We address two technical challenges in agriculture that as of yet have not been solved satisfactory: weed control and soil compaction.
Without weed control, almost all agricultural crops would have to compete with wild plants for light, water, and nutrients. Not surprisingly, weed control becomes even more of a problem when a field is irrigated and fertilized, as improved conditions invite an ever broader range of species.
Weed control can be looked at from the point of view of conventional agriculture, and from the point of view of ecological agriculture.
In conventional agriculture, the challenge is to find an alternative to herbicides. Herbicides have many disadvantages: they have a negative impact on human health through direct contact (in particular for farmers), residues on the food product, and through the contamination of ground water, soil, and air. Herbicides have a negative impact on field flora and fauna, be it microorganisms in the soil or birds in the sky. Herbicides are the main reason why agriculture needs transgenics: often, a herbicide and the matching herbicide-resistant transgenic are sold in tandem.
Whaterver their benefits, herbicides are not guaranteed to be effective for long, as weeds can and most likely will evolve resistance to herbicides. The future of agriculture must not be dependent on herbicides.
While ecolological agriculture does not use herbicides, it does not offer an entirely satisfactory solution to weed control. The challenge is to find an alternative to mechanical weeding. Mechanical weeding is energy intensive and requires a high degree of precision. Tractor and animal powered tools generally only weed between the crop lines. Tractors tools are energy hogs that give ecological agriculture a distinctively negative energy balance. Animal powered tools are disadvantage because drag animals (horses, oxen) generally have only one speed, which is difficult to combine with the high degree of precision needed for weeding. Generally, the handling of drag animals requires a high degree of skill and physical ability that give animals little advantage over the third option, human labor.
In ecological agriculture one needs to weed between one and three times between planting and harvest. Weeding is done when the plant is small, as large plants do not allow the weeds to grow anymore. The time between weeding is three and six weeks. Onion, leek, garlic, and carrots are the most intensive for weeding. Onion, for example, needs six or seven month to grow. The first weeding accours three weeks after planting the seedlings, and needs to be repeated in intervals of three weeks, two or three times in total, until the plants are large enough to successfully compete with further weeds. The last three month or so they grow without weeding. Weeding also loosens the top soil, preserving humidity. Spinach and lettuce need only one weeding. Cabbidge two times. Mais again needs three time.
Except corn everything needs to be weeded between the plants as well, which is almost always done by hand.
A conventional tractor achieves traction by weight. The weight pushes the profile of the tires into the soil, giving them grip, translating the rotational force of the tires into forward force of the tractor. The weight depends on the force to be generated. The surface area of the tires depends on the soil condition.