Technical Information & General Information:

PLASTIC MULCHING FOR CROP PRODUCTION

Introduction
Mulching is the process or practice of covering the soil/ground to make more favourable conditions for plant growth, development and efficient crop production. Mulch technical term means ‘covering of soil’. While natural mulches such as leaf, straw, dead leaves and compost have been used for centuries, during the last 60 years the advent of synthetic materials has altered the methods and benefits of mulching. The research as well as field data available on effect of synthetic mulches make a vast volume of useful literature. When compared to other mulches plastic mulches are completely impermeable to water; it therefore prevents direct evaporation of moisture from the soil and thus limits the water losses and soil erosion over the surface. In this manner it plays a positive role in water conservation. The suppression of evaporation also has a supplementary effect; it prevents the rise of water containing salt, which is important in countries with high salt content water resources.

Advantages of plastic mulching

1. 1. It is completely impermeable to water.
2. 2. It prevents the direct evaporation of moisture form the soil and thus limits the water losses and conserves moisture.
3. 3. By evaporation suppression, it prevents the rise of water containing salts.
4. 4. Mulch can facilitate fertilizer placement and reduce the loss of plant nutrient through leaching.
5. 5. Mulches can also provide a barrier to soil pathogens.
6. 6. Opaque mulches prevent germination of annual weeds from receiving light.
7. 7. Reflective mulches will repel certain insects.
8. 8. Mulches maintain a warm temperature even during nighttime which enables seeds to germinate quickly and for young plants to rapidly establish a strong root growth system.
9. 9. Synthetic mulches play a major role in soil solarisation process.
10. 10. Mulches develop a microclimatic underside of the sheet, which is higher in carbondi-oxide due to the higher level of microbial activity.
11. 11. Under mulch, the soil structure is maintained during cropping period
12. 12. Early germination almost 2-3 days.
13. 13. Better nodulation in crops like Groundnut.
14. 14. Less nematodes population.
15. 15. Water erosion is completely averted since soil is completely covered form bearing action of rain drops.
16. 16. When compared to organic mulches, it serves for a longer period.

Moisture conservation

1. 1. Plastic film with its moisture barrier properties does not allow the soil moisture to escape Water that evaporates from the soil surface under mulch film, condenses on the lower surface of the film and falls back as droplets.
2. 2. Thus moisture is preserved for several days and increases the period between two irrigations.
3. 3. The irrigation water or rainfall either moves into the soil thru holes on the mulch around the plant area or through the un-mulched area.

Weed control

1. 1. Black plastic film does not allow the sunlight to pass through on to the soil.
2. 2. Photosynthesis does not take place in the absence of sunlight below black film hence, it arrests weed growth.

Limitations

1. 1. They are costly to use in commercial production when compared to organic mulches.
2. 2. Probability of ‘burning’ or ‘scorching’ of the young pants due to high temperature of black film.
3. 3. Difficulty in application of top dressed fertilizer.
4. 4. Reptile movement and rodent activities are experienced in some places.
5. 5. More runoff.
6. 6. Environmental pollution.
7. 7. Difficult in machinery movement.
8. 8. Can not be used for more than one season using thin mulches.
9. 9. Weed penetration with thin films.
10. 10. Toxic to livestock.

Areas of application

Mulching is mainly employed for

1. a. Moisture conservation in rainfed areas.
2. b. Reduction of irrigation frequency and water saving in irrigated areas.
3. c. Soil temperature moderation in greenhouse cultivation.
4. d. Soil solorisation for control of soil borne diseases.
5. e. Reduce the rain impact, prevent soil erosion and maintain soil structure.
6. e. Reduce the rain impact, prevent soil erosion and maintain soil structure.

Types of mulch film

1. A wide range of plastic films based on different types of polymers have all been evaluated for mulching at various periods in the 1960s. LDPE, HDPE and flexible PVC have all been used and although there were some technical performance differences between them, they were of minor nature. Owing to its greater permeability to long wave radiation which can increase the temperature around plants during the night times, polyethylene is preferred. Today the vast majority of plastic mulch is based on LLDPE because it is more economic in use.

Basic properties of mulch film

1. a. Air proof so as not to permit any moisture vapour to escape.
2. b. Thermal proof for preservation of temperature and prevention of evaporation.
3. c. Durable at least for one crop season.

Importance of parameters of the plastic film

a) Thickness
Normally the thickness of the film does not affect the mulching effect except when it is used for solorisation. But some of the recent references do indicate the impact of film thickness on crop yield. Since it is sold by weight it is advantageous to use as thin a film as possible but at the same time due consideration should be given for the longevity of the film. The early mulch film used were of 60-75 micron (240-300 gauge) thickness, and today it is possible to have 15 micron thick film due to advent of film extrusion technology. These films are mechanically weak, as shown by their easy tearing when pulled tension.
b) Width
This depends upon the inter row spacing. Normally a one to one and half meter width film can be easily adopted to different conditions.
c) Perforations
The perforations may be advantageous under some situations and disadvantageous for some other situation. The capillary movement of water and fertilizer distribution will be better and more uniform under unperforated condition. But for prevention of water stagnation around the plants, perforation is better. But it has got the disadvantages of encouraging weed growth.
d) Mulch colour
The colour of the mulch affects

1. i. Soil temperature
2. ii. Temperature of air around the plants
3. iii. Soil salinity
   1. a.Due to lesser quantity of water used
   2. b.Due to reduction in evaporation and prevention of upward movement of water

Transparant film - Deposits more salt on soil surface
Black film - Restricts water movement and upward movement of salt is reduced. iv. Weed flora - Black film
Insect control - Opaque while film acts as golden colour and attracts insects

Selection of mulch

The selection of mulches depends upon the ecological situations and primary and secondary aspects of mulching.
Rainy season - Perforated mulch
Orchard and plantation - Thicker mulch
Soil solarisation - Thin transparent film
Weed control through solarisation - Transparent film
Weed control in cropped land - Black film
Sandy soil - Black film
Saline water use - Black film
Summer cropped land - White film
Insect repellent - Silver colour film
Early germination - Thinner film

Methods of mulching

1. • Orchard/Fruit/Established trees
2. • Mulching area should preferably be equivalent to the canopy of the plant.
3. • Required size of mulch film is cut from the main roll.
4. • Clean the required area by removing the stones, pebbles, weeds etc.
5. • Till the soil well and apply a little quantity of water before mulching
6. • Small trench could be made around the periphery of the mulching area to facilitate anchoring of the mulch film.
7. • Cover the film to the entire area around the tree and the end should be buried in the ground.
8. • Semi circular holes could be made at four corners of the film in order to facilitate water movement.
9. • The position of the slit/opening should be parallel to the wind direction
10. • Cover the corners of the film with 4-6 inches of soil on all sides to keep the film in position.
11. • In hard soil, make a trench of 1’x1’x2’ depth on four corners of the mulching area and fill it up with gravel or stones, cover the trenches with the mulch film and allow the water to pass through the mulch to the trenches via semi circular holes on the film

Mulch Laying Techniques

1. i. Mulch should be laid on a non-windy condition
2. ii. The mulch material should be held tight without any crease and laid on the bed
3. iii. The borders (10 cm) should be anchored inside the soil in about 7-10 cm deep in small furrows at an angle of 45°.

Pre planting mulch:

The mulch material should be punctured at the required distances as per crop spacing and laid on the bed. The seeds/seedlings should be sown/transplanted in the holes.

Mulching techniques for Vegetables /close space crop

1. • Very thin film is used for short duration crops like vegetables.
2. • Required length of film for one row of crop is taken and folded in ‘thaan’ form at every one metre along the length of the film.
3. • Round holes are made at the center of the film using a punch or a bigger diameter pipe and a hammer or a heated pipe end could be used.
4. • One end of the mulch film (along width) is anchored in the soil and the film is unrolled along the length of the row of planting.
5. • Till the soil well and apply the required quantity of FYM and fertilizer before mulching.
6. • Mulch film is then inserted (4-6”) into the soil on all sides to keep it intact
7. • Seeds are sown directly through the holes made on the mulch film.
8. • In case of transplanted crops, the seedlings could be planted directly into the hole.
9. • For mulching established seedlings, the process of punching the hole is the same. One end of the film along the width is burried in the soil and the mulch film is then unrolled over the saplings. During the process of unrolling, the saplings are 8 held in the hand and inserted into the holes on the mulch film from the bottom side, so that it could spread on the topside.

Precautions for Mulch Laying

1. • Do not stretch the film very tightly. It should be loose enough to overcome the expansion and shrinkage conditions caused by temperature and the impacts of cultural operation.
2. • The slackness for black film should be more as the expansion, shrinkage phenomenon is maximum in this color.
3. • The film should not be laid on the hottest time of the day, when the film will be in expanded condition.

Removal of mulch

In case the mulch film needs to be used for more than one season (thicker film) the plant is cut at its base near the film and the film is removed and used. By compounding appropriate additives into the plastics it is possible to produce a film, which, after exposure to light (solar radiation) will start to breakup at a pre determined time and eventually disintegrated into very small friable fragments. The time period can be 60, 90, 120 or 150 days and for maize a 60-day photodegradable mulch is used. However there are still some further problems to resolve. It has been observed that the edges of the mulch, which are buried to secure the mulch to the soil, remain intact and become a litter problem when brought to the surface during the post-harvest ploughing. Currently much development effort is being made to find a satisfactory solution to this problem. In direct contrast in developing countries which have agricultural labour available a different approach can be made. Fro example in the people Republic of China trials have been made using a plastic mulch of 15 micron thickness on a sugarcane crop. After the cuttings have been planted through the mulch they are left to grow for a period of one month. Then the mulch is removed by hand and wound up so that it can be utilized for a second season. A yield increase of 26% was obtained.

These two examples not only demonstrated the diversity of mechanisms available for resolving the problems of mulch removed, but also illustrate the different technique, which have been developed in different countries. It also indicates the necessity for each country to adapt and develop mulching technique to meet its own specific requirements 9 of climate, resources and economics. To undertake such technology development there is a specific requirement that both plastics and agricultural development facilities are available.

Irrigation practices under mulching

1. • In drip irrigation the lateral pipelines are laid under the mulch film
2. • In case inter-cultivation need to be carried out, it is better to keep the laterals and drippers on top of the mulch film and regulate the flow of water through a small pipe or through the holes made on the mulch film
3. • In flooding the irrigation water passes through the semi circular holes on the mulch sheet.