Alfalfa is a high producing, labor intensive, high cost and high return crop. Therefore, it only makes sense not to limit its production or longevity by establishing it on unsuitable soil or by the use of unsound fertility practices. It is the aim of this paper to propose practices which will not limit the production of alfalfa, but, also allow it to be done as efficiently as possible with only the necessary inputs

Murdock, Lloyd W.

English

University of Kentucky

-18-SOIL AND FERTILITY MANAGEMENT Lloyd W. Murdock Department of Agronomy, University of Kentucky Alfalfa is a high producing, labor intensive, high cost and high return crop. Therefore, it only makes sense not to limit its production or longevity by establishing it on unsuitable soil or by the use of unsound fertility practices. It is the aim of this paper to propose practices which will not limit the produc-tion of alfalfa, but, also allow it to be done as efficiently as possible with only the necessary inputs. Soil Alfalfa is a deep, taprooted plant that makes its vegetative production from stem growth from the plant crown. Therefore, the best soils for alfalfa production are deep, well-drained soils with a medium texture and brightly-colored subsoils. These soils store high amounts of water and won't put alfalfa under adversely wet conditions. Soils which fall in this group include Pembroke, Maury, Decatur, Elk and Memphis series. These types of soil more or less guarantee that the soil will not limit pro-duction. If these soils are available to a farmer, he should give high priority to establishing alfalfa on them. Alfalfa performance on deep, well-drained soils is superior because the subsoil pH is not lower than 5.5 and excess water doesn't remain in the profile for a long time. Excess water kills alfalfa both by impeding aeration anytime and by causing heaving during the winter. Even though the deep, well-drained soils are most desirable, rather good growth can be obtained with high fertility and good management on shallower soils, well-drained alluvial soils and soils with pans at depths of two and-a-half feet or greater. Such soils include the Eden, McAfee, Huntington, Collins, Zanes-ville, Mercer, and Grenada. Kentucky has a rather large acreage of soils which are not prime alfalfa soils but will support good alfalfa growth. If alfalfa is established on these soils, additional management is required. The soils with a pan that are only moderately well-drained will grow alfalfa successfully if adequate surface drainage is provided. Heaving can be a pro-blem, especially during the first year of production on these types of soils. This could probably be reduced by spring seeding. This would give the alfalfa a chance to establish a more extensive root system before winter. The acidity of the subsoils of these soils as well as shallower soils is important. Subsoils with extreme acidity effectively reduce root growth. Fields with long histories of good liming programs tend to have subsoils that are not acid. A good combination of drainage and pH substantially improves the success of alfalfa on pan soils. -19-The chances of successful alfalfa production are reduced on poorly drained soils such as Henry, Taft, Melvin, and Purdy. Soils subject to flooding would not be considered suitable. Fertility One of the most important links to a good fertility pro-gram is a proper pH. A pH of 6.5-7.0 gives an optimum range for activity of nitrogen-fixing bacteria and the availability of plant nutrients in the soil. Having the pH properly adjusted is especially important for stand establishment and for long-term maintenance of the stand. If the pH is below 6.0, there may be toxic amounts of aluminum and manganese that can inter-fere with alfalfa root growth. Keeping the pH above 6.0 removes the problem, but molybdenum may still be limiting. If the pH is not at least 6.2 at time of seeding, apply one pound of sodium molybdate (6.4 oz. of Molybdenum) per acre. Since molybdenum is not mobile in the soil, it should be incorporated. All legumes, including alfalfa, are especially responsive to phosphorus, and available phosphorus levels in the soil should be built to the high level and maintained there for prolonged high production. Responses to potassium is more dependent on soil type. Responses to potassium have been found consistently on Maury and Tilsit soils, but are not as dependable on soils like Pembroke and Eden. Soil testing will help in this respect. Seasonal removal of phosphate (PzOs) and potash (KzO) from the soil by a high yielding crop (5-6 tons hay/ac) is on the order of 75-100 pounds PzOs and 300-400 pounds of KzO per acre. This is why it is so important to maintain a high level of these nutrients in the soil. There are basically two approaches which can be taken to providing these high fertility needs in the soil. One way is to rapidly raise soil test to high by a large appli-cation of phosphate and potash, then maintaining it there with lower annual topdressing rates made largely to compensate for the difference between plant removal and what the soil can naturally supply. The other approach would be to fertilize each year on the basis of existing soil test levels. This program would require higher annual topdressing rates than the first approach. The U. K. College of Agriculture fertilizer recommen-dations are: -20-Phosphate and Potash (Higher rates will be necessary to get im-mediate build-up of soil test levels.) Soil Test Level High (over 60P, 250K) Medium (60-30P, 250-165K) Low (less than 30P, 165K) New Seedings lbs/a 0 0-100 100-160 0 0-100 100-160 Established Stands* 0 0-100 60-120 lbs/a 0 0-100 160-240 *For y2eld goals over 4 T/A, increase P205 by 30 lbs/a and K20 by 60 lbs/a. There is always the question of when to put the fertilizers on and if it should be split. Dr. Bill Thorn carried out an ex-periment near Elizabethtown on a Sonora soil to help answer these questions. Time of Fertilizer Application* 1 2 Fall (100%) Fall (50%) Early Spring (50%) Aft. 1st Har. (50%) Aft. 2nd Har. (50%) Yield of Hay (12% Moisture) 1980 1981 1982 Avg. ~------- Tons/ac ------~ 7.6 7. 8 7.5 8.3 8.2 8.1 6.0 6. 2 5.8 7.3 7.4 7.1 *Initial soil test was medium in P and K. The differences are small, although there does appear a small advantage to applying some or all of the fertilizer in the fall. The overriding factor is that the fertilizer is applied. Soil ·tests are very important in determining the amount of applied fertilizer on the maintenance of a stand: The average removal for a ton of alfalfa hay is about 14 bls/a of P 2o5 and 45 lbs/a of K2o. However, the additions of these "maintenance" amounts of fertilizer will probably not stabilize the soil test. This is due to the complex nature of soils. Therefore, soil test themselves become the overriding factor in the fertility program. Effect of and after P2o5;yr. Applied 0 90 135 180 K20/yr. Applied 0 100 150 200 -21-applied and removed P205 and K20 on soil tests before 6-years of alfalfa production on a Pembroke soil. 64 82 82 85 K20/yr. Removed 318 368 379 382 Soil Tests Before Study After Study March 1970 March 1976 lLb~s~/~a~c-------------- -55 55 55 55 21 97 145 155 Before Study After Study March 1970 March 1976 lbs/ac ---------------------240 145 240 195 240 260 240 363 Avg. Hay Yield T/a/yr. 5.65 6.23 5.98 6.05 Avg. Hay Yield T/a/yr. 6.07 6.33 6.48 6.13 The above table is from work done by Wells, Vaught and Driskill in Warren County. As you can see, the soil tests stabilized at a high level when fertilizer application rates were below the nutrient removal rate. It will depend a lot on the soil. Consequently, fertilizing by soil test is more accurate than using maintenance fertilizer based on the amount of hay removed from the field. Boron availability is often a limiting nutrient for alfalfa production, and alfalfa should receive 1.5-2.0 pounds of elemental boron (B) per acre per year. There is no universal response to boron in Kentucky but it is cheap insurance. 

Soil and Fertility Management

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Soil and Fertility Management

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