Plants Testing
Why do I need plant testing?
There are three main reasons for plant analysis, these are predictive, diagnostic, and long-term monitoring and research. Nutrient imbalances are normally not known until the physical symptoms appear on the plant, with predictive plant analysis we are able to find and rectify nutrient issues before they are able to be seen in crop and cause yield reduction. With diagnostic analysis a plant that is presenting with poor growth and is visually abnormal may be tested and a nutritional overview may be given. Sometimes nutrient symptoms may be difficult to pinpoint especially if there is also insect damage or pathological infection. Plant tissue testing can give a more accurate nutritional overview. The long-term analysis is normally used in conjunction with soil testing and such parameters as yield monitoring, fertiliser input and management practices. This is normally conducted over many years and all information complied help to determine the optimum practices for peak yield.
When and how to collect plant samples for testing
Plant sampling is easy if you follow our list of Do's and Don'ts. The area where most errors occur in plant analysis is in the sampling.
When done correctly it can help you attain optimum yield more easily and ensure you aren't wasting fertiliser. Done incorrectly you can end up confused with data that you can't really use! Nutrilab always informs the sender if the plant(s) have suffered any degradation due to transportation, however we cannot distinguish if the choice of plant or environmental conditions at time of sampling are correct.
This is particularly important when Nitrate N is being tested. Nitrate N can be quickly remobilised as it is very mobile within the plant itself. If the environmental conditions are not optimum the nitrate value we detect will not be an accurate representation as to field conditions. Although nitrate N can be quickly remobilised this also means it is more sensitive and a better indication of nitrogen in the crop than total N but is also less reliable due to its greater variability.
When to Sample
The timing of plant tissue testing depends on the reason for testing. If you are trying to determine a nutrient deficiency/toxicity or why you are having areas of poor growth - TEST NOW! Testing as soon as possible ensures you will receive results in time to rectify any problems before you suffer any further yield reduction.
When testing to ensure adequate nutrient status to adjust fertiliser rates for obtaining optimum yield, analysis should coincide with plants growth stage and peak nutrient needs. For most commercial plants there is optimum data available to compare with at specific growth stages. For example, for grain crops data has been calibrated for early, mid and late tillering as well as stem elongation and booting. For cotton the suggested testing growth stages are late vegetative to early squaring, early flowering, mid flowering, first max size boll and first open boll.
Particular attention must also be paid to the time of day the plants are sampled. At Nutrilab we test for nitrate nitrogen which is very mobile in the plants. Care should be taken to try and completed sampling before 10:00 am to ensure the nitrate is where we need it (dependent on seasons).
What part of the plant
In a plant, different parts may be especially sensitive to variation in nutrient supply dependent on the mobility of the nutrients in question. For this reason, particular plant parts are specified for analysis of certain nutrients. The general rule of thumb is the uppermost recently mature leaves (approx. 25-30) and their corresponding petioles (for nitrate N).
For cotton petiole tests have been calibrated for nitrate and potassium with other nutrients tested from the leaf. To collect, remove the youngest mature leaf where the petiole connects to the stem, separate the petiole from the leaf (to prevent nutrient transfer) and place in a clean labelled paper bag. To acquire a representative sample at least 50 petioles need to be collected. For larger leaves approximately 40 provide enough fresh material for nutrient analysis.
In wheat, oats, barley, and sorghum the nitrate analysis has been calibrated from the basal stem, with the other nutrients needing the youngest fully expanded leaf blade. Nutrilab only tests Nitrate-N, with any total N analysis needing to be out-sourced. This is only required when we have not received any or very little basal stem or the sample is extremely low in Nitrate-N.
Sampling Do’s and Don’ts
- DON’T SAMPLE abnormal plants. This includes but is not limited to soiled, diseased, insect or mechanically damaged plants.
- DON’T SAMPLE plants affected by abnormal environmental conditions. This includes but is not limited to plants near head ditches, tail water or leaking channels, plants growing in dung, urine patches or in the immediate vicinity of trees.
- DON’T SAMPLE Stressed plants – including water and temperature stress. Do not sample immediately before or after an irrigation.
- DON’T SAMPLE on cloudy or raining days – overcast weather can affect nutrient concentrations especially nitrate.
- DON’T SAMPLE after mid-morning – dependent on season.
- DON’T USE plastic bags – ONLY USE PAPER!
- DO develop a sampling procedure to adequately cope with environmental, logistical, site and crop variability. Once developed – stick to it!
- DO ensure the sampling procedure satisfactorily represents the situation being examined.
- DO provide sufficient material required for analysis.
- DO keep collected samples cool and sent to the lab as soon as possible (DO NOT FREEZE).
- DO use paper bags.
- DO wash hands before collecting samples to reduce contamination.
- DO minimise external contaminations, take particular care where trace elements need testing. Use clean plastic gloves and stainless-steel cutting implements.
Each step in sample collection, handling and preparation can contribute errors. These errors can have a cumulative effect on the final nutrient composition of a plant tissue sample. Standard procedures should be implemented to help minimise or prevent these errors.
Sample Handling and Transport
Adverse handling and transportation conditions MUST be avoided to ensure the data collected is a correct and true representation of the plant’s nutrient status. Unfavourable conditions may cause sample deterioration and allow enzymatic changes to occur. Once collected the samples should be placed in a clean paper bag and kept cool, preferably in a refrigerator at 5°C. Samples need to be dried within 24 hours of collection - if unable to be delivered to Nutrilab in that time they need to be dried. Before attempting to dry the plant yourself please contact Nutrilab for more details on this process. Most samples are either sent by courier or delivered in person.
Normally washing of plants is not recommended unless absolutely necessary. Research has illustrated loss of many nutrients associated with washing of plants and it is only conducted directly after an application of folia spray to the plant or when accurate measurement of iron is more important than other nutrients that may be lost. Normal washing procedures do not always completely remove external deposits, and this must be considered when the results are interpretated. Nutrilab does not wash samples received unless it is requested.
Reuter and Robinson (1997, Plant Analysis and Interpretation Manual) state “the greatest opportunity for error in plant testing arises during sampling, inaccurate or careless sampling invariably leads to inconsistent and erroneous interpretations and can ultimately discredit the value of plant testing itself”. Nutrilab always informs the sender if the plant(s) have suffered any degradation due to transportation, however we cannot distinguish if the choice of plant or environmental conditions at time of sampling are correct.
Turn Around Time
From sample receipt it may take from 1-8 working days to receive results. Plant samples are analysed on a Wednesday with reports available the following day (Thursday). Plants need to be received before 2pm on Tuesday to allow for overnight drying. During our busier summer months (cotton petiole testing) we try to run this service more often based on sample numbers. Any samples received after this time will not be dried overnight. ALL SAMPLES RECEIVED BEFORE 2:00PM WILL BE DRIED DAILY.
