|The emphasis below will be on lawns, which require special attention, but the recommendations apply equally well to the rest of the garden.|
Updated version of an article published in Gan VeNof, June 1983
The soil is the medium within (and on) which lawn and garden plants grow, and accordingly it must supply the plants with nutrients, water and air.
In addition, in the case of lawn, the soil must provide a surface to walk on.
The soil as storeroom for the plant's food, water and air
The storage capacity of a storeroom is determined by its volume, the number of shelving units it contains, and the spacing of the shelves in each unit, while the width of the passages between these units determines the storeroom’s handling rate and capacity.
The soil is composed of particles (‘shelves’) of various sizes carrying varying electric charges. The texture of the soil reflects its composition in terms of: the size of the particles and the particle size distribution; water content; nutrients (in the form of minerals) adsorbed on the surface of the particles. The greater the number of small particles in a given volume of soil (in other words, the greater its surface area), the greater will be the adsorption capacity of that soil.
Soil particles clump together to form aggregates (the ‘shelving units’). The stabler and the larger these aggregates, the larger the free spaces (pores) provided by the soil structure. Such pores promote free and rapid flow of water and gases and make it easier for roots to grow and reach the moisture and nutrients.
Hence it is desirable to have a soil with large aggregates – aggregates that in turn consist of smaller particles – because such a soil structure will have a large nutrient and moisture storage capacity and at the same time will allow free passage of air, ensuring a favorable exchange of gases (penetration of oxygen and other essential gases and removal of carbon dioxide and other harmful gases).
The volume of the ‘storeroom’ is determined by the following factors.
1. The depth of the root zone. The root zone is the soil layer in which the plant’s roots are active. In most species and varieties of warm lawn grown in Israel, the root zone extends to a depth of 150 cm. The root zone of water-sparing shrubs and trees, on the other hand, reaches down to 7 17 m (as measured at Nir Oz; see also the article entitled “Landscaping as a Basis for Harvesting Water Run-Off'.” and the illustration in the presentation “Our garden in the desert – an ecological success story
2. The depth of the soil. As the storage capacity of the soil increases, so will the reserves of food and water available to the plant (provided we replenish them in time), and correspondingly the more infrequently these reserves will have to be recharged. Aside from convenience and labor savings, less frequent reloading also reduces damage and risks associated with errors in timing and volume delivered.
The soil as a surface to walk on
Most lawns are expected to serve as a surface to walk on, as well as for recreation, games, sports, or even parking. Treading exerts pressure on the soil, resulting in compaction of the aggregates, destruction of soil structure, and ultimately exclusion of air and water from the soil. To withstand the strong pressures due to walking, the soil must have a stable structure.
Characteristics and limitations of soils
Sandy soil is composed of relatively large particles that lack electric charge. Sandy soil has a poor ability to store nutrients and water, but has a well aerated structure that is penetrable to water. Its structure is very stable and resists compression, and such a soil is therefore suitable for conditions of pressure and treading.
Heavy soil is composed of many small particles bearing an electric charge. Its nutrient and water storage capacity is very high. Its penetrability to air and water will be determined by its structure – the coarser the structure (larger aggregates) the better.
Light soil is a mixture of small soil particles and sand. Its properties are intermediate between those of sandy and heavy soils and are influenced by the proportion of each particle size class present.
It should be mentioned that the terms ‘light’ and ‘heavy’ refer to the ease or difficulty of cultivating the soil and have nothing to do with its weight.
Preparing the soil for a lawn or garden
Soil preparation is designed to enable cultivation over the long term. Any error or omission in the process of preparation will be very difficult to repair after planting. Therefore this is not the place to economize on materials and means. Every ‘savings' before planting will result in significant loss in terms of maintenance of the lawn and its quality.
Stages of soil preparation
1. Clearing and shaping the topography to conform to the landscaper’s plan
2. Deep plowing
3. Applying compost or fertilizer
4. Final grading of the surface
5. Planting the lawn
See part - 2