Agriculture Reference
In-Depth Information
Seed Counting and Spacing
Counting boards are generally used for counting and spacing large seeds such as corn, beans, and peas.
They consist of two perforated wooden or plastic boards approximately the size of the planting substratum
with 50 or 100 holes slightly larger than the seeds to be counted (Fig. 5.1). The two perforated boards are
off-set to permit seeds in the holes of the upper leaf to rest on the solid portion of the bottom board. Seeds
are placed on the upper surface of the counting board which is shaken to allow a single seed to fall into each
hole. Excess seeds are removed by tilting the board and allowing them to slide or roll off into a suitable
container. The counting board is placed directly over the planting substratum and the top board is retracted
until the holes in each board are aligned, allowing the seeds to fall through onto the planting surface.
Vacuum counters are generally preferred for small, smooth free-lowing seeds although they can be
used for large seeds if enough vacuum is available. A suction capacity of 5 to 8 ft
3
/min is adequate for clo-
vers, while larger seeds such as corn or beans require 15 to 18 ft
3
/min. Counting heads have both front and
back faces with a space for air passage between (Fig. 5.1). They are about the size and shape of the plant-
ing surface and made of metal (brass or aluminum) or plastic, which is preferred for large counting heads
because of its lighter weight. The face is ridged around three sides of its periphery to retain the seeds and
has 50 to 100 evenly spaced holes. Seeds are placed on the counting head and the vacuum turned on allow-
ing the seeds to spread over the head surface. Although the suction of the vacuum retains a seed over each
hole, the analyst should ensure that each hole contains only one seed, and that excess seeds are poured off
the head. After a inal check to ensure that every hole has only one seed, the head is inverted and positioned
over the substratum and the vacuum turned off to allow the evenly spaced and counted seeds to drop on the
planting surface.
Proper spacing is important to reduce the potential disease problems associated with microorganism
infestations and to permit certain seeds to increase in size during imbibition without hindering test interpre-
tation. Generally, the distance between seeds should be not less than 1.5 to 5.0 times the width or diameter
of the seed to be tested.
SubSTrATA for GErMInATIon TESTS
The germination substratum must provide adequate moisture and aeration for the germinating seeds, be
nontoxic to germinating seedlings, and free of fungi and other microorganisms. In some cases, seedlings
may exhibit root injury from the chemical toxicity of the paper substratum. When this occurs, check tests
should be conducted on Whatman No. 2 ilter paper. Seeds of celery, celeriac, chicory, dandelion, timothy,
or bermudagrass are particularly sensitive to toxic substrata. Lack of root development indicates that the
substratum is creating the injury and should be replaced. A new supply of paper media can be tested by
planting a few seeds of any of these sensitive kinds.
The substratum must remain moist enough at all times to supply adequate moisture for imbibition and
seedling growth. Excessive water restricts aeration to the developing seedlings, while too little water delays
imbibition and retards seedling growth. For most species germinated on blotters or other paper substrata, a
good rule of thumb is that the substrata is too wet if a ilm of water surrounds the thumb when pressed on
the substrata. The substrata should also be considered too wet if a ilm of water surrounds the seeds. For
sand or soil substrata, the AOSA rules specify the amount of water to be added by the following formula:
118.29 cc (1 gill) sand × (20.2 - 8.0)
=
The number of ml water to add to
Its dry weight in grams
each 100 grams of air-dry sand
This formula gives a general guide for seeds the size of clovers. It may be slightly modiied for larger seeds
by adding more moisture. For soils, add enough water so that a ball is formed when it is squeezed in the
palm but will break freely when pressed between two ingers. After moisture is added, the soil should be
