Growing Media and Nursery Bed Preparation
|Growing Media and Nursery Bed Preparation|
The material in which plants grow in a pot is known as potting material and is commonly called the ‘growing medium’ or ‘potting medium’. The selection of the type of potting material is important as the growth of plants completely depends on it. The main function of the
growing medium is to supply nutrients, air and water to the roots of the growing plants. It supports the plant physically and holds it in an upright position and allows growth against the gravitational force. For the above two functions, it is necessary that the medium facilitates the growth of root within it. It is, therefore, desirable that an ideal growing medium is porous and allows aeration. It must have a good water-holding capacity so that frequent irrigation is not required. It should support and favour the growth of the plant and must be free from toxins, ailments and insect pests. The growing medium should respond well to the application of manures and fertilisers, as well as, pesticides. It should be light in weight, easily available and have a suitable pH level. The chemical composition, as well as, physical structure of the medium favours the growth of the plant.
Types of growing media
Different types of growing media are used for the propagation of plants.
Light and sandy soils are ideal growing media, while loamy, silt or clayey soils are not preferred due to poor aeration and stickiness. The soil contains both organic and inorganic matters. Soil is a common, universal, easily available and comparatively cheaper medium used in a nursery.
Large particle size makes this medium more porous, aerated and well-drained. The water-holding capacity of this medium decreases with an increase in the size of particle. The usual size of sand is 0.05–2.0 mm. Quartz sand is a useful growing medium but it lacks in nutrient content. It is relatively inexpensive and heavy.
Generally, it is mixed with soil and used as a well-drained porous medium.
It is decomposed organic matter used with soil. Dropped leaves, twigs, grass clippings, cattle feed waste, and farm animal excreta are some of the common ingredients that are used for the preparation of compost. All these are allowed to decompose in a pit prepared at the farm. Compost contains major and minor nutrients that plants need for growth.
It has excellent water-holding capacity and can hold water many times its weight. It is commonly used as rooting medium in air layering. It is comparatively costly and not available easily.
Peat consists of residues from a marsh swamp. It comprises some organic nitrogen. It helps in fast vegetative growth. It is commonly used for growing newly rooted cuttings or newly germinated seeds.
It is obtained from coir fibre dust. It is acidic in nature and has a pH of about 5.0. It has a high water retention capacity.
It is chemically hydrated magnesium aluminium iron silicate. It is produced by heat treatment of mica. It is porous and light in weight. It has a good water-holding capacity.
It is a natural mineral of volcanic origin, which is light weight. The pH is usually neutral to slightly alkaline.
These are the by-products of saw mills. It is easily available and cheap. It is poor in nutrient content but can be used after the addition of nitrogen.
For potting of rooted cutting and young seedlings: 1 or 2 part sand + 1 part loamy soil + 1 part peat moss or leaf mould
For potting general container grown nursery stock: 2 part sand + 4 part loamy soil + 2 part peat moss or leaf mould + 1 part well rotted FYM
Nursery bed and its importance
A nursery bed is a well-prepared piece of land used for raising seedlings or rooting planting material. It acts as a temporary place for the development of young seedlings. Seedlings are transplanted at a definite stage of growth from nursery bed to the main field. Nursery bed is a small plot of 1-metre width where the seeds are sown closely width-wise.
There are several advantages of raising the seedlings in the nursery bed.
(i) Due to the small size of a plot, it becomes convenient to look after the germinated seeds and the coming seedlings.
(ii) Favourable conditions can be provided efficiently in a relatively small area.
(iii) Precautionary measures against diseases and pests can be undertaken easily.
(iv) Raised bed avoids water stagnation and provides aeration to roots, enabling their fast growth and better establishment of seedlings.
(v) Due to intense care, the percentage of seed germination improves.
(vi) Seed wastage due to washing away and wrong placement is checked.
(vii) The time period required for the preparation of seedlings in a nursery proves to be a bonus for the preparation of the field or late harvesting of the previous crop.
Site selection for nursery
Ideally, a nursery, should be located in a pollution-free environment. It should be away from brick kilns, smoke emitting industries and heavy traffics. Non-concrete roads deposit a lot of dust on plants. It must be ensured that adequate sunlight is available in the nursery but the plants must be protected against severe heat.
Topography of land
The topography of land at the nursery site must be even to facilitate intercultural operations. If it is undulating, it must be levelled. In hilly areas, the land may be divided into levelled terraces.
It must be preferably loam or sandy loam with large quantity of organic matter. The pH of the soil needs to be slightly acidic to neutral and must not be alkaline or saline. The soil should have good drainage and proper water retention capacity. Aerated, porous, fertile and productive soils are preferable.
Quality water in adequate quantity must be available at the site for irrigation. The nursery must be near to a natural source of water. The water should be free from harmful salts, toxins or salinity.
The nursery site should be free from waterlogging. Water must not be allowed to stagnate for a long duration as it affects gaseous exchange and leads to poor development of roots. Proper drainage facilities must be provided at the site.
Transportation and marketing
The nursery site should be connected with approach roads or railway. It would be convenient to locate the nursery near a market. If the market is far, it will result in high transportation cost and the plants are likely to be damaged.
As nursery work is labour-intensive and requires skilled labour, the availability of skilled labour in the vicinity is important.
Protection from wind and animals
The nursery must be protected by a strong fencing to avoid grazing animals and thieves. Suitable plants are planted as windbreak in the south-west direction to avoid losses from strong wind.
Preparation of nursery bed
Nursery beds can be prepared in three ways.
This type of nursery bed is prepared in dry and windy areas. As the name suggests, a sunk of 10–15 cm deep is prepared from the ground level. Sunk facilitates the deposition of irrigation water or rainwater for longer time. In areas facing water scarcity or shortage, this type of bed helps to conserve moisture. Sunken bed provides protection to the seedlings during heavy winds.
These are prepared on the surface of land to the field level. Bunds are created all round to stop the irrigation water inside. These are made in nursery for raising seedlings during summer and winter season. In rainy season, water may be stagnated and cause rotting of seedlings. Sandy loam or friable soils are preferred for the preparation of flat bed. Flat bed is one-metre-wide, and its length is according to the length of the slope. Water channels run in between providing irrigation water.
Preparation of flat bed
Mark an area for the preparation of a flat bed. The surface of the marked bed is dug off. Make it fine and loose. Manure, FYM or compost is incorporated according to the size of the bed. Some pesticide, like phorate 10D, is also added to avoid termites. Seeds after treatment with suitable fungicides, generally, thiram @3g/kg, are sown to check soil-borne infections.
In this type of a nursery bed, soil is raised to a height of 15–20 cm above the surface. Hence, it is called ‘raised bed’. Layers of soil are placed over the surface of field so that it forms a bedding of soil. The raised height facilitates the drainage of water and provides aeration to the roots of developing seedlings. These beds are preferred during the rainy season to avoid water stagnation. Raised beds are also prepared in soil with poor drainage as height improves both aeration and drainage. Raised bed minimises the risk of damping-off and increases the chances of survival of seedlings during the rainy season.
Preparation of raised bed
The surface of the soil is dug out and brought to fine tilth. Then, the soil all around the bed is pulled over to raise the surface. This automatically creates a trench around the bed, which is later used for irrigating the bed. Manure and fertilisers are added at this time. These beds are also enclosed with bunds. The width of the bed is one metre to facilitate intercultural operations. Raised beds are about 10–12 cm above the ground level and the length may vary according to the slope of soil. Spacing of 30–50 cm is kept between two rows of the bed to facilitate intercultural operations. Treated seeds are sown width-wise in rows or sometimes by broadcasting method. Initially, these beds are watered with sprinkling water or using a watering can, so that the seeds sown are not dispersed. Once the seedlings are well-rooted and reach the ground level, the bed can be irrigated through trenches of the bed attached.
Precautions to be taken during preparation of nursery beds
(i) Nursery beds are, generally, used to germinate the seeds sown or for rooting the cuttings planted in it. Besides nutrition, moisture and aeration are important factors that affect the growth of seedlings.
(ii) Nursery bed should be prepared in fertile soil rich in organic matter content with good drainage and aeration. Soil having more water retention capacity does not need frequent irrigation.
(iii) Excess of irrigation in sunken or flat bed may lead to rotting of seeds, seedlings and damping-off incidence. Watering of the bed depends on the type of soil. Sandy soils need frequent watering.
(iv) Soil-borne infections of nematodes, insects pests and pathogens may be avoided by treating the soil.
(v) Generally, the width should not be more than one metre and the length should be according to the slope of the soil so that when irrigated water reaches each corner of the bed, the whole bed gets irrigated.
(vi) Seedlings are tender and succulents and are prone to heat shock, so the beds should be prepared in the site receiving partial shade. In tropical and subtropical India, direct sunlight facing site should be avoided.
Application of manures and fertilisers
It releases nutrients gradually. When applied, manures are likely to fulfill the leached amount of nutrients from the soil over a period of time. Besides this, it improves soil texture, which improves drainage and aeration. It is, therefore, recommended to thoroughly mix rotten Farm Yard Manure (FYM) at the time of land preparation. During the preparation of nursery beds, the soil is thoroughly mixed with 5–10 kg of rotten FYM per square metre area.
Application of fertiliser at the time of nursery bed preparation and/or at sowing of seeds is called ‘basal application’ or ‘basal dressing’. In this method,fertilisers are spread uniformly across the nursery bed and mixed with soil. This method is suitable for phosphatic and potassic fertilisers.
Broadcasting of fertilisers, particularly nitrogenous fertilisers, in readily available form to growing plants in standing crop is called ‘top dressing’.
It is another method of fertiliser application to nursery crops, particularly for vegetable and flowering plants. Only nutrients, like nitrogen, or micronutrients can be applied through foliar application. If a crop suffers due to deficiency of micronutrients (Fe, Mn, Zn and Cu) deficiency symptoms appear on plants, it can be corrected by foliar feeding. It requires certain precautions, like low concentration of nutrients and availability of sufficient foliage.
Protection of seedlings
Soil or any planting medium used for nursery may be contaminated by pests. The presence of pests in the medium causes huge losses to the crop in a nursery or infection may be carried to the field through seedlings or adhering medium on the roots. It is, therefore, advocated that the medium used for the nursery must be free from infections or infestations. Different methods adopted for soil treatment are as follows:
Solarisation of soil
In this method, temperature of the soil or medium is raised so high (47º C and above) that infested or incubated pests get controlled or destroyed. It is a physical method that utilises the energy of the Sun to increase the temperature. It is, generally, followed in tropical and subtropical India, where the Sun is too hot during summers.
First of all, dig out the soil at the site where the beds are to be prepared. Remove stones, pebbles and weeds. Crush the clods and bring it to fine tilth. Wet soil conducts heat better than dry soil, so irrigate the area thoroughly. Cover the site with a black polythene film of 200 gauge thick and make the covering airtight by covering the margins with compressed wet mud. This rases the temperature of the soil upto 47º C or above. Within 5–6 weeks, the soil is free from any infection or infestation. A nursery bed may be prepared at the treated site or soil may be used for filling pots or polybags.
This method is followed in advanced countries and is not common in India. Hot steam is diffused in the soil to control soil-borne pests. The nursery bed is covered with a polythene sheet to make it airtight. Hot steam is supplied mechanically for at least 4–6 hours continuously to kill the pests.
Commercial formaldehyde is available in liquid form. It is an effective fumigant, highly toxic to organisms of plant and animal origin. Sterilisation of the soil of nursery bed is carried out at a dilution of 0.25%. Beds of desired size are prepared and diluted solution of formalin is drenched at the rate 4–5 litres per sq m area. The solution percolates up to a depth of 15–20 cm. The poisonous fumes penetrate the soil and make it germ-free. The emitting fumes can be retained at the site for 48 hours by covering the treated area with a thick polythene sheet. Remove the cover after 48 hours of treatment. The bed is kept open for 7– 8 days prior to seed sowing. Immense precaution is needed while application. Gloves, masks and goggles must be worn by an applicator to avoid direct contact with fumes.
In nurseries, soil-borne pathogens are responsible for diseases, like wilt, rots and damping-off. Inoculums in the soil may be eliminated by adding or drenching fungicides into the soil. Fungicides, like captan and carbendazim, can be applied to the soil by either method — dry application at the rate 5g per sq m or drenching 4–5 litre of 2.5–3% solution of fungicides to control soil-borne pathogens.
Larvae of many insect pests, inhabiting soil may be a severe problem to nursery plants. These pests can be checked by the application of insecticides in the soil.
Biological method (bio-agents)
Certain biological agents, like Trichoderma spp., are found effective against wilt causing and rotting fungi present in the soil and Pseudomonas control fruit or stem rot. These bio-agents are used at the rate10–25g/sq m and are mixed well in the soil while preparing the beds. Seeds should be sown 2–3 days after the application of bio-agents.
Seed treatment with fungicides has been found to be effective against seed-borne, as well as, soil-borne pathogens. Fungicides, such as bavistin or thiram, are applied at the rate of 2.5–3 g/kg seed not only to prevent seed-borne infections but also to provide protection against soil-borne infections.