Cabbage Integrated Pest Management : An Ecological Guide.

Major Agronomic PracticesSome of the micronutrients are found in the mineral particles of the soil but most come from humus.Humus comes from the break down of organic matter. The micronutrients exist in very complex formsand have to be broken down into simpler forms which the plant roots can absorb. This process iscomparable with the breakdown of leaves in the soil: slowly they will become soft, fall apart into verysmall pieces and eventually disappear. This breakdown process is done by micro-organisms, mainlybacteria that live in the soil. That is why it is important to stimulate the biological activity in the soil: itresults in better soil fertility! To function effectively, the micro-organisms need air, water, neutral soil (pH6 to 7.5) and lots of organic matter.Organic material usually contains both the macro elements N, P and K and micronutrients.3.5.2 Soil testingThe amount of fertilization to be added depends on the amount of nutrients already available in the soil.A soil-testing service can be a good way to find out how much nutrients needs to be added. In somecountries, the Department of Agriculture provides a soil-testing service. There are also portable test kitsthat can examine the main nutrients of the soil. Results and reliability of these portable kits however vary.The test kits are useful to find deficiencies of N, P and K but recommendations for the amount of fertilizerto be added vary, according to local soil conditions.Soil testing usually does not provide information about soil structure, or biological activity, although someestimate of soil organic matter can be included.Past field history should be considered when interpreting soil test results. This is particularly importantwhen past fertilization has been in the form of organic materials, which release nutrients slowly. In thatcase, soil tests may underpredict the amount of soil nutrients actually available to plants over the courseof the entire season (ref. www2).Additional information on possible soil imbalances maybe gained by looking not only at the leaves and topgrowth of the plant, but by carefully digging up a plant,shaking off the soil, and examining the roots for vigorand signs of disease or pest damage. In general rootsgrowing in a fertile soil are more branched than in a poorsoil, and they have a profusion of root hairs. However,the plants must be dug up very carefully to avoid losingthe root hairs. If the roots are growing laterally and arelong and stringy they are searching for nutrients. If theyare long, seem to be searching for something but growvertically, they need water. If they are growing only nearthe surface, the soil is too wet. If they are thick andshort they may be suffering from a toxic element.3.5.3 Role of organic matter and micro-organismsIn general, organic matter additions to a soil will increase its ability to hold nutrients in an available state.Organic matter additions will also increase soil biological activity, and this affects the availability ofnutrients in the soil. Soil that has received organic matter has increased microbial populations and morevaried fungal species than soils receiving chemical fertilizer applications. The long-term objective oforganic matter addition is to build up soil humus. Humus is the more or less stable fraction of the soilorganic matter remaining after decomposition of plant and animal residues.23 Cabbage Ecological Guide - 2000