334 



THE TROPICAL AGRICULTURIST. 



[Nov. 2, 1885. 



"A NEW THEORY:" FIXED AND SOLUBLE 

 INOKEDIENTS IN THE SOU. 



BY flU J. V. I.AWES, BART. IL.D., F. K. S. 



A friend residing in Virginia lias drawn my atten- 

 tion to an article in the October number of the 

 Sovtherii F/aiitcr. It is called "A New Theory," 

 and I do not think that I shall misrepresent the 

 views of the author if I sum them up as follows: — 

 That those fertilizing materials which exist in the 

 soil or are ajiplied in manures cannot be washed out 

 of it by water, whatever may be the quantity applied. 

 The author further says, "this arrangement is so 

 wise as to wear the impress of Deity." In the 

 observations I propose to make regard to the new 

 theory advauced in the pages of the ,SoiitIiei)i Plantci; 

 it will be my endeavor to show that while some 

 ingredients of plant food are fi.xed in the soil, others ai e 

 perfectly soluble; and further, that for the purposes 

 of vegetation it is absolutely necessary that these 

 last should he soluble. lu one of our field at 

 Eothamsted we have four rain ranges, each contain- 

 ing an area of forty-three square feet. One is placed 

 on the surface of the soil to catch the rain as it 

 falls, while the other three are placed underground, 

 and receive the rain after it has passed throut;h 

 twenty inches, forty inches and sixty inches of soil, 

 these being the resprctive depths at which the gauges 

 are fixed. The soil is that of an ordinary arable 

 field, with the exception tiiat no vegetation is allowed 

 to grow upon it. The rain water which falls on the 

 Burface gauge, and that which passes through the 

 three depths of soil has been collected and analyzed 

 for a number of years. Rain water always contains 

 a considerable amount of common salt.* At first 

 more salt was found in the water which passed 

 through the soil llnu in that caught in the open 

 gauge, thus proving that common salt, or some 

 substance containing chlorine, had been used on the 

 land as manure. All this excess has now been 

 washed out, and fur some years the amount of salt 

 passing through the soil is almost identical with the 

 amount which is found in the rain water taken f»im 

 the surface gauge. Here, then, we have an instance 

 of a food of plants— not I admit, a very important 

 food— which is not in any way fixed in the soil, but 

 circulates with the water. 



I now come to a more important substance. Rain 

 waUr contains a considerable amount of ammonia, 

 and very little nitric acid; but after it has pas.sed 

 through a cultivated soil, it contains very httle 

 ammonia, and a considerable amount of nitric acid. 

 It all the nitrogen in the rain water which falls up- 

 on an acre nt land during a year— both in the 

 form of ammonia and of nitric acid— passed through 

 the drain-gauge .soils, we should not obtain more 

 than from four to five pounds, whereas actually we 

 obtain eight or nine times that quantity. We will 

 omit all questions regarding the source of this 

 nitrogen, and confine ourselves to the question of 

 solubility. Here, then, we find a substance of the 

 highest importance as a food for plants, passing 

 through a soil live feet in depth, every year, in 

 such ipiaiititics as w«mld, if taken up by plant.s, be 

 sutiicient to grow crojis, much exceeding those grown 

 upon an average on the soils of the United States ! 

 Such are the results obtained on a soil without 

 vegetation. In our iiermanciit wheat fields we have 

 ordhiary drain jiipis laid at three feet from the sur- 

 face, and whenever sutliciently heavy rains occur 

 for the drains to run, the water is collected and 

 analyzed. Portions of this fiehl receive an apphcation 

 of salts of ammonia, and other portions nitrate of 

 soda. If a Inavy fall of rain takes place within a 

 day or two of the apiilicatiun of these manures, the 

 drainage water from the plot which received the 

 nitrate will contain a large amount of nitric acid, 



* Yes: and we feel more and more couviueeil that 

 the anomalous " mortifying" di,sea.se which attacked 

 eucalypti and cinclion;iS in Ceylon in 1S,S2 was mainly 

 to excess of salt iu the excessive raiufaU. — En. 



while the drainage water from the plot which re- 

 ceived salts of ammonia will contain very little 

 ammonia or nitric acid. Your correspondent may possibly 

 say that the nitrate has not had time to assimilate 

 with the soil. This idea will not, however, explain 

 the facts which I am ab(iut to relate. In a few 

 days the drainage water from the soil which receives 

 ammonia will begin to yield large quantities of nitric 

 acid, and if the two manures are sown in the 

 autumu with the wheat, and there is sufficient 

 rainfall during the winter, by far the largest part 

 of the nitrogen, applied in the ammonia and nitrate, 

 will be found in the drainage water. On the other 

 hand, if the drain runs iu the summer, when the 

 wheat is in the full vigor of its growth, the water 

 contains no nitric acid whatever, though at other 

 times, even on those parts of the field where no 

 substance containing nitrogen has been applied for 

 forty years, nitric acid is always to be found in 

 the drainage water. The only explanation that can 

 be given of these results is that ammonia, on its 

 first application, becomes, fixed in the soil, but rap- 

 idly becomes converted into nitric acid, which is 

 perfectly soluble in water, and forms no combination 

 with the soil. A great deal of our time of late 

 years has been spent in tracing the course of this 

 •ubstance through the soil and subsoil, and in some 

 instances our analyses have reached the depth of 

 nine feet from the surface. Some of our agricultural 

 plants have very deep roots, and as plants evajiorate 

 an enormous amount of water dining their growth, 

 it is certain that water, ard any salt dissolved in 

 the water, must be drawn up from below the area 

 of the roots. 



It is a fact about which there can be no doubt, that 

 while some important ingredients of the food of 

 plants are retained by the soil with great teuacity, 

 other.s are perfectly soluble, and are only fixed by 

 the vegetation growing on the surface. It is the 

 plant, therefore, and not the soil which prevents 

 the escape of the soluble substance; and we see in 

 this a beautiful e.vplanation of the fact, that the 

 operation of nature is always to cover the soil with 

 vegetation of some kind, while man, to supply him- 

 self with food, grows annual plants, the result being 

 that the soil is left bare of its natural clothing 

 for several months in the year. I have more than 

 once pointed out that the exhausting character of 

 grain crops is due not only to the ingredients which 

 are removed in the crop, but also to the loss of 

 those ingredients which the crop has failed to take 

 up ; these, in the absence of vegetation, are washed 

 out of the soil. When we find nitrates existing in 

 the sea, iu all springs and rivers, and passing through 

 all fertile soils, while they are absent in barren 

 and rocky soils — such as are often found in the 

 highlands of Scotland— and when further, it is borne 

 in mind that European agriculturists spend millions 

 every year in the production of nitrate of soda, we 

 cauuot either deny the importance of this ingredient 

 as a food of plants, or the fact of its solubility in 

 the soil. The chauges which take place in the organic 

 substances in the soil; the extreme solubility of the 

 nitrogen as it exists iu such forms of vegetable 

 matter as coal or peat, and the various changes 

 which occur before it assumes its ultimate acting 

 and solulile form of nitric acid, are likely to occnjiy 

 the attvntion of those who study the science of agri- 

 culture for a long time to come. 



In the slight outline I have given of whiit I venture 

 to think is more in accordance with the laws of 

 vegetalde growth in relation to the food in the soil, 

 than the views brought forward by your correspondent, 

 I trust that he may equally see, so far as they are 

 ill accordance with the truth, the impress of infinite 

 wisdom in which the world and all things in it 

 were created. — Southern Phiiiler 



"ey. 



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