■472 



HOETICULTUKE 



September 26, 1914 



ADAPTATION OF PLANTS TO 

 SOILS. 



A paper by George E. Stone, Ph. D., 

 ■Prof, of Botany, Mass. Agricultural College, 

 aud Physiologist and Patbologist of Mass. 

 -Agricultural Experiment Station. Read be- 

 fore S. A. F. at Boston. 



The greatest advance in knowledge 

 concerning tlie adaptation of crops to 

 soils has been achieved through prac- 

 tice and experience rather than by 

 -means of field and laboratory studies 

 of the soil. There are many condi- 

 tions aside from the surface texture 

 which play a part in this adaptation, 

 such as the nature of the substratum, 

 depth of water table, etc.; and some 

 insight into the subject may also be 

 had by studying the distribution of 

 plants as given in any flora. Where a 

 region has been settled for many gen- 

 erations and deforestation and agri- 

 cultural practices have been carried 

 on extensively. we find many 

 changes in our soils and conse- 

 quent modification of the flora. 

 Some of the many factors determining 

 the distribution of plants are com- 

 plex and difficult to eliminate from 

 other factors, and at present not 

 enough is known about them to deter- 

 mine their real significance. 



On soils which only a half century 

 ago supported certain types of vege- 

 tation we now find an entirely differ- 

 ent flora owing to changes in the na- 

 ture of the soil; lack of humus con- 

 tributing largely to this modification. 

 Some plants such as the Canada this- 

 tle, were more common forty years 

 ago in some locations than at present, 

 while some other plants which have 

 been growing for some time under 

 cultivation have recently escaped and 

 become pests. It would naturally be 

 supposed that this is due to a change 

 in the environment, such as soil condi- 

 tions or source of seed. But whether 

 there is in plants as in races of men, 

 -a tendency to a.ggressiveness which 

 sometimes unaccountably breaks out 

 although usually lying dormant, we 

 will not venture to say; still there is 

 some evidence to support such a 

 theory. 



Some plants are confined to bogs, 

 some to sandy soils, and others to 

 heavy, compact soils, and many are 

 adapted to a great variety of condi- 

 tions. Others are limited to salt 

 marshes, and still others to territory 

 within a few miles of the seacoast. 

 Elevation, humus and soil moisture 

 play an important role in plant distri- 

 bution, and some plants are restricted 

 by what is termed "seed habit." the 

 seeds of certain species retaining 

 their germinating capacity for some 

 time and others for only a few weeks 

 or even days. For instance, the seeds 

 ■of the willow, poplar, alder and other 

 species native to wet locations remain 

 viable only a few days or weeks, while 

 others will do so for ten to twenty-five 

 or more years. Seeds with a limited 

 term of viability must therefore find 

 suitable conditions for germination 

 during this time, while the others can 

 afford lo await their opportunity. 



Most garden seeds require a mini- 

 mum of 2 to 3 per cent, of soil mois- 

 ture to germinate at all. and for the 

 best germination a higher percentage 

 is required; therefore during dry sea- 

 sons the seeds of some crops fail to 

 -catch. Purslane and pigweed seed. 



however, will germinate with a very 

 small amount of soil moisture and 

 flourish when more desirable plants 

 will not; therefore during drought 

 periods we find purslane overrunning 

 gardens and pigweed completely mo- 

 nopolizing newly sown lawns. 



The percentage of air in soils plays 

 its part in plant adaptation, as do also 

 the chemical constituents and biologi- 

 cal characters. The soil texture or 

 mechanical properties^ which are in- 

 separably connected with the air and 

 moisture of the soil, together -n'ith the 

 capillarity, etc., are also very import- 

 ant factors in crop production and 

 plant distribution. It should be stated, 

 however, that the specific effect on 

 plant distribution of any one of the 

 factors mentioned is not known; still 

 a great deal is knowm concerning the 

 eifects of chemical constituents on 

 plants, ranch more study having been 

 given tu this subject. Soil differs ma- 

 terially in its chemical composition 

 and mechanical properties, and the 

 configuration of the plant is greatly 

 modified by the different types. Even 

 in a small territory there are charac- 

 teristic variations in the soil which 

 are of sufficient importance to justify 

 specialization in farming. 



The river valleys furnish typical 

 soils adapted to the growth of special 

 crops, the meteorological conditions of 

 these localities also emphasizing the 

 individual character of the crops. The 

 coarse and more friable soils of the 

 .Atlantic seacoast (truck soils) are 

 light and porous and are used largely 

 for such market garden crops as let- 

 tuce, cucumbers, tomatoes, radishes, 

 etc. The soil charactertistic of the 

 Boston district is admirably adapted 

 to truck farming, being very loose and 

 easily worked. It is especially adapted 

 to head lettuce, which is grown more 

 skilfully and successfully in that re- 

 gion than anywhere else. The texture 

 of such a soil is characterized by 

 a predominence of the coarser par- 

 ticles and a relatively small amount 

 of the finer materials such as 

 silts and clay. Except in some 

 few localities the interior soils are 

 not well adapted to the growth of 

 head lettuce; therefore the curly or 

 open type is grown in the heavier and 

 more compact soils of the Middle 

 West. In all its stages head lettuce 

 requires a loose textured soil for per- 

 fect development. These soils are 

 manured heavily year after year, and 

 in the greenhouse are never changed; 

 and the large amount of organic mat- 

 ter furnished by the decomposed horse 

 manure renders the soil even better 

 adapted to this particular crop. 



A more compact soil is a Connecti- 

 cut Valley soil, characterized by the 

 large amount of very fine sand 

 and silt. This soil has long been de- 

 voted to the growth of tobacco, onions 

 and cucumbers and to some extent, 

 melons. It contains little organic mat- 

 ter since commercial fertilizers are 

 used entirely. The soil may even vary 

 somewhat in its texture in a limited 

 region, and this variation will alone 

 affect the quality and value of a to- 

 bacco crop to a considerable degree, 

 and onions to a less extent. The 

 warmer, coarser textured soils are 

 well adapted to melon culture, the 

 crop growing vigorously and maturing 

 early, with less liability to infection 

 from blights, etc. 

 Asparagus is grown largely in some 



sections In very dry, coarse soils hav- 

 ing little water retaining capacity 

 although not especially adapted to 

 these conditions. The finer textured 

 soils are much superior tor asparagus, 

 which sometimes yields at the rate of 

 $1,000 per acre. Besides, in light, 

 sandy soils this crop suffers much 

 more severely from rust than in the 

 finer textured soils. 



The florist must also consider his 

 soil seriously to obtain the best re- 

 sults. The potting bed soil is usually 

 a coarse soil, well supplied with or- 

 ganic matter to insure looseness of 

 texture. Most plants respond more 

 quickly in a loose textured soil than 

 in one of fine texture because more 

 air can be supplied to the roots, al- 

 though seeds germinate better and the 

 seedlings make better growth when 

 the soil is slightly compacted. The 

 total exclusion of air from seeds, how- 

 ever, as shown by experiments with a 

 vacuum, prevent germination. A 

 close textured soil tends to have this 

 same eftect. depending upon the na- 

 ture of the seed as well as upon the 

 amount of air received; therefore It 

 becomes necessary to take into ac- 

 count the depth of the planting of 

 seeds in practical agriculture. Cer- 

 tain seeds and plants are much more 

 susceptible to air than others, and ar- 

 tificial aeration of soil is often bene- 

 ficial. In one experiment where 1500 

 lettuce seeds were sown in two boxes, 

 in one of which the soil was aerated 

 for a few hours each day, there was a 

 gain of 20 per cent, in germination 

 and 46 per cent, of growth of seed- 

 lings in the aerated soil. 



Lettuce or white clover seed planted 

 in a close textured soil that has been 

 firmly tamped will fail to germinate 

 at ail, while such seeds as plantain 

 will germinate quite freely under the 

 same conditions, showing that the 

 l)lantain is better adapted to a close 

 textured soil than the other seeds 

 mentioned. 



In the more intensive agriculture of 

 the future, aeration of the soil may 

 become practical. Aeration affects 

 the respiration process in seed ger- 

 mination and increases growth, be- 

 sides having a beneficial effect on the 

 micro-organisms of the soil, which 

 play an important role in soil fertility. 

 Of the florists' crops which are af- 

 fected by variations in soil texture, 

 the rose furnishes one of the best ex- 

 amples. This crop requires a heavy, 

 fine textured soil for its best develop- 

 ment. 



In the Arlington soil, a typical truck 

 garden soil, the coarser particles total 

 39.1.5 per cent, and the finer particles, 

 40.2.5 per cent. The best rose soils ap- 

 pear to be those possessing 8 to 12 

 per cent, or more of clay and which 

 are well supplied with other grades of 

 finer particles. The percentage of the 

 very fine sand, silt and clay usually 

 exceeds 75 per cent, in an ideal rose 

 soil, but just how important are the 

 clay and the two grades of silt and 

 very fine sand in making up such a 

 soil cannot at present be determined. 

 There are many native species of 

 plants which show an adaptation to 

 soil texture, and many species which 

 are confined strictly to certain types 

 of soils. We have our dry sandy soil 

 species; also those dependent upon 

 humus, but the latter type is contin- 

 ually disappearing in some localities. 

 Variations in the chemical constltu- 



