P lay rna,x yva r k e r.s. Pcr e rce - free s~ Go od. Yod. Course -- Soil and Water Testing in Perennial Crops. February 8, 1989.

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1 FIELD SAMPLING * Identify permanently designated small areas of good, intermediate and poor vine growth approximately 50 ft X 50 ft in size as bench mark areas for monitoring soil and plant analysis. Soil sampling should consist initially of cores 3/4" to 1" in diameter taken randomly from the 50' X 50' area at the following increments: 0-6", 6-12", 12-24", 24-36", 36-48", and 48-60". The following analyses would be desirable: SP, ph,, EC e, Ca, Mg, Na, B, Cl, Exch-K, HCO3-P, and DTPA-Zn. Plant sampling should consist of collecting petioles from each of three bench mark areas during bloom tima the nearer to full bloom the better. ( 300' Pcr e rce - free s~ teitra0+e Or e/eri-, ic... p Yod Go od rt& e r c cl 0 so' tic0 Pvernahe)1+ Marktys So' THE FAMILY CIRCUS by Bil Keane of GLO P lay rna,x yva r k e r.s 8-1 "We're gonna see how tar down the dirt goes." C * Prepared by Roland D. Meyer, Extension Soils Specialist for University Extension Course -- Soil and Water Testing in Perennial Crops. February 8, 1989.

2 PETIOLE SAMPLING INSTRUCTIONS As close to full bloom as possible, take your samples following the easy instructions below: 1. FOR ROUTINE SAMPLING - To determine fertilizer needs; take the petioles which occur opposite either of the two basal flower clusters (see illustration below). Tear off the leaf blade and save only the petiole. Remember, the petiole is the part that connects the leaf blade to the cane. 2. TROUBLE SHOOTING - Sample at the time when symptoms occur. Take the petioles from vines showing abnormal symptoms. Then take petioles from vines that appear normal, from the same general location on the shoots which show abnormalities. Both samples should be taken from the same vineyard, variety, and soil type. We then analyse both normal and abnormal petioles, compare the two, and decide on a course of action. If it is not full bloom time, collect the petioles from the most recently developed, full - sized leaf. This is commonly the 5th or 6th leaf from the shoot tip. 3. Sample Size - Sample one vine, then skip a few vines. The main objective here is to obtain a good representation of your vineyard. Sample until you have at least 100 petioles, 150 if you have small vines. Don't mix different varieties or soil types. 4. Sample Handling - Drying your samples yourself is not necessary unless you plan to ship your samples directly to our lab in Ukiah (use UPS).' You can dry them by placing samples in oven; turn heat as low as it will go, prop open the door and dry them overnight. If you don't want to worry about all this, just put the samples in paper bags (DON'T USE PLASTIC), fill out your sampling form (enclosed), and drop them off at Vinquiry or The Wine Lab. Indicate on the sampling form if you have applied any foliar nutrient sprays this spring and we will wash them before analysing. select petiole opposite either one of the basal clusters at full bloom save petiole - discard blade

3 DELLAVALLE Laboratory, Inc. Chemists and Consultants 1610 W. Waini0 P, Suito 110 Amino, CA (200) SAMPLING TECHNIqUES INS E. NW. An. Tol r CA (2011) $ The nutritional status of your crop or field can be established by laboratory analysis. Proper sampling is essential for valid results. A sample should be a randomly obtained composite that represents the area to be evaluated. TO DETERMINE AREA TO BE SAMPLED: For uniform fields or for an average of a field, samples should be taken from the entire field. Divide the area into acre lots (or any appropriate size) based upon the following: 1. Soil type, texture or color 2. Topography, slope, changes in slope, cuts and fills 3. Variation in crop history 4. Avoid or sample separately areas too small to treat separately or unusual areas such as small spots, sandy strips, old hay yards, old home sites, fill material near roads 5. Separate good areas from poor areas 6. For unusual situations, call laboratory for instructions Non-uniform fields should be sampled by taking a composite sample from areas with the same charactistics. SOIL SAMPLING: Tools: Soil probe or spade A bucket Clean moisture-proof quart-size bag; paper bags may be used if delivery to laboratory is rapid. 1. Walk a zig-zag course around or through the area to be sampled taking 20 to 30 cores or enough to make a quart of soil, stay away from edges of field. a. For furrow or field crops, take soil 12 inches below the surface or to depth of plowing. b. For tree and vine crops, soil samples should be taken at one-foot increments to the depth of rooting. This may require three to five samples from the same area. 2. Mix sample well and place in quart-size bag. 3. Mark each bag with sample description or location. TISSUE SAMPLING: Tools: Knife (optional) and paper bag 1. Uniform fields can be sampled by walking a diagonal pattern through the crops. Non-uniform fields are sampled differently; see section above on choosing sample areas. 31

4 TISSUE SAMPLING (continued) 2. Take petioles or leaves per sample. a. Leaves: Take only fully-expanded mature leaves. b. Petioles: Take only the petioles, removing the blade. 3. Take approximately one sample for every acres. 4. Check the chart below for proper tissue sampling time as timing is important. For crops not listed, please contact the laboratory for specific information. PLANT TISSUE SAMPLES Crop Plant Part to Sample Time of Sampling Alfalfa Asparagus Cabbage Cantaloupe & Cucumber Citrus Deciduous Fruit Trees except peaches Grapes Peaches Tomato Mid stems Fern needles 4" tip section Midrib of wrapper leaf Petiole of 6th leaf from growing tip 5-7 mo. old bloom cycle leaves from nonfruiting terminals Mature leaf, 2-5 mo. old Spur leaves for almonds, apples, apricot, cherry, pear, plum and prunes Petiole - opposite cluster Basal to midshoot leaves Petiole of recently matured leaf (4th leaf from growing tip) 1/10 Bloom September At heading 6-8 true leaves Early fruit set Aug 15 to Oct 15 June and July Bloom June and July Early Bloom, 1" Fruit, 1st Color Woody Ornamentals Recently mature leaf Late June to Deciduous & Evergreen September December to March 38

5 O DELLAVALLE Laboratory, Inc. Chemists and Consultants GRAPE PETIOLE ANALYSIS 1110 W. AleMAME, SuHo 110 Mows., CA (200) INTERPRETATION GUIDE 1949 E. rul wt An. TWoro, CA ( Values are for Thompson Seedless petioles opposite clusters at bloom; with the exception of nitrogen, the information is applicable to most grape varieties. ELEMENT UNIT DEFICIENT LOW OPTIMUM/NORMAL HIGH EXCESSIVE NO3-N ppm * P % * K w,,,, * Zn ppm * Mn ppm * Na % Cl % U B ppm * Mg % *U U.3+ Mb *less than NO3-N (Nitrate Nitrogen): Grapes will produce most efficiently when the bloomtime petiole nitrate level is kept between ppm. Levels higher than 1200 ppm can cause excessive growth, delayed maturity of canes or fruit, as well as reduced sugar and color. Levels above can cause shattering and even leaf burn in extreme cases. The degree that these symptoms appear is also affected by irrigation, weather, pruning and varietal differences. Levels below can lead to reduced growth and yield. P (Phosphorus): Phosphorus deficiency in grapes is very rare at best. Levels at or below 0.1S% are considered questionable although not necessarily deficient. K (Potassium): Low levels of K can be caused by low soil potassium as well as any factors that restrict root growth such as hardpan, nematodes, phylloxera, irrigation problems or pruning. Questionable samples can be resampled in mid season to confirm any deficiencies. Zn (Zinc): Low levels will affect berry set and cause "little leaf". Mn (Manganese): Very high levels of manganese are usually found in vineyards with low soil ph somewhere in the profile. Low levels cause leaf symptoms, but seldon reduce yields. Na (Sodium): Possibly toxic if over 0.5%. Toxicity will cause leaf burn. Cl (Chloride): Possibly toxic if over 0.5%. Toxicity will cause leaf burn. B (Boron): High boron levels are usually a result of high boron soils or irrigation water. Boron deficiency will lead to poor fruit set. Reference: Grapevine Nutrition and Fertilization in the San Joaquin Valley. Publication ,

6 RY DLAGNOSTIC METHODS. Laboratory soil analysis is used to appraise vineyard problems related to ph, salinity, and certain toxicities. For such purposes, only the following analyses need to be considered, depending on anticipated problems: 1. Saturation Percentage (SP) a rough measure of soil texture 2. ph a measure of acidity or alkalinity 3. Electrical Conductivity (EC e ) measure of salinity 4. Exchangeable Sodium Percentage (ESP est.) to evaluate the sodium toxicity and soil permeability hazard a. Calcium plus Magnesium (Ca + Mg) b. Sodium (Na) 5. Boron (B) to test for boron toxicity Analysis is run on saturated soil paste Analysis is run on saturation extract 6. Gypsum Requirement (GR) to estimate the amount of gypsum to reclaim a sodic soil 7. Lime Requirement to estimate the amount of lime needed to adjust the ph of an acid soil Soil analysis is not a reliable means of determining nutritional problems and fertilizer requirements. Field research has repeatedly shown inconsistent relationships between soil nutrient levels and grapevine needs. This is largely due to the wide variety of soil types and depths involved, inherent grape variety and rootstock differences, the effect of root pest and disease problems, and the wide climatic differences among our grape growing regions. 4 WiSitet, Tissue analysis in vineyard nutrition is much more effective and reliable than soil analysis; tissue analysis represents the concentrations of nutrients the grapevine is able to remove from the soil. The principal tissues used are either the leaf petiole or the leaf blade. (See "Foliar Tissue.") The determination of the amino acid arginine in the juice of mature fruit or in dormant canes can also be used to evaluate the nitrogen status. (See "Arginine Test for Nitrogen" at the end of this chapter.) FOLIAR TISSUE How to sample a vineyard The sampling method depends on the objective: (1) determination of nitrogen status or general nutritional levels, or (2) troubleshooting and diagnosing vine disorders. 1. Nitrogen status or general nutritional levels of vineyards. This approach is used when surveying a vineyard for fertilizer needs or when evaluating a fertilizer program. Time to sample. Timing is extremely important. Samples must be taken during bloomtime the nearer to full bloom the better. ("Full bloom" is when approximately two -thirds of the caps have fallen from the flowers.) This normally occurs during mid-may in Fresno County, but can vary between May 1 and 30, depending on the season, location, and grape variety. Plant part to sample. The petioles are normally used those from leaves opposite the clusters toward the base of the shoot. Immediately remove and discard the blades, leaving only the petioles for 4 v 33

7 analysis. Taking a representative sample. Each sample should represent not more than 10 acres, even in uniform vineyards. Areas of different soil types and weak or strong vine areas should be sampled separately. Each sample should consist of 75 to 100 petioles, one petiole per vine from vines uniformly distributed over each area. Care of samples. Put each sample in a new, clean paper bag. A No. 2 bag is a convenient size. Do not use a plastic bag because of moisture condensation and possible molding. Label and keep a record of the pertinent information name, date, variety, location, condition of vineyard, and foliar sprays used. Deliver the petioles to the laboratory immediately. If there is a delay, keep the bags open in a warm, dry, well-ventilated place. This begins the drying process and prevents molding and decay. Foliage contamination from a nutrient spray can give erroneous laboratory results. Do not sample after a nutrient spray unless you (1) are not considering analysis of any nutritional element contained in the spray, (2) have made arrangements with the laboratory for sample washing, or (3) are sampling uncontaminated tissue later in the season. Select petiole opposite either of the basal clusters during full bloom. Save the petiole and discard the blade. Sample each vineyard area separately. Collect petioles taken from the most recently developed, full-sized leaf. 34

8 2. Troubleshooting, diagnosing visible vine disorders, and follow-up sampling. Time to sample. Samples can be collected whenever abnormal appearance is noted. However, for midsummer resampling of an area with a questionable bloomtime potassium level, it is best to sample in mid-july at berry softening. The bloom period offers the advantage of easy, uniform sampling during a definite stage of vine growth. However, both deficiency and toxicity symptoms most commonly appear in midseason or at harvest time. Thus, sampling at this time is useful to diagnose vine disorders and to follow up on questionable bloomtime levels. Plant part to sample. Take the petiole from the most recently matured leaf on a shoot after the bloom period. This would be the first fully expanded leaf, usually the fifth to seventh leaf from the tip of an actively growing shoot. To diagnose toxicities, collect both the leaf blades and the petioles for separate samples, because greater amounts of elements like boron may accumulate in the blade itself.. Taking a representative sample. Uniformly sample the area in question. Where leaf symptoms show, be sure to sample the affected leaves. For comparison, take a second sample from healthy shoots in an unaffected area. Care of samples. Same as for bloomtime samples. What analyses should be made? For general nutritional surveying, have the laboratory analyze bloomtime petiole samples for nitratenitrogen, (NO 3-N), total phosphorus (P), total potassium (K), zinc (Zn), and boron (B). An analysis of other elements, such as magnesium (Mg) and manganese (Mn), which are rarely at deficiency levels, is only necessary for more background information or for leaf symptom diagnosis. For troubleshooting, especially in midsummer to late summer, the samples can be analyzed for possible toxicities of chloride (C1), boron (B), or sodium (Na), or for possible potassium (K) deficiency. Should analyses be done every year? Check the bloomtime nitrate-nitrogen levels for a few successive years so that any necessary adjustments can be made in the nitrogen fertilization program to establish correct vine nitrogen levels. If levels of the other nutrients are adequate, tests for them only need to be rerun every few years to maintain a check. INTERPRETATION OF LABORATORY ANALYSIS The following interpretations give critical values for important grapevine nutritional elements. They are approximate levels, based on the available information to date, and are subject to change as more information is developed. Critical levels are not yet known for all grape varieties, and the levels reported are based mostly on experience with a few of the more important ones. Known important variety differences are mentioned under each element. These data are based on leaf petioles taken from opposite clusters at full bloom, except where stated otherwise. Macronutrients Nitrogen. The following nitrate-nitrogen levels were established for the Thompson Seedless variety. Although other varieties, such as Carignane, appear to fit into these ranges, they should be considered general guidelines to categorize a vineyard as relatively low, medium, or high in nitrogen, and to evaluate nitrogen fertilizer programs from year to year. Yield and fruit-quality effects of nitratenitrogen levels in other varieties have not yet been established. Nitrate-nitrogen levels in the central San Joaquin Valley normally are highest 7 to 10 days before bloom, decline through the bloom period, and reach a relatively stable lower level by 2 to 3 weeks after bloom. Nitrate-nitrogen levels are similar for a given variety during bloomtime if they are taken within several nodes in either direction from the cluster positions. There may be wide differences among grape varieties, rootstocks, and year-to-year fluctuations in the same vineyard. Deficient Questionable Adequate More than necessary Excessive Possibly toxic NO 3-N ppm less than ,200 over 1,200 over 2,000 over 3,

9 Levels over 1,200 ppm can produce excess growth but may be justified where heavy foliage is desired. Levels over 2,000 ppm are sometimes associated with various detrimental effects excessive growth, reduced bud fruitfulness in Thompson Seedless, poorer cane maturity, and reduced fruit set. Levels over 3,000 ppm can produce direct toxic effects, such as leaf burn. Toxic levels commonly begin between 3,500 and 4,500 ppm in Thomspon Seedless but can be higher in other varieties and under different growing conditions. Phosphorus. Deficiency symptoms have not been identified in California vineyards, nor have there been measureable responses in yield and fruit quality in University of California trials thus, the lack of a critical deficiency level. Total phosphorus Opposite-cluster petiole levels usually decline most rapidly from before bloom until 2 to 4 weeks afterwards. Thereafter, they decline gradually or level off through midsummer. Potassium levels are highest in the youngest mature leaf petioles, where they peak at bloomtime and then decline with time and with leaf age. Potassium levels can vary widely (30 to 50 percent) from year to year in the same vineyard. Varietal differences also exist for potassium, although they are not as great as for nitrate-nitrogen. Certain varieties, such as Emperor, French Colombard, and Rubired, tend to be high in potassium; Salvador tends to be low. Thompson Seedless, Carignane, and Barbera are among the intermediate varieties. Magnesium. Total magnesium Possibly deficient Questionable Adequate By midsummer, these levels can drop: less than over 0.15 Total phosphorus Possibly deficient' less than Questionable Adequate more than 0.12 Petiole phosphorus levels tend to decline through the bloom period and to level off through midsummer. Differences among mature leaf petioles along the shoot are minor. There are wide differences among grape, varieties and between year-to-year levels in the 'same vineyard. Potassium. Deficient Questionable Adequate Vines at the questionable level should be resampled 6 to 8 weeks after bloom (about mid-july) by the collection of petioles from the most recently matured leaves. Levels below 0.5 percent K would be deficient in midsummer, whereas a safe level would be above 0.8 percent at this time. 36 Probably deficient Questionable Adequate less than over 0.3 Petiole levels in California vineyards almost always increase as the growing season progresses and tend to be higher in older petioles. Critical petiole levels are probably higher later in the season, but they have not been established. Micronutrients Zinc. Total zinc PI= Deficient less than 15 Questionable Adequate over 26 Differences in petiole levels along the shoot and Potassium changes during the growing season are minor. Bloomtime levels are more critical because of possible berry set effects. less than over 1.5 Manganese. Total manganese ppm Deficient less than 20 Questionable Adequate over 25

10 Differences among the mature leaf petioles along the shoot are minor. No conclusions on variety differences and seasonal changes can be made, because data are limited. Boron. Total boron PPrn Salinity problems Chloride. Leaf injury from chloride sometimes occurs at petiole levels down to 0.8 percent in sensitive varieties and when sodium is high. (Blade analysis may be needed to confirm toxicity.) Total chloride Deficient Questionable Adequate Possibly toxic Toxic less than over 30_ and above* over 300 in blades Possibly toxic over 0.5 at bloomtime Toxic and above in midsummer to late summer over 0.5 in blades *Can be confirmed with blade analysis, presence of symptoms, and/or soil analysis. Petiole levels normally do not vary markedly along the shoot or during the growing season. However, in soils with high or excess boron, the petiole levels increase gradually throughout the season. Boron accumulates more in the blades. Thus, in high-boron areas, the levels increase markedly during the season and are higher in the older leaves. Iron. Critical levels have not been established, because there is no correlation between iron deficiency and tissue levels. Deficiencies are related more to iron immobility within the grapevine than to total iron levels. Petiole levels range widely from 50 to 300 ppm but most typically from 70 to 200 ppm. Varieties and rootstocks differ widely in tolerance. Chloride continues to accumulate during the growing season and does so predominantly in the petiole, even though the symptoms of excess appear in the blades. Sodium. Total sodium. Possible problem over 0.5 over 0.25 in blades Effects of excess sodium have not been clearly defined, because they are usually associated with high chlorides. Sodium may aggravate a chloride problem. ARGININE TEST FOR NITROGEN The amino acid arginine is an important stored form of N in grapevines. It supplies much of the vines' N requirement for rapid shoot growth in the spring, and it is also the main form of N in ripe. fruit. The analysis of arginine in harvested fruit or in dormant grape canes is a good indicator of N deficiency in the Thompson Seedless variety. One suggested sampling technique is to get grape juice samples from grape loads at the winery sampling station. The sampled loads should come from specific, representative, uniform vineyard blocks. If such sampling is impractical, the analysis of the juice from 100 or more randomly selected berries from representative blocks can be used. These juice samples can be frozen for later analysis, if necessary. Dormant cane samples can be taken after pruning by cutting off the end. node along with a full internode from individual canes. At least 20 cane sections per sample are suggested. The critical arginine ranges for Thompson Seedless are: Deficient Adequate Fruit (micrograms per milliliter of juice) below 400 > 500 Canes (milligrams per gram, dry weight) below This method is relatively new and requires further evaluation for varieties other than Thompson Seedless. Critical arginine levels for excess N have not been established. 4 ol 37

11 DELJLAVAILLE Laboratory, Inc. e Chemists and Consultants 1110 W. 4001Usior, Ault, 110 Fr*sae. CA 0371$ (201) S IL Tokyo Ave. T lare. CA MN OWN ASS-0000 SALINITY, SODIUM & FERTILITY ASSAY SOIL INTERPRETATION GUIDE Soil analyses provide information on a soil's nutrient-supplying ability, its salinity, acidity or alkalinity. This information coupled with the field's crop history, water supply and the general level of management are used in making fertilizer and amendment recommendations. The following information is based upon correlation studies conducted under California conditions by university and government researchers. SP SATURATION PERCENTAGE is the grams of water required to saturate 100 grams of soil. Its relation to soil texture is as follows: Below 20 Sandy or Loamy Sand Sandy Loam Loam or Silt Loam Clay Loam Clay Above 150 Usually (Peat or Muck) The water-holding capacity of a soil when irrigated and allowed to drain is approximately half the SP. About half the water-holding capacity is available for crop use. phs DEGREE OF ACIDITY OR ALKALINITY of a soil paste wet to saturation is expressed as ph s. Below 4.2 Too acid for most crops Adapted to growth of acid tolerant crops Adapted to growth of most crops. Above 8.4 Possible sodium problem. However, sodium problems can occur below phs 8.4. EC e ELECTRICAL CONDUCTIVITY of the saturation extract can be expressed as millimhos per centimeter or decisiemens per meter at 25 C is an index of salt content. Salt will restrict crop growth as follows: Below 2 No salinity problem for most crops. 2-4 Restricts growth of very salt sensitive crops. 4-8 Restricts growth of all but salt-tolerant crops Restricts growth of all but salt-tolerant crops. Above 16 Only a few salt-tolerant crops make satisfactory yields. Ca CALCIUM + MAGNESIUM ions in the saturation extract are expressed in milliequivalents Mg per liter. Ca + Mg along with Na is used to calculate ESP. Na Cl SODIUM in the saturation extract expressed as milliequivalents per liter is used to calculate ESP. CHLORIDE in the saturation extract is expressed in milliequivalents per liter. For most crops, chloride is not a factor when the electrical conductivity is in a safe range. ESP GR EXCHANGEABLE SODIUM PERCENTAGE is the degree to which the soil exchange complex is saturated with sodium. It is used to determine the soil permeability and potential crop phytotoxicity. Below 10 No permeability problem; however, sodium-sensitive crops may show phytotoxicity such as chlorosis or slight crop yield reduction Soils with SP above 50 may have permeability problems and/or phytotoxicity. Above 15 Permeability problems are likely on all mineral soils except those with a SP below 20. Most crops show phytotoxicity. GYPSUM REQUIREMENT is the amount of gypsum or its equivalent required to furnish sufficient calcium to correct a sodium-caused permeability problem and/or phytotoxicity. GR is expressed in tons of 100% gypsum per acre-six inches of soil. It will be determined when the ESP is above 10, Ca + Mg is less than three times the ECe or phs is above 8.4. LIME LIME when reported by one to four pluses ( 4 ) Tarcates that acid-forming amendments such as sulfur or sulfuric acid may be used in place of gypsum. The number of pluses is an estimate of the amount of lime present. Acidifying amendments may cause excessive ph reductions if used in the absence of lime. A numeric value is reported when ph s is below 6.0 which indicates the amount of 100% lime (CaCO3 in pounds per acre-six inch) required to adjust ph s to BORON, expressed as ppm in the saturation WiTikt, is required for plant growth but may be toxic. This analysis is used to evaluate toxicity; for deficiencies, a different soil or tissue test is necessary. Below 0.5 Not toxic for crops but may be insufficient for some. Above I Sensitive crops may show visible injury. 5 Semi-tolerant crops may show visible injury. 10 Tolerant crops may show visible injury.

12 Reprinted from American Journal of Enology and Viticulture, Vol. 25, No. 2, pp ARGININE LEVELS IN GRAPE CANES AND FRUITS AS INDICATORS OF NITROGEN STATUS OF VINEYARDS W. MARK KLIEWER and JAMES A. COOK Respectively, Associate Biochemist and Professor, Department of Viticulture and Enology, University of California, Davis Presented in part at the Annual Meeting of the American Society of Enologists, Coronado, California, June 22-24, Accepted for publication April 25, ABSTRACT A field nitrogen trial involving 80 six-vine plots of 'Thompson Seedless' grapes in 1971 and 1973 showed highly significant (P<0.001) curvilinear regressions between crop yields and arginine in canes, arginine in fruits, and nitrate in petioles. The respective correlation coefficients in 1971 and 1973 were 0.71 and 0.79, 0.72 and'0.83, and 0.69 and Arginine in dormant canes and in mature fruits, and nitrate in petioles, were all significantly correlated linearly with each other in both years. In addition, arginine in mature fruits was significantly correlated with pruning weights, with the respective coefficients for the two years being 0.61 and The concentration of arginine in fruits was independent of the level of total soluble solids between 19 and 22 Brix. In this cultivar the critical deficiency ranges were 4 to 6 mg per g dry weight for arginine in dormant canes, 400 to 500 p.g/m1 juice for arginine in fruits at harvest, and 0.12 to 0.15% dry weight for nitrate in petioles at bloomtime. The corresponding adequate ranges were respectively 6.1 to 14 mg, 501 to 1150 and 0.16 to 1.25%. Quantitatively, arginine is the most important form of stored nitrogen in grapevines, accounting for 50 to 90% of the soluble nitrogen in the roots, trunk, and canes, during fall and winter (7, 11). The concentrations of arginine and of soluble and insoluble nitrogen in these tissues vary widely with season, being highest in spring just prior to budbreak and lowest in midsummer. Kliewer (7) and Kliewer and Cook (11) found that arginine stored in the roots, trunk, and canes largely supplies the vine with its nitrogen requirement during the period of rapid shoot growth in the spring. The level of arginine in 'Thompson Seedless' grape berries increases rapidlly during the early period of sugar accumulation following veraison (July through August), and then remains relatively constant between 18 and 23 Brix (10, 12). During the period of arginine accumulation in the fruits, roots are the only part of the vine where arginine decreases significantly, an indication that roots may be a primary source for this amino acid in the berries (7). Amer. J. Enol. Viticult., Vol. 25, No. 2, In previous investigations (11, 12) of 'Thompson Seedless' vines grown in a perlite-vermiculite mixture with Hoagland solutions modified to contain 0, I/2, 1, 2, 4, and 8 mm NO 3, the levels of arginine stored in canes, trunk, roots, and fruits were found to be highly correlated with the concentration of nitrogen in the nutrient solution and with the amount of vine and fruit growth. From those findings, it appeared that arginine may be a good indicator for estimating nitrogen needs of vineyards. To test this hypothesis, the arginine level in dormant cane tissue and in mature fruits from 'Thompson Seedless' vines grown in a vineyard with varying levels of nitrogen supply, were correlated with crop yields and pruning weights over a 3-year period. The results are reported herein. The relationship of petiole nitrate to vine yield was used as a control since this relationship has given some success (4) for estimating vineyard nitrogen needs in the San Joaquin Valley.

13 INDICATORS OF NITROGEN STATUS-117 DISCUSSION Nitrogen is the nutrient most often deficient in California vineyards. Unlike with many other crops, grapevines do not have visual nitrogen-deficiency symptoms until they are at an extreme stage of nitrogen starvation. A quick, accurate, and reliable quantitative method of estimating nitrogen needs of grapevines is needed. Total nitrogen analysis of various vine parts has not been used in California since about 1945 since the range between deficiency and sufficiency is very small. Large numbers of samples replicated many times must be analyzed before reliable results can be obtained, and analysis for total nitrogen is relatively slow and time-consuming (1,5,18). More recently, nitrate concentration in grape leaf petioles has been used to determine the need of vines for nitrogen, but, this method also has its limitations (2,4,5). An irrigation or rainfall shortly before sampling, low temperatures during bloom, type of rootstock, and the cultivar itself, all have large effects on the level of nitrate in petioles. Recent evidence indicates that many perennial woody plants, including grapevines, store much of their reserve nitrogen as low-molecular-weight soluble nitrogen compounds, especially as arginine, in the bark and wood of the roots, trunk, and stems (7,11,15,17). Oland (13) and Taylor and May (16) have shown that the level of storage nitrogen in young apple and peach trees can be estimated accurately by measuring the level of arginine in dormant tissues. Similar results have been obtained with grapevines (11). In the present investigation, arginine levels in 'Thompson Seedless' canes or mature fruits correlated better with vine yields than did petiole nitrate levels. The levels of essential plant nutrients in tissues can be classed as deficient, adequate (sufficient), or toxic. The critical nutrient level is located in a transition zone between the deficient and adequate levels. This zone is usually defined as the nutrient concentration at which there is the first detectable decrease in yield. For practical purposes, however, the critical nutrient level is the level at which economic response to fertilization with a nutrient can be expected. Critical nutrient levels for plants grown under field conditions often vary somewhat from year to year ; therefore, a critical deficiency range is more practical. This may be defined as a range in levels of nutrients in tissues at which occurs an economic yield response to subsequent nutrient (fertilizer) application. In this investigation, the critical deficiency range for nitrate in petioles at bloomtime, arginine in dormant canes (sampled in late February), and arginine in fruits at harvest were respectively 0.12 to 0.15%, 4 to 6 mg/g dry wt, and 400 to 500 p,g per ml juice. The corresponding adequate or sufficient ranges were 0.16 to 1.25%, 6.1 to 14 mg/g dry wt, and 501 to 1150 µg/ml juice. No indication of the toxicity level of nitrate or arginine was observed. The critical nitrate range Amer. J. Enol. Viticult., found in this investigation agrees closely with that reported previously for 'Thompson Seedless' grapes (3). It should be emphasized that the critical and adequate ranges of nitrate and arginine cited above apply only to 'Thompson Seedless,' and that the crop records were for maximum tonnage of fruit for wine and raisins. Different grape cultivars grown side by side on a uniform soil at Davis differ widely (as much as 11-fold) in nitrate and arginine levels (2,8,9). Kliewer (8,9) has classified a number of cultivars according to the predominant amino acid in their fruits at harvest. He found 33 cultivars with arginine predominant, 39 with proline, and 4 with alanine. With such wide differences in arginine and nitrate content their critical levels must be determined for each cultivar. Investigations are in progress to establish these levels for the most widely planted cultivars in California. The use of arginine levels in 'Thompson Seedless' grapes to estimate vineyard nitrogen needs has several advantages over other methods. Foremost among these, at least with grapes for wine production, is that juice or must samples can be obtained at the time of delivery of grapes to a winery, thus avoiding the costly and time-consuming process of sampling, drying, grinding, and extracting tissues, as normally required for petiole nitrate or total nitrogen tests. In other words, grape pickers or mechanical harvesters do the sampling. Most wineries sample each load of fruits to determine total soluble solids. This same juice sample can be used for measurement of arginine, with only a dilution with water being required before assaying. Juice or must samples can be stored for 6 months or longer without loss of arginine. Another advantage of assaying fruits is that the analysis can be made in time to advise a grower whether his vineyard needs nitrogen fertilization during the winter months, in time to correct a deficiency condition for the forthcoming crop year. If the bloomtime nitrate test is used, petioles are sampled usually in late May or early June, too late to correct a nitrogen deficiency condition until the following crop year. Finally, the arginine assay is less time-consuming and less costly than either the nitrate or total Kjeldahl nitrogen methods. LITERATURE CITED 1. Alexander, D. McE. Seasonal fluctuations in the nitrogen content of the Sultana vines. Australian J. Agr. Res. 8: (1957). 2. Cook, J. A. Some problems in determining nitrogen needs in California vineyards. Wines and Vines 42(2):29-30 (1961). 3. Cook, J. A. Use of tissue analysis in viticulture. Proc. Statewide Conf. on Soil and Tissue Testing. University of California, Davis, Calif. Dec , Vol. 25, No. 2, 1974