TO BE APPLIED AT ONCE ? 63 



the action of the saline top-dressing than it had been in April j 

 second, because the field on which the potatoes had been grown, 

 from this crop being generally manured more liberally, might 

 be much richer in compounds of nitrogen than that on which 

 the turnips had been raised, and might therefore have been less 

 thankful for nitrate of potash at whatever period it was applied ; 

 and, thirdly, because we have only one experiment in each case, 

 and one undressed portion to compare it with. As I have 

 already remarked, the limits of natural variation being unknown, 

 we can draw no safe conclusion from Mr M'Lintock's results as 

 they have been recorded. They afford encouragement, however, 

 to further trials of this method of applying substances in suc- 

 cessive portions. 



But Mr Austen, of Chilworth, near Guildford, who farms on 

 the green sand, has informed me, that with common salt alone 

 on his land, he has succeeded in growing an excellent crop of 

 mangel wurtzel, by applying it after the plant was up in suc- 

 cessive doses of two cwt. per acre up to six or eight cwt. Every 

 fresh application appeared to give the crop a new start. This 

 result suggests the propriety, at all events, of further investi- 

 gating the effect of such successive applications. 



c At what period of each plant's growth. As to this point, 

 we naturally conclude that any substance which is to benefit a 

 plant, should be brought within reach of its roots, at the time 

 when those parts of the plant are about to be produced to 

 which this substance is especially necessary, or in which it usu- 

 ally abounds. Should we therefore administer ammonia, nitrates, 

 &c., when the plant is young, and phosphates when it is ap- 

 proaching to maturity, or ought all to be mixed and applied at 

 once when the plant is commencing its most vigorous growth ? 

 On this point experiments are wanting. 



2. The manner or mode of application is not without its 

 influence. It may not only render doubtful the produce of a 

 particular plot, but it may make it impossible to judge of the 

 precise effect of a whole series of experimental trials. For 

 instance : Mr Main, in 1846, made two series the one of six 

 and the other of thirteen experiments, upon the same field of 

 oats. In each set was included a plot to which no application 



