004 STATE BOARD OF AGRICULTURE. 



even lli(Mijj;Ii the lolal (jiiaiitity is very large, the soil cannot hv rijihily 

 designated a fertile soil. According to the law of niinimuni, if one 

 l)lant food elements is lacking either totally or partially and all the 

 oflici- plant food elements are present in abundance, the lacking element 

 becomes the limiting factor, the plant growth is affected and consequently 

 the soil is rightly designated an infertile soil. Again, the phosphates not 

 only do not go into solution in any large amounts or increase the solu- 

 bility of soils as the other single salts, but they ap})ear to have a depress- 

 ing effect upon the solubility of soils. As has already been seen, in 

 none of the soils treated with CaH^fPO.Jo was the solubility product 

 greater than that of the check and in some cases, it was actually much 

 smaller. Now it can hardly be asserted that these soils which show 

 small solubility are made infertile by the -iddilion of pliosi<horus. On 

 the contrary they are as fertile as the corresponding soils Avhich received 

 ■the other salt treatments and which gave a large solubility product. 

 These soils, therefore, are fertile but this fertility power is not in- 

 dicated by the solubility factor because of the depressing effect of the 

 phosphorus. This depressing effect is doubtless due to the combination 

 of phosphorus with the bases of the soil and the decreased solubility of 

 the latter. It is now generally believed that the fixation of phosphorus 

 in the soil depends upon the presence and abundance of bases. When 

 phosphorus combines with these bases not only the phos])horus is 

 fixed, but evidently the bases also become less soluble. If this is true 

 then phosphorus acts as a conserver of bases, and thereby prevents 

 the rapid loss of bases through leaching which ultimately and in- 

 evitablj^ results in the creation of an acid coudilion of soils. On the 

 other hand, it must be stated that when a soil was treated with a com- 

 bination of several salts such as Ca(NO,)„, NaNO,, KNO, KCl, K.SO,, 

 (NHJ0SO4, MgSO,, CaHJPO.U, KH.PO, and NaC.H^O,,, the phos- 

 phates did not have a very marked depressing effect upon the solubility, 

 but when (]SrH^).,,SO,, NaC.H.O.^ were eliminated from the combination 

 then the depressing effect became very marked. PJvidently the ammonia 

 radical of the (NH^).,SO, and the acetate radical of the NaCH.O., were 

 not influenced by the phosphorus. Finally, that the solubility factor may 

 not be an absolute and reliable criterion of the fertility of tlie soil is 

 further found in tlie possibility that the plants may not obtain all their 

 plant food entirely from the soil solution but also from the solid matter 

 itself — the soil particles. Although at present the general belief appears 

 to be that the plants do not themselves obtain any plant food directly 

 from the solid soil except i\}i\t which is made soluble by the excreted car- 

 bon dioxide, yet the writer believes that the plants must in some way 

 derive part of the plant food directly from the soil particles and especially 

 in the case of some of the soils such as clay. 



In spite of these limitations, however, it must be admitted that in 

 general a high soluble salt content which is due partly if not largely to 

 a high solubility, is associated with a high state of fertility. This funda- 

 mental i)rinciple is abundantly supported by a large amount of experi- 

 mental data. The work of King=, Hall, Brenchley, and Underw^ood% 



(2) Invpstisatioii in soil Management, 1904. Madisnii, Wis 



(3) rhil. Trans, Roy. Soc. London. Ser. B. V. No. 307, p. 179 (1913). 



