Soil tilth is the combination of crumb aptitude and crumb durability and is the result of biological soil structure. Tilth is advanced by minimum intervention and a mixed crop cover of plant roots. The crumb structure has to stay stable during the whole season without slaking and silting of the top soil.
Physically, crumb structure is based on neutralisation of the electrical charge of the colloidal soil parts through electrolysis. These parts consist mainly of electrically charged clay and humus particles and are determined by the cation exchange capacity. Biologically the crumb structure is built through microbial bio-agglutination of the primary aggregates (0.1-0.2 mm) and will be stabilized as colloidal aggregates or crumbs(1-3 mm).
Capillary water movement and retention with evaporation protection happen in a living bio-aggregation not in a mechanically crumbled soil. Air and water supply from subsoil to topsoil is activated by cavities between aggregates, the soil pores.
Plant roots and the plant-food web of bacteria, fungi, actinomycetes and earthworms use the active exchange of water and gases of these soil pores. These pores determine the soil air circulation and the soil water storage and circulation, and affect the soil microclimate.
The soil chemistry needs to be balanced in the ration of calcium, magnesium and potassium. The combination of soil chemistry and soil physics creates the environment in favour of soil biology as plant roots grow best in crumbly, aerated and well-metabolised soil. The balance of macro-and micro-nutrients, together with the physical and biological qualities, regulates the growth and health of the vines and grapes which are grown. Soil testing which covers all these parameters is to be engaged.
Cell-tilth and plasma-tilth
The scientific rational is explained by one of the bio-organic pioneers Dr.H.P.Rusch: “Soil is structured in layers where soil tilth in the top layer or A-horizon (3-8 cm) with decomposed plant material is called cell-tilth horizon where bacteria and soil fauna work chronologically in succession and spatially on top of one another. The metabolites in this layer contain phenols and cause root damage, which is the reason for diminished root growth in the cell-tilth layer. Below this layer is the plasma-tilth horizon where the soil is aggregated biologically and colloidally by carbon compounds” (1). (The determination of cell numbers, plasma percentage and biological quality, Soil Fertility, Dr.H.P.Rusch-1980).
“One of the most important carbon compounds in the process of bio agglutination is glomalin, a glycoprotein produced abundantly on hyphae and spores of arbuscular mycorrhizal fungi in soil and roots.
Glomalin stores carbon in both its protein and carbohydrate (glucose and sugar) subunits. It permeates organic matter, binding it to silt, sand and clay particles. Glomalin contains 30-40 per cent carbon and forms clumps of soil aggregates. These aggregates form soil structure and sequester carbon. Glomalin was named by Sara F. Wright in 1996 according to the glomales order of fungi.”
Mycorrhiza fungi need aerobic conditions to thrive and feed on root exudates, which exist mainly at root tips and are used as lubricant and sensor. Plants secrete equivalent amounts of root exudates as plant matter above ground. As long as the plasma-tilth horizon is not disturbed it can grow 1- 2 metres deep. This is the horizon where plant roots feel comfortable and can absorb nutrients of the clay-humus complex at their own demand.
Clean, tidy soils without plant cover lose the biological tilth, start silting and growing weeds. A permanent and living soil cover can be established, either through a permanent under-sowing cover in the mid row or a direct drilling of a mixed flowering strip in spring. Pneumatic direct drilling with disc shares has the advantage of minimum soil movement and minimum weed seed germination. The preparation of a seedbed with the vertical hoe followed by row drilling is a technique which encourages more weed germination and has to be followed up with spring tine harrow. The weed seed potential per square metre is up to 20,000 seeds, the greater the diversity of the seed mix the better the chance of lesser weed germination. Reduce soil pressure, a maximum of 5t and 0.8 Bar wheel pressure as a guideline to prevent any technical damage to optimum soil tilth. Minimum intervention in soil management can reward the grower with optimum soil structure, soil fertility and crop quality.