Ag 101 Week 42




Last week I said I was going to start and break down what goes into a bag of fertilizer. If you recall, I likened each component to a piston in an engine. Put the right pistons together, and you get a locomotive engine, put others together, and you get a Yugo.

You buy a bag of blended fertilizer, and you are getting a mix of nutrients that supply a plant with nitrogen, phosphorus, and potassium - NPK. In some cases, you can get some magnesium, calcium, sulfur, and trace minerals. I’m sure most of you know that already.

So, I want to go over a few questions I get; then we’ll take a look of some more commonly used components within the organic or softer chemistry area of fertilizers.

Why are the numbers, otherwise known as NPK values, so much lower in organic fertilizers than conventional?

The numbers representing NPK are a ratio of the percentage of available nutrients. The amount of the nutrient that is soluble and readily available for the plant to use. The more solvent, the higher the number and the more significant amount that the plant can uptake sooner. In the case of organic fertilizers, you have to also consider variabilities due to the fact components are naturally sourced materials, i.e., mined from clay deposits or animal by-products. Nature is not always consistent. One of the best benefits of organic fertilizers is a more extended nutrient supply over the growing season given the fact they are comprised of soluble and insoluble forms of nutrients. Given adequate moisture, biological actively, and crop type a natural fertilizer can take you through from planting to harvest. Once again, I stress it is crop specific and dependent on other management decisions. I will often suggest a split application if at all possible or fertilizing with a liquid to get through a season depending on all the variables.

Keep in mind from week 5 when fertilizing you are feeding the plant and the soil. Some are hungrier than others and at a different rate.

What is the difference between soluble and insoluble nutrients?

A soluble form of a nutrient is readily available to the plant for immediate uptake. Insoluble nutrients are held in the soil longer and need to be converted to plant available forms by the bacteria and fungi present in the soil. Other factors determining the rate at which they become soluble are soil moisture, temperature, and pH.

 What does it take to ensure a fertility program is effective?

1.      pH management -You want to manage pH to accomplish two things

First be in a range for optimal nutrient uptake based on soil type and crop variety while staying slightly acidic to help make nutrients available through mineralization and biological activity.

2.      Irrigation management

A fertility program is only as effective as your irrigation.

3.      Good amendment & fertilizer practices

Fertilizing is strategic and should be applied at the right rate, time, location using the right source. I discussed that in weeks 6 & 10

You could say I’m finally getting around to talking about the fourth – the source.

Let’s talk about nitrogen-

Nitrogen is used for several functions in the plant including the production of proteins that lead to tissue development

It also plays a role in chlorophyll production.

It is critical in leading to the vegetative growth in a plant but can become problematic when over applied for several reasons.

Such as-

Environmental issues

Increased insect pressure

A plants’ inability to retain blooms, such as in tomatoes

Balancing a plant’s need for nitrogen at the time it is required by the plant is a matter of timing it’s application. Even though it is abundant in the air we breathe, unlike phosphorus and potassium, it is not found in sufficient levels in the soil because it is not present in the parent material giving soil its properties.

By themselves, plants cannot use atmospheric nitrogen. It has to be converted by nitrogen-fixing bacteria in the form of NO3¯ or applied in a plant available form at the right time.

Due to the fact, the form most available to plants has a negative charge, it is not held in the soil and is more sustainable to leaching. If you recall, the cation exchange capacity is a soil’s ability to hold onto positively charged ions.

Nitrogen management is centered around optimizing nitrogen fixation by the soil biology and minimizing loss by using good management practices such as timing and location of fertilizers and manures.

With some conventional forms of nitrogen such as ones that are ammonium based, except ammonium sulfate, they have an acidifying effect on soil. Meaning they lower the pH. This can be an issue with over applying it and repeated long-term use. It is often not seen immediately but as somewhat of a cumulative effect based on cropping history, moisture, temperate, etc.

Over the past several years I have not seen that to be as much of an issue with organic sources. However, I have not found much research or data on the subject either. It should be noted that everything you put into the soil at some point in time effects it, whether immediate or long term.

Let’s talk about some common organic nitrogen components used in fertilizers.

First, I’m going to start with a three that are conventional component equivalents. Meaning they are still a naturally derived source, that can be used in an organic system but is more soluble and available to the plant quicker rather than later making them somewhat similar to that of conventional chemistries.

Blood Meal

It typically has an analysis of 10-13%N

It has been shown to have deer and rabbit repellant properties when used as a top dress. However, it may attract other animals such as raccoons and dogs.

Blood meal is primarily hemoglobin, which is a protein, and iron. In my experience, I have found the concentration of iron not to be an issue, just something to be mindful of

It can be cost prohibited to use it as a single source of nitrogen. However, when added to a blend It is a rapid release source making it a significant component when used with other mid and slower release forms

Chicken Manure

Of all the manures it is, in general, the one highest in nitrogen typically ranging from 2-8%

Keep in mind the analysis of manures of any type can be extremely variable based on source and solid to liquid ratios

It is available in several forms from liquid to pellets and relatively inexpensive depending on what part of the country you are in

It is also a good addition if lime and phosphorus are needed

Sodium Nitrate (Chilean Nitrate)

It is water soluble at a guaranteed 15% total N availability, with 2% potash, and 1% sulfur. The new formulation has allowed for ease of shipping because it is no longer considered a hazardous material.

The fact it is readily solubilized in water makes this the best choice for a starter fertilizer, especially for corn. It gives corn the boost it needs to get out of the ground even if planted into soils that might be cooler than what is generally required to get the best germination rate.

It can be an expensive insurance policy if not used accordingly and applied with good seed to fertilizer placement at the right rate. This is when cleaning, calibrating, and using the right equipment are essential as well.

I highly recommend using it in a blend as opposed to a straight source of nitrogen for several reasons. First, it can be expensive. Second, it is available almost immediately to the plant, making it the first to be used during the growing season, leaving the plant with nothing in reserve for the next several weeks that nitrogen is vital to develop enough vegetation for the plant to efficiently and adequately be able to perform photosynthesis. Remember it is a balance between vegetative growth and reproductive growth.

Next, the following have medium to slow release rates of nitrogen. They are relatively insoluble.

Fish/crab/shrimp meal

Typical analysis ranges from 5-30%N

Typically, fish ranges from 5-9%N depending on whether it is a meal, powder or liquid

Crap and Shrimp range from 10-30%N with 11-18%Ca depending on the shell to meat ratio

Crab makes an excellent addition to a fertilizer blend for the extra calcium, and the addition on an enzyme called chitin that has been shown to help control nematodes in the soil

Peanut meal

A typical analysis is 8-9%N

Can be cost prohibitive and not allowed due to allergen restrictions

Bone meal

A typical analysis is 3-4%N

It is also a good source of phosphorus and calcium

Feather meal

Typical analysis 11-15%N

Apply early in the season to take advantage of slower release rate providing nitrogen over the course of the growing season

 Soybean meal

A typical analysis is 6-7%N

A good source for full season nitrogen supply

Soybean meal has been shown to burn new seedlings and reduce germination rates potentially. Care should be exercised when timing the application


For years now, agricultural manures have gotten a lot of press. After taking the PA Nutrient Management courses, I concluded – shit’s complicated. Gone are the days you cleaned the barn and piled it out of the way so you could spread it when you had more time. Raw manure is the most nutrient dense. The longer it composts it losses its nutrient value. Over applying it, can lead to not only environmental issues also pest and disease challenges.

However, there is one manure that is gaining popularity with tobacco and cannabis growers, and its bat guano. It is cost prohibitive to use on a large scale, but I feel it is important enough to mention as a potential source of not only nitrogen but phosphorus as well, while being low in salts.

A typical analysis is 5-12% depending on the source

It is fast acting and soluble in water making it a great addition to a liquid program for cannabis especially vegetative and flowering stages

I have several growers using it in sub-irrigation systems for starting organic tobacco. They like the fact its water soluble and doesn’t seem to burn the way other fertilizers have a tendency to do if not managed correctly.

 There are several other sources I could mention that are used for nitrogen such as corn gluten, alfalfa meal, legumes, and cottonseed meal.

We’ll cover those and more during the time remaining in the 52 Weeks of Agronomy Series.