Agronomy Talk

Agronomy Talk: IMPACT OF SATURATED SOILS IN COLD CONDITIONS

Published on Wednesday, June 30, 2021

The following aspects of “planting” will help to mitigate cold and saturated soils following planting:

  • Avoid tillage and planting when soils are saturated at the seeding zone
  • Soils, when worked wet, can affect seed-to-soil contact and increase compaction at the depth of tillage – impeding natural moisture, temperature, and air movement
  • Soils planted wet can create compaction in the seed furrow – impeding both seed-to-soil contact and air exchange, and ultimately root development
  • Planting depth should always be maintained for corn and soybeans respectively – we can’t predict the weather

Corn and soybean stand establishment are both dependent on successful germination and emergence and interaction of three key independent factors – environment, genetics, and seed quality as described in Figure 2. Each factor can influence the net stand established. When two or more factors are adverse or stressful, stand establishment will often be less than acceptable. Nebraska Extension provides an in-depth discussion on Factors Influencing Cold Stress in Corn and Soybean1.

Genetically, there are emergence differences amongst corn hybrids and soybean varieties, and they are rated
accordingly. Figure 1. depicts a found field difference. Seed size and shape (grade size in corn) are not correlated
to germination, vigor, or yield. Please reference Beck’s Agronomy Brief, Seed Size, and Crop Establishment2, for a
complete review of this topic.

From a seed quality perspective, both seed corn and soybeans, respectively, are tested for their warm germination
on a percentage basis – required by Federal Seed Labeling laws. In addition, seed corn may also undergo a
Cold Germination test and, potentially, a Saturated Cold Test. These tests are intended to analyze seed quality
characteristics and do not speak to genetics nor environmental factors. In Beck’s Agronomy Brief, Planting Into Cold
Soils3, there is a description of the germination process.

Key conditions for the germination process include:

  • Corn requires approximately 110 to 120 growing degree units (GDUs – 50°F base) from planting to emergence and should be calculated from soil temperatures, not air temperatures4.
  • Corn seed is particularly susceptible to cold stresses during the imbibition of cold water, often referred to as imbibitional chilling.
  • Warm, moist soil conditions for the first 24 to 48 hours after planting can lessen the impact of cold stress.
  • Soybean germination is driven by soil temperature, with 55°F being the recognized base. Data indicates 130 GDUs are needed.

Under both cold and saturated seedbed conditions, not only is the germination > emergence process thwarted because of lack of growth-inducing temperatures (accumulating GDU’s) but, saturated soils deprive the seed of oxygen. The lack of oxygen will delay both germination and emergence and put the seeds at risk of rotting.

In Figure 3., this seed corn was subject to both prolonged cold (<45°F) and saturated soil conditions. The prolonged
germination > emergence process (> 25 days) negated the value of fungicide seed treatments. In this case, Pythium
infected the seedling roots and the coleoptile prior to emergence.

In Figure 4., several seeds [from the same field as Figure 3.] were found to have insect (wireworm) damage in addition to seedling diseases. Ultimately, the severely delayed germination > emergence process prolonged seed respiration [CO2 attracts insects] and resulted in a weak seedling and dilution of the protectant seed insecticide.

A delayed germination > emergence not only increases the exposure of the seed and young seedlings to soil-borne
insects and diseases but surface crusting of a saturated seedbed, seen in Figure 5. Slow germination and mesocotyl
elongation increase the risk of underground leafing out due to soil crusting, seen in Figure 6. Until nodal roots develop, corn seedlings are extremely vulnerable to saturated soils and continued seed or mesocotyl damage from disease pathogens and soil-borne insects. Although seedbed conditions can become cold and/or saturated after planting, avoiding planting into these soil conditions has been proven to be more important toward a successful stand.

In soybeans, a cold, saturated seedbed tends to be just as detrimental following germination. Where the plant needs
to establish a radical root and elongation of the hypocotyl must occur to bring the photosynthesizing cotyledons above the soil surface. In Figures 7. and 8., these soybean seeds experienced cold, saturated soil conditions. In both cases, the seed imbibition process began, but radicle root development was impeded by low temps and lack of oxygen. Malformed growth and poor emergence resulted.

As Mother Nature has the final say on growing conditions following planting, attention to the management of the
planting action must occur. Pre-plant tillage and planting operations are the most critical actions that dictate the
development of the crop for the rest of the year. Manage to get the most out of the genetic potential in every seed.

  • Plant only if the soils are truly “fit,” regardless of your tillage system. The advantages of early planting are negated if the seeds are forced into unfit soils.
  • Both seed furrow compaction and compaction above the seed interfere with critical air exchange and capillary movement of water.
  • Protect against stand (and yield) loss by delaying planting until soils approach 50°F with a warming trend in the forecast.
  • Seedling emergence is reduced when seeds are planted into colder soils or when planting is followed by a cold front that chills the soil water within 24 to 72 hours of planting.
  • Seed that imbibes cold rain or snow-melt water in the first few days after planting often is injured, causing loss of stand or poor seedling development.
  • Saturated soils can inhibit root growth, leaf area expansion, and the photosynthetic process. In addition, roots may die due to lack of oxygen.
  • Residue management in the seed furrow not only affects seed-to-soil contact but, the residue can act as a sponge pulling in excess moisture or as a chimney pulling away heat from the seed.
  • Residue management above and on the row not only affects soil temperature but managing it will give every seed the opportunity to germinate and emerge at a similar time.
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Author: Mike Blaine

Categories: Agronomy, Agronomy Talk

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