Chemicals are widely used for controlling diseases, insects, and weeds in crops. They can save crops from pest attacks only when applied timely. These chemicals must be applied to plants and soil as sprays, dusts, or mists.
As chemicals are costly, equipment ensuring uniform and effective application is essential. Dusters and sprayers are commonly used for applying chemicals.
Dusting, a simpler method, suits portable machinery and requires basic equipment but is less efficient than spraying due to low dust retention. High-volume spraying is effective and reliable but expensive.
Low-volume spraying combines the benefits of both methods while addressing their shortcomings. Spraying serves various agricultural purposes, including:
- Applying herbicides to reduce weed competition,
- Using protective fungicides to minimize fungal disease effects,
- Controlling insect pests with insecticides,
- Delivering micro-nutrients like manganese or boron.
Functions of Sprayers in Crop Protection
The primary function of a sprayer is to break liquid into droplets of effective size and distribute them uniformly over the target surface or space. Another role is regulating pesticide amounts to avoid excessive application, which could be harmful or wasteful.
Sprayers should deliver droplets large enough to wet surfaces effectively. Droplets smaller than 100 microns are often diverted by air currents and wasted. For uniform application, crops should be treated in regular swaths using a boom to ensure consistent machine output and forward travel.
Spraying Techniques for Efficient Pesticide Use
Spraying techniques are classified as high-volume (HV), low-volume (LV), and ultra-low-volume (ULV) based on the liquid volume applied per unit area.
Initially, high-volume spraying was common, but newer pesticides favor minimal carrier liquid. Droplet size varies by application: fine droplets suit insect, pest, or disease control, while larger droplets are ideal for herbicides.
Smaller droplets improve deposition on target areas, but size affects drift and penetration. A balance is needed to prevent drift, ensure wide coverage, and enhance penetration.
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Types of Spraying Equipment for Crop Applications
Various sprayer designs suit different applications and crop conditions. Manually operated hydraulic sprayers, such as knapsack, twin knapsack, foot, and hand compression sprayers, along with air carrier sprayers like motorized knapsack mist blowers (LV) and centrifugal rotary disc sprayers, are ideal for crops.
Modern trends favor concentrated pesticides applied via low- and ultra-low-volume sprayers, enabled by improved formulations and special nozzles.
Controlled Droplet Application (CDA) atomizers, using less than 15 l/ha of spray mixture, are user-friendly. However, specific chemical formulations for these sprayers are limited to particular crops, pests, or diseases.
Always follow manufacturer instructions for ultra-low or low-volume applications.
Pest and Disease Management with Chemicals
Pests and diseases affecting crops must be managed with poisonous chemicals. As technology advances and new crop varieties emerge, new insects, pests, and diseases arise, necessitating advanced control methods.
Many chemicals are unsafe for direct human handling and require application in fine particles, making suitable machinery essential.
Sprayers and Dusters in Agricultural Chemical Application
Sprayers atomize spray fluid (suspensions, emulsions, or solutions) into small droplets and eject them with force for proper distribution.
They regulate pesticide amounts to avoid waste or harm. Dusters, mechanical appliances for distributing dust formulations, are also used.
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Classification of Sprayers by Energy Type
Sprayers are classified into four categories based on the energy used to atomize and eject spray fluid:
1. Hydraulic Energy Sprayers
Hydraulic energy sprayers pressurize spray fluid using a positive displacement pump or an air pump to build pressure in an airtight container. The pressurized fluid is forced through a spray lance, controlling spray quantity and pattern.
2. Gaseous Energy Sprayers
Gaseous energy sprayers generate a high-velocity air stream via a blower, directed through a pipe where spray fluid trickles through a diffuser plate by gravity.
3. Centrifugal Energy Sprayers
Centrifugal energy sprayers feed spray fluid under low pressure to a high-speed rotating device (e.g., disc, mesh cage, or brush), atomizing it by centrifugal force. Droplets are carried by the sprayer’s blower or prevailing wind.
4. Kinetic Energy Sprayers
Kinetic energy sprayers allow spray fluid to flow by gravity to a vibrating nozzle, producing a coarse, fan-shaped spray pattern, ideal for herbicides.
5. Hand Sprayers for Small-Scale Farming
Hand sprayers are small, light, and compact, with container capacities of 500 to 1000 ml. They are ideal for small areas like kitchen gardens or experimental plots.
These hydraulic energy sprayers use a pump with a cylinder, plunger, and rod to suck and pressurize fluid, which is then sprayed through a nozzle. In some models, an air pump builds pressure above the fluid, forcing it through a trigger valve to the nozzle for atomization.
6. Knapsack Sprayers for Field Applications
Knapsack sprayers, carried on the operator’s back, typically feature a hydraulic pump inside the container. A plunger operates within a replacement well for easy maintenance, controlled by an oscillating handle.
An agitator prevents particle settling in suspensions. A delivery tube carries pressurized fluid to the spray lance, with flow controlled by a trigger valve. Compression knapsack sprayers use an air pump to build pressure above the fluid, requiring periodic ground-based pumping.
7. Battery or Ultra-Low-Volume Sprayers for Efficient Application
ULV sprayers reduce chemical and water use, requiring a narrow droplet spectrum (100-250 µm for fine sprayers, 50-100 µm for mists, 0.1-50 µm for aerosols), controllable emission rates, and non-volatile formulations.
They save time by reducing refilling and mixing needs, covering up to 8 ha daily compared to 3 ha with power sprayers.
Battery-operated ULV sprayers use a DC motor with a spinning disc to atomize fluid, designed to release droplets 1 m from the operator, minimizing contamination risks. Post-spraying, atomizers must be flushed with paraffin to prevent pesticide residue buildup.
8. Power Sprayers for Large-Scale Farming
Power sprayers use an internal combustion engine to impart mechanical energy to the spray fluid. Common types include gaseous energy knapsack sprayers with a 1.2-3 HP engine, a blower, and tanks for spray fluid (7-12 liters) and fuel (0.75-2.25 liters).
A pleated hose carries high-velocity air to a shear nozzle, atomizing the fluid. Air currents (2.7-9.1 m²/min at 175-320 km/h) deliver droplets to plant surfaces. For dusting, modifications include removing liquid delivery components and adding a dust agitator and intake tube.
9. Thermal Fogging for Pest and Disease Control
Thermal fogging, widely used in pest control and public health, produces 10-micron droplets via thermo-pneumatic energy.
A pulse-jet engine’s hot exhaust fragments and partially evaporates the formulation (active ingredient with a carrier, usually mineral oil).
Upon meeting cooler ambient air, the stream condenses into a dense fog, penetrating dense vegetation or inaccessible areas effectively.
Types of Formulations for Thermal Fogging
Thermal fogging supports two formulation types:
1. Water-Based Formulations
Water-based formulations avoid oily residues but produce larger, heavier droplets due to water’s poor thermal properties. These droplets may evaporate before reaching targets, limiting use in large spaces. Lower water viscosity requires reduced flow rates to avoid ineffective large droplets.
2. Oil-Based Formulations
Oil-based formulations, most common for their small droplet size, ensure high effectiveness and coverage in large spaces. Their flammability requires strict adherence to safety guidelines in equipment manuals.
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