MULCHES

C L Acharya, K M Hati, and K K Bandyopadhyay,Indian Institute of Soil Science, Bhopal,

Madhya Pradesh, India

� 2005, Elsevier Ltd. All Rights Reserved.

Introduction

Mulch means a layer of dissimilar material separatingthe soil surface from the atmosphere, and mulching isthe artificial application of mulch, practiced to obtainbeneficial changes in the soil environment. Mulchmay be organic (crop residues, stubble mulch etc.)or inorganic (plastic sheet, gravels etc.) in nature. Itmay be grown in situ like previous crop residue mulchleft on the soil surface, produced by a cover crop or itmay be living mulch like perennial legume mulch. Itmay also be grown or produced ex situ and brought infor field application, e.g., straw, sawdust, plasticproducts etc.

The practice of mulching has been widely used as amanagement tool for centuries in many ancient civi-lizations. The Great Plains region of the USA, whichwas once considered to be a dust bowl, has beenturned into the granary of the world through theadoption of conservation tillage, the practice of leav-ing crop residues as the surface stubble or flattenedstraw mulch. The idea of using plastics as mulchoriginated in Hawaii, where it was used in pineapplecultivation with considerable success.

Mulch has a buffering effect and it dampens theinfluence of environmental factors on soil. The mag-nitude of the buffering effect of mulches dependsupon the quality, quantity and durability of mulchmaterial, soil type and the climatic conditions.Mulching influences the soil hydrothermal regimeby influencing the radiation balance, rate of heatand water vapor transfer, and heat capacity of soil.Mulching improves the physical condition of soil byenhancing soil aggregation and helps in conservationof water by checking evaporation, increasing infiltra-tion and retarding runoff loss. It favorably modifiesthe soil thermal regime, retards soil erosion, and im-proves soil chemical environment and biological ac-tivity in soil. Modification of the soil microclimate bymulching favors seedling emergence and root prolifer-ation and suppresses weed population. Organicmulches add nutrients to soil when decomposed bymicrobes and help in carbon sequestration. Favorablesoil edaphic environment under mulch improvescrop productivity, enhances input-use efficiency andchecks environmental pollution. From the conserva-tion viewpoint, mulch simulates the effect of a plant

cover. It is most useful as an alternative to cover cropsin dry areas where insufficient rain prevents the es-tablishment of a ground cover before the onset ofheavy rain or strong winds, or where a cover cropcompetes for moisture with the main crop.

However, improper application of mulches leads tocreation of an anaerobic environment under a heavyrainfall situation, leading to loss of nitrogen throughdenitrification. It may cause disease and pest infest-ation and some allelopathic materials produced insome crop residues retard the crop growth. So propersite-specific methodology needs to be followed underdifferent soil, crop and climatic conditions for effi-cient mulch management to achieve sustainable cropproduction.

How Mulching Influences the SoilEnvironment

Mulching improves the physical conditions, chemicalenvironment and biological activities of soil. Favor-able modification of the soil hydrothermal regime,improvement of soil aggregation and retardation oferosion and soil loss enhance the physical conditionof soil under mulch. Improvement in the soil chemicalenvironment and biological activities by mulching ismainly attributed to the enrichment of soil organicmatter through organic mulching and improvementof the physical condition of soil under both organicand inorganic mulches.

Soil Moisture Regime

Mulching favorably influences the soil moistureregime by controlling evaporation from the soil sur-face, improving infiltration and soil-moisture reten-tion and facilitating condensation of water at nightdue to temperature reversals.

Controling evaporation from the soil surface Directevaporation of water from the soil surface is animportant process, particularly in the case of baresoils or in areas where summer fallow is practised.Mulching reduces evaporation from the soil surfaceby retarding the intensity of the radiation and windvelocity on the mulched surface. It is effective inretarding the evaporation mainly during the initialenergy-limited stage of drying. However, mulchingis not very effective in controling evaporation duringthe falling-rate or supply-controled stage of evapo-ration. During this stage, the soil surface driesunder the mulch and the vapor transfer of water to

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