PHOSPHATES IN MASSACHUSETTS AGRICULTURE. 163 



doubtless only a special illustration of this hastening effect on the ripen- 

 ing process. This effect on color has perhaps most frequently been at- 

 tributed to the apphcation of basic slag meal. It is, of course, understood 

 that many other conditions also affect color. 



4. Ejfect on the Availability of Soil Constituents. — That the action of 

 the soluble phosphates in the soil increases the availabihty of some of 

 the important soil constituents seems to be generally held. This is a 

 point which has not been made the subject of special investigation here. 

 That it will make it possible for the plant to draw more largely upon the 

 soil because of the increase in root development which it causes has been 

 pointed out. ^ Aside from this it is believed that the soluble phosphates 

 exert a direct chemical effect which results in bringing some of the soil 

 constituents more largely into solution. All soluble phosphates contain 

 calcium suKate (land plaster), and this compound is held by many to 

 be the constituent of acid phosphate most active in decomposing the 

 complex silicates of the soil and rendering the potash they contain soluble 

 and available to crops. Long-continued experiments in the use of land 

 plaster, which have been connected with soil tests continued for twenty- 

 six j-ears have not given very material increases in crops which respond 

 in marked degree to an application of muriate of potash alone. The 

 average increase in 13 corn crops grown in this soil test during the twenty- 

 six years, due to the annual application of muriate of potash at the rate 

 of IGO pounds per acre, has been 27 bushels, wliile the average increase 

 due to the annual apphcation of plaster at the same rate has been 2^^ 

 bushels. It seem.s clear that had the plaster exercised a very important 

 influence in m.aking the potash of the soil (present in this case in very 

 large amounts) available there must have been a larger increase in the 

 corn crop following its use. 



The use of superphosphate has been shown to be favoral^le to nitrifi- 

 cation, ^ and must therefore increase the availabihty of the organic nitro- 

 gen-containing soil constituents. 



It has been asserted that some of the constituents of acid phosphate 

 act as catah'tic agents in the soil, and by their action render soil con- 

 stituents available; but that this is the case does not appear to have been 

 fully estabhshed. On the whole, therefore, it seems to the writer that 

 the direct chemical influence of soluble phosphates as affecting the avail- 

 ability of soil constituents is less important than the other secondary 

 effects which have been considered. 



5. Larger Gain of Atmosvheric Nitrogen. — It has been demonstrated 

 that the activity of bacteria wMch have the abiUty to fix atmospheric 

 nitrogen in the soil is increased by the apphcation of superphosphates, 

 and that as a consequence more nitrogen is brought witliin reach of the 

 crop and a larger yield usually obtained.^ 



1 See p. 161. 



s Abst. E. S. R., Vol. XXVIII., p. 216: Patterson & Scott Jour. Dept. Agr. Victoria, 10 (1912). 



s Abst. E. S. R., Vol. XX., p. 621: Lohnis & Pillai, Centbl. Bakt. 2 Abt. 20 (190S), No. 24-25. 



