Mulch is a protective covering, usually of organic matter such as leaves, straw, or peat, placed around plants to prevent the evaporation of moisture, and the growth of weeds. The word mulch has probably been derived from the German word “molsch” meaning soft to decay, which apparently referred to the gardener’s use of straw and leaves as a spread over the ground as mulch.
- reduces the deterioration of soil by way of preventing the runoff and Soil loss
- minimizes weed infestation
- checks water evaporation. Thus, it facilitates for more retention of soil moisture
- helps control temperature fluctuations
- improves physical, chemical and biological properties of soil
- adds nutrients to the soil
- enhances the growth and yield of crops
- boosts the yield by 50–60% over no mulching under rain-fed situations.
CLASSIFICATION OF MULCHES
Advancement in plastic chemistry has resulted in development of films with optical properties that are ideal for a specific crop in a given location. Horticulturists need to understand the optimum above and below ground environment of a particular crop before the use of plastic mulch. These are two types:
- Photo-degradable plastic mulch: This type of plastic mulch film gets destroyed by sun light in a shorter period.
- Bio-degradable plastic mulch: This type of plastic mulch film is easily degraded in the soil over a period of time.
COLOUR OF FILM
Soil environment can be managed precisely by a proper selection of plastic mulch composition, colour and thickness. Films are available in variety of colours including black, transparent, white, silver, blue red, etc. But the selection of the colour of plastic mulch film depends on specific targets. Generally, the following types of plastic mulch films are used in horticultural crops:
- Black plastic film: It helps in conserving moisture, controlling weed and reducing outgoing radiation.
- Reflective silver film: It generally maintains the root-zone temperature cooler.
- Transparent film: It increases the soil temperature and preferably used for solarization.
Apart from the above classification there is another way of classifying Methods in mulching:
- Surface mulching: Mulches are spread on surface to reduce evaporation and increase soil moisture.
- Vertical mulching: It involves opening of trenches of 30 cm depth and 15 cm width across the slope at vertical interval of 30 cm.
- Polythene mulching: Sheets of plastic are spread on the soil surface between the crop rows or around tree trunks.
- Pebble mulching: Soil is covered with pebbles to prevent transfer of heat from atmosphere.
- Dust mulching: Interculture operation that creates dust to break continuous capillaries, and deep and wide cracks thus reducing evaporation from the exposed soil areas.
- Live vegetative barriers on contour key lines not only serve as effective mulch when cut and spread on ground surface, but also supply nitrogen to the extent of 25 to 30 kg per ha, besides improving soil moisture status.
EFFECTS OF MULCHES ON SOIL MOISTURE CONSERVATION
Water is essential for growth and development. It is also a major cost in agricultural systems. The success of many agricultural forms relies on conservative and efficient use of water. Moisture retention is undoubtedly the most common reason for which mulch is applied to soil.
Ingman claimed that the use of things made with plastic or plastic components have become a routine part of our daily lives. In a similar way, over the past 50 years world agricultural systems have rapidly adopted the use of many types of plastic products to grow the food we eat because of the productive advantages they afford. Plastic use in agriculture (plasticulture) continues to increase every year in the ever-diminishing supply of petroleum. There is a common lack of awareness regarding what plastic mulch is, and also a lack of applied research of its use in agricultural communities. However, the use of plastic mulch may actually be one of the most significant water conservation practices in modern agriculture: quite possibly surpassing the water savings of drip irrigation. Even though most of the world’s use of freshwater is spent for irrigation purposes, little research explores how plastic mulch use as a water conservation practice may influence the current and future status of water resources. He used a multidisciplinary approach to understand why Chinese farmers on the margins of the Gobi desert continue to use plastic mulch, and in particular, how its use may relate to water conservation. Next, the study asks to what extent the plasticization of agriculture may influence the income and standard of living for agricultural communities. He was able to prove the role of plastic mulch in conserving soil moisture.
Mulch is used to protect the soil from direct exposure to the sun, which would evaporate moisture from the soil surface and cause drying of the soil profile. The protective interface established by the mulch stops raindrop splash by absorbing the impact energy of the rain, hence reducing soil surface crust formation. The mulch permits soil surface to prevent runoff allowing a longer infiltration time. These features result in improved water infiltration rates and higher soil moisture. An auxiliary benefit of mulch reducing soil splash is the decreased need for additional cleaning prior to processing of the herb foliage. Organic and inorganic mulches have shown to improve the soil moisture retention. This increased water holding ability enables plants to survive during dry periods. The use of plastic mulch can be improved if under-mulch irrigation is used in combination with soil moisture monitoring.
The influence of rainfall events is not as great when plastic mulch is used, necessitating active irrigation management. Under mulch, irrigation of vegetable crops has been shown to improve crop yields more than overhead irrigation systems.
Mulch enables the soil moisture levels to maintain for longer periods. In some cases while providing improved moisture conditions within the soil, the mulch changes microclimate so that it uses more water, thus negating the initial benefits. Plastic mulch conserved 47.08% of water and increased yield by 47.67% in tomato when compared to non-mulched control. Plastic mulching resulted in 33 to 52% more efficient use of irrigation water in bell pepper compared to bare soil.
The conservation of soil moisture through mulching is one of the important best management practices (BMP). The microclimatic conditions are favourably affected by optimum degree of soil moisture. When soil surface is covered with mulch helps
to prevent weed growth, reduce evaporation and increase infiltration of rainwater during growing season.
Different mulching materials helped bell pepper (C. annuum cv. California Wonder) to perform better at water deficits from 25–75% and plastic mulch had highest water use efficiency. Treatment receiving mulch recorded significantly higher net returns and benefit – cost ratio (1.80) compared to control as a result of soil water conservation. A 34–50% reduction in soil water evaporation was observed as a result of crop residue mulching. Mulch slows down evaporation and reduces the irrigation requirement. Liu et al. [31 to 34] also reported that mulching improves the ecological environment of the soil and increases soil water contents.
Plastic mulch helps prevent soil water loss during dry years and sheds excessive
water away from the crop root zone during periods of excessive rainfall. This can
reduce irrigation frequency and amount of water.
Kamal G. S, PhD, Megh R. G, PhD, PE R. P. R, PhD. Best Management Practices for Drip Irrigated Crops – Research Advances in Sustainable Micro Irrigation. Volume 6