March 1914 



Humus in its Relation to 

 Soil Fertility. 



The brown or black organic mat- 

 /ter of surface soils is known as 

 hnmiis, and is deri\€d from se- 

 veral compounds rosultiuji from the 

 decay of both vejjetables and ani- 

 mals. The last result of the fer- 

 mentation of orfjanic matter, whe- 

 ther veg^etable or animal, is a few 

 erases and a little mineral matter. 

 The intermediate disori>-aniscd mass 

 which jfives the upper portion of 

 the soil its dark colour is what 

 we recoqfuise as Humus. When 

 land is first broug-ht under cultiva- 

 tion after being cleared of its tim- 

 ber it possesses a sponsjv texture, 

 and is found to l^e more or less 

 fertile, and adapted to the erowth 

 of such crops as potatoes and oats. 

 As time procuresses the phvsical 

 condition of the soil crraduallv 

 chanjjes, and a new series of crops 

 takes the place of those grown on 

 the virgin land. This rotation is 

 brouofht about by the oxidation of 

 the organic matter, or loss of 

 humus. Many and varied were the 

 theories held as regards the iiseful- 

 ness of vegetable matter in soils 

 by the early chemists. Some 

 thought that humus was the prin- 

 cipal source of the nutritive mate- 

 rial of plants. When later writers 

 showed that the organic matter of 

 plants came from outside the soil 

 (i.e., that the carbon of the at- 

 mosnhere and m.oisture furnished 

 it"> the value of .humus was not 

 held to be of much importance. 



Although the true explanation of 

 the part plaved by humus was not 

 forthcoming in the early times, 

 practical men noticed that soils 

 possessing a high content of veo-et- 

 able matter and those which were 

 well dressed with the excrement of 

 farm animals" were inevitably fer- 

 tile. We now know the reasons 

 of this, the principal ones bein<T 

 the supply of nitrotren furnished 

 by humus, its moisture-hoMino- ca- 

 pacity, and the comparative ease 

 with which soils can be broun-ht 

 into a condition of fine tilth. 

 Humus has other properties of 

 value, such as rendering available 

 the mineral matter of the soil, 

 resulting in a class of compounds 

 called humates, besides warrri"'^ - 

 soil by reason of its dark colour 

 clav soil can be lic^htened by in- 

 corporatine vejretable matter with 

 it, and the reverse is the ease when 

 a sandy soil liable to be shifted 

 bv the wind is treated to an appli- 

 cation of farmyard manure, or 

 green crops are ploughed under. 



THE GARDION AND FIELD. 



From the foregoing it can be 

 readily seen that instead of fol- 

 lowing a system of cult>ire result- 

 ing in an annual decrease of veget- 

 able matter in the soil, it should 

 be the cultivator's sustained wish 

 to preser\e, if not increase, the 

 amount of humus. Of course, he 

 will have to be guided by either 

 factors prevailing, becau.se unless 

 the conditions are such that veget- 

 able matter in the soil undergoes 

 gradual decomposition and fur- 

 nishes its component parts for the 

 nutrition of the nlant, changes of 

 a character inimical to plant- 

 pTowth may arise. If the soij is 

 not well drained, and lacks basic 

 substances, such as lime, the tem- 

 perature will be low, and decom- 

 position products of an acid char- 

 acter formed, or the soil will be 

 what is commonly called sour. 



When the soil is properly drain- 

 ed, naturally or otherwise, and a 

 fair proporticm of lime is present, 

 the amount of humus cannot well 

 be too great, and those systems 

 of handling which, if they do not 

 increase the quantity at least con- 

 serve it, are to be recommended. 



The decline in the crop-producing 

 power can be traced in m.any soils 

 to the exhaustion of the vegetable 

 matter. The nature of the crops 

 f^roAyn is, of course, an important 

 factor in influencing this i-ngredi- 

 ent. Potatoes and such crops, as 

 also cereals, leave not_ too much 

 of root residue. Plence soils show 



visible signs of deterioration, simp- 

 Iv because no effort has been made 

 at a rotation of crops, and the 

 interpolation of clovers and other 

 members of the leguminous order. 



♦ 



Cover Crops. 



Cover crops exert a great influ- 

 ence upon the supply of plant food 

 in the soil, its retention and the 

 addition of vegetable matter. I 

 think, writes an Am.erican orchard-' 

 ist, we are safe in saving, how- 

 ever, that the addition ot vegetable 

 matter is probably of greater iim- 

 portance than the retention of 

 plant food. Orcharding is a sys- 

 tem of cropping which does not 

 return much plant residue to 

 the soil. If clean culture, with- 

 out a cover crop is practiceh, 

 and unless a large amount 

 of barnvard manure be apnli'^d, the 

 productiveness of the orfchard soon 

 reaches a verv low peroeTita"^e of 

 what it shouRJ be trader ordi-n;s^'>- 

 conditions. Taking into considera^ 



44'J 



tion the other benefits derived 

 from the ti« of a cover crop, the 

 addition of vegetable matter bv 

 this ii'etliod is iirobablv the cheap- 

 est which can be employt-d. 



We have already spoken of the 

 use of the cover crop as a food 

 su|)plicr. Persouallv I would 

 place this imder the secondary 

 benefits of the cover crop rather 

 than among its more important 

 phases. There is no question but 

 that the cover crop may be mwle 

 to Bupnly a very large amount of 

 food, however, a great deal of 

 precaution must be exercised or 

 the evil effects will outweigh the 

 benefits. The plant food most 

 largely supjilied by cover crops is 

 nitrogen and while nitrogen is an 

 essential plant food and very ne- 

 cessary to a vigorous, healthv 

 growth, an over supply in the soil 

 is a drawback to fruit production. 

 Nitrogen favors a laree vefetative 

 "■rowth. The activity of the tree 

 cannot be turned strontrlv in two 

 directions at the same time, and 

 if the supply of nitroeen is suffi- 

 cient to cause the tendency of tlie 

 tree towards a large wood orowth. 

 which would be very ant to suffer 

 durinc" the winter, it is not wise 

 to r^row nitrorren-growing crops 

 as icovers continually. Such a pro- 

 cedure would, on ordinar^' c-iv 

 soon o-ive an over-supply of nitro- 

 p^en in the soil, and resi'lt in the 

 conditions "nven above. While cover 

 crops do increase the amount of 

 plant food in the soil they should 

 never be considered as fullv sup- 

 plyin? the needs of the orchard, or 

 because thev are used the fipplica- 

 tion of barnvard m.anures and 

 other fertilizers be abandoned. 



T^Tiere lands are more or less 

 hilly or at least rolling, a f^reat 

 deal of difficultv is experienced in 

 preventing washing bv heavy faU 

 and sprino- rains. To prevent 

 the washino- of soil and the trullv- 

 insr one between trees, becomes a 

 very serious question in clean 

 culture orchards in which the site 

 has considerable slo^p. Qonsider- 

 ino- the washinp^ which take; -nl-- 

 even in summer, it is all the 

 more necessary to euard ap-ainst 

 the same cond tion durinf the 

 winter and early spring. The use 

 of cover crops therefore, becomes 

 nracticallv es.s.ential on such lands 

 if clean culture is to be practiced 

 durin"- the summer. 



— Handling of Cover Crops. — 



One of the auestions most often 

 asked conceminp- cover crops is 

 " When should the crop be sown? " 

 As -with all other phases of or- 



