142 TALKS OX MAXURES. 



taken, was in a condition to yield 14 bushels more wheat, per acre, 

 tiian tliat upon wliicii wheat had been prcviousl}' grown ; the yield 

 of wheat, after clover, in these experiments, being fully equal to 

 that in another field, wiiere large quantities of manure were used. 



" Taking all these circumstances into account, is there not pre- 

 sumptive evidence, that, notwithstanding the removal of a large 

 amount of nitrogen in the clover-hay, an abundant store of availa- 

 ble nitrogen is left in the soil, and also that in its relations towards 

 nitrogen in the soil, clover differs essentially from wheat ? The 

 results of our experience in the growth of the two crops, appear 

 to indicate that, whereas the growtli of the wheat rapidly ex- 

 hausts the land of its availal)le nitrogen, tiiat of clover, on the 

 contrary, tends somehow or other to accimiulate nitrogen witliin 

 the soil itself. If tliis can be shown to be the case, an intelligible 

 explanation of the fact that clover is so useful as a preparatory crop 

 for wheat, will be found in the circumstance, that, during the 

 growth of clover, niliojrenous food, for which wlieat is particularly 

 grateful, is eitlier stored up or rendered available in the soil. 



"An explanation, however plausible, can hardly be accepted as 

 correct, if ba.sed mainly on data, which, although highly probable, 

 are not jiroved to be based on fact. In chemical inquiries, 

 especially, nothing must l)e taken for granted, that has not been 

 proved by direct experiment. The following questions naturally 

 suggest themselves in reference to this subject: "What is the 

 amount of nitrogen in soils of different characters? What is the 

 a:nount more particularly after a good, and after an indiirerentcrop 

 of clover? Why is tiie amount of nitrogen in soils, larger after 

 clover, than after wheat and other crops? Is tlie nitrogen i)rcsent 

 in a condition in which il is available and useful to wheat? And 

 lastly, are there any other circumstances, apart from tlie supply of 

 nitrogenous matter in the soil, whicii help to account for the bene- 

 ficial effects of clover as a prejiaralory crop for wheat ? 



" In order to throw some light on these questions, and, if pos- 

 sible, to give distinct answers to at least some of them, I, years 

 ago, when residing at Cirencester, began a series of experiments; 

 and more recently, I have been fortunate enough to obtain the co- 

 operation of ]Mr. Roliert Valentine, of Leighton Buzzard, who 

 kindly undertook to supply me with materials for my analysis. 



" My first experiments were made on a thin, calcareous, clay soil, 

 resting on oolitic limestone, and producing gencrallv a fair crop of 

 red-clover. The clover-tield formed tlie slope of a rather steep 

 hillock, and varied much in depth. At the top of the hill, tlie soil 

 became very stony j^t a depth of four inches, so that it could only 



