xt79kd1qh71t https://exploreuk.uky.edu/dips/xt79kd1qh71t/data/mets.xml Kentucky Agricultural Experiment Station. 1973 journals 210 English Lexington : Agricultural Experiment Station, University of Kentucky Contact the Special Collections Research Center for information regarding rights and use of this collection. Kentucky Agricultural Experiment Station Progress report (Kentucky Agricultural Experiment Station) n.210 text Progress report (Kentucky Agricultural Experiment Station) n.210 1973 2014 true xt79kd1qh71t section xt79kd1qh71t . *"·\`\llIIlF·4·· ¢“¤¤\\||II||"··:•,•• . `._ V .>·· IQQ §•• C \>`§`· \ Ag? : ° as i A Ai ¤> V ‘ ’ A E 2 Q ( , 5 EA < = °d S »· L ( < AAA?iA=P?5AA’A?AA:=A`1*TA “— . ‘§ 1. Y Q D- : = ° I E _ ·{’‘ `A — _ f A '>“_ N — ~ , » 1 A . ·· ` \A 1 , A ` L 1 E E *‘ » ·· . , A , Q m { Ei-n g E v_»W _ i» » 1 gn |- g) O ci 5 — A é E L A V ‘- Ag _ A ? AA §, \ A Q A v A AA A c '-‘ '_‘ = \ I ` _; , . ` 8 ” . i A A } x ¢ x O ¥ » AA A 1A / In I f`\` N ,A':°_ , . V V » , V “¥ *" {ki; · __¤ $5 u.; ;;.z,; _ * E * —*~* AA Ti $$5 I _ :5 ¤· wi .,2 `b A , Q A V A @-3 m 0 ·~ :5 ¢ Q 94 g ° Q A 2f ‘ \ ¤¤ ¢··»·\¤» ¤ % "‘ N n xy i ¥ W//4 [ '\ \\»®““ % \ "" ****W“‘ ` ’ * · , ~ ·<» A ,~ V , » ,,»V A 0 /’ ‘AVT AAFAYF · CONTENTS Page A Introduction ....................... 3 Soil Factors Influencing Temperatures ............. 3 Plant Response to Soil Temperatures .............. 4 Corn ...................... 4 F Soybeans .................... 5 . Sorghum .................... 6 Cotton ..................... 6 Tobacco ..................... 7 Vegetable Crops .................. 7 . Source of Soil Temperature Data ............... 8 Comparison of Soil Temperatures at Various Planting Depths .... 1 1 Annual Soil Temperature Cycle at Selected Locations ...... 12-21 Henderson .................... 12 Mayfield .................... 13 I Greenville .................... 14 Glasgow ..................... 15 Bardstown .................... 16 Somerset .................... 17 Williamstown ................... 18 Flemingsburg ................... 19 Lexington .................... 21 Freezing of Soils During the Winter Season ............ 20 i Literature Cited ...................... 23 ACKNOWLEDGMENTS The authors acknowledge assistance of personnel of the National Cli- matic Center, NOAA, for their evaluation of the soil temperature observa- tions and to the University of Kentucky Computing Center for help in the preparation of the annual temperature graphs. 2 {5-.- — $0Il TEMPERATURE CUMATOEOGY of KENTUCKY by JERRY D. HILL and ALLEN B. ELAM, ]R.* Soils have several physical characteristics which make them suited or, in some cases, un- suited for man’s use. In addition to a soil’s structure, texture, and profile, there are certain thermal characteristics which determine the temperatures to be experienced at various depths under given conditions of moisture and exposure. These conditions vary over a reasonably wide range, but there are fairly narrow limits in which they will frequently fall. The purpose of this publication is to discuss the effect of soil temperatures on several plant species, to present the . temperatures normally measured in the soil at a variety of locations, and to give a reasonable estimate of what might be expected at any particular time of year. - SOIL FACTORS INFLUENCING TEMPERATURE Except for a very small amount produced by biological processes, the source of all heat reaching the soil is solar radiation. The nature of the soil surface determines the amount of this radiation which will be absorbed and the amount reflected back into the atmosphere. The term "albedo" is normally used to characterize the ratio of radiation reflected to the total initially falling on the surface. Color plays an important role in determining the albedo, with dark soils E absorbing about 80% of the radiation falling on them and light-colored soils absorbing only about 50%. In mid-latitude locations, such as Kentucky, the direct rays of the sun always strike level soil at an angle and never from directly overhead, even in midsummer. Those soils on a south- facing slope face the sun and, thus, receive somewhat more concentrated radiation and have more heat available per unit area of surface than those on a level or north-facing slope. The sun’s energy absorbed by the soil is used initially to raise the temperature of the surface layer, then it penetrates downward to heat progressively deeper layers. The amount of heat required to change the temperature of a given volume of soil by 1 degree is called its heat capacity, while the rate at which it transfers heat downward is called the thermal conductivity. Both properties vary somewhat in a given soil, owing to its moisture content and the amount of air in the pore spaces. As for heat capacity, a typical soil requires about 0.3 calorie of heat energy to raise the temperature of a cubic centimeter of soil by I degree centigrade. For the water and air com- I ponents of the soil, these values are: water—1 calorie per cubic centimeter per degree Centigrade and air—0.00026 calorie per cubic centimeter per degree Centigrade, thus indicating that water requires a much greater amount of heat to raise its temperature by l degree than would an equal volume of air. As the soil surface warms, there is a transfer of heat downward, and the rate at which it proceeds varies with the thermal conductivity as noted before. Again, the values vary consider- ably, but some approximate magnitudes for thermal conductivity are: Silt loam soil - 0.002 calorie per square centimeter per second per degree C., Water - 0.001, Air - 0.00006. *Advisory Agricultural Meteorologist and State Climatologist (retired), NOAA, National Weather Service, respectively. 3 The low thermal conductivity of the air makes it a much less efficient transporter of heat than is soil, while water is of the same order of magnitude as the soil particles themselves. By comparing the values given for both the heat capacity and thermal conductivity, we see that soil with a high percentage of water in it requires more heat to change its temperature than does a dry soil; however, a wet soil conducts heat downward to the lower depths much better. A very dry soil with a large proportion of air in the upper layers would tend to have very high daytime temperatures near the surface but much less of a temperature change below 6 to 8 inches. __ The soil surface in contact with the atmosphere is the point of greatest heat exchange. ii During the day it receives heat from the sun, and at night the heat is radiated away. Since the heat capacity of the soil requires that it lose much more heat than the air before its temperature changes by 1 degree, the soil temperatures tend to remain much more stable than air tempera- tures. Under a sod cover, the soil temperature will have less than l degree variation during the day below a depth of about 20 inches. This means that at night and, usually, during the winter the deeper depths are warmer than the surface and heat flows upward, while on sunny days the surface is warmest and heat flows downward. PLANT RESPONSE TO SOIL TEIVIPERATURES Most biological responses take place at a rate determined directly by the temperature sensed by the organism. For the plant, photosynthesis proceeds at a rate determined by the leaf temperature. This is a complex interaction of air temperature, moisture availability, and the amount of solar radiation falling on the leaf. Many of the other plant processes such as germi- nation, nutrient uptake, and translocation, which take place below the soil surface, depend on the soil temperature at that depth. Since the soil temperature undergoes a daily cycle at most planting depths, we normally speak of a single figure, the daily average, which is the average of the daily high and low temperatures at that point. n Many researchers have studied plant response, particularly germination, in relation to soil temperatures, and it would seem appropriate to list some of their findings here for the principal crops grown in Kentucky. These studies have taken two main approaches, the first being a determination of emergence time required at various temperatures. The basic reasoning here is · that a long period under the soil surface exposes seed to avariety of pathogens and insects, thus reducing the chance of emergence and the probability of a satisfactory plant stand. The second approach is to determine the threshold temperatures below which and above which germination does not occur. Then an optimum range can be established where germination will be most rapid and likely. Since seed is an expensive production item and sometimes in short supply, soil temperatures are a key to obtaining maximum production from available resources. Corn The minimum temperature for germination of corn has been determined to be about 500 F, although the rate here is slow and the optimum would be somewhere above 60°. It would seem that corn planted in a seedbed at temperatures below 50° has very little chance for germination. The upper lethal temperature for the seed is about lO7° which is not an unusual temperature for a bare soil surface in mid-summer. Farmers who might be considering mid-summer planting of short-season hybrids for silage should consider that temperatures at shallow depths in dry soil could very likely exceed the lethal level on a sunny day and result in very poor stands. Results of emergence studies of corn made at various depths and temperatures (l) are shown in Table l. 4 \. _ at TABLE 1.—CORN: DAYS TO 80% EMERGENCE. Soil Temperature Planting Depth (inches) (°F) 1 3 5 44 No emergence in 24 days 56 16 days 21 days 24 days* 68 8 7 8 80 4 4 4 *60% emergence at the end of 24-day test period. There was very little variation in the emergence time at various depths, but temperatures had a much greater effect in determining the time the seed remained below the soil. Soybeans l Emergence studies made on two varieties of soybeans grown in Kentucky (2) indicated 4 about the same response to temperature in both. The seedlings exhibited essentially no growth at 50° and 104° F, with a maximum growth rate at about 86° F. Figure 1 indicates the time required to achieve 50% emergence using a planting depth of 1 inch. 20 15 8 C · §· G E ui E § 10 3 ¤ I.0 3 é 0 5 50 60 70 80 90 100 110 Mean Temperature (Degrees F) at Seed Level Fig. l.—Days to 50 percent emergence at various soil temperatures. 5 Sorghum The sor hums have tro ical ori ins and as a result, seem to ow best at hi h tem eratures. S P 8 , 8* S P A Studies of emergence (6) show that they are less sensitive to depth than to temperature. There appears to be little effect of planting depth on days to emergence except at the cooler tempera- tutes where the deeper planting has a pronounced retarding effect (Table 2). The germination percentage also shows a similar response (Table 3). TABLE 2.—SORGHUM: DAYS TO EMERGE. ‘ - Et- Temperature Planting Depth (inches) (OF) 0.5 1.5 2.5 59 6 9 11 68 7 8 8 77 5 4 5 86 4 4 4 95 4 4 5 . TABLE 3.-—SORGHUM: PERCENT GERMINATION. Temperature Planting Depth (inches) (°F) 0.5 1.5 2.5 59 71 58 56.5 68 80.5 75 72.5 77 79 80 78.5 ‘ 86 77 83.5 82 95 82 82.5 74 Cotton ‘ Because of its long growing season, it would seem advantageous to plant cotton as early as possible. However, cotton does not emerge as rapidly as some other plant species, so early planting at cool soil temperatures is conducive to seed rot and poor stands. To reduce emergence time to about 7 days, average soil temperatures should be 68° F or higher. Each 2 degrees added to the soil temperature can reduce emergence time by about 1 day, as indicated by Fig. 2(5). I2 I I LD E IO P- z B 9 . . . 4 Fig. 2.—Emergence time required by cotton (5). -¤ 5] B 4 [L 1/ (D E E 7 46 O E <`\ (Z Lu 6 u. 2 E " {’ ’° 24 W ' ’ 6 J [B 30 l. 2 I 2, I2 2, I6 so ~ , 1 4 G I2 L_ / ’° "`· } ‘· {I .5 6 5 is 30 , » · 2 2* ° »z ·» / / 20 ` " _A . 2 s 2,, 2l ?·‘· l ·..,_ IT Y { ' _ * 3 I5 V a 4 ‘ ‘ I _ I8 4° :0 9 4 8 3 2 2 I I #* l é Av M 0 · — Mya 0 ~ , " ‘I_ PERIOD I899-ISM E7}! INFORMATION COLLECTEDA kx FROM UNOFFICIAL SOURCES . I Fig. 15.—Average depth of frost penetration (inches), U.S. • 0 WILLIAMSTOWN • 14 FLEMINGSBURG 5 O • 0 LEXINGTON T O • 0 IRVINGTON BARDSTOWN 3 HENDERSON O BEREA I O O · · O • 0 SOMERSET '°'°""'CETON GREENVILLE GLASGOW cuM6I2m.AN¤ 0 GAP O I ` Fig. 16.—Number of days in average year in Kentucky with minimum temperatures less than 32°l·` at 4 inches below sod surface. Datapcriodz l967—71. 22 TABLE 11.-LOW SOIL TEMPERATURES, LEXINGTON, KY., 1967-1971. Number of days in Average Year the Soil Temperature Fell Below 320, 300, 280 F. and Lowest Temperature Recorded (°F) Inches Days Below 320 Days Below 300 Days Below 280 Lowest Temperature Below Under Under Under Under Surface Bare Soil (Sod) Bare Soil (Sod) Bare Soil (Sod) Bare Soil (Sod) 1 33 12 19 1 12 * 150 140 2 26 8 13 O 8 O 170 300 4 13 5 7 O 4 0 180 300 8 8 * 0 O O 0 300 310 *Less than 0.5 day. Other data rounded. _ Figure 16 and Table 11 do not indicate the actual depth of penetration of freezing tempera- tures since observations were made only at certain points in the profile. However, they should be _ of value in supplying some indications of frequency and extent of penetration of freezing temperatures. Penetration of freezing temperatures at a given site is dependent on a number of factors—including moisture content of the soil, soil type, soil cover, and topography. Therefore, it is suggested that for specific locations the data in the attached figures and table be supple- mented by actual reports. For example, utility companies and cemetery custodians often can ' supply such information. LITERATURE CITED 1. Alessi, _]. and Power, _]. F. 1971. Com Emergence in Relation to Soil Temperature and Seeding Depth. Agron. _]. 63:717-719. ‘ 2. Egli, D. B., Hatfield, _]. L., Hill,]. D., and Tekrony, D. M. 1973. The Influence of Soil Temperature on Soybean Seed Emergence. Agronomy Notes, University of Kentucky Dept. of Agronomy, Lexington, Ky. 6(2). 3pp. 3. Hambidge, G. (editor). 1947. The Yearbook of Agriculture: Climate and Man. U.S. Govern- · ment Printing Office, Washington, D.C. 1,248 pp. 4. jaworski, C. A. and Valli, V. J. 1964. Tomato Seed Germination and Plant Growth in Relation to Soil Temperatures and Phosphorus Levels. Proceedings of the Florida State Horticultural Society 77: 177-183. 5. Riley, _]. A., Newton, D. H., Measells, _]. W., Downey, D. A., and Hand, L. 1964. Soil Temperatures and Cotton Planting in the Mid-South. Miss. Agr. Exp. Sta. Bul. 678. · 6. Shaw, B. T. (editor). 1952. Soil Physical Conditions and Plant Growth. Agronomy Mono- graph No. 2. American Society of Agronomy. Published by Academic Press, New York, N. Y. 7. Toole, V. K., Webster, R. E., and Toole, E. H. 1951. Relative Germination Response of Some Lima Bean Varieties to Low Temperatures in Sterilized and Unsterilized Soil. Proceedings of the Am. Soc. for Hort. Sci. 58:153-159. 23 8. Wang, _]. Y. 1967. Agricultural Meteorology. Agricultural Weather Information Service, San jose, Calif. 693 pp. 2M-11-73 ·•. \