CLIMATE RESILIENT
VEGETABLE PRODUCTION
Dr. Avijit Kr. Dutta
Assistant Professor
(Horticulture), School of Agriculture and Rural Development
F/C: IRTDM, Ramakrishna
Mission Vivekananda University
Introduction
India has undergone a series of ups
and downs in agricultural production and the climatic conditions play a major
role particularly in the years of abnormality. One of the major threats to
agriculture is the impact of climate change in achieving sustainable
development together with food security. More
erratic rainfall patterns and unpredictable high temperature spells may consequently
reduce crop productivity. Unless measures are undertaken to mitigate the
effects of climate change, food security particularly in the developing
countries of the world would be under threat. More specifically for our
country, the combined effects of climate change and population growth are
expected to put more pressure on the limited land resources and thereby, increasing
the challenges of sustainable development. Vegetables are generally sensitive
to environmental extremes, and thus high temperatures and limited soil moisture
are the major causes of low yields that would be further magnified by climate
change. Vegetables are the best resource for overcoming micronutrient
deficiencies and provide smallholder farmers with much higher income and more
jobs per hectare than staple crops (AVRDC, 2006). The importance of vegetables
in providing balanced diet and nutritional security has been realized world
over. They are now recognized as healthy foods globally and play important role
in overcoming nutritional deficiencies and providing opportunities of higher
farm income. The worldwide production of vegetables has tremendously gone up
during the last two decades and the value of global trade in vegetables now
exceeds that of cereals. Hence, more emphasis is to be given in the developing
countries like India to promote cultivation of vegetables. Development of
hybrid varieties, integrated insect-pest and diseases management practices;
integrated nutrient management and standardizing improved agro-techniques including
organic farming have already changed the scenario of vegetables production throughout
the globe. Although, the productivity, quality and post-harvest management of
vegetables will have to be improved to remain competitive in the next decades
for reducing malnutrition and alleviating poverty in developing countries
through improved production and consumption of safe vegetables with prior
consideration over the impact of climate change.
Environmental constraints for vegetable production
Environmental stress is the primary cause of crop
losses worldwide, reducing average yields for most major crops by more than 50%
(Boyer, 1982; Bray et al., 2000). Increasing temperatures,
reduced irrigation water availability, flooding, and salinity etc. are
major limiting factors in sustaining and increasing vegetable productivity.
Extreme climatic conditions have also negative impact over soil fertility and
soil erosion. Thus, additional fertilizer application or improved nutrient-use
efficiency of crops is to be needed to maintain productivity or harness the
potential for enhanced crop growth due to increased atmospheric CO2.
The response of plants to environmental stresses depends on the plant
developmental stage and the length and severity of the stress (Bray, 2002).
Plants may respond similarly to avoid one or more stresses through
morphological or biochemical mechanisms (Capiati et al., 2006).
a)
High temperatures: Temperature limits the range and production of
many crops. The rate of growth and phenological development of
individual plant has been found to increase almost linearly from a base to a
limiting temperature threshold (Cesaraccio et al., 2001; Fealy and
Fealy, 2008). Vegetative and reproductive processes in tomatoes are
strongly modified by temperature alone or in combination with other
environmental factors (Abdalla and Verkerk, 1968). High temperature stress
disrupts the biochemical reactions fundamental for normal cell function in
plants. It primarily affects the photosynthetic functions of higher plants
(Weis and Berry, 1988). High temperatures can cause significant losses in
tomato productivity due to reduced fruit set, and smaller and lower quality
fruits (Stevens and Rudich, 1978). In pepper, high temperature exposure at the
pre-anthesis stage did not affect pistil or stamen viability, but high
post-pollination temperatures inhibited fruit set, suggesting that
fertilization is sensitive to high temperature stress (Erickson and Markhart,
2002). Hazra et al. (2007) summarized the symptoms causing fruit set
failure at high temperatures in tomato; this includes bud drop, abnormal flower
development, poor pollen production, dehiscence, and viability, ovule abortion
and poor viability, reduced carbohydrate availability, and other reproductive
abnormalities. In addition, significant inhibition of photosynthesis occurs at
temperatures above optimum, resulting in considerable loss of potential
productivity.
b)
Drought: Water greatly influences the yield and quality
of vegetables; drought conditions drastically reduce vegetable productivity.
Drought stress causes an increase of solute concentration in the environment
(soil), leading to an osmotic flow of water out of plant cells. This leads to
an increase of the solute concentration in plant cells, thereby lowering the
water potential and disrupting membranes and cell processes such as
photosynthesis. The timing, intensity, and duration of drought spells determine
the magnitude of the effect of drought. Efforts toward solving the problem
arising from drought by improving nutrient availability, uptake, transport and
accumulation in plants are based primarily on the selection of the tolerant
genotypes (Waraich et al., 2011). Apart from developing tolerant
genotypes, rational agricultural practices such as grafting, use of beneficial
micro-organisms, and application of organic matter, nutrients, and chemicals
such as proline, silicon and other osmoprotectances (Folkert et al., 2001)
have been recognized worldwide as additional strategies for improving nutrient
uptake and assimilation under drought conditions.
c)
Salinity: Excessive soil salinity reduces productivity
of many agricultural crops, including most vegetables which are particularly
sensitive throughout the ontogeny of the plant. In hot and dry
environments, high evapotranspiration results in substantial water loss, thus
leaving salt around the plant roots which interferes with the plant’s ability
to uptake water. Physiologically, salinity imposes an initial water deficit
that results from the relatively high solute concentrations in the soil, causes
ion-specific stresses resulting from altered K+/Na+
ratios, and leads to a buildup in Na+ and Cl-
concentrations that are detrimental to plants (Yamaguchi and Blumwald, 2005). Plant
sensitivity to salt stress is reflected in loss of turgor, growth reduction,
wilting, leaf curling and epinasty, leaf abscission, decreased photosynthesis,
respiratory changes, loss of cellular integrity, tissue necrosis, and
potentially death of the plant (Jones, 1986; Cheeseman, 1988).
d)
Flooding: Production is often limited during the rainy
season due to excessive moisture brought about by heavy rain. Flooded
tomato plants with low oxygen levels accumulate an increased production of a 4
ethylene precursor; 1-aminocyclopropane-1-carboxylic acid (ACC), in the roots
that causes damage to the plants (Drew, 1979). Severity of flooding symptoms
increased with rising temperatures. Rapid wilting resulting in death of tomato
plants is observed following a short period of flooding at high temperatures
(Kuo et al., 1982).
Strategies
for climate resilient vegetable production
Various management practices have
the potential to raise the yield of vegetables grown under hot and wet
conditions of the lowland tropics. Few of them are furnished hereunder:
a)
Water-saving irrigation management: If
water is scarce and supplies are erratic or variable, then timely irrigation
and conservation of soil moisture reserves are the most important agronomic
interventions to maintain yields during drought stress. Surface irrigation
methods are utilized in more than 80% of the world’s irrigated lands yet its
field level application efficiency is often 40-50% (von Westarp, 2004). The
water saving irrigation systems like sprinkler, drip, or other sub-surface
methods may be the suitable alternatives. It has been reported that the
water-use efficiency by chili pepper is significantly higher in drip irrigation
compared to furrow irrigation (AVRDC, 2005) and long term use of low-cost drip
irrigation system may be beneficial in terms of economic and labour benefits as
recorded in the case of cauliflower (von Westarp, 2004). The use of low-cost
drip irrigation is cost effective, labour-saving, and allows more plants to be
grown per unit of water, thereby both saving water and increasing farmers’
incomes at the same time.
b)
Cultural practices that conserve water and protect crops: Various crop management
practices such as mulching and the use of shelters and raised beds help to
conserve soil moisture, prevent soil degradation, and protect vegetables from
heavy rains, high temperatures, and flooding. Mulching helps to reduce
evaporation, maintains moderate soil temperature, reduces soil runoff and
erosion, protects fruits from direct contact with soil and minimizes weed
growth. In addition, the use of organic materials as mulch can help enhance
soil fertility, structure and other soil properties. Pandita and Singh (1992)
reported that mulching improved the growth of eggplant, okra, bottle gourd,
round melon, ridge gourd, and sponge gourd as compared to the non-mulched
controls.
c)
Improved stress tolerance through grafting: Grafting can provide
tolerance to soil-related environmental stresses such as drought, salinity, low
soil temperature and flooding if appropriate tolerant rootstocks are used. Tomato
scions grafted onto eggplant rootstock grow well and produce acceptable yields
during the rainy season (Midmore et al., 1997). Romero et al. (1997)
reported that melons grafted onto hybrid squash rootstocks were more salt
tolerant than the non-grafted melons. Solanum lycopersicum x S.
habrochaites rootstocks provide tolerance of low soil temperatures (100C
to 130C) for their grafted tomato scions, while eggplants grafted
onto S. integrifolium x S. melongena rootstocks grew better at
lower temperatures (180C to 210C) than non-grafted plants
(Okimura et al., 1986).
d)
Organic farming practices: Agriculture releases a
significant amount of carbon dioxide (CO2), methane (CH4)
and nitrous oxide (N2O) into the atmosphere amounting to around
10-12% of global anthropogenic greenhouse gas emissions annually, mostly methane
from livestock raising, biomass burning and wet cultivation practices, and
nitrous oxides from the use of synthetic fertilizers. If indirect contributions
(e.g., land conversion to agriculture, fertilizer production and
distribution and farm operations) are factored in, some scientists have
estimated that the contribution of agriculture could be as high as 17-32% of
global anthropogenic emissions (Bellarby et al., 2008). The challenge of
greenhouse gas emission could be met through organic agriculture. By increasing resilience within the agro-ecosystem, organic agriculture
increases its ability to continue functioning when faced with unexpected events
such as climate change (Borron, 2006). Resiliency to climate disasters is
closely linked to farm biodiversity; practices that enhance biodiversity allow
farms to mimic natural ecological processes, enabling them to better respond to
change and reduce risk. Thus, farmers who increase inter-specific diversity via
organic agriculture suffer less damage compared to conventional farmers
planting monocultures (Borron, 2006; Ensor, 2009; Niggli et al., 2008). Organic
farming practices that preserve soil fertility and maintain or increase organic
matter can reduce the negative effects of drought while increasing productivity
(Niggli et al., 2008). Water-holding capacity of soil is enhanced by
practices that build organic matter, helping farmers withstand drought (Borron,
2006). In addition, water-harvesting practices allow farmers to rely on stored
water during droughts. Other practices such as crop residue retention, mulching
and agro-forestry, conserve soil moisture and protect crops against
microclimate extremes. Conversely, organic matter also enhances water capture
in soils, significantly reducing the risk of floods (Niggli et al.,
2008).
Developing
climate resilient vegetables
Improved,
adapted vegetable germplasm is the most cost-effective option for farmers to
meet the challenges of a changing climate. Genotypes with improved attributes
conditioned by superior combinations of alleles at multiple loci could be
identified and advanced. Improved selection techniques are needed to identify
these superior genotypes and associated traits, especially from wild, related
species that grow in environments which do not support the growth of their
domesticated relatives that are cultivated varieties. Plants native to climates
with marked seasonality are able to acclimatize more easily to variable
environmental conditions (Pereira and Chavez, 1995) and provide opportunities
to identify genes or gene combinations which confer such resilience. Some
achievements in this context are highlighted below:
a)
Tolerance to high temperatures: AVRDC - The World
Vegetable Center has developed tomatoes and Chinese cabbage with general adaptation
to hot and humid tropical environments and low-input cropping systems. Some
vegetables such as peas, tomato, beans, capsicum are to some extent tolerant to
heat (Rai and Yadav, 2005).
b)
Drought tolerance and water-use efficiency: Plants
resist water or drought stress in many ways. In slowly developing water
deficit, plants may escape drought stress by shortening their life cycle
(Chaves and Oliveira, 2004). However, the oxidative stress of rapid dehydration
is very damaging to the photosynthetic processes, and the capacity for energy
dissipation and metabolic protection against reactive oxygen species is the key
to survival under drought conditions (Ort, 2001; Chaves and Oliveira, 2004).
Some
vegetable crops like melons or crop varieties viz. chilli
(Arka Lohit), tomato (Arka Vikas), onion (Arka Kalyan) and improved
varieties/hybrids of watermelon (Arka Aishwarya, Arka Akash and Arka
Madhura) are drought tolerant and thereby suitable for
rainfed farming (Hazra and Som, 1999; Rai and Yadav, 2005). Few recommendations
that may be taken into consideration under rain deficit moisture stress
conditions are as follows:
i.
Selection of suitable crops and varieties: Vegetable
crops like dolichos bean, cowpea, cluster bean, lima bean, chilli, drumstick,
brinjal, okra are suitable for rain-fed cultivation. Among these, legume
vegetables can be recommended for contingency crop-planning in an eventuality
of late monsoon rains.
ii.
Adoption of soil and moisture conservation techniques:
Contour cultivation, contour trip cropping, mixed cropping, tillage, mulching,
zero tillage, are some of the agronomical measures for the in-situ soil
moisture conservation.
iii. Enhancing soil organic
matter content: Incorporation of crop residues and farm yard
manure to soil improves the organic matter status, improves soil structure and
soil moisture storage capacity. Organic matter content of the soil can also be
improved by fallowing alley cropping, green manuring, crop rotation and
agro-forestry. Vegetable being short duration crop and having faster growth
phases, the available organic matter needs to be properly composted.
Vermicomposting can be followed for quicker usage of available organic matter
in the soil and improving the soil moisture holding capacity.
iv.
Moisture saving methods under limited water resource conditions: Under
limited water situations, water-saving irrigation methods like alternate furrow
irrigation or widely spaced furrow irrigation and drip irrigation systems can
be adopted. Studies conducted on methods of irrigation in capsicum, tomato,
okra and cauliflower indicated that adopting alternate-furrow irrigation and
widely-spaced furrow irrigation saved 35 to 40 per cent of irrigation water
without adversely affecting yield. Wide variety of vegetables can successfully be
grown using mulches. Besides, soil and water conservation, improved yield and
quality, suppression of weed growth, mulches can improve the use efficiency of
applied fertilizer nutrients and also use of reflective mulches are likely to
minimize the incidence of virus diseases. For vegetable production, generally
polyethylene mulch film of 30 micron thickness and 1.0 to 1.2 m width is used. Usually
raised bed with drip irrigation system is followed while laying the mulch film.
c)
Tolerance to saline soils and irrigation water: Tolerance
to saline conditions is a developmentally regulated, stage-specific phenomenon;
tolerance at one stage of plant development does not always correlate with
tolerance at other stages (Foolad, 2004). Success in breeding for salt tolerance
requires effective screening methods, existence of genetic variability, and
ability to transfer the genes to the species of interest. Screening for salt
tolerance in the field is not a recommended practice because of the variable
levels of salinity in field soils. Screening should be done in soil-less
culture with nutrient solutions of known salt concentrations (Cuartero and
Fernandez-Munoz, 1999). Most commercial tomato cultivars are moderately
sensitive to increased salinity and only limited variation exists in cultivated
species. Some vegetables namely melons, peas and onion are also salinity
tolerant (Rai and Yadav, 2005).
Conclusion
Adaptation to climate variability
and climate change requires long term strategic research on adaptation and mitigation
as well as technology demonstrations
and capacity building. For successfulness of the programme, it may require the combined efforts of many national
and international institutions or even public-private sectors linkages and an
effective and efficient strategy to be able to deliver technologies that can
mitigate the effects of climate change on the diverse crops and production
systems. The scientific information and technologies developed through these
initiatives must be readily accessible, consolidated and utilized in a
strategic way. This can only be achieved through collaboration,
complementarily, and coordinated objectives to address the consequences of
climate change on the world's crop production. Vegetable germplasm with
tolerance to drought, high temperatures and other environmental stresses, and
ability to maintain yield in marginal soils must be identified to serve as
sources of these traits for both public and private vegetable breeding
programs. Besides these, agronomic practices that conserve water and protect
vegetable crops from sub-optimal environmental conditions must be continuously
enhanced and made easily accessible to farmers in the developing world.
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