AVERAGE PRODUCE PER ACRE. 113 



of another plant or crop of a different order in the vegetable 

 kingdom. As evidence of the prevalence of this misapprehen- 

 sion and misapplication of scientific truth, it may be worth while 

 to refer briefly to the last example of it that happened to come 

 under our notice. In a very useful book on " Manures " by an 

 American gentleman, Mr. J. Harris, which has gone through 

 two or more editions, the author takes up the consideration of 

 the manures suitable for wheat and for turnips, and says that, 

 judging from analyses, we would think that the manure for an 

 acre of wheat would require to contain more phosphoric acid 

 than the manure for an acre of turnips, and then goes to tell his 

 readers (quite truly) that we know from experience that the 

 reverse is the case, — that phosphoric acid is the great and special 

 manure for turnips and nitrogen for wheat. He even goes the 

 length of showing by calculation, that judging from the ash- 

 analysis of the crops, a " special manure " for wheat should con- 

 tain 42J lbs. per cent, of phosphoric acid, and a manure for 

 turnips only 18^ lbs. of the same. It is to be regretted that 

 the teaching of science should be thus misunderstood and mis- 

 applied ; and it is hoped that some service may be done by an 

 attempt to correct misapprehension on a point of so much 

 importance. After a rather fruitless attempt to account for the 

 supposed anomaly, the writer refen^ed to takes refuge in a 

 quotation from J)r. Voelcker to the effect that " the ash-analyses 

 of plants do not afford a satisfactory guide to the practical 

 farmer in selecting the kind of manure which is best suited to 

 his crop," — a remark which is true only with certain qualifications 

 and under certain circumstances as to soil, &c. We have thus 

 not only a palpable mistake, but an attempt to generalise upon 

 it. And yet the author shows otherwise a very fair acquaint- 

 ance with practical farming and with the chemistry of agricul- 

 ture, both of which, he takes occasion to tell us, he studied 

 under Dr. Lawes at liothamsted. 



The mistake lies, as already indicated, in comparing 100 

 parts, or say pounds, of the ash of one crop with lOU lbs. of the 

 ash of a dilferent crop without considering the amount of ash 

 which the respective crops yield, and, of how much valuable, or 

 comparatively less valuable substances that ash may consist. It 

 is quite true that, in 100 lbs. of the ash of wheat, we find 42 to 

 49 lbs., or 45 lbs. on an average, of phosphoric acid, and that, in 

 100 lbs. of the ash of turnip bulbs, we find only about 10 lbs. of 

 the same valuable ingredient ; but, nevertheless, as we have 

 already said, an average crop of turnij)S draws frum an acre of 

 land twice as mucli phosphoric acid as a good average crop of 

 wheat requires from the same. If we take a crop of wheat at 

 4 quarters, and a crop of turnij)S at 20 tons per acre, we have 

 2016 lbs. of grain and 4480 lbs. of turnip bulbs. JUit then more 



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