Alfalfa is popular with producers because many varieties are grown successfully across the United States. These varieties flourish in the mean annual temperatures of Alaska (-25° C) and the high arid temperatures of California (50° C). Drought conditions result in only a moderate yield decline when compared to other forage crops such as red clover (Trifolium pratense) or birdsfoot trefoil (Lotus corniculatus). Along with alfalfa’s adaptability to harsh climates, it also grows well in either an irrigated or dry land areas (Barnes and Sheaffer, 1995).

Research has shown that phosphate and potassium fertilizers increase total yields. Limited research has been conducted to assess the quality of the increased yields. Therefore the objective of this study is to investigate whether the nutritive values are increased with phosphate and potassium applications.

Alfalfa (Medicago sativa L.) originated in Iran, but many related legume species closely resembling alfalfa have been found scattered across central Asia and Siberia. Colonial Americans introduced alfalfa to North America in the late 1730s, and subsequently Spaniards brought alfalfa to the southwest region in the late 1850s. This South American strain spread from what is now Kansas to northern California (Barnes, et. al, 1995).

In present times alfalfa has become one of the most important forage crops. It is grown in all of the fifty states. Approximately ten to eleven million hectares of alfalfa have been grown in the United States over the last decade. Alfalfa is predominately grown in the north central U. S. were fifty-seven percent of all domestic alfalfa is produced. Western states produce approximately twenty-five percent of the annual harvest with the difference produced on the East Coast (Barnes, et. al, 1995).

Forages, such as alfalfa, are a primary source of livestock rations in the United States, accounting for about sixty-two percent of forages fed to livestock. Cultivated forages occupy 25 million ha of continental cropland and are accredited over 130 million metric tons of dry matter production (Albrecht and Hall, 1995). During the past two decades forage cropland has remained constant, but forage production has increased by approximately thirty percent as a result of advances in technology.

Alfalfa is a perennial legume with a pinnate alternating trifoliolate leaf arrangement along the stem (Teuber and Brick, 1988). Mature alfalfa plants have numerous stems sprouting from a central crown ranging from five to twenty-five stems. The crown is formed at the cotyledon node (seedling growth), with further growth of tertiary stems, which also start at this point. Alfalfa has a distinct taproot system that can penetrate seven to nine meters into the soil. Alfalfa root systems are commonly branched in the upper two meters of the soil (Barnes, et. al, 1995). Approximately sixty to seventy percent of the total root mass of this legume is concentrated in the upper 15 cm of the soil profile (Heichel, 1982).

Seeding of alfalfa generally occurs in early spring or late summer. Seeding time is determined by annual rainfall patterns, whether they occur in late spring or early autumn. These calculated planting times are critical because alfalfa is highly sensitive to precipitation during early growth (Barnes, et. al, 1995).

Alfalfa is also highly sensitive to soil reaction. A reaction level ranged from 6.5 to 7.0 is required to receive maximum yields of forage production (Lanyon and Griffith, 1988). Soil reaction levels also influence nitrogen fixation and availability of essential elements such as phosphorus, potassium, sulfur, and boron (Barnes, et. al, 1995).

Alfalfa is commonly called the "Queen of the Forages" because it provides the highest feed value of all commonly grown hay crops (Marten et al. 1988). Protein production of alfalfa per unit grown is greater than oil seed or grain crops. Furthermore, optimal utilization of alfalfa occurs when it is included in a high energy, corn-based ration. Alfalfa contains 10 different vitamins present and is a major source of Vitamin A (Barnes, et. al, 1995).

Processed forages in the form of hay, silage, haylage, or dehy provide the feed required by livestock during the winter months. The type of processing depends on harvesting practices, location, and moisture levels of the forage (Barnes, et al., 1995).

Forages are commonly baled and stored in the form of hay for feeding of livestock. Quality of sun-cured hay is determined by stage of maturity at harvest. As the forage increases in maturity the protein levels and digestibility of the forage decreases. Curing of hay occurs after the forage has been harvested. Sun curing is efficient as long as relative humidity stays below seventy percent. Relative humidity levels above seventy percent will effect the moisture equilibrium between the hay and atmospheric moisture resulting in insufficient drying of the hay. Storage of hay can either be inside or outside. Hay bales stored outside run the risk of damage from climatic elements such as precipitation and heat exposure (Barnes, et al., 1995).

Precipitation has two adverse effects on hay. During the curing process, precipitation will cause the hay to delay in drying. Furthermore, the leaching effects of water will decrease both dry matter and nutritive values. Heat exposure will damage hay that is stored at high moisture levels. Heat damage will change the color of the hay from green to brown and decrease the crude protein (CP) and dry matter (DM) levels. Additionally, high levels of moisture and heat will promote oxidative reactions, which may result in spontaneous combustion of the hay. Spontaneous combustion occurs on the external rim of the stack because of an oxygen rich environment, as opposed to anaerobic microbial activity that is highly concentrated near the center (Barnes, et al., 1995).

An important factor governing hay quality is maturity of the harvested plants, regardless of the forage species. Greater maturity of plants results in lower digestible dry matter (DDM), proportionally declining crude protein content. Leaves, the most digestible part of the plant, have a higher nutrient content at early maturities than stem tissue at early maturities. As forages age, leaf to stem ratios increase. Stems have greater amounts of neutral detergent fiber, which will decrease the relative feed value (RFV) (Barnes, et al., 1995).

Another important aspect of forage production is proper soil fertility. Phosphorus is a macronutrient utilized by the plant for energy transfer and storage. Most every metabolic reaction of any significance proceeds from phosphate derivatives (Tisdale, 1985). The high alkaline soils in Trans-Pecos Texas fix a large portion of phosphorus, making it unavailable for the plant. To compensate, many producers apply large amounts of phosphorus fertilizer (Tisdale, 1985).

Soil reaction highly affects alfalfa production. Alfalfa requires a range of 6.5 to 7.0 for nodulation and increased nitrogen fixation (Barnes and Sheaffer, 1995).

Phosphorus is utilized in large amounts by plants for energy transfer and storage. Most metabolic reactions involve phosphate derivatives (Barnes, et al., 1995).

Excess calcium carbonate in soil reduces phosphorus absorption. Ca²⁺ ions bond with phosphates to fix phosphorus making it unavailable to the plant (Tisdale, 1985). This reaction occurs in the upper layer of the soil where the primary root system of the alfalfa plant is located (Albrecht and Hall, 1995). To counter this reaction, the application of phosphate fertilizer is required to raise the available soil phosphorus amount to adequate levels.

Furthermore, soil pH affects the rate of soil phosphorus becomes fixation. Phosphorus fixation by aluminum oxides and iron occurs at low soil pH, whereas phosphorus fixation by calcium and magnesium occur at high soil pH (Tisdale, 1985). Phosphorus promotes root growth in young seedling legumes and grasses (Tisdale, 1985). Furthermore, it is also utilized by the plant from gene encoding to being primary mechanism of energy transfer (ATP) (Albrecht and Hall, 1995).

Phosphorus fertilization increases nitrogen and phosphorus uptake within pasture-grown alfalfa (Barnes, et al., 1995).

Applied superphosphates (20% superphosphate, Ammo-Phos (11-48-0)) have shown to increase phosphorus nutrients within alfalfa. Plant phosphorus was shown to have increased one third when applied to alfalfa cropland in calcareous soils of New Mexico (Hinkle, 1942).

When applied to barley at rates of 30kg/ha, phosphorus fertilization would yield 20mg/kg of soil. Assumed fertilization is mixed with the top fifteen centimeters of soil. Increased amounts of P were noted proportionally in the dry matter harvests (Orphanos, 1995).

Ionic potassium (K⁺) is required in its form as a catalyst. Metabolic functions include water transfer at the cellular level, assimilation of ATP, nitrogen uptake, starch synthesis, and protein synthesis. Furthermore, potassium increases tolerance to cold weather, drought, disease, and insects by plant. Potassium fertilization directly increases hay yields (Barnes, et al., 1995). Thus it is important to maintain a potassium rich soil.

Low concentrations of magnesium, calcium, and potassium in cool season grasses during early spring and late fall may cause pasture poisoning in grazing cattle. A study of relationships between phosphorus levels and amounts of these other elements showed that with the increase of phosphorus, levels of magnesium, calcium, and potassium uptake from the soil increase making the grass harmless to the grazing cattle (Reinbott and Blevins, 1990).

Potassium occurs at concentrations of 1.9% in the earth’s crust, and is found in relatively large quantities in most soils. Directly correlated soil potassium and potassium levels within legumes have shown to produce higher yields (Duke, 1980).

After the fifth year of production it is important to maintain a proper balance of phosphorus and potassium. Tested results have shown that there is usually twice the yield when phosphorus and potassium are added to the fertilization mixture than when not added (Barnes, et al., 1995).

Dietary phosphorus occurs as inorganic phosphates and organic phosphoproteins, phosphorylated sugars, and phospholipids. Amounts of inorganic and organic phosphorus depend on the animal’s diet, though most phosphorus is absorbed in inorganic forms. Organic phosphorus is hydrolyzed enzymatically in the lumen of the small intestine to release inorganic phosphates (Groff, et. al, 1995).

Phosphates are utilized primarily for the development of skeletal tissue, which contains eighty-five percent of the total phosphate store. In bone formation phosphorus is a component of calcium phosphate (Ca₃[PO₄]₂). Phosphorus not incorporated within the bone structure is found in intracellular or extracellular fluids. As with plants, the main function of phosphrorus is energy metabolism. Phosphate is a component of nucleic acids (DNA and RNA). Furthermore phospholipids partly make up the cellular membranes which allow passage of nutrients and wastes from cells (Groff, et. al, 1995).

Potassium absorption within the body is ninety-eight percent intracellular, where it is the major intracellular cation (Groff, et al., 1995).

The cropland where this study was located is runs along Monumant Draw. Soil classification of the study area is Iraan silty clay loam (Rives, 1977).

The A horizon is 28 inches in depth. It consists of dark grayish brown silty clay loam. Limestone pebbles are present with a moderately alkaline boundry at approximately seven inches. The remainin twenty-one inches are also dark grayish brown with moderately alkaline barrier. The B horizon ranges from twenty-eight to sixty inches. Soil color is brown, consisting a moist silty loam.

This study was conducted in a pivot irrigated alfalfa field located at McKenzie Land and Livestock Inc. in Ft. Stockton, Texas. A preliminary soil analysis was conducted on ten random samples collected from each plot. Soil samples were analyzed to determine the available phosphorus.

Applications of the fertilizers were conveyed through the use of a standard ground rig. Monoammonium phosphate (48% P₂O₅, and 11-48-0 Nitrogen) was applied at rates 170 and 340 lbs. per acre followed by an application of potassium in the form of soluble potash (0-0-60 K₂O). It was applied to the upper half of each plot using a fixed rate of 120 lbs. per acre.

Hay harvested from four cuttings were measured yield using a convential tractor-trailor scale. Random core samples drawn from individual bales two to three days after harvest. Hay samples were pooled within each treatment and analyzed for dry matter (DM), crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF), gross energy (GE), phosphorus (P), and calcium (Ca).

Dry matter of alfalfa samples was determined by oven dry procedure. All samples were weighed and dried at 110°C for twenty-four hours, and then reweighed. Dry matter equivilents of field dry samples were used in calculating the remaining analysis (AOAC, 1990).

Crude protein was determined by Kjeldahl procedure, by using a Kjeltec System I micro-Kjeldahl apparatus. One gram samples were digested in 25.0 mL of 36N sulfuric acid(H₂SO₄) with a Cupiric Sulfate/Potassium Sulfate catalyst. Samples were heated at ~420°C for approximately seventy-five minutes in the digester to degrade crude protein to ammonia. The solution was cooled, swirled, and diluted to 75mL with distilled water. The digested sample was then distilled into a recieving flask containing the Kjelsorb trapping solution(Boric acid solution premixed with methyl red and bromocresol green indicators). Final determination of crude protein was assessed by titration of the trapped ammonia with 0.504N sulfuric acid (AOAC, 1990).

Available phosphorus analysis was determined by the Molybdate method. Half gram samples were extracted in a 0.93N hydrochloric acid (HCl) and 1.5N ammonium acetate (C₂H₃O₂) buffer solution. After the extract had been stirred for 30 minutes, a pre-mixed reagent (Phosver3Ô ) was reacted with the available phosphorus present in the extract. A Spectro UV-VIS RS spectrophotometer was used to determine the transmittance of light through the extract. Further calculations then yielded the total amount of available phosphorus (AOAC, 1990).

Acid detergent fiber (ADF) and neutral detergent fiber (NDF) were analyzed using the Ankom filter bag method with an Ankom²⁰⁰ fiber analyzer. Half gram samples were thermally sealed in filter bags for digestion. Two thousand milliliters of a premixed solution of 1N sulfuric acid mixed with cetyl trimethylammonium bromide was used for ADF analysis. The NDF digestive solution consisted of a premixed powder (30 g sodium lauryl sulfate, 18.61 g ethylenediaminetetraacetic disodium salt, 6.81 g sotium tetraborate decahydrate, 4.56 g sodium phosphate, and 10.0 mL trethylene glycol) to 1 liter of distilled H₂O. Fiber analyses were conducted with only slight differences in procedure. The samples were digested for one hour then rinsed with three applications of 2L of distilled H₂O. The NDF digestion required four milliliters of alpha amylase and twenty grams of sodium sulfite, and an additional four milliliters of alpha amylase for rinse one and two. Excess moisture was removed by soaking the samples in acetone with the final moisture removed using a drying oven. Samples were then weighed to obtain the final weight of the sample minus the digested fiber (AOAC, 1990).

Data was analyzed using a factorial analysis of variance (ANOVA) and the least significant difference (LSD) tests. Factorial data was organized by treatments of MAP and potassium. Mean nutrient values were organized by cut and treatments. Statisitical analysis was performed using the SAS statistical program (Zar, 1996).

Dry matter and CP results are numerically listed in Table 1. Sun-cured alfalfa harvested at early bloom has a mean CP value of 19.9% when determined on a dry matter basis (NRC, 1989). The mean value of T5 was 24.42% after the first harvest, but later yields of this plot showed lower values. Plots C, T1, T2, T3, and T4 had average values throughout the growing season when compared to the NRC.

Acid detergent fiber and NDF values are listed numerically in Table 2. Harvest one and two indicated a lower concentration of fiber (ADF and NDF). Mean values of ADF and NDF are 31.9% and 39.3% respectively (NRC, 1989). The seasonal values of T1 showed a reoccurring decrease in ADF throughout the growing season. Third harvest results indicated an increased amount of NDF. Lower values of ADF and NDF directly affected digestible dry matter (DDM), relative feed value (RFV), and dry matter intake (DMI). Significant improvements were shown when comparing these values with different cuts, MAP applications, and potassium applications.