 fertilizer would have 10 percent phosphate in its ingredients. If nitrogen is the main element, they are often described as 'nitrogen fertilizers'.

Chemist Justus von Leibig (in the 19th century) contributed greatly to understanding the role of inorganic compounds in plant nutrition and devised the concept of 'Leibig's barrel' to illustrate the significance of inadequate concentrations of essential nutrients. This ammonia is applied directly to the soil or used to produce other compounds, notably ammonium nitrate, a dry, concentrated product.

Implicit in modern theories of organic agriculture is the idea that the pendulum has swung the other way to some extent in thinking about plant nutrition. Ammonia gas (NH<sub>3</sub&g t;) may be emitted following application of manure or slurry or due to inorganic fertilizers (to a lesser extent unless ammonia itself is used directly).

Fertilisers can be buried around a trees roots when it is planted, placed in bore holes near tree roots, spread on to soil, sprayed by hand, or one can stick a bag of fertilizer in the branches.