256 A VISIT TO EOTHAMSTED. 



is compared with plot 8, it is seen that the increase of crop due 

 to this large excess of ammoniacal manure is very small. This 

 shows that the ammoniacal were greatly in excess of the mineral 

 manures, probably to the extent of about 300 lbs. per acre ; and 

 one would naturally expect that this excess would remain in the 

 soil for the use of future crops. But how different is the result 

 here obtained. Since 1864 the manuring was discontinued, and 

 the average crop in the next twelve years scarcely exceeded that 

 of plot 3, which never received any manure at all. Two explana- 

 tions of this extraordinary result are possible : either the mineral 

 food has been exhausted by the previous heavy nitrogenous 

 manuring, or the ammonia salts have disappeared from the soil. 

 That the latter is the true explanation is made evident by the 

 very remarkable and unexpected results obtained on plots 17 

 and 18. 



These two plots have been nominally transposed every year, 

 so that each received ammonia salts and minerals on alternate 

 years. Plot 17, receiving ammonia salt one year, became plot 

 18, receiving minerals the next year. 



It will be seen that the crop of those years during which 

 ammonia salts were applied was nearly double the preceding and 

 succeeding crops, which received minerals only. This seems to 

 show that ammonia salts put into the ground one year are not 

 available to any material extent for the crop of the next. The 

 mineral salts, on the other hand, remain in the soil, and are 

 available for successive seasons, if only the amount of nitro- 

 genous manure present in the soil is sufficient to enable them to 

 come into operation as plant food. The appearances of these 

 two plots presented so marked a contrast that it seemed scarcely 

 credible that they had received the same total amount of manure 

 during thirty-six years. On the one whose turn it was to 

 receive the ammonia salts this season the wheat was long and 

 finely coloured, and seemed a heavy crop ; on the other the 

 straw wos about half the length, pale, and light, and looking 

 exactly like plot 5, which had never received any ammoniacal 

 manure at all. 



Another interesting experimentwith the wheat crop was pointed 

 out, which was long ago instituted for the purpose of testing the 

 accuracy, or at least the applicability to the Eothamsted soil, of the 

 Lois-Weedon method of wheat growing. The proposer of this 

 method of a<j;ricu.lture — the Eev. S. Smith — described the results 

 of a series of experiments made on certain land divided into 

 stripes of alternate wheat and fallow. He found that by growing 

 wheat in that way, and putting each stripe under one year wheat 

 and next year fallow, large crops were able to be raised without 

 the application of any manure ; the rest given to the land and 

 the more thorough tillage it received being apparently sufficient 

 to compensate for the want of manure. 



