314 BULLETIN OF THE BUSSEY INSTITUTION. 
and 1873 were repeated in 1874, as will appear from the following 
table. All of these trials were precise repetitions of those of the 
previous years. They were made for the sake of testing once more 
the effect of persistent cropping in the special cases to which they 
refer. Among the large number of experiments with single fertilizers 
that had been made in the preceding years, the few kinds enumerated 
in the table seemed to be the only ones whose repetition promised to 
be of sufficient interest to justify the trouble of it. 
The good effects produced by the potassic fertilizers, especially by © 
the heavy dressings applied to squares BB 6 and BB 7, are again 
remarkable, as they had been in the previous years, though the crops 
obtained by the repeated use of this single kind of plant food are natu- 
rally smaller than those from the squares that had been treated with 
dung or with a mixture of fertilizers, and so supplied with all three 
of the important kinds of plant food. So, too, the crops from square 
BB 4 that during the four consecutive years had received an enor- 
mously heavy dressing of wood-ashes, are surprisingly good. It 
appears from the analyses that have been reported on page 193, that 
the wood-ashes used in these experiments contained in every bushel 
about 34 Ibs. of real potash and from 1} to 1? lbs. of phosphoric acid. 
Hence there was applied every year to square BB 4, some ten or 
twelve times as much potash, and about twice as much phosphoric acid 
as would have been sufficient, according to the estimates on page 116, 
to supply crops even larger than any that were ever obtained from this 
square. The ashes probably contained no nitrogen, or as good as 
none. But, thanks no doubt to the alkaline property of the ashes, the 
nitrogen in the humus of the soil was made available by them for 
the crops. As has been stated on page 258, a sample of the soil of 
the plain field, collected in 1871 was found to contain rather less than 
a quarter of one per cent of nitrogen. It may be admitted, moreover, 
that upon each of the squares devoted to the experiments there were 
as many as 16,000 lbs. of dry loam, such as that in which analysis had 
indicated 0.24% of nitrogen. Hence there must have been as much 
as 38 lbs., or more than 17,000 grammes of nitrogen in the soil of 
BB 4 at the beginning of the series of experiments; but it will be 
seen on page 116, that the highest estimate of the amount of nitrogen 
needed by either kind of crop is less than 600 grammes per year. 
The squares dressed with cow dung and with horse dung, undoubtedly 
