SRM 212 NOTE COMPILED.pdf

Agricultural Meteorology, its scope & aims Aims The primary aim of agricultural meteorology is to I extend and utilize fully our knowledge of atmospheric and certain associated processes with the objective of maximizing food production and almost equally important secondary aim relates to maximizing...

Agricultural Meteorology, its scope & aims Aims The primary aim of agricultural meteorology is to I extend and utilize fully our knowledge of atmospheric and certain associated processes with the objective of maximizing food production and almost equally important secondary aim relates to maximizing the production of timber and other forest products certain vegetable fibres e.g. cotton, flax and sisal, natural rubber and animal by-products e.g. hides. The very proper concern with the conservation of natural resources and protection of the environment from detrimental usage or even destruction may place constraints upon a particular form of land use in a particular place and time (def. of sustainability). The agricultural meteorology may be and indeed should be constructed when questions of land use come up of the exploitation of resources and the deployment of technological processes are being examined. Short period benefits from the cultivation of semi-arid grasslands may well be at the expense of long period damage of erosion by wind and water. A meteorologist must be prepared to take into consideration processes having very different time scales. The subject of meteorology: The subjects include: (a) The earth (physical sciences; specifically; the physics of the atmosphere i.e the meteorology and the climatology) but also soil sciences and hydrology. (b) Certain biological sciences specifically botany, animal physiology and pathology and associated technologies of agriculture. Agricultural meteorology is concerned with interaction between meteorology and hydrological factors on one hand. Agriculture in the widest sense including horticulture, animal husbandry and forestry on the other hand. Its objects is to discover and define such effects and thus to apply such knowledge of the atmosphere to practical agric. use. N.B: Its field of interest extends from the soil layer of the deepest plant and tree roots through the air layer near the ground in which crops and wood grow and animals live to the highest level of interest in aerobiology. The latter with particular reference with effective transport of seeds, spores, pollens and insects in addition to natural climate and its local variations. Agric. meteorology is also concerned with artificial modifications in environment as brought about e.g. by wind breaks and shelter belts, irrigation and glass houses. Green house allows radiation of light. Air does not flow freely (covered by glass) and traps heat, while screen house is covered by wire netting and protects plants from insect attack. The manual consideration of the relationship between weather and agriculture involves enterprises that may be conveniently classified under 6 main headings. 1. Soil 2. Plants, 3. Farm animals 4. Diseases and pests of crop and animals 5. Farm buildings and equipments 6. Artificial modifications of the meteorological and hydrological regimes. A brief discussion of these 6 items from an agro-meteorological point of view: 1. Soil: Weathering is an important factor in creating and determining the nature of a soil. Climate and weather affect the mechanical, physical and chemical properties of the soil, the organisms it contains and its capacity for retaining heat & moisture. Rainfall on one hand adds chemical constituents to the soil and on another hand washes out (leaches) soil nutrients. The mechanical state of the soil affects cultivation, pest control, harvesting of crop plants. Management of pastures (i.e. stocking density, which is the number of animals per unit grazing land) is much influenced by local weather conditions. The worldwide problems of erosion both by wind and water are vitally influenced by regional and local weather conditions. The extent to which a given trace of land succumb to erosive agents or agencies is largely determined by the presence and vigour of vegetative cover. In all regions with marked seasonal variation in weather, the seasonal changes decisively influence soil conditions and hence the farming programme “Calender”. e.g. the beginning and end of rains. 2. Plants: (botany): is affected at every stage of its growth by environmental conditions. The weather influence further extends to the period before planting and after harvesting (for storage purposes). The quality of the seed sown depends on meteorological conditions during the year in which it was produced and even during previous years while the productivity of certain plantation crops e.g vines, grapes, apple, citrus, timber can be affected by weather over many previous seasons. Post-harvest operations such as drying of grains and other crops are affected by seasonal weather, also is the capacity of food, vegetables farm products to retain their quality in storage. Weather factors play an input role in the occurrence of or defense against forest and grass fires. 3. Farm Animals: Apart from the direct effect of climate on all styles of growth and condition of both the healthy and well fed, as well as the ill-fed and diseased animals, it is expressed through the effect of excess heat or cold. Weather affect livestock critically through the food supply (i.e the crops in terms of their food supply and the soil on which they are kept). It affects their feeding, growth, fecundity (ability to reproduce/lay eggs) and health, and in consequence their geographical distribution. The yield and quality of animal products and their processing are affected. The capacity for storage and transport are also affected. 4. Diseases and Pests of Crops and Animals: Here the effect is 3 fold. Weather influences the susceptibility of plants and animals (i.e. the host) to attack by pest and diseases. It also enters into the biology of the insect and disease organisms thus affecting the nature, numbers and activities of pests and the extent and virulence of the disease (spread and persistence). In important cases, epidemiology of the disease (spread & aerial transport) and its control or eradication depend upon atmospheric agencies. 5. Farm buildings and Equipment: Climatic conditions must be taken into account in the planning of farm buildings and particularly in the design of farm housing and stores for agricultural produce. The choice of farm machinery, its upkeep and the optimum deployment in any situation of both machinery and labour is weather-sensitive. 6. Artificial Modifications: Artificial modifications of meteorological and hydrological regimes e.g. artificial rains in which silver iodide is sprayed into the air and changes climatic condition of the atmosphere causing condensation. Wind breaks and shelter belts, storage and conservation of snow and water (water harvesting). Also, soil cultural practices have an important influence on certain aspects of the local environment such as soil moisture, wind velocity and atmospheric humidity. The greatest degree of control of environmental condition is exercised by the use of glass houses and in intensive animal housing. While varying degrees of independence of external ambient conditions are achieved (at times, at very high degree the cost in materials and energy to achieve this independence will tend to increase as the difference between the desired internal climate and the weather and climate in impinging on the outer shell of the structure becomes greater. Included under this heading is the assessment in relation to agriculture both qualitative and quantitative of climate change aided by or triggered off by man’s activities e.g. changes in the CO2 content of the atmosphere due to the combustion of fossil fuels such as coal and oil. Types of Agro-meteorological problems 1. Protection against or avoidance of adverse production or conservation should be given. This is because disaster always arise more commonly than success. Many potential disaster can to a significant extent be avoided or at least its impact reduced by human action. This danger include: The incidence and extent of pest and diseases of animal and crops. The pollution of the air, soil, the crops and animals, soil erosion, the environmental stress on crops and the animals and the limits and constraint imposed on all farm operations. The danger of forest and bush fires, losses during storage or transport. In Sudan, a few economic benefit are given i.e. in the Sudan gezira irrigation scheme, the traditional crop growing sequence is groundnut. June, July. Then Dura (Sorghum) in July. Cotton in July, August and finally wheat in November to the extent that irrigation H2O remains available. In early 1960. The total H2O area under wheat as established somewhat arbitrary so that in some years the amount of H2O is insufficient to properly irrigate the wheat field. While in other years unused H2O flow down the river. More recently fairly precise calculation of the total H2O required by the cotton, sorghum and groundnut crops for the remainder of their growth cycles have been made in October compared with the irrigation H2O available and the remaining volume of H2O and the potential area of wheat that could be irrigated correctly will be calculated. The net effect has been that an average of about 20,000 acres have been grown under wheat in addition to the area grown earlier adding about 20,000 metric tonnes of more than 2 million US dollars to the national economy. Gambia – In Gambia farmers store their groundnut in heaps in the open air after harvest until the buying agents pass to collect the crops, such heaps could be seen until January. Storage in the open air is favoured because it permits continuous ventilation with the relatively dry air. If the dry pods are subsequently wetted, the risk of contamination with Aspergillus flavus and Subsequent aflatoxin development is great. The price of aflatoxin infected groundnut is often as low as 60% of the price of good groundnut. During these months seasonal rain can occur if there is an incursion of polar air at altitude. Provision of weather information by local weather broadcast can warn farmers of an impending chance of rain so that they can temporarily cover the crop with plastic sheetings saving about 60 US dollars per tonne. Thanks to such broadcast for each % of production saved. The benefit is about 60 thousand US dollars. Meteorological Institutions WMO: World Meteorological Organization: Is a specialized agency of UN with the responsibility of collection and exchange of meteorological observation, information and publication to enhance and promote meteorology throughout the world. The main objective of World Meteorological Organization (WMO) include: (1) to facilitate worldwide cooperation in the establishment of meteorological station network (2) to keep abreast of and promote meteorological development in relation to agricultural meteorology in the scientific and practical field (3) to provide standard methods, procedure, techniques in meteorology including agricultural meteorology (4) to promote rapid exchange of weather information and the standardization and publication of weather observations (5) to study and formulate requirements in the field of agricultural meteorology (6) studying questions relating to observations, measurements, evaluation and suitable presentation of simple or complex factors of weather or climate as they affect soil, plants, animals and their enemies (7) consider the meteorological implications of biological observations (8) applying knowledge of all branches of meteorology to agriculture and provision of advice in these fields (9) provision of advice on weather including forecasting and warning for agricultural purposes. National Meteorological Service The national meteorological service is a scientific institution which discharges all public services related to meteorology at both national and international levels. Nigerian Meteorological Agency- NIMET Major Functions:- (1) to organize, operate and maintain a network of surface or other observation stations (2) to evaluate, process and store observation data (3) establishment, operation, maintenance of an effective telecommunication system. For collection and dissemination of both observed and processed data (4) to promote meteorology throughout the world by international cooperation (5) the national weather service also provides meteorological information and advice including weather forecast; climatological statistics and information of physics on the atmosphere. Others are: FAO- Food and Agriculture Organization WWW- World Weather Watch WCP- World Climate Program AGRHYMET- WMO Regional Centre for Training in Agricultural Meteorology and Hydrology CAgM -Commission for Agricultural Meteorology UNEP- United Nations Environment Programme FCCC- Framework Convention on Climate Change INSAM- International Society for Agricultural Meteorology CGIAR- Consultative Group for International Agricultural Research ICRISAT- International Crops Research Institute for the Semi-Arid Tropics CCAFS- Climate Change Agriculture and Food Security Atmosphere The composition of the Atmosphere The atmosphere can be described as a thin layer of odourless, colourless and tasteless gases held to the air by force of gravity. The atmosphere comprises a stable mechanical mixture of gases. The most important of which is Nitrogen, Oxygen, Argon, CO2, Ozone and Water vapour. Other gases occur in very small proportion and they include: krypton, helium, methane, hydrogen. The Nitrogen : 78.09%. O2 : 20.95%. Argon : 0.93%. CO2 : 0.03% (variable). Neon : 0.002%. Krypton & Helium : Less than 0.001% (5mm is considered a hailstone. Other condensation phenomenon includes; dew, fog and frost. Dew: is the condensation of water vapour on a surface whose temperature has been reduced by radiative cooling to below the dew point temperature of the air in contact with it. Fog: is used to describe the obscurity in the surface layer of the atmosphere in which visibility is less than 1km. This obscuring may be due to minute water droplet or smoke particles or both suspended in the atmosphere. Frost: frost is said to be formed when the temperature of the air in contact with the ground or at screen level (about 1m above the ground) is below freezing point. Giving ground frost and air frost respectively, the term frost also describes icy deposits on the ground. Precipitation types 1) Convective type of precipitation: is caused by vertical motion of an ascending mass of air which is warmer than its environment. Convective type of precipitation is usually more  intense than cyclonic or orographic precipitation though it is normally shorter in duration. Convective type of precipitation is often accompanied by thunderstorm. This type of rainfall is common in the Southern part of Nigeria and in the North i.e. early part of the rainy season. 2) Cyclonic/Frontal precipitation: it is caused by large scale vertical motion of air associated with low pressure system like the depressions. Precipitation is moderately heavy, continuous and affects very extensive areas as the depression moves. Cyclonic precipitation is not as intense as the convective type but has longer duration. Often cyclonic precipitation lasts for 6-12 hours and is a common type of rainfall in Southern Nigeria and Southeast Asia. 3) Orographic/Relief precipitation: is usually defined as precipitation that is caused entirely or mainly by the force uplifting moist air over high ground. In areas liable to orographic rainfall, the hilly areas receive more precipitation than their surrounding lowland. In addition, the windward side of the mountain are known to receive more precipitation than the leeward side. The leeward side suffers from what is referred to as the Rain Shadow effect of the windward slope. The degree of the influence of mountain on precipitation depends on their size and their alignment relative to the rain-bearing wind. Question: Assuming you are given a record of 15mm of rainfall, how much will you have deposited on 1 hectare of land if the water was not allowed to float or infiltrate into the soil? Calculate what depth of water in mm that is needed to fill a circular dam that has a diameter of 10m Note: Rainfall intensity = amount of rainfall per unit time Measurement are done in fluxes. Flux is quantity per unit area per unit time e.g. in measuring rainfall, evaporation, radiation, evapotranspiration. Measurement of Weather Data Types of weather stations: (a) Automatic weather station (electronic device) or (b) Conventional weather station. Instruments used 1) Cup anemometer: for measuring wind speed while Wind vane is used to measure wind direction. The set up uses solar power i.e. batteries that are rechargeable. It has a high memory capacity computer that collects data and information and stores it. It can also program the information and it takes record for every 30 second Types of Sensors a) Temperature and humidity sensors (b) Sensors for solar radiation 2) Pyranometer: measures incoming solar radiation the sun produces in a specific location  3) Rain gauge: an electric device for measuring amount of rainfall. It has two buckets called tipping bucket rain gauge. It has a funnel with an opening ensuring droplets entry of rainfall. Any drop 2mm in size would tip the bucket. Every tip is 0.2mm and sends that as the number of tips received. Number of rainfall per unit time = number of tips × 0.2mm 4) Stevenson screen: is an enclosure containing thermometers (max. and min. thermometers) with a purpose of providing standardized environment in which to measure air temperature (max. and min. temperature), humidity, dewpoint, and atmospheric pressure. Wet and dry bulb thermometer is used to determine relative humidity, dew point and vapour pressure. The wet thermometer is kept wet by a wick which is placed in distilled water to keep it wet. 5) Piche evaporimeter: used for measuring evaporation from surfaces and transpiration in plants. 6) Campbell/Sunshine recorder: measures hours of sunshine. It has cards which are replaced daily because they burn and is calibrated with grooves. Types of cards include summer cards, equinox cards and winter cards. The ball absorbs solar radiation and the card burns. 7) Earth thermometer: used to measure earth temperature 8) Evaporation tanks: used for measuring rate of evaporation. The types of tanks are (a) raised tank, (b) sunken tank, (c) class A evaporation tank. In the class A evaporation tank, water is measured into the tanks with the aid of a calibrated cup. The evaporation tank has a flannel gauge which is calibrated with a pin. As evaporation increases, the pin becomes visible Surroundings of a weather station 1) It should have a plain slope 2) All grasses should be kept low (well mowed) 3) Trees should not be too close to prevent obstruction 4) There should be a source of electricity 5) It should be well fenced Thermometers The instrument used in the measurement of temperature is thermometer. There are various types of thermometers; alcohol in glass, mercury in glass, resistance thermometer, thermistors, voltage/EMF-based thermometers, and thermocouple. The mercury in glass has the dry bulb and the wet bulb. The temperature of the wet bulb will always be lower than that of the dry bulb.  1) Dew point thermometer: is used to know the dew point temperature. The dew point temperature is the temperature in which the surface must be cooled for water to condense on it. DP < WB < DB (DP – Dew point, WB – Wet bulb, DB – Dry bulb) The principle of temperature measurement is based on expansion and contraction i.e. Liquid in glass is capable of expanding and contracting. If the temperature is high, it expands and when it cools, it contracts. 2) Resistance thermometer: are sensors used to measure temperature. Wire’s resistance to voltage is based on temperature 3) Thermocouple: a temperature-measuring device consisting of two wires of different metals joined at each end. One junction is placed where the temperature is to be measured, and the other is kept at a constant lower temperature. Measurement for radiation The instrument most commonly used to measure the fluxes of the global, reflected, direct and diffused solar radiation is called Pyranometer. The sensing elements is the thermopile with black and white segments. Since black absorbs and white reflects radiation, these segments develop different temperatures. The greater the flux density of the radiation, the greater the temperature difference that develops between the black and white areas. Pyranometer is also called Solarimeter. Temperature difference is sensed by a differential thermopile whose output is nearly linear with the flux density of the solar radiation. The glass cover of the pyranometer is a called a dome and must be of a material that permits transmission of the major portion of the solar spectrum. Standard glass dome are permeable to radiation from about 0.28–2.8µm. Equipped with a shaded ring, the same apparatus allows the measuring of diffused radiation with a correction coefficient that depends on the type of shaded ring. Placed back to back a pair of pyranometer enables measurement of a fraction of radiation reflected by the ground or by the vegetation, such an apparatus is called an Albedometer. Photosynthetic Active Radiation (PAR): This is usually measured with filtered photosensitive cells whose sensitivity curve is approximately copying that of solar radiation, between wavelengths of 0.4 and 0.7 µm, physiologists express these values in µmoles of CO2 or in Einsteins (Quantum meters). They are really energy storage measurements of received energy in Watt/m2. Measuring the actual duration of bright sunlight Classic sunshine recorders consist of a sphere of pyrex glass (or crystal) that allows the focusing of sunrays on a pond situated on a special card, The card starts browning when direct radiation is near 120 Watt/m2. The hours and tenths of an hour are counted on the card where the paper burns. Measuring and estimating wind speed and direction 1) Anemometers: for agrometeorological purposes an accurate knowledge of the quantity and blowing wind in meters or km/hr is necessary. This factor among others influences evapotranspiration in plants. Windbreaks are designed to reduce wind speed and thus protect the crops from mechanical damage and to reduce wind erosion. Anemometers are generally used as wind totalisators for wind run measurements by placing them at 2m and 10m above the ground. For precise studies of wind gradient above crops, three or preferably more anemometers are placed vertically above the surface of the crops from 0.2mm upwards and measurements are taken at frequent intervals from 1 minute to 1 hr. There are several types of anemometers, the most reliable are the cup counter anemometers. 2) Wind vane: It tells one the local direction of wind. Caution must be taken in the use of wind vane as it is greatly influenced by nearby obstacles and even by the characteristics of the wind near the ground. 3) Wind cone: It estimates wind speed and direction. It is a very simple instrument being a sleeve of linen opened at its extremity. It is very useful in open terrain and is found at each airport where it offers relevant information to pilots, allowing them to quickly and easily determine the approximate wind speed and direction before taking off or landing.