SILAGE PRODUCTION AND FERTILIZATION

Source : Plant Nutrition Today. International Plant Nutrition Institute.

ผ่านทางPNT: SILAGE PRODUCTION AND FERTILIZATION.

Winter 2010, No. 7

SILAGE PRODUCTION AND FERTILIZATION

Ensilage or ensiling is a process of preserving forage for later use as animal feed. Silage can be defined as any plant material that has undergone fermentation or “pickling” in a silo. And a silo is any storage structure in which green, moist forage is preserved. Silage production is important in parts of the Great Plains, especially where there are significant numbers of animals in feeding operations such as dairies and feedlots.

There are several advantages of silage compared to hay and other forage conservation systems. These advantages include less field and harvest losses, many crop options, mechanization of harvesting, storage and feeding, less likelihood of weather damage during harvesting, relatively low loss of nutrients with proper ensilage, and silage can be used in many livestock feeding programs. The disadvantages of silage include its bulkiness in handling and storage, it requires additional equipment and structures for harvesting, storing, and feeding, high potential for loss if not stored properly, not readily marketable off-farm, and silage must be fed soon after removal from the silo to minimize spoilage.

The major factors affecting silage quality are the type of crop, stage of maturity, moisture content, and length of chop. Within forage species the stage of maturity has the greatest effect on quality. The optimal moisture content depends on the crop and type of silo used, but is generally around 65 to 70%. Material ensiled below 50% moisture is usually called haylage. Length of chop is a factor since it affects air exclusion in the silo. Fine chopping and packing help ensure proper fermentation.

Many crops, including grasses and legumes, can be preserved through ensilage. The most common and perhaps the best adapted is corn. It is high energy and results in good animal performance. Sorghum (grain and forage) is a popular silage crop in some areas. Alfalfa is also used for silage, but the process of ensilage is somewhat more difficult than with other common crops.

As in hay production, the harvest of a crop for silage results in the export of large quantities of nutrients from a field. For example, a 30-ton harvest of corn silage will remove about 250 lb N, 110 lb P₂O₅, and 250 lb K₂O. This is one of the most important points to keep in mind when designing fertility programs for silage crops.

Nitrogen fertilization can affect fermentation of some crops by decreasing the concentration of soluble carbohydrates required to make high quality silage. This is particularly true with cool season grasses since they tend to be relatively low in available carbohydrates to begin with. On the other hand, corn is relatively high in soluble carbohydrates, so N fertilization is not a concern from this standpoint.

Phosphorus and K fertilization of crops for silage should be based on soil test information and experience. Nutrient removal data should also be considered. Phosphorus and K can be rapidly exported and depleted from soils under silage production if adequate amounts of these nutrients are not applied.

There are many excellent sources of information on the topic of fertilization and ensiling of forages. Among these sources is a practical handbook entitled Southern Forages (available through the International Plant Nutrition Institute, http://www.ipni.net). Other good sources are available through land grant universities and local county extension offices.

- WMS -

For more information, contact Dr. W.M. (Mike) Stewart, Southern and Central Great Plains Director, IPNI, 2423 Rogers Key, San Antonio, TX 78258. Phone: (210) 764-1588. E-mail: mstewart@ipni.net.

Abbreviation: N = nitrogen; K = potassium.

TRACKING NITROGEN USE EFFICIENCY ON YOUR FARM: TIPS FOR TRIUMPH

Source : Plant Nutrition Today. International Plant Nutrition Institute.

ผ่านทางPNT: TRACKING NITROGEN USE EFFICIENCY ON YOUR FARM: TIPS FOR TRIUMPH.

Winter 2010, No. 6

TRACKING NITROGEN USE EFFICIENCY ON YOUR FARM: TIPS FOR TRIUMPH

If you were asked how good your N management (source, rate, timing, and place of application) was for the crop(s) on each of your fields this past year, how would you answer? Was N managed at the optimum, most economically rewarding rate? Unless on-farm replicated N management comparisons were made, it would probably just be a guessing game for most of us.

The effectiveness of a given N management program, and the efficiency with which the crop utilizes the applied N, will vary greatly with weather conditions, year in and year out. To try to be as efficient as possible, most farmers use local university research results to guide their initial management decisions, but make modifications based on their own field observations and experiences.

Unless we actively monitor the crop’s N status during the growing season, we never really know how well nourished the crop is or was until harvest time. End-of-season crop assessments and documentation of yields on each field, in and of themselves, can provide important feedback on past decisions and help to influence future N management directions. But such measures are merely looks in the rear-view mirror.

Yet, the importance of those “after-the-fact” looks in the rear-view mirror should not be downplayed. When crop yield is evaluated per unit of N applied (e.g. bushels, hundred weight, tons, or bales per pound of N applied per acre), and those values are tracked for each field each year, over a period of years, a great deal can be learned. There are other ways to measure crop N use efficiency, but these calculated values serve as perhaps the
most practical field-level measure of N use efficiency. An upward trend in the calculated values over time implies that N use efficiency may be improving. If the trend in values of yield per unit of applied N is fl at or declining over time, then closer scrutiny of the N management program, and possibly a detailed assessment of the entire crop management system, is called for.

To begin moving your N management program toward greater effectiveness and efficiency, and to help improve your bottom line while protecting the environment from controllable N losses, start with some simple calculations for each field on your farm. Divide crop yield by the applied N rate, and plot the values for each year, on each field. The results may reveal your prowess as a top-notch N manager … or they could serve as important indicators of the need for a N management tune-up. Either way, tracking N use efficiency for each field can be just as important as monitoring the milking performance of a dairy cow. Without performance records, it is difficult to make critical management decisions that are essential to remaining competitive in the farming business.

- CSS -

For more information, contact Dr. Clifford S. Snyder, Nitrogen Program Director, IPNI, P.O. Drawer 2440, Conway, AR 72033-2440. Phone (501) 336-8110. Fax (501) 329-2318. E-mail: csnyder@ipni.net.

Abbreviation: N = nitrogen.

SOCIAL MEDIA IN AGRICULTURE

Source : Plant Nutrition Today. International Plant Nutrition Institute.

ผ่านทางPNT: SOCIAL MEDIA IN AGRICULTURE.

Winter 2010, No. 5

SOCIAL MEDIA IN AGRICULTURE

Traditionally, agricultural information exchange has been dominated by industrial media such as newspapers, television, and magazines. In recent years, however, technology awareness and computer literacy are increasing across all demographics and various forms of social media are being used more and more by people looking for news, education, and other information related to agriculture. Social media can be defined as internet-based applications that allow the creation and exchange of user-generated content. It is the blending of technology and social interaction that creates value in these types of media.

Education and outreach efforts by industry and university extension personnel have often been identified as valuable or successful based on the face-to-face interaction with clientele. Dr. John Fulton, a precision agriculture extension specialist at Auburn University, sees social media as a means of enriching his efforts, not a hindrance to them. Dr. Fulton says: “If I restrict dialogue only to a one-on-one conversation, then only that person can take advantage of it.” By sharing the information exchanged during one face-to-face encounter through his social media network, Dr. Fulton has the opportunity to serve potentially millions of other growers asking the same questions or facing similar challenges. Social media also provides growers a quick and easy way to build relationships and to interact with people in agriculture that they might never have connected with otherwise.

There are many different forms of social media, including web, social, and micro blogs (a blend of the term web log), podcasts, video, and other file sharing sites. Some specific applications that the International Plant Nutrition Institute (IPNI) currently uses include YouTube and Twitter. YouTube is a video-sharing website where users can upload and view videos. IPNI has created a “channel” on the YouTube site where all of our posted videos are collected. The web address is http://www.youtube.com/PlantNutritionInst. You do not need an account to view videos, only to post your own. All of the videos are also available through the IPNI website,http://www.ipni.net/video. The value of using YouTube is that viewers with no knowledge of IPNI can find the videos and be directed back to the IPNI website to become familiar with the Institute. For example, only 23% of the viewers of one of our posted videos, “The Right Way to Grow Wheat”, were referred from the IPNI website. The majority of viewers find our videos by using a YouTube search or by viewing related videos. YouTube also facilitates downloads of our videos to mobile devices, such as smart phones and iPads, which have become a more frequent means of viewing our material over the past six months.

Twitter is a microblogging service that allows users to post and read text-based messages of up to 140 characters. The messages or “tweets” are usually visible to the public. However, authors may restrict delivery to only their subscribers or “followers”. Users can send or receive messages via the Twitter website or mobile devices. The IPNI twitter account can be accessed athttp://www.twitter.com/PlantNutrition. A tweet from IPNI will typically be a short statement about a new posting on the website and a link to the full article or news item, such as: Better Crops with Plant Food (2010, No. 3) is loaded with articles that focus on spatial variability. #ag http://info.ipni.net/Y53U6

The value of using Twitter to call attention to these postings is that it draws immediate visibility to an item that might not be seen otherwise by people who don’t frequently visit the website. Another advantage is that a user can “retweet” any message to their list of followers, broadening the distribution beyond IPNI subscribers. An additional way to increase the number of viewers is by appending the message with a “hashtag”. In the case of IPNI tweets, the hashtag is #ag. This link makes the tweets searchable to others within the agriculture community who might be following related users but are not familiar with IPNI.

Social media provide a quick and responsive network for people involved in agriculture to gather and exchange information. It allows immediate dissemination of important emerging issues and the sharing of positive information among producers and consumers of agricultural products. IPNI is committed to providing science-based plant nutrition and fertilizer use information to industry, farmers, agricultural and environmental leaders, scientists, and public policy makers. So, follow us on Twitter @PlantNutrition to receive all the latest updates.

-SBP-

For more information, contact Dr. Steve Phillips, Southeast Director, IPNI, 3118 Rocky Meadows Rd., Owens Cross Roads, AL 35763. Phone (256) 529-9932. E-mail: sphillips@ipni.net.

STARTER FERTILIZER – WHY IT’S DONE

Source : Plant Nutrition Today. International Plant Nutrition Institute.

ผ่านทางPNT: STARTER FERTILIZER – WHY IT’S DONE.

Winter 2010, No. 4

STARTER FERTILIZER – WHY IT’S DONE

Starter fertilizer. It’s not the easiest practice to put into place – special attachments, more cost, and logistics of tending tanks or bins to name a few. But many farmers make it a part of their regular planting practices. Why?

First, with starter fertilizer, a little goes a long way. Because it is placed near the seed at planting, it is accessible to a young root system. For some crops, like corn and wheat, roots take up nutrients at the fastest rate early
in the season. A concentrated supply of nutrients within easy reach of a limited root system increases the chances that roots can continue to take up nutrients at a rapid rate without running short. Because they are strategically
placed and timed, starter fertilizers are one of the more efficient applications made.

Starter fertilizers can be used as a strategy for managing within-field nutrient variability. It has been shown time and again that soil fertility varies across the field and so does crop response to applied nutrients. Agriculture is able to measure and document this variability more than in the past. However, site-specific approaches still carry risk that some areas of the field may not be properly characterized and under-fertilized. Applying a small quantity of nutrients across the entire field as starter fertilizer helps manage this risk.

Nutrients in starter fertilizer provide synergistic effects. Nitrogen and P can cause roots to proliferate in the zone where starter fertilizer was applied. Potassium does not proliferate roots, so co-application with N and/or P is needed for roots to more fully explore the K supply in the starter. Nitrogen, in the ammonium form, results in acidification of the zone of soil right around the root. This lower acidity has been shown to increase P uptake by young plants. Phosphorus also supplies needed energy early in the plant for the active uptake of K.

The most commonly observed effect of starter fertilizer is more rapid early season growth. While this response is probably the most visually striking, it does not necessarily mean that a yield response will occur. As a plant continues to develop and its roots explore more soil, starter fertilizer supplies progressively less of the total nutrients taken up, making nutrient supplies elsewhere in the soil profile more important. End of season yield responses depend on how quickly and to what extent a plant root system accesses these other supplies. Under conditions where root exploration is limited or slowed, yield responses are more likely. This holds true as well when soils are less fertile.

Many would argue that when striving to achieve consistently higher yields, a starter fertilization program should be seriously considered. Whether or not it fits a particular farm depends on many things beyond those strictly agronomic. However, starter fertilizer does provide some level of insurance against nutrient variability and adverse growing conditions and is a management practice with a rather extensive body of scientific studies supporting its use.

-TSM-

For more information, contact Dr. T. Scott Murrell, Northcentral Director, IPNI, 1851 Secretariat Dr., West Lafayette, IN 47906. Phone: (765) 413-3343. E-mail: smurrell@ipni.net.

Abbreviations: N = nitrogen; P = phosphorus; K = potassium.

WHAT SULFUR SOURCE SHOULD I USE?

Source : Plant Nutrition Today. International Plant Nutrition Institute.

ผ่านทางPNT: WHAT SULFUR SOURCE SHOULD I USE?.

Winter 2010, No. 3

WHAT SULFUR SOURCE SHOULD I USE?

Sulfur has been recognized as restricting crop production in parts of the world. Soil S budgets are negative in many areas, where more S is removed from the field in harvested crops than is supplied by various inputs.
Much of the S in soil is present in organic matter, where it is unavailable for plant uptake until it is converted to sulfate. Plants require adequate S for many reactions, including synthesis of proteins and enzymes.

When additional S is needed to meet crop needs, there are many excellent sources of this nutrient. Elemental S was once mined directly from the earth. It is now more typically obtained from coal, crude oil, and natural
gas during refining or during scrubbing of combustion gases. A number of common earth minerals are also used as S sources for agriculture.

Elemental S is not water soluble and must be oxidized by soil bacteria to sulfate before it can be taken up by plant roots. The speed of this microbial process is governed by environmental factors such as soil temperature and moisture, as well as the physical properties of the S.

Various approaches have been used to enhance the conversion of elemental S to plant-available sulfate. The speed of elemental S oxidation is directly related to the particle size, where smaller particles have a greater surface area for the soil bacteria to act on. Therefore, large particles of S may require months or years of biological action before oxidizing significant amounts of sulfate. Fine, dust-sized particles are oxidized quickly, but are not easy to apply.

One approach to enhance the rate of S oxidation is to add a small amount of clay to the molten S prior to cooling and forming small pellets (“pastilles”). When added to soil, the clay swells with water and the pastille disintegrates into fine particles that are rapidly oxidized.

Very thin layers of elemental S can be incorporated during fertilizer granule manufacturing. This S is quick to oxidize and become available for plant uptake. This reaction can have a positive impact on the plant availability of some micronutrients, such as zinc and iron, which become more soluble as the pH declines. Finely ground elemental S is sometimes added to fertilizer suspensions. Elemental S is also used as a fungicide for crop protection. Elemental S and sulfuric acid are commonly used in the reclamation of calcareous soils that contain elevated sodium and in the treatment of irrigation water containing excessive bicarbonate.

A number of excellent soluble sulfate fertilizers are available to provide a rapid supply of nutrients. The selection of a particular soluble material depends on price, availability, form, and the other nutrients that accompany the sulfate. A few examples of commonly used S fertilizers include:

Non-Soluble – Elemental S
Semi-Soluble – Gypsum (15 to 17% S)
Soluble – Ammonium sulfate (24% S); Epsom salt (13%); Kieserite (23% S);
Langbeinite (22% S); Potassium sulfate (18% S); Thiosulfate (10 to 26% S)

- RLM -

For more information, contact Dr. Robert Mikkelsen, Western North America Director, IPNI, 4125 Sattui Court, Merced, CA 95348. Phone: (209) 725-0382. E-mail: rmikkelsen@ipni.net.

Abbreviation: S = sulfur.

THE ROLE OF POTASSIUM IN REDUCING THE INCIDENCE OF CROP DISEASES

Source : Plant Nutrition Today. International Plant Nutrition Institute.

ผ่านทางPNT: THE ROLE OF POTASSIUM IN REDUCING THE INCIDENCE OF CROP DISEASES.

Winter 2010, No. 2

THE ROLE OF POTASSIUM IN REDUCING THE INCIDENCE OF CROP DISEASES

Potassium is essential for all plants. It is considered one of the macronutrients, along with N and P, because it is used in relatively large amounts compared to other nutrients. For example, an 80 bu/A barley crop will take up about 106 lb N, 43 lb P₂O₅ and 93 lb K₂O. Barley grain contains the majority of the N and P, with 74% and 79%, respectively. The majority of K, about 74%, is in the straw or residue of the crop. Although K is important to many vital plant functions such as plant enzyme activation, water regulation, energy capture from photosynthesis, N uptake and protein synthesis, starch synthesis, and root growth, K is not part of plant manufactured components such as proteins and oils. However, it also contributes to grain or fruit quality, helps prevent lodging, and increases crop disease resistance.

The simple explanation for increasing crop resistance to plant diseases is that by providing balanced plant nutrition, including adequate K, crop plants are healthier. A healthy plant is more able to resist invasion by disease organisms, and recover from a disease episode. However, besides just being healthier, there are other ways that K specifically helps plants resist disease.

Potassium helps crop plants resist disease organism invasion or penetration by strengthening cell wall structure. Plants having adequate K will have thicker cell walls compared to plants deficient in K. This makes it harder for disease organisms to penetrate plant cells and establish an infection. This applies to fungal, bacterial, nematode, insect, and viral disease organisms. Another indirect benefit from stronger cell walls is that plants are less prone to lodging, and stem and leaf architecture is more upright and spread out, thus improving airflow through the crop canopy. This can help slow down the spread of any disease organism through the crop canopy, and result in lower humidity levels that can reduce the growth of pests and diseases that prefer moist environments.

Potassium is also vital for water regulation in plant cells. There are two mechanisms of water regulation that help plants better resist disease establishment. Potassium is important for stomate cell regulation for pore openings on plant leaves. Adequate K nutrition will allow the plant to maintain smaller stomatal openings compared to a K-deficient plant, and also pores are opened and closed more easily and timely, which helps limit the successful invasion of disease organisms into plant leaves. The second water regulation mechanism that can help reduce disease organism penetration into plant cells is that adequate K nutrition helps the plant to maintain increased turgor, or water pressure in cells. A cell with optimum turgor pressure will tend to push organisms away from the cell membrane when the invading organism attempts to push through the cell membrane.

Adequate K in plant cells improves utilization of the building components required for synthesis of starches and proteins. This results in a lower concentration of low molecular weight carbohydrates such as sugars in plant cells. Many disease organism growth rates are increased if there is an ample supply of simple sugars or carbohydrates compared to larger structures such as starches. In a similar way, complex protein structures are more slowly utilized by many disease organisms, whereas higher concentrations of mineral N in the form of ammonium and nitrate, or N contained in basic amino acids, can facilitate more rapid disease organism growth.

Incidence of crop diseases can be reduced if attention is given to supplying crops with adequate supplies of K. There are two ways to assess whether or not a crop will have, or does have, adequate K. Soil testing for plant available K can show whether or not more K should be applied as fertilizer prior to planting. Plant sampling and tissue testing of crop plants during the growing season might show less than optimum levels of K in plant tissues, and increased K fertilizer rates should be considered for future short-season annual crops. In the case of long-season or perennial crops, there may be a benefit to topdressing K. Advice can be obtained from your local consulting agronomist or certified crop adviser, or from a soil and plant testing laboratory agronomist, to know whether or not K fertilizer might be beneficial.

-TLJ-

For more information, contact Dr. Thomas L. Jensen, Northern Great Plains Director, IPNI, 102-411 Downey Road, Saskatoon, SK S7N 4L8. Phone: (306) 652-3535. E-mail: tjensen@ipni.net.

Abbreviations: N = nitrogen; P = phosphorus; K = potassium.

SOIL FERTILITY SHIFTS IN RESPONSE TO CROP NUTRIENT BALANCE

Source : Plant Nutrition Today. International Plant Nutrition Institute.

ผ่านทางPNT: SOIL FERTILITY SHIFTS IN RESPONSE TO CROP NUTRIENT BALANCE.

Winter 2010, No. 1

SOIL FERTILITY SHIFTS IN RESPONSE TO CROP NUTRIENT BALANCE

Soil fertility rises and falls in response to crop nutrient balances. Nutrient surpluses raise soil test levels; deficits draw them down. It’s not always easy to predict how much, or what the consequences will be, so it’s important
for the crop manager to monitor both as closely as possible. Recent surveys of soil tests and nutrient balances on the state and province scale point to the need to pay close attention to the same on the farm and field scale.

A new soil test summary is out. The International Plant Nutrition Institute recently completed a survey of the public and private soil test laboratories of North America, similar to surveys done every 4 to 5 years for the past several decades by the Potash & Phosphate Institute. There are numerous challenges to conducting such surveys, since soil test methods and interpretations vary among states and provinces, and change over time as well. Nevertheless,
important and consequential trends are showing up.

The 2010 survey included more samples than any previous survey. An estimated 4.4 million soil samples were submitted across North America for this survey compared to about 3.4 million for 2005. The increase likely reflects more widespread and intensive soil sampling by producers, arising from higher and more rapidly fluctuating prices for fertilizers and crop commodities seen in recent years.

In Eastern Canada and the northeastern United States, the soil fertility shifts varied. In many areas, soil test levels for K have moved downward since 2005. For example, in the province of Ontario the proportion of soils testing 80 ppm or less in K grew from 15% in 2005 to 20% in 2010. Soils testing in this range are likely to produce K deficiencies in almost any crop in the absence of fertilization. This trend is not surprising, considering that the amount of K applied to Ontario cropland in the form of fertilizer and manure was only about half that removed by crops in 2009.

However, elsewhere the shifts varied in size and direction. In Pennsylvania, the distribution of soil test K hardly changed at all, while in New York and Virginia, it appears to have shifted upwards.

Soil test P levels often fall into a bimodal distribution. A substantial proportion are in the responsive range, but another large proportion are at levels far above the critical level for crop response. The very high levels result from many years of historical nutrient surpluses. Such soils need to be managed in ways that eliminate the surplus, maximize utilization of the P fertility for the benefit of crop production, and minimize surface runoff and erosion to protect water quality. The frequency of very high soil P tests continued to decline in Ontario, but increased in New York, New England, and Pennsylvania.

The soils of the region remain quite variable in fertility. Even in states and provinces with overall nutrient surpluses, many soils needing nutrient additions can be found. On the other hand, many soils have built up fertility to the point where inputs of P and K amounting to less than crop removal of the nutrient can continue for years. Of course, in such situations it would be important to monitor the decline with regular soil testing.

So, nutrient decisions need to be supported not only by crop nutrient balances, and not only by soil tests, but by both. Using the two tools, you can manage nutrients sustainably.

More detailed information on these changing nutrient balances and soil test levels can be found at this site: http://nane.ipni.net.

-TWB-

For more information, contact Dr. Tom Bruulsema, Northeast Director, IPNI, 18 Maplewood Drive, Guelph, Ontario N1G 1L8, Canada. Phone: (519) 821-5519. E-mail: Tom.Bruulsema@ipni.net.

Abbreviations: K = potassium; P = phosphorus; ppm = parts per million.

CONSIDERING CHLORIDE FOR WHEAT

Source : Plant Nutrition Today. International Plant Nutrition Institute.

ผ่านทางPNT: CONSIDERING CHLORIDE FOR WHEAT.

Fall 2010, No. 7

CONSIDERING CHLORIDE FOR WHEAT

Chloride (Cl^-) has been formally recognized as a plant nutrient since the 1950s. It is classified as a micronutrient, but plants may take-up as much Cl^- as secondary elements such as S. Concentrations of Cl^- in wheat flagleaf and corn earleaf at flowering are commonly in the range of 0.25 to 1%.

Chloride is involved in several important roles in plants, including,

• Photosynthesis and enzyme activation

• Transport of other nutrients in the plant

• Stomatal activity

• Accelerated plant development

• Reduced lodging

Chloride is an anion and is therefore mobile in the soil. It can be leached from the soil profile where internal soil drainage is good. Chloride may be supplied to soils from several external sources, including fertilizer input, atmospheric deposition, and irrigation water. Thus, low soil Cl^- level is favored where: 1) there is limited application of Cl^--bearing fertilizer such as muriate of potash (KCl); 2) where there is low atmospheric Cl^- deposition (deposition is highest in coastal regions and decreases inland), and 3) in non-irrigated conditions. These conditions are met across much of the Great Plains.

Response of wheat to Cl^- fertilization has been observed throughout the Great Plains from Texas to Canada. Much has been reported over the past 20 years or so on work from this region. A recent update and summary of Cl^- work in Kansas was published in a 2009Better Crops magazine article (Vol. 93, No. 4). It is generally accepted that there is little difference in performance among Cl^- sources on winter wheat, and that topdress and preplant applications are effective. However, where there is potential for leaching, topdress application in the spring may be advantageous.

Increases in wheat yield from Cl^- fertilization are usually due to either a classical nutrient response and/or suppression of fungal diseases. Under low soil Cl^- conditions, some varieties may exhibit Cl^- deficiency symptoms, sometimes referred to as physiological leaf spot syndrome. These symptoms are similar in appearance to tanspot or septoria, but are not caused by a pathogen. The absence of leaf spotting does not always mean that Cl^- is not deficient since spotting is dependent upon wheat variety. Chloride has been shown to reduce the severity of several root and foliar diseases. In one Texas study, leaf rust infection of the flag leaf was reduced from 68 to 27% by topdressing with 40 lb Cl^- /A as muriate of potash.

Whether or not wheat will respond to Cl^- usually depends upon soil Cl^- level, disease pressure, plant Cl^-, and variety. Response to Cl^- is likely when soil Cl^- levels are less than 45 lb/A from 2-ft. deep soil samples. Kansas State University recommends 10 lb Cl^- /A application when the soil level is 30 to 45 lb/A, and 20 lb application when soil level is below 30 lb/A. It has been shown that some varieties are much more responsive to Cl^- than others.

Chloride response in wheat can ultimately be expressed in terms of increased yield, higher test weights, and greater kernel plumpness. Therefore, it is worth considering the need for Cl^- on the upcoming wheat crop.

-WMS-

For more information, contact Dr. W.M. (Mike) Stewart, Southern and Central Great Plains Director, IPNI, 2423 Rogers Key, San Antonio, TX 78258. Phone: (210) 764-1588. E-mail: mstewart@ipni.net.

Abbreviations: S = sulfur.

Note: Plant Nutrition TODAY articles are available online at the IPNI website: http://www.ipni.net/pnt

WHAT IS THE BEST NITROGEN RATE FOR YOUR FIELD?

Source : Plant Nutrition Today. International Plant Nutrition Institute.

ผ่านทางPNT: WHAT IS THE BEST NITROGEN RATE FOR YOUR FIELD?.

Fall 2010, No. 6

WHAT IS THE BEST NITROGEN RATE FOR YOUR FIELD?

Most farmers strive to implement a cropping system and nutrient management strategy that will allow them to capture favorable growing conditions which at least meet historic average crop yield potential. The fertilizer N rate chosen has traditionally depended on results from land grant university research and extension replicated studies, which may span several years and environmental conditions. In the past, many such public studies were nearby, but in recent times, because of declining budgets and program cuts, farmers have had fewer such studies to rely on in guiding their N rate selections.

Ideally, one could match the applied N rate in perfect synchronization with crop uptake demand, with a perfect knowledge of soil N release. However, we recognize that a sizeable portion of the N that plants take up comes from the soil, as microbes breakdown organic matter and organic N is converted to ammonium and then nitrate forms; the forms essential for plant nutrition. Unfortunately, we still can’t predict the amount of N that will become available, and when it will become available, from the full soil profile or rooting volume; especially across an entire growing season. Yes, there are some soil N tests which have met with moderate success, but their use and success in the field under differing conditions and geographies have been limited.

If recent local research results on similar soils and cropping system conditions are not available, then a plan should be developed to evaluate existing N rates against alternative N rates: both above and below the current practices. As crop yield potential is raised with improved genetics, questions are being asked about the potential need for higher N rates (or changes in timing and placement). To help answer these questions, some leading farmers are partnering with their crop advisers and fertilizer dealers to establish N rate tests on their own farms. Such N rate comparisons can provide valuable information, but they should be repeated over several years, and they should be randomized and not just simple side-by-side contrasts. Treatment randomization is important
because unseen gradients in soil fertility, moisture holding capacity, and internal drainage in many fields can skew the results in side-by-side comparisons and mislead interpretations.

Sensor technologies are also available, which detect the greenness of the crop (e.g. corn, wheat) during the growing season, and which reflect the N nutritional status. Such monitoring can allow one to adjust to conditions of improved yield potential (e.g. favorable weather) or to adapt to conditions that may have caused unmeasured volatile, leaching, runoff, and drainage losses of N. The calibration for these “N sensing” applications should be locally or regionally based. Several university and USDA research programs have made progress with such calibrations. Farmers, crop advisers, Extension agents, and fertilizer dealers are increasingly employing the technologies where they have been proven economically feasible.

Field-average hind-sight or “post-mortem” evaluations of N sufficiency are important, but replicated tests to evaluate the crop response under different N rates and different management systems are considered more valuable, especially when coupled with monitoring of plant N status during the growing season. Use of yield potential alone is no longer considered the best approach in determining the N rate for a given field. Consider ways to evaluate the performance of your N management program by partnering with others who are skilled in on-farm evaluations. Such tests can help instill confidence in the fertilizer N management program, and help ensure that both economic and environmental protection goals are achieved.

-CSS-

For more information, contact Dr. Clifford S. Snyder, Nitrogen Program Director, IPNI, P.O. Drawer 2440, Conway, AR 72033-2440. Phone 501-336-8110. Fax 501-329-2318. E-mail: csnyder@ipni.net.

Abbreviations: N = nitrogen.

PRECISION COTTON FARMING IN THE SOUTH

Source : Plant Nutrition Today. International Plant Nutrition Institute.

ผ่านทางPNT: PRECISION COTTON FARMING IN THE SOUTH.

Fall 2010, No. 5

PRECISION COTTON FARMING IN THE SOUTH

At the recent 10^th International Conference on Precision Agriculture, Daniel Mooney from the University of Tennessee discussed the results of a 2009 survey of southern cotton farmers. Growers in 12 states (Alabama, Arkansas, Florida, Georgia, Louisiana, Mississippi, Missouri, North Carolina, South Carolina, Tennessee, Texas, and Virginia) were surveyed regarding their attitudes toward, and use of, precision farming technologies. A total of 1,692 surveys were returned, of which 63% identified themselves as precision farming adopters, indicating that they had used information gathering technology, variable-rate management, or GPS guidance.

Grid and zone soil sampling were the two most widely used information-gathering technologies being used by southern cotton farmers (46% of respondents). Yield monitors with GPS, soil survey maps, and aerial photography were the next most commonly used information gathering technologies (15% to 20%). Least used by adopters were yield monitoring without a GPS, satellite imagery, handheld GPS/PDA, COTMAN plant mapping, digitized mapping, and electrical conductivity (less than 10%).

A yield monitor with GPS was the technology most frequently used to make variable-rate fertility or lime decisions. Handheld GPS units and electrical conductivity were also used to make fertilizer and lime decisions, while GreenSeeker optical sensors and aerial/satellite imagery were used most commonly for growth regulator and harvest aid decisions. Of the growers using variable-rate fertilization, 36% were using it to apply N, 73% for P, and 76% for K. Ninety-two percent of the respondents using a variable-rate management plan were varying lime application rates. Fifty-three and 69% reported a decrease in inputs after adopting variable-rate fertilizer and lime management plans, respectively. Conversely, 29 and 18% of the respondents experienced an increase in inputs using variable-rate fertilizer and lime, respectively.

Nearly half of respondents (47%) reported having adopted GPS guidance. Divided into guidance categories, one-third of adopters used GPS auto-steer technology, while one-quarter used GPS light-bar technology. Adopters used guidance for an average of 2.5 different field activities including spraying (79%), planting (63%), and tillage (59%) operations. One of the main reasons cited for adopting a guidance system was to improve overall input efficiency and an overwhelming majority (88%) indicated that guidance had met their expectations. Sixty-one percent of growers did not see any fertilizer cost savings as a result of using GPS guidance. However, just over half of the respondents reported chemical input savings of at least $5/A.

Nine out of 10 adopters believed precision farming would be profitable in the future. For non-adopters, 60% agreed that precision agriculture technologies have a profitable future in southern cotton farming. Findings from this survey will be useful to university extension and industry personnel in developing outreach efforts to support growers making decisions regarding precision farming technologies. The complete survey and accompanying publications can be accessed at: >http://economics.ag.utk.edu/precisionagpubs.html<.

-SBP-

For more information, contact Dr. Steve Phillips, Southeast Director, IPNI, 3118 Rocky Meadows Rd., Owens Cross Roads, AL 35763. Phone (256) 975-3841. E-mail: sphillips@ipni.net.

Abbreviations: GPS = global positioning system; N = nitrogen. P = phosphorus; K = potassium.

NOT ALL FERTILIZER BANDS PLAY THE SAME SONG

Source : Plant Nutrition Today. International Plant Nutrition Institute.

ผ่านทางPNT: NOT ALL FERTILIZER BANDS PLAY THE SAME SONG.

Fall 2010, No. 4

NOT ALL FERTILIZER BANDS PLAY THE SAME SONG

The often used expression, “Same song, different verse,” refers to something that is practically the same as something else. So often, P and K are used in the same sentence when people talk about banded fertilizer applications, as if both were different verses of the same song. Actually, P and K fertilizer bands play different “songs” because they behave differently in soil.

One of the primary reasons fertilizer is banded is to increase short-term efficiency of use by the plant. Bands of P are known to cause an increase in root proliferation, as are bands of N. Bands of K, however, do not have this effect. This means that bands of P will be explored more thoroughly by root systems than bands of K. The implication, of course, is that applying P and K together in a band will help make better use of the concentrated K supply, due to the increased root growth caused by P.

Bands of K may not remain as concentrated in soils over time as bands of P. There are a couple of reasons for this. First, crops like corn and soybean take up more K than P during the season. Corn takes up about two-and-a-half times as much K as P while soybeans take up about twice as much (expressed as K₂O and P₂O₅). Secondly, K moves more in soils than does P, causing bands of K to become more diffuse over time relative to P. So, greater uptake combined with greater mobility limits the longevity of concentrated bands of K.

In the short-term, corn and soybean plants themselves redistribute K in soils to a greater extent than P. This occurs for a couple of reasons. First, K leaches from plant residue and unlike P, does not require microbial decomposition to be released. This means that K in the plant is returned to the soil more quickly than P. Secondly, a greater proportion of the K taken up by the above-ground plant biomass exists in the plant residues returned to the field. For corn, about 80% of the total K taken up is in the stover, compared to only about 30% for P. For soybean, the percentages are 45% for K and 20% for P. A lot of the K leached from plants occurs during senescence, before crop harvest, meaning that most of the K is redistributed into the crop row. Consequently, plants become effective redistributors of K in the soil, moving it from throughout the root zone and concentrating it to the row, particularly at the soil surface. While P is also redistributed in this manner, it is not done so to the degree that K is.

Just how long P and K bands will last in soil depends upon many factors. Soil mineral composition, rooting depth, environmental conditions, and soil wetting and drying cycles are but some of the many factors at play. To gain an idea of how long bands will last under a specific set of conditions, on-farm monitoring through soil testing is suggested. Select areas can be monitored frequently to gain a sense for band longevity, remembering that if bands are placed near crop rows, concentration of K by the plant may overwhelm detection of lower rates of banded K.

So the next time P and K bands are assumed to be the same, remember that they really have very different characteristics, both in the soil and in the way they interact with plants. Bands of P and K really do play different songs.

-TSM-

For more information, contact Dr. T. Scott Murrell, Northcentral Director, IPNI, 1851 Secretariat Dr., West Lafayette, IN 47906. Phone: (765) 413-3343. E-mail: smurrell@ipni.net.

Abbreviations: N = nitrogen; P = phosphorus; K = potassium.

ARE YOU OVERLOOKING MAGNESIUM?

Source : Plant Nutrition Today. International Plant Nutrition Institute.

ผ่านทางPNT: ARE YOU OVERLOOKING MAGNESIUM?.

Fall 2010, No. 3

ARE YOU OVERLOOKING MAGNESIUM?

In most discussions of plant nutrition, the importance of magnesium (Mg) is too often overlooked. Since an adequate supply of Mg is required for many key reactions in plants, both yield and quality will suffer when it is lacking.

The yellowing of older leaves is the classic Mg deficiency symptom. Up to one-third of the total plant Mg is found in the chloroplasts. Leaf chloroplasts are where sunlight is converted to chemical energy (sugars) through the process of photosynthesis. The appearance of yellow leaves from a lack of Mg is more common with high light intensity than in cloudy or shaded conditions.

When plants are lacking in adequate Mg, many growth processes are stunted before any visible damage can be seen. For example, under low-Mg conditions, plants are not able to properly transport sucrose from the leaves to the rest of the plant. Consequently, root growth is stunted and overall plant growth is reduced, long before any symptoms are noticeable. Similarly, proper development of seeds and fruit can be disrupted by a lack of sucrose transport in low Mg conditions.

Magnesium in most soils is present in various minerals and clays. Depending on the parent material that formed a particular soil and the types of clay present, Mg may be in abundant supply or may be lacking. Plant-available Mg is generally held on soil cation exchange sites and it can be easily measured through routine soil testing.

When the Mg supply is inadequate, there are many excellent sources that can be used to meet crop demands. They are commonly divided into two classes: soluble sources and semi-soluble sources. Depending on your location, the availability and price of the different products may vary. Some common North American sources are listed below.

Soluble Magnesium Sources	Semi-soluble Magnesium Sources
Kieserite: MgSO4•H2O; 15% Mg Dolomite: MgCO3•CaCO3; 6 to 20% Mg	Dolomite: MgCO3•CaCO3; 6 to 20% Mg
Magnesium Chloride: MgCl2; 25% Mg Hydrated Dolomite: MgO•CaO/MgO•Ca(OH)2; 18 to 20% Mg	Hydrated Dolomite: MgO•CaO/MgO•Ca(OH)2; 18 to 20% Mg
Langbeinite: 2MgSO4•K2SO4; 11% Mg Magnesium Oxide: MgO; 56% Mg	Magnesium Oxide: MgO; 56% Mg
Magnesium Nitrate: Mg(NO3)2; 13% Mg Struvite: MgNH4PO4•6H2O; 10% Mg	Struvite: MgNH4PO4•6H2O; 10% Mg
Magnesium Sulfate (Epsom salt): MgSO4•7H2O; 9% Mg
Magnesium Thiosulfate: MgS2O3; 4% Mg
Various foliar sprays

Two recent articles in Better Crops with Plant Food magazine feature more information Mg. You can find them at this website: >www.ipni.net/bettercrops<.

-RLM-

For more information, contact Dr. Robert Mikkelsen, Western North America Director, IPNI, 4125 Sattui Court, Merced, CA 95348. Phone: (209) 725-0382. E-mail: rmikkelsen@ipni.net.

Note: Plant Nutrition TODAY articles are available online at the IPNI website: http://www.ipni.net/pnt

SOIL pH AND THE AVAILABILITY OF PLANT NUTRIENTS

Source : Plant Nutrition Today. International Plant Nutrition Institute.

ผ่านทางPNT: SOIL pH AND THE AVAILABILITY OF PLANT NUTRIENTS.

Fall 2010, No. 2

SOIL PH AND THE AVAILABILITY OF PLANT NUTRIENTS

Soil pH is a characteristic that describes the relative acidity or alkalinity of the soil. Technically, pH is defined as the negative (-) log or base 10 value of the concentration of hydrogen ions (H⁺). Pure water will be close to a neutral pH, that is 10 to the minus 7 concentration of H⁺ ions (10-7 [H⁺]). This concentration is expressed as 7. Any value above 7 means the H⁺ ion concentration is lower than at a neutral pH and the solution is alkaline and there are more hydroxyl (OH^-) ions present than H⁺ ions. Any value below 7 means the H⁺ ion concentration is greater than at neutral pH and the solution is acidic. Soils are considered acidic below a pH of 5, and very acidic below a pH of 4. Conversely, soils are considered alkaline above a pH of 7.5 and very alkaline above a pH of 8. Typically, soil pH values are measured when 10 g of air-dried soil is mixed with 20 ml of double-distilled water or 20 ml of 0.01 M CaCl₂ solution, and the pH is measured using an appropriate electrode connected to a pH meter. This soil analysis is a regular part of most if not all soil test protocols.

The availability of some plant nutrients is greatly affected by soil pH. The “ideal” soil pH is close to neutral, and neutral soils are considered to fall within a range from a slightly acidic pH of 6.5 to slightly alkaline pH of 7.5. It has been determined that most plant nutrients are optimally available to plants within this 6.5 to 7.5 pH range, plus this range of pH is generally very compatible to plant root growth. Nitrogen, K, and S are major plant nutrients that appear to be less affected directly by soil pH than many others, but still are to some extent. Phosphorus, however, is directly affected. At alkaline pH values, greater than pH 7.5 for example, the HPO₄ ^2- phosphate ions tend to react quickly with calcium (Ca) and magnesium (Mg) to form less soluble compounds. At acidic pH values, the H₂PO₄^-phosphate ions react with aluminum (Al) and iron (Fe) to again form less soluble compounds. Most of the other nutrients (micronutrients especially) tend to be less available when soil pH is above 7.5, and in fact are optimally available at a slightly acidic pH, e.g. 6.5 to 6.8. The exception is molybdenum (Mo), which appears to be less available under acidic pH and more available at moderately alkaline pH values.

In some situations, materials are added to the soil to adjust the pH. On a field scale, this is most commonly done for acidic soils to raise the pH from an acidic level of 4.5 to 5.5 up to 6.5 or approaching neutrality. This is done by applying and incorporating a liming material, often finely ground calcitic (CaCO₃) limestone, or dolomitic [CaMg(CO₃)₂] limestone, that is spread using specialized lime spreaders, or spin-spreaders adapted with vibrating systems to prevent bridging of the material in the hoppers of the spreaders. It is possible to lower the pH of a soil using a liquid acid solution, or finely ground elemental S that oxidizes to sulfuric acid through the action of soil inhabiting S-oxidizing bacteria. However, this is rarely done on a field-scale basis because of the high cost. It is more commonly done in horticulture production applications where individual plant containers or limited areas (e.g. <10 to 20 acres) are managed to lower the pH for acidic soil adapted plants such as some flowers, trees, and/or small fruits (i.e. blueberry and cranberry). It is important to note that most on-going crop production, especially where NH₄ ⁺ based, or NH₄ ⁺ releasing N fertilizers (e.g. anhydrous ammonia, ammonium sulfate, and urea) are applied, will gradually lower the soil pH, as the H⁺ ions are released from the NH₄ ⁺ ions when they are converted over to nitrate (NO₃^-) by soil microbes.

Whether or not you try to adjust pH, it is important to understand other methods to increase the availability and use of added nutrients. This can be done in a number of ways for the nutrients mentioned above that are adversely affected by extremes in soil pH, acidic or alkaline. For example, P-containing fertilizer can be applied in or close to the seed-row at planting to facilitate early season uptake of phosphate ions by crop roots before allowing it to react with soil cations dominating under acidic (e.g. Al³⁺ or Fe³⁺) or alkaline (e.g. Ca²⁺ or Mg²⁺) soil pH conditions. Under alkaline soil pH values, the phosphate fertilizer can be applied in bands with fertilizer which generates NH₄ ⁺ as noted above. That will allow slight acidification of the soil adjacent to the fertilizer band. Another method is to manufacture compound nutrient fertilizer granules that contain the N, P, and even elemental S-containing fertilizers, for application to alkaline soils so the soil adjacent to the granule will also be acidified slightly and allow enhanced P uptake when the crop roots intercept the granules. Yet another example is the foliar application of soluble Fe fertilizer compounds to Fe-deficient crops grown in high pH soils where the Fe³⁺ ions of the Fe fertilizer react so fast with soil that the nutrient is tied up and unavailable to plants. This is why soil applied Fe fertilizers often do not successfully correct Fe deficiencies. By avoiding the soil and applying the Fe to the leaves, the small amount of plant-required Fe is successfully introduced into the crop.

Next time you have soil samples taken on your fields, take time to note what the pH values are in your results. It is useful to compare these values to previous soil test pH values and determine if there is a trend of soil pH change. By monitoring the pH values regularly (every 2 to 3 years) in a field, you may consider action to raise the pH of the soil from acidic to near neutral pH values by liming. Increased nutrient availability and improved crop growth can be achieved when adding liming material to an excessively acidic soil. This can be especially important for crops requiring neutral pH, such as legume forages or pulses, as the Rhizobia species bacteria do not nodulate and fix N effectively under pH values less than 5.5.

-TLJ-

For more information, contact Dr. Thomas L. Jensen, Northern Great Plains Director, IPNI, 102-411 Downey Road, Saskatoon, SK S7N 4L8. Phone: (306) 652-3535. E-mail: tjensen@ipni.net.

Abbreviations: N = nitrogen; NH₄⁺ = ammonium; P = phosphorus; S = sulfur.

MORE INTENSIVE CROP NUTRITION EVADES GREENHOUSE GASES

Source : Plant Nutrition Today. International Plant Nutrition Institute.

ผ่านทางPNT: MORE INTENSIVE CROP NUTRITION EVADES GREENHOUSE GASES.

Fall 2010, No. 1

MORE INTENSIVE CROP NUTRITION EVADES GREENHOUSE GASES

Doesn’t fertilizer actually increase emissions of greenhouse gases? Well, yes, in its manufacture and in its use, but… when one looks at the big picture instead of the partial details, it’s surprising how much the answer to a question can change! The higher yields of better-fertilized crops have spared land from conversion to agriculture, avoiding emissions of a huge quantity of greenhouse gases.

Agricultural intensification can reduce greenhouse gas emissions. A recent study published in the Proceedings of the National Academy of Sciences estimates that the gains in crop yields since 1961 have, globally on a net basis, spared emissions of 350 to 650 million short tons of carbon dioxide equivalents. Those higher-yielding crops do emit more greenhouse gases, but not as much more as alternative scenarios in which larger areas of land would have been converted to agriculture.

Crop yields have more than doubled since 1961. The increased yields have made it possible to feed the world’s growing population with only a 27% increase in land area. Without the yield increases, 292% more land would have been required to attain the crop production levels of 2005. Even to simply maintain the per capita production levels of 1961 would have required a 221% expansion in cropland.

Converting land to crop production entails very large emissions. The removal of trees, shrubs, and other vegetation, and breakdown of soil organic matter under cultivation releases carbon dioxide. The authors of the report—Jennifer Burney, Steven Davis, and David Lobell in Stanford, California—analyzed the literature carefully and concluded that, around the globe, the average acre available to be converted to crop production would lose the equivalent of 172 tons of CO₂ per acre. That emission is huge in comparison to the emissions increase related to higher input use.

Fertilizer use grew from 34 to 182 million tons of primary nutrients since 1961. In the alternative scenarios, fertilizer use per acre would have stayed constant, but the total use would have increased to between 74 and 97 million tons. Greenhouse gases are emitted when fertilizers are manufactured, and application of N fertilizers can increase emissions of nitrous oxide, a potent greenhouse gas. The fertilizer associated emissions, however, were dwarfed by those associated with land use change in the comparison of these scenarios.

Increasing yields to avoid greenhouse gas emission has been cost-effective. The authors calculated that the cost of investment in crop yield improvement (including public and private research) amounted to less than four dollars per ton of emission reduction. That compares favorably with many other mitigation efforts being considered currently.

Continued improvement in crop yields is a viable strategy for a healthy planet. The study’s authors concluded, “Further yield improvements should therefore be prominent among efforts to reduce future greenhouse gas emissions.”

The carbon footprint of fertilizer needs to include its contribution to yield improvement. Higher crop yields arose not only from fertilizer, but from a combination of better genetics, better management, and better crop nutrition. Improving nutrient use efficiency can only be a viable greenhouse gas mitigation strategy in the context of continued increases in the productivity of cropping systems.

-TWB-

For more information, contact Dr. Tom Bruulsema, Northeast Director, IPNI, 18 Maplewood Drive, Guelph, Ontario N1G 1L8, Canada. Phone: (519) 821-5519. E-mail: Tom.Bruulsema@ipni.net.

Abbreviations: N = nitrogen.

SULFUR—THE 4TH MAJOR NUTRIENT

Source : Plant Nutrition Today. International Plant Nutrition Institute.

ผ่านทางPNT: SULFUR—THE 4TH MAJOR NUTRIENT.

Summer 2010, No. 7

SULFUR—THE 4TH MAJOR NUTRIENT

Sulfur is an essential nutrient in crop production. It is classified as a secondary element, along with Mg and Ca, but it is sometimes called “the 4th major nutrient”. Some crops can take up as much S as P. Sulfur has become more important as a limiting nutrient in crop production in recent years for several reasons. These include higher crop yields that require more S, less S impurities in modern fertilizers, less use of S-containing pesticides, reduced industrial S emissions to the atmosphere, and a greater awareness of S needs.

Sulfur serves many functions in plants. It is used in the formation of amino acids, proteins, and oils. It is necessary for chlorophyll formation, promotes nodulation in legumes, helps develop and activate certain enzymes and vitamins, and is a structural component of two of the 21 amino acids that form protein.

The crop’s need for S is closely associated with N. The relationship between S and N is not surprising since both are components of protein and are involved in chlorophyll formation. They are also linked by the role of S in the conversion of nitrate to amino acids. Crops having high N need will usually also have high S needs.

The majority of S in most soils is contained in organic matter. Organic S must be mineralized to the inorganic sulfate anion before it can be taken up by crops. Organic matter decomposition and the resulting S release is affected by temperature and moisture, and generally conditions that favor crop growth also favor mineralization and release of S, although this may be less likely with cool season crops. Sulfate, like most anions, is somewhat mobile in soils and therefore subject to leaching. Soil conditions where S is most likely to be deficient are low organic matter levels, coarse (sandy) texture with good drainage, and high rainfall conditions. But, these are generalizations and S can be deficient under other conditions as well.

Several factors should be taken into account when making S fertilization decisions. Among these are crop and yield goal, soil and plant analysis, organic matter content, soil texture, and contribution from other sources such as irrigation water and manure. High yielding forage crops such as alfalfa and hybrid bermudagrass remove more S than most grain crops and tend to be relatively responsive. Soil test S is usually a measure of sulfate-S, and as with nitrate-N samples should be taken deeper than normal (0 to 2 ft.) because of sulfate mobility in the soil. Soils containing less than 2% organic matter are most commonly S defiient; however, deficiencies do occur in soils with higher organic matter. Coarse textured soils are more apt to need S, but finer textured soils can also be deficient. Sulfur content of irrigation water should be determined since in some cases it can deliver signifi cant amounts of S.

There are several S fertilizer sources available. Most soluble S fertilizer contains sulfate, but others such as bisulfites, thiosulfates, and polysulfides are also available. The most common insoluble S fertilizer is elemental S, which must be oxidized to sulfate before plants can use it. This is a biological process and is affected by temperature, moisture, aeration and particle size. This process also produces acidity, and elemental S can be used in some instances specifically to acidify soils.

Sulfur is an important component of complete and balanced crop nutrition, and has justifiably gained more attention in recent years.Several factors should be considered to make the best decision regarding S need and fertilization.

-WMS-

For more information, contact Dr. W.M. (Mike) Stewart, Southern and Central Great Plains Director, IPNI, 2423 Rogers Key, San Antonio, TX 78258. Phone: (210) 764-1588. E-mail: mstewart@ipni.net.

Abbreviations: Mg = magnesium; Ca = calcium; P = phosphorus; N = nitrogen; S = sulfur.