Environmental Engineering Reference
In-Depth Information
Soil Modification
If topsoil was removed before rough grading, it should be brought back
and redistributed over the surface. If the topsoil is of poor quality and
contains: (i) a high percentage of clay and a low percentage of sand and
loam, (ii) a very high percentage of sand and very little loam or clay or
(iii) very little organic matter, then high-quality topsoil from another site
should be brought in and spread over the surface in a layer at least 10-15-
cm thick. A quite popular practice among homeowners - spreading
1-2 cm of highly organic soil over the poor soil or mixing in a similar
amount - simply wastes time and money and is not recommended.
Such a small amount is insufficient to change soil conditions. At least
a 10-cm-thick soil is required to accomplish favourable changes in
water retention, aeration, cation exchange capacity and infiltration.
After the topsoil is redistributed or modified, it should be allowed to
settle undisturbed for about 1-2 weeks. Therefore, if an underground
irrigation system is to be installed, the installation should take place
before redistribution of topsoil.
Application of fertilizer and lime
A soil test should be done to determine pH and lime requirements. If lime
is needed, it should be applied at this stage and mixed with the soil
before seeding or planting. Lime does not move with water, so later
applications on established turf-grass are not very effective. The same
rule applies to phosphorus. If it is not mixed with the soil before planting,
later applications may not be effective. Only a soil test can determine
precisely how much of each nutrient should be applied, but application
of phosphorus and potassium at 1-2 kg per 100 m 2 (100-200 kg/ha) is
generally sufficient. Timing of potassium application is less critical, but
nitrogen should be applied only 1 or 2 days before planting. Nitrogen
applied earlier can be lost to leaching and volatilization (see Chapter 5,
this volume) and can serve to promote the growth of competitive weeds.
Final Soil Preparation
Ideally, final soil preparation should take place just 1 day before planting.
The goal is to prepare the best possible environment for the new turf-
grass plants. The final seedbed should be firm, moist but not wet, and
free of clods, stones and other rubble. If possible, it should be lightly tilled
less than 24 h before planting or seeding. If weeds have germinated since
the last tillage, a light application of glyphosate can be used. Application
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