AGVISE Potato Petiole Analysis: Informative, Accessible, and Easy-to-Understand Reports

For potato petiole analysis article

Irrigated potato production is an intensive cropping system. It requires proactive labor, critical decision-making tools, and well-timed nutrient management. There is a fine line between supplying adequate plant nutrition and applying too much, which could cause potato tuber defects like mishappen tubers or hollow heart, reducing the marketable potato yield.

Before seed potatoes go in the ground, potato agronomists begin with a good soil fertility plan based on precision soil sampling (grid or zone). Once potatoes have emerged, the next step is monitoring the soil and plant nutrient status to ensure the potato crop has no deficient or excess nutritional problems. The in-season monitoring is done with paired potato petiole and soil samples. The petiole and soil sampling starts about 30 days after emergence, then taken every week during the growing season.

A successful in-season potato monitoring program requires fast turnaround and reliable service on petiole and soil samples. This is where AGVISE Laboratories has excelled in serving the potato industry because we know the petiole and soil test results will be used immediately to make fertilizer and irrigation decisions on the fly. To make the data immediately available, the petiole and soil test results are posted online to the AGVISE website with next-day turnaround after the samples arrive at the laboratory.

It is also critical that the petiole and soil test results are easy to interpret and understandable to everyone on the agronomy staff. The AGVISE petiole and soil test report displays results in a graphic format, enabling agronomists to quickly evaluate plant nutrient levels and watch trends over the growing season. An example potato petiole and soil nutrient report is shown below. The report includes a weekly graph of petiole nitrate, phosphorus, and potassium alongside with soil ammonium- and nitrate-nitrogen.

For most irrigated potato producers, weekly potato petiole sampling is a given. But, an increasing number are also including soil samples for ammonium- and nitrate-nitrogen analysis each week. The soil nitrogen data is critical for timing an in-season nitrogen application. There are periods where very fast potato vegetative growth can cause unusually low petiole nitrate-nitrogen levels. The soil nitrogen data prevents overreaction to low petiole nitrate-nitrogen levels and avoids application of extra nitrogen, which could create potential tuber quality issues down the road.

AGVISE Laboratories has provided potato petiole and soil analysis services to the potato industry in the United States and Canada for over 40 years. In 2020, we analyzed over 12,000 potato petiole samples for potato growers at our Northwood, ND and Benson, MN laboratories. We know that timely information is important to our customers, and we are always making improvements to our service and support. If you have any questions, please talk with one of our agronomists or soil scientists about getting started with potato petiole analysis.

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Molybdenum: The Micro-est of Micronutrients

Molybdenum (Mo) is an essential plant nutrient, necessary for nitrate assimilation and biological nitrogen fixation. Legumes, relying on symbiotic nitrogen fixation, have greater Mo requirement than non-legumes. Nevertheless, the Mo requirement of plants is the lowest among all micronutrients, with critical deficiency concentrations ranging from 0.1 to 1.0 ppm in plant leaves. The very low Mo concentration lies near the detection limit for most laboratory instruments used in commercial soil and plant analysis, so you may see Mo concentration reported as “below instrument detection limit.”

Plant-available Mo in soil is present as molybdate (MoO42-). Unlike most other micronutrients, molybdate availability in soil increases with soil pH. On soils with pH greater than 6.0, Mo deficiency is exceptionally rare. In the northern Great Plains and Canadian Prairies where most soils have high pH, Mo deficiency is virtually unknown, and background plant Mo concentration in legumes ranges from 4 to 8 ppm, indicating that plants obtain sufficient Mo from soil naturally. In the upper Midwest where low pH soils are more common, crop response to Mo fertilization has been limited to legume crops grown on strongly acidic, sandy or peat soils.

Since Mo deficiency is so uncommon and most soils are limed above pH 6.0, no reliable plant-available soil test method for Mo has been developed in the region. The acid ammonium oxalate method was infrequently used in the southeast United States, but the prediction of crop response to Mo fertilization aligns more closely with soil pH than soil test Mo. If soil pH is less than 6.0 and Mo fertilization is necessary, a molybdate fertilizer seed treatment or foliar application is usually sufficient. Overapplication of Mo fertilizer is not a concern for grain production. In forage production however, overapplication is a serious concern because excessive Mo in forages can cause Mo-induced copper deficiency (molybdenosis) in ruminant livestock.

Corn Stalk Nitrate Test

To help evaluate nitrogen management in corn, you may want to try the corn stalk nitrate test as a post-mortem tool. The corn stalk nitrate test is a late-season or end-of-season plant analysis on mature corn stalks. Iowa State University developed the corn stalk sampling protocol and interpretation. If corn did not have sufficient nitrogen, the corn stalk nitrate level will be low. If corn had excess nitrogen, the corn stalk nitrate level will be high.

The corn stalk nitrate test can be useful in cropping systems with manure or corn-after-alfalfa, where a significant portion of the crop nitrogen budget comes from nitrogen mineralization. It is also helpful in more humid climates, where the residual soil nitrate-nitrogen test is not utilized. For corn silage production, it is easy to collect corn stalk samples on the go during silage harvest, making it a quick and useful tool.

Since the corn stalk nitrate test is a post-mortem tool with the goal to provide information for future years, it is not recommended in years with abnormal precipitation. In drought years, potential crop productivity is reduced, so the plant nitrogen requirement is lower than normal. In high precipitation years, soil nitrogen losses will reduce the available nitrogen supply. As a result, the corn stalk nitrate level can be very high in drought years or very low in wet years. Such results say more about environmental conditions, not the adequacy of the nitrogen fertilizer program.

When to sample

  • Early: One-quarter milk line (R5 growth stage) on majority of corn kernels. Nitrate concentration may be high if collected early.
  • Optimum: One to three weeks after physiological maturity (black layer, R6 growth stage) on 80% of corn kernels.
  • Late: Up to harvest. Nitrate concentration may be low if rainfall has leached nitrate from plant material.

How to sample

  • Measure 6 inches from the ground, cut the next 8 inches of corn stalk (the 6-14 inch stalk section measured from plant base). Remove outside leaf sheath.
  • Collect 12 to 15 corn stalks.
  • Place corn stalks in ventilated plant tissue bag. Do not use plastic or zipped bag.
  • Do not collect diseased or damaged corn stalks.

Table 1. Corn Stalk Nitrate Test Interpretation

Nitrate-N (NO3-N), ppm Interpretation Comment
<250 Low Nitrogen supply was likely deficient and limited corn grain yield
250-2000 Sufficient
>2000 High Nitrogen supply exceeded plant requirement

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AGVISE Laboratories: Trusted by University and Industry Researchers

While you may know AGVISE Laboratories for the soil and plant analysis services we provide you and your producers, AGVISE also has a long history of supporting university and industry research. For the past 30 years, many university-operated soil testing laboratories have closed in the region. This has left a gap in the on- and off-campus research capacities at some institutions. To help bridge the gap, AGVISE partners with university and industry researchers to provide the laboratory analysis services they need to further research in soil fertility, plant nutrition, nutrient use efficiency, and many other areas. Researchers choose AGVISE for their research projects because of our reliability, consistence, and standard of excellence.

Each year, AGVISE analyzes thousands of soil and plant samples for researchers across the United States and Canada. You may have even heard of some recent research projects for which we provided the analysis services. A unique collaborative project was the Public–Industry Partnership for Enhancing Corn Nitrogen Research, which included eight land-grant universities and USDA-ARS. AGVISE analyzed thousands of soil and plant samples for researchers from the University of Illinois, Purdue University (Indiana), Iowa State University, University of Minnesota, University of Missouri, University of Nebraska, North Dakota State University, and University of Wisconsin. We are proud of our small part in support of this research that provided critical information to corn producers and helping them improve nitrogen management. You can read more about the project in the links below.

Another research project that AGVISE is helping with is the Potato Soil Health Project, supported by USDA-NIFA Specialty Crop Research Initiative (SCRI) and spearheaded by the potato industry. The research project includes eight potato-growing states across a range of diverse soils. In addition to soil fertility analysis, AGVISE is also helping evaluate soil health using biological activity (24-h CO2 respiration), active carbon (POXC), bioavailable nitrogen (ACE), and soil aggregate stability. AGVISE Laboratories is a strong supporter of soil health research, and we are excited to have been chosen to provide soil health analyses for the research project.

In addition to these large research projects, AGVISE also provides analysis services for many research organizations and universities throughout the region, including Agriculture and Agri-Food Canada, University of Manitoba, Montana State University, University of Saskatchewan, and South Dakota State University.

The next time you send your soil or plant samples to AGVISE Laboratories, you can be confident that you will be receiving the highest quality analyses and service, just like we provide to researchers across the United States and Canada.

Some open-access articles from AGVISE-supported university research projects

A Public-Industry Partnership for Enhancing Corn Nitrogen Research and Datasets: Project Description, Methodology, and Outcomes

When to Use a Single or Split Application of Nitrogen Fertilizer in Corn

Which Recommendation Tools Are Best for Achieving the Economically Optimal Nitrogen Rate?

The Potato Soil Health Project funded through USDA-NIFA SCRI

 

Plant Analysis Sampling Guide

Plant nutrient analysis is a useful management tool. The AGVISE Plant Analysis Sampling Guide discusses the importance of plant analysis in proper crop nutrition and how to collect plant
samples. It is important to collect the correct plant part at the correct plant growth stage to ensure accurate interpretation of plant analysis results. To ensure we have enough plant material to analyze in the laboratory, please collect a minimum number of whole plants or leaves per sample as instructed in the guide. To obtain the most accurate plant analysis information, follow the instructions on plant growth stage, plant part, and minimum sample size.

View the Plant Tissue Sampling Guide