FAQ - Ag Water Conservation Practices

Q: What are Phreatophytes and what can producers do to manage or control their impact at the farm level?
A: Phreatophytes are plants such as Russian Olive, tamarisk, willows and cottonwood, that obtain water from the water table or the unsaturated zone just above it. Often found along water supply canals, phreatophytes can consume significant quantities of water through evapotranspiration, reducing the availability of water to a cropping system and its users. Methods of control depend upon the specie and may include mechanical, chemical, and biological treatments or a combination of all three in order to remove, reduce, or manipulate unwanted communities.

Q: How do conservation (reduced) tillage practices aid water conservation efforts?
A: Conservation or reduced tillage refers to the practice that supports continuous crop production on a field with at least 30% residue from the previous crop on the soil surface. No-Till and ridge tillage strategies are also considered conservation practices. Concerns related to irrigation uniformity have discouraged many producers from adopting conservation tillage practices, however they are known to reduce runoff, increase infiltration and snow capture and reduce evaporation.

Q: What is meant by water conservation?
A: Water conservation refers to practices, techniques, and technologies that improve the efficiency of water use, thereby reducing overall demand. Increased efficiency expands the use of the water resource, freeing up water supplies for other uses, such as population growth, new industry, and environmental needs. Ag water conservation goes beyond efficiency to include reduced crop consumptive use, decreased evaporation losses, and decrease uptake and use by nonbeneficial weeds and phreatophytes.

Q: What are drought tolerant crops and how do they achieve more efficient water use?
A: Whole plants respond to drought through morphological, physiological, and metabolic modifications. Drought tolerant crops must be able to withstand low water and high-heat conditions while still maintaining some ability to yield grain, fruit or desirable biomass. Plants have several methods of tolerating drought stress, including altered canopy architecture or leaf area index, leaves that are waxy, hairy or have reduced stomata, deep and vigorous root systems. At the cellular level, plant responses to water deficit may include internal osmotic adjustment mechanisms. Some drought tolerant plants survive periods of reduced summer water by going dormant and then resuming growth when water is available – so called drought avoidance. Other plants may avoid drought through delayed or changed timing in initiating reproduction. The objective of drought-adaptation mechanisms is to decrease transpiration and to improve water and carbon uptake. The development of succulence in leaves and roots, sunken stomata, reduction of transpiring surfaces even by the shedding of leaves or the presence of specialized photosynthetic pathways (C4 and CAM plants) are examples of drought-avoidance mechanisms.

Q: What are some of the proven ways to reduce irrigation water use in agriculture?
A: In most cases, upgrading irrigation systems increases water use efficiency and uniformity but does not necessarily reduce consumptive use. Consumptive use or reduced ET occurs when:
  1. Irrigated acres are decreased.
  2. Crop selection is changed from a summer crop to a cool season crop.
  3. Crop selection is changed to one with a shorter growing season.
  4. Deficit irrigation is practiced, applying some amount less than full ET over the growing season.
  5. Evaporative losses from the field surface are reduced as a result of conservation tillage, mulching, and or drip irrigation.

Q: What is meant by irrigation scheduling and how can irrigation scheduling contribute to ag water conservation?
A: Irrigation scheduling means determining the timing of irrigation, the duration of irrigation, and the amounts of water applied based upon crop needs, soil water storage capacity and climatic conditions, all leading to efficient water use.

Q: From an irrigated cropland perspective, what are the processes and mechanisms that contribute to water losses – and which can be managed or influenced to contribute to ag water conservation?
A: Not all water withdrawn from surface or ground water supplies for irrigation is ‘consumed’ by the irrigated crops, or lost from the immediate hydrologic cycle. In many instances, a portion of pumped, withdrawn, or irrigated water is returned to the immediate or near-immediate hydrologic cycle through conveyance losses, infiltration, drainage below the crop root zone, or field runoff. Some of these mechanisms are critical to long-term sustainability of agricultural crop land; for instance, leaching of salts below the crop root zone and adequate drainage are critical to sustainable crop production. In contrast, agricultural water conservation can be achieved through minimization of conveyance losses, scheduling irrigation timing and amounts to balance crop needs with soil water storage capacity and climatic conditions, by assuring uniform irrigation applications, by minimizing field-end runoff, and by adopting cropping system practices that maximize the capture and utilization of precipitation.

Q: What is the distribution of water use among irrigators in the U.S.?
A: Within the past few decades, irrigated acreage has increased in many regions of the United States, much in part to reducing production risks associated with drought. Most irrigated farms are small farms (under $250,000 in annual sales). But larger farms ($250,000 or more in annual sales) use the most irrigation water, and the largest 10 percent of irrigated farms ($500,000 or more in annual sales) account for half of total farm water applied. Farms in the 17 Western States use a wide variety of irrigation systems, about half of which are gravity-based (e.g., flooding furrows or entire fields) and half are efficient pressure systems (e.g., center-pivot sprinklers).

Q: What is meant by conveyance losses and how can irrigators minimize these losses?
A: The U.S. Geological Survey defines conveyance loss as water that is lost in transit from a pipe, canal, conduit, or ditch by leakage or evaporation. Generally, the water is not available for further irrigation use; however, leakage from an irrigation ditch, for example, may percolate to a ground-water source and be available for further use. Additionally, conveyance losses often create wetlands and associated wetlands.

Q: What is the most efficient irrigation system?
A: As a general rule, buried drip. Irrigation efficiency is defined as the amount of water stored in the root zone of the crop divided by the amount of water applied to the field. Typically surface irrigation is the least efficient, followed by sprinkle and drip and trickle irrigation is the most efficient. However, efficiency greatly depends on management and characteristics of a particular system.

Q: What is uniformity? Why is it important?
A: Uniformity is the ability of an irrigation system to apply water evenly across the soil surface, achieving a uniform depth of application. If an irrigation system has poor uniformity, some plants won’t get enough water, some will get too much, and excessive water will leach below the root zone and be lost. In order to adequately irrigate all plants in a field with an irrigation system that has poor uniformity, excess water must be applied.

Q: How much water am I applying?
A: To manage irrigation effectively, it is very important to know your application rate. This is how much water is being applied in a given time period (inches/hour). The most accurate way of determining this application rate is to measure it. For sprinkler irrigation this can be done by putting a straight sided can (catch can) underneath the sprinkler for a given time period and measuring the depth of application in the can. Since no irrigation system applies water perfectly uniformly, it is often a good idea to put out several cans in different areas where the sprinkler throws water and take an average. There are calculators for various irrigation systems including center pivots, drip, hand-line and wheel line, and solid set sprinklers.

Q: What are some irrigated cropping system practices that contribute to water conservation?
A: One of the most effective ways to conserve water, i.e., reduce the amount of water needed to sustain an irrigated operation, is to adopt crop rotations which include crops with low water use requirements – both daily and seasonally. Correspondingly, cultural practices such as reduced or minimum tillage, minimum soil disturbance, uniform plant spacing, appropriate variety selection, and crop sequencing or rotation can all contribute to ag water conservation.

Q: Do crops grown under drip irrigation systems actually require less water than crops irrigated with more conventional flood or sprinkler irrigation practices?
A: The answer to the question literally interpreted (as written) is NO. The amount of water a crop requires is not determined or controlled by the type of irrigation system but rather by the crop type, variety, growing conditions, and climate. That being the case, whether the crop is irrigated with a surface or buried drip system, a sprinkler or pivot, or a flood system has no bearing on how much water a crop requires. However, the type of irrigation system and how it is managed does determine the efficiency of water use, which is the percentage of applied water that is used by the plant. Consequently, drip irrigation systems actually require less water than sprinkler systems, which typically require less water than conventional flood methods of irrigation. Considering that a buried drip irrigation system might be 95% efficient, a center-pivot sprinkler system might be 85% efficient, and a well-managed flood system might be 50% efficient, the difference in gross seasonal water required can be 3 acre feet per acre or more.

Q: Are there practices that are minimal in cost that I can implement to improve irrigation efficiency?
A: Irrigation scheduling and monitoring are generally the most cost effective mechanisms to improve efficiency.

Q: What are the efficiency modifications I can make to my irrigation system that will give me the biggest bang for my buck?
A: This question absolutely depends upon the suitability of the current system for the field it is used on, the management and labor available, and the crops grown. It is fun to generalize, but not advisable for such a field and crop specific question.

Q: What practices can be implemented to minimize field-end runoff?
A: For surface irrigation: shorter set times, altered length of run, slope modification, use of surge irrigation techniques are the most common. For sprinkler irrigation: proper nozzle packages and depth of application are most common practices. In situations where soil type and slope are such that runoff is common, changed tillage and planting practices can help reduce runoff.

Agricultural Water Conservation Clearinghouse, Ag Water, Ag Water Economics , Biotechnology and GMO for drought , Brackish Water, Center Pivot, Conservation Tillage , Consumptive Use , Cool Season Crops , Crop Rotation , Crop Selection , Crop Water Use , Cropping Systems , Deficit Irrigation , Ditch Canal Lining , Drip and Micro Systems , Drought Tolerant Crops , Dryland cropping , Effluent Water , ET Measurement , Evapotranspiration , Flood irrigation , Furrow diking , Furrow irrigation , Interruptible supply agreements , Irrigation Management , Irrigation Systems , Leaching , LEPA , LESA , Level basins , Limited Irrigation , Low Pressure Pivot , LPIC , Field leveling , Lysimeter , Municipal , Ogallala Aquifer , Pest Management , Phreatophyte , Planting Scheme , Polyacrylamide (PAM) , Precision Water Application , Rotational Fallowing , Salinity Management , Short Season Crops , Soil Moisture Measurement , Source Water , Surge flow irrigation , Tail Water , Underground Irrigation Piping , Water Application Measurement , Water Banking , Water Conservation , Water Conveyance and Delivery , Water Law/Policy , Water Leasing , Water Modeling , Water Recovery/Reuse , Water Scheduling , Water Storage , Water Supply , Water Transfers , Water Use Efficiency

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