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Drainage for Improved Soil Health: Norms for Planning and Design

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Drainage for Improved Soil Health: Norms for Planning and Design Efficient sub-surface drainage for improved soil health: Norms for planning and design Felix Reinders ARC-Institute for Agricultural Engineering COMING UP…. Introduction Background Technical guidelines Conclusion Introduction The purpose of agricultural drainage is to remove excess water from the soil in order to enhance crop production. In some soils, the natural drainage processes are sufficient for growth and production of agricultural crops, but in many other soils, artificial drainage is needed for efficient agricultural production This presentation emanate from a 4 year project : Development of technical and financial norms and standards for drainage of irrigated lands Initiated and Funded by the Water Research Commission Project team Objective To develop technical and financial standards and guidelines for assessment of the feasibility of surface and sub-surface drainage systems under South African conditions. Specific objectives 1. To review internationally and nationally available norms and standards and to give an overview of current drainage systems, practices and technology; 2. To evaluate the interaction between irrigation, drainage practices and impact on the natural environment; 3. To describe technical/physical/biological/financial requirements for drainage; Specific objectives 4. To refine and develop technical standards for drainage with reference to soil types, crops, irrigation method, water tables, salinisation, water quality and management practices; 5. To refine and develop financial standards for drainage with reference to capital investment, financing methods, operation and maintenance expenditure and management practices; 6. To evaluate the technical and financial feasibility of drainage based on selected case studies; 7. To develop guidelines for design, installation, operation and maintenance of drainage systems. Location of the selected Schemes Impala irrigation scheme Vaalharts scheme Breede river irrigation scheme Backgound Soil health and productivity can be obtained through well- drained soils and efficient irrigation. Artificial drainage in agriculture is a practice to improve the natural drainage conditions and has been practiced for many years in the world. In South Africa drainage was introduced in the late fifties and early sixties and various approaches and techniques have been used and are still been used to drain agricultural fields in South Africa. 500,000 ha of the total world‘s agricultural land are being lost out of production every year due to poor drainage The extent of cultivated area worldwide is estimated at 1500 million ha, out of which about 390 million ha are said to be provided with sustainable water management systems, being irrigation, drainage, or both Drainage plays an essential part to sustain food production Drainage % of total irrigated area (%) in different countries Country Area Drainage % of irrigated Area drained total irrigated area (ha) (ha) (%) Egypt 3 246 000 3 024 000 93 India 48 000 000 5 800 000 12 The Philippines 1 530 000 1 500 000 96 South Africa 1 600 000 160 000 10 • In South Africa an area of 16 000 000 ha is being cultivated and 1 600 000 ha is being irrigated. • It is estimated that 240 000 ha is affected by rising water tables and salinisation and problems appear to be expanding. • There is also an indication that costs of drainage have increased quite significantly. • Various approaches and techniques have been used and are still been used to drain agricultural fields in South Africa. In South African subsurface drainage systems are installed on 60,000 ha of the total irrigated land of 1 600 000 ha and another 100,000 ha with surface drainage systems The main centres where we have drainage problems are: •The areas along the Orange River, especially at Vaalhartz, Douglas and Upington. •Winter Rainfall area at Robertson, Worcester, Swellendam, Ceres and Wellington •KwaZulu Natal Region – Pongola and Nkwalini •Eastern Cape – Gamtoos valley, Sunday River valley and Fish River valley. •Limpopo– Loskopdam and Hartbeespoortdam Irrigation schemes •And mainly where there is a concentration of irrigation going on. Drainage The purpose of agricultural drainage is to remove excess water from the soil in order to enhance crop production. In some soils, the natural drainage processes are sufficient for growth and production of agricultural crops, but in many other soils, artificial drainage is needed for efficient agricultural production The spectrum of agricultural water management (Delany, 2012) HYDROLOGIC CYCLE (with tiles) Integrated drainage Two types of drainage • Surface Surface drainage is the removal of water that collects on the land surface. • Subsurface Subsurface drainage can be defined as the removal of water from below the surface Surface drainage Surface drainage is affected by the topography and vegetation. • AIM – to remove excess water from the land surface to create more favourable conditions for plant growth preventing long periods of ponding without excessive surface erosion. Typical structures broadly described as :- 1. Land levelling 2. Open storm water drains 3. Contour banks 4. Artificial waterways SURFACE CONTOUR MAP Jvd Merwe SURFACE FLOW LINES SURFACE RUNOFF CONTROL PLAN Subsurface drainage Subsurface drainage may be defined as the control of ground water and salts using water as vehicle. • The source of water may be long term irrigation, percolation from precipitation or topographic movement of water from higher elevation. • Any form of drain designed to control or lower the ground water is considered subsurface drainage. The main objective of subsurface drains are to accomplish aeration in plant root zone to favourably grow crops. • To provide improvement in soil moisture conditions for operation of tillage, planting and harvesting. • To increase length of growing season. • To remove toxic substances like salts rising in the root zone from saline / alkali water tables by evaporation. Principles of subsurface drainage Drain types System of drains Cut off drains Targeted drains Longterm Yield Trends SUGARCANESUGARCANE YIELDYIELD (T/Ha)(T/Ha) versusversus WATERTABLEWATERTABLE DEPTHDEPTH (m)(m) 150 140 130 120 110 100 90 80 70 SUGARCANEYIELDt/ha SUGARCANEYIELDt/ha 60 50 40 30 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 AVERAGE DEPTH OF WATERTABLE (m) Irrigation without Drainage Non-effective irrigation application. Shallow root development. Field operations more difficult. Greater control of weeds is required. Rise of the water table. Salt accumulation. Reduction in plant available water. Development of bad patches in the field. No or limited yield. No Drainage 70 tons of sugercane/ha J vd Merwe, Irrigation with Drainage Initial high implementation cost. Lowering of the water table. Reduce soil compaction and destruction. Leaching of accumulated salts. Field operations without water logging. Extended growing season. Increased root development. Improved yields. Better drought resistance. Sustainable long-term Irrigation. With Drainage 111 ton of sugercane / ha J vd Merwe, Improved root growth and plant health The demand for the use of irrigation water and technologies to improve efficiency is a derived demand from the whole farm profitability of farming with irrigation crops. The major reason for installing drainage is to improve the productivity of the farmland. Reduced productivity of farm land = waterlogged soils – anaerobic microbial activity (bad bugs) Improved land productivity = aerated soils stimulate aerobic microbial and fungi activity (good bugs) Higher yields translate into more returns. So the investment decision is based on whether the higher crop returns will justify the investment in drainage Micro –organisms operation http://www.artemisthai.com TECHNICAL GUIDELINES Guidelines SOIL CONSERVATION ACT Control measures as stated in the Act • Cultivation of virgin soil • Cultivation of land with a slope • Protection of cultivated land against erosion through the action of water • Protection of cultivated land against erosion through the action of wind • Prevention of waterlogging and salination of irrigated land To remove excess water from the surface To remove excess salts from the profile To maintain groundwater at a desired level Origin of Drainage Problems Most lands have periods during which excess water occurs. As long as the quantity of water is small, or the period of waterlogging (when the soil is saturated with water) is short, or it occurs during the non-critical growing period of the crop, this will not be too harmful. It is only when large quantities of water occur for extended durations during critical growth periods that the removal of water with an artificial drainage system may be required. Poor natural drainage ? Losses can be 20 to 70% J vd Merwe Water table survey assists in determining the extent of the drainage problem HYDRAULIC PERMEABILITY - K 2r HYDRAULICHYDRAULIC PERMEBILITYPERMEBILITY -- KK NGL ERNST equation 400.r 2 Y x If S = > H : K = Y Y ( H+20r ) ( 2 - H ) T 360.r 2 Y If S = 0 : x K = Y ( H+10r ) ( 2 - Y ) T Watertable H Y =Rise in water level during test (mm) D T = Time recorded to final test level (sec) r = Radius of augerhole (mm) H = Depth From watertable to bottom of augerhole (mm) Y D = Total depth of augered hole (mm) H Y Y = Depth of watertable at beginning of test (mm) S = Depth of impermeable layer below augerhole invert (mm) W = Static watertable level from NGL prior to test (mm) K = Hydraulic permeability m / day Valid parameters :- Static watertable prior to test greater than
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