NITROGEN : WHY AND WHERE CROPS MUST GET IT. 201 



and the planted strips of the previous year were in their turn sub- 

 jected to thorough tillage. Thus the system was continued for 

 twelve years and without the use of a particle of manure. The 

 results were somewhat astonishing. You will observe that on 

 each acre of wheat only half was really occupied by the crop, in 

 each year ; while the other half, consisting of the three-foot vacant 

 spaces, was being cultivated in preparation for the next year. But 

 on each acre so treated — only half of it really bearing a crop, and 

 that half in rows a foot apart — the yield was as great as on 

 manured land prepared for and sown with wheat in the ordinary 

 manner. The average crop per acre was 25 bushels ; and in the 

 eleventh year the yield amounted to 37 bushels, with 2 tons of 

 straw . 



Now experience and experiment go to show that wheat is, 

 generally, especialh- thankful for a manuring containing nitrogen ; 

 on Mr. Lawes' experimental grounds any other constituent of 

 manures could be spared better than the nitrogen ; hence it is 

 reasonable to infer that the extremely thorough and unceasing 

 tillage of the soil at Lois Weedon, exposing as it did constantly a 

 fresh and porous surface to the air, so facilitated this direct absorp- 

 tion of ammonia, or (as it may yet appear) of nitrogen in some other 

 shape, from that great reservoir, as to make these large crops pos- 

 sible without the addition of any nitrogenous manure to the soil. 



There is yet another wa}', already incidentally named, for ni- 

 trogen compounds in the air to reach the plant through the soil. 

 Besides ammonia, there is always some nitrate in the air. Both 

 compounds are ver}' soluble in water, and consequently every 

 rain will carr}' nitrogenous plant food to the soil. At several 

 of the experiment stations in Prussia, the quantities of nitrogen 

 thus brought within the reach of vegetation during the j'ear were 

 carefully determined ; these quantities were found to be quite 

 different in different places ; the largest amount was 21 lbs. to the 

 acre, and the smallest 2 lbs. ; and it was also found that nitrogen- 

 ous manures were most effective at that place where the natural 

 supply of combined nitrogen was smallest. This is one observa- 

 tion going to show that these natural supplies have an appreciable 

 value. 



Various averages have been given for the quantity of com])ined 

 nitrogen thus carried down to the soil in the course of the year. 

 Where extremes may be so far apart, averages have to be taken 



