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Guides to fertilization

• Chemical soil tests
• Plant analysis

• Avoiding nitrate pollution of groundwater
• How much N to apply
• Timing and placement of fertilizer N
• Nitrogen-carrying fertilizers
• Harvest and N deficiency

• Determining the need for fertilizer P
• Rates, placement, and timing

• Potassium (K)
• Sulfur (S)
• Other deficiencies

• Soil sampling
• Sampling plants
• Analytical methods

This bulletin presents guidelines for the use of soil and plant analysis to improve the efficiency of sugarbeet fertilization. The procedures outlined and the suggestions offered should not be considered absolute recipes for success. Many factors can affect the outcome of a recommendation based on soil and plant analysis, and an element of uncertainty is always present. We are confident, however, that wellcalibrated soil and plant tests, when used with an understanding of basic principles of mineral nutrition, can greatly improve efficiency in the use of fertilizers, benefiting farmers, sugar processors, and the environment, as well as conserving energy.
 

Chemical soil tests

A chemical soil test estimates the concentration or amount of a nutrient in the soil and, when correlated with crop response, can be used to predict the need for additional amounts of the nutrient. The interpretation of a chemical sod test can never be exact, because it depends on how well the soil sample represents the nutrient supply actually available to the crop and the degree to which other factors may limit or enhance production. For example, a test may indicate that a certain nutrient should be added as a fertilizer, but the crop may fail to respond to this addition, because: the soil sample may not be representative of the field in question; an unsuspected source of the nutrient may be available; or another factor may be seriously limiting growth, such as an inadequate stand, lack of available soil moisture, or a pest or disease. Despite these drawbacks, however, a well-calibrated soil test can serve as a general guide and aid in making fertilizer management decisions.

Plant analysis

Plant analysis is based on the relationship of a nutrient's concentration in a specific plant part to the growth of the plant. Through research and experience, reference concentrations of mineral nutrients in specific plant parts have been determined and are used as guides to indicate how well plants are supplied with these nutrients at the time of sampling. Such reference concentrations provide a tool to assist the agriculturist in evaluating nutrient disorders and improving fertilizer practices.

The critical concentration is defined for a given form of a nutrient and plant part as that threshold concentration at which the growth rate of the plant begins to decline significantly. Plants well above the critical nutrient concentration are adequately supplied with that nutrient; plants at or below the critical nutrient concentration are deficient in that nutrient. The earlier the deficiency occurs in the growing cycle, and the longer the deficiency persists, the more likely it is that the crop will respond to additions of the nutrient. In plants with a nutrient concentration at or below the critical level, the response to added amounts of the nutrient will depend on how fast the nutrient is taken up, the severity of the deficiency, the relative adequacy of other growth factors, and the growth stage of the crop. When overall growth conditions are good, the addition of a deficient nutrient will give a relatively large increase in yield, but if limiting factors arise, the increase will be relatively small. Also, the later the deficiency appears in the growing season, the less chance there is for a significant yield increase.
 

Large amounts of N are required to ensure adequate top and root growth, but if storage roots are to be high in sucrose concentration, the plants must be deficient in N about 4 weeks before harvest. This deficiency retards the utilization of sucrose for growth and allows it to accumulate in storage roots. Overfertilization with N can reduce sugar yield, increase the cost of production, waste fertilizer N, and result in the eventual leaching of N to groundwater supplies.

In more than 20 field trials conducted throughout the sugarbeet growing areas of California (1970 to 1977) the amounts of fertilizer N required for maximum sugar yield varied from none in five fields to 240 pounds per acre in five others, with the remainder responding most profitably to rates of 60 to 180 pounds N per acre. Figure 1 illustrates the range of responses obtained. Figure 2 uses the data from field B of Figure 1 to show how underand overfertilization affect the return to a producer.

Soil texture had little relation to fertility; both sandy and clay soils exhibited low and high N fertility. Basing a fertilizer recommendation on the average amount of N required for maximum sugar yield in these trials would result in underor overfertilization of many sugarbeet crops.

Avoiding nitrate pollution of groundwater

When sugarbeets are moderately fertilized for maximum sugar yields with amounts of up to 140 pounds of N per acre, a productive crop usually takes up as much fertilizer and soil N in its roots as is applied as fertilizer. Therefore, such fertilization contributes little excess N for eventual leaching to groundwater (Table 1). After fertilizer N has been applied, it is important to avoid water applications that will leach it below the root zone. Delaying major N fertilizer additions until after the heavy furrow irrigations that may be required for germination and emergence pre- vents these irrigations from leaching nitrate to underground water. Subsequent irrigations when the crop is well established should apply no more water than that required to bring the soil to field capacity to a depth of 3 feet. This allows sugarbeet roots to extract a larger percentage of the available nitrate by the end of the growing season.

How much N to apply

Because of the many factors that can affect crop growth, and because of the constant changing of N from one form to another in the soil, it is uncertain now whether future technology can ever make it possible to determine with absolute accuracy the amount of fertilizer N to use. Despite these difficulties, however, a reasonable estimate of the amount needed can be made by understanding how the sugarbeet grows and develops, by knowing the previous crop and fertilizer history of the field in question, and by obtaining appropriate soil and plant analyses.

Soil nitrate and crop history. Figure 3 shows a correlation between the amount of soil nitrate per acre 3 feet at the start of the growing season and the resulting sugarbeet root yields. Each point on the graph represents the results from a single field trial. The 21 trials were conducted throughout the sugarbeet growing areas of California.

Note that extrapolation of this regression line to zero N03-N per acre 3 feet predicts a root yield of 21.1 tons per acre. In part, this reflects the fact that much of the N taken up by a crop comes from N mineralized from organic matter. Despite this well-known fact, however, figure 3 shows the importance of N03-N in the soil at the start of the growing season and allows a rough prediction of the root yield a field would produce without additional fertilization. These trials also indicate that a sugarbeet crop requires, on the average, about 16 pounds of fertilizer N per ton of increased root yield resulting from fertilization (Hills and Ulrich, 1976).

Using the equation of Figure 3 and the 16 pounds of fertilizer N needed per ton of root yield increase, we can estimate the amount of fertilizer N needed as follows. Determine the amount of soil N03-N per acre 3 feet (see "Test Procedures" section). If, for example, N03-N in the soil is loo pounds per acre 3 feet, the predicted root yield without fertilization would be 21.1 + 0.042(100), about 25 tons per acre. Experience indicates that it is best to be conservative and determine the initial application of fertilizer N on the basis of fertilizing to achieve a 30-ton per acre root crop. Thus, the grower needs to fertilize to produce the extra 5 tons (30 to 25), and 5 x 16 pounds N per ton gives 80 pounds N per acre to be added as fertilizer. Table 2 uses these criteria to estimate fertil- izer N needed in varying levels of soil nitrate.

Figure 4 data are from the same experiments as Figure 3 and show that there was a response to fertilizer N in only one out of seven trials where soil NO.3-N exceeded 225 pounds per acre 3 feet. Thus when soil N03 is 200 or more pounds of N per acre 3 feet it is best to apply no fertilizer N at all and to rely on petiole analysis (discussed in the next section) to indicate a need for more N in the unusual case where more may be needed.

The decision as to how much fertilizer N to apply should be modified to some extent by crop history. If a large amount of high-N crop residue was turned under from the previous crop-for example, residue from beans or alfalfa-such organic matter may contain an unusual amount of N which, with irrigation and warrn temperatures, will soon be released. Follow- ing such a crop, it may be wise to be conservative with the initial N application and to rely more heavily on plant analysis to determine whether or not additional fertilizer N is needed.

Correcting underfertilization. Petiole analysis can be used to decide whether or not more N fertilizer is needed for the current season's crop.

When petioles of recently matured sugarbeet leaves contain more than 1,000 ppm N03-N on a dryweight basis, the plants are absorbing sufficient nitrate for maximum root growth. Concentrations below this critical level indicate that the beets were deficient in N when the sample was taken. Figure 5 gives results of petiole analyses from a field experiment and shows
that sugarbeets N-deficient for about 8 weeks before harvest gave maximum sugar yield.

To decide whether additional fertilizer N is needed, start taking petiole samples about one month before midseason. (See "sampling plants" in test procedure section.) These samples should be promptly analyzed and the field average plotted in a graph similar to figure 6. Another set of samples should be collected 2 weeks later and average results also plotted on the graph: To estimate the approximate time the concentration of petiole N03-N will reach 1,000 ppm, bisect the angle formed by the horizontal and the indicated rate of decline and extend the bisect to the critical level. If the rate of petiole nitrate decline indicates that the plants will be below 1,000 ppm NO3-N for more than 10 weeks before harvest (Fig. 6, Field B) 'then 40 to 60 pounds of N per acre can be applied at about midseason to prevent the impending deficiency. For sugarbeets that will be overwintered, use November I as the effective date of harvest in determining the length of the deficiency period before harvest. Several field experiments have shown that overwintered beets in northern California do not require more fertilizer N than is needed for maximum sugar yield for a late fall harvest.

Sugarbeets respond to N deficiency by an increase in sucrose percentage of storage roots and the change results from an inhibition of vegetative growth, which permits a higher proportion of the sucrose produced in the leaves to accumulate in the roots rather than be used in growth. The degree of this shift in growthstorage balance depends on length and degree of the deficiency, root size, the amount of photosynthesis, and the temperature regime when the deficiency occurs. Maximum increases in sucrose content are usually obtained in 4 to 8 weeks. However, plants deficient in N for periods of up to 12 weeks often contain more sucrose in storage roots than do N-sufficient plants. Beyond this time, N-sufficient plants usually contain more sucrose because of their more rapid root growth. Thus, the objective of N management should be to allow plants to become deficient from 4 to 10 weeks before harvest. If an error is to be made, it appears desirable to make it on the side of underfertilization because under most field conditions deficiency periods of up to 12 weeks can be tolerated without appreciably reducing total sugar yield.

Season-long evaluation, The collection of two additional sets of petiole samples can provide an evaluation of how well the fertilizer program met the needs of the crop. These samples should be taken half way between mid-season and harvest and again just before harvest. Figure 7 shows smoothed petiole nitrate depletion curves for three hypothetical fields. Field B illustrates the desirable situation in which petiole NO, stays above the critical level from 4 to 10 weeks before harvest.

Timing and placement of fertilizer N

Sugarbeets are often fertilized at one or more of three times: just before planting when planting beds are listed; at thinning time (four- to eight-leaf stage); and at midseason.

It is not good practice to apply N fertilizer in the fall or winter preceding the planting of a sugarbeet crop. In many areas, N so applied is lost through leaching by winter and spring rains. In addition to losses by leaching, anaerobic conditions brought about by water saturation of soils can cause the reduction of nitrate to gaseous forms and the loss of N to the atmosphere.

Many soils are sufficiently fertac to supply enough N to meet the early needs of a crop. However, if plants will need fertilizer N soon after geffnination, a portion of the total amount to be applied can be used as a starter application. This can be as much as 40 pounds of N broadcast and listed into planting beds at the time of seedbed preparation or up to 20 pounds of N placed 3 to 4 inches below the seed at planting time.

A broadcast starter application of N is effective if phosphorus or potassium is to be applied also. It is not advisable to apply more than 40 pounds of N per acre for incorporation into planting beds unless irrigation will be by sprinklers. Fertilizer N in the form of nitrate will move with furrow-irrigation water to the tops of beds where it cannot be absorbed by plant roots.

Subsequently, this N may be leached into the active root zone by late-season rains and may stimulate vegetative growth, thus decreasing the sucrose concentration of storage roots.

Even low concentrations of free ammonia are toxic to germinating seeds. Anhydrous or ammonia solution applied when beds are formed should not be placed directly below the seed row. It is best to place this material about 8 inches outside the seed row and at least 6 inches below the top of the bed so that the material is an inch or two below the level of the furrow bottom.
In this position, there should be adequate soil between the point of application and the seed row to trap and-hold all free ammonia.

When a large amount of fertilizer N (more than 20 pounds per acre) is applied at planting or thinning time, it is usually placed as shown in figure 8A. A later application, when plants are larger, can be placed just below the soil surface of the furrow bottom midway between each pair of rows (fig. 8B).

The major, if not the entire, amount of N to be used on the crop should be applied after the irrigations that are required for seedling emergence. Fertilizer N applied before this time may be subject to leaching by the considerable amounts of water that often must be applied to obtain germination and emergence of seedlings. However, if irrigation is done carefully, sugarbects can usually take up fertilizer N applied at all three times with approximately equal efficiency (table 3).

Nitrogen-carrying fertilizers

Experimental results and field experience show no important differences in sugarbeet response to various N fertilizers when they are applied to furnish equal amounts of N. In an Imperial Valley test (Loomis, et at., 1960), sugarbeets were sidedressed with 120 pounds of N per acre from several N carriers at midseason soon after depletion of a preplant application of 80 pounds of N per acre from ammonium nitrate. Figure 9 shows the effect of the N carriers on the concentration of nittate-N in petioles. Table 4 gives the estimated time lags in raising the petiole NO,3-N concentration to 1,000 ppm and shows the resulting root yields and sucrose concentrations at harvest.

This experiment illustrates several important points related to the use of the various fertilizer N sources at midseason: 1) Nitrification of urea and ammoniacal sources is rapid. Even at soil temperatures averaging 50' F, as was the case with these rnid-januaty applications, the time required for nittate-N to appear in the petioles from ammonium sulfate and urea was very short when compared with the time in which like concentrations appeared from calcium nitrate. Nitrification of anhydrous ammonia was also rapid but lagged slightly. 2) Considerable N loss can occur when ammonium hydroxide (aqueous ammonia) is applied in irrigation water. Losses are due to volatilization of ammonia from water and the soil surface as water evaporates. An additional disadvantage to the application of any soluble N material in irrigation water is that its distribution will be no better than that of the irrigation water, which can be quite erratic. 3) If midseason N applications are depleted before harvest, there is little danger of seriously depressing the sucrose content of storage roots. Note that the petiole nitrate-N from all N carriers was low for about 6 weeks before harvest (figure 9) and that none of the midseason applications affected root sucrose concentration (table 4).
 
Harvest and N deficiency

When there is a choice of fields to be harvested, -tEeresults of a systematic petiole analysis program may serve as a guide to scheduling. Those fields depleted of N first would be scheduled for an early harvest, and those high in this nutrient would be delayed until the N is depleted or held as long as possible before harvesting.

It is common for sugar factory tare laboratories to assay pulp collected for sugar analysis for nitrate content. This technique has proved useful in showing growers when a low sugar content may be due to overfertilization with N.

    Sugarbeet root samples can be collected from a field and pulp from the roots analyzed quantitatively for nitrate-N as is done with petioles. The nitrate content of root tissue is also a good indication of the N status of the plants. Collecting root samples from a field, however, is a difficult task and is seldom worth the extra work over collecting and analyzing petiole material.

The sugarbeet crop takes up relatively small amounts of P. A 30-ton root crop may contain only 20 pounds of P (46 pounds of P₂0₅) in its tops and roots. On soils where sugarbeets respond to P fertilization, 50 to 100 pounds Of  P₂0₅ per acre (20 to 40 pounds P) from a water-soluble P source is usually all that is needed. In contrast to N, applying more P fertilizer than the current crop needs is of small concern, because the P moves little from where the fertil- izer is placed, remaining in the root zone where it will be slowly available for subsequent crops.

Determining the need for fertilizer P

Soil samples properly taken, analyzed, and interpreted, can serve as an approximate guide to the need for P fertilization of a sugarbeet crop. Table 5 gives concentrations of P in soil from two different methods of analysis and indicates the kind of response to expect. The sodium bicarbonate method of analysis is recommended for mineral soils, and the water extraction method for organic soils (10 percent or more organic matter). Although this table is based on considerable field experience, it should be viewed only as a guide and is subject to revision with more experience. Plant analysis data from the previous crop can also be a guide to the need for P fertilization. If the previous crop showed adequate to high levels of P in plant tissue throughout the season, sugarbeets following this well-supplied crop are not likely to respond to P fertilization.

Rates, placement, and timing

For mineral soils of neutral to slightly alkaline reaction, P fertilizer can be broadcast just before bed formation, then listed into the planting beds. From 50 to 100 pounds of P₂0₅ per acre applied in this manner should be satisfactory for a sugarbeet crop.

Another method of applying P, particularly useful on acid soils with a high capacity for fixing P, is to band the material about 3 inches below the seed. Up to 50 pounds Of P₂0₅ per acre can be so applied to ensure rapid seedling growth.

In general, water-soluble P materials give best results.

Sugarbeets often respond to large applications of sugar factory waste lime. Several of our field trials have produced evidence that this response is probably due to the P contained in the lime. One ton of wet waste lime (32.5 percent water) contains about 17 pounds of P₂0₅. Pive tons of this product contain about 80 pounds of P₂0₅ and, when broadcast at this rate and listed into planting beds, have given sugarbeet yields comparable to those from 80 pounds Of P₂0₅ supplied by superphosphate applied in the same manner. However, the use of waste lime to furnish P should be evaluated on a cost basis with other P sources along with the potential effect of liming on soil acidity.

A 30-ton sugarbect root crop contains about 180 pounds of K2,0 (150 pounds K) in its tops and roots. Despite the removal of relatively large amounts of K from the soil, very few fields in California need K fertilization. On some soils of the Sacramento-San Joaquin Delta, sugarbeets may respond to K fertilizer.

There is little experience to indicate critical levels of K in soil at which fertilizer K may need to be applied for sugarbeets. However, from limited greenhouse tests, 80 ppm of exchangeable K in the top foot of soil is suggested. Soils testing less than this should be fertilized or watched closely for K deficiency symptoms (Uliich and Hills, 1969). Early-, mid-, and late-smon blade samples can identify fields where K fertilization should be considered (see table 6).

Sulfur

Sugarbeets growing on some soils of the upper Sacramento Valley, particularly on those of the Vina, Farwell, and Anita series, occasionally show symptoms of S deficiency (Ulrich and Hills, 1969). S deficiency is easily separated from N deficiency by a positive test with diphenylamine reagent on the cut surface of petioles of the light green to yellowish leaves. Positive identification is made by analyzing blades for sulfate-S (table 6).
Where the deficiency is anticipated, it can be avoided by using sulfur-bearing N or P fertilizer. If not detected until after N and P materials have been applied, the plants may be sidedressed with potassium sulfate or single superphosphate or other sources of sulfate-S to furnish about 50 pounds S per acre. Gypsum (calcium sulfate) is an excellent source of S but does not flow easily and therefore is dffficult to sidedress.

Other deficiencies

Other macroand micro-nutrient deficiencies of sugarbeets in California are extremely rare. Zinc deficiency, for example, although somewhat common on other crops, is seldom seen on sugarbeets.
Occasionally, vigorously growing sugarbeets with large tops show "tip burn" of new leaves, indicative of a temporary calcium deficiency (Ulrich and Hills, 1969, and table 6). This condition usually is not due to a lack of calcium in the soil but to the inability of the plants to take up enough calcium under certain conditions. The deficiency usually does not last long, and affected crops usually produce well.

In general, the sampling unit should be one-quarter of the field to be planted to sugarbects. For a field larger than 80 acres, more than four samples per field are recommended, so that a composite sample represents no more than 20 acres. When there are sizable areas within a field with major differences in soil series, or type, or both, each area should be sampled separately. Small areas of different soil types should be avoided. In other words, the soil samples should reflect the major areas to be farmed.

For nitrate nitrogen. Samples should be taken as close to the start of the active growing season as pos-
sible. When the main N application is to be made at thinning, the best time to sample is just after emergence so that the samples will reflect leaching that may have occurred during the irrigations for germination and so that time remains to plan the major N addition near thinning. If the main N addition is to be at listing, soil samples must be taken a week or two before that operation.

Divide the field to be sampled into four quarters (or a larger number of areas for large fields). Walk roughly parallel to the beet rows near the center of each section to be sampled, and collect and composite 5 to 10 soil cores taken in the plant rows to a depth of 3 feet. Distribute the core locations more or less equally along each section, but take each core from a different row. This sampling method allows appraisal of soil variability and makes it possible to fertilize a particular location differently from the others, if a sample result so indicates.

Cores for each section should be placed in a large bucket, or paper or plastic bag, with room for mixing. If soil conditions permit thorough mixing, this should be done at this time. If mixing is not possible, the sample must be ground and thoroughly mixed after it is dried.

Samples should be oven-clried the same day they are collected. If this is not possible, the cores should be kept in sealed plastic bags and frozen until they can be delivered to the laboratory. Each sample should be labeled with a field designation, section and depth sampled, and the date sampled.

After drying and thorough mixing, the samples should be analyzed for N03-N by approved methods and the results reported as ppm (dry soil basis) N03-N. Pounds of N03-N per acre 3 feet are approximated by multiplying ppm by 12.

For other nutrients. To sample soils for nutrients such as P, K, or Zn, the same general sample collection procedure is used, except that the sample cores need be no deeper than 12 inches. Another difference is the time the samples are taken.
Fertilizers other than N are usually most efficiently applied before planting. A convenient time to sample is just before bed listing to allow application of P, K, or Zn just before or during the listing operation.

Sampling Plants

The primary consideration in deciding what part -oT the plant to sample is the degree to which the nutrient concentration in a given plant part reflects the overall nutrient status of the plant. In particular, it is important to use a plant pan that gives a sharp transition from a concentration reflecting a deficiency of the nutrient in question to one that indicates an adequate supply of the nutrient.

For the sugarbeet, the youngest, fully matured leaves best meet this criterion. This type of leaf is located about midway between the young center leaves and the leaves of the oldest leaf whorl (Fig. 10). The petiole of such a leaf is the best indicator of the N and P status of the beet plant.

Petioles also satisfactorily indicate K status when sodium concentrations are high (I. 5 percent and above, table 6). When sodium in the plant is low, the leaf blade is superior as an indicator. For S, and for all other nutrients, the blade of a young, fully matured leaf is the most suitable for analysis. In separating the petiole from the blade, the petiole should be broken where it joins the blade.

Sampling for nutrient status. Divide the sugarbeet field to be sampled into approximately four equal parts (fig. 11). Again, if the field is larger than 80 acres, it should be divided into six or eight equal parts so that each area sampled represents no more than 20 acres. Walk across the center of each section at right angles to the plant rows and collect about 30 leaves per section. At least four samples are collected from each field (A, B, C, and D in fig. 11). If you are interested only in the status of N or P, break the leaf blade frorn the petiole and discard the blade. If samples are to be analyzed for other nutrients the blades can be kept also. Place each sarnple in a paper bag of convenient size and label it with field, section, and date.

Samples should be collected in this sytematic manner unless the field has areas of obviously differing plant growth characteristics. If there are distinct growth differences, each area should be sampled independently to ascertain possible reasons for such differences.

Special samples. Much can be learned about abnormal growth of sugarbects within a field by collecting special samples.

Where abnormal growth occurs, the sampler wants to know why the plants are not growing properly. For this situation, it is desirable to collect one sample containing only material from leaves exhibiting the abnormal characteristics and another from comparable leaves of plants close by, usually in the same field, that appear normal. If a nutritional problem is involved, comparative analyses of such samples frequently reveal the cause.

In collecting leaf samples from poorly growing plants, it is essential that the leaves be taken within a few days of the appearance of the symptoms. Otherwise, secondary reactions that often take place in the mineral content of plants will obscure the real cause of the deficiency symptoms.

Wide differences in the concentration of a nutrient in abnormal as compared with normal plants often indicate that a lack or excess of the nutrient in question is the reason for the abnormal growth. Plants can be normal, however, yet vary considerably in nutrient concentration. Table 6 has been prepared as a guide to concentrations of various nutrients in specific parts of the sugarbeet that were found to be associated with certain deficiency symptoms and with normal conditions. Analytical work can often be reduced by confining the analyses to those nutrients most likely to be deficient as identified in the color atlas (Ulrich and Hills, 1969).

Preparing samples. Samples should be taken to a laboratory for processing as soon as possible. Avoid delays of more than 4 to 8 hours at ordinary temperatures. Do not store samples in closed compartments of automobiles during warm weather. If it is necessary to store samples before drying, keep them at a temperature of about 40' F. At this temperature, concentrations of N03-N, P04-P, and K on an air-dry basis change very little in petioles over a 5 -day period.

For mictonutrient analysis, plant material must be free of dust. Leaves should be washed for 30 seconds in a bath containing 0. I N HCI, followed by two successive rinses in distilled water.

Reduce the sample in size by cutting it into small pieces (about 1/4 inch), thoroughly mixing the pieces. Place a sub-simple (about loo grams of fresh material) in a cut-down paper bag or other suitable container and dry it overnight in an oven, preferably with a forced draft, at 158' to 176 * F. After drying, grind the samples to pass a 40-mesh screen and store them in small glass or plastic vials. A label slipped on the inside surface of the bottle readily identifies the ground sample.

Analytical methods

The methods selected for analyzing soil and plant material must be both accurate and rapid . Whenever feasible, the analytical error of the method used should be far less than the error associated with the soil or plant samples.

The time between collection of samples and reporting of results to growers must be as brief as possible if the current season's crop is to benefit. Even with older methods of analysis Oohnson and Ulrich, 1959; Chapman and Pratt, 1961) samples can be analyzed and the results returned to growers within 3 to 7 davs. When more modern methods are used, such as specific ion electrodes or methods involving atomic absorption or fluorescence spectroscopy, the time lapse can be much shorter.

As a rule, any analytical method that has been tested and found to be reliable under laboratory conditions may be utilized for the chemical analysis of soil and plant material. A reference sample of known composition should be included in triplicate with each set of determinations. Any significant deviation from the known value for the reference sample can be detect- ed by the analyst, and the cause of the problem corrected before erroneous results are reported by the laboratory.

For example, the petiole samples may be analyzed for nitrate-N either by the phenoldisulfonic acid (PDSA) method after the removal of chloride with silver sulfate Uohnson and Ulrich, 1959) or by any other method that has been calibrated against the PDSA method; otherwise, the critical value of 1,000 ppm nitrate-N, dry basis, is not valid. Similarly, an
accurate, highly sensitive method for determining phosphate soluble in 2 percent acetic acid should be used to cover the range from I oo to 10,000 ppm, with emphasis on accuracy in the iinpor=t I oo to 500 ppm deficiency range; such accuracy is readily achievable by the stannous chloride molybdenum blue procedure gohnson and Ulrich, 1959).

Pretreatment of 125 or 250 mg of plant material in a graduated digestion tube with concentrated nitric acid, followed by a nitric-perchloric acid wet digestion gohnson and Ulrich, 1959), using a sand or metal block digestor, is recommended for the determination of Na, K, Ca, Mg, Fe, Mn, Zn, and Cu by atomic absorption, and of total P by a calorimetric method. Sulfate-S on blade material should be determined by the methylene blue method Oohnson and Nishita, 1952).

Hills, F. J., and A. Ulrich
1976. Soil nitrate and the response of sugarbects to fertilizer nitrogen. J. Am. Soc. Sugar Beet Technol. 19:118-24.

Johnson, C. M., and A. Ulrich
1959. Analytical methods for use in plant analysis. Bulletin 766. Berkeley: University of California, Agricultural Experiment Station. pp. 26-78. (Out of print)

Johnson, C. M., and H. Nishita
1952. Microestimation of sulfur in plant materials, soils and irrigation water. Anal. Chem. 24:736-42.

Loomis, R. S., J. H. Brickey, F. E. Broadbent, and G. F. Worker,jr.
1960. Comparisons of nitrogen source materials for midseason fertilization of sugar beets. Agron.j. 52:97-101.

Ulrich, A., and F. J. Hills
1969.   Sugar beet nutrient deficiency symptoms, a color atlas and chemical guide. Priced Publication 405 1. Berkeley: University of Caffornia, Division of Agricultural Sciences. 36 pp. $3.00.1

 
1. Priced Publications 4034 and 4051 are available from: Agricultural Sciences Publications, University of California, 1422 Harbour Way South, Richmond, California 94804. Make checks payable to: The Regents of the University of California. California residents please add sales tax.
 
 

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