Nursery Techniques - Afforestation, Reforestation and Forest Restoration in Arid and Semi-arid Tropics - page 33

Table 2.5 Components of potting mix
Sr.
no.

Type Role/importance

of component

Desired specifications Portion

(% v/v)

Test of adequacy
of component

1 Clay Fertility, moisture

retention, mineral
exchange

Should be free from
salinity, toxicity and
weeds

20-40 Potting mix

forms lumps,
has
mouldability

2 Sand Drainage, aeration of

root zones

Free from salinity,
stones, toxic wastes,
and weed seeds

40-60 Water drains

steadily and
properly

3 Manure Improves soil

structure, adds to
fertility

Free from pests, well
rotten, clear of
stones/pebbles

20-40 Coarse

structure, can
be seen

4 Pesticide Prevents attack of

pests such as white
ants

Environmental safety,
effectiveness

Minute Direct

monitoring

assured. The three components of a good potting mix are manure, clay, and sand.
Manure is required to improve fertility of soil, whereas clay provides, apart from
nutrients and minerals, the binding property for clump formation so that plants are
not damaged while handling, potting, and planting. Sand improves drainage so that
waterlogging can be avoided.
Correct ratio of the three components should be maintained (Table 2.5 ), as each
of these components controls a particular property of the mix. If cost factor is taken
into consideration, quantity of manure can be changed to suit quality requirements.
If no compromise in quality is to be made on grounds of cost, then a ratio of 1:1:2
(manure:clay:sand) may be chosen in most cases. However, most of the xerophytic
species used in arid and semiarid areas are not stringent in nutrient requirements and
an average mix of 1:2:3 can also be adopted as a general rule.
Manure can be procured locally in most places. The goat and sheep droppings
form a better manure, as it is less likely to contain weed seeds and termites. Short of
this, cow dung compost or compost of other farmyard manure (FYM) can be used,
but care should be taken to ensure that such organic matter is thoroughly decomposed
and rotten. Peat, humus, or forest soils rich in organic matter can be used in lieu of
FYM. Advantage of forest soil is that it inoculates the potting mix with microflora,
such as mycorrhizae, which form symbiotic association with roots of plants. Manure
should be clear of stones, sand, grit, and other foreign material. It should be dry if
cost based on unit weight is to be paid. It should be procured well in advance of the
time of filling polypots to avoid last-minute rushes and compromises on cost and
quality.
Clay can be procured from a nearby place. Clay may naturally occur as the normal
soil in the area or, more likely in arid and semiarid area, found in water tanks and
ponds. If silt from canals or dams is used, it should replace the sand portion as well.
Care should be taken to ensure that the clay being procured is free from salinity and
seeds of weeds. Normally, clay should not cost money by itself but its transportation
incurs considerable cost and it will be best to procure clay from the nearest possible