Keywords

1 Introduction

Mulching is actually the process of covering the soil surface with the help of organic materials like straw, husks, stocks, or any biological biomass which could be the biomass of a weed that is uprooted and spread on the soil surface. Or mulch could be any inorganic material like black or white plastic etc. which should bio-degradable.

Mulches generally limit the weeds growth using the resource limitation principle, thus the available light is hampered and the growing weeds are smothered. Rice straw used as mulch controlled the weeds growth effectively. Also the living mulches substantially decreased the biomass of the weeds growing with the main crop. Also, the biomass of weeds was effectively decreased in vetch plots that were treated with oat plants as mulch and grazing was also conducted, in comparison with the bare plots with no mulch applied. Further, the different mulching materials have a variety of effects on the growth of weeds. For instance, the straw mulch and use of polythene significantly suppressed the weeds growth, however the other mulch types resulted in no effect.

In sericulture, mulching gives a greatly favorable environment to the mulberry trees to effectively utilize the organic manures as well as the bio fertilizers so that the quantity and quality of the mulberry leaves are improved. The bio and organic amendments in the mulched treatments in addition to the reduced doses of inorganic fertilizers resulted in the improvement of the chemical, physical and biological features of the concerned soils.

Many of the cover crops growing in winter such as peas, hairy vetch, crimson clover, and rye can effectively manage the plant diseases like the fruit rots in tomato. Further, the hairy vetch and rye as cover crops substantially improved the fruit yield of tomato, as compared with the fallow plots (control). The polyethylene as mulch and the spent mushroom compost both effectively enhanced the fruit yield of tomato and significantly suppressed the growing weeds in organic production of tomato crop.

2 Pros and Cons of Mulches for the Management Weeds

Pros

The benefits of mulching are numerous. Many of the possible benefits are listed below in detail.

  • Soil moisture conservation

    Mulches prevent rapid evaporation and make water and nutrients available to the crop roots and thereby create conditions favorable for the new root growth.

  • Improved rain infiltration

    The rain water is sufficiently absorbed into the soil by capturing and slowing down the movement of water through mulches.

  • Inhibition of weed seed germination

    Mulches reduce seed germination of weeds by preventing light from hitting the soil surface.

  • Reduction in weed biomass

    This can also be termed as smothering of weeds or weeds suppression. Field trials in commercial vineyards showed an annual loss of 50–65% of the covered weed biomass. Some follow-up with hand crews or spot herbicide applications is often necessary to achieve complete weed control with mulches. To be effective, mulches must be applied in a uniform layer to soil before weed germination and replenished on a regular basis.

Mulches are capable of suppressing the weeds growth in several ways. These include, (1) there is physical influence of the mulch and its depth. In this way, there are several factors involved which make a combined effect. These factors include decrease in soil temperature, moisture, and also lack of light availability. (2) the mulch inhibits the seed germination due to the phyto-toxic constituents produced by the micro-flora living within the composted material. This is probably because the immature composts are greatly effective in suppression of weeds.

The phyto-toxic components mentioned above include a variety of the volatile organic constituents, which include phenolic acids, ammonia, and organic acids (i.e. acetic and propionic acids, isobutyric and isovaleric acids together). The compost maturity and its C:N ratio determine the levels of these chemicals. A very higher C-N ratio always results in the excessive accumulation of the organic acids. On the other hand, a very lower C-N ratio ends in the amassing of ammonia compound. These chemical compounds effectively inhibit the seeds germination; can cause injury to these plants, especially when the composts are very immature. Thus, a rationale is lying there for using these composts in the distances between the plants, but should be put very adjacent to them.

  • Crop seed protection

    Mulches are spread over the surface of the soil to protect seed from the erosive effects of water and fluctuations in soil temperature and moisture. Mulches can sometimes be applied together with seed or fertilizers. However, too much mulch mixed with seed can result in poor stands. Netting, disking, and asphalt spray are among the methods used to anchor loose mulch in order to prevent loss via erosion.

  • Improving soil chemical environment

    Organic mulches add organic matter and plant nutrients to soil upon decomposition. Thus, they improve carbon sequestration.

  • Improvement in soil structure

    Mulches improve the soil structure through addition of organic matter to the soil.

  • Reduction in nitrogen loss

    The volatilization and leaching loss of nitrogen is reduced under mulched condition. During decomposition of organic mulches soil mineral nitrogen is immobilized by microbes and thus its loss is minimized.

  • Increase in soil fertility

    Cation exchange capacity is substantially influenced by organic matter content in soils containing predominantly low activity clays. Improvement in the cation exchange capacity of soil improves the fertility status of these soils. Mulches also influence the availability of nutrients through their effect on physical conditions, hydrothermal regime and biological activity of the soil.

    The weed growth is indirectly promoted by the N fertilizer application, and as a result the weed competition with rice crop has decline the rice yield to much extent. However, the effect of the placement of nitrogen fertilizer on the weeds population has not been studied yet.

  • Reduction in soil pH

    Furthermore, decomposition of organic mulches add organic acids to the soil resulting in low soil pH which influences the bioavailability of many plant nutrients viz., Fe, Mn, Zn, Cu, etc.

  • Soil protection from rain splash

    Mulches protect the soil from rain splash which reduces the soil erosion and splashing of pathogen inoculum on to the plants.

Cons

  • Cultivation or irrigation practices that disturb the mulch barrier limit the effective life of the mulch.

  • Mulches made up of organic materials will decompose in response to normal microflora and microfauna activity.

  • Mulches have little or no impact on re-growth of perennial weeds such as field bindweed.

  • Vertebrate pest activity may increase or be hidden by mulches.

3 Types of Mulches Used for the Management Weeds and Diseases

Generally, there are two types of mulches including organic and inorganic mulches.

3.1 Organic Mulch

There are various positive attributes of the organic mulch, which effectively conserves the soil moisture through reduction in the water loss via evaporation, diminishes the soil erosion through wind and water, keeps the soil temperatures quite normal for the crop plants, hampers the growth and number of weeds, helps in development of beneficial soil microbes, and last but not the least decreases the spread of soil borne pathogens due to protection of the soil from splashing upon the crop plants during watering or rainstorms. Further, the mulching process can help in avoiding the mowing practices around trees and shrubs, which is also helpful in preventing mechanical injury to the tree trunks. Mulch also stops the process of heaving (i.e. upward protrusion of the plant roots out of soil) when it is used as a winter protection tool, during freeze and/or thaw periods. The eroded areas can also be stabilized, which helps prevent the soil erosion through wind and water both. Organic mulches get decomposed with the passage of time, which improve the soil quality and structure, and the nutrients are returned to the soil. The inorganic mulches are mostly utilized for creation of barriers to the growing weeds; and are sometimes used for the purpose of decoration. Inorganic mulches include rocks or gravels which do not decompose readily. The rocks absorb and then reflect heat that can be fatal to the plants in hot and dry weather conditions. Due to extremely slow decomposition, the inorganic mulches are not capable of improving the quality of the soil.

4 Different Types of the Organic Mulches

  1. 1.

    Tree barks (softwood)

    The softwood bark is also one of the by-products of the lumber and paper industries. The pine bark is one of the common examples of softwood and is mostly utilized under the larger trees and also the shrubs. The pine bark is somewhat acidic in nature i.e. having lower pH. It takes sufficient time to get decomposed, and does not required replacement quite often, unlike the other types of organic mulches do.

  2. 2.

    Tree barks (hardwood mulch)

    The shredded and torn hardwood is considered a by-product of the lumber and paper industries. The size of this hardwood ranges from shredded smaller chips to somewhat larger nuggets. This kind of mulching is mostly applied around the trees and/or shrubs and in the perennial beds too. The natural or dyed varieties contain this shredded bark. The dyed varieties are mostly a mixture of the hardwood or the recycled wood waste that contain the artificial dyes.

  3. 3.

    Cocoa bean hulls/cocoa bean mulch

    The cocoa hulls are one of the by-products of the chocolate industry. The weight of the hulls is light due to which they are easy to handle and can be used for any planting area. These hulls smell pleasantly as well. These should be applied up to one inch deep and must be watered lightly to hold them firmly. These hulls get decomposed rapidly and thus should be applied annually. These chocolate by-products are detrimental to the grazing animals if it is consumed; therefore it is better to choose another mulch type if there are pets frequent moving in the area. We can develop the leaf mulch at home with composting of the shredded and aged leaves that can be used in all types of garden beds. The leaves infected with scab, anthracnose, or leaf spot should be eliminated and must not be used in the compost for mulch purpose. The grass clippings should be spread in layers across the perennial beds and should be turned over when growing season is getting close to end. Dry up each layer before adding any additional layer. In addition, the application should not be made in thick layers because clippings get mat. Also, the clippings from lawns should not be used if the lawn is already treated with a herbicide or an insecticide. Further, the grass clippings that started seeding should not be applied in order to stop the growth of undesirable turf grass in the garden beds.

  4. 4.

    Municipal tree waste

    The utility companies and the city or village arborists mostly prepare mulches and make them available free of cost for the home owners. This type of mulch is normally composed of somewhat larger and not-aged wooden chunks. Thus, the fresh material use higher amounts of the soil nitrogen as it gets decomposed, and this mulch type is particularly useful in making pathways.

  5. 5.

    Composted animal manure

    Well-composted animal manure can also be utilized as mulch or as a soil amendment. This animal manure is a best option for any new planting beds because it adds nutrients to the soil and boosts the soil quality. Fresh animal manures must not be applied in garden beds as the plant roots might be burnt with it. Extreme care must be taken when the animal manure is being used in the vegetable gardens. The manure must be well-composted before using it as mulch in temperatures between the ranges of 130–140°F for a period not more than a week, and be composted for about 4–6 months in order to eradicate the potential disease causing organisms. The layers of white and black newspapers may be applied for weeds suppression. Two to three layers can be applied at a time and must be covered with an organic material i.e. leaf mulch or grass clippings for the purpose of holding it in place. The newspapers will finally get decomposed which may then be incorporated into the soil.

5 Types of Inorganic Mulches

  1. 1.

    Landscape fabric

    The landscape fabric is the best choice for a long-term effect on the weeds suppression because the landscape fabric allows the water and air to pass through it. It is also used along with other organic mulches and gets decomposed more rapidly than any other inorganic mulch. Examples of stones include crushed gravel, marble chips, and volcanic rock. Stones cannot sustain moisture and thus cause heat stress on the nearby plants. The light reflection and ground heating causes the roots to burn.

  2. 2.

    Plastic film (polyethylene)

    The plastic film is an impermeable film i.e. in which the water and nutrients cannot penetrate. To warm the soil in spring vegetables the plastic film is used along the rows; however for long-term use, it is not the best choice. Plastic film gets deteriorated upon exposure to the sunlight and can be used for one season only.

  3. 3.

    Rubber as mulch

    The rubber mulch comprises of recycled or ground tires of the vehicles. This type of product is still under research; however, the initial studies showed some possibility of toxicity levels and also there is a risk of flammability as well. Also, the rubber mulch can be functional in the soil for an indefinite time. It is therefore not recommended for application in the home landscape practices.

6 Instances Where Mulches Worsened the Practice of Weeds Management

The organic mulch can enhance the soil acidity (i.e. lowering the soil pH) which negatively affects the crop productivity (Tables 1, 2, 3 and 4).

Table 1 Different types of mulches and their effect on weeds and crops (Chopra & Koul, 2020)
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Table 2 Mulching treatment for weed management in different crops (Chopra & Koul, 2020)
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Table 3 Type of mulch and soil used in accordance with the existing conditions
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Table 4 Enhancement in soil moisture content under different mulches
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7 Conclusion and Recommendations

Mulching provides a favourable environment for effective utilization of plant biomasses, food wastes, organic manures and other biological materials for the purpose of improving the growth and yield of crops. Bio and organic amendments in mulched plots along with reduced dose of inorganic fertilizers play a vital role in improving the physical, chemical and biological characteristics of soil, thereby optimizing the yield potential of crops. The use of organic mulches under water stress condition along with the systematic inputs of organic fertilizers including bio fertilizers may be recommended for sustainable farming (Fig. 1).

Fig. 1
Five photographs of fields where different mulches are used. a) Pebbles, b) Dry leaves, c) Ash, d) Plastic, e) Stubbles as mulch.

Various fields where different mulches are used: a Pebbles as mulch, b Dry leaves as mulch, c Ash used as mulch, d Plastic used as mulch, e Stubbles as mulch

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The role of mulch is not ignorable in agricultural practices. Like a coin having two sides, mulches also have some positive as well as negative impacts on the associated crops, weeds and soils. In addition, mulching helps in soil moisture retention, in controlling weeds growth, and in enhancing the crop yields. It also affects the soil pH, making the soil acidic that indirectly diminishes the fertility of soil and then decline the crop yield ultimately. Therefore, the selection of proper mulches by farmers is an important aspect with the purpose to increase the crop productivity. Thus, mulch type must be chosen by considering the soil type, the crop that is to be cultivated, the climatic conditions of the area, and the target weeds to be managed.

The physical methods also play major role in the organic and integrated plant protection strategies. Like the vegetable crop, mulches must also be regularly applied in the medicinal plants under row cultivation. There are numerous similarities in growing the vegetables and the medicinal plants including the fact that both are grown in smaller areas, pesticides are limitedly used in both and the weeds are the major trouble in their cultivation. Therefore, out of the various physical weed control methods, mulches seem to be the best option.