| Agricultural Uses | A mycelial micro-fungus or a visible growth of such a
fungus is called mould. A blue mould or a green mould is
caused by Penicillium spp., a grey mould by Botrytis
cinenu, a sooty mould by one of the members of family
Capnodiaceae
The term is, however, sometimes used incorrectly
for the growth of Cludosponzun spp. and other fungi
giving black powdery appearance on foliage.
Movement of fertilizer
The relative mobility of a nutrient in soil is of prime
importance. N, S, B and Cl are considered to be mobile in
soils.
Nitrogen is mobile in soil but can easily be lost from
the root zone. Phosphorus is considered relatively
immobile in soils. It is subjected to a number of reactions
and transformations that can reduce its availability to
plants. Placement techniques of phosphorus-containing
fertilizers can minimize the effects of these
transformations, enhancing the phosphorus availability.
Nutrients reach the roots by mass flow, by diffusion
and/or by the root interception.
The movement of soluble fertilizer salts from the
point of application differs from one salt to another. Soil
properties and climatic conditions influence the
movement. The movement of phosphorus is generally
limited since the H2PO4+ ion is only slightly mobile in
soil. The nitrate ion moves more readily than nitrogen in
the ammonium ion (NH4+) form. Potassium is also
relatively immobile because, like ammonium, it is
adsorbed on the soil colloidal complex. As the soil dries
out, the soil water moves upward and deposits salts on the
surface. The soluble salts move downward with rains.
Soluble salts in excessive concentration can be
injurious to plant roots and germinating seeds. This
occurs through plasmolysis, which is the contraction and
leakage of the protoplast of a plant cell consequent upon
the loss of water from the cell. Plasmolysis results in a
limited moisture availability or actual toxicity, known as
fertilizer burn. Free ammonia, urea, DAP, ammonium
carbonate [(NH4)2CO3] and ammonium hydroxide
(NH4OH) may cause more damage than MAP,
ammonium sulphate [(NH4)2SO4] and ammonium nitrate
(NH4NO3).
Broadcast application or fertilizer placement is
effective in avoiding salt injury. Potential problems
related to fertilizer salts are the greatest in coarsetextured
soils. |