P K Ray
Horticulture Department
Rajendra Agricultural University, Pusa - 848
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Horticulture crops, in
general, are more knowledge and capital intensive than staple crops. Today
horticulture in the country is a more vibrant and dynamic sector than ever before. It
contributes nearly 30% of the agricultural GDP. Annual production of 81.28 million
tonnes of fruits, 162.18 million tonnes of vegetables and 1.73 million tonnes
of loose flowers (NHB, 2013) have to be increased substantially to cope with
increasing demand of these commodities due to increasing population and
expanding domestic and external markets. Short-term growth and long-term viability of any sector are
critically dependent on access to technical knowledge, the ability to adapt
that knowledge to local conditions and the flexibility to develop new
production systems as market conditions change. Successful production of
a horticultural crop depends on understanding of various factors affecting
plant growth, fruiting, and manipulation of these factors for higher
productivity and improved quality cultural activities.
Climate change
There are growing evidences to show that
climate change has already affected agricultural productivity and will put
increasing pressure on agriculture in the coming decades. Record breaking
extreme weather events in the recent past different parts of the world offered
a glimpse of the challenges climate change would bring. Analysis of recorded
climatic data sets clearly indicates that there has been a 0.3oC to
0.6oC warming of earth surface since the late 19th
century. The average global temperature has increased by 0.80C in
the past 100 years and is expected to rise by 1.8oC to 4.0oC
by the year 2100. For Indian region (South Asia), the Intergovernmental Panel
on Climate Change (IPCC) has predicted 0.5 to 1.20C rise in
temperature by 2020, 0.88 to 3.160C by 2050 and 1.56 to 5.440C
by 2080, depending on the scenario of future development. The atmospheric
warming will also be associated with changes with rainfall patterns, increased
frequency of extreme events of drought, frost and flooding. Since the late
1970s, there have been increases in the percentage of the globe experiencing
extreme drought or extreme moisture surplus.
The Intergovernmental Panel on Climate
Change (IPCC) predicts that by 2050, mean temperatures around the planet may
rise by between 2 and 5°C or more and atmospheric CO2 concentration
are likely to be > 550 ppm (cf. 380 ppm at present). Tropical and
semitropical climates in particular are expected to experience dramatic
increases in temperatures, as well as more variation in rainfall. Of serious concern is the fact that
most of the world’s low-income families dependent on agriculture live in
vulnerable areas, namely in Asia and Africa. Farmers having small land holdings
in India will need to adapt to higher temperatures and shifting precipitation
patterns. In addition, climate variability will likely cut into global food
production, exacerbating the existing problems of poverty, food insecurity, and
malnutrition. Furthermore, the greenhouse gas emissions are once again rising
rapidly, making the climate change challenge to food security much greater.
In general, alterations in our climate
are governed by a complex system of atmospheric and oceanic processes and their
interactions. In the context of crop production, relevant atmospheric processes
consist of losses in beneficial stratospheric ozone (O3)
concentration and increasing concentrations of the surface-layer trace gases,
including atmospheric carbon dioxide (CO2), methane (CH4),
nitrous oxide (N2O) and sulphur dioxide (SO2). Surface
level O3; SO2; and CO2 have direct impacts on
crops, while CO2, CH4 and N2O are critical in
altering air temperature.
Particular attention is
paid to likely changes on extreme events and sea level alterations. It is
reported with high to very high confidence that in the 1990–2100 periods most
extreme events will increase in intensity or frequency, or both. The published
reports on the subject predict higher maximum temperatures and a greater number
of hot days, higher minimum temperatures and fewer cold days, reduced diurnal
temperature ranges, more intense precipitation events, increased risk of
drought in summer periods, increases in peak wind intensities of cyclones, and
increases in mean and peak precipitation intensities of tropical cyclones. On
top of that, sea level is predicted to increase by 0.09–0.20 m.
Consequences on Horticultural Production
Climate variability leads to economic and food security risks
throughout the world because of its major influences on crop production. Weather
is the most important cause of year-to-year variability in crop production,
even in high-yield and high technology environments. There has been
considerable concern in recent years about possibility of climatic changes and
their impact on the crop productivity. Today the entire world is suffering from
global warming and its consequent climate change. Its impact on productivity
and quality of crops has been documented fairly well. Since a crop could be defined as a biological
system tailored to give certain products, the product output and quality is
bound to vary with change in the growing environment.
The major changes in the earth’s
atmosphere are the concentrations of CO2, which have increased by about 25%
since the beginning of the industrial revolution. The CO2 concentration has
increased from pre-industrial level of about 280 ppm to 393 ppm in2010. Carbon
dioxide enhances photosynthesis and depresses plant respiration; these effects
are expected to increase plant growth as well as affecting various other
processes. However, a number of plant physiological processes are also affected
by changes in temperature, ozone, ultraviolet radiation, nutrients and water,
all of which are variable factors often associated with climatic change.
Crop productivity will not only be
affected by changes in climatically related
abiotic stresses (i.e. increasing temperatures , decreasing water
availability, increasing salinity and inundation) and biotic stresses (such as increases in pests
and diseases), but also changes in the atmospheric concentration of carbon
dioxide, acid deposition and ground level
ozone. Hence, a key challenge is to assess how crops will respond to
simultaneous changes to the full range of biotic and abiotic stresses. In
general, horticultural crops need intensive cultural care and thus are more vulnerable
to climate change than cereals and pulses. Responding to these challenges to
specific crop will require advances in crop research and the adoption of
appropriate technologies to conduct these studies.
Impact
on fruit Production
The recurrent developmental events of
phenology and seasonality in vegetative flushing or bud differentiation
distinguish trees from annual or agricultural crops. The fact that trees live
over multiple growing seasons implies that every year there is a considerable
renewal cost of some organs (leaves and fine roots), and that trees are more
responsive or susceptible to climatic changes. When horticultural productivity
is the goal, the allocation of resources toward reproductive processes must be
maximized. However, the tree must also preserve its growth potential for future
years; thus, a delicate C balance must be maintained between vegetative and
reproductive needs. In spring, stored
sugars and nutrients support actively growing shoots and inflorescences.
Competition occurs between vegetative and reproductive meristems, and the fruit
is growing essentially on the currently produced photosynthates. Fruits
represent a major C sink in tree crops. The relationship between fruit load and
photosynthetic activity, as well as the effects of several climatic variables,
has been intensively studied. Among all tree crops, cultivated fruit trees are
the ones most adequately supplied with water and nutrients; thus, there should
be few, if any, constraints to a positive CO2 response.
Climatic change effects are not caused by
a single factor (e.g. elevated CO2), but originate from complex interactions
among various factors such as atmospheric CO2, air temperature, nutrient
supply, tropospheric ozone level, UV-B radiation, drought frequency, etc. A
reduction of stomatal conductance under elevated CO2 might have a significant
effect on water transport in trees, since the latter is roughly proportional to
stomatal conductance. Hydraulic conductivity was reported to decrease with
elevated CO2 but this effect is very species-specific. A decrease in stomatal
conductance in response to CO2 enrichment is commonly observed in many crops.
However, under elevated CO2, the increase in WUE is usually greater than the
reduction of stomatal conductance, especially under drought conditions.
Among all plant organs, fine tree roots generally show the
greatest response to elevated CO2. In addition to increases in
fine-root density, trees may enhance their nutrient uptake capacity through
alterations in root morphology and architecture. Trees grown under elevated CO2
initiate more lateral root primordia, leading to increased root branching and a
more thorough exploration of the soil. In addition to changes in fine-root
density, morphology and structure, alterations in root functioning are also
frequently observed in the changed environments. However, it has been a general
observation that the long-lived plants have more time to acclimate to changing
environmental conditions than the short-lived organisms. On a time scale, this
acclimation might occur in the order of several years. The acclimation process
might be influenced by seasonal changes in environmental conditions.
Extreme events although
vary from short-lived, violent phenomena of limited extent such as tornadoes,
flash floods, cyclones and severe thunderstorms, to the effects of prolonged
drought and floods. Drought and floods are responsible for more significant
impacts on productivity of mango, guava, litchi and other perennial orchards.
Short-lived cyclones during early or later stage of fruit growth can inflict
severe damage to the orchardists. However, some positive impacts of natural
disasters have also been reported as increased rainfall to inland areas from
tropical cyclones, the fixing of atmospheric nitrogen by thunderstorms, the
germination of many native plant species, and the maintenance of fertility of
flood-plain soils due to flooding. In litchi, fruits crack severely after heavy
rainfall at the end of prolonged dry spells. High temperature (>380C)
and dry westerly wind or heat-waves in May often lead to sun burning of the
fruit skin in litchi which induces cracking towards harvest. Majority of our
fruit orchards are rain-fed and thus scanty rain or drought brings considerable
reduction in production and quality of the produce.
Impact
on Vegetables Production
Increasing CO2 will enhance photosynthesis and improve
water-use efficiency, thus increasing yield in most vegetable crops. Relative
benefits from increased CO2 can often be maintained with modest
water and N deficiency, but yield benefits on an absolute basis are reduced
when water or N limit growth. The impact of increasing temperatures is more
difficult to predict. Seed germination will probably be improved for most vegetables,
as will vegetative growth in regions where mean daily temperatures during the
growing season remain under 25°C, assuming adequate water is available.
Reproductive growth is extremely vulnerable to periods of heat stress in many
important vegetable fruiting crops, such as tomato, pepper, bean and
sweet-corn, and yield reductions will probably occur unless production is
shifted to cooler portions of the year or to cooler production regions. This
vulnerability results from the shortened duration of grain, storage tissue, or
fruit-filling and from failure of various reproductive events, especially the
production and release of viable pollen. Processing crops, which are sometimes
direct-seeded and are more frequently grown in cool-summer areas, are more
likely than fresh-market crops to benefit from higher temperatures. In general,
crops with a high harvest index, high sink demand, indeterminate growth and
long growth seasons are considered most likely to respond positively to the
combination of higher CO2 and temperature. Relatively few crops have
been studied, however and cultivars within a crop often differ in their
responses, thus making generalizations difficult.
In many crops, high
temperatures may decrease quality parameters, such as size, soluble solids and
tenderness. For fresh-market vegetable producers, even minor quality flaws can
make their crops completely unsalable in some markets. Reduced or more
irregular precipitation will also decrease vegetable yields and quality,
although soluble solids and specific weight may increase in some crops. Leafy
greens and most Cole crops (cabbage, cauliflower, kohlrabi (knolkhol),
broccoli, brussels sprouts etc.) are
generally considered to be cool-season crops, so heat stress during the growing
season would be detrimental to these species. High-temperature effects on
lettuce and spinach and low-temperature effects on Cole crops include induction
of flowering and elongation of the seed stalk. Perennial crops also require an
overwinter cool period. Thus, planting dates, production areas and cultivars
may need to be adjusted if temperatures change.
Significance
of Weather Forecasting
The term weather is used to describe day-to-day variations in our
atmosphere. This includes precipitation, temperature, humidity and cloud cover,
among other variables. Weather forecasts are essentially short-term, as the
reliability of forecasts falls off rapidly after five days. Weather is
therefore an instantaneous concept. The climate of a region is described by
collating the weather statistics to obtain estimates of the daily, monthly and
annual means, medians and variability of the weather data. Climate is therefore
a long-term average of weather. Weather is certainly the most important factor
that determines the success or the failure of a crop in a particular area or
region. It manifests itself through its
effects on plant growth, flowering, fruiting intensity, overall yield, pest dynamics
and soil health. A plant suffering from stress at any stage of growth is much more
susceptible to pest problems than the normal ones. A greater proportion of the
total annual crop loss results from aberrant weather. It has been estimated
that weather directly and indirectly accounts for approximately three fourth of
the annual loss in farm production. However, the crop losses can be reduced
substantially by affecting adjustments through timely and accurate weather
forecasts. Such weather forecast support and provides guidelines for long range
or seasonal planning and selection of crops best suited to the anticipated
climatic conditions.
Weather forecasting
service to agriculture is designed to help the user solve a variety of
weather-induced problems. The user for an agricultural weather forecast program
can be anyone in the production and marketing chain of the crops. Agricultural
planning i.e. strategic (long-term) and tactical (less than 10 days) ; needs to weigh
climate-related and other risks to attain the producer’s goals and to spell out
the sort of information that farmers need to aid their planning of crop, its
production and marketing. While a number of weather parameters are important to
agriculture, the main benefit to farmers comes from communication of the
criticality of weather at a time when an important operation to produce the
crop is to be taken up. This may be planting, weeding, irrigation, and
harvesting, crop protection (general), insect control, disease control, and
appropriate selection of crops or sites for crops or its varieties. During
the growing season, the vulnerability of crops to different weather events can
change. Varying timescales and key agricultural decisions are also important,
especially in terms of the need to recognize how different climate and weather
systems affect different farming decisions. Consequently, it is of primary
importance to understand the relationship between the stage of development of a
crop and weather as the growing season progresses.
The Agro-Meteorological Advisory Service (AAS)
The agro-meteorological
advisory service (AAS) rendered by India Meteorological Department is a
mechanism to apply relevant meteorological information to help the farmer make
the most efficient use of natural resources (soil, water, solar energy etc),
with aim of improving agricultural production, both in quantity and quality. It
is a step to provide weather information based crop management strategies and
operations to enhance crop production and ensure food security. Several Govt.
agencies at district or agro-climatic zone level are involved in translating
weather and climate information into farm advisories using existing research database
on crop production. Weather forecast up to 5 days is made with respect to
rainfall, maximum, minimum temperature, wind speed and direction, relative
humidity and cloudiness, besides weekly cumulative rainfall forecast. The
weather forecast based agro-met advisory bulletin contains information on
important crop management practices and
gives warning to farmers much in advance regarding variations in rainfall, in
its intensity and other weather factors like high velocity wind, cyclones,
frost and information related to pests and diseases of important crops grown in
the area in a particular season. Based
on this information, a farmer is better prepared to decide about crop
production practices like time for sowing, wedding, irrigation and fertiliser
application and harvesting. These advisories are thus helping them to make
appropriate decisions to get the best from their investments and hard work.
In general, weather
forecasts for agriculture can be grouped into short range forecast (up to 48
hours), medium range forecast (3-10 days) and long range forecast (one month to
entire season). Each plays an important role in farm operations and planning of
agricultural activities. The most common forecast uses are changes in sowing
date and crop variety with the latter being more prevalent where a wider choice
of varieties exists. Mixed strategies generally used more inputs like manure or
chemical fertilizers coupled with another strategy such as changing sowing date
along with irrigation and fertilization schedules. Yield estimates recorded in
different areas/ zones suggest that forecast use definitely leads to yield
gains.
Prominent Concerns
It is obvious that weather forecast can minimise losses through
proper management of crop production practices and thus, helps in increasing
the economic benefits. Consequences or effect of the important weather
parameters recorded in the observatory are communicated in advisories in terms of forecasts of rain, thundershowers,
cyclone, temperature rise and fall, frost
, fog, heat-waves, flood, drought etc. Rain is definitely one of the most important
factors of crop production, not only as a necessary source of plant moisture
but also as a harbinger of disease.
Forecasting rain, intensity and duration, can provide useful information
to growers who need to save water and protect crops from attack of diseases due
to prolonged moist weather. Prediction for prolonged incessant rain indicates
towards the risk of flood. The producers may harvest even premature vegetables,
from their standing crops in low-lying areas that are expected to be inundated
due to floodwater. Rivers like Burhi Gandak, Bagmati, Kosi overflow during
rainy reason and pose threats for water inundation in the lower surroundings.
The growers should avoid taking vegetables that are unable to tolerate waterlogging
even for few days.
The
agro-meteorological advisory also highlights the chances of getting an insect
pest or disease. Typically, the onset of Potato or Tomato Blight disease can be
estimated by the duration of cloudy weather, frost or rain during the later
stages of crop growth. Protection may follow in the form of a fungicide spray
or irrigating the field to provide protection against frost. Horticultural
crops particularly vegetables, flowers require frequent irrigation for good
yield. Forecasts of draught or insufficient rains provide farmers with
information for managing irrigation scheduling. Forecast schemes based on temperatures,
wind, and evaporation have been successful in devising suitable irrigation
schedules for higher productivity.
Forecasting cyclones
associated with mild or heavy rains high velocity winds and the time of day when
it occurs is important for taking up aerial application of pesticides and
herbicides. Unwanted spray drift can
become a serious problem where adjacent fields contain crops that are not to be
sprayed with the same chemicals or where environment protection may be an
important issue. Similarly, horticultural crops like grape, strawberry, tomato,
capsicum, cucumber, roses, chrysanthemum, gerbera etc are considered high-value-crops.
Many such crops are grown now under precision farming that happens to be a data
intensive practice where both the physical and environmental factors affecting
crop production are continuously monitored and analysed. The results of this
monitoring and analysis are used as management tools to produce the highest
quality crop. The scale of monitoring
and management define how “precise” the farming will be. This will likely also
require that forecast resolution match the observations. Since agriculture is
highly vulnerable to year-to-year climate variability, a network of small growers
in an area may require a more realistic forecast for higher profitability from
their endeavour.
Estimates of potential changes to flood
risk due to climate change can be of great value but are difficult to estimate
for various reasons including uncertain rainfall projections and problems
associated with transforming model rainfall values into runoff and inflows at
relevant catchment scales. The Kosi River in north Bihar has a long history of
causing serious flood events. Changes to the risk of more serious floods is
assumed to depend on changes to either the magnitude or frequency of extreme
rainfall events combined with changes to the amount of water actually stored in
the catchment area.
Conclusions
There is broad consensus that, in
addition to increased temperatures, climate change will bring about regionally
dependent increases or decreases in rainfall, an increase in cloud cover and
increases in sea level. Extreme climate events will also increase in intensity
or frequency, such as higher maximum temperatures, more intense precipitation
events, increased risk and duration of drought, and increased peak wind
intensities of cyclones. Predictions indicate possibilities of increases in
temperature of 1 to 3°C by 2050 combined with some complex spatially explicit
changes in rainfall. However, there remains high uncertainty in predictions of
extreme events, especially hurricanes. Consequently, climate change is likely
to invoke substantial changes to production of horticultural crop in a region and
the severity with which biotic and abiotic stresses will affect the
productivity of these crops. Since climate change can be expected to have
varying effects in different areas on the expression of drought, salinity,
waterlogging and pest infestation, the mitigation strategies also vary
according to the prevailing situations. While there will be increased
irrigation under drought conditions, urgent measures are required for
irrigation in drought areas and drainage of water from localities getting excessive
rain or flood causing waterlogged situations.
Considering the large areas of
horticultural crops production in different parts of the country, the estimated
economic potential is very high. However, there are a number of challenges to
realize these benefits. These challenges are generally related to the
uncertainty of climate forecasts and to the complexities of the agricultural
production systems involving so many factors. Accurate short (1-2 days), medium
(3-10 days) and long term (1-6 months) forecasts of climate ahead of time can
potentially allow growers and traders to make decisions to reduce unwanted
impacts of climate or take advantage of its expected favourable impacts.
However, potential benefits of climate forecasts vary considerably because of
many physical, biological, economic, social, and political factors. However, improved
scientific knowledge of the processes controlling climate predictability has
the potential to improve our understanding of the climate and its damaging or
favourable impact on productivity of the crops. Working on the interactions
between providers and users of climate information is thus of crucial
importance. Identifying effective ways to co-design and co-generate climate
services with the users is becoming one of the most important challenges that
climate service science needs to tackle.
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