NITROGEN BMPs FOR
There are approximately 12,000 small farms in Idaho, Oregon, and Washington, mostly near large cities and towns. The number of small farms is growing rapidly and may double by the end of the decade. Small farms range in size from 1 to 20 acres. Many small farm owners have horses or other livestock which are fed by intensive management of the farm, often using quantities of fertilizers and chemicals far exceeding quantities used on large scale farms (on a per acre basis).
Small farms can have a significant impact on water quality. Most small farms are concentrated near the larger cities and towns in Idaho, Oregon, and Washington. These farms, or ranchettes, often contain several horses and other livestock. The owner tries to produce all feed for these animals on this small acreage. Thus forage crops are important. Because most small farm owners are relatively affluent and derive most of their income from off-farm sources the cost of chemicals used in the production of forage crops is often not a limiting factor in management. This results in a very high chemical use rate per land unit area.
Large numbers of small farms are appearing in King, Spokane, Pierce, Thurston, and Snohomish counties in Washington; near Portland, Medford, Bend, and in the Willamette and Rouge River valleys in Oregon; near Boise, Coeur d'Alene, and in Canyon county, Idaho. Because of their proximity to urban areas these farms are often situated on or near some of the most sensitive aquifers and surface waters in the Pacific Northwest.
Most small farm owners are environmentally sensitive; however, this group has totally been neglected as far as educational programming for pollution prevention. Numerous programs are in place to educate the urban dweller on home and garden chemicals. Massive federal programs are targeted at the larger farmer. However, since small farms are not eligible for cost share programs, these people often fail to get technical assistance supplied by agencies such as the Soil Conservation Service.
The purpose of this slide set is to provide a background that will enable a small landowner to utilize nitrogen best management practices on his or her small farm.
|1. Slide Title|
This slide set is entitled "Nitrogen best management practices for small farms in the Pacific Northwest." Funding for the development of this slide set was provided by a grant from the Pollution Prevention Program of EPA Region 10. Owners of small farms that utilize the best management practices introduced in this slide set will help protect both surface water and groundwater quality in the Pacific Northwest.
|2. Humans Need
Nitrogen (N) is an element essential for all plant and animal life. Humans have a nutritional requirement of 55 pounds of protein per year. Nitrogen is a component of protein. There are 8.8 pounds of nitrogen in 55 pounds of protein. In the USA a typical person obtains half their protein from animal sources, and the other half from vegetable matter.
|3. Efficiency of N
Even though, in theory, it takes only 8.8 lbs of N to supply a person's annual protein needs, inefficiencies in ecosystems must be considered. It takes much more than 8.8 lbs of N to meet a person's needs because plants and animals are not very efficient in scavenging N from ecosystems. Plants are considered to be 50% efficient -- that is they can convert only about 50% of the N available to them into protein. On the other hand, animal systems are much more inefficient with values averaging only 15% of conversion of N into protein. If we assume that the average person in the USA obtains 1/2 from plants it actually takes 38 lbs of N per year to meet a person's protein requiement instead of the theoretical 8.8 lbs.
|4. Protein Needs|
In an unfertilized environment -- or natural ecosystem in temperate regions of the world it takes about 2 acres of land to supply one's protein needs. In densely populated countries N additions to soils are necessary to produce enough food. Even in land-rich countries like the USA N additions are an important part of our agriculture. From an ecological standpoint this is not all bad because intensive agriculture with N inputs allows us to keep marginal lands out of production. Many of the marginal lands not in agriculture today contain important ecosystems that should receive as little disturbance as possible. N additions include commercial fertilizers, animal manures, plant manures, and industrial by-products that contain N.
|5. The Nitrogen Cycle|
The interlocking succession of N reactions occuring in the soil is known as the nitrogen cycle. This cycle is a complex of chemical pathways that trace N transformations and movement in an ecosystem. From an environmental standpoint with a special interest in water quality, problems occur when some forms of nitrogen leak from the system.
|6. The Nitrogen Cycle|
This diagram represents a simplified nitrogen cycle. Agriculture affects both N additions and subtractions to the soil. Additions include N fertilizers, crop residues, N fixation by legumes, and manures. Subtractions attributed to agriculture include crop removal (harvesting), plant uptake, and N leaching. Plants can use two forms of N -- ammonium and nitrate. Nitrate is the plant available form of N that can leak or leach from the system and have a detrimental effect on the environment. Another important aspect of the N cycle is the process called mineralization. In this process organic matter (OM) breaks down and forms plant available ammonium and eventually nitrate. Crops residues, animal and plant manures, and composts when added to the soil become part of the soil OM which when mineralized will form ammonium and nitrate.
|7. Nitrogen Cycle --
Anytime we have leaks in the nitrogen cycle there are some environmental concerns. The two biggest problems which can impact water quality are leaching and erosion. Nitrates are mobile in soils and can leach into our groundwater supplies. On the other hand soil erosion has a negative impact on surface water quality -- our streams, rivers, and lakes. Organic matter is concentrated on the soil surface. Consequently, if soil erosion occurs, this nitrogen containing organic matter washes off the land into our surface water sources.
|8. Nitrogen Use in PNW
Nitrogen is one of seventeen essential nutrients required for plant growth. Most crops remove more nitrogen than any other nutrient from the soil. Plants contain anywhere from 1 to 5% nitrogen on a dry weight basis. The importance of nitrogen to all agricultural systems is unquestionable.
|9. Nitrogen Use in PNW
Agriculture in the Pacific Northwest depends on using large quantities of nitrogen fertilizers. Commercial N application rates range from 50 to 350 pounds per acre depending on the crop being grown. An average nitrogen application rate on farmland would be about 120 pounds per acre. High nitrogen use is not confined to large scale production agriculture, however. Even the home gardener in a city that uses compost as their source of nitrogen often adds upwards of 100 pounds of N per acre to their garden soil without realizing it.
|10. Sources of
There are several plausible sources of nitrogen that are used in agricultural ecosystems. Common N sources include the decomposition of soil organic matter, commercial N fertilizers, animal manures, plant residues, and composts. The decomposition of soil organic matter -- called mineralization is a natural process that occurs in all soils. In non-agricultural ecosystems, organic matter mineralization is the major source of nitrogen for plants.
|11. Forms of Nitrogen|
All sources of materials applied to soils to provide nitrogen for plants eventually produce ammonium or nitrate, plant-available forms of nitrogen. Nitrate is the nitrogen form most often taken up by plants in agricultural ecosystems. Nitrate is nitrate -- it does not matter to the plant whether it came from commercial nitrogen fertilizer or if it mineralized from a compost pile.
|12. Nitrates in
Nitrates are mobile in soils. Consequently, when excess water is applied to land -- either by over-irrigation or by excessive amounts of rainfall nitrate can leach through soils and contaminate groundwater. Federal and state standards dictate that drinking water should not contain more than 10 parts per million (ppm) nitrate-nitrogen. Recent surveys have shown that about 2% of the rural wells in the PNW currently exceed this 10 ppm nitrate-nitrogen drinking water standard.
|13. Nitrates in
Despite the fact that only 2% of rural wells in the Pacific Northwest exceed the federal standard of 10 ppm nitrate-nitrogen, there are localized areas that have a significant portion of wells that have high nitrate levels. Many of these identified areas have been linked to areas where intensive agriculture is practiced. Environmental officials conclude that in several cases high nitrate levels have been traced to poor nitrogen management by agriculture.
|14. Sources of
Numerous natural and man-made sources of nitrogen can contribute to nitrate contamination of groundwater. Agriculture is definitely a major source of nitrates. Nitrate additions to or nitrogen transformations in soils associated with agriculture include: fertilizers, soil organic matter mineralization, nitrogen fixation by legumes, animal manures, and composts.
|15. Sources of
Agriculture is just one industry that produces nitrates. There are many non-agricultural sources of nitrates. These nitrate sources which can end up in groundwater include setpic tanks, industrial plants, lawns and gardens, golf courses, organic matter mineralization in natural ecosystems, and certain geologic parent materials. Septic tanks which are not properly maintained leak substantial amounts of nitrates. In rural areas that have a high density of small farms, septic tanks have the potential to produce levels of nitrates similar to agriculture. For this reason there has been a major effort to sewer these rural areas as the population density increases to the point that these areas become more suburban thatn rural-like in the Spokane Valley of Washington State.
Proper nitrogen management on small farms is important for three reasons. Proper nitrogen management improves crop quality. Proper nitrogen management improves farm profitability. And proper nitrogen management protects the environment.
When we talk about proper nitrogen management to prevent water pollution there are two key concepts one needs to become familiar with. The first concept is nitrogen use efficiency, commonly abbreviated as NUE. The second term is best management practice, commonly abbreviated as BMP. Let's look at each concept in some detail.
|18. Nitrogen Concept|
Nitrogen use efficiency or NUE can be defined as the percentage of plant available nitrogen in the soil which is taken up by the plant. This value is expressed as a percent and can range from 0 to 100 percent. Ideally, we would like to see an NUE value of 100%. The greater the NUE value -- the less plant available nitrogen is left in the soil. Plant available nitrogen left in the soil could leach and contaminate our groundwater supplies. A high NUE value is important for two reasons -- (1) environmental protection, and (2) farm profitability.
|19. Nitrogen Concept|
What is the N in NUE? The nitrogen is plant-available nitrogen in the soil. It includes both nitrate and ammonium. This would be the sum total of ammonium and nitrate that got into the soil by the following means: (1) ammonium and nitrate mineralized from soil organic matter, (2) nitrogen added as a commercial fertilizer, and (3) residual ammonium and nitrates left in the soil that were not used by last years' crops.
|20. Nitrogen Concept|
Across the country, nitrogen use efficiency averages about 50% for most crops. Intensive management using best management practices can result in NUE values approaching 70% in production agriculture. On the other hand, poor or careless management often results in NUE values less than 30%. Small farms lend themselves to intensive management. Consequently, a NUE goal of 75% is realistic when nitrogen best management practices are employed.
|21. Nitrogen Concept|
As an example, what does 45% NUE mean? It simply means that 45% of the plant-available nitrogen -- ammonium and nitrate -- in the soil was taken up by the plant. What happened to the other nitrogen that constitutes the 55% not taken up by plants? Well, a portion of it remained in the soil, a portion may have leached, and a portion was utilized by soil microbes or taken up by weeds.
The greater the NUE value, the less residual N is left in the soil . . . A high NUE value minimizes the potential for environmental pollution.
|23. Nitrogen Concept|
The other concept of importance is best management practice, or BMP. Best management practices can be defined as implemented strategies which eliminate or minimize non-point source agricultural pollution. There has been extensive research to design best management practices for nitrogen management.
|24. Nitrogen Concept|
Best management practices have been designed to be compatible with agricultural ecosystems. Best management practices that you will see in this slide set can protect the environment without compromising the profitability of agricultural enterprises.
|25. Nitrogen BMPs|
There are seven important nitrogen best management practices that should be considered for adoption on small farms. The first and most important nitrogen best management practice is to use the optimum nitrogen application rate on each field of your small farm. To do this correctly, you must consider the following: soil testing, setting realistic yield goals for the crops in each field, providing nitrogen credits from soil organic matter, providing nitrogen credits for manures and legumes incorporated into your fields, and you need to consider the overall vulnerability of groundwater to contamination. The greater the threat -- the more BMPs that should be considered for implementation.
|26. Nitrogen BMPs|
You must test your soil to determine its organic matter content and the amount of plant-available nitrogen -- ammonium and nitrate present. This is a necessary best management practice.
|27. Nitrogen BMPs|
It is not difficult to get a good representative soil sample from your field. If you need information on how to take a soil sample contact your local county extension office. Soil samples for OM content should be taken to a depth of 12 inches. For ammonium and nitrate the soil sample should be taken to the effective rooting depth of the crop that will be planted. Your local extension office can help here also. The soil samples should be taken 3 to 4 weeks prior to planting. The soil sample should be analyzed by a reputable laboratory. The numbers provided by the soil testing laboratory can be interpreted by your county agent. Base your N application rate on your soil sample analysis using a fertilizer guide for the crop you select.
|28. Nitrogen BMPs|
Nitrogen application rates should be based on a soil sample and a projected crop yield. Your yield goal should be realistic. A realistic yield goal will allow accurate determination of optimum nitrogen rates for crop production. Yield goals that are too low will under estimate nitrogen needs and result in both reduced yields and profits.
|29. Nitrogen BMPs|
Yield goals that are too high will over estimate nitrogen needs. This will result in excess plant available nitrogen in the soil profile. This increases the potential for groundwater contamination with nitrates.
|30. Nitrogen BMPs|
In addition to accounting for the nitrogen in a soil test one must consider giving credit to nitrogen obtained from other sources. You should take into account the nitrogen in soil organic matter, legumes, animal manures, composts plus other soil additives, and sludge.
|31. Nitrogen BMPs|
Nitrogen credits should be given for the amount of organic matter in the soil. Organic matter breaks down in soils at the rate of 1.5% per year. As soil organic matter breaks down by the process called mineralization, plant-available forms of nitrogen -- ammonium and nitrate -- are produced. The general rule of thumb for crops grown in the Pacific Northwest is that a soil with 1% organic matter should be credited with 15 pounds of plant-available nitrogen. So 15 pounds of plant-available nitrogen should be credited for each percent of OM there is in the soil.
|32. Nitrogen BMPs|
This table shows the plant-available nitrogen credits for fields with 1 to 10% organic matter. As you can see -- the rule of 15 pounds per percent organic matter in the soil can be used to accurately predict the amount of organic matter mineralized into plant-available nitrogen in any soil.
|33. Nitrogen BMPs|
Nitrogen credits should also be given if legumes were grown last year in your field. Residue from these legumes will provide some nitrogen for the next crop. Peas, beans, alfalfa, birdsfoot trefoil, and clovers are legumes which can provide a nitrogen credit. Peas and beans provide a nitrogen credit of 10 to 20 pounds per acre. Alfalfa, birdsfoot trefoil, and clovers provide a credit of 30 to 50 pounds of nitrogen per acre.
|34. Nitrogen BMPs|
Animal manures applied to soils mineralize like OM and can provide a substantial N credit. Only a portion of the nitrogen in the manure would be mineralized during the first growing season after application. This table provides information on nitrogen credits for manure for the first season after application. For example, if one ton of solid beef manure had been appplied over an acre the nitrogen credit would be 4 pounds nitrogen per acre. If 6,000 gallons of swine manure had been spread across an acre the N credit would be 66 pounds (11 X 6 = 66).
|35. Nitrogen BMPs|
Another material which can provide nitrogen credits to a field is sludge. Sludge does contain some nitrogen -- however, the nitrogen content varies from batch to batch. Annual sewage sludge applications should be limited by the amount of nitrogen required for crop growth. You should test sludge for its nutrient content.
|36. Nitrogen BMPs|
An important best management practice for nitrogen is to make sure that the fertilizer rate applied is sound -- based on research. Nitrogen application rates should be based on scientific information. The three Northwest land grant universities -- Oregon State University, Washington State University, and the University of Idaho have developed fertilizer guides for over 50 crops grown in the region.
|37. Nitrogen BMPs|
These fertilizer guides take into account the residual plant-available nitrogen in the soil profile, the amount of nitrogen that is mineralized from organic matter during the growing season, the crop yield potential, and plant residue from the previous crop. The appropriate fertilizer guide for your crop of interest can be obtained from your local county extension office. Your agricultural extension agent can help you use the appropriate guide.
|38. Nitrogen BMPs|
Another important best management practice is the correct timing of nitrogen fertilizer applications. The correct timing of nitrogen application is an important factor affecting the efficiency of nitrogen uptake -- nitrogen use efficiency. The best strategy is to apply the majority of nitrogen right before the plants need it -- not several weeks in advance.
|39. Nitrogen BMPs|
Some timing of nitrogen applications you should consider include: (1) fall versus spring nitrogen applications, (2) preplant nitrogen applications, (3) split or multiple applications of nitrogen, and (4) sidedress applications of nitrogen. Your timing of nitrogen application strategy depends on your crop growth habits.
|40. Nitrogen BMPs|
Correct nitrogen fertilizer placement is another best management practice that can help protect water quality. The strategy is very simple -- put nitrogen in the vicinity of plant roots to maximize nitrogen uptake and nitrogen use efficiency (NUE). The two most often employed placement strategies are banding and broadcast placement.
|41. Nitrogen BMPs|
This slide shows two forms of N fertilizer placement -- banding and broadcast. Banding can be defined as placing fertilizer in a small area, a band. The fertilizer is usually placed 2 to 5 inches below and to the side of the seed at planting. In contrast, broadcast refers to a uniform placement of fertilizer. Broadcast can occur either before or after planting. If before planting, it is uniformly applied to the soil surface and then mixed into the soil with an implement. If applied after planting -- it is uniformly applied to the soil surface -- water is required to move the fertilizer into the root zone. By looking at both diagrams it is obvious that the plant that has received a banded nitrogen application has better access to the fertilizer.
|42. Nitrogen BMPs|
Some advantages of banding fertilizer nitrogen compared to broadcast placement include: an improvement in nitrogen use efficiency; you fertilize the crop to be grown -- not the weeds; the nitrogen is close to the roots -- better chance of uptake; and the close proximity of the nitrogen often improves early season crop growth.
|43. Nitrogen BMPs|
Water management is a very important best management practice. Water management is a key to groundwater protection. Since nitrogen is mobile in soils -- it moves in the soil water -- you must also consider any nitrogen in the irrigation water as a credit.
Nitrogen is mobile in soils -- nitrate moves with water in the soil. Over-irrigation or excess precipitation results in nitrate leaching. Nitrogen management alone will not effectively reduce nitrate leaching. You must couple it with irrigation/water management. To protect groundwater, never over-irrigate.
|45. Credits For NO3-N in
Your irrigation water source may contain some nitrogen. Nitrogen present in irrigation water can be used by plants. Get your irrigation water source tested for its nitrogen content. If it contains nitrogen it has some fertilizer value. The nitrogen value of irrigation water can be calculated as follows: multiply the nitrogen concentration in the water by 1.35 by the number of acre feet of water applied. This gives you your nitrogen credit value. Many surface water sources have some nitrogen content.
|46. Nitrogen BMPs|
Slow-release nitrogen fertilizers are a best management practice ideally suited to small farms. Big farms generally don't have the flexibility to try these unique materials. Slow-release materials improve nitrogen use efficiency (NUE) by plants. Slow-release materials make nitrogen available to plants as they need it. These slow-release materials reduce the potential for leaching losses of nitrates.
|47. Nitrogen BMPs|
Advantages of slow-release nitrogen fertilizers include: (1) the potential to reduce leaching losses of nitrogen, (2) the potential to reduce salt damage to seedlings, (3) you can apply all nitrogen fertilizer at one time -- no split applications are necessary, and (4) nitrogen becomes plant-available as the plants need it.
|48. Nitrogen BMPs|
If slow-release fertilizers have all these advantages -- then why doesn't everyone use them? Probably because slow-release fertilizers also have one big disadvantage! Cost! On a pound of nitrogen basis, slow-release materials cost between 35 and 40% more than traditional nitrogen sources. However, if nitrogen use efficiency (NUE) is substantially improved with a slow-release material -- its cost may be competitive.
|49. Nitrogen BMPs|
To show you how a slow-release fertilizer can be competitive let's look at an example: Let's say that under normal management -- 50% NUE -- you need to apply 90 lbs of N. With a conventional N fertilizer -- let's say ammonium nitrate which costs $.30 per lb N. Using 90 lbs at $.30 per lb would cost $27.00 per acre. A slow-release material would cost more -- $.41 per lb N -- but it would also result in high NUE -- 75% vs 50%. At 90 lbs per acre at $.41 per lb the cost would be $36.90 per acre.
|50. Example cont.|
But you don't need as much N with the slow-release material -- only two-thirds as much so instead of $36.90 it is $36.90 X .66 = $24.35 or $.59 lbs of N. So you actually save money and protect the environment.
|51. Nitrogen BMPs|
The final nitrogen best management practice for your consideration is your choice of both crop rotation and crop selection. The selection of crops in a rotation has an influence on the movement of nitrogen through soils. Alternate your crops so that every other crop has a high nitrogen demand.
|52. Nitrogen BMPs|
Crop selection is also important. Use cover crops between cash crops to scavenge excess nitrogen in the soil profile. Select the best crop variety available to effectively utilize soil nitrogen.
|53. Nitrogen BMPs|
The best management practices presented in this slide set are practices designed to protect water quality and to still provide an acceptable economic return. Remember the following. Use preplant soil profile nitrate testing and soil and plant nitrate testing when appropriate during the growing season. Base nitrogen application rates on realistic yield goals.
|54. Nitrogen BMPs|
Credit nitrogen contributions from legumes, manures, and other organic wastes. Plan nitrogen applications to correspond with crop demand and availability to the crop. Uniformly apply manure across a field in accordance with crop nutrient requirements.
|55. Nitrogen BMPs|
Schedule irrigation to minimize leaching. Diversify crop rotation to include crops that utilize deep residual nitrogen.
This slide script, WQ-20, was prepared by R. L. Mahler
and K. A. Mahler of the Soil Science Division, University of Idaho,
Moscow, Idaho 83844-2339.
This slide set and script was funded by a grant from the Pollution Prevention Program of the Environmental Protection Agency, Region 10.
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All contents copyright © 1997-2003. College of Agricultural and Life Sciences, University of Idaho. All rights reserved. Revised: January 3, 2003