Plants need warmth (not too much or too little); water (not too much or too little); light (and for some, day length matters a great deal!); air (carbon dioxide for photosynthesis, and oxygen for respiration); and a mixed bag of inorganic minerals which serve as nutrients. They may also need extra nutrients in the form of small organic molecules. This is speculative, but if it is so, then it could prove very important. Since animals ultimately depend on plants, and since they are adapted to the world as it is, they need all of the above too, at least at second hand. They also prefer a certain level of comfort, including freedom from draughts, and shade, and (at least for chickens) freedom from aerial attack, and so on. All this the farmer must provide.
Warmth is a matter of local climate which in turn depends on factors both large- and small-scale, for all of us live in micro-climates which can be very different from the prevailing conditions. The maxima and minima of temperature day by day and season by season depend on latitude, distance from the sea, altitude, and topography; whether the plants and animals are exposed to some cross-wind, or sheltered behind a mountain range or a hedge or whatever; whether or not they sit in frost pockets, the cold air rolling downhill with nowhere to go.
The water supply depends on rainfall and irrigation – from rivers, lakes, or aquifers (underground water, including fossil lakes), sometimes renewable and sometimes not. Water depends too, crucially, on whether the ground is well drained, as sandy soils tend to be, or clings tightly to water, as clay does, or whether it is spongy and holds just the right amount, as organic matter tends to do. It depends, too, on whether the ground is flat or sloping, whether the farmer has taken steps to get shot of the surface water quickly with drains and ditches and up-and-down furrows or seeks instead to control the run-off with trees and barriers (swales) along the contours. Everything is interlinked. Plants are more sensitive to soil temperature than to air temperature, and wet soil retains its heat better than dry soils but also heats up more slowly so plants may be slow to “get away” in spring if the soil is too wet. Waterlogged soils also leave no space for air and so the roots lack oxygen.
Whichever way we look, soils high in organic matter (itself an immensely complex matter, as only now is being properly appreciated!) seem to win out. They are spongy, and tend to hold just the right ratio of water and air; and, if things are well arranged, they ensure that vital nutrients are always on hand in just the right amounts. In the words of Eve Balfour, founder of the Soil Association, “Take care of the soil and the crops will take care of themselves.”
It all sounds, and is, immensely complex. Fortunately, human beings in general and farmers in particular seem to grasp the complexities intuitively, and can feel when things are working well and when they are not. But the devil is in the detail, and no-one can know too much.