Soils and fertilizers . acterial flora is dense. On the other hand, in verysandy soils, desert soils and water-logged soils, bacteria arefew in number. While there are usually many bacteria in fertile soil, it isnot always the case that there are more in such soils thanin less productive ones. The number of bacteria that asoil may contain cannot be considered a measure of its pro-ductiveness. The numbers of bacteria found in one gramof soil of different kinds and treated in different ways aregiven in the following table: Table 29. — Number op Bacteria to a Gram of Soil .DtrRiNOSome Period of t
Soils and fertilizers . acterial flora is dense. On the other hand, in verysandy soils, desert soils and water-logged soils, bacteria arefew in number. While there are usually many bacteria in fertile soil, it isnot always the case that there are more in such soils thanin less productive ones. The number of bacteria that asoil may contain cannot be considered a measure of its pro-ductiveness. The numbers of bacteria found in one gramof soil of different kinds and treated in different ways aregiven in the following table: Table 29. — Number op Bacteria to a Gram of Soil .DtrRiNOSome Period of the Growing Season Soil Depth Chop Number ofBacteeia Stiff clay .... 3 inches Orchard in highstate of cultiva-tion. In covercrops 2,200,000 Adjoining soil above 3 inches Meadow for twelve 450,000 and of same char- years acter Of same type as 3 inches Vegetables and 1,800,000 above .... heavily manured Same type as above Scarlet cloverplowed under andalternated withmaize for ten years 3,360,000 128 SOILS AND FERTILIZERS. 157. Conditions affecting bacterial growth. — The en-vironment is a controlling influence in the development ofbacteria as it is of all organisms. Among the importantenvironmental influences are the supply of air and moisture,the temperature, the presence of organic matter, and the presence or absence ofacidity in the soil. 158. Air supply. —While all bacteria requiresome air for their growth,certain of them are ableto get along with muchless than others. Thoserequiring an abimdant•p supply of air have beencalled aerobic bacteria Fig. 23 -Diagram showing therdative ^j ^^^^ ^^^^^ thrivesizes oi bactena and some soil particles.(A) a fine sand particle, (B) a large clay better On a Small air SUp- ^gJ^;i;UhiTamerat::- ^^ ply are termed auaerobic. The bacteria that are ofthe greatest benefit to the soil are, in the main, aerobes, andthose that are injurious in their action are chiefly , however, have more or less abiUty to adapt them-selves t
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