U-2 



THE AGIUCULTUEAL NEWS. 



May 



1908; 



PLANT FOOD IN THE SOIL. 



'J'he following note-s dealing with available and 

 unavailable plant, i'ood in the .soil, and the dependence 

 of plant life upon the soluble portion of tlie ietlilizing 

 constituents present, originally appeared in the (laixh-n- 

 ers' Chronicle, and are of sufficient interest to wan-ant 

 their reproduction herewith: — 



I'lant.s are composed of two cla^jse.s of clieiiiical sulistaiices, 

 the oi'ganic or volatile compounds, which ai'e destroyed by 

 burning ; and tlie inorganic, or fixed elenient.s, w-hich remain 

 in tlie ash after burning. The importance of the inorganic or 

 fixed elenient.s to jilant life rests in the fact that, no matter 

 what sort of a soil is under cultivation, a healthy plant 

 carrier awa}' about the same amount of these constituents 

 whirli it obtains from the soil for the building up of its 

 structure. At the same time, while the .same species of plant 

 vhen matured may yield to analysis very similar ipiantities of 

 the.se elements, different species will show different results as 

 to kind and quantity ; and the more remote the natural affinity 

 of the species to each other, the wider, as a rule, will lie these 

 differences. 



l-'erfect jjlants cannot be produced, much less can fruits, 

 on soils where one or more important con.stituent is absent. 

 The most \aluable materi;Us are phosjjhoric acid, potash, 

 nitrogen, and lime. Accordingly, where .soils have been 

 t.xhausted by the growth and carrying away of crops, to 

 a point below that of remunerative cultivation, they may 

 lie restored to fertility by making a judicious return of the ash 

 or mineral constituents along with the element nitrogen. 

 This last-named, the nitrogen, belongs to the organic class of 

 plant foods. 



While it is true that scpim. idiuvial soils possess vast 

 stores of plant food, both of nitrogenous and of mineral 

 .substances, .so as to be regarded as practically ine.\hrtusti))le, 

 yet liy ronstant cro])ping, without a suitable return in manure, 

 tliev will in time become uniir<iductive. 



Now the greater \y,vct of the ])laiit food ennstituents 

 iiece.s.sary to profitable crop eidtivation are licked ujj in an 

 inert condition, in which stale fni- tlii' most pait, they remain 

 until united with a solvent sup[ilied as manure. For example, 

 in <ine of the experimental plots of the late Sir John Lawes 

 at I'lothamsted, to which no manure whatever w^as applied 

 for thirty-eight years, the soil at the end of that period was 

 found, on analysis, to contain in the top 9 inches as much 

 as 3f),()0+ lb of potash |)er acre, and 2, -50:! lb. of pho.sjdioric 

 acid per acre. Of these very large amounts of i)lant food in 

 the .soil, only 91 lb. of potash, and l.'!9 lt>. of phosphoric acid 

 ])er acre were in a snjiilile enndition anil a\aililile tn iilaiits. 

 The addition iif .'! cwi. nf superplios]iliate ]ier acre tci ijiis 

 same .soil, (in an adjiiiniiig iijnt. increased tie soliiliilil\ .4 

 the plant fnod to l(i.") lb. of potash per acre, and to 1,17(1 lb. 

 of phosphoric acid per acre. 



Having by this means brnnglit tie inert mineral eon- 

 siitiieiits iuin a eiinchtinn nf .Niijiiliilily. llie ailditicin of 

 nitrogen in tlie form of ammonia-salts as manure to this 

 name land raised the produce from ii to 43 busliels of barley- 

 grain per acre, anil the straw from II cwt. to iX cwt. per 

 aere. 



The ])lant grown in exhausted soil is therefore starving, 

 with mineral elements cvc.rywhere in the soil, and organic 

 elements everywhere in the atmosphere, and innie availalile 

 for use. 



Tliii. tie eliief office of inanure is to furnish assiniilaliie 

 fi"iil fur I lie immediate u.se of growing cro[i.s, and tn 

 combine witli and suiiiilement the natural food sn[i|ily 

 existing in the soil. When it is .said that certain constituents 



in the soil are lacking-, it does not always mean that the .soil 

 does not contain them, but that it does not supply to the 

 growing plants as much as they need. It is not so much, 

 therefore, because soils have been worn out of plant food,- 

 but rather because the food is locked up in such combina- 

 tions that the plant roots cannot get at and use it, that an 

 artificial siqijily of soluble food in manure becomes necessary. 

 It is believed that the beneficial effects of commer- 

 cial fertilizers are due as much to the timely supply -as to 

 the amount of nourishment they contain. This timely 

 suiiply enables the plants to enlarge their root system, 

 whereby they are able to secure more nourishment from tJie 

 soil over and above that furnished by the fertilizers, than 

 they could have secured without such supply. If this be so, 

 it is seen that the use of concentrated manures in small 

 ipiantities may not only largely increase the yield of crops, 

 but may also serve to deplete the soil of some of its elements 

 of jilant food more rapidly than would the same kind of crop 

 and tieatmcnt without their use. 



PHYSICAL CONDITIONS OF SOILS. 



The fact that the healthy and flourishing conditioa 

 of plants is as much dependent upon suitable physical 

 conditions of the soil as upon the provision of the 

 elements of plant food is perhaps not always remem- 

 bered by cultivators. And yet, if through want of 

 drainage, neglect, etc., land is allowed to get into an. 

 unhealthy condition, this condition is soon reflected in 

 the character of the herbage growing upon the soil. 



I^-obably the chief danger resulting fioni unsuitable- 

 physical condition of land is poor drainage, w'ith consei|uent 

 excess of water, and lack of sufficient oxygen in the soil. 

 Such a state results in the weakening, and it may be, even the- 

 death of the roots of plants growing in such soils. This 

 jiarficnlaily applies to crops grow-ing in heavy clay .soils, 

 especially where there is an impervious subsoil. Such crops 

 will often have many of their feeding roots killed by suffoca- 

 tion during extended w-et periods, lioots that may ju.st be 

 forming while the .soil is in a suitably moist condition are often 

 killed in tw-o or three days if the .soil becomes .saturated with 

 water The vitality of the whole plant is weakened, not only 

 liV tie loss of its feeding roots, but by tliedevelopnient, under 

 tlie uiiliealthy prevailing conditions, of iiijurimis prmlucts in 

 tie cells of t!ie rnots that are not killed. 



.\gaiii, plants growing where the surface soil is liable t<» 

 beciime caked and packed are likely to suffer from want of 

 oxygen for tin- roots. This perhaps applies especially to 

 trees. L'luler .such conditions the annual growth is retarded, 

 and the plants hxse vitality. Plants in this state readily 

 becDine the |)rey of in.sect and fungus pests. Deej) and 

 careful cullivatiim is of course the remedy for sucli a condi- 

 tion, and the iirovision of some organic fertilizer, such as pen 

 manure, not only provides plant food for new- growth of the 

 roots, but also lightens the physical nature of the soil. lame is 

 also useful for this latter jiurpose in the ca.se of heavy clay soils;. 

 To re.-dize fully the importance of the physical condition 

 of the soil to plant life growing upon it, it is only necessary 

 to remember that the roots of all plants must have a supply 

 nf oxygen, witlinui, w-liicli development is im|iossible. If 

 tley do not gel this supply llu-y will die of siitfoeation. The 

 plant w-ill bo poisoned by its own decomiiositinn products, 

 and w-ill star\-e, or, become the [irey of parasitic enemies 

 which it is too weak to resist. 



