Nutrients


Tate’s Tips
A Series of Reflections on growing grass for forage

Issue 4.
Nutrients

Since I have gone fairly basic on this series, I might as well continue with some fundamentals.

The most fundamental elements of growing forages are the nutrients. I will try to address nutrients from a layman’s viewpoint. I will address them in what I think are the order of importance.

The most important nutrient for forage production is plain and simple water. If we have rain at normal intervals and in appropriate amounts then grass will grow. Three months of hot dry weather will leave you with nothing and you can only hope that when rains return the forages will come out of dormancy and regenerate. Enough hot and dry weather can kill any stand of grass that has been otherwise stressed. That suggests the topic of supplemental water or irrigation but we will save that as a separate topic.

Normal rainfall in central Virginia is historically about 42 inches per year. If all things were equal then that would be 8 tenths of an inch per week. But nature is seldom that predictable. 2003 is the last excellent crop year we had across the board in our area. 2009 was not a bad year but the weather patterns were extremely spotty. Parts of Caroline county suffered horribly under drought. Other parts had a great crop year.

Rainfall volume this fall has been unprecedented in my lifetime. None of us has much influence on the weather so we have to take what we can get and deal with the averages.

I deal with all kinds of crops but in this series I am talking mostly about grass forages. Summer of 2002 was a brutally dry year. But that fall in early September we had a tropical storm that brought four or five inches of rain and grass that was brown and dry sprang to life and grew at a prodigious rate through the early fall. Even fields that were a bit short on other nutrients, experienced what I refer to as compensatory growth and put forth good growth in an effort to rebuild their root reserves and survive. 2003 followed with a year of moderation in summer temperatures and regularity of rainfall. It was an excellent forage and livestock year.

Forages need water to survive, produce, flourish and reproduce. It is the first and most limiting nutrient. Nothing grows without water. A couple of years ago there was big news all over TV and the internet that Death Valley was in bloom. It had experienced the first significant rain or possibly snow in something like twenty years. In just a few weeks plants emerged, flowered, set seed. Death Valley was a place of beauty and grandeur, but it grew hot and dry again and the plants wilted and then faded under the unrelenting sun and temperatures of the climate. But those seed will lie in wait for the next rain. We have all seen the monsoon shows about the perils of the rainy and dry periods in Africa.

Normally here in temperate Virginia things are a bit more even but Mother Nature can be a cruel taskmaster. We have to talk about normal conditions, acknowledge the possibility of abnormal conditions and hope for the best.

This fall we have been dealing with scattered reports of Ark building.

Nationally syndicated garden talk show host Andre Viette recommends watering lawns deeply and inch or two at a time once every ten days. 1.15 inches of rain every 10 days would give us our annual average of 42 inches per year. Of course a little more in the hot summer and a little less in the winter would balance things nicely. But then July and August are typically the heaviest rain months of the year anyway. See……. Ma Nature is trying to help us along.

links to climate data for Ashland Va. below.

http://www.usclimatedata.com/climate.php?location=USVA0028

http://www.climate-charts.com/USA-Stations/VA/VA440327.php

This year we went into the fall with a rainfall deficit of about 9 inches. After the rainiest November on record we are now going into winter with a rainfall surplus. Not to mention the mud surplus.

So water is the most limiting nutrient and it is the single factor that usually will make or break any cropping enterprise.

The second most limiting nutrient is pH. pH is the measure of the level of acidity or alkalinity in the soil.

Basic information. Most but not all crops prefer a pH range of 6.0 to 6.8 with 6.0 being a bit low but acceptable and 6.8 being a bit high. There are some acid loving plants like azaleas and such that prefer a lower pH but most agronomic crops will fall within the 6.0 to 6.8 range.
What does pH mean?
This is a measure of how acidic or alkaline a substance is. The initials pH stand for “Potential of Hydrogen.” Acids have pH values under 7, and alkalis have pH values over 7. If a substance has a pH value of 7, it is neutral-neither acidic or alkaline.

Because the pH scale is logarithmic, a difference of one pH unit represents a tenfold, or ten times change. For example, the acidity of a sample with a pH of 5 is ten times greater than that of a sample with a pH of 6. A difference of 2 units, from 6 to 4, would mean that the acidity is one hundred times greater, and so on.

From the above information you can quickly see that the range of 6.0 to 6.8 is actually pretty broad with 6.0 being eight times more acid than 6.8.
So what does this mean when trying to grow grass? It means will your grass be happy and survive and thrive in the pH of the soil you want it to grow in. It also determines whether or not the other expensive nutrients will be used by the crop you want to grow. Excess acidity or alkalinity can inhibit uptake and use of expensive fertilizers.
At risk of sounding like a broken record the first step to good agronomy is a proper soil test. The soil test will give you a minimum of the soil pH and the Phosphorous and Potassium levels. Most soil test will give you a recommendation of what is needed if you provided information on what you wish to grow.

In this part of Virginia the natural condition is for the pH to be low. Forest land or fallow land will typically test down to 4.5. Streams running through significant portions of such land will also test low in pH. Newly cleared land in our area will almost always have a very low pH.
To correct low pH the cure is the addition of Lime. The standard for lime is Calcium Carbonate equivalent. Limes from various sources vary and the proper amount needs to be adjusted to meet the calcium carbonate equivalent. Lime may be from ground Limestone, hydrolytic lime, calcium carbonate or calcium sulfate (gypsum). Lime is usually broadcast by the ton or part thereof.
In no case is it beneficial to apply more than two tons of lime per acre. That is the maximum amount that the soil biota can metabolize and make use of. Lime does not immediately take effect. It is a slow and biological process. If pH is extremely low the standard advice is to apply up to two tons of lime in a given season and retest the soil annually for additional recommendations until proper pH is reached.
As mentioned above the level of the pH impacts the effect of other nutrients. Soil nutrition is chemistry and I am not a chemist.
Low ph is like trying to grow something in battery acid.
High pH is like trying to grow something in baking soda. Neither is a very good growth medium.
Potassium and Phosphorous are two widely needed nutrients. If you add Phosphorous to acid you will make some amount of phosphoric acid. Plants won’t grow in phosphoric acid either. If you add potassium to baking soda you will make some amount of Potassium Hydroxide which is a strong caustic and nothing will grow in that. So getting the soil pH correct is the first step to adding nutrients.
An additional good discussion of this topic is available at
http://www.heronswoodvoice.com/?utm_source=121509-Balancing-Garden-Soils&utm_medium=email&utm_campaign=Hvoice

Phosphorous this section is taken from earthworks at

http://www.soilfirst.com/tnm_02_1998.htm

Phosphorous is perhaps the most misunderstood of all the basic plant nutrients. An anion, phosphorous is very reactive, and often tied up in the soil with calcium and other cations. These calcium-phosphate bonds are often very hard to break, especially in biologically weak soils, leaving the plant deficient. Phosphorous is found in all plant tissue but is most pronounced in the seeds, flowers and youngest shoots. It is the backbone of many enzyme and amino acid systems, including photosynthesis. It regulates the breakdown of carbohydrates and energy transfer. Without phosphorous, cell division is weakened and plant growth suffers. These deficiencies can lead to plant stress, susceptibility to disease, insect attack, and even weed infiltration.
Potassium
Potassium is often referred to as “the band director.” It helps to direct free nutrients (such as carbon, hydrogen and oxygen) out of the atmosphere and into the plant. Without this activity photosynthesis would be severely restricted and the plant would struggle to make starches, sugars, proteins, vitamins, enzymes and cellulose. Potassium aids in helping the plant through the cold of the winter and the heat of the summer. In short, when potassium is out of balance plant stress is very high. However, one of the great fallacies in our industry is that you can not overdo potassium. You can overdo everything!
Potassium is a positively charged cation and should saturate only 3 – 5% of the soil colloid. When too much potassium is used, other important cations suffer, most notably calcium and magnesium. In fact, potassium can drive pH more aggressively than magnesium or calcium by quickly replacing them and creating an imbalance in base saturation. Potassium tends to be relatively mobile in the plant. When excesses occur not only does the soil suffer, but imbalances are created intra-cellularly and stress is actually created. As soil pH climbs above 6.5, potassium mobility slows down, and as the soil reaches 7.0 mobility is severely hindered.
Nitrogen
“..any nutrient introduced to the soil is first digested by micro-organisms before the plant has a chance to eat.” Joel Simmons
Without nitrogen there would be no photosynthesis and, therefore, no plant. However, nitrogen is also the most overused nutrient in our industry, and the negative impact it can have on the soil ( and water) can be tremendous.

Urea > ammonia (NH3) >
nitrite (NO2) > nitrate (NO3) >
into the plant.
(The arrows in this diagram represent soil microbes which are responsible for breaking down the nitrogen fertilizer into plant usable forms.)
Nitrogen (N) is a key nutrient in manipulating plant growth. Most nursery/floral producers use large quantities of N fertilizers in a “blanket” attempt to meet the needs of their crops. However a thorough understanding of N nutrition Can be useful in optimizing both the concentration and form of N best suited for the plant species, stage of growth, time of year and production objectives.

Plants require N in relatively large quantities and in forms that are readily available.

Nitrogen metabolism is a well studied and a vital aspect of plant growth. Nitrogen is one of the important building blocks in amino acids:
H

R C COOH

NH2
Amino acids are typically made up of an amino group (NH2), carbon (C), a carboxyl group COOH), and a variety of molecular structures (R) which define individual amino acids (glycine, serine, licine, alanine, etc.). When these amino acids link together in long chains they form proteins. Proteins are also vital components in a variety of metabolic pathways and processes. Proteins makeup the molecular structure of DNA, RNA and a host of other critical metabolic processes required for plant growth.

When N is deficient in plants restricted growth of tops and roots and especially lateral shoots may occur. Plants also become spindly with a general chlorosis of entire plant to a light green and then a yellowing of older leaves. This condition may proceed toward younger leaves. Older leaves defoliate early.
Since I am now on page 6, this might be a good place to stop and take a nutrient break and assimilate the little nuggets we have taken in so far.

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