MANURING IN THEORY AND PRACTICE. 



116 



In considering the yield of nitrogen by Turnips of 

 the order CitieifertB, and Sugar Beet of the order 

 Chenopodiaeea, we again find a marked decline in the 

 stock of fertility during the thirty-six years that 

 these experiments have been carried on ; and from 

 analyses of the soil made at different periods, it has 

 heen ascertained that not only has there been a 

 decline of organic nitrogen in the soil, but of potash 

 and phosphoric acid also. 



It follows, therefore, that although the fertility of 

 a rich garden soil may be sufficient to grow crops of 

 vegetables, or fruit or flowers, for a very long 

 period without further manuring, yet true eco- 

 nomy in horticulture is not to be attained by a 

 simple lessening of expenditure in the matter of 

 manuring, but by studying and applying the proper 

 nourishment to plants, and so obtaining the greatest 

 production with the maximum amount of profit. 



It may further be observed that those who main- 

 tain that the atmosphere is an important source of 

 the nitrogen of our crops, assume that many descrip- 

 tions of plants, if provided with a small quantity of 

 nitrogenous manure to favour their early develop- 

 ment, will obtain the remainder of their food-supply 

 from the atmosphere. How far this is the case may 

 be illustrated by the following results, which are the 

 average produce of fifteen years' successive growth 

 of Swedish Turnips, and five years of Mangel 

 Wurzel, all grown on the same land, and in each 

 case with the same manure year after year. 



Average produce per acre of Swedish Turnips, 

 fifteen years, 1856-70 :— 



Manures applied. 



1. Superpliospliate of Lime 



and Sulpliate of Fotosli , 



2. As No. 1, and 36i lbs. 



Ammonium salts . 



3. As No. 1, and 400 lbs. Am- 



monium salts . 



Average produce per acre of Mangel Wurzel, four 

 years, 1881-84: 



Thus the annual application of about 8 lbs. of 

 nitrogen as ammonia salts increased the crop of 

 Swedish Turnips by only 6 cwts. per acre per 



annum. And the same amount applied to Mangel 

 Wurzel increased the growth of roots by 33 cwts. 

 per acre, with an excess of 5 cwts. of leaves per acre 

 also. An appUcation of 400 lbs. of ammonium salts 

 nearly doubled the Swedish Turnip crop, and in- 

 creased the produce of Mangel Wurzel roots from 

 6 to 14 tons, and the leaves from 20 cwts. to 66 

 cwts. per acre per annum. 



It is obvious, therefore, that a small quantity of 

 nitrogen applied as manure does not enable plants to 

 obtain much, if any, nourishment from atmospheric 

 sources, and that a further direct supply of plant- 

 food becomes necessary. These results also afford 

 confirmation of the view, that it is the reduction of 

 the available supply of organic nitrogen within the 

 soil, that is the cause of the decline in the annual 

 produce of a garden. 



It is not in the difference of the capacity of 

 certain plants for taking up nitrogen from the 

 atmosphere, that the gardener must look for an 

 explanation of the distinctive function of difierent 

 crops. The explanation is rather to be found in 

 variation of chai-acter, and length of life of different 

 plemts ; in the nature of their roots in regard to 

 number, range and^ size, and to their aptitude to 

 derive more of their food and moisture from the 

 surface or from the sub-soil ; finally, in the greater 

 capacity of some plants for liberating and assimi- 

 lating food not available to others, or for arresting 

 nutritive matters which would otherwise be washed 

 out of the soil by heavy rains. 



Evidence further shows that the so-called " root- 

 crops," which may include Potatoes, Beet, Onions, 

 &c., exhaust the superficial layers of a soil of its 

 available supply of fertility more completely than 

 do deep-rooted plants, whose main feeding-ground is 

 the sub-soil. 



It is well known among agricultural chemists that 

 the growth and removal of a highly nitrogenous 

 crop of either Beans, Peas, or Clover, is one of the 

 best possible preparations for the growth of Cereal 

 crops, which characteristically require luxurious 

 manuring. And notwithstanding the fact of the 

 large amount of organic nitrogen, and of potash, 

 lime, magnesia, and phosphoric acid removed from 

 the land by the growth of leguminous crops, yet 

 these plants actually leave the surfac? soil richer in 

 nitrogenous plant-food than it was before. 



Plants of one family wiU often grow luxuriantly 

 where other plants fail, and vice versa. For a long 

 time it was supposed that certain substances were 

 given off from the roots of plants, which in time 

 accumulated in the soil, and so poisoned the plant 

 which had excreted them. These explanations have, 

 however, been long exploded. We now know that 

 failure does not arise from anything left in the boU, 



