Scientific Agriculture. 



437 



[November, 1909. 



nitrogen in a greater or less amount. 

 When the organic matter decays, the 

 supply of available nitrogen in the soil 

 is increased. 



We have found that nitrogen is needed 

 to promote the growth of plants ; that 

 if there is not a sufficient amount of 

 nitrogen in the soil we cannot have 

 plants. Since this is true, and siuce 

 practically all of the nitrogen in soils 

 comes from its humus content, we can 

 see the absolute necessity of humus in 

 soils. All plants, except legumes, obtain 

 their nitrogen from the soil. Legumes 

 have the power to gather this element 

 from the great store in the air, if there 

 is not enough in the soil to promote their 

 growth. Since plants must obtain their 

 nitrogen from the soil, and the soil's 

 supply is obtained principally from 

 humus, we can again see the importance 

 of humus. 



1. Nitrogen is the most expensive of 

 the three elements needed by all plants. 

 To grow the common crops more of it is 

 needed than any of the three plant foods. 

 Since it is the most expensive of plant 

 foods, and so much of it is needed in the 

 production of crops, and its supply can 

 be maintained without any material 

 cash outlay, if we maintain the supply 

 of humus, we can again see the great 

 value of humus in the soil. 



2. The presence of humus in soils pro- 

 motes' chemical action on the mineral ele- 

 ments in the soil which are not available 

 at the time for the needs of the plants. 

 The soil may be rich in phosphorus or 

 potash, yet nearly all of these elements 

 may be unavailable for the needs of the 

 plant ; they may not be in a state to be 

 utilized so that the growth of the plant 

 will be very slow. If tbe soil is rich in 

 humus, the acids contained in the humus 

 together with those of the character of 

 crenic and apocrenic acids will act upon 

 the insoluble elements and make tham 

 available for the plant. 



3. Besides being the source of nitro- 

 gen and rendering the mineral elements 

 already in the soil available, the appli- 

 cation of humus adds plant food to 

 the soil. Not only do all organic 

 materials add nitrogen, but they all 

 contain a greater or less amount of the 

 other plant foods needed to make soils 

 rich. This is especially true of manures 

 voided by animals raised on the farm, 

 Horses, cattle, hogs, sheep, and poultry 

 void manure rich in nitrogen, phosphoric 

 acid, and potash. The degree of rich- 

 ness, of course, will depend on the 

 animal and the kind of feed and atten- 

 tion received. It the manure of these 

 animals is added to increase the supply 

 of organic matter, the supply of all 



three plant foods is increased by the 

 amount applied in the manure. 



4. Another influence that humus has 

 on the fertility of soils is the fact that 

 it increases the number of earth worms. 

 The farmer's son who wishes to go fish- 

 ing does not get bait from the clay 

 bank on the hill-side ; he knows that 

 no fish worms can be found there. 

 Instead, he goes out behind the barn, 

 where the manure has been thrown for 

 years, and there in the black earth, 

 rich in humus, he digs down and finds 

 the worms. Earth worms' of all kinds 

 make their home in soils rich in organic 

 matter. Their presence greatly in- 

 creases the supply of available plant 

 food. And in some cases they burrow 

 down into the subsoil, and on their 

 return bring up a little of the mineral 

 elements to increase the supply in the 

 surface layer. This may seem like a 

 very insignficant matter ; but, after 

 all, it is the little things that count in 

 fertility of soils. This is one of the 

 little things. 



5. Besides being valuable by directly 

 increasing the supply in the nitrogen and 

 indirectly increasing the available sup- 

 ply of other plant foods, humus benefits 

 the mechanical condition and texture 

 of the soil. Soils rich in humus are 

 better retainers of moisture than those 

 with but little humus. This property of 

 soils containing humus is of special im- 

 portance in arid and semi-arid countries. 

 Where there is but little rainfall during 

 the months when crops make their 

 heaviest growth, it is important that 

 the soil have the power to contain and 

 retain moisture as long as possible. If 

 the soil cannot contain much moisture, 

 no matter how much it rains before the 

 dry weather comes, the excess moisture 

 will drain off, and just what the soil can 

 contain is all the crop will have to draw 

 from in the time of dry weather. If the 

 soil can contain a considerable amount 

 of moisture and has the power to retain 

 it, there is a greater probablity of saving 

 the crop when the dry weather arrives. 



Experiments show that soils rich in 

 humus have the power to contain more 

 moisture than soils deficient in it. This 

 is true, because pure humus will contain 

 more moisture than sand or clay, and 

 the more humus there is in a soil, the 

 more moisture it can contain. It has 

 been found that 100 pounds of sand 

 will contain only from 25 to 29 pounds 

 of water. If any more than this amount 

 is applied it will leach through aud pass 

 of in the drains. One hundred pounds 

 of clay will contain from 40 to 50 pounds ; 

 100 pounds of garden earth, from 85 to 90 

 pounds ; while 100 pounds of pure humus 



