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Tomatoes 2008
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Description
The metal is the seventh most abundant and makes up about 1.5 % by weight of the earth's crust. Potassium is an essential constituent for plant growth and it is found in most soils. It is also a vital element in the human diet. Potassium is never found free in nature, but is obtained by electrolysis of the chloride or hydroxide, much in the same manner as prepared by Davy. It is one of the most reactive and electropositive of metals and, apart from lithium, it is the least dense known metal. It is soft and easily cut with a knife. It is silvery in appearance immediately after a fresh surface is exposed. It oxidizes very rapidly in air and must be stored under argon or under a suitable mineral oil. As do all the other metals of the alkali group, it decomposes in water with the release of hydrogen. It usually catches fire during the reaction with water. Potassium and its salts impart a lilac color to flames. Potassium fertilizersPotassium occurs in the soil in three forms: as exchangeable (available) potassium (K+) adsorbed onto the soil CEC; fixed by certain minerals from which it is released very slowly to available form; and in unavailable mineral forms (most of the potassium in soils). Plants take up potassium as the K+ ion. The common source of fertilizer potassium is muriate of potash (0-0-60), which chemically is potassium chloride (KCl). Potassium chloride is highly water soluble. At excessive rates, muriate of potash can cause salt damage to plants. Other potassium materials used in specialty fertilizers also are listed in Table 1.2-11. Blended fertilizersBlended fertilizers are made by physically mixing fertilizer materials to give a desired grade. The individual particles remain separate in the mixture, and segregation may occur. This problem can be reduced by using materials with the same particle size. In granulated complete fertilizers, as contrasted to blended ones, each particle contains all of the nutrients in the grade. For example, a 10-20-10 blend contains individual particles of the nitrogen, phosphorus, and potassium sources used. In a granulated 10-20-10 fertilizer, each particle theoretically contains 10% nitrogen, 20% phosphate, and 10% potash. If properly made so as to reduce segregation during transportation and application, blends generally are equal in agronomic effectiveness to granulated complete fertilizers. Blends have the added advantage of allowing a very wide range of fertilizer grades, thus making it possible to match a fertilizer exactly to a soil test recommendation. When using a blend as a starter fertilizer, avoid urea and diammonium phosphate as ingredients. Both materials produce free ammonia, which can hurt seed germination and seedling growth. Granulated complete fertilizer and ammoniated fertilizer often are confused. Most granulated complete fertilizers are ammoniated; any blended fertilizer that contains DAP, MAP, or ammonium polyphosphate also is ammoniated. Fluid fertilizersFluid fertilizers are becoming more and more common. The latest fertilizer statistics for Pennsylvania indicate that nitrogen solution (UAN) is the most common source of nitrogen used in the state. Multinutrient fluid fertilizers also are becoming more popular. The fluid fertilizers may be categorized into two groups: clear solutions and suspensions. In clear solutions, nutrients are dissolved completely in water. The major advantage is in handling. The disadvantages are the generally higher price and lower possible analysis compared to dry fertilizers, especially when the material contains potassium. Suspension fertilizers are fluids in which the components' solubility has been exceeded and in which very fine undissolved particles are kept from settling out by the inclusion of clay. Again, the major advantage of these materials is in handling. Suspensions also can be formulated at much higher analyses than can the clear solutions. Analyses similar to those for dry materials are possible. The major disadvantage of suspensions is that they require constant agitation, even in storage. Furthermore, suspension fertilizer cannot be used as a carrier for certain other chemicals. The bottom line in comparing fluid fertilizers with dry fertilizers on the basis of amount of plant food, is that they are equal in agronomic effectiveness when each is used properly. Remember, when making calculations of fluid fertilizers, that the analysis is given as a weight percentage, not on a volume or "per-gallon" basis. Most fluids weigh between 10 and 12 pounds per gallon. The following is an example to illustrate the calculations. One gallon of the 10-34-0 liquid weighing 11.4 pounds per gallon contains: It would take about 9 gallons of this liquid to equal 100 pounds of a dry material with the same analysis. For comparing fluids on a price-per-ton basis, divide the weight per gallon into 2,000 to get the number of gallons per ton. In the above example, the calculation is: This conversion can be used to compare a liquid priced in dollars per gallon with a solid priced in dollars per ton. MANURE NUTRIENT MANAGEMENTApproximately three-fourths of the nutrients harvested in crops grown on a farm, and in the purchased feed and supplements fed to the livestock, may be recycled back to crop fields in manure. Thus, manure nutrient management always has been and continues to be an important economic consideration on farms with livestock or poultry. There is growing concern, however, about the effect of nutrient management on environmental quality. A nutrient management law requiring some farms with high animal concentrations to have a formally approved nutrient management plan went into effect in Pennsylvania in October 1997. This law affects farms that have more than 2 animal equivalent units (AEUs) per acre. (One AEU = 1,000 lb of live weight of any animal.) Environmental concerns thus add to the importance of proper nutrient management on all farms in Pennsylvania. Nutrient management is not the same for all farms. It is important to recognize the differences among farms and realize how they affect the choice of appropriate management strategies. As an aid for determining the appropriate nutrient management options, farms can be classified into the following three management categories. Category 1-Less than 1.25 AEUs per acre routinely manured, or less than 50% of the feed coming from off the farm. Available manure on these farms generally is not adequate to meet total crop nitrogen needs. Thus, additional nutrients in the form of purchased fertilizer or other sources are required for achieving optimum crop yields. Usually, because of the nutrient deficit, these farms are not as likely to cause environmental problems unless there is gross mismanagement. Nutrient management plans for this type of farm emphasize practices designed to make the most of nutrient efficiency and achieve the maximum crop response from manure nutrients. A well-planned nutrient management program emphasizing economic and agronomic efficiency should reduce the need for purchased inputs and thus should improve farm profitability. Category 2-1.25 to 2.25 AEUs per acre routinely manured, or 50 to 80% of the feed coming from off the farm. Available manure on these farms can meet a significant part, if not all, of the nitrogen requirements for crop production. Because these farms often are at the upper limit of being able to safely handle all the nutrients produced, nutrient management changes on these farms may offer potential environmental benefits. Practices to maximize the safe use of manure and to balance nutrient inputs with removals from farm fields are emphasized, rather than nutrient use efficiency. The economic return from improved nutrient management on this category of farm is likely to be minimal. That is, a large cost probably will not be associated with implementing improved nutrient management practices; but unlike the first category of farm, little profit incentive exists either. The incentive for change on this category of farm is environmental protection. Category 3-More than 2.25 AEUs per acre routinely manured, or more than 80% of the feed coming from off the farm. Manure on these farms generally exceeds nitrogen requirements for crop production. It is unlikely that all of the manure can be used safely on these farms. Only part of the nutrient management program is field based. A significant component involves off-farm cooperation for acceptable off farm uses for the excess manure. An economic cost is likely to be associated with implementing an environmentally sensitive nutrient management plan for this category of farm. Nutrient management programming most likely will result in environmental benefits, as excesses on the farm are reduced. This simplified classification scheme is intended to demonstrate the
implications of differing situations for nutrient management approaches.
Individual farms in each category will not necessarily fit all the
characteristics described for the category. When a question exists about the
classification, it should be resolved based on more comprehensive, specific
information. The animal unit criteria in the categories above are for
nitrogen-based planning. These criteria should be cut in half for phosphorus-
based planning purposes. Phosphorus vs nitrogen manure ManagementIn most cases nutrient management plans are based on balancing nitrogen. This is based on our scientific understanding of nitrogen behavior and generally greater concerns with the environmental fate of nitrogen and the potential negative human health effects of nitrates in water. Recently, however, attention in nutrient management has been shifting from nitrogen to phosphorus. Phosphorus is an essential nutrient for crops. A critical component of crop production is managing phosphorus for optimum economic benefit. However, if phosphorus is allowed to move off the land and get into water, it can be a pollution problem. Unlike nitrogen, excess phosphorus is not toxic but can result in eutrophication of water bodies. Eutrophication is the increased growth of undesirable algae and other aquatic plants, which limits the use of the water for drinking, fisheries, recreation, and industrial use. Historically, a major source of phosphorus in water was wastewater treatment plants. However, as the amount of phosphorus getting into water from this source has been reduced, agricultural sources of phosphorus have gotten more attention. Manure in particular has been identified as a source of phosphorus to the environment. Agriculture has evolved toward greater and greater specialization. Consequently, animal feed is often produced in a different location from where the animals are fed. Feed containing phosphorus is transported to the animals. However, the manure containing much of the phosphorus that was in the feed is spread locally and not recycled back to where the crops were produced. This has resulted in phosphorus accumulating in excess amounts in some areas of high animal concentration. At the same time, we have long recognized that one of the consequences of basing nutrient management plans on nitrogen is that, in most cases, excess phosphorus will be applied to the soil because the nutrient content of manure does not match the nutrient requirement of most crops. On the other hand, if the phosphorus requirement of the crops is balanced with the phosphorus in manure, two to four times as many acres are required to utilize the manure, and nitrogen fertilizer will be required to meet the needs of the crop. This is not an ideal situation, but from our understanding of phosphorus behavior we know that there are things that we can do to minimize the environmental impact of this excess phosphorus in many cases. Consequently, we have consistently emphasized that, while the official guidelines for manure management are based on nitrogen, we cannot ignore phosphorus. This is the reason for including practices such as soil and water conservation, balancing manure applications over crop rotations, cover crops, etc. in nutrient management plans. Research has shown that a majority of the phosphorus from agricultural fields lost to water comes from a limited area in most watersheds and from a few storm events. There are two factors that must be considered in developing effective management strategies. For nutrient loss to occur, there must be a source of phosphorus and there must be a mechanism for transporting it to the water. A key concept to effectively managing nutrient pollution is to focus on where these two factors overlap; i.e., a high source coupled with high transport. Tools to help identify where these critical source areas are, and to suggest manure management strategies to address these areas, are being developed. Since agriculture is changing rapidly, farm classifications may change with
time. Therefore, farmers periodically should evaluate their farm's nutrient
management status to adjust their strategy as appropriate. More detailed
evaluation of fields and practices will be necessary to identify specific
management options or best management practices (BMPs) for each individual
situation. Since manure is an important component of nutrient management on crop
and livestock farms, the following sections discuss some of the specific
properties and management of manure where field application is an appropriate
strategy for the farm. Manure is a good source of all crop nutrients, including the major and micronutrients, but nitrogen (N) generally is the manure nutrient with the greatest value and often the highest potential for pollution. Therefore, manure is best used for crops that have large N requirements. Average amounts of N, P2O5, and K2O in manure for various animal types are shown in Table 1.2-13. Although these values are good average figures, they are inadequate if you wish to accurately account for manure nutrients on your farm. Analyzing a sample of well-mixed manure is essential for good manure nutrient management. For best results when submitting a manure sample for analysis, sample the manure that is in the tank or spreader box being delivered to the field for application. Such samples will be most representative, because the liquid manure pit is likely to have been agitated in order to load the tank, and semi-solid manure scraped from the barn is moderately mixed after being loaded into a box spreader. Collect several samples of semi-solid manure from the box spreader, mix well, and fill a laboratory container three-quarters full. With daily haul manure-handling systems, periodically repeat this sampling procedure throughout the year. If liquid manure has been agitated well, one sample is sufficient to adequately determine the nutrient status of the manure in the pit. Take a sample from the tank and fill the laboratory container three-quarters full. Caution: do not completely fill the container; leave space for gas expansion. In many manure storage systems, there is considerable variation in the manure nutrient content, even within the storage unit. For example, in a liquid manure storage, the phosphorus content may be higher in the bottom of the storage than in the top. Also, because the ammonium nitrogen can vary with depth in the storage, the manure nitrogen availability to the crop will change as the storage is emptied, unless there is adequate agitation. In these situations, no manure in the storage actually matches the average results from the analysis of a single composite sample. To overcome this problem, it is recommended that a detailed analysis of the manure be performed at least once after the manure storage is constructed to determine the amount and nature of the variation. The process involves sampling the manure periodically as the storage is emptied for field application. Samples may be taken every so many loads or whenever a significant change in manure consistency occurs. After this intensive sampling and analysis, the farmer will have a basis for making manure rate changes or supplemental fertilizer changes to compensate for the variation. If the management of the storage is constant, or if thorough agitation is accomplished, this intensive sampling may not be necessary every year. Previous results can be used to make adjustments in following years. On farms with a deficiency of nutrients, using manure can greatly reduce your fertilizer needs and thus their expense. On farms with an excess of manure, however, these nutrients can represent an environmental threat if they are not used properly. |