When can you expect soybeans to respond to fertilization? How large is a response likely to be? How much fertilizer will be needed to obtain the maximum economic response? These are questions that College of Agriculture personnel must answer in making recommendations. Farmers should also consider these questions when deciding how much fertilizer to use

Rasnake, Monroe

English

University of Kentucky

University of KentuckyUKnowledgeSoil Science News and Views Plant and Soil Sciences6-1983Soybean Response to FertilizationMonroe RasnakeUniversity of Kentucky, mrasnake@uky.eduRight click to open a feedback form in a new tab to let us know how this document benefits you.Follow this and additional works at: https://uknowledge.uky.edu/pss_viewsPart of the Soil Science CommonsThis Report is brought to you for free and open access by the Plant and Soil Sciences at UKnowledge. It has been accepted for inclusion in Soil ScienceNews and Views by an authorized administrator of UKnowledge. For more information, please contact UKnowledge@lsv.uky.edu.Repository CitationRasnake, Monroe, "Soybean Response to Fertilization" (1983). Soil Science News and Views. 168.https://uknowledge.uky.edu/pss_views/168COOPERATIVE EXTENSION SERVICE ~epartment of Agronomy Soil Science News&Views Vol. 4, No. 7 June 1983 Soybean Response to Fertilization Monroe Rasnake • When can you expect soybeans to respond to fertilization? How large is a response likely to be? How much fertilizer will be needed to obtain the maximum economic response? These are questions that College of Agriculture personnel must answer in making recommendations. Farmers should also consider these questions when deciding how much fertilizer to use. • Answers to questions such as these must be found in the results of tests ~one by researchers in Kentucky and other states. For example, in the case of potash fertilization of soybeans, one of the most dramatic responses was obtain~d in a North Carolina test. The soil was a sandy loam and tested very low in potassi~. The response was from seven bushels per acre with no potassium added to 48 bushels per acre with about 90 pounds of potash per acre added. This was an extreme example. A more normal expected yield increase on soils testing low in potassium might be about 25 percent, or for example, from 28 to 35 bushels per acre. On soils testing medium in potassium, yield responses are less likely to occur and will be mucr smaller. Soils testing in the high range are not likely to re$pond to added fertilizer. The story on soybean response to phosphorus fertilization is very similar to that of potassium. This is illustrated very well by the following table: Soybean Response to Phosphorus Fertilization* Phosphate (lbs/a) Soil Test 0 40 80 ----------- yield (bu/a) -------------Very Low 11 27 37 Low 33 39 41 There was a good response to phosphorus at both soil test levels, but the low soil test did not respond as much as the very low soil test. When the soil test reaches the medium level or higher, yield responses to added phosphorus are unlikely. *Bulletin Y-69. Soybean Production, Marketing and Use. NFDC-TVA 1974. The College of Agriculture Is an Equal Opportunity Organization wtth respect to education and employmen t and tsaut hortzed to provtde research. educational lnfonnalion and other services only to individuals and lnstitullons that function without regard to race. color. national ortgtn. sex. reltgton. age and handicap. tnqulrtes regarding compliance with Title VI and Title VII oflhe Civi l RlghlsActof 1964. Title lX of the Educational Amendments. Section 504 of the Rehabilitation Act and other relaled ma tters should be directed to Equal Opportunity Office. Kentucky Cooperative Extension Service. University of Kentucky. Room S-105. Agrtcult ural Science Buildi ng-North. Lexington. Kentucky. 40546. UNIVERSITY OF KENTUCKY, KENTUCKY STATE UNIVERS ITY, U.S. DEPARTMENT OF AGRICULTURE, AND KENTUC KY COUNTIES, COOPERATING Soybean Response to Residual Fertilizer Not all the fertilizer applied for a crop is used, Often this unused ferti-lizer (especially phosphorus and potassium} remains in the soil and can be used by future crops. This is basically what happens when we build soil test levels. A UK experiment conducted at Lexington to see how potash applied in previous years would affect soybean yields gave results illustrated in the following graph: -------------0 0 -------------0 Late Planted Beans Medium Potassium Soil Test Levels High The low, medium and high soil test levels resulted from different rates of potassium fertilization in prior years. The difference between the low and high soil test levels is about the same response as might be expected by adding potash fertilizer to soils testing low in potash. Response to Nitrogen (N) Fertilization • Soybeans are heavy users of N. Fifty bushels of beans contain about 200 pounds of N. Add to this the 50 pounds contained in the stems and leaves and we see that a 50 bushel bean crop must take up 250 pounds of N. A test with uninoculated soy- • beans in North Carolina had a yield of 18 bushels per acre when no N was added. With 200 pounds of N/A, the yield increased to 43 bushels per acre. This shows that large amounts of N must be available for high bean yields. Fortunately, when soy-beans are well nodulated, they are capable of providing their own N. For this reason, well nodulated soybeans very rarely respond to added N. ~espouse to Minor Elements The University of Kentucky does not predict response of soybeans to minor elements based on soil analysis of these nutrients. Rather, the likelihood of re-sponse is based on previous experiences with observed deficiencies in a specific area or on the soil pH. Only two minor element deficiencies of soybeans have been observed to any extent in Kentucky. These are molybdenum and manganese. Both are closely tied ·to soil pH. Molybdenum responses might occur when the soil pH falls below 6.2. Manganese problems are mainly confined to terrace and bottomland soils in McLean, Hopkins, and Daviess Counties. These soils are usually not well drained and have a pH of 6.5 or above. The higher the pH, the greater likelihood of manganese deficiency. 

Soybean Response to Fertilization

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Soybean Response to Fertilization

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