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Management of crops in frost
By Muhammad Amjad Ali and Dr Shahid Niaz  

SEVERE winter weather conditions can create many problems for crop plants jeopardising their health and even their lives. The frost can significantly damage different parts of the plants resulting in low agricultural productivity. Various measures can be taken to tackle this problem.

Frost occurs when temperature around the plant drops below 0°C. At this temperature, water turns into ice crystals on the surface of the plants. Frost can injure active tissues that are insufficiently ‘hardened’ to withstand the cold temperatures which may lead to stunted growth and even death of plants. Flower buds, vegetative buds, branches, stem, crowns, bark, roots, or even the whole plant may be injured by frost.

Winter desiccation commonly called “winter drying” or “winter burn, occurs due to intensity of frost spells. During severely cold weather, the ground may freeze to a depth beyond the extent of the root system, thereby cutting off water supply to the plants. Injury due to desiccation is commonly seen as discoloured, burned leaves or whole plant. It is worst on the side facing the wind thus causing extra damage. Frost prevents plants from having firm contact with the soil and exposes the roots to wind desiccation.

There are many variables that affect the actual critical temperature for a given plant and the amount of frost injury. These are duration of cold, growing conditions prior to the cold event, cultivars: (because of plant habit, or avoidance, rather than genetic differences), stage of development, super cooling (in the absence of ice nucleation points, plant sap can cool below the freezing point without forming ice crystals), soil type and condition (moist dark soil holds more heat than dry light soil), incidence of freezing wind.

Soil moisture and compaction can have a significant effect on temperature. A moist compact soil will store more heat than a loose dry soil and therefore has more heat to transfer to the crop at night. Cultivation just before a frost can increase the risk of injury, because the soil is looser and drier after cultivation. Soil under a grassy cover crop will hold more heat if the grass is mowed short.

Although it is difficult to manage frost occurrence in various crops, different practices can be helpful in this respect. Proper revised irrigation schedule can be helpful to cope with low temperature injury. Irrigation frequency should be increased in case of heavy frosts with less amount of water per irrigation. This will moisten the soil resulting in more uptake of water by plants. This water will help the plant sap to move efficiently from leaves to other plant parts. One negative side effect of more frequent irrigation for frost protection is increased potential for disease outbreaks. Pathogens of many diseases grow rapidly in moist and humid conditions.

Mulching is one of the most important ways to maintain healthy plants under frosty temperature. Mulch is any material applied to the soil surface for protection or improvement of the area covered. Mulches keep the soil cooler in the summer and warmer in the winter, thus maintaining a more even soil temperature. In addition to many advantages, mulch such as dried grass clippings, hay or straw, leaves can be used temporarily to cover tender plants to protect them from frost injury.

Another approach to modify the micro-climate to enhance plant productivity by plastic material is the use of row covers. Row covers may be used during the cold season to conserve warmth, stimulate germination and early growth, protect plants from frost injury, and improve the quality of the crops. Row covers reduce evaporative cooling and the rate of cooling under the cover.

Desiccation injury can be minimised by placing a protective barrier and wind breaks over or around plants to protect them from winter winds and sun will help to reduce the incidence of this injury. Anti-desiccant sprays applied once in late autumn and again in mid-winter may also prove helpful.

Growing of crops under green house conditions might also be effective to circumvent heavy frost. Plastic sheet will conserve and retain the temperature trapped inside the tunnel at the day time. This is due to the accumulation of CO2 gas in the inner climate.

This concludes that frosty temperature causes serious damage to crop plants, because it is a natural phenomenon, it can not be wiped out but can be managed through various means like proper irrigation, row covers, mulching, protective barrier and wind breaks and green house cultivation. All these practices are economically diverse but have good impact on crop productivity.

Courtesy: The DAWN;

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