Vol. XI. No. 261. 



THE AQRICULTUKAL NEWS. 



13.5 



THE TEMPERATURE OF THE SOIL 



UNDER DIFFERENT CONDITIONS. 



The following article has been receivetl Iroin 

 Mr. W. R. Dunlop, Agricultural and Science blaster, 

 St. Kitts-Xevis. It deals with observations carried out 

 "by him in connexion with soil temperatures in the 

 tropics, and is of particular interest as it treats of 

 a subject that has not received any great attention 

 under the conditions described: — 



The warmth of the soil under different conditions is an 

 important matter, since it is closely connected with root 

 development, bacterial activity and the conservation of soil 

 moisture. 



During March 1912, observations were made in 

 St. Kitts, under as widely different conditions as possible, 

 ■with a view to ascertaining the e.xtent of temperature varia- 

 tions in ordinary cultivated fields. The first series of 

 observations consisted in taking readings, simultaneously 

 twice a day, for one week, in plots situated respectively in 

 the dry and wet localities of the island. Molyneu.x estate 

 was selected for the purpose in the case of the latter locality 

 and La Gucrite in the case of the former. Readings were 

 taken at 7 a.m. and 1 p.m., at a depth of 3 inches. The 

 main result of these observations was the indication 

 that the surface soil at Molyneux estate maintains a tem- 

 perature 2°F. lower in the early morning and 5°F. lower in 

 the early afternoon than the surface soil at La Gucrite. The 

 cause of this is attributed to the cooling effect of rainfall, 

 with its subsequent evaporation; to direct sea breezes; and to 

 the absorption of radiant heat in the afternoon by the clouds 

 and mountains of the Molyneux district. Xt both La Gucrite 

 and Molyneux the temperatures kept fairly constant, day by 

 day; at La Gucrite, at 7 a.m., the temperature was '5° to 

 77° F; at 1 p.m. it was 91° to 94' F. The thermometer at 

 Molyneux showed, at 7 a.m., 72' to 75° F, and at 1 p.m. 

 85° to 89° F. The lowest readings could in every case be 



• correlated with fall of r.un on the day that readings were 

 taken. 



The second series of observations had for its object the 

 determination of the temperature of the soil at diflferent 

 depths. Readings were taken every hour from 8 a.m. to 

 8 p.m., and at 6 a.m. on the next morning, at a depth of 

 S inches, 6 inches, and 1 and 2 feet. 



The temperature of the soil at a depth of 3 inches, at 6 a.m. 

 was 72° F., and increased with the intensity of the heat 



" from the sun. The maximum of 91 ' F. was reached at 1 p.m. 

 -During the early hours of the afternoon this temperature 

 remained fairly constant, but there was a quick drop after 

 sunset. The diurnal range at 3 inches was twenty degrees. The 



"temperature at (J inches remained more constant; it was lower 

 during the day than at 3 inches, but higher, at night. There 

 was, however, a steady rise and fall, but the maximum of 

 89' F. was not reached until 4 p.m. Again, a quick drop 

 occurred after sunset. The diurnal range at 6 inches was 

 ten degrees. 



At a depth of one foot, the temperature remained nearly 

 constant during the day, but it was two degrees lower at 

 night than during the day. The maximum temperature was 

 85° F. 



At a depth of 2 feet, the temperature was 83= F., and 

 remained constant day and night. A heavy shower of rain 

 lowered the temperature by one degree, on another occasion. 



The temperatures of soils of different texture and colour 

 were investigated, in the third series of observations. Readings 

 were taken at 7 am. and 1 p.m , at a depth of 3 inches, in 

 four plots, composed respectively of dark-grey sand, reddi,sh- 

 brown clay, dark brown pen manure mixed with sandy soil, 

 and lime mixed with a small amount of sandy soil. The 

 temperatures of these soils were taken under tv.ro difl'erent 

 conditions: (a) after the soils had lain untouched for one 

 month; (b) the day after the soils had been forked, raked and 

 watered. The sand plot was warmer at 1 p.m. than the soils 

 of the other plots, and was cooler at 7 a.m. The temperature 

 of the untouched sand at 1 p.m. was 99° F.; that of the cul- 

 tivated sand 90' F. The temperature of the dry sand had 

 a diurnal range of 26' F.; this was considerably greater than 

 that of the air. In the case of all the plots, the effect of water 

 in levelling up the specific heats was clearly indicated. At 

 1 p.m. the clay was warmer than the humus plot, but cooler 

 at 7 a.m. The lime plot (untouched) was thirteen degrees 

 cooler at 1 p.m. than the sand plot (untouched), and the lime 

 plot also possessed the lowest diurnal range, which amounted 

 to 6 til 8 degrees. 



The fourth series of observations consisted in an investi- 

 gation of the temperature of the soil under different condi- 

 tions of cultivation, at a depth of 6 inches The first point 

 of interest lirought out was the cooling effect of cultivation, 

 particularly forking or ploughing. Rolling warmed the soil 

 in dry weather, but had the opposite effect when the land was 

 wet. As regards ridging or banking up, the important 

 fact was brought out that land cultivated in this manner 

 from east to west is at least three degrees warmer 

 during tlie day than when the soil is ridged north and 

 south. At a depth of 3 inches the difference would 

 be at least six degrees. The well known fact that wind 

 cools the soil was also supported by observations made 

 in .sheltered and unsheltered places. The soil under pas- 

 ture was rather cooler than arable soil, and covering arable 

 soil with light trash lowered the temperature during 

 the day by four degrees. Finally, observations in connexion 

 with the soil warmth of cacao plantations showed that soil 

 thus shaded and sheltered was eleven degrees cooler, at 

 1 p.m., than the soil exposed to the sun, outside; and at 

 7 a.m., it was cooler by three degrees. 



DEPARTMENT NEWS. 



Mr. H. A. Ballou, AI.Sc, Entomologist on the 

 Staff of the Imperial Departntent of Agriculture, lefb 

 Barbados on April 17, 1912, by the 8.8. 'Korona', 

 for 8t. Kitts, for the purpose of conducting investi- 

 gations regarding insect pests of plants in the Leeward 

 Islands. 



Mr. P. T. Saunders, M.R.C.V.S., Veterinary Officer 

 on the Start' of the Imperial Department of Agriculture, 

 left Barbados on April 16, by the S.8. '(_^caino', in o)-der 

 to visit St. Vincent in connexion with his otticial 

 duties. 



