title of the second part of my essay Seed Quality Is Not Always the Problem I
chose an old-time maxim of farmers in the U.S. Midwest, especially maize
farmers. It reminded them to plant three seeds for every plant desired because
there was a substantial probability that one would succumb to an adverse
climatic condition, i.e., snow, another would succumb to a biological hazard,
i.e., a crow (bird), while, hopefully, the third seed would survive, germinate,
emerge and develop into a plant. This old-time maxim recognized that many factors
other than poor quality seed can contribute to crop emergence failures, that
seed quality is not always the problem. Indeed, the multiple hazards
encountered by seeds in fulfillment of their propagative and disseminative
functions were taken into account from the beginning in the evolutionary
equation for seed bearing plants that factored in an abundant seed production.
seed production habit of the higher plants greatly favored humankind's early gathering
of seed/grains for food and, subsequently, the domestication of food crops.
Just consider how meager and different the human diet would be if our main food
grain crops, i.e., wheat, rice, maize, soybean, etc., produced only a few
rather than many seeds/grains per plant! There is, of course, a downside to the
abundant seed production habit: it contributes importantly to the persistence
and rapid spread of undesirable plants (weeds) in cultivated fields.
of the main hazards encountered in establishing economical crop stands or
populations were discussed in the first part of this essay: unfavorable soil
temperatures, deficient or excessive soil moisture and mechanical impedance of
soil crusts. There are several other hazards, one of major importance and several
of less general importance but which can be locally and periodically severe.
These are discussed in the following sections.
seedbed is not sterile. It has a large, diverse and important biological component
that varies among climates, soil types, seasons, and cropping systems. This
biological component consists of fungi, bacteria, nematodes, insects and
assorted other bioforms that under certain conditions can and do attack,
infest, infect, rot, or consume seeds introduced into the seedbed and/or
activities of the biotic component against seeds are favored by Unfavorable temperatures
and moisture levels that delay germination and emergence and by poor physical
and physiological quality of the seeds planted.
seed protectants are the most commonly use defense against microorganisms in
the soil that attack seeds. They are usually applied as a coating on the seed
but in some cases are applied as a planter box treatment, i.e., the chemical is
introduced into the seed zone in the soil at the time of planting. Many seed
protectants are available representing a variety of chemistries with general or
specific activity against the most troublesome microorganisms. During my
teaching days I gave much attention to the role of mechanical injury to seeds
in their susceptibility to attack by microorganisms. It was emphasized that
cracks, scratches and abrasions of the seed coat (covering of the seed unit)
resulted in a loss of its critical protective function and allowed easy entry
of microorganisms. In an important sense, therefore, chemical seed protectants
replace the physical protection of the seed coat lost through injury with a
realized then, of course, and concede here that this line of teaching was a huge
oversimplification. But, it was used for a purpose that was considered worthy,
viz., to imprint in students as deeply as possible the importance of minimizing
mechanical abuse to seeds. Damaged seeds are indeed more susceptible to deleterious
attack from soil microorganisms but so are low vigor, deteriorated seeds. And,
as already pointed out even high quality seeds can succumb to microorganisms in
seedbeds that are too cold or too hot, too dry or too wet. Crop establishment
problems are most frequently associated with the interactions of several levels
of factors, physical, biotic, physiological, that can be very complex.
seeds can be attacked and consumed by insects and grubs in the soil, birds and
even animals. Chemical and biological insecticides are applied to seeds to
protect them from soil insects. Various chemicals have been and are used with
variable success to protect seeds against birds and other varmints.
developed and adopted conservation production systems involving minimum tillage
and no tillage appearto exacerbate the crop establishment problem in several
ways. First, conservation production systems do not produce as favorable
conditions for seed germination and emergence as does conventional tillage
systems; most importantly, perhaps, relatively poor contact between the seeds
and soil particles delays germination.
there are usually rather wide differences in the biotic components of the
seedbed environment between minimum or no tillage and full tillage production
systems, e.g. microorganisms and insects involved in decay of organic matter
are much more abundant and active in the minimum and no tillage systems. For these
reasons, the use of seed protectant chemicals is considered to be critically
important in conservation production systems for some crops. For example, the
use of chemical seed protectants for soybean seeds has increased in line with
the increasing adoption of conservation production systems.
variety of chemicals are introduced on or into the microenvironment of the
seedbed to provide nutrients (fertilizers), control weeds (herbicides), control
insects and nematodes (insecticides, nematocides), improve aggregation of soil
particles, alter soil acidity, reduce salinity, and a variety of other purposes.
Some of these chemicals can adversely affect germination when placed in the
seed zone in contact with the seeds. More importantly, however, are the direct
and residual effects of herbicides. Improper use of herbicides in terms of the
timing of application and planting can have disastrous results. The rotation of
crops can expose usceptible crop seeds to the residual activity of a selective herbicide
used for the previous crop.
important, therefore, to maintain good records of the type, rate and time of
herbicide applications and the applications of all other chemicals to the
different crop lands as well as the sequence of crops over time and seasons.
are other causes of crop establishment problems that I term miscellaneous not
because they are not serious but because they are infrequent and most commonly
the result of poor farming practices. In a previous essay I related one of my early
professional embarrassments when after a superficial examination I diagnosed a
crop establishment complaint as due to poor quality seed when subsequent
digging in the seed bed revealed that the seeds had simply been planted too
deeply and were struggling to emerge. So, poor emergence can result from
planting too deep or too shallow, from delaying irrigation too long when
moisture is deficient, from inadequate preparation of the seedbed, and so on. Good
and attentive management is the main defense against these sorts of stand establishment
was mentally outlining this two-part essay on crop establishment problems I
envisaged an informative and innovative final section on strategies for
minimizing or evading the multiple causal factors. Now that I am in the final
stage, my vision has about deserted me. The obvious strategy to avoid the
adverse effects of unfavorable soil temperatures is not to plant too early or
too late based on the long-term mean temperatures, but temperatures fluctuate
widely from the mean. The solution for deficient moisture is irrigation if
irrigation is available and economical, while the solution for excessive
moisture is improved drainage that might or might not be feasible and
from good farming management, the most technically and cost effective defense
against crop establishment problems is the use of good quality seed treated with
a recommended chemical seed protectant at the proper dosage. Thus, while seed
quality is not always the problem, it is almost always a part of the solution.