Tilth can be defined as the character of soil that has been cultivated and prepared for planting, the soils degree of readiness for garden use.
The long-term fertility and productivity of soil can be accomplished through sustainable agriculture; maintaining soil nutrients with amendments, irrigation, crop rotation, and companion planting.
It’s best to think of your soil as a living entity defined by its biodiversity which needs to eat, drink and breathe rather than an inert body. The benefit of organic matter and other amendments is to feed the wide range of soil organisms, fungal and bacterial. With out these organisms your plants struggle to process and absorb nutrients from the soil which then limits the yield and nutritional value of food grown in that soil.
There are three soil mediums; sand, clay, and rock. Depending on your existing soil type, promoting your soil organisms can be a long and slow process with several factors to be considered. Sandy soils are the first to warm in the sun and the first to drop in temperature as the sun sets. Microorganisms struggle to take hold due to the extreme temperature fluctuations and water flowing through with ease and washing away existing organic matter carrying the microorganisms with it. The compost mediums help sandy and rocky soils absorb and hold moisture which in turn aid and maintain an even temperature. Clayey soils benefit from these compost mediums because they help break up the dense and sometimes compact soil particles allowing water to drain while also helping organisms and root systems to breath. By adding compost mediums, all three soil types get a boost of nutrient levels increasing your soils biodiversity and readiness to accept plants and/or seeds. Sandy, clayey and rocky soils all benefit from manures as well as woody/ leafy compost. Over time the soil will change and be less likely to revert to its original raw state.
The bacterial and fungal organisms thrive beneath the soils surface hence the benefit of tilling and mixing amendments into soil as opposed to setting on the surface. Over tilling can be an issue, such as; tilling too frequently or as I like to think of it, as bruising the soil. Which exposes your soils micro-organisms to too much UV light, killing many and damaging membranes of others. Practicing good tillage: #1) Tilling and/or mixing amendments into soil anywhere from 4″-15″ deep is enough when preparing soil for annual plants as well as many perennial plants. When planting trees, same rule applies, the only difference is you till and mix the soil 10″-15″ beneath where the root systems of your tree will be resting. #2) Manipulation of soil once, maybe twice per year is plenty. Timing is important, tilling in the middle of the growing season causes more damage to the soils microorganisms and fungal membranes, again, bruising and damaging their growth pattern. Early and/or late tilling is permissible for the biota enter a stage of dormancy and can rebound from the damage of tilling since they have a longer period of undisturbed growth cycle. If you are tilling or feel it is necessary to till more than that because your soil becomes compacted and hinders plant growth, know that there are better solutions. For example; using mulch between rows (dry straw, leaves, etc.) helps reduce water evaporation, maintains soil temperatures, protects biota from UV light, helps reduce stagnant water from puddling, and also hinders weed growth reducing competition for nutrients. Further more, over tilling and damage of the soils biota causes soil to become compact due to the breaking of layers of membranes. #3) Using your plants to your advantage. Certain plants have stronger root growth than others and will push deeper into the soil, up to 8′ deep, essentially tilling and aerating the soil for you. Other plants have a shallow root system that spreads along the surface of the soil. Neither plants root systems of which are competing against each other for water or nutrients and sometimes benefiting each other by either attracting pollinators or deterring pests, A.K.A. companion planting.
In conclusion “variety is the spice of life”. Planting and maintaining many varieties of plants season after season will promote good tilth and save you from excessive labor.