. Productive agriculture . y no air spaces, all thespaces between the soil grains being occupied by water. Whenclay soils of very fine texture are puddled, then dried and baked,they become hard or even stony. This is the basis of the processof common brick making. Cultivating soils, driving over fields, or grazing pastures whilewet, are bad farm practices. Soils should be stirred only whenthe structure and tilth of the soil will not be harmed. 2. Frequently, soils puddle readily because of a lack of organicmatter. The addition of organic matter partially protects soilsfrom beating rains, and a
. Productive agriculture . y no air spaces, all thespaces between the soil grains being occupied by water. Whenclay soils of very fine texture are puddled, then dried and baked,they become hard or even stony. This is the basis of the processof common brick making. Cultivating soils, driving over fields, or grazing pastures whilewet, are bad farm practices. Soils should be stirred only whenthe structure and tilth of the soil will not be harmed. 2. Frequently, soils puddle readily because of a lack of organicmatter. The addition of organic matter partially protects soilsfrom beating rains, and also helps to hold the soil particles matter aids aeration, percolation, and bacterial develop-ment, and makes for conditions which prevent the breakingdown of the soil structure. A soil rich in humus and decayingplant hfe does not puddle so easily as does a soil that is devoid ofhumus and organic matter. (See Exercise 2.) 3. Soils often pack and puddle because of the absence of lime, STRUCTURE OF THE SOIL 273. Limed soil— Unlimed soil soil particles are —soil particlesflocculated. remain separate. Fig. 130. This benefits which improves the soil structure. The grouping tendencyof the soil is increased by the addition of lime. Lime effervescesin the presence of soil water and keeps the soil loose and compounding of soil particles isindicated in Fig. 130. In the figure shown it will benoted that in the limed soil the par-ticles have formed into groups, andare said to be flocculated. In theunlimed soil, the particles remainseparate. Such a soil puddles easily.(See Exercises 3 and 4.) 4. Proper drainage rids the soil of surplus in several ways: a. It permits more air to get into the soil. h. Bacteria thrives better in a well-drained soil, and nitrifica-tion is hastened. c. A well-drained soil warms up more quickly in early spring. All of these points, due to proper drainage, improve the tilthof the soil. Summary. — Soil structure refers to th
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