Chapter 2. DEFINITION OF COVERING AND PROPERTIES OF COVERING
MATERIALS
2.1 Introduction
There are many kinds of covering materials and techniques available and used in practical agriculture. It is rather difficult to distinguish one technique from the other in some cases because the principle involved is the same. The following terms are used for these systems: mulchings, row covers (tunnels). floating mulches (floating row cover). Rain shelters, and unheated greenhouses. There is a definite difference between mulching and the other techniques. In mulching.
plants grow over the cover; in the others, they grow under. Some of them are combined in use. Figure 2.1 shows pictorial definitions of these techniques.
Fig. 2. 1. Covering techniques.
2. 2 Mulching
Several kinds of materials - not only plastics but also organic materials - are used for mulching. In mulching, the soil surface where crops are growing is covered directly by these materials, with a very thin air space between the cover and the soil surface. In order to improve the thermal environment of the soil, film mulching is widely used both in open fields and in greenhouses. The soil surface of each row is covered by a sheet of film with many holes. Plants are
town or transplanted into each hole, and grow over the cover. Since most of the soil surface is covered by film, evaporation from the surface is prevented. It is clear that the soil is kept warmer than it would be without mulching.