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Mulching is putting all kinds of
organic waste materials like leaves, weeds, wood chips, bark etc., in
the field with purpose of providing a cover over soil so that weeds do
not grow. Some time black plastics, small stone or brick pieces and
charcoal are also used as mulch. Much is said about “Mulch and its
advantages”, but our experience showed that mulch was beyond ordinary
description. It could truly be described as magic. Although the
advantages of mulch are well-known, yet it is too costly to carry-out
on commercial scale even where cheap labour is plentiful. Its cost can
only be off-set by high density planting and advanced technologies.
Ten years ago we decided to use weeds growing between the tree rows in
the fruit orchard as mulch to suppress weeds under the trees. We were
aware of the disadvantages of flood irrigation, which creates
temporarily anaerobic conditions after every application, which is
frequent in our hot and dry weather, resulting in to reduction in
yield. We therefore planned to irrigate indirectly by planting and
trees on ridges about 2 meters (6 feet 8 inches) wide and 25-30 cms
(10-12 inches) high and apply water in the furrows. Furrow width
varied between 2.5 - 4.0 meters (8 feet 4 inches to 13 feet) depending
upon the type of fruit tree. High density planting on the ridges was
done. In our sub-tropical desert area on 25°-37’N and 68°-36’E,
climate is like that at Carnorvon Western Australia. The
pan-evaporation is approximately 30 cm (one foot) per month from 15th
April to end August. Winters are mild, but yet evaporation of 4-6 cms
(1.5 - 2.4 inches) is common in January the coldest month. Average
annual rainfall is 15 cms (6 inches), which occurs in July-August and
is spread over 7 days. Rainfall of 12.5 cm (5 inches) can occur in 24
hours one in every 10 years. Annual evaporation is about 2.3 meters
(90 inches). Under such climate all kinds of perennial and
non-perennial weeds grow profusely and year around. Since the labour
in Pakistan is cheap and in high density and close spacing trees,
machines can not do the mowing, we decided to mow the weeds manually
and spread them on the ridges under the trees. Initially the volume of
weeds was not too high, but after a few mowing weeds started
multiplying fast and we could harvest them 4-5 times a year and dump
them on the ridges. Much got digested fast and in about 2 ½ months its
bulks reduced to about 20%, when fresh mulch was added raising the
pile height to about 30 cm (12 inches). We did not know the exact
process by which mulch was digested. The pesticide companies
representatives who visited us periodically, were frightened by
presence of large number of insects in the mulch and advised to remove
and burn it up. We observed that these insects do not climb the trees
and therefore could be harmless. We also found that perennial weeds do
come up on the ridges, but they become week, sickly and dwarf and can
easily be pulled out with their roots by hand. The perennial weeds
were gradually reduced to nil or negligible. One thing happened that
annual weeds started flourishing in the furrows, their bio-mass
increased and they virtually have become permanent ground cover. We
found one advantage that the soil under mulch was moist all the time
and had become very porous so much so that instead of driving a fork
into soil, we could push our five fingers in the soil and take a good
hand full out without much effort, as if it was sand. Since soils
under mulch were moist longer than without ridges and mulch, we
readjusted irrigation cycle from one week to ten days in summer and
from 10-15 days in winter. We still did not know that what was going
on but found the trees very healthy, growing very fast and producing
first crop within 20-32 months after planting i.e., in the year two of
three. The yield started rising and in three to four years doubled. In
new plantations under mulch yield was three times in five years.
Initially we were putting fertilisers along the bottom 4 inches wall
of the ridge and applying 4 inches dose of water so that most of the
fertiliser seeps in to ridge as soon as water is applied, though we
knew that some of it would seep down in the nearby furrow and promote
weeds. For small plants we also had reduced the ridge width to 0.6
meters by simply cutting a trench 30 cms wide, and 60 cms long and
deep to furrow level so that water reaches it quickly. This gave us a
small channel, for irrigation water to reach the plant roots. These
small channels are filled with mulch from ground level to top level of
ridge, so that weeds do not grow. In the year 3 we found that the dry
weight of the mulch material applied annually was about 25 tons per
hectare. In the year 5 yield of small trees was at par with national
average of mature trees, usually 15 year old. It was out-come of
increased root growth, canopy diameter and density, improved leaf
colour as compared to clean cultivation and herbicide use. |
