Emergency Tillage Operations. Sometimes it is not convenient to compact the seed bed or break lumps before planting. In this case, if the soil is still too loose or lumpy, grain and even corn land may be rolled after the crop is up. This should be done when the plants are small.

When grain is grown on heavy soils, it is best to leave the seed bed covered with a layer of small, loose lumps. This is not so favorable for the formation of crusts as in case of finely pulverized soil.

Heavy rains often pack the soil so firmly after the crop is planted that hard crusts form, which prevent the penetration of shoots and stems. A spike-tooth harrow is often used to break the crust, and sometimes a roller gives best results. Beans often break their necks in trying to get through a hard, crusty soil. In such a case the hoe or the careful use of a cultivator is best to break the crusts.

Home Experiments and Projects. To Demonstrate That it Pays to Cultivate corn.

Procedure.-Secure a small plot of ground, preferably heavy, silt loam (about 14 acre), and divide equally into three parts. Treatment up to cultivation time should be the same on all plots. Plant each plot to the same kind of corn. Give the corn on plot No. 1 thorough cultivation, and maintain a good mulch especially during dry periods. Plot No. 2 is to receive no cultivation at all, but all weeds should be kept down with a sharp hoe. The soil should not be stirred in the least. All weeds should be allowed to grow in plot No. 3. At harvest time cut out the row between adjoining plots. Discard. Determine yield of corn on acre basis. Keep cost accounts to ascertain comparative profits. (During seasons of frequent and sufficient rains, but little difference may result in yields on the first two plots. It would be best to continue this project for at least 3 or 4 years.)

To Determine the Advantage, if any, in Hilling Corn.-Procedure.-Select 14 rows of corn in a corn field. Practice level cultivation on seven of the rows and hill the other seven rows. Discard the middle row, and determine comparative yields. What are some of the disadvantages of hilling?

Field Studies.-Examine different plows, harrows, cultivators, rollers, and planting machines. Study their action in relation to the soil.

It would be well, if possible, to compare the work of a stubble plow in plowing sod with that of a sod plow.

QUESTIONS.

1. What is the relation of good tilth to soil fertility? Give the meaning of good tilth.

2. What constitutes a good seed bed? What is intertillage?

3. Name and discuss the factors influencing the development of a good seed bed.

4. Name the common tillage tools. What should guide the farmer in his purchase of tillage and planting implements?

5. What are some of the common objects of tillage?

6. State some (eight) of the principles governing tillage. 7. What is the use of the plow?

8. Name the parts of a common walking plow. What is a jointer? Coulter? Illustrate by sketch the proper adjustments of jointers and coulters. (Fig. 74.)

9. Describe the pulverizing action of the moldboard; illustrate by diagram or otherwise.

10. How does stubble plowing differ from sod plowing?

11. What constitutes good plowing? (Figs. 68, 71, 76, 78, and 87).

12. What is a disk plow and when is it used? Why are they not recommended for light, loose soils?

13. Name some of the advantages of late fall plowing. Disadvantages. Why leave fall plowed land rough?

14. What is a puddled soil?

15. Discuss spring plowing-advantages and disadvantages.

16. Why and when is deep plowing generally best? When is shallow plowing best?

17. Why is it not good practice always to plow at the same depth? What is a better way?

18. What is subsoiling? Is it generally recommended? Why? What about deep tilling?

19. How may dynamite be used in connection with tillage?

20. What is a hillside plow and how used? What are gang plowstheir advantages?

21. What are harrows? Name and describe the use of the different types. 22. What is meant by summer fallowing?

23. What is a planker and for what is it used?

24. Name and describe the common rollers or clod crushers. When should they be used? When not? What is a precaution to observe in the use of a smooth or drum roller?

25. Why are light, loose soils especially benefited by cultipackers?

26. What are the advantages of good tilth or a firm seed bed in relation to planted seeds and growing plants? Discuss another advantage in having a firm seed bed.

27. What has been the effect of the principle of good contact between the seed and the soil on the construction of many planting and seeding machines?

28. What is a good program to follow when alfalfa is to be sown broadcast on loose, loamy land?

29. Which is better to use for sowing grain-drills or broadcast sowers? Do all drills give the same satisfaction? Explain.

30. Under what conditions is disking better than plowing for grain, particularly oats? Why?

31. What is listing? Where and how is it done? What is a "middle-buster"? 32. Give the meaning of cultivation. What are cultivators?

33. Name and discuss the objects of intertillage.

34. Name and discuss the use of the different implements used in intertillage. 35. What should guide the farmer as to what particular tool to use, and how and when to cultivate?

36. What is the depth of cultivation best for humid farming? Why?

37. How is a farmer to know when he is cultivating too deep?

38. What machine adjustments may be made to eliminate injury in cultivation?

39. Discuss level cultivation and hilling.

40. What are weeders, and when do they prove effective tools?

41. Does it injure grain or corn if it is necessary to roll land when the plants are small?

42. How may crusts be broken after crops are planted?

43. Have you ever known of cases of harrowing small grain while young?

What were the results?

44. For an outline summary of this chapter, see table of contents.

CHAPTER XI

SOIL ORGANISMS IN RELATION TO SOIL FERTILITY

IN Chapter II it was stated that millions of organisms live in the soil, and that many of them bring about changes that are fundamentally important in determining fertility. These many organisms may be classed as bacteria, fungi, yeasts (Fig. 113), algæ (ǎl'je), worms, insects, and rodents. The first three groups are classed as "microorganisms" because they are of microscopic dimensions. The majority of the bacteria are not more than

A

B

A

FIG. 113. Other soil organisms. A, a common mold; B, yeast plants.

0.0000197 of an inch in diameter, and it is believed that some are too small to be seen with the aid of the most powerful microscope. In one-third of a thimbleful (one gram) of normal field soil have been counted from 140,000,000 to 400,000,000 microorganisms; and in manured soil, as high as 750,000,000. The most tiny ones (bacteria) are in greatest abundance, and it is they which play a large part in nature's plans, and stand in close relationship to the practices which make possible successful crop production.

In this chapter will be considered in particular three groups of the helpful soil organisms, viz.: (a) Those which cause decomposition or decay; (b) those which cause nitrification, and (c) those which gather nitrogen from the air.

ORGANISMS OF DECOMPOSITION

Microorganisms Clear the World of Trash (Fig. 114-A).— What would this world be were it not for the fact that all plants

and animals finally disappear after they die? If this were not so the world long ago would have become choked with dead material. Most of the rubbish of the earth is buried in or is thrown upon the soil, and through decay, it is reduced to the fundamental elements, becoming again the dust of the earth, water and gases. This decay is the work of many kinds of microorganisms, particularly the bacteria and fungi. It is a wise provision of nature that all organic matter can again break down into the elements of which it is composed, since through these changes sustenance is provided to prolong the life on the earth and to make possible new life.

FIG. 114. The important soil bacteria. A, common bacteria causing decomposition; B, nitrifying bacteria; C, nitrogen-fixing bacteria; a, free nitrogen-fixing; b, nodule bacteria.

No Crops Without Decay. Soils continue to weather1 after they are formed from rocks; and because of weathering, crops are able to secure from the mineral rock particles the mineral elements so necessary for their growth. But crops also require nitrogenand the nitrogen in the soil is held there, not in the mineral particles, but mainly in complex, insoluble compounds in the form of organic matter. Crops cannot absorb this organic matter any more than they can consume the mineral particles of the soil. Before plants can secure any nitrogen from this organic matter, and before any crops can be grown successfully at all, the organic matter must first undergo decomposition. Herein myriads of microorganisms do a most important work.

Crops Secure Mineral Elements From Two Sources.-At the

1 Weathering is a broad term meaning the breaking up and decay of material things wrought by natural forces. Decay of soil is largely the result of chemical forces acting independently or through the aid of microorganisms.

NITRIFICATION EXPLAINED

173

same time that the nitrogen compounds in the soil organic matter pass through the changes necessary to provide available nitrogen, the mineral elements, which this organic matter contains, likewise become available. Thus a crop such as corn, for example, secures its supply of nitrogen from one main source-the soil organic matter; and its supply of mineral elements from two sources-from the mineral soil particles and from organic matter.

Decay of Organic Matter Aids Decay of Mineral Particles.— The organisms which cause the decomposition of the soil organic matter perform a two-fold work. They not only bring about the necessary changes in the organic matter to provide available nitrogen and mineral elements for use by plants, but in an indirect way they aid in the liberation of mineral elements contained in the mineral soil particles. This is explained through the fact that in all organic decay, acids are formed which are effective agents in dissolving mineral matter. We can now understand more clearly why it is important to maintain a good supply of organic matter in soils to enable crops to secure needed and sufficient elements. It is significant that rich, garden soils usually have a high content of organic matter, and that they are much more abounding in life than ordinary field soils. We can explain, too, why some light-colored soils rich in all the important mineral elements and having a low productive power, can be made to produce much larger yields simply by plowing under a good growth of green rye.

Some Fertilizers Valueless Without Decay.-Were it not for the organisms of decomposition, fertilizers such as tankage, blood meal, cottonseed meal, etc., would be of little or no value. Moreover, some insoluble mineral fertilizers, such as rock phosphate, would be practically useless, but for the presence of decomposable organic matter in the soil, or because of the organic matter in which the fertilizer may be mixed when applied. Rock phosphate has been found to give best results in most soils when it is mixed with manure or plowed under with green rye or clover.

NITRIFICATION

Nitrification Explained. The accompanying diagram (Fig. 115) is helpful in gaining a clear idea of the meaning of nitrification. This diagram explains that the nitrogen in organic matter is held there in the form of complex, insoluble compounds which must be broken down, through decomposition, into simpler com