42 THE ROTHAMSTED EXPERIMENTS. 



Nitrogen Keferring to the results given in the lower division of the 

 ousresidue. Table (12) relating to the amounts per acre of dry matter, 

 nitrogen and total mineral matter, it is seen that, comparing 

 the other series with Series 1, there is a considerable increase 

 in the amount of dry substance per acre in the root, and some 

 in the leaf also, due to nitrogenous residue. There is, more- 

 over, notable increase in the amount of nitrogen stored up in 

 both the root and the leaf over a given area, due to residue ; 

 but much less than there was under the influence of direct 

 supply. 

 mtrogm Comparing the average annual amounts of dry substance, 

 almatter*' °^ n i tr °gen, and of mineral matter, per acre, over the two 

 in the root, years of the action of residue with those over the three years 

 of direct supply, there is in each of the Series 2, 3, 4, and 

 5, less than half as much dry matter per acre in the roots 

 over the two as over the three years. There is about or less 

 than half, and even only one-third, as much nitrogen 

 accumulated in the roots over the two years ; and there is 

 also generally less than half as much increase of nitrogen in 

 the leaves over the two years. Further, though the supply 

 was the same each year, there was less than half as much 

 total mineral matter in the roots, and generally less than 

 half as much in the leaves, under the influence of the re- 

 stricted supply of nitrogen and coincident restricted growth. 

 In reference to these points, it is to be borne in mind that 

 the leaves were always returned to the land. 

 Exhaustion Whilst there is in the above facts clear evidence of con- 

 tra *"" siderable effect from previously unexhausted nitrogenous 

 manure and crop-residue, there is at the same time in the 

 lower percentage of nitrogen in the roots, and in the much 

 lower amounts per acre, both of dry substance and of nitro- 

 gen in the crops growing under the influence of only residual 

 supply, clear indication that the nitrogenous accumulations 

 available within the soil, whether from manure- or from crop- 

 residue, were rapidly becoming exhausted. 

 Potash in The figures relating to the potash per cent in the dry 

 the root. matter of the roots, and per acre in the roots, show (with the 

 continued annual supply of potash), as in the case of the 

 three years, a high percentage in the dry matter with high 

 luxuriance — that is, where there had been a large amount of 

 nitrogenous manure- and crop-residue; and the percentages 

 are with one exception higher over the two years, with the 

 same supply of potash, but much less available nitrogen, and 

 much less luxuriance and total growth, than over the three 

 years with the direct supply of nitrogen. On the other hand, 

 the quantities of potash per acre in the roots, although much 

 larger with nitrogenous residue and increased growth than 

 with the mineral manure alone, are, with the much less 



