292 THE TURNIP CROP. 



Wheat and turnips may be taken as good instances in 

 point. Wheat (a seed-bearing crop) has a minimum 

 amount of leaf- surface, and requires a large amount of 

 nitrogen compounds in its grain produce; turnips (an 

 herbaceous crop) have a maximum amount of leaf-surface, 

 and a proportionate feeding capacity, while their nitrogen 

 requirements are very small. We therefore infer that 

 nitrogenized manures are more necessary to the one than 

 to the other ; and we consequently recommend " Peruvian 

 guano" as most effective for wheat, and "superphos- 

 phate" for the turnip crop. 1 



The valuable experiments of Messrs. Lawes and Gilbert, 

 and of Dr. Voelcker, in reference to manurial applications, 

 show us how satisfactorily practice confirms the theory 

 of the present case. Each year we have the details of 

 numerous experiments with different manures to different 

 crops, but chiefly to turnips, placed before us, and we see 

 as great a variation in the results. Now, this constant 

 variation, which so materially reduces their general value, 

 is due to the impossibility of securing in each case the same 

 conditions of soil, climate, and 'season each of which 

 largely affects the action of any manurial substance used. 

 We often hear of a manure being followed by the best 

 results in one place and being a total failure in another, 

 while the most successful application in the latter was 

 placed low on the trial scale in the former place. Yet 

 both may be equally suitable for the conditions under 

 which they were applied the difference in their results 

 proving how disastrous they may be if applied indiscri- 

 minately, without a proper knowledge of the conditions 

 inseparable from their successful application. We must 

 not, therefore, place too much reliance on the results ot 

 these various trials, especially when made in a different 

 district, as regards climate and soil, from our own ; neither 



1 Roy. Agn. Soc. Jour., vol. xviii. p. 491. 



