126 



THE AGRICULTURAL NEWS. 



Api:il 18, 1908. 



NITROGEN AS A PLANT FOOD. 



No plant food is of more importance than nitrogen, 

 since this is the element removed from the soil in 

 largest quantity by the great majority of crops. The 

 available supply of nitrogen in most soils, too, is very 

 readily exhausted by continuous crop growing, and it 

 is the most costly of manurial elements to replace. As 

 most planters are aware, an economical method of 

 increasing the store of nitrogen in the soil is by includ- 

 ing in the rotation an occa.sional crop of leguminous 

 plants, such as cow pea.?, velvet beans, ground nuts, etc., 

 which thus serves a double purpose. The following 

 notes dealing with the subject of nitrogen as a plant 

 food, are taken from a lengthy article entitled ' Relation 

 of Nutrition to the Health of Plants ', that appeared in 

 the yearbook of the United States Department of 

 Agriculture, 1901 : — 



Nitrogen is an important con.stituent both <>( i)lant ami 

 animal food. It is essential to the formation of albnniinoiils 

 and of various constituents of the protoplasm or living sub- 

 stance of the plant. By farthemost important source of nitrogen 

 foi- most agricultural crops, under ordinary circumstances, is 

 the nitrates of the soil. The main source of nitrogen in the 

 soil, besides the decay of organic matter, is the fixation of 

 the nitrogen of the atmosphere through the agency of micro- 

 organisms. Though about 7-5 per cent, of the volume of the 

 air is nitrogen, it does not become available to ordinary crops. 

 In the case of leguminous crops, however, nitrogen is absor- 

 bed by micro-organisms, and converted into nitrates or some 

 other high nitrogen compound wliich can then be utilized as 

 plant food by the growing crop. ^lany varieties of bacteria 

 and fungi have been found which can absorb free nitrogen if 

 they are furnished with carbohydrate fond. This is usually 

 tlerivcd from decomposing vegetable matter or from living 

 rout cells. The bacteria live on, or in, the roots of the 

 leguminous jdants, forming swellings or tubercles on them. 

 The great importance of this to agriculture is at once 

 apiiarent, and the study of the conditions fa\-ouriiig the growth 

 of these benetirial miro orgaui-ims is of the highest iira<'tical 

 value. 



The lack of a sufficient supply of nitrogen to growing 

 plants is usually manifested by reduced leaf and stem growth 

 on the part of the ero|i, aii<l a tendency to the production of 

 flowers and fruit at a very early period, though the amount 

 of fruit jn'oduced is correspondingly small. In this respect the 

 etVect of a lack of nitrogen is similar to that of a lack of 

 water. ( )ii the other liaiid, an excess of nitrogen acts like 

 an excess of water, stinudating the production of vegetative 

 growth at the expense of Howers and fruit. This growth is 

 rich iu nitrogenous matter and water, ami i> \r>y easily 

 injured by unfavourable conditions. It is a well known I'ael, 

 for example, that many cereal crops have not only soft leaves 

 and weak stems under such conditions, but the phmts are 

 more .subject to rust and nnldew, and various otlier parasitic 

 diseases. This is true, not only of cereals, but practically of 

 nil ordinaiy phmls. In ndlure under glass lliesi' conditions 

 can be eontidlleil and rcnieilied, Imt in the lield it is more 

 dilficult. Drainage ami methoils of enlti\atiiin also in 

 a measure afford means of check to ra]iid and succulent 

 growth in wet seasons. 



Besides these general effects of the lack or excess of 

 nitrogen on growth, attention should be directed to some 

 ob.scure diseases whore nitrogen assinulation appears to be 

 involveil. Among these may lie nientione.l ' mo.saic ' disease 

 <)f tobacco, winter blight of tomato.^, ' ilie back' of llu- 



ra-ange, and t'alifonda vine disease. As already stated, }>lants 

 obtain most of their nitrogen through the absorption of 

 nitrates by the roots. The dilute solutions pass up through 

 the stem to the leaves, where, through the aid of the 

 chlorophyll, the nitric ,acid unites vi'itli sugars to form the 

 more highly organized nitrogen compounds such as anudes 

 and proteids, wliich ser-s'e as food for the growing cells. The 

 yiiung cells cannot use the original soil nitrates any more 

 than animals can, so that if anything interferes with the 

 process of proteid organization, nitrogen starvation will 

 follow, even in the presence of large quantities of nitrate. 

 For the organization of proteids, sugars are required, and 

 sugar cannot be produced unless the chloroplasts are in good 

 working order, and exposed to light and heat of the piroper 

 intensity. The proper mineral nutrients — lime, potash, 

 phosphoric acid, magnesium, iron, etc., must always be 

 pireseiit. With insufficient light or heat there is no proteid 

 formation from nitrates, neither is there any in albino leaves, 

 or those devoid of chlorophyll. In both of these cases, 

 therefore, nitrates accumulate in the plant. With the 

 renewal of the activity of the chloroplasts the accumulation 

 of nitrates is gradually worked up into [iroteids, exccjit, of 

 course, in albino leaves, ^\here the chloroplasts may have 

 permanently lost their functional activity. In sucli cases the 

 cells usually remain comparatively rich in nitrates. 



It is known from exi)erimental investigation that 

 a large excess in nitrates may in itself cause a yellowing 

 in the chlomplast.s, and thus serve directly to prevent further 

 nitrate assimilation. At first, plants overfed with nitrate 

 of .soda, or other strong nitrogenous fertilizer, liecome a brighter 

 green and grow rapidly, but as the nitrate accumulates in the 

 cells faster than it is used, the leaves begin to turn yellow 

 on the edges ami along the vascular bundles, growth 

 is checked and the plant dies back. This is cspt;;ially likely 

 to happen in the the c^ise of crops that are not gross feeders. 

 Yellowing and death of the edges of leaves (thimgh not follow- 

 ing a stinuilated growth) is caused by an over-application of 

 almost any quickly soluble salt (potash, sodium chloride, etc.). 

 In the case of the orange, it has been observed that the 

 disease known as ' die back ' appears to be greatly fa\oured, 

 if not cau.sed, by excessive fertilization with organic manures 

 rich in nitrogen. It is not known whether nitrogen from 

 mineral fertilizers has the some effect. 



Webber also observes that on the poor sandy soils of 

 Florila, ; u'|)hate of ammonia and nitrate of .soda stimulate not 

 only vegetative growth of the orange, but the production of 

 fruit as well, while organic manures are more likely to stimu- 

 late vegetative growth at the expen.se of fruit, the fruit 

 produced with organic nitrogen being coarser, thicker skinned 

 ami of poorer i|uality tiian when mineral fertilizers are u.sed. 

 I'cn manure acts in this way like organic manures, as nuglit 

 lie expected. 



RUBBE^R PRODUCTION IN PARA. 



'Ihe Ci(jvei nor of I'ara, in a recent nn'i.sage to the 

 Legislati\-c Assembly of Brazil, gave the following 

 figures with reference to the output of rubber during 

 l!)0(i-7 : - 



'I'hc rnlibcr production of I'ara in the season 1 !!()() 7 

 (unounted to 1 1, 1()7 tons, valued at £.3,3112,000. In l!)().")-G 

 thcoutput'Of rubber fioni this State was 11,832 tons, valued 

 at £3,()23,440. The total rubber croi) of Brazil in 1906-7 

 amounted to 37.1:)9 tons. Practically the whole of it was 

 exportel to New York, Liverpool, Hamburg, Havre, and 

 Antwerp. The quantity of rubljcr on hand on .June 30 last 

 was ab:jut Hi.") Ions. 



