Cabbage Integrated Pest Management : An Ecological Guide.

Major Agronomic Practices3.4.2 Soil typeSoil is made up of a mixture of different-sized particles, sand, silt and clay. In nature sand, silt and clayare almost always mixed together in a great variety of combinations which give the soil its characteristictexture. Terms as sand, sandy loam, loam, clay loam, clay, heavy clay indicate the particle size in thesoil. Light soil is composed largely of sand and the name indicates the ease with which it is worked.Heavy soil is soil which contains large amounts of silt and clay. The name refers to the difficulty ofworking and not to the actual weight of the soil.The term ‘structure’ refers to the arrangement of the different particles into soil aggregates. The microorganismsin the soil are responsible for mixing the soil and building of soil structure. Soil particles arebound together by fungal branches and bacterial gums. These help to bind them into aggregates betweenwhich the air and water holding pores areformed. In the pores between the aggregates the soilair is found, an important source of oxygen for rootHumusrespiration. Like humans, most plants and their rootsneed air (oxygen) for respiration! A good soil structurepermits the movement of water through the soil andTopsoilit facilitates the development of a good root system.A good soil can be compared with a new spongethat can absorb plenty of water.SubsoilThe best part of the soil is the dark layer of topsoil,which takes many years to develop. Topsoil is richin plant nutrients and beneficial soil organisms. Underthe topsoil is the yellow, light brown or reddish subsoilwhich may be more acid and is harder for plants to grow in. Humus is the more or less stable fraction ofthe soil organic matter remaining after decomposition of plant and animal residues. Adding organicmaterial such as well-rotten compost, improves the structure of most soil types including heavy clay andlighter sandy soils. The organic matter should be properly composted (well-rotten).Cruciferous crops grow well in any soil that is well-drained and moisture retentive. On heavy soils, plantsgrow slower but the keeping quality (shelf-life) of the cabbages is usually better.A soil pH of 6 to 6.5 is optimal, although cabbage is sometimes grown at higher pH (pH >7.2) for clubrootcontrol. Lower pH values reduce growth. See section 3.4.5 on soil pH.A good site has not grown any cruciferous crops for at least two years. This reduces the chance of (soilborne)diseases. See section 3.12 on crop rotation.Related exercises from CABI Bioscience/FAO manual:2-A.3. Soil structure and effects on root growth2-A.8. Soil test kits3.4.3 Soil infectionNext to the beneficial decomposers or neutral organisms in the soil, soil may also contain organismsthat are harmful to the crop. These include insects and pathogens like fungi, bacteria and nematodes.Soil-borne pathogens can enter a field in numerous ways. They may be attached to pieces of soil on theroots of seedlings, to soil particles on tools used in several fields, or with bits of soil on your slippers orshoes! They may also be spread with the ground water.17 Cabbage Ecological Guide - 2000