790 



THE TROPICAL AGRICULTURIST. 



[May I, 1884. 



CONSTITUENTS OF SOILS. 

 [the eeason wht.] 



>A^hat are phosphates? They are salts formed by a com-- 

 biuation of phosphoric acid, with a substaace or base, capable 

 of uniting with an acid and forming a neutral salt. The 

 phosphates of principal importance to agriculture are, the 

 phosphates of lime, of magnesia, potash, soda, alumina, &c. 

 Their composition may generally be illustrated by the phos- 

 phate of lime, the difference between it and the others de- 

 pending upon the base, with which the phosphoric acid 

 combines. 



What is phosphate of Ume? It is a salt formed by a 

 combination of phosphoric acid, with lime as a base. Phos- 

 phoric acid consists of phosphorus and oxygen in a state of 

 solution ; and a phosphate is phosphoric acid in a state of 

 combination, with a base, forming what is termed a salt. 

 Phosphate of lime constitutes the base of bones of animals, 

 and is therefore an important ingredient in vegetables em- 

 ployed as food. The bones of man, and of animals in general, 

 have their origin from phosphate of lime, which is never 

 absent from fertile land. The bone earth passes from the 

 soil into hay, straw, and other kinds of food, which are 

 afterwards consumed by animals. Eight pounds of bones 

 contain as much phosphate of lime as one thousand pounds 

 of hay, or of wheat-straw, and twenty pounds of bones, as 

 much phosphoric acid as one thousand pounds of the gi'ain 

 of wheat or oats. 



AVhat are sulphates? Sulphates are salts formed by 

 sulphuric acid in combination with any base, as sulphate of 

 lime, sulphate of soda, sulphate of alumina, potash, gypsum, 

 magnesia, &c. Sulphuric acid consists of sulphur and oxygen 

 only, and is known as the oil of vitriol of commerce. In its 

 piure state, it is an eiceedingly sour and corrosive liquid, 

 destroying both animal and vegetable structures; but com- 

 bined with potash, soda, lime, magnesia, &c., it contributes 

 in certain instances to the fertility of the soil. It is rarely 

 met with in nature in an uncombined state. 



Whence do plants obtain phosphate of lime? Phosphate 

 of lime is found in natural .soils, as are other phosphates, 

 such as the pboshhate of alumina, ammonia, magnesia, &c. 

 The phosphate of lime is added to soils by the decay of 

 vegetable animal matter, and especially by bones .and shells. 

 When alkaline or earthly phosphates are wanting in the 

 soil, or when they are not introduced in the form of manure, 

 the seeds are not developed. We may di-aw this conclusion 

 that the development of plants, and the amount of the 

 constituents of the blood they contain, are directly pro- 

 portionate to the quantity of phosphates suppUed to and 

 taken up by them. Phosphatus, so necessary to the form- 

 ation of the blood, and to all animal life, are no less essential 

 to the existence and to the propagation of all vegetable 

 beings. 



Whence do plants obtain sulphates ? As far as our pre- 

 sent knowledge extends, they receive their sulphur from the 

 sulphates di.-isolved in the water .absorbed by their roots from 

 the soil. The water of springs is entirely derived f.'om the 

 rain which falls upon the surface of the earth; the water, 

 percolating through the earth, dissolves all soluble materials 

 which it may meet in its course. The subst.ances thus dis- 

 solved communicate to the water properties which are not 

 possessed by pure water. Thus rain precipitates the ammon- 

 ia suspended in the air, and presents it to the roots of 

 plants: at the same time that it presents sulphur, in some 

 combined form, which it has met with in percolating the 

 earth. — Lemltr. 



REPLANTING WOODLAND, AND CAUSES 

 OF FAILURE. 



Whatever diversity of opinion prevails among foresters as 

 to practical management, nearly all are agreed as to the 

 impolicy of replanting with the same description of trees, 

 at any rate until a certain period has elapsed. There must be 

 time for the soil to become sweetened, for fresh mineral 

 food to be prepared, or for the destruction of enemies, in- 

 sect and fungoid. Let iis examine these various catises. 



Unless the soil be so specially suitable, by the abundance of 

 requisite food for a particular class of trees, it is only natural 

 to conclude that after proving material for fifty or sixty 

 years' growth there will be exhaustion, even though much 

 of the suppUes are returned as decayed leaves, branches, 



&c. This is what we gather from our experience as re- 

 gards the iniiuence of rotation, but it only expLains one, 

 and perhaps the least important, reason of the fact that 

 immediate replanting with similar kinds of trees seldom 

 results in equally ^agorous growth. 



A more potent reason for failure arises from the poisonous 

 nature of the excreta, which, until sweetened by oxidation, 

 are prejudicial to the young plants. Of course this applies 

 in some degree to whatever kind of trees are planted, but 

 is more especially injurious when like follows like. It is for 

 this reason that all experienced foresters so strongly re- 

 commend that, before replanting, the land should be tho- 

 roughly drained ; this advice we emphatically indorse. None 

 but aquatic plants can flourish in a water-logged soil. The 

 matrix under such conditions is saturated with acid pro- 

 perties, and it is only by the aeration of the soil, which 

 follows the removal of water, that a healthy condition is 

 induced, that acids are neutralised, and plant food gradu- 

 ally set free. It is. in short, as absolutely essential to the 

 healthy growth of timber as of our crop and pastures, that 

 the laud should be thoroughly drained. 



A third reason against replanting with .similar material 

 is the injury to be anticipated from insect .and fungoid 

 parasites. It is well known that the eggs of the beetles 

 — such as Hylobius abietis, Hylurgus piniperda, the pine 

 beetle, and Adelges laricis, the larch bug — are deposited 

 underground on old roots, and the grubs live on dead wood 

 It is therefore most important that all dead wood should 

 be removed, and all decaying matter burnt, before replanting; 

 also, if possible, that a period of three or four years should 

 elapse between cutting down and replanting. 



We have now to consider other causes of failure. It must 

 be understood that, as a general rule, hards woods should 

 be followed by larch and pines. Even if we plant a cert- 

 ain proportion of hard woods to remain for the perman- 

 ent crop, these should be of a different nature. Thus, 

 if the previous crop were oak, ash or sycamore will be 

 suitable to follow. It is betcer that these should occupy 

 different parts of the same wood than that they should 

 be mixed; the latter kinds, being the hardier, are best 

 adapted to the most exposed part of the land. For the 

 same re.ason, the Scotch fir is useful as a shelter to the more 

 delicate larch, which, notwithstanding heavy loss from disease 

 of late years, is under favourable conditions, -the most pro- 

 fitable of quick-growing woods, not only on account of 

 intrinsic value, but because it is the best nursery for the 

 permanent crop. 



Opinions differ as to the reasons for the great mortality 

 and in many cases total destruction, of young larch wood 

 of late years. The causes .are various — we m.ay allude to 

 some of the more prominent. Climate is an important element. 

 The natural home of the larch is on the slopes of mou.tt- 

 ainous ilistricts; it enjoys above everything a dry, porous 

 soil, in which air has free access to the roots. Strong soils 

 are not favom-able, and stagnant water is fatal; and, even 

 where drain,age is good, low damp bottoms, suliixt to fogs, 

 are injurious to healthy growth. It is well known that the 

 severe.st frosts occur in low valleys, and a great deal of the 

 mortality which has occured of late years has, we believe, 

 been mainly due to severe frosts late in spring when the sap 

 was up, and which destroyed the smaller cells. The com- 

 parative healthiness of larch on hill sides sheltered from the 

 colder winds is proof of this. Indeed, so great has been the 

 mortality in young larch plantations in flat countries, that 

 it is a serious question whether, under such conditions, the 

 growth of larch should not be discontinued for a time. 



Failure may often be traced to want of care in the pre- 

 paration of the young plants, and too immediate change of 

 soil from the nursery ground to their perm.anent home. 

 The seedlings are often grown under the forcing conditions 

 of highly-manured soil, of free, open nature, in sheltered 

 situations; and, if at once transferred to a soil of different 

 character, where the circumstances are much le.ss favouaable 

 the change is too sudden, and a severe check is experienced ; 

 necess.iry supplies of food are wanting, and the vitality of . 

 the plant is weakened, rendering it liable to fungoid attacks. 



The management of the nursery is a matter which recpiires 

 more attention than it often receives. Mr. Brown, in his 

 work on Fori^stry, says that "in no c.a,se should one year 

 seedling larch be more than Sin. high, nor one yenr seed- 

 ling, one year tran.splant^d more than 10 in. high, nor three 

 year old plants more than 20 iu. high." It is undoubtedly au 



