Soybeans - Liming and Fertilization Soybeans grow best on soils of medium to high fertility and with a favorable soil pH. Maximum yields are possible only when producers meet plot nutritional requirements and other basic production factors. Using the best soybean varieties and cultural practices will not allow soybeans to reach full potential unless soil fertility is properly managed. Adequate soil fertility helps reduce risks from weather stresses, diseases, and nematodes, allowing a plant to achieve maximum potential. Soil fertility often is overlooked in crop production. A 5-year soil testing summary by the Extension Soil Testing Laboratory at Mississippi State University found about 25 percent of the soil samples for soybeans tested low or very low in available phosphorous and potassium. In addition, less than optimum control of soil acidity limits production. The past economic status of soybeans, the large amount of rented acreage, and the fact many growers fail to recognize lime's importance contribute to reduced yields for Mississippi soybean producers. A frequent question is, "Should I fertilize my soybeans?" Yes, if they need it. Do not guess at soil fertility; have your soil tested regularly. The most economical thing available to soybean producers is a soil test.   Lime Needs Many Mississippi soils require lime to control soil acidity for soybean production. Lime requirements vary, and there is no way to guess the needs. Since lime is important and relatively expensive, a soil test accurately determines where and how much lime to apply.   Lime Quality and Economics Although almost half of the soil samples tested in the last 5 years indicate a need for lime, many producers failed to lime because of the high initial cost. Lime application, however, is an investment in the productivity of the land and lasts about three growing seasons. Vendors of agricultural liming materials are required by law to provide samples for state testing for calcium carbonate equivalent (CCE) and fineness of grind, and to provide the results to buyers. The CCE indicates relative purity of a liming material. The smaller the lime particles, the more rapidly they will neutralize soil acidity. Particles coarser than 10 mesh have little or no value for changing soil pH. It is impossible to predict if and when these large particles will dissolve and what impact they will have on the pH of the soil. Half of the particles finer than 10 mesh but coarser than 60 mesh, and all particles finer than 60 mesh, will likely dissolve and react with the soil within 4 years. Regulations adapted in 1997 define Mississippi Grades A and B for limestone-based agricultural materials. Grade A lime meets the standards used before 1997 (90 percent minimum CCE, 50 percent passing a 60-mesh sieve). Grade B lime allows for lower purity and a coarser grind (80 percent CCE, 30 percent passing a 60-mesh sieve). You can use the CCE and fineness information for a particular liming material in a simple calculation to estimate its effectiveness for neutralizing soil acidity. The following is an example for calculating the relative neutralizing value of a liming material: CCE 92 Percent passing a 10-mesh screen 94 Percent passing a 60-mesh screen 50 RNV= 0.92 X ([94 - 50]/2) + 50) = 66.2% In this formula half of the percentage of lime between sieve sizes 10 and 60 is added to the percentage passing the 60-mesh sieve (50 in this example). This sum is multiplied by the CCE value (0.92 for this liming material). This means about 66 percent of this sample will effectively change soil pH in an acceptable time period. You can use relative neutralizing values to adjust liming recommendations from soil testing laboratories and to compare prices of various materials. Recommendations are normally based on materials with CCE of 100 percent, so you need to adjust application rates to reflect the material actually used. You can calculate the economic value of different materials using RNV data. For example, to compare agricultural liming materials, one at $25 per ton with a 66 percent RNV, to one with an RNV of 85 percent at $30 per ton. You can determine the actual cost by dividing the price per ton by the RNV decimal value. $25/0.66 = $38 $30/0.85 = $35 This shows the material with the higher up-front cost actually is the more economic purchase based on its agronomic worth. Grade A lime meeting the minimum standards has an RNV of 63 percent, whereas the minimum standards of Grade B lime allow an RNV of 44 percent. Significantly more Grade B lime is necessary to equal the neutralizing power of Grade A lime at the minimum standards. Some producers are tempted to apply Grade B materials with the idea it dissolves at some unknown point in the future. Research shows coarse lime particles may take from 4 to more than 20 years to dissolve in the soil; therefore, application of cheap material with the hope it will eventually work is a poor business decision.   Molybdenum and Lime Relationships The minor element molybdenum generally is deficient in acid soils. The chance of a soybean yield response to molybdenum increases as soil pH decreases. Molybdenum is especially important where no lime will be used in the non-Delta region, on the Delta foothills, and on the sandy and silt loam soils of the Delta with a pH less than 6.2. When soil acidity is below 5.5, however, apply lime and molybdenum to achieve maximum yield potential. Molybdenum, however, has been found not to be needed on the heavy clay soils of the Delta, even at pH levels below 5.6. Molybdenum is not a substitute for lime but can help offset acidity problems.   Molybdenum Rates and Methods of Application Seed treatment is the most common and practical method of application. Use a material that provides half an ounce of sodium molybdate per bushel of seed. Uniform coating of each seed is important. Liquids applied at the processing plant or in the hopper provide better coverage than do dry powders. You might also use a material that is combined with a fungicide if it is needed. Foliar treatments also are effective when applied before bloom. For foliar sprays, use 1 ounce of sodium molybdate per acre in 10 to 20 gallons of water. Before mixing any pesticides, read label for instructions.   Yield Increases from Lime and Molybdenum Yield increases depend on several factors. For maximum benefit the first year, apply finely ground lime several months in advance of planting. (You may get some benefit from application just before planting.) Response to lime depends on how acid the soil is at the time of liming and the soil properties.   Fertilizer Soil testing is critical for determining fertility needs. Soybeans require moderate amounts of plant food for high yields. A 30-bushel yield removes 24 pounds of phosphate and 42 pounds of potash in the grain per acre. Some soils are high in fertility and can supply everything the plant needs; however, many soils require supplemental fertility for maximum production. Base fertilizer grade and application rate on soil and plant needs as determined by the soil test. Information and supplies for submitting soil samples are available at your county Extension office. Take soil samples at least every 3 years. If you do not apply fertilizer, test annually to determine the status of soil nutrients. In Mississippi many Delta soils have not required P and K fertilization for soybean production. However, you need to soil test to determine lime requirements and to monitor the soil levels of P, K, and organic matter. It is important to use soil testing for P and K management in the Hill section of Mississippi. It is not a "Best Management Practice" to apply insurance levels of fertilizer without soil tests. Phosphate not used by growing crops is attached closely to soil particles and, therefore, prone to loss by erosion.   Response to Fertilizer The important result of a soil test report is not the absolute number provided for P or K, but rather the index, or ranking of the soil sample, on a scale from very low to very high for each nutrient. Table 2 shows the likely yield response for each P and K index, as measured by the Soil Testing Lab at Mississippi State, and the required fertilizer to achieve maximum yield. The yield expected without any additional fertilizer is 35 to 80 percent of the potential yield for a very low phosphate index. To address this potential yield loss, 120 pounds of phosphate are recommended the first year of soybean production for a soil testing very low. For this particular index, phosphate fertilizer can then be lowered to 60 pounds per acre for subsequent soybean crops in a 3-year soil test cycle. These recommendations are designed to achieve maximum economic yield potential and not average yields. When index levels are high, or very high, response to fertilizer is difficult to achieve, and fertilization is not economical. Recommendations at the medium level are designed to maintain levels of nutrients in the soil against crop removal. Table 1. Expected response of soybeans to phosphorus and potash at various soil testing levels Level Yield expected without fertilizer Required fertilizer Phosphate Potash Phosphate Potash ..... % ........ .... lb/a ..... V. Low 35 - 80 50 - 80 120* 120 Low 75 - 96 75 - 96 60 60 Medium 92 - 100 92 - 100 30 60 High 100 100 0 0 V. High 100 100 0 0 * After first year, reduce to 60 lb/a   Sulfur Sulfur deficiencies in soybeans are seldom found in Mississippi. However, because of fewer complete fertilizers that contain sulfur, lower sulfur emissions from automobiles, improved smokestack-scrubber technology, and the sandy nature of many Mississippi soils, sulfur deficiencies are becoming more common in some crops. Soybeans may respond to sulfur on sandy soils or soils low in organic matter.   Other Secondary and Micronutrients Generally, there isn't a need for secondary nutrients (for example, magnesium) or micronutrients (for example, boron, zinc, or cobalt) to be applied to soybeans in Mississippi. Producers regularly see temporary iron deficiency symptoms (yellow leaves with green veins) in the high pH soils of the Black Belt region, but soybeans generally outgrow this condition. Treatments have failed to increase yield, and work is needed to address varietal tolerances. Manganese deficiencies occasionally occur in the flatwood region of the Gulf Coast. This deficiency also shows yellow leaves with green veins. Soil and plant analyses are beneficial in diagnosing these and other isolated cases of unusual deficiencies.   Nitrogen and Inoculation Research found no general need for nitrogen fertilizer when soybean roots are well nodulated. To ensure nodulation, inoculate the seed with a fresh source of commercial inoculant when planting on land not previously planted in soybeans or on land where soybeans have not been planted in 3 to 5 years. Inoculant applied dry in the hopper or prepackaged with molybdenum or fungicides may be ineffective. The best procedure is to buy the inoculant, molybdenum, and fungicide separately, as needed, and apply to the seed before placing in the hopper. Another option is to apply a granular inoculant directly in the furrow. Inoculants are live bacteria and if seed are left over at the end of the day, re-inoculate before beginning planting the next day.   Double-Cropping Fertilization Where you double-crop soybeans with small grains or ryegrass, you can apply all the recommended phosphate and potash for both crops combined or to either crop. Generally, it is more practical to apply all of the fertilizer during seedbed preparation for the small grain or ryegrass so you can plant soybeans with minimum delay. Extension Publication 1380, Double Cropping Soybeans, can provide more detailed information.   When and How To Fertilize Fall or spring applications of fertilizer are satisfactory on most soil types. Restrict fall applications of potash to soils with a CEC of 8.0 or above to avoid excessive leaching. Banded application of fertilizer places nutrients in the immediate root zone and improves fertilizer efficiency. When banding, be sure to offset the fertilizer several inches to the side and below the seed depth to prevent salt injury. Broadcast application is a common, convenient, and satisfactory means of fertilization if spreading is uniform. On very acid, low-testing soils, shallow incorporation and the use of low rates may reduce the effectiveness of broadcast fertilization. Banding is a better alternative in this particular situation.   Solid or Liquid Fertilizer When used properly and at equivalent rates of nutrients, dry- or liquid-mixed fertilizers are equally effective; therefore, base your choice on comparative costs, ease of handling, labor, and equipment requirements rather than on the differences in effectiveness. Revised by Dr. Alan Blaine, Extension Soybean Specialist, Dr. Larry Oldham, Extension Agronomist, and Dr. Keith Crouse, Extension Soil Testing Specialist. Mississippi State University does not discriminate on the basis of race, color, religion, national origin, sex, age, disability, or veteran status. Information Sheet 873 Extension Service of Mississippi State University, cooperating with U.S. Department of Agriculture. Published in furtherance of Acts of Congress, May 8 and June 30, 1914. Ronald A. Brown, Director Copyright by Mississippi State University. All rights reserved. This document may be copied and distributed for nonprofit educational purposes provided that credit is given to the Mississippi State University Extension Service. Visit: DAFVM || USDA Search our Site || Need more information about this subject? Last Modified: Wednesday, 12-Sep-07 13:44:58 URL: http://msucares.com/pubs/infosheets/is0873.htm Mississippi State University is an equal opportunity institution. Recommendations on this web site do not endorse any commercial products or trade names.