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| Fruit Culture under Climate Variability in Sub- tropics | | | Dr. Banarsi Lal & Dr. Vikas Tandon | 10/13/2018 9:59:12 PM |
| Over the years horticulture has emerged as an indispensable part of the Indian agriculture, offering a wide range of choice to the farmers for crop diversification. This is a core sector of the Indian agriculture and contributes about 24.5 per cent of agricultural GDP from just 8 per cent area. Horticultural crops include fruits, vegetables, floriculture and plantation crops. This sector contributes significantly to the economic and ecological development, employment generation, export and nutritional requirement of the people. Since India is endowed with different agro-climatic conditions and topography, the scope for strengthening various commercial activities is enormous. Horticultural crops are adapted to a wide range of climatic conditions, produce higher biomass per unit area as compared to field crops, are more remunerative for replacing subsistence farming and thus may aid in alleviating poverty in difficult agro- ecosystems as rain fed, dry land, hilly and coastal areas. There is also great potential to improve wastelands for productive use. These crops require lesser irrigation and provide higher employment opportunities round the year. Increase in demand for horticultural produce due to greater health awareness, rising income, export demand and increasing population poses the challenge for further increasing the production and productivity of horticultural crops. The issue of climate change and climate variations has resulted in more uncertainties and risks in this already high capital intensive system. This has resulted in further aggravating the constraints on horticulture production system. The major challenges before us is to have sustainability, higher levels of production, competitiveness to stay in market, regular production in conditions of declining, land, water and more importantly threat of climate change. In order to meet the above challenges we need innovations for improving production in changed scenario.
The natural change in our climate has been caused by various factors in space and others in our earth itself. The climate change refers to additional and rapid change in our climate mainly due to human activity. Variation in either mean state of climate or in its variability persisting for an extended period is referred as climate change. This may be due to natural internal processes or external forcing or due to anthropogenic changes in composition of atmosphere or in patterns of land use. The earth is the unique planet that supports life, which is due to its unique composition of atmosphere. The main elements are the water, oxygen rich atmosphere and a suitable land temperature. Our atmosphere has proper depth and chemical composition. About 30 percent of incoming energy from sun are reflected back to space while the rest reaches earth, warming the air, oceans and land and maintaining an average surface temperature of about 15 0 C.
The chemical composition of atmosphere is Nitrogen 78%, Oxygen 21% and Carbon dioxide only 0.036%. Oxygen is required by all living things to survive while carbon dioxide is only required for photosynthesis by plants. The energy received from sun warms oceans, land and other land forms which absorb some part of it and releases back the rest to atmosphere. All this released heat is not lost back to space but is partially absorbed by some gases present in very small quantities in atmosphere also known as green house gases. These are mainly carbon dioxide, methane, nitrous oxide, water vapour, ozone and few others. In the absence of emission of heat, imbalance is created. Thus, increased concentration of these greenhouse gases leads to increased temperature which in turn impacts world climate, leading to phenomenon called climate change.
The earth's climate makes small adjustments so as to maintain a firm balance between the energy reaching earth surface and energy reflected out of it. Even a small rise in temperature could mean substantial changes in cloud cover and wind pattern. Some changes may enhance warming or some may counteract warming effects. Increase in small particles of matter or liquid produced naturally or by manmade activities known as aerosols results in cooling effect. Increase in water vapour due to increase in evaporation due to high temperatures can further add to rise in warming effect. The significant change may impact agriculture/ horticulture/ fish/ livestock and consequently our food supply. Climate change results in erratic rainfall pattern, heat waves, more warm spells, and crop failures. However, climate change may have some beneficial effect to a limited extent. More availability of carbon dioxide may lead to improved yields of root crops and increased temperatures may lead to enhanced maturity.This issue has posed a greatest challenge to the very survival of mankind . Climate change refers to a change in state of climate. The global warming and rise in temperature have been attributed to increase in concentration of green house gases in earth's atmosphere. Activities like consumption of fossil fuel to meet energy needs of mankind have caused considerable accumulation of these green house gases like carbon dioxide, methane, nitrous oxide and chlorofluorocarbons. The global average temperature has increased by 0.740C between 1906 to 2005. As per IPCC projection, a temperature increase of 1.8 to 4.00C is anticipated by the end of century.
The vulnerability of horticulture or agriculture or animal husbandry depends on both expected regional climate change and that sector's ability to adapt to the change. The projected or anticipated increase in temperature, variability in precipitation pattern and increase in frequency of extreme weather events such as heat, cold waves, frost days, drought, and floods would severely affect the production of horticultural commodities. These stresses at different crop development phases in varying intensities would ultimately determine productivity and quality. The burning of fossil fuel and anthropogenic activities has resulted in enriching of carbon dioxide in the atmosphere which influences the carbon fixation and productivity of crops.In order to assess the quantity of impact of climate change we need to have detailed information on physiological responses of the crops, effects on growth and development, quality and productivity.The sensitivity of individual crop to temperature depends on inherent tolerance and their growing habits. Indeterminate crops are less sensitive to heat stress conditions due to extended flowering compared to determinate crops. The temperature rise may not be evenly distributed between day and night and between different seasons. In tropical regions even moderate warming may lead to disproportionate decline in yields. In high latitudes, crop yields may improve as a result of small increase in temperatures. In developing countries, which are predominantly located in lower latitudes, temperatures are already closer to or beyond thresholds and further warming would reduce rather than increase productivity. Thus the effect of climate change is likely to vary with the region and with the type of crop.
Indian climate is dominated by monsoon, responsible for most of the regions precipitation, poses excess and limited water stress conditions. Fruits and vegetables being sensitive and succulents are generally more sensitive to environmental extremes. High or low temperatures and water stress are the main cause of low yields. Under climate change scenarios the impact of these stresses would be compounded. The horticultural crops having C3 photosynthetic metabolism have shown beneficial effects due to elevated carbon dioxide. Studies have indicated increase in yields in onion by 26% due to increase in bulb size at 550ppm CO2. Tomato has shown 24 % increase in yields due to more number of fruits. The extreme hot and cold wave conditions have been reported to cause considerable damage to many fruit crops. In perennial, crops like mango and guava, temperature is reported to have influence on flowering. The percentage of hermaphrodite flowers is more in late emerging panicles, which coincided with higher temperatures. Though grape originated in temperate regions, modifications in production system has enabled it to adapt to subtropical and tropical climates. Under climate change conditions there would be changes in availability of growing degree days leading to hastening of the phonological processes. Most of the subtropical fruits are grown in rainfed conditions and are vulnerable to climatic variability and drought conditions caused due to shifts in rainfall pattern and temperature fluctuations.
The rise in temperature will influence the survival and distribution of pest populations. The rise in temperature increases nutrient mineralisation in soils which will decrease fertiliser use efficiency. Increase in temperatures at fruit maturity stage results in rise in events as fruit cracking and burning of litchi and premature ripening in mango. Low fruit setting is observed due to sudden rise in day temperatures (>35oC) during peak flowering in mango. Low temperatures (4-11oC) in January, accompanied with high humidity (>80%) and cloudy weather delays panicle emergence. During peak bloom period, high temperature (35oC) accompanied by low humidity (45%) and long sunshine hours result in excessive transpiration and dehydration of panicles. Untimely winter rains promote vegetative flushes in citrus instead of flowering flushes. Dry spell during flower emergence and fruit setting affects flower initiation and aggravates pest incidences. In wine grapes, anthocyanin development is influenced by difference between day and night temperatures with high variations (15-20oC) promoting colour development.
In citrus, severe water stress causes reduction in leaf initiation, leaf size gets reduced and leaves becomes leathery and thick. Root growth is adversely affected by water stress. It may lead to increase in root depth and higher proportion of feeder roots in citrus. Grape wines under stress reduce shoot growth and flower induction. Water stress results in reduced berry growth but does not influence its characteristic double sigmoid growth curve. In papaya, water stress imposed by suspending irrigation for 34 days arrested growth, induced leaf abscission and drastically decreased photosynthesis. Thus, it is evident that impact of water stress is more influenced by stage of growth, water stress before flowering is essential to get flowering while stress at the growth stage of fruit is detrimental.In mango, flooding simultaneously reduced net CO2 assimilation and stomatal conductivity after 2-3 days. However, flooding did not affect leaf water potential, leaf extension growth or shoot dry weight, but stem radial growth and root dry weight are reduced. Mortality of flooded trees was 0-45% and hypertrophied lenticels are observed on tree that survived flooding but not on trees that died. The reduction in gas exchange, vegetative growth and variable tree mortality indicates that mango is not highly flood tolerant, but appears to have certain adaptations to flooded soil conditions.The productivity will continue to decline up to 1,500 m amsl to the tune of 40-50% due to warmer climate and lack of shilling hours during winters and warmer summers in lower elevations. This will result in shifting of apple production to higher elevations (2700m, amsl). Snowfall in winter months affects flowering. In spring low fluctuating temperatures results in poor fruit settings while higher temperatures during this period results in desiccation of floral parts. Mild winters followed by warmer springs advances bud burst and expose them to frost damage in almonds and apricot. High temperatures and moisture stress increased sunburns and cracking in apple, apricot and cherries.
Many slow growing fruit crops require heavy investment on establishment of orchards. Changing the existing varieties would be difficult and very costly under the impact of climate change. In Kullu district of Himachal Pradesh, farmers have shifted from apple cultivation to either pomegranate cultivation or to vegetable growing. While, in Shimla district at relatively higher altitudes orchards have been replaced from high chilling requiring apple cultivars (Royal Delicious) to low chilling requiring cultivars and other fruit crops as pear, plum and kiwi etc. In mid hills the trend is altogether shifting from apple cultivation to vegetable cultivation due to erratic weather conditions and reducing chilling hours. It is corroborated by declining trend in snowfall and apple productivity in Himachal Pradesh and Jammu and Kashmir. Thus in replanting orchards and in new plantations during these years, selection of low chilling types may be advisable.
This is an example of impending impact of climate change. Hence, under such circumstances, we would have to identify varieties and regions suitable for production of quality fruits. With global warming production areas for specific crops and/or time of planting could be changed. For many horticultural crops areas have been defined for fruit crops and creating new infrastructures in new areas would not be an easy task. Location of important production area is often defined as much by available land, markets and infrastructure as by climatic conditions. Thus, climate change and CO2 are likely to alter important interactions between horticultural plants and pollinators, insect-pests, diseases and weeds etc. Keeping in view the nature of crop, its sensitivity levels and the agro-ecological regions, the crop based adaptation strategies need to be developed, integrating all available options to sustain productivity. To prepare ourselves for climate change and for formulating a sound action plan we must identify the gaps in information, prioritise researchable areas, and formulate concrete policies. It is now understood that next 50-100 years are going to be crucial and how these climatic changes would affect growth, development and quality of horticultural produce. |
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