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Last week we outlined the first two Critical Points of Influence–bud initiation and bloom.

In this third installment of the series, we’ll be discussing the next three Critical Points of Influence–Cell Division, Fruit (or Grain) Fill, and Ripening–how growers can influence crop expression during those stages, and what nutrients are required to achieve those effects.

Cell Division

Cell division is the period after blossoming and pollination, when cells divide in the embryo. All of the cells that will be in the finished fruit or grain are created during this stage, which lasts 10-14 days in many crops, though it can last up to 6 weeks in apples and other crops. After cell division, the number of cells in the embryo stays constant, and those cells just expand in size to grow the fruit. So the goal in this phase is to achieve as much cell division as possible, which in turn will allow for the largest possible fruit.

What can we influence at this point?

Rapid Cell Division

Having as many high quality cells as possible allows for:

  • bigger, heavier, firmer fruit
  • resistance to bruising
  • higher test weight
  • in short: most of the quality markers which increase profitability

Critical Minerals

Calcium

  • Calcium is required for new cells to form membranes
  • As cells multiply in the embryo, a calcium shortage will limit cell reproduction

Limited Potassium

  • Excess potassium limits calcium moving into a cell
  • That in turn limits the number of cells that an embryo can form
  • What we perceive as calcium deficiency disorders in fruit are often potassium excess
  • In most cases, you shouldn’t apply any potassium during the cell division phase

Manganese

  • Manganese limits the transfer of excessive potassium into an embryo

Boron

  • Boron is synergistic with Calcium

Fruit/Grain Fill

The prior 3 stages that we’ve discussed (bud initiation, bloom, and cell division) are reproductive. Fruit/grain fill, by contrast, is a vegetative stage.

What can we influence at this point?

The overall quantity of sugars produced

The amount of sugar transported from leaves into the fruit or grain

Many of the quality parameters we look for, including:

  • test weight
  • protein content
  • aroma, color, flavor
  • storability
  • firmness
  • bruise resistance
  • etc.

Critical Minerals

Potassium

  • Carbohydrates are transported by potassium
  • So, potassium is responsible for storing sugars in fruit

Nitrogen

  • Note well: this will be the only time that nitrogen shows up on these lists of nutrients required at critical points of influence
  • This is the only phase when nitrogen has a critical effect on yield

Manganese, Zinc, Boron

  • Manganese, zinc, and boron are correlated with auxin synthesis
  • The more Mn, Zn, and B a plant has, the more auxins will be produced
  • The more auxin in a plant, the more sugars will be directed into the fruits

Calcium

  • In most plants, the majority of calcium present in the mature fruit will move into the embryo in the prior stage: cell division
  • But in really healthy plants, a constant supply of calcium continues to enter the fruits from their roots
  • As long as calcium is present in the soil, it can continue moving into the fruit during the fruit fill stage

Copper

  • Copper gives resistance to many skin-infecting pathogens
  • Copper also helps build strong stem and skin elasticity, so it can prevent fruit from snapping off or splitting

Ripening

Generally, ripening is defined as when plants begin senescing. In some crops, this stage is very similar to fruit fill.

What can we influence at this point?

Color, flavor, aroma, and other quality characteristics.

Changing timing of senescence–either earlier or later

  • In cotton, you can speed up senescence and get bolls to open earlier
  • You can get wheat to dry down more quickly to harvest earlier

Producing a ripe crop on green plants

  • This means the grain would be totally dry, but the leaves would be completely green–that’s what proper senescence looks like

Critical Minerals

Boron

  • Boron is a plant’s control switch for sugar translocation
  • It speeds up the rate at which sugar moves
  • To harvest or dry down a crop earlier, a strong boron foliar will move sugars out of leaves and into grain
    • This is much better than using a dessicant, which causes a loss of all the sugars in leaves
  • Boron can also encourage dormancy on plants that tend to grow too late into the fall, like alfalfa

Cobalt

  • Cobalt does the exact opposite of boron–it delays senescence, and extends a plant’s life span
  • It inhibits the formation of ethylene
  • Cobalt can keep fruit on a plant for longer.

Manganese, Sulfur, Molybdenum

  • Nitrate disturbs proper senescence
  • Manganese, Sulfur, and Molybdenum reduce nitrates in a plant, allowing it to ripen and mature properly

 

 

Our noble bloggers will be off next week for Christmas. Stay tuned the following week as we talk about the final critical point of influence: Vegetative Growth, and reveal some truly fascinating properties of calcium in plant physiology.

Until then.