IRRIGATION WATER ANALYSIS

Transcription

1 IRRIGATION WATER ANALYSIS MIDWEST LABORATORIES, INC B STREET OMAHA, NE FAX

2 TABLE OF CONTENTS Acknowledgements... ii I. Irrigation Water Quality Criteria...1 A. Salinity...1 B. Sodium...6 C. Cabronate & Bicarbonate D. Phytotoxic Substances E. Other Phytotoxic Substances F. Sediment G. ph H. Nutrient Availability Components II. Sampling and Handling Guidelines A. Sample Size B. Special Instructions C. Conversions, Equivalents and Abbreviations References Cited Table and Figures Index LIMITATION OF LIABILITY The information in this publication is based on the best information available to the author at the time of publication. It is not intended to be used in place of instructions issued by the manufacturer of any product. All agricultural materials should be used in strict compliance with label directions, and the user assumes all liability for results of deviation from such directions. Copyright 1994, Midwest Laboratories, Inc., Omaha, Nebraska i

3 ACKNOWLEDGEMENTS The following people have lent considerable time and effort into making this publication both understandable and credible. Their efforts and contributions are sincerely appreciated. Steve Curley; C.P.Ag./S.S. John Menghini; C.P.Ag. Midwest Laboratories, Inc. Editors Robert Hecht; C.P.Ag. Midwest Laboratories Agronomist Seneca, Kansas Richard Goff; C.P.Ag. Midwest Laboratories Agronomist New Ulm, Minnesota Kennard Pohlman; C.P.Ag./S.S. Managing Director and President Midwest Laboratories, Inc. Omaha, Nebraska ii

4 1 INTERPRETATION OF IRRIGATION WATER ANALYSIS Irrigated crop production largely depends upon management of irrigation water quality. Proper interpretation of the irrigation water analysis is essential in providing management guidelines in the areas of irrigation water suitability, as well as soil and crop management under irrigated conditions. Irrigation water classification guidelines have been developed to allow for proper interpretation of the interrelationships of the various analytes used in establishing irrigation water quality criteria. I. IRRIGATION WATER QUALITY CRITERIA There are four principal hazards related to the chemical nature of a given irrigation water: salinity (sometimes termed total concentration), sodium, bicarbonates, and boron or other phytotoxic substances (7). A fifth hazard can also be added relating to the physical nature of water, that being suspended solids primarily sand, silt and clay sediment (referred to on the irrigation water analysis as total dissolved solids or TDS) (5) (6). A. Salinity (Total Concentration) Salinity has been cited as probably the single most important criterion of irrigation water quality ( 4). Salinity of irrigated soil solution is usually dependent on, and determined by, the salinity of the irrigation water. The salinity of irrigation water is the sum of all the ionized dissolved salts in the water, hence the expression, total concentration, also is used in labeling salinity (i.e., NO 3- N, SO 4=, Cl -, CO 3=, HCO 3- ). Salinity is characterized by electrical conductivity (EC), because the ability of water to conduct electricity is directly related to the number of ions present in the water. Units of EC are most commonly expressed as millimhos per centimeter (mmho/cm), and is the most common and preferred unit of salinity in the United States (7). 1. Salinity Effects The principal effect of salinity is restriction of soil water availability to the plant root system. From a plant physiology standpoint, the presence of salt in soil water increases the energy plant roots expend to remove water from the soil. Figure 1 depicts the typical relationships between the energy with which a soil holds water and soil water content for varying salt concentrations in the soil water.

5 2 fig. 1. Soil Characteristic Curves for Soil Water with Different Salt Concentrations 15 Wilting Range Field Capacity Water Potential (bars) % Salt 0.2% Salt 0.1% Salt "0" Percent Soil Moisture Excess salinity can profoundly affect crop physiology and yield by retarding cell enlargement and division, protein and nucleic acid production, and related increases in plant mass and physiological processes (5). Visible crop injury symptoms, such as leaf burn, most likely occur only at extremely high salinity levels (EC >5 mmho/cm), however, yield losses can occur in certain crops at EC values as low as 1-3 mmho/cm. Figure 2 illustrates a typical relationship between crop yield and salinity, where crop yield is shown to be independent of salt concentration as long as salinity is below a threshold salinity level. Above the threshold salinity level, crop yields decrease proportionately as salinity increases. The salinity at the zero yield level is an estimate of the maximum salinity a crop can tolerate: crop production is not normally possible when salinity exceeds the zero yield level for a given crop. fig. 2. Crop Yield-Salinity Relationship Relative Crop Yield (%) Low Threshold Salinity Level Salinity Zero Yield Level High

6 3 Table Crop Tolerance of Salinity Crop salinity rating groups as a function of threshold and zero yield salinity level are shown in Table 1 (5). Threshold and Zero Yield Salinity Levels for the Four Salinity Rating Groups Table 2. Threshold Salinity 1/ Zero Yield Salinity 1/ Salinity Rating Groups (mmho/cm) (mmho/cm) Sensitive Moderately sensitive Moderately tolerant Tolerant / Electrical conductivity of soil saturation extract. The relationship between crop yield and salinity varies considerably with each crop. Salt tolerant crops, such as barley and cotton have threshold salinity levels that exceed the zero yield values of salt sensitive crops such as onions and beans. Table 2 summarizes salinity tolerance ratings for selected agricultural crops, and also depicts salt tolerance thresholds and percent yield decline due to salinity above the tolerance threshold level for selected crops. Salt Tolerance and Percent Yield Decline of Trickle Irrigated Crops as a Function of the Electrical Conductivity of the Soil Saturation Extract 1/ Sensitive Percent Yield Decline a Percent Yield Decline a %/(mmhos/cm) %/(mmhos/cm) Almond 19 Lemon Apple Okra Apricot 24 Onion 16 Avocado Orange 16 Bean 19 Peach 21 Blackberry 22 Plum 18 Boysenberry 22 Raspberry Carrot 14 Strawberry 33 Grapefruit 16 Moderately Percent Yield Decline a Percent Yield Decline a Sensitive %/(mmhos/cm) %/(mmhos/cm) Alfalfa Pepper 14.0 Bentgrass Potato 12.0 Broadbean 9.6 Radish 13.0 Broccoli 9.2 Rhodegrass Cabbage 9.7 Rice, paddy Clover Sesbania Corn (forage, grain, sweet) Sorghum Cowpea 14.0 Spinach 7.6 Cucumber 13.0 Sugarcane 5.9 Flax Sweet potatoes 11.0 Grape 9.6 Timothy Lettuce 13.0 Tomato 9.9 Lovegrass Trefoil, big Meadow Foxtail Vetch Millet, Foxtail Orchardgrass a Percent yield decline is the rate of yield reduction per Peanut 29.0 unit increase in salinity beyond the threshold. 1/ Source: G. J. Hoffman, R. S. Ayers, E. J. Doering, and B. L. McNeal, "Salinity in Irrigated Agriculture." In Design and Operation of Farm Irrigation Systems (1981), M. E. Jensen (Ed.), ASAE Monograph 3, p Copyright 1980 by ASAE, pp Reprinted by permission of ASAE.

7 4 Table 2. (cont.) Salt Tolerance and Percent Yield Decline of Trickle Irrigated Crops as a Function of the Electrical Conductivity of the Soil Saturation Extract Moderately Percent Yield Decline a Percent Yield Decline a Tolerant %/(mmhos/cm) %/(mmhos/cm) Barley (forage) Safflower Beet, garden 9.0 Soybean Bromegrass Sudangrass Canarygrass, reed Trefoil, Birdsfoot, narrlowleaf Fescue, tall 5.3 Wheat Hardinggrass Wheatgrass, crested and Olive slender Ryegrass, perennial Wildrye, beadless Tolerant Percent Yield Decline a Percent Yield Decline a %/(mmhos/cm) %/(mmhos/cm) Barley, grain Sugarbeet Bermudagrass 6.4 Wheatgrass, fairway and tall Cotton 7.7 Wildrye, Altai and Russian Date Palm 3.6 a Percent yield decline is the rate of yield reduction per unit increase in salnity beyond the threshold. Table Salinity Control Salinity control measures include leaching salts out of the soil-root profile, maintaining high soil-water profile, maintaining high soil-water contents, improving internal soil drainage and selecting more salt tolerant crops. a. Leaching Salts Salts are leached out of the soil-root profile via percolating drainage water. Sufficient water must be applied to leach salts away from the root zone. Tables 3 and 4 show leaching requirements for salinity hazard and leaching requirement for highest allowable conductivity respectively. Leaching Requirements for Salinity Hazard 1/ Electrical Conductivity Salinity Hazard of the Water Low Medium High mmhos/cm Leaching Requirement* % 13% 9.5% % 27% 20.0% % 41% 30.5% *Assuming 24 inches of irrigation water plus 10 inches of rain per growing season. The percentages listed are the amounts of excess water which will be required to maintain each of the three classes of irrigation water. 1/ Determining Water Quality for Irrigation Publication C396, August 1968 Cooperative Extension Service Kansas State University Manhattan, Kansas

8 5 The leaching requirements needed to maintain low, medium or high salinity hazards for three classes of irrigation waters are shown in Table 3. Leaching requirements for waters which will result in the highest allowable soil conductivity, mmhos/cm, for the low, medium and heavy textured soils respectively are shown in Table 4. Table 4. Leaching Requirement for Highest Allowable Conductivity Salinity Hazard LOW MEDIUM HIGH Soil Water Leaching Water Leaching Water Leaching Texture Conduc- Require- Conduc- Require- Conduc- Requiretivity ment tivity ment tivity ment mmhos/cm mmhos/cm mmhos/cm Light % % % Medium % % % Heavy.87 15% % % Assuming 24 inches of irrigation water plus 10 inches of rain per growing season. Proper use of Tables 3 and 4 must include certain assumptions: 1). Adequate drainage is present and salt added by soil mineral weathering and from fertilizers, manures, chemicals, etc., equal the salt removed by precipitation as insoluble minerals and with the harvested crop. 2). The underlying ground water and rainfall salt carried by capillarity into the root zone are negligible compared to the irrigation water. 3). The initial salinity of the root zone is at or below the desired threshold value (initial leaching to reduce salinity of soils high in natural salt contents to the desired threshold level may be necessary). In general, 80 percent of the soluble salts initially present in a soil profile will be removed by leaching with a depth of water equivalent to the depth of soil to be treated (5). Salt-sensitive crops may have a higher leaching requirement, while salt-tolerant crops have a lower leaching requirement. A saturation extract EC (EC determined from solution extracted from a saturated soil paste) can be used to determine the adequacy of the initial leaching application to achieve acceptable salinity threshold levels. During subsequent irrigations, actual salinity levels will exceed the saturation extract EC since the soil will not usually be saturated with water. b. Maintaining High Soil Water Contents Lower soil salt concentrations result when the water content of the soil is maintained at high levels, since salt concentration of the root zone increases as soil water is depleted by evaporation and plant transpiration. Use of more saline water is possible by increasing the frequency of irrigation, which

9 6 B. Sodium maintains high soil water levels. High frequency trickle irrigation has been effectively used to apply extremely saline waters; however, caution must be exercised when sprinkler-type irrigation is used with highly saline water as severe leaf burn may result. c. Drainage Adequate soil drainage characteristics are essential for soil and crop management utilizing saline irrigation water. Salts from irrigation water, ground water, natural soil sources, fertilizer, manure, and other chemical sources must be allowed to drain away from the root zone. Naturally high water tables will complicate drainage of salts and installation of drainage control measures such as drainage tile or ditches may have to be added to insure response under these conditions. Subsoiling may also be of benefit to the improvments of internal drainage. Soil amendments may have to be integrated into the drainage improvement plan as well; gypsum, elemental sulfur, and sulfuric acid are the most commonly used and cost-effective means via soil application to help improve soil structure and internal drainage (7). The benefit from these amendments can only be realized if the internal drainage can be improved. d. Salt-Tolerant Crops A cultural management tool used under highly saline irrigated conditions would be to select crops and/or varieties of crops with high tolerances to salt (see Table 2) (6, 7). Sodium (Na + ) is unique among the cations in its effect on the soil. High concentrations of sodium in irrigation waters and soils eventually cause deterioration of soil structure (dispersal of soil particles leading to decreasing soil permeability to air and water) and reduction in hydraulic conductivity (decrease in soil water drainage). Additions of even low amonts of exchangeable sodium to soils tends to make moist soils impermeable to water and air, and on drying, soil will form dense crusts which interfere with tillage, and seedling germination and emergence. Indexes developed to form criteria for the tendency of irrrigation water to form exchangeable sodium in the soil include the exchangeable-sodium-percentage (ESP), the sodiumadsorption-ratio (SAR) and the adjusted SAR of soil extracts or irrigation waters. 1. ESP: Equation 1 is used to calculate ESP (5). Eq. 1. Exchangeable Na + (meq / 100g soil) ESP = X 100 cation exchange capacity (meq / 100g soil) Generally, higher ESP levels can be tolerated in coarse-textured than in finetextured soils.

10 7 2. SAR This is the most reliable index of the sodium hazard of irrigation water to form exchangeable sodium in the soil (5), as shown in Equation 2: Eq. 2. SAR = Na + ( meq / liter ) ( ) Ca 2 + meq / liter + Mg 2 + ( meq / liter ) 2 Because large amounts of bicarbonate in irrigation water can increase the sodium hazard in soils, the sodium adsorption ratio (SAR) should include an adjustment factor to account for the added effects the precipitation or dissolution of calcium in soils related to carbonate (CO 3 2- ) and bicarbonate (HCO 3 - ) concentrations. As the calcium is precipitated by the high HCO 3 - and CO 3 2-, it is easily displaced leaving sodium as the dominant cation. The soil stucture can then change causing futher drainge problems. The adjusted SAR equation is shown in Equation 3: Eq. 3. adj. SAR = Na Ca + Mg 2 [ 1 + ( 8. 4 phc )] phc = (pk 2 - pk c) + p(ca + Mg) + palk pk 2 is the second dissociation constant for H 2 SO 3 and ph c is the solubility constant for CaCO 3 both corrected for ionic strength. p(ca + Mg) is the negative logarithm of the molal concentration of calcium plus magnesium. palk is the negative logarithm of the molal concentration of the total bases (CO 3 + HCO 3 ). ph c is theoretical, calculated ph of irrigation water in contact with lime and in equilibrium with soil CO 2. Obtained from Water Analysis {(pk 2 - pk c) is obtained from using the sum of Ca Mg + Na in meq/l p(ca + Mg) is obtained from using the sum of Ca + Mg in meq/l p(alk) is obtained from using the sum of CO3 + HCO3 in meq/l Sum Sum Concentration pk 2-pK c P(Ca + Mg) p(alk) Concentration pk 2-pK c p(ca + Mg) p(alk) (meq/l) (meq/l) Example: Ca = 1.82 meq/l CO3 = 0.05 meq/l Mg = 0.75 meq/l HCO3 = 0.3 meq/l Na = 6.70 meq/l Ca + Mg + Na = 9.27 meq/l From the table: pk 2 - pk c = 2.3 Ca + Mg = 2.57 meq/l p(ca + Mg) = 2.8 CO3 + HCO3 = 0.35 meq/l p(alk) = = phc

11 8 The relationship between ESP and SAR can be related by a nomogram, as shown in figure 3. fig. 3 Nomogram for Determing the SAR value of Irrigation Water and for Estimating the Corresponding ESP value of a Soil that is at Equilibrium with the Water Under field conditions, the actual ESP may be slightly higher than the estimated equilibrium value, since the total salt concentration of the soil solution is increased by evaporation and plant transpiration which results in a higher SAR and correspondingly higher ESP (7). Permeability effects are complicated by the interaction of SAR and salinity. Large concentrations of dissolved salt tend to neutralize the effect of sodium on soil dispersion. Figure 4 illustrates the interaction between EC and SAR and provides a guideline for predicting possible permeability problems (5).

12 9 fig. 4 Guidelines for Predicting Possible Permeability Problems Soil Permeability Problem 3 2 EC mmhos/cm 1 None Increasing Severe Adj. SAR Source: A. Marsh, "Guidelines for Evaluating Water Quality Related to Crop Growth." In: 1982 Technical Conference Proceedings, copyright 1982 by The Irrigation Association, 72 pp. Reprinted by permission of The Irrigation Association. fig. 5 All water quality combinations of EC and SAR that lie above the curved band should have no permeability problems. Those lying within the curved band have increasing problems. Those lying below the band will likely develop severe permeability problems even when low SAR waters are utilized. Diagram for the Classification of Irrigation Waters SODIUM (ALKALI) HAZARD

13 10 3. Irrigation Water Classification Procedure The U.S. Salinity Laboratory has developed a procedure for the classification of an irrigation water analysis, relating on a graphic analysis basis, the SAR and the salinity hazard, as shown in figure 5 (7). The horizontal axis represents salinity as expressed by conductivity EC (in mmho/c), and the vertical axis represents SAR. To classify an irrigation water analysis, the numerical values for conductivity and SAR are plotted on the diagram figure 5 as coordinates, where the position of the point determines the quality classification of the water. The significance and interpretation of these quality ratings described in figure 5 are summarized as follows (7): a. Salinity Classification: C1 C2 C3 C4 LOW SALINITY WATER can be used for irrigation with most crops on most soils, with little likelihood that a salinity problem will develop. Some leaching is required, but this occurs under normal irrigation practices except in soils of extremely low permeability. MEDIUM SALINITY WATER can be used if a moderate amount of leaching occurs. Plants with moderate salt tolerance can be grown in most instances without special practices for salinity control. HIGH SALINITY WATER cannot be used on soil with restricted drainage. Even with adequate drainage, special management for salinity control may be required, and plants with good salt tolerance should be selected. VERY HIGH SALINITY WATER is not suitable for irrigation under ordinary conditions but may be used occasionally under very special circumstances. The soil must be permeable, drainage must be adequate, irrigation water must be applied in excess to provide considerable leaching and very salt-tolerant crops should be selected. b. Sodium Classification: S1 S2 S3 LOW SODIUM WATER can be used for irrigation on almost all soils, with little danger of the development of a sodium problem. However, sodium-sensitive crops, such as stone-fruit trees and avocados, may accumulate injurious amounts of sodium in the leaves. MEDIUM SODIUM WATER may present a moderate sodium problem in fine-textured (clay) soils unless there is gypsum in the soil. This water can be used on coarse-textured (sandy) or organic soils that take water well. HIGH SODIUM WATER may produce troublesome sodium problems in most soils and will require special management good drainage, high leaching, and additions of organic matter. If there is plenty of

14 11 gypsum in the soil, a serious problem may not develop for some time. If gypsum is not present, it or some similar material may have to be added. S4 VERY HIGH SODIUM WATER is generally unsatisfactory for irrigation except at low- or medium-salinity levels where the use of gypsum or some other amendment makes it possible to use such water. Table 5. Summarizing the discussion on classification and interpretation of water analysis, first consideration should be given to the salinity and sodium hazards referring to figure 5, and the quality-class ratings that follow the diagram. Other independent characteristics should then be considered, such as bicarbonate and boron or other phytotoxic substances, any one of which may change the quality rating of the water. Final use of a water then must also take into account infiltration rate, drainage, quantity of water used, climate, rainfall, and salt tolerance of the crop (7 ). In using the guidelines outlined in the classification scheme based off figure 5, average conditions with respect to one or more of the factors mentioned are assumed. This relationship to average conditions must be accounted for with the use of any general method for the classification of irrigation waters, since unusual circumstances may alter a recommendation regarding safety of a given water for irrigation. C. Carbonate and Bicarbonate Bicarbonate (HCO 3 -) concentration in irrigation waters is primarily important in its relation to calcium (Ca 2+ ) and magnesium (Mg 2+ ). There is a tendency for both calcium and magnesium to react with bicarbonate in the water and/or soil precipitating as either calcium carbonate (CaCO 3 ) or magnesium carbonate (MgCO 3 ). Since magnesium carbonate is the more soluble, there is less tendency for it to precipitate. The precipitation of either calcium or magnesium from a water as carbonate salts increases the relative proportion of sodium which directly raises the sodium hazard rating. The potential bicarbonate hazard rating is shown in Table 5. Potential Bicarbonate Hazard Potential Hazard None to Slight Moderate Severe Very Severe (ppm HCO 3 ) Bicarbonate Eq. 4 The increase in sodium hazard due to bicarbonate can be determined by calculating the residual sodium carbonate (RSC) as shown in Equation 4: RSC = (CO 3 2- meq/l + HCO 3 - meq/l) - (Ca 2+ meq/l + Mg 2+ meq/l)

15 12 Table 6. Earlier studies have indicated that waters with RSC values > 2.5 meq/l are probably not suitable for irrigation purposes; waters containing 1.25 to 2.5 meq/l are marginal; and those waters containing < 1.25 meq/l RSC are probably safe (7). Marginal waters might possibly be made safe with the use of gypsum. RSC values may become less useful for waters where concentrations of both calcium and bicarbonate are about equal and high (i.e., in the order of 10 meq/l or greater), rendering a very low or zero RSC value. Such waters will precipitate some calcium carbonate and should be considered marginal at best (7). D. Phytotoxic Substances While boron (B) is an essential plant micronutrient, certain irrigation waters have been shown to contain phytotoxic concentrations of boron. Boron toxicity symptoms typically appear as yellowing, spotting or drying of leaf tissue at the tip and along the edges of older leaves. The damage gradually progresses interveinally toward the midleaf. A gumosis or exudate on limbs or trunks is sometimes noticeable on boron toxicity affected trees such as almond. Many boron sensitive crops show toxicity symptoms when boron concentrations in leaf blades exceed 250 ppm (4). Not all boron sensitive crops accumulate boron in their leaves, such as stone fruits (i.e., peach, plum, and almond), and some pome fruits (i.e., pear, apple, and others), rendering leaf analysis for these crops an unreliable boron toxicity indicator (4). Boron tolerance has been tested for a wide range of crops in sand cultures. Table 6 summarizes relative tolerance of selected crops to boron and rates potential toxicity from boron in irrigation water. Relative Tolerance a of Crops to Boron Tolerant Semitolerant Sensitive 4.0 mg/l of boron 2.0 mg/l of boron 1.0 mg/l of boron Asparagus Sunflower, native Pecan Date Palm Potato Walnut, black and Persian or English Sugarbeet Cotton, Acala and Pima Jersualem artichoke Garden beet Tomato Navy bean Alfalfa Radish Plum Broadbean Field pea Pear Onion Olive Apple Turnip Barley Grape Cabbage Wheat Kadota fig Lettuce Corn Persimmon Carrot Sorghum Cherry Oat Peach Pumpkin Apricot Bell pepper Thornless blackberry Sweetpotato Lima bean Orange Avocado Grapefruit Lemon 2.0 mg/l of boron 1.0 mg/l of boron 0.3 mg/l of boron Source: G. J. Hoffman, R. S. Ayers, E. J. Doering and B. L. McNeal, Salinity in Irrigated Agriculture. In Design and Operation of Farm Irrigation Systems (1980), M. E. Jensen (Ed.), ASAE Monograph 3, p Copywrite 1980 by ASAE, pp Reprinted by permission of ASAE. arelative tolerance is based on the boron concentration in irrigation water at which boron toxicity symptoms were observed when plants were grown in sand culture. It does not necessarily indicate a reduction in crop yield. btolerance decreses in descending order in each column between the stated limits.

16 13 Table 7. Rating Potential Toxicity from Boron Boron (ppm) Safe < 0.5 Marginal with Increasing Problems Problems Can Occur > 1.0 Data in Table 6 are based on the boron level at which toxicity symptoms were observed and do not necessarily indicate corresponding reductions in yield. Studies on many crop nutritional interactions between boron in the soil and plant and potassium, calcium, and soil and water ph have yet not fully established a sound relationship between boron concentration and crop yield (4). E. Other Phytotoxic Substances Very few substances other than boron occur in toxic concentrations in natural waters ( 7). Excess chloride concentrations in soil solution have been shown to be phytotoxic for certain crops (some citrus, stone fruit, avocado, grape, olive, some berries and strawberries) (6). Table 7 shows irrigation water ratings for potential toxicity from chloride. Potential Toxicity from Chloride Rating Chloride (ppm) Table 8. Safe 0-70 Marginal with Increasing Problems Problems Can Occur > 300 Other phytotoxic substances contained in irrigation water may be from those waters obtained from industrial waste effluent that have been discharged into surface streams. Irrigation water analysis is a critical management component of crop and soil management when irrigating from surface water sources. Table 8 shows guidelines for field application of pulpmill effluents (7). Guides for Field Application of Pulpmill Effluents BOD < 200 lb/acre day Color Individual site investigation ph SAR < 8 on permeable soils The possible effects or residues from pesticides that are normally encountered in irrigation waters cannot entirely be ignored, however minute the pesticide quantity may be. The greatest concern would come from irrigating with tailwaters or reuse pits, streams and/or runoff control stuctures. No firm evidence has been established whether or not significant amounts of pesticides and herbicides enter waterways used for

17 14 irrigation or leave by way of irrigation return flow (7). Some chlorinated pesticides are known to persist for long periods in the soil, but is conjectural to assume they are washed from the soil to reappear in water courses. Some evidence has been found that where water channels are sprayed for weed control with herbicides such as 2,4-D and 2,4-5-T, residues (in parts per trillion) were more likely to be persistently found in irrigation return flow (7). F. Sediment Sediment hazards contained in irrigation water are primarily a concern limited to trickle irrigation systems. However, if the irrigation water source is from natural stream waters, or holding ponds, any irrigation system may be subject to clogging of intake screens and pumps. Table 9 shows classification of screens and particle sizes in micrometers (µm), with figure 6 showing the relationship of different particle sizes (6). Table 9. Classification of Screens and Particle Sizes fig. 6 Screen Equivalent Particle Equivalent Mesh No. Diameter Designation Diameter (micrometer) (micrometer) Coarse sand > Medium sand Very fine sand Silt Clay < Bacteria Virus < Relationship of Different Particle Sizes 150 µm 2 µm 20 µm 50 µm

18 15 Table 10. A total dissolved solids (TDS) in units of ppm is determined to assess sediment content effect on any given irrigation water quality analysis. Filtration may be required for optimum irrigation system performance and is usually always required for optimum trickle irrigation system performance. Settling basins, sand or media filters, screens, cartridge filter and centrifugal separators are the primary devices used to remove suspended material in irrigation water (5). Tables 10, 11, 12, and 13, along with figure 7, summarize filter effectiveness, requirements, and various schematic descriptions of sediment removing devices. Physical, Chemical and Biological Contributors to Clogging of Trickle Systems A. Physical B. Chemical C. Biological (Suspended Particles) (Precipitation) (Bacteria and Algae) a. Organic a. Calcium carbonate a. Filaments (1) Moss, aquatic b. Calciumsulfate b. Slime plants, and algae c. Heavy metal, hydroxides, c. Microbial deposition (2) fish, snails, etc. oxides, carbonates (1) Iron b. Inorganic silicates, and sulfides (2) Sulfur (1) Sand d. Fertilizers (3) Manganese (2) Silt (1) Phosphate (3) Clay (2) Aqueous ammonia (3) Iron, zinc, copper, manganese Source: D. A. Bucks, F. S. Nakayama, and R. G. Gilbert, "Trickle Irrigation Water Quality and Preventive Maintenance." Agricultural Water Managment copyright 1979 by Elsevier Science Publishing Co., Inc. p Reprinted by permission of Elsevier Science Publishing Co., Inc. and authors. Table 11. Control of Trickle System Clogging Filter Effectiveness Filter Type Size Range (microns) Sediment basins > 40 Slotted cartridge > 152 Sand media Sand media > 20 Screen ( mesh) Screen (200 mesh) > 100 Screen > 75 Separator a > 74 Separator a (two stage) > 44 Source: W. M. Shannon, "Sedimentation in Trickle Irrigation Laterals," unpublished M. S. Thesis (1980), Washington State University, Pullman, 133 pp. aseparators remove 98 percent of particles larger than size indicated.

19 16 Table 12. Filtration Capabilities of Different Screen Mesh Sizes Mesh Filtration to Micron Size Note: For example, a 100-mesh screen will filter everything larger than 147 microns in size out of the irrigation water. Table 13. Filtration Requirements for Selected Physical Clogging Agents Water Quality Suggested Treatment Inorganic Solids < 10 mg/l Particles greater than 100 microns in diameter Particles less than 100 microns in diameter < 10 mg/l Particles over or under 100 microns Organic Solids < 10 mg/l Particles over 100 microns < 10 mg/l Particles over 100 microns Slug loadings of organic solids with particles under 100 microns Remove with stainless-steel screen. (Particles larger than one-sixth of emitter orifice diameter should be screened out) These particles may pass through the irrigation system if the Fe and S concentrations are not too high. If slug loadings are frequent, then automatic screen cleaning may be required. Automatic cleaning of screens suggested. Sand filters are required. Recommended flowrate through sand filter is 20 gpm/ft 2. of bed area. Manual backflushing should be satisfactory. Sand filters with automatic backflush are required. Recommended flowrate through sand filter is 20 gpm/ft. 2 of bed area. High suspended solids loadings of this type of materal may not pass through the trickle irrigation system. In this situation, sand filters will remove a larger volume of material. Automatic backflushing of the sand filters will most likely be required. Treatment with chlorine may be required periodically during the season to prevent accumulation of particles under 100 microns.

20 17 fig. 7 Schematic Description of Various Sediment Removing Devices Typical (a) "Y" and (b) basket filters used for secondary filtration in trickle irrigaion systems. They are normally installed at the upstream end of submains and laterals.

21 18 fig. 7 (continued) Sand Medial Filter. (a) Filtering process. (b) Backwash process. Screen Filter. (a) Filtration Progress. (b) Throughflush process. G. ph ph is a measurement for acidity or alkalinity. A ph of 7.0 is considered neutral, while a ph reading below 7.0 is considered acidic, and a reading above 7.0 is considered alkaline. Most well waters tend to be in the alkaline range, with ph s in the 7.0 to 8.3 range, while some stream waters may be slightly acid (ph 6.5). With alkaline waters being utilized for irrigation, care may have to be taken if certain fertilizer and/or herbicides and pesticides are to be injected into the water (fertigation/chemigation). Fertigation of ammonium polyphosphate (APP) and certain micronutrients (notably zinc, manganese and iron) into an alkaline water will generally cause those fertilizer nutrients to precipitate out as insoluble compounds and rendered plant unavailable. APP solutions may react in hard water (high calcium, magnesium and bicarbonate content) forming a precipitant (calcium ammonium pyrophosphate) ( 2) which collects on the walls of the pipes and nozzles and eventually causes plugging. A simple test for APP compatibility with the irrigation water follows (3): 1. Measure amount of irrigation water in milliliters (ml.) equal to the gpm pumping rate, i.e., 950 gpm = 950 ml. 2. Add the number of ml. of APP equal to the desired APP pumping rate to the measured amount of irrigation water. 3. If a cloudy precipitate forms, the addition of APP to this irrigation water is not advisable. 1/ Urea-phosphate solutions (UP) are acid-based phosphate fertilizer formulations that have shown promise for use in irrigation systems with hard water. These formulations 1/ The Tennessee Valley Authority (TVA) has conducted studies showing that formation of insoluble calcium and magnesium pyrophosphates upon additions of APP into hard irrigation water could be avoided by adding phosphoric acid to decrease the ph of the APP base solution to 4 or lower (1).

22 19 will sequester calcium and magnesium preventing formation of precipitate in the irrigation water ( 1). Base solutions made from UP and water resulting in an grade have a ph of 1.5, made by dissolving crystalline UP in water with added heat (125½ F: dissolution time of five minutes; heat of 150½ F allows dissolution in one minute). Studies conducted by TVA with two relatively hard irrigation waters (the Republican River near Culbertson, Nebraska, and the Colorado River in Colorado) using a UP solution showed no precipitation difficulties (1). Resulting ph of the applied irrigation water was 7.0 and 6.8, respectively. For practical use in irrigation systems, about 800 gallons of water per pound of P 2 O 5 per acre should be applied. This rate of application in hard water is possible using UP base solution, while in the same waters only 25 gallons of water per pound of P 2 O 5 can be applied without precipitation problems using APP (1). H. Nutrient Availability Components Table 14. Essential plant nutrients included in Midwest Laboratories irrigation water report include calcium (Ca 2+ ), magnesium (Mg 2+ ), nitrate nitrogen (NO 3 - -N), sulfate (SO 4 = ), phosphorus (P), potassium (K + ), chloride (Cl - ), and boron (B). All nutrient concentrations are expressed as ppm. Following is a brief discussion of the plant-essential nutrients contained in the irrigation water analysis: 1. Nitrate-Nitrogen (NO 3 - -N) NO 3 - -N is commonly found in irrigation water sources either from soil application of ammoniacal nitrogen fertilizers or conversion of soil organic matter nitrogen via nitrification to NO 3 - -N. Determination of NO 3 - -N content in irrigation water plays an important role in irrigated crop nitrogen management strategies. To determine available nitrate-n per acre inch of waer applied, multiply ppm NO 3 -N by Phosphorus (P) and Potassium (K) Determination for these elements is made primarily for crop nutrient management strategies. 3. Chloride (Cl - ) and Boron (B) While both of these nutrients are plant-essential, their content in irrigation water is more of a concern when evaluating water quality criteria; Cl - and B are discussed in that light in the water quality section, pp. 12 to 13. Nutrient Availability in Irrigation Water (ppm) Rating Ca Mg K P N NO 3 SO 4 S Low < 20 < 10 < 5 < 0.1 < 1 < 5 < 30 < 10 Normal High Very High > 80 > 35 > 30 > 0.8 > 20 > 100 > 180 > 60

23 20 Table 15. Trace Element Tolerances for Irrigation Water For Water Used For Short-Term Use Continuously on on Fine-Textured Element All Soils Soils Only ppm ppm Aluminum (Al) Arsenic (As) Beryllium (Be) Boron (B) Cadmium (Cd) Chromium (Cr) (hexavalent) Cobalt (Co) Copper (Cu) Fluorine (Fl) (*) (*) Iron (Fe) (*) (*) Lead (Pb) Lithium (Li) Manganese (Mn) Molybdenum (Mo) Nickel (Ni) Selenium (Se) Tin (Sn) (*) (*) Tungsten (W) (*) (*) Vanadium (V) Zinc (Zn) *No established level. II. SAMPLING AND HANDLING GUIDELINES Proper sampling is a must in obtaining a representative water sample. Irrigation water samples should not be collected until after the well has pumped for a period of one or two hours or until the water has cleared. Stream, pond and catch pit water samples should be taken during the period of tme when they are being used for irrgation or a water source for livestock. It may be necessary to collect several samples during the season to correlate to evaporation and dilution. A. Sample Size An 8-16 ounce sample of water is sufficient for most quality and nutrient analysis. Rinse the contaienr several times with the water being sampled before collecting the final sample. Remember to rinse the lid also. Make certain that the bottle cap is tightly sealed before packaging shipment. B. Special Instructions 1. Clean plastic containers can be used for most regular analysis. However, for samples which are to checked for the presence of organic residues, such as

24 21 insecticides or herbicides, a glass container must be used. 2. Accurate iron tests can be made only if the sample has been made acid immediately after collection. This will require a separate sample. Ask the laboratory for special instructions. 3. Mail the sample(s) to the laboratory as soon as possible after collection. C. Conversions, Equivalents, and Abbreviations 1. Common Conversions To convert P to P 2 O 5, multiply by 2.29 To convert K to K 2 O, multiply by 1.23 To convert Mg to MgO, multiply by To convert Ca to CaCO 3, multiply by 2.50 To convert SO 4 to S, multiply by To convert NO 3 to N, multiply by Equivalent Weight of Ions Equivalent Equivalent Cations Weight Anions Weight Calcium (Ca) 20 Carbonate (CO 3 ) 30 Magnesium (Mg) 12 Biocarbonate (HCO 3 ) 61 Sodium (Na) 23 Sulfate (SO 4 ) 38 Chloride (Cl) Symbols--Abbreviations--Conversions EC... EC X EC X SAR... meq... meq/l... ppm... L... Electrical Conductivity in mhos/cm Electrical Conductivity in millimhos/cm Electrical Conductivity in micromhos/cm Sodium Absorption Ratio Milliequivalent Milliequivalent/L Parts per million Liter grains per gallon to parts per million ppm = 17.1 x grains per gallon one U.S. gallon weighs pounds one cubic foot of water weights pounds < less than > greater than 450 gallons per minute (gpm) = 1 acre-inch per hour 1 cubit foot per second (cfs) = 1 acre-inch per hour pounds of water = 226,500 x acre-inches one acre foot of water weights 1,360 tons ppm x 0.23 = lbs./acre inch

25 22 COMMENTS: LEVEL FOUND ELEMENT PROBLEM AREAS ELEMENT CRITICAL LEVEL LEVEL FOUND ELEMENT G R A P H I C NO APPARENT PROBLEMS POTENTIAL PROBLEMS PROBLEMS LIKELY LEVEL FOUND ELEMENT REPORT TO: REPORT DATE REPORT NUMBER "B" Street Omaha, Nebraska (402) FAX (402) IDENTIFICATION: COPY TO: SODIUM Na ppm pg CALCIUM Ca ppm pg. 18 MAGNESIUM Mg ppm ph pg. 19 NITRATE NITROGEN NO 3 -N ppm pg. 1-6 IRRIGATION WATER ANALYSIS SULFATE SO 4 ppm pg. 1 TOTAL CONDUCTIVITY DISSOLVED mmhos/cm SOLIDS (TDS) ppm pg pg. 19 pg. 11 SAMPLE IDENTIFICATION: LABORATORY NUMBER: pg. 13 pg. 12 SAR PHOSPHORUS POTASSIUM BICARBONATE CHLORIDE BORON P ppm K ppm HCO 3 ppm Cl ppm B ppm SODIUM CALCIUM MAGNESIUM ph NITRATE-N SULFATE CONDUCTIVITY TDS SAR PHOSPHORUS POTASSIUM BICARBONATE CHLORIDE BORON SODIUM CALCIUM MAGNESIUM ph NITRATE-N SULFATE CONDUCTIVITY TDS SAR PHOSPHORUS POTASSIUM BICARBONATE CHLORIDE BORON ADDITIONAL ELEMENTS Signed Midwest Laboratories, Inc. REV. 9/93

26 "B" Street Omaha, Nebraska (402) FAX (402) WATER SAMPLE SUBMITTAL FORM ACCOUNT NUMBER REPORT & BILL TO IDENTIFICATION COPY TO PHONE ( ) ZIP SAMPLE NUMBER IDENTIFICATION BASIC BASIC BASIC BASIC BASIC W-1 W-2 W-2A W-3 W-3A * BASIC W-4 * BASIC W-1: Livestock Suitability: Sodium, Calcium, Magnesium, Chloride, Conductivity, Total Dissolved Solids (by calc.), Sulfate, Nitrate Nitrogen, ph, Iron, Copper BASIC W-2: Irrigation Suitability: Sodium, Calcium, Magnesium, Chloride, Conductivity, Sulfate, Nitrate Nitrogen, ph, Carbonate, Bicarbonate, Phosphorus, Potassium, Boron, Total Dissolved Solids (by calc.), and SAR BASIC W-2A: Same as W-2 plus dissolved Iron, Manganese, Copper, and Zinc BASIC W-3: Domestic Suitability: Total Coliform, Sodium, Calcium, Magnesium, ph, Total Hardness, Conductivity, Total Dissolved Solids (by calc.), Nitrate Nitrogen, Iron, Manganese, Sulfate, Chloride, Fluoride BASIC W-3A: Same as W-3, but without Coliform bacteria BASIC W-4: Nitrate Nitrogen and Coliform bacteria Rev. 01/0 SIGNATURE OF SAMPLER DATE & TIME OF SAMPLING DATE SAMPLES SHIPPED SUBMIT TO: Midwest Laboratories, Inc "B" Street, Omaha, NE ZIP Total Coliform * NITRATE (NO 3 ) CHECK TEST DESIRED Lead & Copper OTHER LAB USE ONLY REMARKS * Samples submitted for Coliform Bacteria analysis must be collected in a sterile container and returned to the lab within 24 hours of sampling*

27 24 REFERENCES 1. Achorn, F. P Acid fertilizers. In Proceedings: Great Plains Fertility Workshop. Denver, Colo. 12 p. 2. Duis, J. H Polyphosphates in Irrigation. Solutions Magazine. March-April, Hergert, G. W Sprinkler application of fertilizer nutrients. Solutions Magazine Hoffman, G. J. Management Principles: Salinity. P In: F. S. Nakayama and D. A. Bucks (ed.) Developments in Agricultural Engineering 9: Trickle Irrigation for Crop Production; Design, Operation and Management Elsevier. 5. James, L. G. Water for Irrigation. P In: L. G. James (ed.) Principles of Farm Irrigation System Design John Wiley and Sons, Inc. 6. Nakayama, F. S., Operational Principles: Water Treatment. P In: F. S. Nakayama and D. A. Bucks (ed.) Developments in Agricultural Engineering 9: Trickle Irrigation for Crop Production; Design, Operation and Management Elsevier. 7. Wilcox, L. V. and W. H. Duram. Quality of Irrigation Water. P In: R. M. Hagan, H. R. Harse. T. W. Edminster (ed.) Irrigation of Agricultural Lands. Agronomy Monograph No. 11. American Society of Agronomy. Madison, Wisconsin.

28 25 TABLES AND FIGURES INDEX Bicarbonate, potential hazard (Table 5) Boron tolerance (Table 6) toxicity Chloride, toxicity (Table 7)...13 Clogging, physical, chemical and biological contributors (Table 10) Crop-yield salinity relationship (fig. 2)... 2 Filters clogging effectiveness (Table 11) various designs (fig. 7) Filtration capabilities (Table 12) requirements (Table 13) Irrigation water classification (fig. 5)... 9 nomogram for SAR and ESP relationship (fig. 3)... 8 Leaching requirement for highest allowable conductivity (Table 4)... 5 for salinity hazard (Table 3)... 4 Nutrient availability in irrigation water (Table 14) Particle size relationship (fig. 6) Permeabiliy problems guidelines (fig. 4)... 9 Pulpmill effluents, guides for field application (Table 8) Salinity levels, threshold and zero yield (Table 1)... 3 Salt tolerance, percent yield decline of irrigated crops (Table 2)... 3 Screens, classifications and sediment particle sizes (Table 9) Soil characteristic curves, soil water and salt concentrations (fig. 1)... 2 Trace element tolerances for irrigation water (Table 15)... 20