202 



THE ROTHAMSTED EXPERIMENTS. 



Variation 



with 



seasons. 



No man- 

 ure. 



With 



superphos- 

 phate. 



Mixed 

 manure. 



Nitrogen 

 for tur- 

 nips. 



confined. In this table, however, as well as in those relating, 

 respectively, to the barley and the wheat, averages are given 

 at the foot of each division of the tables, not only for the 

 eight intermediate courses — second to ninth, but also for the 

 two succeeding courses — tenth and eleventh, for which pot- 

 ash, soda, and magnesia were used as well as superphosphate. 

 But, for the leguminous crops, the averages are, for reasons 

 that will be explained, taken differently. 



The first point to notice in the results is that, under each 

 condition as to manuring, there is very great variation in the 

 amount of produce from year to year according to the seasons. 

 Thus, in 1868, the crop entirely failed on all the plots, although 

 seed was sown twice. Again, whilst the complex manure con- 

 taining nitrogen yielded more than 22 tons of roots in 1880, 

 the same manure gave little more than 4 tons in 1860 ; the 

 average yield over the eight courses being about 13£ tons. 

 Against this, the average by superphosphate alone ranged 

 from about 6| to about 7£ tons ; whilst without manure there 

 was an average of only about 1 ton. 



Referring to this last result, it is particularly to be observed 

 that this assumed restorative crop yields practically no pro- 

 duce at all when grown without manure. 



The plot with superphosphate alone gives very much more 

 than that without manure, but still very much less than an 

 average agricultural crop. The increase, such as it was, was 

 largely due to the greatly increased development of feeding- 

 root within the surface-soil under the influence of the phos- 

 phatic manure ; and the necessary nitrogen, beyond the small 

 amount of combined nitrogen annually coming down in rain 

 and the minor aqueous deposits from the atmosphere, has 

 doubtless been gathered under the influence of the increased 

 root-development from the previous accumulations within the 

 soil itself. There is, in fact, perhaps no agricultural practice 

 by which what is termed the condition of land, that is the 

 readily available fertility due to recent accumulations, can be 

 so rapidly exhausted as by growing turnips on it by super- 

 phosphate alone — provided, of course, that the seasons are 

 favourable. 



Compared with the produce with superphosphate alone, the 

 mixed manure, supplying, besides superphosphate, not only 

 salts of potash, soda, and magnesia, but a liberal amount of 

 nitrogen, yielded, on the average of the eight courses, nearly 

 twice as much, or between 13 and 14 tons of roots ; though, 

 as already pointed out, it yielded in some seasons over 20 

 tons per acre. There can be no doubt that, the necessary 

 mineral constituents being available, there was a large in- 

 crease of produce due to the supply of nitrogen in the manure. 



