lEANSACTIONS OF SECTION B, 523 



agricultural experience that the growth and removal of a highly nitrogenous 

 leguminous crop should leave the land in high condition for the growth of a grami- 

 neous corn crop, which characteristically requires nitrogenous manuring ; and the 

 determinations of nitrogen in numerous samples of the soil taken from the two 

 separate portions of the field, after the removal of the barley, and the clover, respec- 

 tively, concurred in showing considerably more nitrogen, especially in the first 

 9 inches of depth, in the samples from the portion where the clover had been 

 crown, than in those from the portion whence the barley had been taken. Here, 

 then, the surface soil at any rate, had been considerably enriched in nitrogen by the 

 growth and removal of a very highly nitrogenous crop. 



Lastly, clover has now been grown for twenty-seven years in succession, on a 

 small plot of garden ground whicli had been under ordinary garden cultivation for 

 probably two or three centuries. In the fourth year after the commencement of the 

 experiment, the soil was found to contain, in its upper layers, about four times as 

 much nitrogen as the farm-arable-land surrounding it ; and it would doubtless be 

 correspondingly rich in other constituents. It is estimated that an amount of nitro- 

 gen has iDeen removed in the clover crops grown, corresponding to an average of not 

 far short of two hundred pounds per acre per annum ; or about ten times as much as 

 in the cereal crops, and several times as much as in any of the other crops, growing 

 on ordinary arable land ; and, although the yield continues to be very large, there 

 has been a marked decline over the second half of the period compared withthe 

 first. Of course, calculations of the produce of a few square yards into quantities 

 per acre can only be approximately correct. But there can at any rate be no doubt 

 whatever, that the amount of nitrogen annually removed has been very great ; and 

 very far beyond what it would loe possible to attain on ordinary arable land ; where, 

 indeed, we have not succeeded in getting even a moderate growth of clover for more 

 than a very few years in succession. 



One other illustration should be given of the amounts of nitrogen removed from 

 a given area of land by different descriptions of crop, namely, of the results obtained 

 when plants of the gramineous, the leguminous, and other families, are growing 

 together, as in the mixed herbage of grass-land. 



It is necessary here to remind you that gramineous crops grown separately on 

 arable land, such as wheat, barley, or oats, contain a comparatively small percentage 

 of nitrogen, and assimilate a comparatively small amount of it over a given area. 

 Yet, nitrogenous manures have generally a very striking effect in increasing the 

 growth of such crops. The highly nitrogenous leguminous crops (such as beans and 

 clover), on the other band, j-ield, as has been seen, very much more nitrogen over a 

 given area, and yet they are by no means characteristically benefited by direct 

 nitrogenous manuring; whilst, as has been sho-wni, their growth is considerably 

 increased, and they jdeld considerably more nitrogen over a given area, nnder the 

 influence of purely mineral manures, and especially of potass manures. Bearing 

 these facts in mind, the following results, obtained on the mixed herbage of grass 

 land, will be seen to be quite consistent. 



A plot of such mixed herbage, left entirely unmanured, gave over twenty years, 

 an average of .33 pounds of nitrogen per acre per anmmi. Over the same period 

 another plot, which received annually a complex mineral manure, including potass, 

 during the first six years, but excluding it during the last fourteen years, yielded 

 46'3 lbs of nitrogen ; whilst another, which received the mixed mineral manure, 

 including potass, every year of the twentj^ yielded 55-6 lbs. of nitrogen per acre 

 per annmn. "Without manure, there was some decline of yield in the later years ; 

 with the partial mineral manuring there was a gi-eater decline ; but with the com- 

 plete mineral manuring throughout the whole period, there was even some increase 

 in the yield of nitrogen in the later years. 



Now, the herbage growing without manure comprised about fifty species, repre- 

 senting about twenty natural families; that growing with the limited supply of 

 potass comprised fewer species, but a larger amount of the produce, especially in 

 the earlier years, consisted of leguminous species, and the yield of nitrogen was 

 greater. Lastly, the plot receiving potass every year yielded still more leguminous 

 herbage, and, accordingly, still more nitrogen. 



