John Kempf

Cell division for fruit size and quality

Potential fruit or grain size is determined during the cell division period immediately after pollination. The cell division process can continue for as little as 5 days, to as long as 40 days, but most crops have a 10-14 day cell division window. During this window, the cells in the embryo are rapidly dividing, 2-4-8-16-32-64 and so on. At the end of this 10-14 day window, cell division stops completely, and the remainder of the fruit fill or grain fill period is focused on cell expansion, filling each cell with proteins, sugars, and water.

Fruit that are tightly packed with more smaller size cells are firmer, store better, are crisp, and crunchy. Fruit with more cells can be much larger in size when all the cells are filled with water and nutrients. Fruit with more cells are resistant to cracking and splitting. In general, almost all the fruit quality characteristics we seek can be improved by increasing the number of cells formed during the cell division period, with the exception of some fruit where excessive size is a negative.

The nutritional factor which limits the number of cells formed during the cell division period is calcium, because calcium is needed to form the cell membranes for all the rapidly dividing cells in the fruit embryo.

An easy step to produce exceptional quality and yield is to ensure a peak of available calcium during the cell division period.

This means any soil applications of calcium need to be timed so the peak of the release curve coincides with the crops peak demand curve during cell division. Applying gypsum or limestone on tree fruit in the spring is much less effective than a fall application, because it doesn’t release quickly enough to be available during cell division right after pollination.

In almost all cases, when fruit express physiological symptoms of inadequate calcium, which we call blossom end rot, bitter pit, or cork, it is because there is inadequate calcium supply during the cell division period.

Quite often, this inadequate calcium level in the plant or in the embryo may not be the result of low calcium in the soil. Poor calcium absorption can be the result of excessive potassium, low boron, or low manganese availability in the soil. Any of these conditions will limit calcium absorption, and thus negatively impact fruit quality.

I have been framing the discussion around fruit, but these concepts hold equally true for grain crops.

These grapes are still 3-4 weeks from harvest, and each berry is about 60% of mature size. When was the last time you bought grapes like these? Would you like to grow crops at an equivalent level of health and quality? If so, managing calcium and the associated nutrient interactions during the cell division stage becomes a top priority.

The first thing you will cut is all potassium applications until after the cell division stage is completed. To achieve this, you likely needless fertilizer application, not more. And most likely also timed very differently.

John Kempf2020-06-09T20:19:17-05:00June 10th, 2020|Tags: boron, calcium, cell division, grapes, manganese, potassium|

Boron salts for weed control and as a desiccant

Recently I have received many questions about alternative forms of weed control, and if nutrients might be a possible means of control, specifically boron.

This is not an area where I have personal experience, and I am not personally familiar with how to manage boron applications to produce this effect. Test for yourself, with eyes wide open, and please let me know. I would love to learn more.

From what I have been able to read, it seems that boric acid and sodium borate can be used as an effective means of killing weeds. While the information I have been able to find is not particularly clear, it seems effective control is solution concentration dependent rather than quantity per area dependent.

Recommended rates I have been able to uncover are for either three ounces of boric acid or four ounces of sodium borate per gallon of water. Typically, boric acid contains 17% boron, and sodium borate usually contains 10% boron, so these recommended application rates don’t equal the same quantity of applied boron on a per-acre basis.

We need to be aware of the quantity of boron being applied on a per-acre basis, and the boron sensitivity of the crops we are growing. In our agronomic recommendations, based on soil analysis and plant sap analysis we often recommend between one and three pounds of actual boron per acre per year. The rate varies with the crop, soil levels of boron, and annual rainfall. In low organic matter soils, ten inches of rainfall can leach about one-half pound of boron per acre. Thus, if you get forty inches of rainfall per year, you need to add two pounds of boron annually just to replace what the rainfall removed. As organic matter increases, and soils anion exchange capacity increases, less boron is leached through the soil profile.

If we follow the recommended concentration rates, and apply 20 gallons of solution per acre, with each gallon containing four ounces of 10% boron, this application will give us eight ounces of actual boron per acre. This rate is well within the range of what is routinely applied as a soil amendment or nutrition source of boron on many soils and crops. This type of application would also supply much more uniform soil distribution than a broadcast application of pellets with some distance between the pellets as occurs with such small application rates.

Obviously, this application is non-selective, and should not be applied directly on crop plants.

With the exception of a very few boron sensitive crops, I do not expect that boron toxicity to the crop is nearly the danger that it is sometimes made out to be. Boron toxicity in most plants is simply a calcium deficiency. In cases where excessive boron was applied in the past, a foliar application of calcium will snap a crop out of boron toxicity in a matter of days, even when tissue analysis levels are ten times higher than desired values.

What these experiences suggest to me, is that using boron salts as an herbicide is likely to produce the biggest effect on calcium deficient soils and that soils with adequate or generous calcium may require stronger application rates to produce the same effect. Of course, crop sensitivity to the boron application will also depend on soil calcium levels.

It is important to mention that using boron as a form of weed control is specifically prohibited under USDA NOP rules for organically certified producers. It can be used as a nutrient source with restrictions, but not as an herbicide.

If you would like more information on the toxicity of boron in the environment, the National Pesticide Information Center link provides very thorough and useful information.

National Pesticide Information Center

EPA Boric acid restrictions on boron in crops (based on used for insect control in grain storage)

John Kempf2020-03-16T14:00:49-05:00February 7th, 2020|Tags: boron, weed control, weeds|

Using boron to speed up natural maturity and senescence

One of the characteristics boron is known for is to facilitate rapid nutrient transport to the sugar sinks. This effect can be very valuable to speed up crop maturity and senescence while also increasing harvest quality.

When an alfalfa crop is growing rapidly and still very vegetative in late fall as we approach winter dormancy it is possible to quickly trigger senescence and rapidly move the sugars contained in the plant down into the crown with a generous foliar application of boron. A treated section can turn brown within a few days to a week (depending on weather and time of year), as all the sugars move down into the crown and the plants begin to senesce. The following spring, the section treated with boron in the fall will emerge from winter dormancy much faster and with many more shoots than an untreated section, because the crowns have much more energy from the stored sugars. Any perennial crop with a similar growth pattern will show this effect.

This effect can also be used to speed up the natural maturity process of other crops. A generous foliar application of boron on fruit such as tomatoes or apples will speed up the natural sugar transport into the fruit. This can help the fruit color and mature quickly and evenly days to weeks earlier than plants without a generous supply of boron.

This effect of boron on speeding up maturity and natural ripening can also be used on small grains in place of a desiccant or harvesting aid. Wheat that receives a foliar application of boron can mature rapidly and dry down as much as five to ten days faster than plants without adequate boron. The upside is that there is often a gain in test wheat and protein content, since boron produces this effect by increasing photosynthate and protein transport into the grain rather than reducing transport to the grain as a desiccant might.

Boron does not produce these effects if the crop is not at the right stage of growth. It can only speed up the plant processes which are occurring naturally. Managed well, boron applications can speed up these natural processes dramatically, and produce a higher quality grain or fruit, with an improved nutritional content.

How much boron is required? It varies based on the existing boron content of the soil and the crop. Many crops and soils are deficient, which is why crops are not maturing well in the first place. Often, the upper end of label rates are required if this is the only application being applied in the season. It is better to supply the crops foundational boron requirements during the growing season, and then top off the requirements with a lighter application a few weeks before maturity to produce the optimal effects we are looking for.

John Kempf2020-03-16T14:00:31-05:00February 6th, 2020|Tags: boron, maturity, nutritional solutions, ripening, senescence|