Once you have a plan and have put it into motion, it is very important to monitor your progress and success and make adjustments and refinements to make sure that you get the results you want. When dealing with the dynamic nature of the world of soil and crop health, there isn't just one right answer and, in fact, the right answer one day, may not be the right answer the next. This is because external conditions can change rapidly and can greatly affect the outcomes and effects of inputs. One great way to keep your finger on the pulse of your plants is to monitor their health on a regular basis. At critical crop stages, it is wise to collect plant tissue to be analyzed for nutrient levels. Knowing these will help identify critical health indicators and provide the information you need to make adjustments to your plan that will keep it tracking straight toward your goal.
Plant tissue analysis measures nutrient levels in the plant during their growth. The supply of available nutrients is reflected in the nutrient content of the crop. Therefore, use of plant tissue analysis allows a producer to evaluate the effectiveness of your whole fertility program. Producers who do not soil test can still use routine plant tissue analysis to evaluate their fertilizer management program to determine whether they are using the correct types and amounts of nutrient.
Plant tissue analysis can be used to diagnose crop nutrition production problems. For example, at times, a plant growth problem occurs and cannot be explained. Soil, climatic, and other environmental conditions seem favourable, essential plant nutrients were supplied, and other sound management practices were followed. A plant tissue analysis can indicate if nutrient levels may be associated with the problem. Hidden hunger is illustrated in Figure 1.
Hidden Hunger is a term used to describe a plant that shows no obvious symptoms, yet the nutrient content is not sufficient to produce the top profitable yield. Fertilization with the "sure" rate rather than the bare economic optimum for an average year helps to obtain the top profitable yield. (Courtesy of the Potash & Phosphate Institute, Atlanta, Ga.) Source: Tisdale, et al., 1985
For reliable results and useful interpretation, producers must follow proper procedures for plant sampling and sample handling. The sample should accurately represent the crop from which it was taken. Management decisions based on plant tissue analysis results reflect the quality of the sample provided.
For most crops, an adequate sample will contain between 20 and 50 individual plants. Samples should be collected in the morning (or on cool or cloudy days) because heat and moisture stress often occurs mid-day and mid-afternoon, on hot sunny days, or immediately following a rain. Plant samples should be cut with a clean, sharp, rust free knife, blade or scissors. Clean plastic containers should be used for sample collection. In subsequent handling, clean brown paper bag can be used.
1. Remove loose soil particles with a clean, dry cloth or brush.
2. Do not wash the sample.
3. Lay out the sample on clean paper until completely air dried at normal room temperature (25 to 35°C).
4. Do not oven dry samples.
Completely dried samples can then be placed in a plant tissue sample bag or clean brown paper bag. Information sheets from a testing lab should be completed for each sample as this information helps when interpreting the results. The sample bag and the corresponding information sheet should each be carefully labeled with the same identity so that samples and sheets can be matched in the laboratory.
The laboratory will determine the levels of each nutrient in the plant sample. We analyze this data and provide guidance regarding the results which indicates if each nutrient level is excessive, adequate, marginal or below a critical level. The critical concentration of a nutrient is the point where crop growth may be 10 per cent or less than the maximum. This system uses a previously established set of standards for nutrients in a specific plant part, sampled at a particular growing stage, and then compares those normal to the findings in the sample. The principle of this system lies in the relationship between nutrient concentration and crop yield (Figure 2).
Figure 2. Relationship between nutrient concentration in plant tissue and top yield, showing the proposed critical nutrient range. (CNR) Source: Dow and Roberts, 1982
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