Why leaf and soil sampling are important for tree crops

Nici De Beer

By Jaques Landman
Technical Manager
Agri Technovation New Zealand

Nutrient deficiency or excess will cause trees to grow poorly and produce sub-optimal yields and/or poor fruit quality. For this reason, diagnosis of potential nutritional problems should be a yearly routine for fruit-growing farmers. Quantifying nutrients in soils and trees (leaf testing) eliminates assumptions when adjusting a fertiliser program.

LEAF SAMPLING

Leaf analysis enables us to directly measure the nutritional status of trees. The results can then be compared with known standards to determine whether the tissue contains excessively high or low concentrations of critical macro- and micro-nutrient elements. The nutrient supply can then be adjusted to bring the levels of the mineral nutrients in the tissue back to within acceptable limits.

LEAF ANALYSIS HAS SEVERAL ADVANTAGES:

1. An exact picture of the nutrient content at any given time is provided, from which correlations with production can be drawn.

2. The presence or absence of individual nutrients in soil samples may not be related to the total quantity of those nutrients available in the fruit tree.

3. Leaf analysis helps in understanding the internal functions of nutrients in each fruit crop.

4. Identifies hidden toxicities and deficiencies when visible symptoms are not present.

5. One can distinguish between nutrients which have similar deficiency symptoms.

6. Evaluates the effectiveness of nutrient programs and provides a way to compare several fertilizer treatments.

HOW SHOULD LEAF SAMPLES BE TAKEN?

Leaf sampling is traditionally carried out annually/biannually and must be done correctly if a reliable result is to be obtained. However, growers are starting to see the power of sampling leaves every season to make sure that they are on track with the tree’s nutritional needs. Since the levels of most elements in the leaves change during the season, it is important that leaf sampling should be carried out at the correct time during Summer, Autumn, Winter and Spring.

For most deciduous tree crops, leaf analyses are usually done between February – April. Agri Technovation takes leaf samples at different phenological stages of the specific crop. With more than 30 000 leaf samples taken annually, we can constantly refine the norms for other phenological stages in the season to ensure good monitoring of your orchard nutrient status. Wherever soil classification maps are available, leaf samples should preferably be taken as representative of the specific soil types.

This information is essential for the interpretation of the analytical results and for the formulation of recommendations.

The accuracy of the recommendations will depend on both the extent to which the sample is representative of the orchard and on the accuracy of the information that is supplied. No recommendations can be given if this information is inadequate.

SOIL CHEMISTRY (SOIL SAMPLING)

Soil chemistry provides answers to the producer’s soil nutrient status opportunities and risk before the start of a season. Conducting precision-based soil chemical analysis (GPS tagged sampling) on a pro-active basis also identifies specific areas where certain nutrient corrections need to be made. This enables farmers to make informed decisions on where to allocate fertiliser where it will have biggest impact on yield and quality, while at the same time save money. Crops are usually grown on a very wide variety of soil types which all have different fertilizer requirements, depending on the soil health and condition.

Why should precision soil sampling be done?
1) To gain knowledge about the soil condition and how to improve it
2) It is the first step into soil fertility management
3) To minimise fertiliser expenditures
4) To avoid over-fertilisation
5) To avoid soil degradation

Soil analysis is helpful in formulating and improving a fertilization program as it measures the pH and extractable nutrients. When conducted for several consecutive years trends in the soil chemistry can be observed. The single most useful soil test in an orchard is for pH. Soil pH greatly influences nutrient availability.

Some nutrient deficiencies can be avoided by maintaining soil pH between 5.5 and 6.5.

A grower cannot rely on soil analysis alone to formulate a fertilizer program or to diagnose a nutritional problem in an orchard. Leaf sample analysis and observations of leaf deficiencies and toxicities should also be used.

Figure 1: Map example with the interpretation of precision soil analysis of phosphate levels in the soil. These maps are created for each soil element that was analysed.

CONCLUSION

Leaf and soil analysis are powerful tools to confirm nutrient deficiencies and toxicities, identify “hidden hunger” (a situation in which a plant needs more of a given nutrient yet shows no deficiency symptoms), evaluate fertilizer programs, study nutrient interactions, and determine fertilizer rates.

However, if any steps in site selection, sampling or analysis are faulty, the results may be misleading. Tree age, cropping history, sampling techniques, soil test interpretations and leaf analysis standards all must be considered before making a final recommendation. If done properly, leaf and soil analysis will lead to a more economical and efficient use of fertilizers.

Let Agri Technovation help you with your precision soil and leaf analysis:
We send our Field technicians to your farm to undertake all the precision sampling (leaf and soil) for you. This saves you labour and laboratory costs.

Sampled areas and samples are marked with a GPS device.

Soil samples are taken according to a map grid on existing or planned orchards, fields and/or net houses. All samples are sent to an accredited laboratory for soil and leaf analysis. The laboratory results are processed and hereafter, Agri Technovation will integrate individual samples and create maps with the interpretation of soil analysis, which will include the ratios between nutrients and the possible corrective recommendations (Figure 1). Soil chemical maps contain approximately 30 individual maps and includes a topographical map. All this data is loaded onto our online cloud-based platform MYFARMWEB™.

MYFARMWEB™ is supported by advanced technology and can integrate huge volumes of historic and newly captured agricultural data into one synchronised database. It is a very user-friendly system.

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For more information, contact Agri Technovation or your Laeveld Agrochem representative