328 



SCIENCE, 



[Vol. XIV. No. 354 



ATMOSPHERIC NITROGEN AS PLANT-FOOD. 



Farmers in all older portions of the country buy large quantities 

 of nitrogen in artificial fertilizers. Nitrate of soda, sulphate of 

 ammonia, dried blood, cottonseed-meal, and fish-scraps owe their 

 fertilizing value mainly, and Peruvian guano and tankage largely, 

 to nitrogen ; and the same element is one of the chief ingredients 

 of bone manures, amraoniated phosphates, and many other fertil- 

 izers. According to an estimate by the Connecticut Experiment 

 Station, not less than five hundred thousand dollars are expended 

 annually for commercial fertilizers in Connecticut. A large amount 

 of this goes for nitrogen, which is one of the dearest of the ingre- 

 dients of fertilizers, and costs at retail from eight or ten to eighteen 

 cents or more a pound. 



The Storrs School Agricultural Experiment Station, Mansfield, 

 Conn., in its October bulletin, reports a continuation of an investi- 

 gation of atmospheric nitrogen as plant-food, begun some years 

 ago at Wesleyan University, Middletown, where the chemical 

 work of the station has been carried on since the establishment of 

 the latter in iS88. The details of the experiments there reported 

 were conducted by Mr. C. D. Woods, formerly assistant in chem- 

 istry in Wesleyan University, and now chemist of the station. 



The quantities of nitrogen in ordinary crops, and the cost of the 

 same in the better commercial fertilizers, vary from 31.5 pounds for 

 potatoes, to 80.3 pounds for clover-hay, costing from $4.73 to 

 $12.05. 



The plants must have this nitrogen, or they cannot grow. They 

 obtain part of it from the soil, and the rest from the air. The ni- 

 trogen of the soil has either been accumulated in the past or is 

 -supplied in manures. A small quantity, in the form of ammonia 

 .and other compounds of nitrogen, is continually brought to the 

 soil by rain or snow. Late research implies that soils acquire ni- 

 trogen from the air by the aid of microbes or electricity, or proba- 

 bly both. The nitrogen in the soil is being continually leached 

 -away by drainage- waters, and more or less of it escapes into- the 

 air. Soils which are not cultivated, and from which the produce 

 is not removed, accumulate more nitrogen than they lose, so that 

 many virgin soils have a large stock. By ordinary cultivation and 

 ■ cropping, the nitrogen is gradually exhausted, unless it is returned 

 iby manures or otherwise. 



The main questions have been, first. Can plants make use of at- 

 mospheric nitrogen to any considerable extent ? second. If they do, 

 is it the free nitrogen of the air that they acquire ? There are cer- 

 tain kinds of plants, like clover, beans, and others belonging to the 

 family of the legumes or PapilioJiacea, which generally get on very 

 well without nitrogenous fertilizers in worn-out soils ; an"d it would 

 seem as though these plants, at any rate, must in some way be able 

 to make use of the nitrogen of the air. But the classic experi- 

 ments of Boussingault in France, of Lawes and Gilbert in Eng- 

 land, and others, have been widely accepted as proving that plants 

 cannot use the free nitrogen of the air, and that they get practi- 

 cally very little combined nitrogen from the air, so that they are 

 dependent upon that previously stored in the soil or supplied in 

 manures. Still many experimenters have not regarded the question 

 as definitely settled. 



While the experiments of Boussingault, and Lawes and Gilbert, 

 differ in their details, they agree in this, that the plants were under- 

 conditions widely different from those in ordinary culture. The 

 especial object was to find whether plants acquire free nitrogen ; 

 and the plants were for the most part grown under cover, to ex- 

 clude combined nitrogen, and in artificial soil containing little or 

 no nitrogen. The growth was generally stunted and abnormal. 



Later experiments on more or less similar plans have brought 

 similar results. Investigations by Ville in France, however, im- 

 plied that plants can acquire nitrogen from the air, but his conclu- 

 sions were not generally accepted. 



Some years ago a series of experiments was conducted by Mr. 

 C D. Woods, in which the conditions were more like those in which 

 , plants commonly grow. The method used was that of sand-cul- 

 •ture. By proper management, feeding, and watering, plants may 

 be grown as large, as healthy, and in every way as well developed, 

 .in pure sand as in the richest soil. For these experiments sea-sand 

 was used. To remove all traces of material containing nitrogen 



(except, of course, air), the sand was carefully sifted, then washed, 

 and finally heated in iron pots in a furnace, so hot that the pots 

 nearly melted. It was then put in glass jars, and water was added 

 in which were dissolved salts containing the mineral elements of 

 plant-food, potash, lime, iron, sulphuric acid, phosphoric acid, etc., 

 and in some cases nitrogen in the form of nitrate of potash or lime. 

 The seeds were then sown, and the plants grew. They were kept 

 in the open air in a building erected for the purpose. The arrange- 

 ment was such that the plants were exposed in the day-time in 

 pleasant weather, but put under cover when it rained and at night. 

 They had enough plant-food to enable them to make more or less 

 growth independently of the nitrogen of the air, but were free to 

 get the nitrogen from the air in case they were able to do so. They 

 grew well. Many of them were as well or better developed than 

 those in a rich garden-soil near by. 



The amount of nitrogen in the seeds and in the nutritive solu- 

 tions was determined by analyses at the beginning of the experi- 

 ments. The same was done with the nitrogen in the plants at the 

 end of the experiments, and with that left in the nutritive solutions. 

 The quantities of nitrogen supplied to the plants at the beginning, 

 and contained in them at the end, of the experiment were thus de- 

 termined. The plants were found to contain more nitrogen than 

 had been supplied by the nutritive solutions and the seeds. For 

 this gain there was but one possible source, the atmosphere. The 

 peas had in some way acquired nitrogen from the air, and in some 

 cases the quantities of atmospheric nitrogen , thus obtained were 

 very large. 



Since that time a number of investigators have obtained similar 

 and even more striking results, and much light has been thrown 

 upon the ways by which the plants are enabled to obtain the nitro- 

 gen from the air. 



Professor Hellriegel in Germany has found from a large number 

 of experiments that pea, lupine, and serradella plants obtain large 

 quantities of nitrogen from the air, while oats, barley, and buck- 

 wheat seem to be restricted to that supplied to them in the soil 

 and obtained through the roots. He has furthermore brought out 

 the very important fact that there is a connection between the 

 nitrogen acquired and the tubercles which are found on the roots 

 of leguminous plants. The root-tubercles are the bulb- like en- 

 largements, from the size of a pin-head to that of a pea or larger, 

 sometimes called " warts," which are found on the roots of beans, 

 peas, clover, cow-peas, and other leguminous plants. They are 

 often thought by persons not botanists to be indications of disease. 

 This suggests that minute organisms, termed " microbes," which 

 are in some way connected with these tubercles, may be the agents 

 by which the plants obtain nitrogen from the air. 



To test the influence of t~he microbes in the soil, Professor Hell- 

 riegel prepared soil-infusions by putting small quantities of soil in 

 water, shaking the mixture thoroughly, and letting it settle. The 

 water was then assumed to contain the microbes. The infusions 

 thus prepared were put into the sand in which the plants grew. In 

 a very remarkable series of trials it was found that where legu- 

 minous plants were supplied with mineral but no nitrogenous food, 

 and received these infusions, they grew well, had tubercles upon 

 their roots, and contained large quantities of nitrogen when mature. 

 Those which received no infusions, or infusions which had been 

 sterilized, i.e., in which the microbes had been killed, made very 

 little growth, had few or no tubercles, and showed no gain of nitro- 

 gen. In another experiment Professor Hellriegel grew peas and 

 buckwheat inside a large glass globe, as Boussingault had done, 

 except that soil-infusions were added. In both Hellriegel's and 

 Boussingault's experiments the plants had practically no nitrogen 

 except that in the seed and the free nitrogen of the air. Boussin- 

 gault's plants made very little growth, and showed no gain of 

 nitrogen. The same was true of Hellriegel's buckwheat ; but his 

 peas grew well, and gained considerable nitrogen. In other words, 

 where the microbes were present, the peas evidently utilized the 

 free nitrogen of the air. 



Professor Wolff in Germany has reported experiments with 

 clover which imply acquisition of atmospheric nitrogen. Numer- 

 ous other late experiments indicate that both plants and soil obtain 

 nitrogen from the air. 



The experiments now described in this bulletin may be divided 



