Title : Control of soil compaction
Visit Count : 2307 Time(s)
Upload Date : 8/8/2016 - 4 Year(s) ago
Category : agricultural technical notes
Monday, August 8, 2016
Visit Count : 2307 Time(s)
Upload Date : 8/8/2016 - 4 Year(s) ago
Category : agricultural technical notes
Adding Organic Matter
To reduce soil compaction, cultivate organic soil amendments into the top six to eight inches of the soil. In compacted/clayey soils, anything less can lead to a shallow rooting system with reduced plant growth, lower vigor, and lower stress tolerance. General application rates for organic soil amendments are based on the type of product and the salt content. Table 1 gives standard application rates for compost products. Compost made solely from plant residues (leaves and other yard wastes) is basically free of salt problems, so higher application rates are safe. Compost that includes manure or biosolids as a component has a potential for high salts. Excessive salt levels are common in many commercially available products sold in Colorado. For compost made with manure or biosolids, the application rate is limited unless a soil test on that batch of product shows a low salt level. An amendment with up to 10 dS/m (10 mmhos/cm) total salt is acceptable if incorporated six to eight inches deep in a low-salt garden soil (less than 1 dS/m or 1 mmhos/cm). Any amendment with a salt level above 10 dS/m (10 mmhos/cm) is questionable. Do not leave compost in chunks as this will interfere with root growth and soil water movement. As the soil organic content builds in a garden soil, the application rate should be reduced to prevent ground water contamination issues.
Manage Traffic Flow
Traffic over the soil is the major contributor to soil compaction. For example a moist soil could reach 75% maximum compaction the first time it is stepped on, and 90% by the fourth time it is stepped on. Raised bed gardening techniques, with established walkways, eliminate compaction in the growing bed. In fine-textured clayey soils, limit routine traffic flow to selected paths. Soils are more prone to compaction when wet. Soil water acts as a lubricant allowing the soil particles to readily slide together reducing large pore spaces.
Use Mulches
Some types of mulch effectively reduce the compaction forces of traffic. For example, three to four inches of wood or bark chips will minimize the effect of foot traffic. Mulch minimizes the compaction forces of rainfall and sprinkler irrigation. In fine-textured clayey soil, keep garden beds mulched year round to minimize the compaction forces of summer and winter storms. Organic mulches create an ideal home for beneficial earthworms and soil microorganisms, which play a key role in improving soil tilth.
Aerate Lawn and Around Trees
In a lawn or tree’s rooting area, where organic matter cannot be cultivated into the soil, reduce compaction with soil aeration. Make enough passes with the aerator to have plugs at two-inch intervals.
Avoid Excessive Cultivation
Avoid cultivating fine-textured clayey soils except to incorporate organic matter and fertilizer, and to prepare a seedbed. Use mulches to help manage weeds.
Avoid cultivating overly wet or dry soils
Never cultivate a clayey soil when wet as this will destroy soil structure; the clods created by tilling wet clay may last for years. To check dryness, take a handful of soil and gently squeeze it into a ball. If the soil is dry enough to crumble, it may be cultivated. If the ball only reshapes with pressure, it is too wet for cultivation. On some clayey soils, there may be only a few days (or even hours) between the time when the soil is too wet and too dry (too hard) to cultivate. In years when frequent spring rains prevent the soil from drying, planting will be significantly delayed.
Avoid Fill Over Compacted Soil
Adding a thin layer of topsoil over compacted soil is a common practice that leads to future landscape management problems. It is often justified as “a way to get plants established.” However, root growth into the compacted layer will be restricted or even minimal. Do not create a layer with added topsoil that is of a different texture than the soil below. This change in texture (actually pore space) interferes with water movement and root spread. Where additional fill is desirable, lightly mix the fill with the soil beneath. Long-term landscape management will be much easier by breaking up surface compaction with tilling and organic matter amendments. Before planting a yard, enhance soil organic content to the extent feasible. A minimum of 3 to 4 cubic yards of organic matter per 1,000 square feet is recommended.
What About Adding Sand?
Some gardeners try to improve fine-textured soils by adding sand. The practice may help the gardeners feel that they have done something, but it will have a limited or even negative impact on the soil. Adding sand to a clayey soil may actually reduce large pore space until enough medium-to–coarse-size sand is added to reduce the clay content well below 20%. In clayey soils, this actually become a process of soil replacement rather than soil amendment. In some situations, adding sand to clayey soil can create concrete-like soil properties. To improve the soil, put efforts into adding organic matter, not sand.
What About Adding Gypsum?
Gypsum is a salt also known as calcium sulfate. When added to calcareous clayey soils (typical of Colorado), it simply increases the already high calcium content. Gypsum will not break up a compacted soil, but can increase the soil’s salt levels. Gypsum is useful when a soil has a high sodium problem. Sodium has a unique physical characteristic that brings soil particles closer together, reducing large pore space and “sealing” soils to water penetration. The calcium in gypsum replaces the sodium on the soil cation exchange site and the freed sodium is then leached out by heavy irrigation. Good quality (low salt) irrigation water must be available to successfully reclaim a high sodium soil. The use of sulfur has also been incorrectly acclaimed to break up compacted soils. Over a period of time, sulfur may have an acidifying effect on a soil (if the soil is not high in lime). Adding sulfur to a calcareous soil only creates gypsum (calcium sulfate).
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