PNS/BAFS/PAES 217:2017 Irrigation Water Requirements

• Philippine National Standard PNS/BAFS/PAES 217:2017 relates to the determination of irrigation water requirements.

Foreword

• The Agricultural Machinery Testing and Evaluation Center (AMTEC) initiated the formulation of this national standard
• The project was entitled "Enhancement of Nutrient and Water Use Efficiency Through Standardization of Engineering Support Systems for Precision Farming", funded by the PCAARRD - DOST
• The Bureau of Agriculture and Fisheries Standards (BAFS) has been mandated to develop standard specifications and test procedures for agricultural and fisheries machinery and equipment by Republic Act 10601, also known as the Agricultural and Fisheries Mechanization Law (AFMech Law of 2013)
• BAFS has endorsed this standard for the DA Secretary's approval through the Bureau of Agricultural and Fisheries Engineering (BAFE) and the Bureau of Philippine Standards (BPS)

Standard Compliance

• The word "shall" is used to indicate mandatory standard requirements
• The word "should" is to indicate a recommendation, but without excluding other options

Standard Outline

• Scope defines the guidelines and minimum requirements
• References list normative documents containing provisions of this national standard
• Definitions provides a glossary of terms
• Initial Investigations details the data required
• Development of Cropping Calendar details how to plan for increased production
• Crop Water Requirement details how the crop water requirements should be calculated
• Farm Water Requirement details how to replenish crop water requirements
• Diversion Water Requirement outlines the total quantity of water diverted from a water source
• Bibliography provides a list of resources
• Annexes provides more data and equations

Definitions

• Actual Crop Evapotranspiration (ETa) is the rate of evapotranspiration, affected by soil water, salinity, and field size
• Application Efficiency (Ea) is the ratio of infiltrated water depth stored in the root zone to the applied water depth
• Conveyance Efficiency (Ec) is the ratio between water received at the inlet for a block of fields to that released at the project's headwork
• Crop Coefficient (kc) is the ratio of crop evapotranspiration to potential evapotranspiration
• Crop Evapotranspiration involves the rate of evapotranspiration of disease-free crops under optimal conditions, water loss through plant transpiration, water evaporation from the soil surface, and evaporation from wet leaves
• Cropping Pattern refers to a sequence of different crops grown in order on any particular field or fields
• Crop Water Requirement (CWR) is the amount of water used for crop production, including evapotranspiration and seepage/percolation losses
• Diversion Water Requirement (DWR) is the total quantity of water diverted from a stream, lake, or reservoir, or removed from the ground in order to irrigate a crop
• Effective Rainfall (ER) signifies the amount of rainwater directly used by crops for growth and development, excluding deep percolation, runoff and interception
• Effective Rooting Depth describes the soil depth from which the bulk of the roots of the crop extracts most of the water needed for evapotranspiration
• Evapotranspiration constitutes the combination of water transpired from vegetation and evaporated from the soil, water, and plant surfaces
• Farm Water Requirement (FWR) represents the amount of water needed to replenish the crop water requirement and compensate water losses, reduced by effective rainfall
• Hydrologic Frequency Analysis estimates the odds of a specific event by determining the frequency curves of best fit to samples of hydrologic data
• Land Preparation Water Requirement (LPWR) is the amount of water required in lowland rice production which includes water losses through evaporation, seepage and percolation and land soaking
• Land Soaking Water Requirement (LSR) represents the water required in lowland rice production, depending on initial soil moisture and physical properties
• Pan Coefficient constitutes the ratio between reference evapotranspiration (ET॰) and water loss by evaporation from an open water surface of a pan
• Pan Evaporation signifies the rate of water loss by evaporation from an open water surface of a pan
• Percolation is the vertical flow of water to below the root zone and is affected by soil texture, bulk density, mineralogy, organic matter content, the content of salt type, and salt concentration
• Reference Crop Evapotranspiration (ET॰) notes the rate of evapotranspiration from a hypothetical reference crop with an assumed crop height of 0.2 m, a fixed surface resistance of 70 s/m and an albedo of 0.23
• Residual Moisture Content describes the moisture left in the soil before the initial irrigation water delivery and the extent of water depletion from the soil when the water supply has been cut-off
• Seepage involves water escaping from water conveyance facilities such as open ditches, canals, natural channels, and waterway

Initial Investigation

• A layout of irrigation components and the general processes in determining irrigation water requirements is required
• Area to be irrigated, water supply, soil, crop, meteorological data, and irrigation method are required.

Crop Calendar

• Climate description, ideal crop types, planting months, and growing periods are in Annex A, Tables A.1 to A.4
• Cropping patterns such as crop rotation and multiple cropping can increase production

Crop Water Requirement

• Crop water requirement is calculated using Annex H.1
• The values of kc obtained from experimental plots vary by growth stage, and must be reflected in the cropping calendar
• Seepage and percolation in the field/service area can be determined using reference values listed in Table 5 or Annex C