Humans have been practising agriculture for about 10,000 years after agriculture was independently invented in at least Mesopotamia, America and New Guinea.
For all that we know, there may have been other independent inventions of agriculture in other societies, but so far, we have no evidence of this.
The development of agriculture allowed humans to settle in one place and so have better shelter, and also own more possessions than they could carry around.
Farmers were generally able to produce more food than they and their families needed, and this opened the way to some people being able to specialize.
Some parts of the farming cycle left farmers with nothing to do but watch their crops grow. This gave them time to think, to observe, and perhaps even tinker.
Farmers were able to observe the same basic situation, year by year, with slight differences that allowed them to observe cause and effect at close hand.
One of the key changes that allowed agriculture was the development of systems of irrigation, but these required more organized societies to maintain them.
The aqueduct was an early means of transporting water with no energy cost, using gravity to carry the water, although inverted siphons were also used at times.
The aqueduct could work by gravity when builders could survey a suitable route, build supports and construct a waterproof channel to carry water without leaks.
The qanat of ancient Persia was an early means of transporting water with no energy cost, relying on a tunnel going upwards, beneath the water table in hills.
Irrigation, combined with agriculture, delivered regular food surpluses allowing some people to specialize in making things that they could sell or barter.
Irrigation and agriculture together led to a society in which some people could become full-time soldiers and rulers, while others could become scholars.
In 1630, Johann Glauber suggested the use of saltpeter, sodium nitrate, as a fertilizer, implying a recognition of the need for nitrogen when growing plants.
In 1645 Sir Richard Weston described crop rotation as he saw it in Flanders: the first reference in English to the habit of using different crops in one field.
Around 1701, Jethro Tull invented the seed drill, allowing farmers to sow seed more efficiently and more economically, increasing the efficiency of large farms.
Most crops are grown as monoculture crops, making massive outbreaks of pests easier, but offering large economies of scale. Sprays make the risk less.
Most sprays kill more than just the pests they are aimed at. Many of the pesticides are accumulated to dangerous levels, either in the soil or the food chain.
Many organohalogens are used as pesticides in farming, and the use of these pesticides in agriculture is driven by a consumer demand for blemish-free food.
Overgrazing can be a problem in some situations, trading off long-term viability of a farm for short-term gain by a farmer. Economic pressures may favor this.
In many cases, the energy output from a farm in the form of food is less than the energy input in terms of materials like fertilizer and pesticides, and fuel.
This file is http://members.ozemail.com.au/~macinnis/scifun/splatstechag.htm, first created on January 25, 2006. Last recorded revision (well I get lazy and forget sometimes!) was on January 25, 2006.