Does Fertilizer Harm Soil Microbes?
Microbes in the soil are important to the nourishment of plants. Many of them facilitate the chemical conversions and physical transport needed to make nutrients available. Some people claim that soil microbes should supply all the nutrients needed by plants. Some also claim that applying soluble forms of plant nutrients harms the biology in the soil and reduces its capacity to make the native soil nutrients available. Let’s look at the evidence.
The microbes that supply nitrogen (N) are from two categories—symbiotic and freeliving. The symbiotic types are mainly rhizobial bacteria that infect the roots of legumes, such as alfalfa and soybeans. These bacteria supply the bulk of the N needs of legumes. However, even genetic engineering has not yet been able to coax the non-legume crops—corn, wheat, canola, potatoes, and many others—to fix N. Most crops depend on N applications in the form of fertilizer, manure, or organic materials.
The free-living bacteria in the soil supply some N as well, but the amounts are limited and are not influenced by fertilizer. A paper published in the journal Nature in 1998 compared nutrient dynamics in three Pennsylvania crop rotations: one fertilized, one manured, and one legume-based. The study found that the free-living bacteria supplied less than 5 lb/A/year, an amount that did not differ between the three rotations. No evidence of harm.
Microbes that help supply phosphorus (P) form an association with plant roots. The association is called “mycorrhizae”, a term that means “fungus-root.” Fungi explore the soil better than roots, because their hyphae are narrower. They can bring P to the root from as far as 4 in. away. Mycorrhizal fungi depend on the plant for energy in the form of sugar. It is well known that they are more active when P is deficient. But sugar used to feed the mycorrhizae is sugar taken away from grain yield. For example, in a recent field experiment in Quebec, corn depending on mycorrhizae yielded 14% less than when fertilized with P. The fertilizer—even though it was applied at twice the recommended rate—reduced the density of fungal hyphae by 24%, but certainly did not eliminate it. When soil test levels are low, P additions can actually increase mycorrhizal development.
Scientists have recently discovered that mycorrhizae produce a unique substance called glomalin. It may form as much as 30% of the organic matter in soil, and it seems to help maintain soil structure. Dr. Sara Wright, a noted expert on glomalin, recently stated that the best field-scale management for the production of glomalin is to “use minimal disturbance, add no more phosphorus than is required for crop production, and use cover crops.”
Soil microbes depend on plants for their nourishment. Fertilizers that nourish plants also nourish the biology of the soil.
Drinkwater, L.E., P. Wagner, and M. Sarrantonio. 1998. Legume-based cropping systems have reduced carbon and nitrogen losses. Nature, vol. 396, 19 Nov.
Ellis, J.R. 1995. Mycorrhiza—An essential part of most plant root systems. Better Crops 79(1): 10-11.
Wright, S.F. 2003. The importance of soil microorganisms in aggregate stability. Proc. northcentral extension-industry soil fertility conf. 19:93-98.
These soybean root nodules contain Nfixing
bacteria. Phosphorus encourages root
growth and N fixation in legumes such as
alfalfa, soybeans, and other crops.
Crop Fertilization Helps Stabilize Carbon in the Soil
The primary role of crop fertilization has been and will continue to be that of increasing crop yield and quality. An additional benefit is improved environmental protection. It has been shown that proper fertilization results in fast growing, vigorous plants that rapidly close their above-ground canopy to protect the soil from the effects of wind and water—and thus runoff and erosion. Also, healthy crops develop massive root systems that help to hold the soil in place. Another environmental benefit of fertilization is that it contributes to the stabilization of carbon (C) in the soil. Carbon dioxide (CO2) is one of the three primary global warming gases. When C is tied up or stabilized in the soil, the release of CO2 into the atmosphere is lowered, thus reducing the potential for global warming.
There is strong evidence that there is a relatively stable sink of CO2 in North America. For example, the U.S. exports more C in agricultural and wood products than it imports. Further, it stores about 500 million tons of C annually in forest and non-forest soils. Indications are that the agricultural sector is storing more C in soil organic matter and crop residues than it once did, in part due to use of conservation tillage and crop fertilization.
A proper nutrient management system, one that considers existing soil fertility and the need for supplemental fertilization, aids in the capture of atmospheric CO2, improves photosynthesis, enhances the release of oxygen into the atmosphere, and increases soil organic C. For example, research conducted by the U.S. Department of Agriculture (USDA) has shown that nitrogen (N) fertilization increases both soil organic C and the soil’s productivity.
Extensive reports from long-term research indicate that whenever N fertilization results in higher crop yields, the accumulation of C in soil organic matter also increases. Furthermore, there is evidence that N itself is chemically involved in the stabilization of soil C. It is thought that N compounds are involved in the formation of humus and, as a result, help to stabilize C in soil organic matter. Other long-term studies have shown that soil organic C levels are highest when conservation tillage is combined with rotations of high residue crops and adequate fertilization to increase yields.
The role of crop fertilization in protecting the environment is undeniable. Helping to stabilize C in the soil is an important example. The key to the total benefit of crop fertilization—for yield and quality increases and environmental protection—is a sound fertilization program. Proper nutrient management should be an integral part of every farmer’s overall management program.
Crop Fertilization and Air Quality
Fertilization, including both organic and inorganic sources, accounts for nearly 40% of crop yield in North America. In some countries, up to 75% of total production is the result of fertilization. Obviously, proper nutrient use is essential if farmers are to continue to grow sufficient amounts of food to meet the needs of a growing world population. Without adequate fertilization, billions of people could face starvation.
At the same time, the use of nitrogen (N) fertilizers, particularly animal manure and other organic sources, can also impact environmental quality by returning certain global warming gases back to the atmosphere. The three gases of primary concern are nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2). In addition, significant amounts of gaseous ammonia (NH3) can be released into the air as a result of crop fertilization. With careful management, NH3 losses are minimal.
All forms of N fertilizers—inorganic and organic—have the potential to release N2O to the atmosphere. However, direct loss of N2O from fertilizer is usually less than 1%. Other factors, such as cropping systems, soil management, and unpredictable rainfall have a much greater influence on N2O losses than do the various inorganic nitrogen fertilizer sources.
Liquid manure can greatly increase the rates of N2O loss. In one southeastern U.S. study, high rates of liquid manure produced denitrification rates 10 to 100 times higher than those resulting from the application of inorganic N fertilizers. Denitrification is a key step in the production of N2O in the soil and, thus, its loss to the atmosphere.
Methane gas released to the atmosphere because of agricultural production comes predominately from ruminant animals, livestock manure, wetlands, and rice production. Very little is associated with crop fertilization.
Improved fertilizer management can help to eliminate most losses of the global warming gases. High, efficiently produced crop yields can actually contribute to a drop in the production and release of global warming gases, particularly CO2, because of crop fertilization. As crop yields increase (because of fertilization), more biomass is produced, resulting in the buildup of organic matter in the soil. Carbon is a component of soil organic matter, and as long as it is held in organic form, it is not available to be converted to CO2 and released to the atmosphere.Although crop fertilization has the potential to contribute to the production of global warming gases, proper nutrient management minimizes its effect while significantly increasing the amount of food grown worldwide.
Carbon is a part of soil organic matter.
As long as itis held in the organic form,
it is not available to beconverted to CO2gas.
Aglime…It’s Good for the Environment
Farmers apply aglime to neutralize soil acidity…and for a host of other reasons. Aglime improves the physical, chemical, and biological conditions of soil. It increases crop growth and improves nutrient and water uptake, which helps protect the soil from wind and water erosion. It enhances the effectiveness of some herbicides and improves fertilizer nutrient efficiency.
Best plant growth, and greatest fertilizer efficiency, occurs at an optimum soil pH range of about 5.8 to 7.0 for most crops. (A few crops prefer acid soils.) Liming soils to the optimum range can increase fertilizer use efficiency by as much as 50%. And a doubling of efficiency means half as much fertilizer is needed for optimal crop growth and that cuts fertilizer costs. In addition to affecting plant nutrients and crop growth, aglime improves the performance of certain herbicides, increasing their ability to control weeds that rob the crop of nutrients and water.
Liming acid soils can dramatically increase crop and forage yields. That means more of the fertilizer nutrients…and soil nutrients…are removed from the field with crop harvest. So, potential losses to leaching are reduced. Aglime helps get the crop off to a fast start, with quicker canopy cover, which helps to minimize the impact of rainfall and reduces runoff and erosion. Also, increased crop yields mean more plant roots and more crop residues to build soil organic matter and improve soil aggregation and tilth.
There are many benefits from applying aglime. There is also a great need. A recent survey suggested that aglime is needed on about one-third of the farmland in North America. Summarized results from 34 public and 31 private soil testing laboratories showed that 34% of the 2.5 million samples collected in the fall of 2000 and spring of 2001 had a pH less than 6.0. Soil pH in more than half the samples was less than 6.5, suggesting that acidity may be limiting crop yields.
Aglime does more than simply increase soil pH. It also improves the soil’s productivity and in so doing helps protect the environment.
Percent of soils testing 6.0 pH or below.
(From: Soil Test Levels in North America,
PPI/PPIC/FAR Technical Bulletin 2001-1,
Aglime application has environmental benefits as well
as increased crop yields.
Human Health and the Use of Animal Manure in Crop Production
Animal manure (and certain other organic materials) is a good source of essential plant nutrients when properly used. It improves soil fertility and biological and physical properties. However, manure has several disadvantages when compared to commercially produced fertilizers, including low nutrient content and high volume, making it uneconomical to transport far from its production source. Manure continues to release nutrients during periods when crops aren’t actively growing to take them up. This can result in unused nutrients being left in the soil, to potentially be washed into surface water through erosion and runoff or leached into groundwater. Careful timing of application and incorporation can offset these concerns. Because nutrient contents of manure vary with animal species and management, it is critical to analyze its nutrient content and factor that into nutrient management planning.
There are other disadvantages to the use of animal manure as well.Its somewhat fixed nutrient ratios have led to widespread concern of excessive buildup of phosphorus (P) in heavily manured soils because crops require much less P than nutrients such as nitrogen (N) and potassium (K). So, when manure is applied to the soil in quantities necessary to meet crop need for N, soil P levels can be built to excessive levels. This leads to potential degradation of water quality. Animal manure may also carry pathogens that can present dangers to human health.
The U.S. Environmental Protection Agency has cited pathogenic bacteria as a leading cause of water quality impairment in streams, rivers, and estuaries.There are more than 150 organisms that can spread infection from animals to humans. Many of those can be found in animal feces and urine. They include bacteria—such as E. coli, Salmonella, and Campylobacter— viruses, and protozoa. The U.S. Centers for Disease Control (CDC) estimates there are more than 70,000 cases of infection in humans each year from E. coli alone. Food-borne illnesses are considered the most serious food safety problem in the U.S. The application of raw manure is one way pathogens are spread in the environment. Manure is not applied directly to crops intended for human consumption. Composting kills many harmful pathogens, reducing the human disease risks. Composting also reduces the volume of manure, making it more practical to transport.
Scientists at Ohio State and North Carolina State universities are involved in a 4-year project, working together to try and prevent dangerous foodborne pathogens in animal manure from spreading to the environment and negatively affecting human health.They are attempting to evaluate every food-borne pathogen in manure to see if there is a risk associated with human health. Their goal is to find the most economical method of handling animal waste which will result in the elimination of food borne pathogens found in manure. Their success with this project can make the use of a valuable resource safer, thus leading to the production of higher, more efficient crop yields and a healthier population of consumers.
While livestock manure can be useful as a
nutrient source in agriculture, certain
bacteria and other organisms can
contaminate water and foods if not carefully
managed. Researchers are evaluating
various methods of livestock waste handling
to assure human health and safety.
Crop Production and Environmental Protection
Since man first began to cultivate the soil for the purpose of growing food, crop production has had an impact on the environment. It affects both soil and water quality, and those effects have not always been positive.
In the early history of America, most farmers tilled their fields, harvested their crops, and gave little thought to putting back the nutrients the crops removed. Over a period of time,soils became infertile, resulting in poor yields, increased erosion and runoff, and the pollution of rivers and streams. As soils ‘wore out’, farmers and their families moved on to new locations and began the process all over again.
In many parts of the world even today, poor soil and water stewardship is practiced by farmers, many desperate to grow enough food to survive. Sloping, hilly soils are cultivated, often resulting in massive loss of topsoil and surface water pollution. Soils are mined of their fertility, then left to the ravages of nature. The environment suffers.
However, farmers in North America and many other parts of the world have helped to change the relationship between crop production and the environment. They are good stewards of our soil and water resources and are aware of this important role they must play. They recognize that crop management and planning, including the use of fertilizers, must consider the long term—for sustained production—rather than simply those results expected for the current crop year.
As the world population grows and the demand for food increases, farmers are challenged to produce more crops per acre of land.To do this, they use fertilizer to supplement soil nutrients. At the same time, though, they must be careful to maintain a close balance with nature, and they are doing a credible job of that. The results tell the story.
Per-acre yields are continuing to increase.So does the efficiency of fertilizer use, as reflected by the fact that significantly more units of crops are now being produced per unit of fertilizer applied to the soil. What does this mean? It means that the economics of crop production are improving, and that’s good for farmers and their families. It means that more of the fertilizer is going into crops, not staying in the soil to be potentially washed into surface waters or leached into groundwater. It means that more fragile lands can be taken out of crop production and set aside for wildlife, human recreation, wetlands, and other uses protective of the environment.
There is often a thin line between environmental protection and potential damage to our soil and water resources. Modern farmers walk that line every day. It’s good to know that because of their concern for the environment, high yield agriculture will continue to feed the world well into the foreseeable future.
There is no question that phosphorus (P) is essential to crop production.Agronomically, it is one of the three primary plant nutrients, along with nitrogen (N) and potassium (K). It is also essential for healthy fish and other aquatic life in our lakes and streams. Yet, excess P (and N) can lead to algal blooms and other problems in surface waters. Public water supplies are vulnerable to these effects, and treatments to reduce offensive odors and tastes can be expensive.
It should be emphasized that most agricultural soils must be supplemented with fertilizer P before crops can reach their yield potential. In North America, nearly half the soils test medium or lower in P, and soil P levels have been declining in some key production states. Sound nutrient management programs must include consideration for P. In recent years, more attention has been given to the potential negative impacts of too much P getting into surface waters, particularly where there has been an over-application of animal manure. While manure is a good source of P and other nutrients, when it is applied —year after year—at rates in excess of crop use, there is a heightened risk of P loss to surface waters. It is not unusual to see soil P levels in the excessive range in those areas where confined animal feeding operations exist.
Scientists have long considered P to be an immobile nutrient in soils. However, leaching can occur when the ability of the soil to hold P is exceeded. Further, the transport of P bound to soil sediments can pose a significant threat to water quality when it is carried to nearby streams and other surface water bodies by erosion and runoff.
There are management techniques available to correct problems arising from excessively high soil P levels. One is to discontinue the use of fertilizer P, including mineral fertilizers and manure, until soil tests are reduced to appropriate levels. Vegetative filter strips have been shown to be quite effective in reducing P runoff losses. Conservation tillage, alone or in combination with other practices such as vegetative filter strips, helps to keep P in place by reducing erosion and runoff. Other best management practices can also be implemented.
|Finally, there is no reason why P fertilization and environmental protection can’t go hand in hand. The key is to stay on top of nutrient management and take special care when manure is being applied to the land. Keep soil tests in the optimum range to allow the crop to develop to its fullest agronomic and economic yield potential. Monitor progress with soil testing and plant analysis and follow other best management practices that complement the use of P. The result will be profitable crop production and a protected environment.||
Vegetative filter strips can be effectivein reducing runoff and nutrient movement from fields to surface water areas, such as streams.
Managing Nitrogen to Protect Water
Nitrogen (N) is usually the first limiting essential nutrient for non-legume crops such as corn, wheat, and cotton. These and other high yielding grasses commonly require much more N than is supplied by the soil. Thus, it is necessary to make up the difference with fertilizer N. Mineral fertilizers are preferred for several reasons, including ease of management. Organic materials can also be used successfully when they are available, provided they are handled properly.
One of the advantages of mineral fertilizers is that they can be managed more precisely than organic sources, resulting in less potential for N entering groundwater. Following are some of the techniques scientists have developed, and today’s farmers use, to control the fate of fertilizer N when it is placed in the soil.
- Application of N source that provides N when the crop needs it. Nitrate-N…the form used in greatest amounts by plants…is highly water soluble and moves freely through the soil. It is critical that N be applied as near to the time the crop uses it as is possible. Otherwise, significant amounts might be leached out of the soil, possibly affecting groundwater quality.
- Application of N rates that match plant requirements. By applying N at rates near those levels required by the growing crop, the potential for N loss by leaching is minimized or eliminated. Research has shown that when N is applied according to crop need, subsoil nitrate-N levels are similar to those where no N is applied.
- Split N use into several applications to give the crop time to use it before it can be lost from the crop’s rooting zone. Dividing the crop’s total N requirement into several applications rather than one large application is an effective way of increasing N use efficiency. The results are higher yields and less N left in the soil.
- Application of ammonium forms of N. These N forms are stable in the soil and can be taken up and used by the crop before being converted to nitrate-N. After conversion to nitrate, the N can still be used by the crop before it has a chance to leach from the root zone. There are N stabilizers available that will keep N in the ammonium form until the crop needs it.
- Use a balanced fertilizer program. One of the best methods of increasing N use efficiency – maximizing N uptake by the crop and minimizing soil losses – is to implement a balanced nutrient management program. Balancing N with other essential nutrients such as phosphorus (P) and potassium (K) results in higher, more profitable crop yields and improved environmental protection.
- Application of N source that provides N when the crop needs it. Nitrate-N…the form used in greatest amounts by plants…is highly water soluble and moves freely through the soil. It is critical that N be applied as near to the time the crop uses it as is possible. Otherwise, significant amounts might be leached out of the soil, possibly affecting groundwater quality.
|Nitrogen fertilization is essential to crop production. Farmers can’t grow enough food to meet ever increasing world demands without it. The good news is that with proper management of available N fertilizer sources, farmers can achieve their yield goals and sustain water quality at the same time. In the long run, N fertilization is a win-win situation…more food for people and protection for our water resources.|
|Nitrogen-deficient areas in fields may appear yellow or unhealthy, with poor growth (as shown in the plot at right in this photo). Best management practices assure that N is available when needed by crops, and that the nutrient won’t be lost from fields.|
Crop Fertilization and Water Quality
It has been estimated that fertilization accounts for more than a third of all crop yield in North American agriculture. In other parts of the world, where farm land has been abused for enturies or where new land is brought into production and quickly mined of its nutrients, fertilization might contribute as much as 75% of total food production. Proper crop fertilization is ssential to prevent massive global starvation. Yet, the most common perception among non-agriculturists is that fertilizer use damages the environment, specifically water quality…not that helps feed the world’s billions of people.
The truth is that high, efficiently produced crop yields, and environmental protection —including water quality, and balanced fertilization – go hand and hand. Consider some of the benefits of fertilizer nutrient use that is in balance with crop requirements. Proper nutrition helps to produce a healthy, fast growing crop that has a vigorous root system and establishes a dense canopy to protect the soil surface, resulting in:
- less runoff and erosion;
- increased water infiltration to supply crop needs and boost yield potential;
- more biomass left after crop harvest to help keep the soil stable and to contribute to organic matter levels.
By developing nutrient management plans and fertilizing according to soil tests, farmers help to assure that most of the fertilizer nutrients they apply are taken up by the crop being grown, not left in the soil for possible entry into nature’s water system. Nitrogen (N) and phosphorus (P) are the only nutrients of concern with regards to potential water problems from fertilization. But, when they are used in balance with other essential nutrients such as potassium (K), and within systems utilizing best management practices, there is little danger to either surface water or groundwater.
In order to protect water quality, care should be taken to avoid over fertilization. However, significant danger to water quality is also associated with too little fertilization. When crops are produced without proper nutrition, their growth is less robust, and they offer little protection from the potential impacts of wind and water erosion. If the crop can’t take up the nutrients it needs because of low soil fertility or improper fertilization, erosion – with the potential loss of soil P to surface water – is more common, as is N leaching into groundwater. Needless to say, farmers then produce lower yields per acre, they can feed fewer people, and their incomes suffer.
|Crop production is a dynamic system. Because it is biological in nature and not ontained in a controlled environment, there is always the potential for nutrient leakage from the system. Thus, fertilization is not fool proof. There are far too many variables for 100% control. Nevertheless, a well managed fertilization program is the best alternative to meeting the world’s food needs and protecting our precious soil and water resources.|
|Modern crop production practices—which include reduced tillage, returning plant residues to the soil, and proper fertilization—help to build soil organic matter and improve crop quality.
Crop Fertilization and Heavy Metal Accumulation in Soils
Trace elements and heavy metals occur naturally in all agricultural soils. Several of them are either essential or beneficial to plants as well as animals. However, they can become toxic if accumulated in excessive amounts. Proper fertilization, which results when both agronomic and environmental considerations are included in the development of a nutrient management plan, can prevent or greatly reduce the potential for such toxicities.
In recent years, there have been reports of heavy metal contamination from fertilizers manufactured from industrial byproducts. However, more than 97% of the mineral fertilizers used in North America are made from natural sources such as atmospheric gases and mineral deposits. Further, according to the U.S. Environmental Protection Agency (EPA), typical rates of heavy metal additions to soils in mineral fertilizers are well below U.S. biosolids annual pollutant loading rates and the Canadian Fertilizer Act limits. In other words, fertilizers are safe.
The only heavy metal of concern is cadmium (Cd). It occurs naturally in phosphate rock, the mineral most commonly used to make phosphorus (P) fertilizers. During the manufacturing process, much of the Cd in the ore is carried through to the final fertilizer products. Cadmium is also present in organic fertilizer sources such as animal manures and biosolids. Further, it can be added to the soil through atmospheric depositions as a result of forest fires, volcanic eruptions, and air pollution due to industrial output.
Sewage sludge can contain high levels of Cd and has been blamed for contamination in some areas. However, biosolids such as sewage sludge are applied to only limited areas and affect a relatively small proportion of agricultural land. Manures are of concern because more than 90% of the Cd ingested by animals passes into the manure. And, manure helps to mobilize soil Cd, making it more available to plants.
Cadmium buildup and availability in the soil are affected by several factors in addition to fertilization, including soil organic matter content, soil pH, crop species grown, and crop rotation. While there should be concern about Cd, adoption of measures that might limit the use of P fertilizers and crop production are not necessary. For example, using a worse case scenario of applying a P fertilizer source high in Cd, it would take almost a thousand years to reach the EPA cumulative limits in the soil.
|It is important that we understand and utilize all our management options in taking the necessary steps to protect public health and the environment. It is just as critical that we maintain a profitable and productive agricultural system.Fortunately, the proper use of crop fertilization allows us to accomplish all these objectives, including the safe management of heavy metals.||Relating to parts per million…
Concentrations of “heavy metals” in some fertilizers, animal manures, and biosolids such as sewage sludge are typically indicated in parts per million (ppm), or sometimes in parts per billion (ppb). Concentrations are monitored to assure the levels are within set standards. To help put these units in perspective, here are a few examples for comparison.
|One part per million is equivalent to:
One part per billion is equivalent to:
Nutrient Use and Beneficial Soil OrganismsSoil organisms are essential to crop production. In addition to their role in soilforming processes, they are important recyclers of soil nutrients. A major benefit is to break down organic materials in crop residues and release the nutrients they contain in the inorganic form so crop plants can use them.
Common microorganisms include bacteria, fungi, and algae. All are present in the soil in large numbers. For example, a single gram of soil—a 28th of an ounce – might contain 3 billion or more bacteria, a million fungi, and a quarter of a million or more algae.
Certain bacteria living in a symbiotic relationship on plant roots convert (fix) atmospheric nitrogen (N) into a form legumes such as alfalfa and soybeans can use.They play an important role in crop production by helping to supply much of the N needs of legumes and the crops that follow them. The amount of N these bacteria can fix depends on several factors—legume crop being grown, overall plant health as determined by management, soil pH, temperature, etc. The average is in the range of 75 to 100 pounds per acre per year, but can be as high as 300 pounds.
The presence of the more highly developed organisms such as earthworms is generally indicative of a high quality soil with good structure and low in salt content.Earthworms are also excellent nutrient recyclers. Unfortunately, other higher organisms such as nematodes and insects have a detrimental effect on crop growth…even though they play a role in nutrient cycling.
Since most of these organisms have such a vital role in crop growth, one of the measures of soil quality and sustainable production is their abundance in the soil.Does the use of fertilizer nutrients – from inorganic and organic sources – have an impact on these organisms? The answer is yes.
Research has shown that indiscriminate use of both mineral fertilizers and animal manures can result in a decline in the numbers of beneficial organisms in the soil.However, when properly applied and used, the overall impact of fertilizer nutrients is a positive one. Generally, those management decisions that optimize the efficiency of nutrient use also impact beneficial soil organisms in a positive way.
Historically, the primary reason for applying fertilizer nutrients to the soil has been to increase crop yields and improve quality. During the past few decades, however, the impact of nutrient use on environmental quality has received its share of attention as well – and rightly so. Nutrients do affect the quality of both soil and water. The good news is that when proper nutrient management is practiced, crop yields and soil and water quality are enhanced. This includes the impact of nutrients on beneficial soil organisms.
Nutrient Balance Can Be Achieved Using Both Inorganic and Organic Sources
The impact of modern agriculture on the environment has been the subject of much discussion. Some challenge the sustainability of high yield crop production, particularly from an environmental standpoint. Some claim that any synthetic input—such as commercially produced mineral (inorganic) fertilizers—will eventually damage, if not destroy, the environment. The fact is that nutrient balance, using both inorganic and organic sources, goes hand-in-hand with high yield agriculture and environmental protection.
In crop production, commercially produced fertilizers are more manageable than organic sources. Their impact on both crop and environment can be controlled through proper selection of rates, sources, placement, and timing. Through careful management, it is possible to supply nutrients close to the optimum levels and time of crop needs for best economic and environmental efficiency. On the other hand, it is extremely difficult to provide balanced soil fertility requirements and plant nutrient demands solely through the use of animal manures and other organic sources such as biosolids.
Long-term use of manures often results in the buildup of soil phosphorus (P) because the manures contain nitrogen (N), potassium (K), and P levels disproportionate to crop needs and removal.That is, crops need more N and K than the manures contain, while not requiring all of their high levels of P. The end result can be detrimental to surface waters because of the loss of the excess P by erosion and runoff.
Nutrient Balance: Critical to Crop Production and Environmental Protection
People and crop plants are a lot alike in several ways, one in particular. They both need balanced nutrition for normal growth and good health. Unlike people (who require a variety of foods) crop plants need only 17 nutrients, some obtained from air and water, to grow normally – if those nutrients are supplied in the proper balance. When crops have balanced nutrition, an added bonus is increased environmental protection.
Nutrient balance results in increased nutrient use efficiency. For example, research has shown that when nitrogen (N) is balanced with phosphorus (P), potassium (K), and other essential nutrients, crop yields increase and so does N use efficiency. That means more N is used by the crop and less is left in the soil as a potential pollutant. In a 40-year irrigated corn study in Kansas, balancing N with P resulted in average yield increases of 46 bu/A per year while reducing nitrate-N (NO3--N) in the upper 10 ft. of soil by two-thirds when compared to N only.
Another benefit of balanced nutrient use is increased water use efficiency by crops.Water use efficiency can be increased by as much as 200% and more simply by supplying essential nutrients in the proper balance. In many areas of North America, there is increasing competition between urban areas and agriculture for limited surfacewater and groundwater supplies. Thus, anything agriculture can do to increase water use efficiency is obviously a good thing for both the urban population and farmers. People must have clean water to drink, but they must also have food to eat.
By growing more crops per acre through proper nutrient balance, farmers help to alleviate the detrimental effects of global warming. Increased crop biomass results in more carbon (C) being stored in the soil, thus slowing atmospheric enrichment of the greenhouse gas carbon dioxide (CO2). Healthy, vigorous crops—the result of balanced nutrition—produce a quicker canopy to protect the soil against rainfall and wind, thus reducing the potential for erosion. Extra surface residue left behind after the harvest of high yielding crops further protects against erosion and runoff.
|Well-fertilized crops produce more yield per acre, releasing fragile lands for other important—and safer—uses such as wildlife habitat and recreational areas. This is a critical point to consider since arable land per person in the world is shrinking, and in some countries, land unfit for sustained agricultural production continues to be farmed.In order to maintain a balance between adequate food production and environmental protection over the long term, crop yields must continue to increase. Science leaves no doubt that such increases will be possible only through the proper use of plant nutrition and other best management practices.||
Properly balanced crop nutrition
results in higher, more efficient yields,
while also safegua
Crop Fertilization Improves Soil Quality
Consider all the roles the soil plays in the production of food and fiber for the world’s people. It is the medium in which plants grow and the source of most plant nutrients. Soil water and air bathe plant roots and help keep them and above-ground plant parts healthy and growing. The quality of soil in which plants grow is extremely important in determining yield potential as well as the sustainability of crop production.
One of the greatest benefits of crop fertilization, aside from increasing crop yields and improving farmer profit potential, is its effect on soil organic matter. It has long been known that organic matter positively influences structure, tilth, bulk density, water infiltration rates, water holding capacity, and water and air movement within the soil, thus improving soil quality. Organic matter helps to bind soil particles together, reduces soil crusting, increases the stability of soil aggregates, acts as a reservoir for plant nutrients, and reduces soil runoff and erosion losses.
Farmers have known for hundreds of years that crop fertilization, whether it was a fish in a hill of corn or ground up rock phosphate applied to the soil surface, increased their yields. As science learned more about the benefits of fertilization, it was discovered that long-term sustainability of crop production is dependent on building and maintaining soil fertility, an important soil quality measurement. Later, it was demonstrated that organic matter levels could be maintained and even increased through balanced fertilization. Harvested crop yields increase as a result of crop fertilization, but so does unharvested plant biomass left on the soil surface and crop residues remaining in the soil. Much of the unharvested surface biomass and underground residues wind up as soil organic matter.
Both organic and inorganic (mineral) fertilizer sources contribute to the buildup of organic matter in soils. There is widespread public misperception that organic agriculture is more environmentally friendly and better maintains soil organic matter levels. However, there are no generally accepted scientific experiments to support the superiority of either organic or inorganic plant nutrient sources. In fact, long-term experiments from around the world indicate that sustained yields and soil productivity can be accomplished with balanced nutrient applications using animal manures and/or commercially produced mineral fertilizers.
|The key, then, is the wise use of crop fertilization to boost crop yields, improve farmer profits, and protect the environment.An important part of environmental protection is improved soil quality through the buildup of organic matter, which can be accomplished by fertilization, both organic and mineral.|
|Modern crop production practices—which include reduced tillage, returning plant residues to the soil, and proper fertilization—help to build soil organic matter and improve crop quality.|
Organic or Inorganic:
Which Nutrient Source Is Better for Plants?
A quick answer to the question asked in the title is that neither organic nor inorganic (manufactured or mineral) nutrient sources are better for plants.Both have their places and should be used where appropriate. Each has its advantages and disadvantages. Their relative merits need to be explored further, however.
Organic materials such as animal manures and biosolids should be viewed as economic and agronomic nutrient supplements along with mineral fertilizers in the production of crops. They contain varying amounts of plant nutrients and provide organic carbon (C). They improve the biological, chemical, and physical properties of soils. There are, however, concerns associated with their use.
- In the case of animal manures produced in confined geographic areas, nutrient loading can occur in crop fields near production facilities. This can pose a threat of excessive nitrate (NO3–) leaching to groundwater and phosphorus (P) moving into surface waters through runoff and erosion. Their relatively fixed nutrient ratios can result in excessive P loading in heavily manured soils because crops usually require much less P compared to nitrogen (N) than that contained in the manure. Significant amounts of ammonia (NH3) can also be lost to the atmosphere.
- Indiscriminate use of animal manures and human waste (sewage sludge) can create human health hazards through the accumulation of heavy metals and pathogens in the soil.
There are other disadvantages associated with the use of organic sources. They are usually low in nutrient content. It is also virtually impossible to time the release of the nutrients they contain so as to match the needs of the growing crop and minimize residual amounts that can impact the environment. Further, their relative low analyses make it uneconomical to transport them far from their point of production.
On the other hand, mineral fertilizers contain precise—guaranteed—levels of nutrients, in forms that are readily available for plant uptake and use. Their application can be timed to meet crop requirements, assuring efficient nutrient use and minimizing any potential impact on the environment. Because of their high nutrient content, mineral fertilizers are easy and economical to ship to great distances from their point of production.
It should also be understood that crop plants can take up and use nutrients only in the inorganic form—as is found in mineral fertilizers. Nutrients in organic materials cannot be used until the materials decompose and release them to the inorganic soil nutrient pool.
|What ’s the N-P-K Analysis?|
|Storage, handling, weather, and other factors result in big differences in nutrient content of organic materials, while the nutrient content of inorganic (mineral) fertilizers can be
(or whatever analysis
|Nutrient content of livestock manures and other organic material varies considerably. Inorganic commercial fertilizers contain guaranteed ratios of nutrients and can be easily adjusted to crop and soil needs. Relatively low analyses usually make it impractical to transport organic sources very far.|
- 1 มิ.ย.’กรุงไทย’ลดค่าธรรมเนียมโอนเงินผ่านเน็ต-มือถือ
- กสทช.เคาะ ค่าย้ายค่ายเบอร์เดิม 29 บาท
- หุ้นไทยครึ่งวันเช้าลบ 0.99 จุด ‘ทรู’ซื้อขายสูงสุด
- ‘ผศ.ดร.ธนวรรธน์’คาด กนง.ยอมลดดอกเบี้ย0.25%
- หวั่น’เฟด’หยุดQE ฉุดดาวโจนส์ร่วง
- พิสูจน์ชัด! ขายแพงจริง 2โรงหนังดัง
- แจงครม.แบ่งเงินกองทุนพัฒนาสตรีแล้ว อุตสาหกรรมแจกงบ 1.3 พันล้านให้ตั้งตัว
- ‘บุญทรง’เรียกประชุม กกร.ด่วนรับมือของแพง
- Google แผนที่ตำบล 76 จังหวัด
- นพ. ต่อพงศ์ คล้ายมนต์
- Apichaya Claimon
- พญ.อภิชญา คล้ายมนต์
- ตระกูล “คล้ายมนต์”
- Building Soils for Better Crops
- Fertilizer Best Management Practices
- Fertilizer Manual
- Fertilizers and their use
- Hydroponics: the complete guide to gardening without soil
- Micronutrients for Sustainable Production
- Plant Analysis Reference Procedures
- Fertilizer news and articles
- Plant Nutrition
- Soil Taxonomy 2Ed.
- สทท NBT
- อสมท MCOT
- ไทยพีบีเอส Thai PBS
- Blog Stat
- FAO EcoCrop
- KU eMagazine
- The Nation