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Boosting Fertility Through Testing

Petiole and leaf tissue analysis represent important tools in fertility management of potato crops.

New advances in tissue analysis of potato crops could give growers an early warning of nutrient deficits that could be impinging on yield potential — as well as allow them sufficient time to take remedial action, according to Jez Wardman, a plant nutrition specialist at fertilizer company Yara UK.

“While soil analysis can help identify potential issues and plan fertilizer programs,” he says, “petiole or leaf tissue analysis is a far more effective agronomic tool to tailor in-season inputs.”sprng14_tubertalk_1

Kyra Stiles, agri-environmental development co-ordinator at the Prince Edward Island Department of Agriculture and Forestry, agrees that tissue sampling can help to identify in-season crop growth limitations related to nutrient deficiencies or toxicities.

“The tissue analysis indicates what the plant was able to take up from the soil, but does not reflect what nutrients are present in the soil supply,” she says. “Referring to a recent soil sample taken or collecting a soil sample at the same time of tissue sampling, will add to the interpretation of the tissue analysis by giving an indication of the supply of nutrients within the soil.”

For most of the micronutrients that are critical to the plant’s growth, research has pinpointed the peak demand is from 20 to 60 days after emergence; for tuber formation, that demand increases to 90 days. “If it cannot get the required nutrient on the day that it is needed, it will be subjected to stress that starts to limit potential for final yield and tuber quality,” Wardman warns.

Wardman points to the importance of certain nutrients for specific potato-related characteristics:

  • Influencing dry matter content — nitrogen, potassium, magnesium
  • Influencing starch content — nitrogen, phosphate
  • Reducing internal spotting — calcium, boron
  • Improving skin finish — calcium, sulphur, boron, zinc
  • Reducing potato bruising — potassium, calcium, boron
  • Reducing tuber discolouration — potassium, magnesium, boron

Wardman notes that if growers start to see symptoms that indicate a deficiency of one or more nutrients, the adverse impact on yield and quality will already have taken place. According to him, the actual nutrient uptake and utilization by potato plants could be far in excess of the so-called crop requirement. As an example, he points out that for boron, the crop required four times as much for healthy development during growth than would finally be removed.

Although it is often too late to reverse the effect of nutrient deficiency on the crop’s yield for the season when a crop begins to display visual nutrient deficiency symptoms, it may provide a better indication of how to prevent these deficiencies within future crops, according to Stiles.

Tissue Test Timing

Wardman advocates that tissue analysis should ideally be taken within 30 days of plant emergence to enable any remedial action. “Petiole analysis is regarded as more accurate early in the season, whereas leaf analysis tends to be later in the season,” he advises. “The recommendation for petiole analysis is to sample the fourth petiole from the top of the plant, so this will need to be a couple of weeks after emergence.”

However, Wardman acknowledged that with continual uptake and movement of different nutrients within the plant according to climatic conditions and growth stage, the results always require appropriate interpretation.

Many factors play an important role in tissue sampling, according to Stiles. “Sampling the appropriate plant part at the appropriate growth stage, based on the crop, is crucial in determining accurate nutrient concentrations within the plant.”

Stiles points out that depending on the crop, different areas of the plant (such as older tissues versus juvenile tissues) can range in nutrient concentrations, as some nutrients are less mobile within the plant, or are stored in various plants parts. Sampling the wrong plant tissues can skew the nutrient analysis, and give imprecise results.

Stiles says correct procedures need to be followed when taking samples from the field for analysis. Firstly, when preparing to collect tissue samples from your field, growers should always refer to their analytical lab for the correct sampling protocol for your tissue analysis, she says.

In general, potato tissue sampling should begin at the flowering stage (often 40 to 45 days after planting) and can be repeated frequently throughout the season, based on desired sampling objectives.

“Samples should be collected from the first fully matured leaf (often the fourth leaf from the top of the plant), and stripped of the leaflets with only the main stem remaining,” Stiles says. “Samples should be collected in a zig-zag pattern across the field to provide a representative composite sample from the entire field.”

To have a consistent sampling technique, growers should take a petiole from the same location on the plant each time the field is sampled. Stiles recommends that approximately 100 grams of petioles (the equivalent of approximately 60 to 80 petioles dependent on the growth stage of the plant) should be collected to provide adequate material for lab analysis.

If there are specific areas of the field that are not consistent with the majority of the field, these areas should be avoided and sampling should be done separately from the whole field analysis, she says. Problem areas should be sampled and analyzed separately to provide better insight into particular nutrient deficiencies, diseases or stressors that may have had an effect on the crop within these areas.

Storing Test Samples

Stiles adds petioles should be stored in a small paper bag in a cool, dry place, and brought to the lab the same day for analysis. Bags should be properly labelled with the sample identification name or number, grower name, date of sampling, and growth stage of the plant.

Stiles also points out that it is essential to ensure that the integrity of the tissue samples are maintained from the point of tissue sampling until they are brought into the analytical lab. Samples should be clean and dry, and kept cool to prevent any damage to the sample during travel, which could have an effect on the results of the tissue analysis. If samples are not taken and handled properly, the results may be incorrect and may influence proper fertility recommendations, she adds.

“Samples should be submitted for analysis on the same day they are taken,” Stiles says. “If multiple tissue samples will be taken over time, the time of day in which they are taken should remain consistent as the movement of nutrients in the plant can vary throughout a day and can thereby influence results.”

Generally, the amount and value of information obtained from tissue analysis will be directly related to the effort and attention put into the sampling. It’s important to keep in mind that tissue analysis is neither foolproof nor all-inclusive. Growers should not expect all their questions to be answered with a single tissue sample.

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