66 S.S. Jagtap, A.K. Chan Agricultural and Forest Meteorology 103 2000 59–72
the latex out of the cups, resulting in what is known as ‘wash-out’. When rains fall after tapping, the trick-
ling of water down the trunk may interfere with the ‘late-drip’ Wycherley, 1967.
3.4. Strong wind In the Asian humid and sub-humid regions, wind
speeds are generally in the region of 1–3 ms with stronger winds in coastal areas, reaching about 4 ms.
However, strong winds in the form of downdrafts from thunderstorms occur frequently. Damages from such
strong winds happen in various forms. Annual crops may be lodged and trees may be uprooted on soils with
impeded drainage or where rooting has been limited to the surface layers. Young plants may suffer stem
bending which requires corrective pruning or roping. Wind can also desiccate the plants during dry spells,
thus weakening and predisposing them to diseases. In Indonesia it was found that susceptibility of rubber tree
to wind damage was greatest at the time of maximum girthing and canopy development which was related to
the branching structure Dijkman, 1951. Trees with narrow crotches are particularly prone to breakage.
3.5. Forest fires Forest fires which usually occur during the dry
spells, result in not only loss of forest materials but also in widespread haze problem. During the 1997–1998
ENSO warm episode, thousands of hectares of forest in Indonesia were burnt, causing a thick blanket of
haze to envelop Indonesia, Malaysia, Singapore and Brunei. Haze not only causes health problems but
also reduces incoming solar radiation substantially, thereby lowering crop productions. It has been ob-
served that a significant decrease in oil extraction ratio in oil palm bunches in Malaysia appears to be
related to the occurrence of widespread haze caused by forest fires in one of her neighbouring country.
3.6. Pests and diseases Pests and diseases are common in the hu-
mid and sub-humid Asia. The perceptual warm and moist conditions favor the development of
many bacteriavirusvectors. It is not uncommon for widespread and often excessive use of pesti-
cideinsecticidefungicide to check the spread of these pests and diseases. However, it leads to pollution
of the environment. There is a growing opposition among the people to the use of chemicals to con-
trol pest and diseases. Pests and diseases particularly affect cocoa, which is grown in many parts of the hu-
mid and sub-humid areas of Asia. Estimates of losses in cocoa production due to diseases indicate values
of between 20–30 which are relatively high Pad- wick, 1956. Air humidity, temperature and rainfall
are the major meteorological factors influencing the development of cocoa diseases.
4. Challenges and future prospects
4.1. Technological needs The literature is replete with references to the inno-
vativeness of small farmers in Africa, and the fact that they have adopted new crops and improved practices
over a long period of time. A group consisting mainly of African scientists examined whether there currently
exists an important stock of appropriate technologies that are under-utilized due to policy and technology
transfer constraints Goldman and Block, 1993. They concluded that much greater emphasis needs to be
placed on resource management research emphasiz- ing rainfed systems, timely and reliable climate fore-
cast, and intensive production systems. Attempts to introduce input intensive, infrastructure dependent, ir-
rigation based technologies into Africa are generally likely to be met with failures, so technologies must
rely heavily on internal sources of inputs.
4.2. Agro-meteorological information needs The contact established between the agricultural
community and meteorological personnel and the im- proved services rendered open more avenues for more
agrometeorological services. The services required by the agricultural community are increasing and progres-
sively becoming more technical and more difficult to meet. From the basic and general queries of where,
what and when to grow, the agricultural community are now requesting information on the specific effects
S.S. Jagtap, A.K. Chan Agricultural and Forest Meteorology 103 2000 59–72 67
of various weatherclimate factors on crop growth and performance.
4.3. Management of water resources The demand for fresh water has also risen steadily
from agriculture, industry and human usage. A pru- dent water management policy is needed to distribute
available water to competing users in order to assure sustainability. There is also a need for vigorous, re-
newed investment in irrigation schemes that can raise yields while minimizing economic costs and environ-
mental damage. Farmers also know that the correct estimation and interpretation of moisture status of the
soil will be of help in deciding the best time for culti- vation, sowing, fertilizer applications and to maximize
use of limited water. Standard procedures are now available for estimation of crop water consumption us-
ing weather data as driving inputs. Such information needs to be disseminated widely to farmers. Methods
to better predict occurrence, continuation and cessa- tion of drought need to be developed. These methods
should also consider the soil characteristics and topog- raphy of the area involved. Such technique has been
used by various nations, particularly India, to help in planning of crop sequence.
4.3.1. Early warning system To be able to obtain and make available the infor-
mation of the weather and its impact on agriculture in the scale of the country, a national early warning sys-
tem needs to be set up in each country. The system can be used not only to mitigate the impact of bad weather
but also to help farmers to benefit from the effects of favorable weather. It also assists policy makers in their
formulation of marketing strategies. In this aspect, a Geographical Information System GIS, a well-tested
software, and satellite information will be of immense help. It is useful and appropriate for national meteoro-
logical agencies to acquire GIS in order to better serve the agriculture community. In Malaysia, the employ-
ment of satellite information has been used to monitor the performance of rice in her main rice bowl area.
A normalized vegetative index based on the values of two channels of the NOAA satellite had been de-
rived. The index was observed to be related with the amount of biomass of the crop. This exercise can be
further developed into a comprehensive early warning system.
4.3.2. Pestdisease management The threat of pest or disease losses is so great in
some agricultural practices that preventive or cura- tive action in the form of regular periodic spraying
is often taken. This may be effective, but it is not always economical and it has opened door to possi-
ble environmental pollution. Farmers now recognize that a sensible form of protection is to base applica-
tion of insecticidepesticide on weather conditions and know the relationship between the development of the
pestdisease and other environmental beside weather factors. The need for such techniques has been ex-
pressed often. However, limited resources within me- teorological agencies only allow them to meet a very
few of these needs.
4.3.3. Micrometeorology In annual crops of small stature, periodic destruc-
tive sampling of a portion of the crop can assess pro- ductivity. The carbon dioxide exchange with the atmo-
sphere can be determined by enclosing the plants in suitably ventilated chamber that measures the carbon
dioxide concentrations of the incoming and outgoing air streams. However, such methods are inappropriate
for large perennial tree crops such as oil palm, rubber and cocoa due to high cost of equipment, consider-
able technical expertise to operate and maintain them and the magnitude and complexity of data handling.
In view of the importance to the climate and agricul- ture of crop cover in the tropics, there is a need to ex-
tend the usage of such techniques to the tropics. Such extension will not only meet the need to monitor the
exchanges of gases and momentum over tropical crop cover but also facilitate the development of technical
resources in developing nations.
4.4. User requirements 4.4.1. Growing demand for agrometeorological
services The awareness of the importance of agrometeorol-
ogy among agricultural communities has grown and their level of appreciation of usefulness of agrome-
teorology has also risen. In the 1960’s and 1970’s,
68 S.S. Jagtap, A.K. Chan Agricultural and Forest Meteorology 103 2000 59–72
the national meteorological agencies were trying to educate and encourage the use of agrometeorological
services in agricultural activities. Besides requesting for weather forecast, the next most common area that
the agriculture sectors sought help was to know what crops to grow at a given location or where to grow a
selected crop. This question requires more background work before it can be satisfactorily answered. Some
agricultural agencies particularly the research insti- tutes have indicated the need to develop crop-weather
models to simulate growth and development of crops. Investigations in this area are still being actively pur-
sued and will likely yield more promising results for future practical application on a wider scale. The me-
teorological staff needs more training to cope up with the demand of agrometeorological services.
4.4.2. Better weather forecast The need of accurate weather forecasts by farmers is
one of their main requirements in agrometeorological services. The farmers need weather forecasts to plan
and organize their field activities. Accuracy of the tim- ing and as well as the location of weather phenomenon
are often crucial to their activities. In the earlier days, the most common expressed need in the use of mete-
orology in agriculture is simple short-range weather forecasts to plan or guide operational activities. Grad-
ually, the request extended to medium and long-range weather forecasts. Today, some agricultural agen-
cies are using short and medium range forecasts for planning daily, weekly and even monthly operational
field activities and long-range forecasts quarterly to 1 year to manage long term agricultural planning.
The capability of general circulation models coupled with an ocean model to predict ENSO warm and cold
episodes has increased the reliability and usefulness of long-range weather forecasts. This has helped the
agricultural community to be better prepared for the coming favorable or unfavorable weather conditions.
4.4.3. Micrometeorological techniques The request for micrometeorological measurements
in crop canopies has also increased. Users need help to measure fluxes of momentum, gases and water vapor
in crop canopies. Information and methods on artifi- cial modification of microclimate by means of shel-
ter belt, shading, mulching, evaporation suppression and others which alter the conditions of the air or soil
or air–soil interface surrounding the crops are also required. However, due to lack of human and finan-
cial resources, meteorological services could not meet most of these needs.
4.5. Application tools Agriculture,‘the most weather-dependent of all hu-
man activities’ Oram, 1989, is the endeavored most critical for human survival and the most important
sector of most national economies. People in Africa and Asia are particularly vulnerable to the impacts of
weather variability on agriculture due to its overde- pendence on rainfed agriculture. Agricultural vulner-
ability to weather variability is expected to increase as the population increases and more marginal lands are
brought into production. One of the reasons that cli- mate variability is often so devastating to agriculture
is that we do not know when to expect either favorable or unfavorable weather conditions, and we are thus
unprepared. Many critical agricultural decisions from timing of farm operation to policy-making have com-
plex interactions with weather conditions and must be made several months before the impact of weather.
If farmers had better weather predictions that are made sufficiently ahead of time, it may be possible to
modify decisions to decrease unwanted impacts and take advantage of favorable conditions. Conventional
empirical approaches are inadequate for addressing the complexity of the interactions between global cli-
mate, regional weather variability, decision making, agricultural productivity and economic responses.
The rapidly advancing information technology offers opportunities and challenges to agrometeorologists
to improve the service of meteorology to agriculture. Information may be communicated through electron-
ically using, for example, the Internet or networking. These means offers fast way to disseminate agrom-
eteorological information in useful formats to users. Research findings and new methodologies can be
packaged into user-friendly software for distribution among agricultural users.
4.5.1. Agroclimatic zonation In an attempt to meet the need of knowing what and
where to plant, some national meteorological agencies
S.S. Jagtap, A.K. Chan Agricultural and Forest Meteorology 103 2000 59–72 69
have divided their country into agroclimatic zones. These exercises essentially graded areas into suitabil-
ity zones according to the degree to which the cli- matic and soil resources have met the requirements
of selected crops. Maps have been produced for ma- jor crops of each country. However, the complexity in
the zonation and scale of the maps differ among the nations. The usefulness of the agroclimatic and crop
suitability maps depends on the accuracy of the data used, the viability of the methodology and the scale of
the maps. If the climate and soil data employed in the exercise is not reliable, and then the maps are not only
useless but also harmful because they could mislead planners. A common characteristic of soil and climate
data is that they have significant spatial variation. This factor also relates to the scale of the map. If the spa-
tial distribution of the data is sparse, then the maps need to be of smaller scales. It is pointless to produce
detailed maps using a coarse data set. However, maps without enough spatial details are not practically use-
ful. On the other hand, maps with proper scales are tools that agriculture planners or managers will not
want to do without. Whether the method used in delin- eating area into agroclimatic or crop suitability zones
is viable depends on how much is known about the crops, particularly their behavior in the changing envi-
ronment, and how well the climate of the location has been monitored. Presently in most part of the coun-
try, there are, relatively speaking, more reliable and available climate data with respect to time and space
than crop data. However, enough is now known about crops in general that it can be used to guide planning
activities in a more objective and scientific manner. A good agroclimatic and crop suitability zonation should
also include information on unsuitability of cropssites for chosen sitescrops. This information will help to
prevent misuse of land resources with possible conse- quences of failures of agricultural projects. Such fail-
ures have serious adverse impacts not only on the eco- nomics but also on the social-welfare of the people
involved in the projects.
4.5.2. Computer-assisted farming Advances in computer technology have been used
to improve agriculture. Software has been produced to assist agricultural activities. An example of this
is the ‘Enviromax’ — a PC-based user-friendly soft- ware for selecting rubber-planting material Rubber
Research Institute of Malaysia, 1983. In this system, the rubber-growing areas have been divided into envi-
ronments according to factors e.g. wind damage and fungal diseases that act as constraints in the selec-
tion of clones. Clones are recommended based on the underlying principle of maximizing the yield poten-
tial of a particular locality, subject to the inhibitory influence of wind damage, fungal diseases, problem-
atic soils and terracing, and moisture stress. The soft- ware is distributed with a small charge to plantation
rubber growers, thus enabling the widespread use of proper planting technology Leong, 1991. This soft-
ware is meant for professional rubber grower who has some knowledge on rubber cultivation. Another ex-
ample is DSSAT, the computer software for the deci- sion support systems which enables research scientists
throughout the world to gain access to the latest agro- nomic understanding of major food crops, now en-
capsulated within computer simulation models Jones, 1993.
A good example of the use of information tech- nology is demonstrated by the China Meteorologi-
cal Administration that developed practical software for agricultural use. The meteorological agency has
a pool of software experts that work in teams, often for years, to develop programs that meet specific agri-
cultural needs. Some examples are the programs de- veloped to use satellite data for monitoring crop per-
formances, land-use change, floods, and forest fire. A specific example is the software entitled Agrometeoro-
logical Information and Prediction System developed by the staff of Jiangsu Provincial Meteorological Bu-
reau. This program enabled a central office to receive and decode agrometeorological information from sur-
rounding stations, predict the productions of crops, an- alyze historical data and communicate the information
to users.
4.5.3. Integrated pestdisease management system Uncoordinated or uncontrolled application of in-
secticidepesticidefungicide often results in excessive use of chemicals that may harm human health and the
environment. It is equally effective if some chemical treatment can be carried out together with other con-
trol measures thus reducing the use and dependence on chemicals. This will not only reduce the harmful
effects on human health and the environment but also save money sometimes. For example, in certain loca-
70 S.S. Jagtap, A.K. Chan Agricultural and Forest Meteorology 103 2000 59–72
tions, a number of cocoa diseases can be controlled by simple field sanitation which might involve a change
in level of shade, or improved drainage, though in other cases spraying may be necessary. Considerable
success in controlling of cassava mealybug has been achieved in Africa using biological control agents col-
lected from ecologically similar areas where cassava originated. This was made possible using meteorolog-
ical homologues in the two continents Neuenschwan- der et al., 1989.
4.5.4. Crop modelling Models have been developed for projecting the
yields of crops. Some of them are statistical models while others are process-based simulation models.
Described further are some examples and uses of these models. There were studies Robertson and
Foong, 1977; Foong, 1981 which predict yields based on climatic factors using mathematical modelling.
Factors used were water deficit, solar radiation, maxi- mum and minimum temperatures. These factors were
found to be important at times corresponding to floral initiation, sex differentiation, spear elongation and
abortion. In another study by Ong 1982 in southern Malaysia, high correlation was found between yield
and rainfall and dry spells with temperature and sun- shine also being taken in consideration. Chow 1991
using a step-wise regression approach constructed a statistical model of crude palm oil production yield
with trend, season, rainfall and lagged yield. He found that 53–57 of the variation in crude palm oil pro-
duction can be explained by season effect, 12–24 by rainfall and 10–20 by lagged yield effect. Similarly,
using solar radiation data, Chan 1991 presented a simple method of predicting the potential yield of oil
palm of an area.
Use of the DSSAT family of models in Africa has been concerned with making better use of available
resources to optimize crop production in climatically variable regions. In recent years, many parts of Africa,
has witnessed phenomenal growth in maize produc- tion replacing traditional crops such as sorghum and
pearl millet. However maize is generally considered to be more susceptible to drought than sorghum or the
millets, and because of the uncertainty of the rains, there is a high risk of crop failure. Evidence also shows
that even in the case of Maize, a crop noted for its high input demands, fertilizer use by farmers is low
Byerlee and Heisey, 1992. Nitrogen use efficiency is often poor because of a number of loss mechanisms
whose extent and relative importance depend on the amount of rainfall received, fertilizer type, crop, fertil-
izercrop management, soil and climatic factors Legg and Meisinger, 1982.
In an attempt to assess nitrogen requirement by maize across agroecological zones in Nige-
ria, Amissah-Arthur and Jagtap 1995 used the CERES-Maize model to simulate seasonal variability
in maize yield subjected to rainfall and N fertilization. The sites Onne, Ibadan, Kaduna, and Kano differed
greatly in terms of rainfall received, thus providing contrasting conditions for maize production. Seasonal
rainfall across the sites were divided into low, normal and high rainfall seasons on the basis of cumulative
probability of growing season rainfall deviations from the mean. Large yield responses to N levels among
sites and between seasons were observed because of seasonal rainfall variability. During normal rainy
seasons, farmers could heavily fertilize their maize without undue risk of crop failure. The risk could
be further reduced by strategies that minimize N losses by mulching or split applications. The simu-
lation study showed that the ‘optimum management’ strategy varied among the zones to N and rainfall
regime. Therefore, it may be impossible to identify a single fertilizer strategy that is optimal across sites
and seasons. Linking climatic forecasts of expected seasonal rainfall with appropriate crop models would
enable assessment of the cropping potential of a pe- riod or area and the risks of yield variability. Such
information could enable tactical intra-seasonal crop management planning and decision making especially
as regards fertilizer use.
5. Summary
