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Learn the effects of different nitrogen forms found in commercial water-soluble fertilizers on plant health and substrate pH. Gain the knowledge needed to make informed decisions and optimize crop yields in your greenhouse operation.
Water-soluble fertilizers are the most common fertilizer choice for growers in greenhouse production. When looking at a fertilizer label, the first and usually largest number represents nitrogen. However, that number only refers to the percentage of total nitrogen in the fertilizer and not the form of nitrogen, of which there are three. To find this information, you must look at the guaranteed analysis on the label (Tables 1 and 2). Nitrogen is an essential nutrient that plants need in relatively large amounts, and because it can influence the pH of your substrate over time, it's important to understand the different forms of nitrogen in water-soluble fertilizers to produce high-quality crops.
Nitrogen in water-soluble fertilizers can exist in different forms: nitrate, ammoniacal nitrogen and urea. Each form of nitrogen has different characteristics that affect how it reacts in the substrate and how plants uptake and assimilate it.
Nitrate is the most mobile form of nitrogen and easily dissolves in water. When applied to the substrate, it moves readily with water and does not attach to substrate particles. This mobility can have advantages in some situations but can also result in nitrate leaching and loss. Generally, nitrate is the form of nitrogen most often used in plug and liner production as well as finished crops. Nitrate assimilation is regulated by the plant, reducing the occurrence of toxicity.
For this reason, nitrate-nitrogen is usually the most abundant form in greenhouse fertilizers, especially in dark-weather feeds. Fertilizers with a high percentage of nitrate-nitrogen are labeled as having potential basicity (Table 1) because the uptake of nitrate by the plant increases the substrate pH. Fertilizers with potential basicity are often used to fertilize micronutrient-efficient crops like marigolds and geranium. Due to the production process, nitrate-nitrogen tends to be more expensive than the other forms listed in this article.
Table 1. A simplified version of a commercial water-soluble fertilizer guaranteed analysis label. This fertilizer has a low percentage of ammonical nitrogen and a high percentage of nitrate nitrogen, giving it a potential basicity.
15-0-15
Guaranteed analysis
Total nitrogen (N)&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;.15%
0.58% ammoniacal nitrogen
12.12% nitrate nitrogen
2.3% urea nitrogen
Soluble potash (K2O)&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;.15%
Potential Basicity: 319 lb. Calcium carbonate equivalent per ton.
Ammonium, labeled as "ammoniacal nitrogen" on fertilizer labels, is a readily available form of nitrogen. While ammonium is water-soluble, it readily attaches to organic matter particles, which helps prevent it from being leached. Fertilizers with a moderate to high percentage of ammoniacal nitrogen are labeled as having a potential acidity (Table 2) because they decrease the substrate pH. Fertilizers with potential acidity are often used to fertilize micronutrient-inefficient crops like calibrachoa and petunia. Growers should consider the growing environment when deciding if ammoniacal nitrogen suits their crops since ammonium toxicity is problematic in cool and dark environments.
Table 2. A simplified version of a commercial water-soluble fertilizer guaranteed analysis label. This fertilizer has a high percentage of ammonical nitrogen giving it a potential acidity.
25-5-15
Guaranteed analysis
Total nitrogen (N)&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;.25%
10.75% ammoniacal nitrogen
14.25% nitrate nitrogen
Available phosphate (P2O5)&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;..5%
Soluble potash (K2O)&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;.15%
Potential Acidity: 608 lb. Calcium carbonate equivalent per ton.
There is a perception that using a fertilizer with a high percentage of ammoniacal nitrogen can stimulate growth. However, research performed at North Carolina State University in the early s showed that the form(s) of nitrogen did not influence plant size. Instead, it was the relatively high levels of phosphorus present in fertilizers with a high percentage of ammoniacal nitrogen that stimulated growth. Therefore, for more compact growth provide less phosphorus, and for more elongated and lush growth, provide more phosphorus, independent of the form of nitrogen.
Urea is another form of nitrogen commonly found in water-soluble fertilizers. Urea-based fertilizers are typically more affordable than other forms of nitrogen. Urea-nitrogen and ammoniacal-nitrogen are almost identical in how the plant responds and utilizes nitrogen. Therefore, all the characteristics and risks mentioned for ammoniacal nitrogen also apply to urea-nitrogen. The main difference between urea-nitrogen and ammoniacal-nitrogen occurs before the conversion of urea to ammonium.
Urea dissolves in water and moves with substrate water, like nitrates. Before plants can utilize nitrogen in urea, it must convert to both ammonia and ammonium forms. Urea can be lost through leaching if it does not convert to ammonia, and ammonia can be lost to volatilization if it does not convert to ammonium. Under warm-growing conditions, this conversion can happen in as little as a few hours.
The choice of nitrogen form in your greenhouse water-soluble fertilizer depends on various factors including the crops grown, water alkalinity and environmental conditions. In most cases, at least two forms of nitrogen are simultaneously used. Some growers initially utilize ammoniacal or urea-based nitrogen because of their affordability. However, a predominantly nitrate-based fertilizer is usually advised to prevent ammonium toxicity and a decrease in substrate pH over time. Excessive ammoniacal nitrogen content, exceeding 30%, can potentially lead to ammonium toxicity in plants from late fall through early spring. Therefore, several factors should be considered when determining the nitrogen forms and their percentages to apply to greenhouse crops including specific crop responses, environmental conditions, water alkalinity and the potential risks associated with each form of nitrogen. Consult with a university extension educator or greenhouse fertilizer supplier to help you make more informed fertilizer decisions.
Nitrate
Ammoniacal
Urea
Risk of leaching
X
X
Risk of ammonium toxicity
X
X
Lowers substrate pH (acidic)
For more urea 46-0-0 nitrogen fertilizerinformation, please contact us. We will provide professional answers.
X
X
Raises substrate pH (basic)
X
Understanding The Different Nitrogen Types in Fertilizer
There is no shortage of different types of nitrogen available when it comes to designing a nutrient management plan for your turf. There are, however, some very distinct differences on how each type actually provides the nitrogen. Understanding how each of the three major types (beyond straight urea) functions and differs from one another becomes the key in utilizing the proper one to achieve the expected performance from your turf.
The two most common types are called &#;slow release nitrogen&#; (SRN) and &#;controlled release nitrogen&#; (CRN). Many times these terms are used interchangeably, but they really shouldn&#;t be; they do not mean the same thing. While they both release nitrogen at a slower rate than straight urea, the mechanism of their release is vastly different.
At the most basic level, SRN and CRN sources are separate by one defining attribute, coated or non-coated. SRN does not employ any type of coating to provide extended release nitrogen, while CRN is completely dependent on coatings to delay the release of nitrogen. These coatings are at the heart of the main difference between the two nitrogen types.
Slow Release Nitrogen (SRN)
Slow release nitrogen&#;s most popular form is methylene urea which is created through a manufacturing process where long-chain molecules are created by chemically combining a nitrogen source with an aldehyde. These long-chain molecules provide the delayed release of nitrogen by being broken down by the microbes in the soil feeding on them at predictable rates. The microbial activity slowly breaks down the molecules, converting it to ammonium nitrogen, which then becomes ammonium nitrate. Ammonium nitrate is the only form of nitrogen that the turf plant can uptake and use.
It should be highlighted that the duration of release in a slow-release nitrogen type is controlled by the effectiveness of the microbial organism&#;s molecular breakdown which is dependent on other environmental factors. These factors include the properties of the growing medium, moisture levels and temperature. The hotter and wetter the soil is, the more active the microbes are which will lead to increased nitrogen release.
It&#;s been well documented that the release rate of SRN very closely mimics that of the turf plants innate needs for nitrogen, meaning that the nitrogen is being supplied to the plant at the same time as it is needing it. In cooler weather when the plant grows much slower and it&#;s nitrogen needs are much lower, the amount of microbial activity is also decreased so there is no nitrogen loss to the soil. This is one of the largest benefits of SRN when it comes to choosing the proper nitrogen type for your turf.
LebanonTurf offers our own proprietary slow release, non-coated, nitrogen types in the forms of MESA® and Meth-Ex® which are included in a wide range of products primarily in our ProScape® and Country Club® branded lines.
Controlled Release Nitrogen (CRN)
Controlled release nitrogen differs fundamentally from SRN in both technology and mode of nitrogen release. CRN particles are completely encapsulated in a organic resin or polymer coatings. These coatings are the secret to delaying the release of nitrogen in a CRN type.
The coatings on the CRN particles act as a semi-permeable membrane &#; a barrier to some molecules, but allowing certain different molecules to pass through. When CRN is applied to an adequately-moist growing medium, there is a one-way passage of water through the coating to the inside of the particle. This phenomenon is called &#;osmosis&#;. The absorbed water partially dissolves the urea inside the prill to create a highly-concentrated solution. At this point, the CRN diffuses the urea solution out of the particle into the soil medium.
The rate of nitrogen release for CRN types are heavily affected by both soil moisture and temperature. Adequate moisture level is critical for the reaction to take place inside the CRN particle and the temperature of the soil directly impacts the permeability of the pore spaces of the coating.
LebanonTurf offers products manufactured with controlled release, coated nitrogen types such as Sulfur Coated Urea (SCU) and Polymer Coated Urea (PCU).
Benefits of Using SRN and CRN
The major benefits from using slow release or controlled release fertilizers over readily-soluble &#;straight&#; fertilizers in a nutrient management plan include:
Stabilized Nitrogen
Stabilized nitrogen products, sometimes called &#;inhibitors,&#; are often misunderstood. Their use extends the time that nitrogen remains in the form of urea or ammonium in the soil, but they&#;re not the same as slow or controlled-release fertilizers. While they do have an impact on nitrogen availability, they work differently than some of the more familiar products like sulfur-coated urea, methylene urea, or polymer coated urea. In short, stabilized nitrogen extend the amount of time that nitrogen is available for plant uptake.
Before plants can take up nitrogen from urea fertilizer, that urea must be converted via two processes, the first of which is called hydrolysis. Urea is broken down into ammonium, and the urease enzyme is an important element of that process. There&#;s also a potential loss mechanism called &#;volatilization&#; where the ammonium is converted to ammonia gas and releases into the atmosphere. Stabilized nitrogen inhibits this urease enzyme from doing it&#;s job for several days.
The second step in the process is called &#;nitrification,&#; where ammonium is converted to nitrate. Both ammonium and nitrate can be taken up by the plant, but because ammonium is positively charged, it can be attracted to and held by negatively charged soil particles. Nitrate is negatively charged, so it&#;s not attracted to soil particles and can therefore leach from the system with excess water. Stabilized nitrogen prevents this conversion from ammonium to nitrate allowing more time to be taken up by the plant.
LebanonTurf offers our own proprietary stabilized nitrogen in the forms of Lebanon Stabilized Nitrogen (LSN®).
Benefits of using Stabilized Nitrogen
Potential advantages of utilizing stabilized nitrogen over readily-soluble &#;straight&#; fertilizers in a nutrient management plan include:
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