BS 7562-3 irrigation.pdf

BRITISH STANDARD BS 7562-3: 1995 Planning, design and installation of irrigation schemes — Part 3: Guide to irrigation water requirements British Turf and Landscape Irrigation Association Health and Safety Executive National Farmers’ Union National Rivers Authority Silsoe College. having been prepared under the direction of the Engineering Sector Board. upon which the following bodies were represented: ADAS Agricultural Engineers’ Association British Agricultural and Garden Machinery Association Ltd.BS 7562-3:1995 Committees responsible for this British Standard The preparation of this British Standard was entrusted to Technical Committee AGE/30. Date Comments The following BSI references relate to the work on this standard: Committee reference AGE/30 Draft for comment 88/73803 DC ISBN 0 580 25375 9 . Irrigation and drainage equipment. No. Cranfield Institute of Technology Silsoe Research Institute UK Irrigation Association Well Drillers’ Association This British Standard. was published under the authority of the Standards Board and comes into effect on Amendments issued since publication 15 December 1995 © BSI 10-1999 Amd. BS 7562-3:1995 Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 References 1 3 Definitions 1 4 Design considerations 1 5 Crop water requirements 2 6 Soil water 2 7 Irrigation efficiency 8 8 Choice of irrigation program 8 Figure 1 — Typical soil classification triangle 3 Figure 2 — Typical range of crop effective rooting depths 4 Figure 3 — Typical infiltration rate relative to time for different soil types 5 Figure 4 — Typical effect of droplet size on infiltration rate 6 Figure 5 — Effect of crop cover percentage and crop type of infiltration rate 7 Table 1 — Available water holding capacities of soils 3 Table 2 — Typical effect of slope on reduction of infiltration rate 5 List of references Inside back cover © BSI 10-1999 i . It embodies the experience of engineers successfully engaged on the design and construction of irrigation schemes so that other reasonably qualified engineers may use it as a basis for the design of similar irrigation schemes. design and installation of irrigation schemes in the UK. Users of British Standards are responsible for their correct application. — Part 5: Guide for irrigation equipment. It is intended for the use of engineers and farmers having some knowledge of the subject. ii © BSI 10-1999 . an inside front cover. It is the responsibility of engineers concerned with the design and construction of schemes to remain conversant with developments which have taken place since publication. — Part 6: Guide for feasibility and implementation procedures. This will be indicated in the amendment table on the inside front cover. A British Standard does not purport to include all the necessary provisions of a contract. pages 1 to 10. inevitably. This Part of BS 7562 contains information and represents good practice at the time it was written and. — Part 2: Guide for acquisition of site data. This standard has been updated (see copyright date) and may have had amendments incorporated. Compliance with a British Standard does not of itself confer immunity from legal obligations.BS 7562-3:1995 Foreword This Part of BS 7562 has been prepared by Technical Committee AGE/30 and contains recommendations on good practice in the planning. — Part 4: Guide to water resources. pages i and ii. — Part 3: Irrigation water requirements. an inside back cover and a back cover. BS 7562 has been prepared in six Parts as follows: — Part 1: Glossary of terms. Summary of pages This document comprises a front cover. technical developments may render parts of it obsolescent in time. Water availability should be Subsequent amendment to. field capacity Climate data on a location close to the irrigated 3. 2. 1) From 1 April 1996 the Environmental Agency will be the appropriate authority to contact. These normative references are cited BS 7562 shows how this essential information can at the appropriate points in the text and the be assessed. 3. or revisions of. irrigation water requirements.1 General In designing an irrigation system it is essential that 2 References the total amount of water to be applied over the 2. growth stage of the crop and crop variety.2 Rainfall (AWC) that can be used by the crop without The designer should decide to what extent. write to Customer Information.4 irrigation cycle This Part of BS 7562 gives guidance and information on irrigation water requirements. London W4 4AL. Editions of A seasonal profile of the crop water requirement of these publications current at the time of issue of this each crop should be determined to assess how often. by reference. © BSI 10-1999 1 . 3 Definitions The peak water requirement should also be established as this determines the irrigation system For the purposes of this Part of BS 7562 the capacity. the crop value and response to water and economics of the design.2 area.1 Normative references growing season is specified as well as how this will This Part of BS 7562 incorporates.1 view varied. should be soil water reservoir obtained. definitions given in BS 7562-1:1992 apply together Rainfall levels are an important factor in the design with the following. The rainfall data obtained need to be soil water deficit site specific due to for example. of irrigation systems as UK weather conditions are 3. commenced. adversely affecting its growth that monthly rainfall figures are taken into account NOTE This is normally regarded as water available at tensions in the irrigation system design. This Part of BS 7562 refers to other publications that provide information or guidance. over a recent 20 year period. particularly as peak provisions from specific editions of other demands are likely to be experienced. but and by how much. the time between the start of successive irrigation applications on the same field It covers the subjects of crop water requirements. BS 7562-3:1995 1 Scope 3. it will need to be supplemented reference should be made to the latest editions. standard are listed on the inside back cover. scheduling and total volumes of water required for the design and 4 Design considerations operation of irrigation schemes. any of checked with the local National Rivers Authority these publications apply to this Part of BS 7562 only (NRA)1) office before any detailed planning is when incorporated in it by updating or revision. irrigation schedules for design purposes. vary through the season. 4. with irrigation. outset of the project. rain shadow areas the amount of water required to restore the soil to and exposed coastal sites. if at all. BSI.3 NOTE The detailed calculations required in these estimates easily available soil water can be processed with the aid of a suitable computer program2). 2) For information on the availability of a suitable computer program. This Part of publications. The value of the fraction depends mainly on the soil type but also on the type of crop and its transpiration rate. This should provide a reliable estimate of average weather conditions given the considerable the water storage available in the soil within the annual variation in weather experienced in the UK. effective rooting depth of the crop Shorter periods will reduce the accuracy. This decision will be of 2 bar or less. This NOTE The soil water reservoir is affected by variation of root weather data can then be used to simulate possible depth. 389 Chiswick High Road. based on many factors including the level of risk at which the site owner wishes to operate. This information establishes requirements for licensing and storage purposes.2 Informative references Two important issues should be considered: seasonal and peak irrigation requirements. that fraction of the available water holding capacity 4. This assessment should be made at the publications are listed on the inside back cover. and general climatic equation: conditions. is given by the stages of crop development.3 Crop factors can enter the soil and be stored in the root zone to be The crop factor or crop coefficient kc.BS 7562-3:1995 Only a proportion of high intensity and heavy rains 5. salinity of soil and the E is evaporation (in mm). is determined approximately by field sampling or provided by irrigation. method of irrigation. largely reference crop.3). more accurately by a simple laboratory technique. The way water crop cover. Rae = Rt – (O + P + E) It is essential to collect local data on the crop where growing season and the rate of crop development. Its accuracy. 5 Crop water requirements Typically for design purposes. All of these should be considered at the system planning stage. This is known as the moves into the soil. climate. Soils vary widely in their available water holding ETr is the reference crop evapotranspiration capacity (AWC) ranging from low water holding (in mm) (see 5. silt and clay allows for different stages of crop growth. 5.1 Soil types Factors affecting CWR are climate. capacity in sandy soils to high water holding capacity in clay loam soils (see Table 1). status of soil water. of roughly 50 %. the reference crop by means of a crop factor which The relative proportions of sand. CWR can be calculated using the The soil type determines the amount of water that modified Penman approach [1]. are nearly 100 % effective in this respect. effective rainfall. CWR is particles in the soil. In the UK. the infiltration rate. Rae (in mm). the reference crop is grass determines the design of the water application grown to a specific height. when used for calculations under UK climatic conditions.2). This approach the soil can hold for crop use and affects the determines the water requirements for a full green calculated average irrigation cycle. Frequent light rains between potential crop evapotranspiration (ETcrop) intercepted by plant foliage with full ground cover and the reference crop evapotranspiration (ETr). crop type and stage of growth. the one normally used. The factors which should be taken into account The effective rainfall should be considered in the when selecting the appropriate kc value include the system design and planning. Typically CWR varies between 400 mm and 800 mm per season. is the ratio usefully used by the crop. kc is the crop factor (see 5. generally falls within ± 10 % and rarely exceeds a variation of ± 20 %. This is met in The water holding capacity of a soil can be part by rainfall and the shortfall.1 General Crop water requirements (CWR) are the basis of the 6 Soil water design and operation of an irrigation system. calculations are done on a monthly basis. 6. freely transpiring. in the UK. The agriculturally crop characteristics. Other crops are related to system.e. time of planting or sowing.2 The modified Penman approach is not all easily available to the crop and the The modified Penman formula for the calculation of irrigation system design should take account of this ETr is the most accurate of several methods and is in the calculation of irrigation cycles. 5. 2 © BSI 10-1999 .4 Crop evapotranspiration O is the run-off (in mm). where Standard soil analysis methods identify the ratio of sand. silt and clay (see Figure 1). Factors which can affect the crop evapotranspiration (ETcrop) include aspects of the P is the deep percolation (in mm). together with the amount of given (in mm) by the equation: organic matter or humus determine the soil texture. CWR = kcETr The soil texture triangle shows the 11 soil classes. The water theoretically available in a particular soil 5. i. Rt is the total rainfall (in mm). Figure 1 — Typical soil texture classification triangle Table 1 — Available water holding capacities 6. BS 7562-3:1995 NOTE This figure is reproduced by permission of ADAS from reference [2]. Sandy clay 170 b) the age of the crop and its stage of development. Peats 350 © BSI 10-1999 3 . Silty clay loam 160 d) the type of soil management. The rooting depth for the holding capacity same type of crop varies considerably according to Soil type (AWC) mm/m the type of soil.2 Crop effective rooting depths of soils The rooting depth of the crop determines the extent Available water of the soil water reservoir. Sandy silt loam 190 g) the water supply in the early part of the Silt loam 220 growing season. Clay 180 e) the amount and placement of soil nutrients. Clay loam 170 c) the soil type. Silty clay 180 f) the nature of the soil drainage. Sandy 80 Variation of root depth occurs for additional reasons (which need to be taken into account by the Loamy sand 120 planner): Sandy loam 170 a) each crop and species of crop has its own Sandy clay loam 170 specific root system (see Figure 2). for example. a ring EAWC is approximately 50 % of AWC. b) soil structure. f) crop type and crop cover percentage This ensures that water is applied at the most (see Figure 5). 6. depth and may need to be taken into account. infiltrometer.1 General d) droplet size (see Figure 4). 4 © BSI 10-1999 . essential for the design of the irrigation system. include: It should be noted that the proportion of water abstracted by the plant roots varies according to a) soil texture.2 Determining infiltration rate in the field Easily available water capacity (EAWC) can be Infiltration rates can either be assessed from determined from published information but in the published tables/graphs or from actual absence of this. efficient rate without causing compaction.5. erosion or damage to the crop or soil.5. 6. it is common practice to assume that measurement in the field using.5 Infiltration rate c) slope of soil (see Table 2).3 Easily available water 6. An accurate knowledge of the soil infiltration rate is e) soil water content.4 Soil water depletion Factors affecting the infiltration rate of the soil (see Figure 3).BS 7562-3:1995 Figure 2 — Typical range of crop effective rooting depths 6. 6. BS 7562-3:1995 Figure 3 — Typical infiltration rate relative to time for different soil types Table 2 — Typical effect of slope on reduction of infiltration rate Slope Reduction of infiltation rate % % 3–5 10 6–8 20 9–12 40 13–20 60 U 20 75 © BSI 10-1999 5 . BS 7562-3:1995 Figure 4 — Typical effect of droplet size on infiltration rate 6 © BSI 10-1999 . BS 7562-3:1995 Figure 5 — Typical effect of crop cover percentage and crop type on infiltration rate © BSI 10-1999 7 . 7 Ground water contribution is 25 mm at a 30 mm SWD so as to make good most Shallow groundwater contribution can affect the of the deficit but leave a small margin for water required by the crop. decreases with time as the crop cover increases. common practice in the UK to leave a small SWD However. For example a common irrigation application 6. applications varies considerably with crop water requirements. which allows a balance sheet of SWD to be drawn balance sheet but several computer programs are commercially available that can help to perform this function. Traditional design practice calls for a 10 % The soil will only hold a certain amount of water and allowance to cover water loss between the therefore in heavy rain or when irrigation is applied application head and the crop. The irrigation cycle I (in days) is given by the equation: I = EAWC ------------------ CWR 8 © BSI 10-1999 . The common practice is to accept a 30 mm the crop water needs can be met from this source. The plan for each crop should state the level of SWD Evaporation from the soil surface.8 Soil water deficit part of the growing season to reduce the incidence of Winter rainfall usually ensures that most soils are scab and so improve the quality of the crop. run-off more than one recording position may be necessary. On soils important. SWD depending on the type of crop. maintained. In order to manage the irrigation system the Changes in SWD for each crop should be recorded changes in SWD should be followed on a daily basis daily. SWD level for many irrigated crops in the UK but it Accurate estimates of this effect are difficult to will need to be reduced for soils with a very low make but an attempt should be made to adjust for water holding capacity or for shallow rooting crops this extra supply of water where it is likely to be including those at an early stage of growth. evaporation from the soil gradually margin to allow for subsequent rainfall. It is until the crop achieves 100 % cover of the soil. In most irrigated soils the upward movement of The SWD at which irrigation commences is water from the water table can be ignored but in dependent on the crop and the soil but it should be some fen peat and silt soils. while the addition of rain when to irrigate and how much water to apply. Subsequently. However. soil type and stage of crop growth. at field capacity in early spring. for the early 6. A running balance of water gains (rainfall and using a running water balance referred to above. Hence the rainfall should be recorded on a daily basis on the site. then the irrigation requirement will be are 12 mm at a 15 mm SWD or 40 mm at a 50 mm reduced. Other typical applications occurs. where potatoes are prone to attack by scab a lower SWD should be used. On a large site Inherent losses such as deep percolation. management of equipment could lead to a higher This should be allowed for within the balance sheet.1 Irrigation levels important at the time of sowing the crop. If and when contribution subsequent rain. poor prematurely.6 Bare soil evaporation 8 Choice of irrigation programme Evaporation from the soil surface is especially 8. 8. with a crop at which irrigation is applied and the amount of growing from seed. area (see clause 5). percentage being required to cover water loss The period between successive irrigation through poor and untimely irrigation application. or irrigation will reduce it. irrigation) and losses (evapotranspiration) is thence NOTE The calculations needed can be done with a properly obtained. rooting depth.BS 7562-3:1995 6. where the water table is chosen so as to prevent loss of crop yield and/or controlled at high level. and poor application uniformity are associated with The evapotranspiration (ETo) is not as variable as irrigation application equipment and its rainfall and is generally given over a 40 km square management.2 Irrigation scheduling direct evaporation from the soil and transpiration from the crop will remove water and so increase the Irrigation scheduling is concerned with establishing soil water deficit (SWD). a significant proportion of quality. Irrigation is applied whenever SWD reaches a predetermined level for each crop. some water will be lost to field drains. occurs from the time of planting irrigation to be given at each application. of say 15 mm. Local rainfall can vary considerably over a small area and can therefore greatly influence local 7 Irrigation efficiency irrigation scheduling. h) planting and harvesting dates for each crop. b) detailed climatic data. The following data are typical of that required for such a simulation: a) location of the site to be irrigated. f) crops to be grown. assessed directly for each field as data from soil maps are not sufficiently detailed. with their rotation.3 Computer simulation Computer simulation allows for a more comprehensive estimate of irrigation needs to be made. j) critical SWD for each crop and stage of growth. 8. BS 7562-3:1995 where EAWC is the easily available water capacity (in mm). g) root depth for each crop. CWR is crop water requirements (in mm/day). c) soil types. e) effective soil depth. © BSI 10-1999 9 . d) soil water holding capacity. i) crop data. 10 blank . Leaflet No. BS 7562-3:1995 List of references (see clause 2) Normative references BSI publications BRITISH STANDARDS INSTITUTION. Soil texture. Meaden Vale. Gleadthorpe. 1977. © BSI 10-1999 . [2] ADAS. 895. London: HMSO. The Grange. BS 7562-1:1992. Nottinghamshire NG20 9PS. London BS 7562. Obtainable from ADAS. 1984. Informative references [1] FAO Handbook 24. Food and Agricultural Organisation of United Nations. Planning. Mansfield. Irrigation and drainage papers — Crop water requirements. Glossary of terms. design and installation of irrigation schemes. Rome. Subscribing members of BSI are kept up to date with standards developments and receive substantial discounts on the purchase price of standards. in the UK. 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