Basic calculations of Measures for Water Management

Training Module 03

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TR03: Basic calculations of Measures for Water Management

Introduction

Water needs for agriculture must be supplied taking into consideration a decreasing availability, due to:

  • environmental awareness,
  • population growth,
  • economic development and
  • global change.

Water management for agriculture is then inter-related with:

  • traditional water resources management,
  • food production,
  • rural development and
  • natural resources management.

Climate change negative impacts:

  • reduce water availability for agriculture environmental awareness,
  • extreme whether events
➥ current water management at risk ➨ Adaptation measures

An adaptation measure/strategy is an intervention to reduce the vulnerability of the agricultural sector to climate change effects.

Best practices:  are a selection of interventions proven to work well and produce good results.

Contents

2.1. Technological practices: sub-irrigation

2.2. Technical practices: Rooftop water harvesting from greenshouses

2.3. Cost considerations – typical costs

2.4. Some examples

1. Climate change adaptation measures

Adaptation Need Adaptation Measure Best Practice Type Best Practice Number
Responding to changes in water availability Reuse of treated wastewater for irrigation Technological BE_05
Underground irrigation strips with integrated dripper Technological ES_01
Automation of irrigation systems Technological ES_02
Reverse osmosis desalination plant Technological ES_08
Rooftop rainwater harvesting Technical IT_05
Supplemental irrigation ponds Technical IT_06
Drip Irrigation on rice Technological IT_08
Adaptation Need Adaptation Measure Best Practice Type Best Practice Number
Responding to floods and droughts Wetlands and pools Technical CZ_03
Weir Technical BE_01
Controlled drainage Technical BE_02
Farming insurance Economic ES_03
Adaptation Need Adaptation Measure Best Practice Type Best Practice Number
Responding to increased irrigation requirements Mulching in tropical crops Agronomic ES_04
Change Variety/Breed Agronomic ES_06
Water harvesting with pits Technical ES_07
Soil coverage Agronomic CY_01
Subsoiler Agronomic CY_03
Hydroponics Agronomic CY_04
Adaptation Need Adaptation Measure Best Practice Type Best Practice Number
Responding to deterioration of water and soil quality Construction of contour trenches (swales) Technical CZ_01
Diversified agriculture Agronomic CZ_06
No tillage Agronomic CY_02
Agroforestry Agronomic DE_02
Improved soil management Agronomic IT_01
Adaptation Need Adaptation Measure Best Practice Type Best Practice Number
Responding to loss of biodiversity Innovative agronomic practices Agronomic CZ_02
Stream and wetland revitalisation Technical CZ_07
Regenerative farming Agronomic DE_03
Utilization of landraces and evolutionary populations Agronomic IT_04

2. Basic calculations examples

Agronomic practices: No-tillage

  • AGRIWATER Best Practice
  • Conventional or full tillage rearranges the entire topsoil. It may require several passes to turn the soil and then break it down into a friable seedbed prior to sowing.
  • Minimum tillage (reduced tillage) is generally a one-pass tillage operation at sowing synchronous with seed placement, typically achieved using total cut-out points or full cut-out one-way or offset discs to break up the entire soil surface. It may include shallow cultivation between seasons to control weeds; it may be called reduced tillage.
  • No-tillage or zero-till involves one pass during which a part of the soil surface is disturbed or “opened”, and the seeds are placed concurrently in that disturbed zone. The seeder opener may be a knife-point as little as 5 mm wide on a tine or a single, double or triple-disc set at a slight angle to the direction of travel.
  • In general, we can use “conservation tillage” as a generic term that covers any tillage system that reduces soil and water loss compared with conventional tillage. Some have defined it more tightly to include treatment of residues specifying that at least 30 per cent of the soil surface should be covered with residues after sowing to reduce erosion by water. It is likely to include zero, minimum and reduced tillage systems within the definition.
Source: FAO

Effects of no-tillage:

  • It can reduce labour, fuel, irrigation and machinery costs.
  • No-till can increase yield because of higher water infiltration, storage capacity, and less erosion.
  • Another possible benefit is that because of the higher water content, instead of leaving a field fallow, it can make economic sense to plant another crop instead.
  • No-tillage and conservation tillage measures have considerable benefits also in terms of a decrease in soil temperatures if combined with mulching
  • No-tillage and conservation tillage measures have considerable benefits also in terms of a decrease in soil temperatures if combined with mulching
Source: https://southernirrigation.com/2020/10/29/designing-an-sdi-system-with-southern-irrigation/
  • AGRIWATER Best Practice
  • Before the system is designed, the systems’ goals or expectations should be identified: increased manageability, better crop quality and uniformity, increased yields, uniform application of water and nutrients water savings, and/or increased profits.
  • Field: an undulating or sloped field will require pressure compensating emitters, and a flat field will use non-pressure compensating emitters. The tubing diameter is also critical to supplying the system’s flow. We want to achieve no more than a 7% difference between the highest and lowest emitter flow rate from a design point.
  • Soil: Clay soils allow water to travel much further (upward and laterally) than sandy soils. Clay soils also hold much more water and absorb water much slower. Therefore, drip lines and emitters are generally installed closer together in sandy soils, while in clay soils, these spacings can be increased but with lower emitter flow rates due to the lower absorption rate.
  • A water analysis needs to be carefully reviewed to understand the level of filtration and treatment required to prevent the dripline from clogging or calcifying. In most cases, the quality of the water can be easily corrected.
  • It is good practice to monitor the system’s operation flow and the crops’ water use.
  • Fertilizer injection: Fertilizer injection systems inject nutrients and chemicals into the system for maximum crop performance and maintain the dripline over a long time. Flexible fertigation capabilities will help the system pay for itself faster than any other component in the system. Injection systems should meet expected demands for all chemicals, be easy to operate and calibrate and have provisions to prevent unwanted precipitates.
  • Winterizing the system is a necessary maintenance procedure as water will freeze and expand, possibly damaging plastic and metal system components. Water from filters, valves, chemigation equipment, pressure regulators, and subsurface pipes should be emptied – especially at the lower ends of the field where water typically accumulates. Polyethylene drip lines are not subject to damage from freezing since the drippers provide drainage points and polyethylene is flexible.
  • Routine maintenance of all system parts (such as filters, pumps, valves and fertilizer injectors) will extend the system’s life. Maintenance should follow a regular schedule and should be recorded for later reference.
Catchment Area (m2 ) = Length (m) × Width (m) Where:
  • Length = length of the catchment surface (m)
  • Width = width of the catchment surface (m)
Supply (litres/year) = rainfall (mm/year) × greenhouse roof area (m2 ) × runoff coefficient of polyethylene film (PE) The runoff coefficient is the amount of water that drains free of the surface relative to the amount of rain that falls on the surface. It reflects how much of the rainfall is lost to infiltration and other abstractions. In the case of greenhouses, the materials typically used are various forms of plastic (polyethylene film (PE)) which have little to no infiltration capacity, and thus nearly all the water runs off. However, there are losses to evaporation and splashing and detention such that the general runoff coefficient for the polyethylene greenhouse film is estimated to be 0.8. This means that of the total volume of rain that falls on the catchment surface, 80% drains off the surface; the other 20% stays on the surface.  
  • Plot a cumulative roof run-off graph, by summing the monthly runoff totals.
  • Add a dotted line showing cumulative water use (water withdrawn or water demand).
  • A residual storage of 5 m3 should be incorporated for the rainwater remaining in the tank at the start of the wet season
  • Design costs
  • Cost for legal authorizations
  • Land preparation
  • Eventual machinery rent
  • Materials and spare parts
  • Labor
  • Ordinary maintenance
  • Extraordinary maintenance
  • Disposal of materials (used plastic pipelines, chemicals storage, etc.)
  • Drip irrigation on rice: 800 – 1300 E/ha for the materials (The 1300 € /ha cost include the assistance from the provider); 200 € /ha/y for the maintenance
  • Pit based water harvesting for trees: the hourly cost of the operator is €35, resulting in a cost of €1.3 per tree, at a rate of 25 trees/hour. This measure requires biannual maintenance at a rate of €0.65 per tree.

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