Agriculture Reference
In-Depth Information
the root zone of the plant, and a very small amount of the fertiliser may be available
to the roots.
In poorer soils, with species more demanding in nutrients, manure may be prefer-
able to fertilisers. It is better to mix crushed or pulverised sheep and goat droppings
or other manure free from insects and termites. Fresh or raw cow dung is often
avoided because it contains weeds and attracts termites and other pests that may
cause damage to the plants. Composts—well decomposed mix of cow dung and
litter or farm waste—can be used instead. If plants show poor progress and it is
decided later to amend the soil, manure or compost can be mixed with the soil after
a hoeing operation, while refilling the mixed soil around the root zone of the plant
and then irrigating it thoroughly so that the manure leaches down to the roots.
In high-value plantations in difficult sites, biofertilisers can be used in addition to
fertilisers and manure. Biofertilisers (e.g. rhizobium, azotobacter, azospirillum, blue
green algae) act as a catalyst rather than as a direct source of plant nutrients. They
are concentrated cultures of useful microflora that assist the plants in the uptake of
nutrients by breaking down organic matter, and solubilising inorganic phosphates.
They also supply metabolic products including certain enzymes that fortify the root
system. Some of them such as the azotobacter and the rhizobium fix atmospheric
nitrogen. Many fungi form symbiotic association with plant roots in which the total
surface area of root hairs is increased, making roots more effective in absorption of
nutrients. However, biofertilisers may not always be available, particularly those that
are host-specific. If broadband biofertilisers are easily available and the soil of the
plantation site is sterile—that is, devoid of biological activity—then the cost incurred
on procurement and application of biofertilisers may well be justified.
It is enough to manure plants once a year, though chemical fertilisers will have
to be used more frequently, probably thrice in a growth season. However, it will no
longer be necessary or cost-effective to manure the plants after 3 years of age. It is
only in a high-value plantation that such a regimen is required. In case of extensive
and low-cost afforestation works it will be enough to apply manure once to tidy over
a crisis of nutritional deficiency, and to assist plants in taking a good growth until
their roots are adequately developed.
6.12
Growth of Plants
Each plant species has an inherent growth rate which is modulated by the edapho-
climatic conditions obtaining at the site. Species of trees and shrubs can be broadly
categorised as slow and fast growing. Within a species and a given provenance,
the plus trees may outgrow mongrel trees. Inherently slow-growing species have a
longer seedling establishment period and will not take on growth until a while. Cer-
tain species have a characteristic growth profile in which growth is very slow for the
first few years but faster thereafter. On the contrary, certain other species may show
very promising growth in the beginning but the rate of growth may decrease later.
Complex enough though it is, this behaviour may vary depending upon the type of
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