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The Weekly Florists^ Review* 



Decbmbeb 26, 1907. 



supplying phosphorus to the soil from be- '•'-/' 

 low. . ••- 



■:^^^'K*'-*' _:■ Structure. ■•. , , ', 



From the standpoint of structure, soils 

 differ very widely, both in the extent of 

 their internal surface and in the char- 

 acter and extent of the segregation or 

 their particles. These differences are 

 fundamental, and very important in de- 

 termining the relative productive capac- , , 

 ity and In directing agricultural prac- ^ 

 tice. An acre-four-foot of one-foot gran- ^" 

 ite blocks would possess an internal sur- . \ 

 face of twenty-four acres to which water 

 might adhere, upon which plant food 

 might develop and where it might be 

 stored, over which the roots of plants 

 might spread and feed and where soil , 

 organisms might dwell. To reduce the 

 diameters of these cubes from one to 

 one-thousandth of a foot would increase 

 the internal surface one. thousand-fold, 

 making it aggregate 24,000 acres per 

 acre of field. But even this surface is 

 too small to maintain a high productive 

 capacity. Our coarsest sandy soils pos- 

 sess an internal surface per acre-four- 

 feet exceeding forty-five square miles 

 per acre of field; our loams, 270 square 

 miles ; while our finest clay types pos- 

 sess an internal surface exceeding 1,300 

 square miles per acre of field. It is 

 clear, therefore, that there must be wide 

 differences in the productive capacity of 

 soils due to differences of internal sur- 

 face alone, even where their chemical 

 natures may be identical. This must be 

 80, because where there is more surface 

 more water can be retained, plant food 

 may form more rapidly and more may be 

 stored and held in reserve and even ac- 

 cumulated during intervals of small de- 

 mand, as well as retained against loss 

 by leaching. , 



The innermost portion of water films 

 investing soil grain surfaces, in my 

 judgment, is held there with so much 

 force as to be little subject to change, 

 either by drainage or capillary move- 

 ment, and also becomes highly charged 

 with plant food, which likewise is strong- 

 ly retained, escaping only by the slow 

 process of diffusion when the roots of 

 plants are placed in contact with the soil 

 grain surfaces or when the excess hydro- 

 static and capillary portions of water 

 are moving by. We have found, for ex- 

 ample, that when a chemically cleaned 

 sand was charged with a solution of 

 potassium nitrate, ten repeated washings 

 in twice its weight of distilled water 

 still left in the films of moisture retained 

 by the sand grains enough of the nitrate 

 to represent 244 pounds per acre-four- 

 feet. Plant food so retained by soils 

 may still be available to crops, for their 

 root hairs are similarly invested with 

 water films and when placed in apposi- 

 tion with the soil grains the water film 

 becomes common to the two and simple 

 diffusion permits the root to feed upon 

 the plant food so retained. 



Proper Drainage. 



This brings me to consider a principle 

 underlying prdper land drainage. It is 

 very important that when rain falls upon 

 a field the excess water remain only just 

 long enough on its way through the 

 open water passages to saturate the soil; 

 anything longer than this provides time 

 and opportunity for the most valuable 

 plant food materials carried in the water 

 films about the soil grains to diffuse out 

 into the moving water and so become 

 lost in the drainage. 



TTo be continued.) 



The food of plants, derived from the 

 soil, is only certain substances which are 

 dissolved in the soil moisture or which 

 are carried in the soil in a form which 

 may be readily so taken up as it is 

 needed; and the amounts of these pres- 

 ent in the root zone of field crops at 

 any one time are relatively very small 

 when compared with the arnounts of the 

 plant food elements from which they 

 are derived. Much more is a soil like 

 a pasture where plant food grows than 

 like a bank or granary where it is 

 stored, and just as a rich pasture may 

 produce suflBcient grass to carry a large 

 herd, so may a fertile soil produce from 

 day to day plant food sufficient for good 

 crops. Just -as pastures differ in the 

 amounts of herbage on the ground and 

 in the amounts they are able to add to 

 this as it is fed away, so do fields differ 

 both in the amounts of plant food pres- 

 ent in the root zone at any one time 

 and in the amounts they are "able to add 

 as this is withdrawn. 



An Actual Experiment. 



Our own observations, published by 

 the Bureau of Soils, have demonstrated 

 that four good soils, observed to pro- 

 duce 2.5 times the yield of corn and 

 potatoes per acre that four poorer soils 

 did under identical treatments, also gave 

 up, when washed three minutes in five 

 times their weight of pure water, 2.58 

 times as much plant food. Not only 

 was there this difference in the amounts 

 of plant food carried in water-solilble 

 form in the best and in the poorer soils, 

 but the amounts of this same plant food 

 taken out of like areas of field by like 

 numbers and kinds of plants during the 

 same time was 3.2 times as great in the 

 sap of the plants which gave the high- 

 est yield. Such observations would ap- 

 pear to fully justify the general convic- 

 tion that increased yields should be di- 

 rectly attributed to better feeding and 

 that better feeding is a direct result of 

 larger amounts of plant food available 

 to the crop. It is taught, however, by 

 the Bureau of Soils, that all soil solu- 

 tions are sensibly identical in composi- 

 tion and in concentration ; that they are 

 strong enough for large yields and that 

 this strength will be indefinitely main- 

 tained. From these conclusions the Bu- 

 reau further teaches that mineral fer- 

 tilizers, green and stable manures and a 

 good rotation of crops owe their ef- 

 ficiency to the power they have of neu- 

 tralizing toxic principles which tend to 

 accumulate in cultivated soils, rather 

 than to any power of increasing avail- 

 able plant food, an abundance of which 

 at all times and in all soils is held to be 

 present. 



Availability of Plant Food, 



While it is true that good soils may 

 yield to pure water two, three and more 

 times the amounts of plant food • that 

 poorer soils will, and while the absolute 

 differences may be as 3,200-pounds per 

 acre-four-feet to 1,200 pounds, yet these 

 quantities are so small in proportion to 

 the total water present in the soil that 

 one may with truth say, from the stand- 

 point of the chemical balance, as Pro- 

 fessor Whitney does, that the composi- 

 tion and concentration of all soil solu- 

 tions are sensibly the same. Neverthe- 

 less it is undoubtedly true that aoil solu- 

 tions are measurably different, "both in 

 composition and concentration, and from 

 the standpoint of plant functions they 

 must be profoundly so, for organic life 



is almost inconceivably sensitive to small 

 quantities of matter. 



Our published results show, too, that 

 we are able to recover from the surface 

 four feet of good soil as much water- 

 soluble plant food of both potassium 

 and phosphorus as would be removed 

 from a field by nine forty-bushel crops 

 of wheat per acre, and from poorer soils 

 as much as would be removed by six 

 such crops, and here is what has been 

 thought a safe foundation for the con- 

 tention that even in water-soluble form 

 the poorest soils contain plant food 

 enough for good yields. So there is, 

 in absolute quantity, but not in 

 available quantity. For example, a 

 three-horse tread-power may be in 

 such condition that when one horse 

 is put upon it no work is done; adding 

 a second horse may yet yield only half 

 an available horse-power, but when the 

 third horse is put in place its whole 

 weight may yield effective power, so that 

 the available work becomes three times 

 what it was with two horses. So it may 

 be with soils. Plant food enough for 

 perhaps many crops must be present in 

 order that enough for one may become 

 available. • - 



Nature's Metfxod of Fertilizing. 



So far as we know, either from pub- 

 lished data or on a priori ground, there 

 is no foundation for the hope that the 

 supply of plant food in soils may be in- 

 definitely maintained simply by good till- 

 age and suitable crop rotations, which 

 make positive additions only of nitrogen 

 to the soil. The only way Nature has 

 ever produced crops, and this is the way 

 she has always maintained soil fertility, 

 has been to return to the field the whole 

 crop, and by working along this line for 

 a thousand years together she never did 

 and never can bring all her fields to an 

 equality in productive capacity, as should 

 be the case if all soils carry an abund- 

 ance of plant food. 



A very simple calculation, based on 

 well-established data, will show that an 

 exhaustion of the plant food elements, 

 large as these amounts are, must neces- 

 sarily follow any system of cropping 

 which involves no return to the soil oth- 

 er than nitrogen. The amounts of plant 

 food removed by certain crops are defin- 

 itely known; the absolute amounts of 

 plant food elements carried by good soils 

 are known, and taking twenty tons of 

 potassium per acre-foot, which is about 

 the amount carried, a quantity equal to 

 the whole of this would be removed in 

 about 1,400 years by wheat yields of for- 

 ty bushels per acre ; and the entire 

 amount of phosphorus carried by the sur- 

 face foot is equivalent to only about 400 

 such crops. Careful records have shown, 

 too, that the Mississippi river carries 

 out to sea annuAlly enough material to 

 lower its entire drainage area one foot 

 each 4,000 to 6,000 years, which means 

 that the surface foot of soil may be com- 

 pletely removed and replaced by a cor- 

 responding layer from below at the same 

 rate, but the rate of removal of potas- 

 sium by a forty-bushel crop of wheat is 

 three to four times as rapid as this, and 

 the crop exhaustion for phosphorus is 

 ten to fifteen times as rapid as rock is 

 being converted into new soil on the 

 average over the Mississippi valley. 

 Were Professor Whitney's contention 

 true, the mean productive capacity of 

 the soils in the Mississippi valley should 

 be no more than three to four bushels 

 of wheat per acre, for this is the rate 

 at which rock weathering and erosion are 



