1. MULCHES 521
MULCHES
C L Acharya, K M Hati, and K K Bandyopadhyay, cover. It is most useful as an alternative to cover crops
Indian Institute of Soil Science, Bhopal, in dry areas where insufficient rain prevents the es-
Madhya Pradesh, India tablishment of a ground cover before the onset of
ß 2005, Elsevier Ltd. All Rights Reserved. heavy rain or strong winds, or where a cover crop
competes for moisture with the main crop.
Introduction However, improper application of mulches leads to
creation of an anaerobic environment under a heavy
Mulch means a layer of dissimilar material separating rainfall situation, leading to loss of nitrogen through
the soil surface from the atmosphere, and mulching is denitrification. It may cause disease and pest infest-
the artificial application of mulch, practiced to obtain ation and some allelopathic materials produced in
beneficial changes in the soil environment. Mulch some crop residues retard the crop growth. So proper
may be organic (crop residues, stubble mulch etc.) site-specific methodology needs to be followed under
or inorganic (plastic sheet, gravels etc.) in nature. It different soil, crop and climatic conditions for effi-
may be grown in situ like previous crop residue mulch cient mulch management to achieve sustainable crop
left on the soil surface, produced by a cover crop or it production.
may be living mulch like perennial legume mulch. It
may also be grown or produced ex situ and brought in
for field application, e.g., straw, sawdust, plastic How Mulching Influences the Soil
products etc. Environment
The practice of mulching has been widely used as a
Mulching improves the physical conditions, chemical
management tool for centuries in many ancient civi-
environment and biological activities of soil. Favor-
lizations. The Great Plains region of the USA, which
able modification of the soil hydrothermal regime,
was once considered to be a dust bowl, has been
improvement of soil aggregation and retardation of
turned into the granary of the world through the
erosion and soil loss enhance the physical condition
adoption of conservation tillage, the practice of leav-
of soil under mulch. Improvement in the soil chemical
ing crop residues as the surface stubble or flattened
environment and biological activities by mulching is
straw mulch. The idea of using plastics as mulch
mainly attributed to the enrichment of soil organic
originated in Hawaii, where it was used in pineapple
matter through organic mulching and improvement
cultivation with considerable success.
of the physical condition of soil under both organic
Mulch has a buffering effect and it dampens the
and inorganic mulches.
influence of environmental factors on soil. The mag-
nitude of the buffering effect of mulches depends Soil Moisture Regime
upon the quality, quantity and durability of mulch
material, soil type and the climatic conditions. Mulching favorably influences the soil moisture
Mulching influences the soil hydrothermal regime regime by controlling evaporation from the soil sur-
by influencing the radiation balance, rate of heat face, improving infiltration and soil-moisture reten-
and water vapor transfer, and heat capacity of soil. tion and facilitating condensation of water at night
Mulching improves the physical condition of soil by due to temperature reversals.
enhancing soil aggregation and helps in conservation
of water by checking evaporation, increasing infiltra- Controling evaporation from the soil surface Direct
tion and retarding runoff loss. It favorably modifies evaporation of water from the soil surface is an
the soil thermal regime, retards soil erosion, and im- important process, particularly in the case of bare
proves soil chemical environment and biological ac- soils or in areas where summer fallow is practised.
tivity in soil. Modification of the soil microclimate by Mulching reduces evaporation from the soil surface
mulching favors seedling emergence and root prolifer- by retarding the intensity of the radiation and wind
ation and suppresses weed population. Organic velocity on the mulched surface. It is effective in
mulches add nutrients to soil when decomposed by retarding the evaporation mainly during the initial
microbes and help in carbon sequestration. Favorable energy-limited stage of drying. However, mulching
soil edaphic environment under mulch improves is not very effective in controling evaporation during
crop productivity, enhances input-use efficiency and the falling-rate or supply-controled stage of evapo-
checks environmental pollution. From the conserva- ration. During this stage, the soil surface dries
tion viewpoint, mulch simulates the effect of a plant under the mulch and the vapor transfer of water to