After reading this article you will learn about:- 1. Subject Matter of Diagnosis and Recommendation Integrated System (DRIS) 2. Establishment of DRIS Norms 3. Determination of Relative NPK Requirement 4. Calculation of DRIS Indices 5. Using DRIS Indices to Diagnose NPK Requirements 6. Time of Sampling DRIS 7. Surveys of DRIS 8. Routine Use of DRIS 9. Crop Logging of DRIS 10. Isotopic Dilution Techniques for DRIS.
Subject Matter of Diagnosis and Recommendation Integrated System (DRIS):
DRIS is new approach to interpreting leaf or plant analysis which was developed by Beaufils at the University of Natal, South Africa. It is a comprehensive system which identifies all the nutritional factors limiting crop production and in so doing increases the chances of obtaining high crop yields by improving fertilizer recommendations.
Index values which measure how far particular nutrients in the leaf or plant are from the optimum are used in the calibration to classify yield factors in order of limiting importance.
Some of the essential features of DRIS approach is as follows:
To develop a DRIS for a given crop, the following requirements must be met whenever possible:
1. All factors suspected of having an effect on crop yield must be defined.
2. The relationship between these factors and yield must be described.
3. Calibrated norms must be established.
4. Recommendations suited to particular sets of conditions and based on correct and judicious use of these norms must be continually refined.
Establishment of DRIS Norms:
A survey type of approach is first employed in accumulating the basic data required to establish a data bank from which norms are determined. In this phase a large number of sites where a crop is growing are selected at random in order to represent the whole production area of a country, state or district.
At each site, plant and soil samples are taken for all essential element analyses. Other parameters likely to be related directly or indirectly to yield are also recorded. In additions, details of soil treatments (fertilizers, herbicides, etc.), climatic conditions (rainfall, etc.), cultural practices and any other relevant types of information are recorded and stored in a computer for ready access.
Second, the entire population of observation is divided into two subpopulations (high and low yielders) on the basis of vigour, quality and yield. Each element in the plant is expressed in as many ways as possible. For example, the percentage of N in the dry matter or ratios N/P, N/K, or products N-P, N-K, and so on, may be used. The mean of each type of expression for each subpopulation is calculated.
Each form of expression which significantly discriminates between the high- and low-yielding sub-populations is retained as a useful diagnostic parameter. The mean values for each of these forms of expression then constitute the diagnostic norms. Using N-P-K in com leaves, as an example, the significant forms of expression were found to be N/P, N/K, and K/P.
Determination of Relative NPK Requirement:
An example follows on how to diagnose the relative NPK requirements of corn using the DRIS chart illustrated in Figure 28.3. The chart is constructed of three axes for N/P, N/K, and K/P, respectively, with the mean value for the subpopulation of high yielders (> 160 bu/A) located at the point of intersection for each form of expression. These values are N/P = 10.04, N/K = 1.49, and K/P = 6.74.
This point of intersection of the three axes therefore represents the composition for which one is striving and at which one should achieve the highest yield permitted by limiting factors other than N, P, and K. The concentric circles can be considered as confidence limits, the inner being set at the mean Â±15% and the outer at the mean Â± 30% for each expression.
A qualitative reading of this chart can be done by using arrows in the following conventional manner. Horizontally for values within the inner circle of the chart (between 1.30 and 1.71 for N/K, 8.73 and 11.55 for N/P and 5.86 and 7.75 for K/P) corresponding to a nutritionally balanced situation; diagonally [â†˜â†—] for values between the two circles representing a tendency to imbalance (e.g., between 1.15 and 1.30 or 1.71 and 1.94 for N/K) and vertically [â†˜â†—] for values found beyond the outer circle (e.g., beyond 1.15 or 1.94 for N/K) representing nutrient imbalance.
The way in which this chart is used will be illustrated by means of an example. N, P, and K concentrations for corn leaves are presented in Table 12-2 from which the expressions N/P, N/P are calculated. Because an excess of one plant nutrient corresponds to a shortage of another, by convention only insufficiencies are recorded for the purpose of diagnosis, which is done stepwise for each function.
Identical diagnoses are obtained by considering either excesses or insufficiencies or both. Using the data in the first line of Table 27.1 as an example, one finds that the value of the function N/P (13.33) lies in the zone of phosphorus insufficiency, giving: (1) NP â†“ K; while the value of N/K (1.27) lies between the two circles adding a tendency to nitrogen insufficiency: (2) Nâ†˜ Pâ†“ K; while that of K/P (10.48) lies in the zone of phosphorus insufficiency, giving: (3) Nâ†˜ P â†“â†“ K.
Once the three forms of expression have been read, the remaining element is assigned a horizontal arrow. The final reading then becomes: (4)Nâ†˜ Pâ†“â†“ Kâ€”>, which gives the order of N-P-K requirements of the crop in terms of limiting importance on yield: P > N > K.
Calculation of DRIS Indices:
The arrow notation used thus far can be quantified by calculating DRIS indices. The equations used for calculating such indices will not be given here, but they appear in Sumner’s technical papers. When using these indices, keep in mind that the most negative index is the one most required, while the most positive one is least needed.
Using DRIS Indices to Diagnose NPK Requirements:
An example of using DRIS indices in diagnosing the N-P-K requirements of corn is presented in Table 28.1. These data are taken from a field experiment in which yield responses to nitrogen, phosphorus, and potassium were obtained. The indices will be used to show that they are capable of diagnosing the yield responses observed in the field.
Starting with the control plot 0-0-0, one diagnoses that phosphorus is the most limiting nutrient. In order to see the response to phosphorus, one selects the treatment in which phosphorus was applied (e.g., 0-50-0). One finds that phosphorus application increased the yield and that potassium is now the most required nutrient.
The potassium requirement is satisfied by selecting treatment 0-50-60. When this is done the yield has been increased by the potassium treatment and phosphorus is again the most limiting nutrient. When phosphorus is applied in treatment 0-100-60, the yield increases further and nitrogen becomes the most limiting factor.
Addition of nitrogen in treatments 100-100-60 and 200-100-60 results in the yield increasing to the maximum. At this stage, the diagnostic criteria indicate a relatively well-balanced N-P-K nutritional status, which means that factors other than N-P-K are limiting yield.
The same diagnosis is made by both the qualitative (arrow) and quantitative (index) procedures. One can see that requirements for phosphorus (treatment 0-50-60) and for nitrogen (treatment 100-100-60) were correctly predicted by the DRIS system when the nitrogen and phosphorus levels in the leaf were above the critical values.
In many cases, the DRIS system is capable of diagnosing requirements that would not be obvious when using the critical or sufficiency level approach.
Irrespective of the age of the crop when leaf samples were taken, the DRIS approach diagnoses that phosphorus is more required than potassium, which is more required than nitrogen (e.g., P > K > N). Using the critical value norms, the diagnosis would only have been possible after the 80-day stage.
Thus the DRIS approach results in greater flexibility in diagnosis. It has also been shown that the DRIS method of determining N-P-K requirements of corn is little affected by other factors, such as leaf position on the plant or cultivar.
Although this discussion of the DRIS approach has dealt only with the nitrogen, phosphorus, and potassium requirements of corn, it has been successfully applied to other crops, including sugarcane, rubber, soybeans, potatoes, wheat, sunflower, alfalfa, and ryegrass. Also, norms for calcium and magnesium in com have been established and additional norms for other essential nutrients are expected in the future.
In summary, the DRIS system has a number of distinct advantages over the classical critical level approach in making diagnoses for fertilizer recommendation purposes:
1. The importance of nutritional balance is taken into account in deriving the norms and making diagnoses. This is particularly valuable at high yield levels where balance is often critical in determining yield.
2. The norms for the elemental content in leaf tissues can be universally applied to the particular crop, regardless of where it is grown.
3. Diagnoses can be made over a wide range in stages of crop development, irrespective of cultivar.
4. The nutrients limiting yield either through excess or insufficiency can be readily identified and arranged in order of their limiting importance on yield.
Time of Sampling DRIS:
The percentage of certain plant nutrients may drop rapidly from early to late stages of growth. This tendency is portrayed in a large decline in the nitrogen, phosphorus, and potassium concentrations in corn. Hence stage of growth for sampling must be carefully selected and identified.
Surveys of DRIS:
Analysis of plant samples from many fields gives a general indication of the levels of nutrients. To permit interpretation these levels, of course, must be compared with critical levels observed in controlled plots. This method has been particularly useful in obtaining preliminary information on elements such as zinc, boron, cobalt, and copper.
Caution should be exercised in extrapolating plant-nutrient concentration data from controlled growth-chamber and greenhouse experiments to crops grown under field conditions. The short growing periods, environmental conditions, interactions, and so on prevailing in these kinds of experiments will often result in nutrient concentrations that are unrepresentative of those occurring in naturally grown crops.
Routine Use of DRIS:
Quantitative plant analyses are employed extensively in research to obtain another measure of the effect of treatment; however, crops on a commercial scale, such as sugarcane and pineapples, are analyzed periodically in many areas. Public and commercial analytical services are often available for tree crops, numerous public and private organizations maintain a plant analysis service on agronomic and horticultural crops.
Crop variety has an effect on plant analyses in some instances. When one looks at an average on many fields the effect may not be apparent but when one is evaluating a given situation the influence may be significant.
Plant analysis is another helpful tool in evaluation the nutrient status of the plant. It must be considered along with soil testing and crop-management practices in diagnosing problems. Its use in crop logging is a case in point.
Crop Logging of DRIS:
An excellent example of the use of plant analyses in crop production operations are the crop logging carried out for sugarcane in Hawaii. The crop log, which is a graphic record of the progress of the crop, contains a series of chemical and physical measurements. These measurements indicate the general condition of the plants and suggest changes in management that are necessary to produce maximum yields.
A critical nutrient concentration approach is used in the crop log system and nutrient concentrations in leaf sheaths 3, 4, 5 and 6 are utilized for diagnosis of calcium, magnesium, sulfur, and micro-nutrient deficiencies. It uses complex indices based on tissue nutrient concentration, sheath moisture, and other factors to diagnose nitrogen, phosphorus, and potassium deficiencies.
Isotopic Dilution Techniques for DRIS:
The radio-chemical analyses of plants grown on soils which have been treated with fertilizers containing elements such as radioactive phosphorus may be used to calculate the phosphorus supply of the original soil. Two isotopic dilution equations have been developed by researchers in the United States and Europe.
Equations for the two approaches are given below. These equations, based on the concept that a plant will absorb a nutrient from two sources in direct proportion to the amount available from each source, reduce essentially to identities in which A = Y.
Fried and Dean (or A value): A =B(1 â€“ y)/y
Larsen (or L value): Y = x(C0â€“ C)/C
where A or Y = Available phosphorus in the soil
B or x = Amount of phosphorus applied to soil
y = Fraction of phosphorus taken by the plant from B
C0 = k x total phosphorus in the plant
C = k Ã— phosphorus taken by the plant from x
k =Proportionality constant
For example, if 50 lb/A of phosphorus were applied and 20% of the phosphorus in the plant came from the fertilizer, the A or Y values would be -200 lb/A. Both equations are applicable to studies with other labeled nutrients.
Potential sources of error in both the A and L-value techniques are related to the assumptions that (1) the amount of nutrient absorbed from the soil is independent of the rate of fertilizer application, and (2) the utilization percentage of the fertilizer is the same for all rates of application.
These assumptions are not always correct because uptake of soil phosphorus as well as fertilizer phosphorus is known to vary with increased rate of application. When the applied phosphorus or other nutrient stimulates root development, soil supplies of nutrients become more accessible.