250 A VISIT TO EOTHAMSTED. 



Another important purpose served by these long continued 

 experiments, and one which is proving of good service at this 

 time, is the assurance they give that continuous white crops may 

 be raised successfully, and that whatever may have been the 

 necessity for restrictions in cropping under the old system of 

 agriculture, no such necessity exists under the modern system of 

 intensive farming, l)ut that complete liberty of cropping may be 

 accorded to good farmers ^\■ithout risk of detriment to the fer- 

 tility of the soil. 



The paramount importance of nitrogenous manures for the 

 production of a full crop of this cereal is evident from a com- 

 parison of the four plots in series 0, which received no nitro- 

 genous manures with those in the next three series wliich 

 received ammonia salts, nitrate of soda, and rape cake respec- 

 tively. Eoughly speaking the crop has been doubled both in 

 grain and straw by the application of nitrogenous manures, and 

 this is especially noticeable in the average produce of the second 

 twelve years to which attention deserves to be specially directed, 

 inasmuch as any irregularities due to former manuring are 

 eliminated in that stage of tlie experiment. 



A comparison of the four plots of each series yields some 

 interesting information. Thus in series the unmanured plot. 

 No 1, is seen to be rapidly losing its fertility. On plot 2 the 

 addition of superphosphate increased the crop during the first 

 twelve years in making good the annual drain of phosphoric acid 

 and in making up for a deficiency of it in the soil; but the exhaus- 

 tion is still very rapid, and it is now reduced to a lower level 

 than the original unmanured soil, but this is certainly not due to 

 any want of phosphoric acid, nor is it due to the want of potash 

 or other mineral manures, as seen by a glance at plot 4, where 

 the further addition of mixed alkalies does not materially diminish 

 the rate of exhaustion. The sole application of mixed alkalies on 

 plot 3 is attended with very little benefit, and has the effect also 

 of rendering the exhaustion even more rapid than that of the 

 unmanured plot. The cause of all this is manifest from the results 

 of series A, where the addition of ammonia salts alone immedi- 

 ately raise the crop 13 bushels per acre. What is wanting in 

 series is nitrogen, and the application of other manures only 

 tends to exhaust the land all the more rapidly by enabling a greater 

 amount of the nitrogenous wealth of the soil to be taken away 

 annually by the crop. When, in addition to nitrogenous manure, 

 a quantity of superphosphate is applied, the increase in the crop 

 is very marked, ^az., 17 bushels per acre, thus shewing that there 

 was a deficiency of phosphoric acid in the soil, and it required 

 that both nitrogenous and phosphatic manures should be applied 

 in order to yield a full crop. The very slight excess of 3 A over 

 1 A shews that there was no deficiency of potash in the soil, as 



