Cabbage Integrated Pest Management : An Ecological Guide.

Major Agronomic Practices3.4.7 Soil conservation and erosion controlMany farmers are concerned about how to keep or restore soil fertility in order to maintain good yields.Very often, the emphasis is on adding nutrients, not so much on protecting soil through soil conservation.Fertilization and soil conservation are actually equally important. Nutrients are linked with chemicalqualities of the soil, conservation also emphasizes the physical and biological characteristics of soil.Conservation is not only keeping soil parts where they are, but also keeping a good soil structure andstimulating the activity of micro-organisms in the soil.Some principles of soil conservation and fertilization (modified from Murakami, 1991):1. Keeping the soil covered.When soil is uncovered, it is easily attacked by rain, wind and sun heat. This is the main cause fordegradation of soil structure and soil erosion. During growth of a crop in the field, the soil can becovered by a mulch (such as rice straw) or a “living mulch” which is a crop that grows together withthe main crop but is not harvested. When no production crop is planted in the field, consider sowinga cover crop. This will keep the soil covered and thus protected from erosion by wind or water and itis a very good way of fertilizing the soil. See section 3.5.3.2.2. Regular supply of organic material to the soil.Adding organic material to soil is essential for good crop production! Organic matter such ascompost can supply all necessary nutrients to plants and it stimulates activity of micro-organisms inthe soil. Micro-organisms help releasing nutrients from organic material in the soil. See section 3.5.3on organic material.3. Vegetation on field or farm boundary areas.Another useful practice is to plant trees and grasses in boundary areas of a farm. Such vegetationprotects soil from run-off by rain and wind, it becomes a source of organic fertilizer, fodder, fuel, food(fruits), or timber and it also acts as a windbreaker. When flowering plants are used, they may attractnatural enemies such as hover flies, and provide shelter for natural enemies such as spiders.4. No use of pesticides on soil.Pesticides disturb the activity of micro-organisms in the soil and may create imbalances in soilfertility.5. No / Low use of chemical fertilizers.When large amounts of organic material are supplied to the soil every year, usually no chemicalfertilizers need to be added. Chemical fertilizers may create an imbalance in the soil ecosystem.They disturb the activity of micro-organisms by adding only a few nutrients. In addition, nutrientsupply has been known to cause disease problems in plants. In some cases it can be good to usea small amount of e.g. nitrogen to push plants through a stressful period such as downy mildewattack in the nursery.6. Building terraces on steep slopes.On steep slopes, building horizontal terraces is a common and good practice to prevent soil erosion.Often, a small “dike” is made (or a row of weeds is allowed) at the border of a terrace. A commonpattern is the following:21 Cabbage Ecological Guide - 2000