July-August - 10

GLVPN VEG CONNECTION
Vegetable
crop yields
Comparing nitrogen management
technologies
BY ZACK HAYDEN
ASSISTANT PROFESSOR, DEPARTMENT OF HORTICULTURE,
MICHIGAN STATE UNIVERSITY
N
itrogen (N) is the nutrient most likely to rob high
demand vegetables of yield. But when supplied in
excess, it can also reduce produce quality, erode
farm profits and harm the environment.
Fertilizing enough, but not too much, is an ageold
challenge. The dynamic nature of N adds to the
difficulty. Availability from organic sources (including
soil organic matter) can be difficult to predict, and once
in plant-available forms, N can be readily lost from the
soil system.
Fortunately, tools and technologies exist to support
in-season N management decisions. Each has strengths
and weaknesses, but understanding current and
emerging options can help you improve N management.
Soil testing
Soil testing is the only tool that gives you an estimate
of both current and future N supply. It's like looking at
a bank statement - the higher the balance, the more
confident you can be that you'll make it through the
average season without another deposit.
You may recognize this well-studied approach as the
pre-sidedress soil nitrate test (PSNT) because it is most
valuable for informing sidedress/topdress decisions
prior to rapid crop uptake. It involves collecting a soil
10 | JULY/AUGUST 2023
MSU researchers collect
samples to evaluate soil
nitrogen supply in a muck
celery field. Photos courtesy
of Zack Hayden.
sample from the crop rooting depth, submitting it to a
lab for analysis of nitrate (and sometimes ammonium)
concentration, and then using typical soil bulk density
to estimate the total amount of available N in the soil.
Published thresholds are available that vary by crop,
soil type and other factors, but all rely on the basic
concept of comparing estimated available N in the soil
with remaining crop demand.
Our research has found PSNT useful for identifying
muck fields where onions or celery are unlikely to
respond to additional N fertilizer due to high soil organic
matter N mineralization. Similarly, we've used it to
confirm sufficient N availability from spring manure
applications in organic crops grown on sandy soils.
However, like all physical sampling methods,
PSNT has weaknesses related to time, labor, cost and
variability. While many commercial labs offer rapid
turnaround, there is still a delay between sampling and
results. Expenses can balloon if finer sampling grids
are needed to address field spatial variability, and
N loss conditions (like heavy precipitation or flooding)
after sampling can muddy the waters.
Plant tissue testing
Tissue testing provides a snapshot of current plant
N status. Analysis of total N in whole leaves and
nitrate-N in the sap of petioles or other plant parts are
common. In general, sap nitrate-N is considered a more
dynamic indicator of current conditions, while total N

July-August

Table of Contents for the Digital Edition of July-August

Editor's Letter
Grower Profile: Central Florida leafy greens
GLVPN Veg Connection: Vegetable crop yields
Organic Grower
Ag Tech: Fields of drones
Plant & Soil Health: Fusarium wilt
Great Lakes EXPO News: Connecting growers through the digital market space
Farm Market & Agritourism: Agreements between growers provide additional opportunities
Ag Labor Review
Classifieds
Advertiser Index
July-August - 1
July-August - 2
July-August - 3
July-August - Editor's Letter
July-August - 5
July-August - Grower Profile: Central Florida leafy greens
July-August - 7
July-August - 8
July-August - 9
July-August - GLVPN Veg Connection: Vegetable crop yields
July-August - 11
July-August - 12
July-August - 13
July-August - 14
July-August - Organic Grower
July-August - 16
July-August - 17
July-August - 18
July-August - 19
July-August - 20
July-August - 21
July-August - 22
July-August - 23
July-August - 24
July-August - 25
July-August - 26
July-August - 27
July-August - 28
July-August - Ag Tech: Fields of drones
July-August - 30
July-August - 31
July-August - Plant & Soil Health: Fusarium wilt
July-August - 33
July-August - 34
July-August - 35
July-August - Great Lakes EXPO News: Connecting growers through the digital market space
July-August - 37
July-August - Farm Market & Agritourism: Agreements between growers provide additional opportunities
July-August - 39
July-August - Ag Labor Review
July-August - 41
July-August - Classifieds
July-August - Advertiser Index
July-August - 44
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