The red clay soil of Porto Rico

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Be GN AGRTON,

Assistant Chemist.

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Bees Seis - _ WASHINGTON: if ;
oI Gs GOVERNMENT PRINTING OFFICE.

1914. Steg
Roe

FRONTISPIECE.

Bul. 14, Porto Rico Agr. Expt. Station.

‘GNV7] AV1IO Gay dO AadAL

Vv ‘AATIVA OOSVNY JO MSA V

Issued March 19, 1914.
PORTO RICO AGRICULTURAL EXPERIMENT STATION,

D. W. MAY, Special Agent in Charge,
Mayaguez, P. R.

Bulletin No. 14.

THE RED CLAY SOIL OF
PORTO RICO.

BY

P. L. GILE,
Chemist

AND

C. N. AGETON,

Assistant Chemist.

UNDER THE SUPERVISION OF
OFFICE OF EXPERIMENT STATIONS,

U. 8. DEPARTMENT OF AGRICULTURE.

WASHINGTON:
GOVERNMENT PRINTING OFFICE.
1914.

PORTO RICO AGRICULTURAL EXPERIMENT STATION.

[Under the supervision of A. C. Tru, Director of the Office of Experiment Stations,
United States Department of Agriculture.] ,

WatteR H. Evans, Chief of Division of Insular Stations, O fice of Experiment Stations.

. W. May, Special Agent in Charge.

. L. Giz, Chemist.

L. Fawcett, Plant Pathologist.

F. KinmMaAn, Horticulturist.

G. Rrrzman, Animal Husbandman.

.H. VAN ZWALUWENBURG, Entomologist.
. N. AGETon, Assistant Chemist.

.B. McCLELiann, Assistant Horticulturist.
. E. Hess, Expert Gardener.

C. Atemar, Jr., Clerk.

(2)

qyHOon Hoan

Withdrawn

LETTER OF TRANSMITTAL.

Porto Rico AGRICULTURAL EXPERIMENT STATION,
Mayaguez, P. R., June 20, 1913.

Str: I have the honor to transmit herewith a manuscript by P. L.
Gile and C. N. Ageton on the Red Clay Soil of Porto Rico. This
represents several years’ work on soils, some of which have been de-
voted almost continuously to cane culture and are now in such con-
dition that some radical treatment is necessary for their amelioration.
The data contained herein will doubtless prove of value to planters
and, it is hoped, will lead them to make further studies of means of
improving these soils.

I respectfully recommend that the manuscript be issued as Bulletin

14 of this station.
Respectfully,
D. W. May,
Special Agent in Charge.
Pr A.C. Teun,

.
|
| Director Office of Experiment Stations,
| U. S. Department of Agriculture, Washington, D. C.
|
|

Recommended for publication.
A. C. True, Director.

Publication authorized.
} D. F. Houston,
Secretary of Agriculture.

y (3)

COUN oe NaS

Page.
Introduction 2.8 cose ose ya ek a ee ee err 5
Description of Porto, Ricamired iélay® - 4, 3:25. 2e see 5
Color, formation, location, and.crops'srowm >}. 23. . 222-52 -- 24. - eee 5
Physicalcharacteristies.<. 22... 1 :.).gs Se aoe en 6
Chemicalcharacteristi@s: 202). 6.250 ances Sector teh et 7
Experiments‘on normalered clay soil: ...:2222-2) 2 ee ee ee 10
Experiment wath limeiat Amasco.2 24/2452. 209292. ces ee 10
Experiment with fertilizers at Anasco .-- 22-32. 5..5-252-5)25.22212iBseee 11
Experiment on the value of phosphoric acid in a bat guano.............. 12
Experiment with lume at: Mayaguez : 55.3555 222 20.6 oe ee 13
Summary Of Fesults.). 25 oh ea ei aaskyec oe ee ae = ee 14
Experiments‘on “sick”? ted'clay soikaue cs) 2 Jie A Ae eee 14
Experiment on thorough aeration of the soil before planting.............- 15
Experiment with lime and stable manure. Rees 16
Experiment with fertilizer, stable manure, ee Tsaines ae green
MAMURE Se - sean Ch wale Hien Moyen OS ciara a Siavcre etal Sere ee 17
Experiment with tricresol, fertilizer, and stable manure.................. 18
Experiment with fertilizers by Sugar Producers’ Station.................. 19
pummaryof Tesubish. 37423093 a dee oe ee ee 19
On the difference between the normal and ‘‘sick” red clay soil..............- 20
General requirements of Porto Rican red clay. 22:-3:-2-5-52. 202228 5 2a eee 22
SUMIMAT Ys. sase eae ees oe ee 8 i ie alee eg 23
Acknowled@ment..2 P22 ode sca cols oan os Se I, ee 24
ILLUSTRATION.
Page.
A view of Anasco Valley, a type of red clay land....................-- Frontispiece.

(4)

THE RED CLAY SOIL OF PORTO RICO.

INTRODUCTION.

In 1902 the Bureau of Soils made a soil survey of a strip of country
10 miles wide extending from Arecibo to Ponce.! Within this area
19 different types of soil were encountered, and this by no means
embraces all the soil types that occur on the island. One of the
chief types in respect to area, though not in fertility, is the red clay
soil which is classified by the Bureau of Soils as Adjuntas clay.
During the last six years considerable experimental and analytical
work concerning the nature and treatment of this red clay soil has
been carried on. The experiments are being continued, but inas-
much as such work is never really closed, it has seemed advisable to
publish the results obtained thus far, with the idea that although
they do not definitely answer all questions that may arise concerning
this soil, they should aid in its more intelligent and profitable treat-
ment.

DESCRIPTION OF PORTO RICAN RED CLAY.

COLOR, FORMATION, LOCATION, AND CROPS GROWN.

The Porto Rican red clay soil, or Adjuntas clay, as it has been
classified, is a bright-red, dark-red, or brown clay. The color varies
considerably, according to the content and state of oxidation of the
iron, the amount of organic matter, and the moisture content.
When dry the soil is brown or dark red, but when moist is bright or
brownish red. In the lowlands there is generally little distinction
between the surface soil and subsoil, the first foot or 8 inches being
slightly darker in color than the subsoil. On the hill land the surface
soil is generally a brighter red than that of the lowlands; the subsoil
is also distinct im color from the surface soil, being a lighter red or
yellow. On much of the hill land that is exposed to washing there is
practically no surface soil.

Dorsey and his associates? describe the soil as residual, ‘‘being
formed by the breaking down and decay of the igneous and volcanic
rocks that form the backbone of the island. This disintegration has

1 Porto Rico Sta. Bul, 3. * Porto Rico Sta. Bul. 3, p, 30.

(5)

6

taken place to considerable depths, as shown by the soil mantle, in
some places reaching a depth of 15 feet, the rock often showing decay
beneath this.’ In the vegas or lowlands the surface soil has been
formed partially by the decomposition of the rocks in situ and par-
tially by washings from the surrounding hills.

This type of soil occupies the Anasco Valley (see frontispiece), the
district around Mayaguez, the greater part of the San German
Valley, certain areas on the east coast near Naguabo, and a large
part of the interior around Adjuntas, Lares, Las Marias, and Caguas.
It is one of the principal soil types im respect to area.

Coffee and sugar cane are the chief crops grown on the soil, coffee
in the hill land and sugar cane in the valleys. In the hills bananas
and native oranges are raised with the coffee. Some corn and small
crops, aS yams, yautias, and beans, are grown on the hill lands m the
spring. Yams and yautias grow well on the soil. Tobacco is grown
to some extent, but only successfully on lands where the drainage
happens to be good.

PHYSICAL CHARACTERISTICS.

Physically the soil is a heavy clay. The five mechanical analyses
made by the Bureau of Soils show that most of the particles are less
than 0.05 mm. in size. The average composition of the five samples
analyzed was as follows:

Per cent.
Oreanievmaler: 223.520.2420 Se ee ee eres 0. 64— 3.17
Gravel; @ totum us (6 Ae ee ee. See eee eee .00- .74
Coarsesand. 1 toca mm. soe e cet semen eee eters . 28— 1. 50
Mediunmisand) 0/o%to: 0.25 momsen ee bee Ea .40- 1.70
Finersand:"0:25) to:0. mintise oe eee eee eee 1. 94— 7. 46
Wety fineisand: 10.1 to'@05) many. 52): sees eet eee 3. 48— 8. 90
Silt, :0:05;t0 (0.005 mmit Sereso! 2 eects eee re 32. 56-52. 30
Clay;0,005,10'0;0001 mimeo. sco ee ee ae eee

On account of its heavy nature the soil drains poorly in seasons of
heavy rains and bakes badly during the dry months. After a pro-
longed dry period the soil cracks and fissures so that it dries out to a
considerable depth. This fissuring is due to the shrinkage in volume
of the soil on drying; it can be prevented by methods of conserving
the soil moisture, such as surface cultivation and leaving trash
between the rows of cane. The fissuring not only damages plant
roots but increases the evaporation from the soil by exposing a
greater surface to the air. The physical nature and difficulty of
cultivation of the soil are its chief drawbacks, rendering it unsuitable
_for many crops.

The surface soil is often underlain by a layer of the parent rock
which has been decomposed in situ so that it shows the original

| 7

stratification but is quite impervious to water. In the alluvial
lowlands this impervious layer may be at a considerable depth below
the surface, but on the hills much exposed to erosion it is practically
at the surface.

The lowland requires considerable ditching for successful cultiva-
tion. Tile drainage has also been found advantageous, but as water
percolates through the soil very slowly the tile drains ought to be
supplemented by some surface ditches for carrying off the excess of
water from heavy rains. After continued heavy rains water often
stands on the surface of the lowland soil for several days.

One of the prime requisites for the successful management of the
soil is thorough and frequent cultivation. Unless the soil is main-
tained in good mechanical condition the full value of the plant food
in the soil or of fertilizers applied can not be realized. Poor mechan-
ical condition also enhances the damage done by root diseases of
sugar cane. The benefits accruing from good cultivation in general
are well known and they apply particularly to this soil. Without
going into detail, some of the beneficial effects of plowing and culti-
vation are: Increasing the area and depth of the plant’s root system;
heightening bacterial activity that renders available certain com-
pounds; affording a better circulation of air about the plant’s roots;
and conserving soil moisture in time of drought. Steam plowing of
the soil to a depth of 20 to 30 inches has been found to improve the
yield of sugar cane for several crops.

Care should be used in the cultivation of the soil. If cultivated
when too moist the clay will puddle and it will be impossible to
secure the ‘‘crumb”’ structure again for some time. When partially
dried, or baked, cultivation is almost impossible. After a prolonged
dry period, however, the soil cracks and fissures to such an extent
that cultivation is again possible, the soil breaking up fairly well.
The soil can be cultivated best after a few rains following a dry period.

CHEMICAL CHARACTERISTICS.

Analyses of 11 samples of surface soil and 6 samples of subsoil
from different localities have been made by the method of the Asso-
ciation of Official Agricultural Chemists. The results of these analy-
ses and a description of the samples are given in Table I. The loss
on ignition represents the combined water and organic matter.

8

TaBLE I.—Acid analyses of red clay soil.

3 = Ac iss “ =~ ae =
zz his 2 |x| & S| sea] 8) eS z
bh | S Fieh | ee S|: 2 Sale esp Ee
Description of sample.| § 2 5 a lies 3 = eb ee A a= i=
3 2 = 4 g SS Za BS aS I ins
Su | SSS ara ae Ce) ea ee SS
3 | 2 Sree SS |e lee tees S| o
Sr. > | & < Bet er ieee ares Z |e
; PACED reAeL: Per cent Pb. APACE: | Pa Cha PECL ae CE Ee
Mayaguez Experi-| 18 | 60.38 | 11.55 23.91 0.85 | 3.58 | 0.30 | 0.20 | 100.77 | 0.19 | Acid
ment Station, val-
ley soil.
Mayaguez Experi-| 19 | 59.44} 10.69 25. 95 -60 | 3.32 -47 -14 100.61 12 Do
ment Station, val-
ley subsoil.
Mayaguez Experi-| 20} 71.76 | 10.99 16. 74 Pe i) ay) Bl i 2: 2) es 1 ne ee Do.
ment Station, hill
soil.
Mayaguez Experi-| 21 | 58.49 | 11.74 29.31 obs e25aly (285) ets OOsSO 09 Do
subsoil.
Mayaguez Experi-| 74 | 71.34 | 11.55 16. 94 14 21 11 11 | 100.40 - 20 Do
ment Station, hill
soil.
Mayaguez Experi-| 75 | 66.50} 11.59 21.7 04/}- .19 13 16 | 100.31 il Do
ment Station, hill
subsoil.
ee, Cambalache,| 15} 62.16 | 12.28 24. 91 33 44 22 17 | 100.51 18 Do
soil.
Anasco, Buenaven-| 22 | 55.61 | 11.29 31. 64 49 73 40} .26 | 100.42 12 Do
tura, upper valley
soil.
Naguabo, San Cris-; 68] 73.00; 8.41 16.19 1.12] 1.55] .15}| .07,; 100.49} .15 Do.
tobal, soil.
Maynsuer, Aurelia, | 158 | 46.13 | 18.60 | 11.58 { 23.73] .32] .65] .06] .08] 101.15] .32 Do.
soil. i
DOs ss eee aes 159 | 52.01 | 13.76 -13 -09 | 100. 07 13 Do.

13.07 | 20.71 ae. OF
Hormigueros, San | 448 | 60.43 | 12.43 | 10.97 | 13.76] .61| 1.26] .18| .18| 99.82] .14 Do.
Francisco, valley
soil.
Hormigueros, San | 449 | 59.91 | 12.11
Francisco, valley
subsoil.
Hormigueros, San | 450 | 62.11 | 10.90
Francisco, valley
soil.
Hormigueros, San | 451 | 62.77 | 10.40
Francisco, valley

10.82 | 13.49} .56] 1.70} .19| .20} 98.98] .10 Do.

11.76 | 11.84] .74| 2.04] .13] .17] 99.69] .i1 Do.

|

ment Station, hill

| |
11.78 12.20 81 | 2.35 .22 -13,| 100.66 aS Do.

subsoil.
ADS Oe, val- | 456 | 64.53 | 10.38 | 10.08 | 12.73 Gan eats av -18 | 100.00 Fu Do.
ey soil.
Anasco, Pagan, val- | 457 | 61.75 | 11.69 9.77 | 15.00 a 0h i 1243 .34 -19 | 100. 88 otk Do.
ley subsoil. |

No carbonates were present in any of the samples and they were
all more or less acid to litmus. The content of iron and aluminum
is very high in all the samples, ranging from 16 to 35 per cent. The
hill land of this type of soil seems to contain much less lime and mag-
nesia than the low land. Some samples are low in phosphoric acid,
potash, or nitrogen; the average of the samples, however, shows that
the soil is not particularly lacking in any one element. The subsoil
runs higher in potash than the surface soil. Chemically the chief
characteristic of the soil is the high content of iron and aluminum.
In those places where much of the iron is present in the soil as oxid
or hydrate, instead of silicate, it may influence the fertility, since iron
oxid promotes the oxidation of organic matter in the soil Some of
the hill land seems to contain considerable oxid of iron.

1Storer. Agriculture in Some of its Relations with Chemistry. New York, 7. ed., vol. 1, p. 495.

9

The amount of organic matter in the red clay soil depends on the
erosion to which the surface has been exposed and on the methods of
cultivation. On the hill lands planted to coffee the content of organic —
matter is largely controlled by the erosion; in favored spots where the
surface has not been washed there is a large amount of organic matter
and the soil is of good texture; where it has been washed, however,
the surface soil is very thin, low in organic matter, and of poor texture.
The valleys, having received the surface washing from the hills, havea
richer, deeper soil with considerable organic matter. The hill land,
which is alternately in grass or corn and small crops, is generally very
low in organic matter, as these hills are at times exposed to consid-
erable erosion and no attempt is made to supply organic matter. A
bad case of erosion of the hill land is shown in the frontispiece. In
the lowlands, which are almost exclusively planted to sugar cane, the
content of organic matter is low in the souls that have been cultivated
most, as it has generally been the custom to burn the trash remaining
after each crop of cane, and the only organic matter incorporated in
these cases has come from weeds and grass turned under in the course
of cultivation. The cultivation, by increasing bacterial action which
oxidizes the humus, has tended to exhaust the humus and only very
little organic matter has been returned.

The red clay soil is uniformly acid in its reaction to litmus. Con-
taining no carbonates, the soil tends to become more acid with in-
crease in organic matter and with the use of acid fertilizers or ferti-
lizers that leave an acid residue, as ammonium sulphate. Besides the
acidity due to organic acids, formed in the decomposition of the organic
matter, there is possibly an acidity due to certain silicates in this soil.

Soil acidity is supposed to have an injurious effect on the general
fertility of the soil by influencing the bacterial flora, the free living
bacteria which assimilate atmospheric nitrogen and the nitrate-form-
ing bacteria thriving best in a neutral or slightly alkaline medium.
Many studies have shown that in acid soils the bacterial flora is
depressed and the fungus flora increased. It has been well substan-_
tiated that many plants will not thrive in acid soils, that some plants
seem indifferent to the acidity, while a few plants, such as the blue-
berry and sphagnum moss, require acid soils. Why different plants
vary in this respect and how the plants sensitive to acidity are inju-
riously affected has not been discovered.

The acidity of the red clay is more or less injurious to sugar cane,
as is shown by the increased yields obtained by liming. Whether
coffee is much affected is not known, as thus far comparisons between
the limed and unlimed soil with this crop have not given decisive
results. Tobacco has been benefited by liming, and the growth of
beans and corn on this soil should be consideraby increased by the
same means. Malojillo, or Para grass, grows luxuriantly on the red
clay of the lowlands, so is apparently well adapted to acid conditions.

23559°—Bull. 14—14-—2

10

EXPERIMENTS ON NORMAL RED CLAY SOIL.

Experiments have been carried out on the red clay soil of the low-
lands to determine the lime and fertilizer requirements. As sugar
cane is the chief commercial crop grown, all the following experiments
have been with cane. .

In 1911, 45 tenth-acre plats were established on this soil in the
Anasco Valley at Central Pagan. The analysis of the soil and sub-
soil is given in Table I under Nos. 456 and 457. The field where the
plats were established had been in continuous cane culture for six
years, five crops of ratoon cane having been grown. Previous to
this the land had probably been in pasture for several years, as it
had been the custom on this plantation to plant only one-third of
the land each year. The field where the three following experiments
were carried on was plowed by a steam plow to a depth of 2 feet in
May and replowed by bulls in August. Cristalina cane was planted
in September, 1911, and cut in January, 1913. The fertilizers were
applied in November in the furrow.

EXPERIMENT WITH LIME AT ANASCO.

This experiment comprised 16 plats. Liming at the rate of 1,500,
2.000, and 4,000 pounds per acre was tried, both with and without
a complete fertilizer. Burnt lime partially slaked was applied in
May and plowed under. The complete fertilizer used was made up of
tankage, basic slag, and muriate of potash, and was applied so as to
afford 50 pounds each of nitrogen, phosphoric acid, and potash per
acre. The yields of cane from the various plats are given in Table II.

TaBLE Il.—E fect of lime at Anasco.

Treatment of plats. ee a fcane duplicate
Tons Tons.

Cheek! nophinses ob Ss wil tele eae iu ee WEE Geecrc to.
Lime, 1,500 pounds per acre. .-.....- 2.2.2.2 - == nn ne we ne ence nnn { eS ; Os 6 if-cceeeeee
ime, 2.000 PONG POE AC EO seats era a ala alate ole leet { ie Oe 4 \ ees
inie, 4,000 POUNGS PEE ACC. one cece cs ecie eae ne ees eee eeetdenenaee S QO. 5 \ Be peste
STU G ep Oa gS 98 Sao tee See Somat ome eee en terre nescence bacis4 is a \ 26.1
Lime, 1,500 pounds per acre and complete fertilizer............-......---- { 2 ae \ 26.7
Lime, 2,000 pounds per acre and complete fertilizer. ............-.....---- { Ae a8 \ 30.0
Lime, 4,000 pounds per acre and complete fertilizer. ................------ i “E eee \ 31.7

1 Weight lost.

The cane from plats 1 to 4 was mixed in the cutting, so the weight
of the individual plats could not be secured, but the average weight

i

for the four plats was 20.2 tons of cane per acre. Summarizing the
results, the differences due to the lime can be seen in Table ITT.

Taste III.—Increased yield of sugar cane produced by different amounts of lime.

Average Increase
Numbers yield of in yield

Amount of lime applied per acre. of plats. 3 plats, | due tolime,
per acre. per acre,
Tons. Tons.
DY OTRG)- 3 hood SSS e SOR SB eE CE IR EEC cee ete ies tras 22 emia sen es he a 22,6, 18 DA Beers cpa mleastelors
LAADO [aaa Ree pe ICO SSO br CORO COCOGORCONC SP oO donc iQpemcacecicccnos 2 20,5, 16 26. 3 1.5
6 SDT GLS Soe ES RS Ey: Se ee ey aa See 21, 8,17 28, 1 3.3
LOU (OWEN po da gcondecdo do SsBUS Pass bD SCE Bode boticise cuscoactiad coo gue 23,7, 19 30. 3 5.5

The eight plats in this table which received no fertilizer! averaged
22.6 tons of cane per acre, while the eight plats with the complete
fertilizer averaged 28.6 tons, a gain of 6 tons of cane per acre for the
complete fertilizer.

EXPERIMENT WITH FERTILIZERS AT ANASCO.

This experiment comprised 19 plats and was intended to show

whether the soil is benefited by a complete fertilizer and whether any
fertilizmg element or elements are particularly effective.
’ All the plats in this experiment received lime at the rate of 1,500
pounds per acre. The different fertilizers were applied so as to afford
50 pounds of nitrogen, phosphoric acid, or potash per acre. The
nitrogen was derived from nitrate of soda, the phosphoric acid from
basic slag, and the potash from muriate of potash. The fertilizers
and yields of the various plats are given in Table IV.

TABLE 1V.—L fect of different fertilizing elements at Anasco.

Wield off |) ev oeee

Fertilizers applied per acre. aoe cane per ribigot on
* acre
treatment.
Tons. Tons
1 (?)
me 20 25.6
GCGm ye tonthiner se eal Os eer te eet tte lied seer 30 28. 0 28, 8
| 34 30. 8
42 BOindl
Hy OOM ES iS Des pain ee bd os eh de oo abn ob a xs note { A . ae \ 23.8
Mnsph orig tipld PO pernds, <.ckcrs i spas cnc anna so detes x22 242 { ae 0 |} 24. 6
Paina DBD PIOTIIGN gd oi plans nafs on ween beth ao.dc abewteawanaenecuciten: { a aes \ 31,0
Potash and phosphoric acid, 50 pounds each.....................-.. { a a \ 31. 2
Potash and nitrogen, 50 pounds each................2.ccceeeeceee eee] { re one \ 33.0
Phosphoric acid and nitrogen, 50 pounds each....................... { ny rf : \ 35.8
Nitrogen, phosphoric acid, and potash, 50 pounds each............... { a a : \ 35, 2

1 These include plats 1 to 4, of which the average weight only was obtained. 2 Weight lost.

12

The above results show some variations due to irregularities in the
experimental field. It is evident, for mstance, that plats 31, 32, and
33 were situated in a poor part of the field, but the differences be-
tween these three plats are of the same order as the differences be-
tween the three duplicate plats, Nos. 39, 40, and 41, which were in the
better part of the field. Because of this poor spot the averages of
these plats are not to be compared with the other averages in the
table, although the comparison of these three with each other is
probably accurate.

The results show that the complete fertilizer has increased the
yield by 6.4 tons of cane per acre. The preceding experiment also
showed an increase of 6 tons of cane for the complete fertilizer. In
regard to the relative value of the single fertilizing elements it seems
evident that potash is not needed, since nitrogen plus phosphoric
acid gave the same yield as these two elements plus potash. It
appears that phosphoric acid is also unnecessary and that nitrogen
alone increases the yield as much as a complete fertilizer. Because
of the irregularities in the field it is not quite clear that phosphoric
acid is entirely superfluous, but the results in general seem to point
to that conclusion. The following experiment throws some light
on this.

EXPERIMENT ON THE VALUE OF PHOSPHORIC ACID IN A BAT GUANO.

This experiment comprised 12 plats and was intended to show the
value of the phosphoric acid in a bat guano, compared with the
phosphoric acid of basic slag, on this soil. Since the soil included in
this block of plats did not respond to phosphoric acid, no data were
secured as to the relative value of the two sources of phosphoric acid,
but the results are given here, as they tend to substantiate the con-
clusion of the preceding experiment that phosphoric acid was super-
fluous.

The plats were all limed at the rate of 1,500 pounds per acre. The
nitrogen and potash applied were derived from the same sources as
in the preceding experiment. The bat guano used contained 7.8
per cent total phosphoric acid, 3 per cent phosphoric acid soluble in
ammonium citrate, and 0.4 per cent total nitrogen. The bat guano
was applied in three different quantities, so as to afford 25, 40, and
60: pounds of total phosphoric acid per acre. The yields of the plats
are given in Table V.

13

TaBLe V.—Test of bat guano compared with basic slag.

Average
cals, Meigldlofy |. aioe:
Fertilizers applied per acre. ice cane per eer
S cane
per acre.
Tons. Tons.
Mitropen, 50 pounds; potash: 75 pounds... 0... ose. cece emannace a Hae \ 34.9
Nitrogen, 50 pounds; potash, 75 pounds; phosphoric acid (from basic 9 28.6 \ 39.0
THER, WAN poets Bose ene coke bee Geos anee a lnae abHear Lserneceradubte 28 35. 4
Nitrogen, 50 pounds; potash, 75 pounds; phosphoric acid (from basic 12 35.1 \ 39.4
S1G}e9) CE Ovid BIS eae eee eee See se ene cos eme osecrintcrenscat 24 29.7
Nitrogen, 50 pounds; potash, 75 pounds; phosphoric acid (from bat 10 30.3 \ 35,2
LITO) POND OUM OSs sr os fis a1 abate ic ss eats rare a elo slate cater inion 26 40. 0 ¢
Nitrogen, 50 pounds; potash, 75 pounds; phosphoric acid (from bat 14 37.8 \ 36.0
TTATIO) VAMP OCG S yates ore alas ai clelaye Somers ates opps iaiciate arate nel oitiatetarstetate 27 34, 2 ‘
Nitrogen, 50 pounds; potash, 75 pounds; phosphoric acid (from bat 15 39. 1 \ 36.9
STIANO) GO NMDOUT GS sfotea sec e's Sete ateectasts u/s asis civlere Siciorsitetelerlerera’ staleictale stele ll 34. 6

The plats with nitrogen, potash, and phosphoric acid averaged
about the same as the plats with only nitrogen and potash, hence it
appears that phosphoric acid was unessential.

EXPERIMENT WITH LIME AT MAYAGUEZ,.

This was a small experiment comprising five twentieth-acre plats
planted to sugar cane, variety B 1753. Burnt lime was applied at the
rate of 500 and 3,000 pounds per acre, both with and without a com-
plete fertilizer the first year. For the ratoon crop all the plats except
the check received tankage. The complete fertilizer applied to plats
4 and 5 the first year contained 7.3 per cent nitrogen, 2.5 per cent
phosphoric acid, and 4.5 per cent potash from dried blood, acid
phosphate and sulphate, and muriate of potash. This was applied
at the rate of 1,100 pounds per acre. The tankage, applied at the
rate of 400 pounds per acre to plats 2, 3, 4, and 5 for the ratoon crop,
contained 10 per cent nitrogen and 3 per cent phosphoric acid.

After planting it was noticed that the check plat did not drain as
readily as the other plats, which were quite uniform in drainage. It
is probable that the yield of the check plat is thus not comparable
with the others. The results, given in Table VI, show, however, the
differences in yield between the plats receiving 500 and 3,000 pounds
of lime per acre.

TaBLe VI.—# fect of lime at Mayaguez.

Yield per
Treatment of plats. Number | acre of first

of plat. crop of
cand. ratoon crop.

Yield per
acre of

EA SELEU Rte 6 I ia ES. ieee Oe 2 ae ae ees eee rae S
ame RN OR MOM ACEO aoc Undine oe aes cabieek ohincteecak idoee
POPE SH UM TIO LO DOL GOTO =. 2 te. cei eeee ean a aaa ee nlidndn Reims Cas
Lime, 500 pounds per acre, and fertilizer..........5.......--..---e0---
Lime, 3,000 pounds per acre, and fertilizer

ork WD
[o>]
ite}
ew
Oo ~ re
SESES
mW wH ©

ee

14

It will be seen that 3,000 pounds of lime per acre gave an increase
over 500 pounds of lime both for the plant cane and the ratoons. If
we leave out the results of plat 3 the first year, which seems abnor-
mally high, the increase varies from 3.2 to 6.4 tons of cane per acre.
This experiment alone is not conclusive but substantiates the other
experiments.

SUMMARY OF RESULTS.

The preceding experiments show that this red clay soil was
improved by liming and fertilization. The larger the applications of
lime the greater were the increases obtained, so possibly the optimum
amount is somewhat greater than 4,000 pounds of burnt lime per
acre, which was the heaviest application tested. Nitrogen alone
seemed to increase the yield of sugar cane on this soil as much as a
complete fertilizer. In regard to the general applicability of these
results it must be borne in mind that they are definite for the place
where they were carried on, and, as the field was typical, they are
instructive for considerable areas of the red clay but not for all of it.
These results do not hold true for this type of soil which is in the
“sick”? condition.

EXPERIMENTS ON “SICK” RED CLAY SOIL.

In some places the red clay soil which has been in continuous —
cane cultivation for a long series of years has become very un-
productive and does not respond to fertilizers or the usual soil amend-
ments. Soil in this condition has been termed “‘sick”’ or “tired”
rather than ‘“‘worn out,” although in what the sickness or tiredness
consists has not been definitely determined.

Certain fields at Hormigueros in the San German Valley are at
present in this tired condition. These fields have been in continuous
cane cultivation for a long series of years, although for just how
many years it is impossible to say as no records are available; report
gives it as from 30 years to ‘“‘always.’’ Experiments have been car-
ried on in this valley to see if the productivity could not be increased
by some method of soil treatment other than resting. Under the
economic conditions that cane is grown here, especially where the
land is leased, it is desirable to plant all the land in cane every year.

In 1906-7 some fertilizer plats were tried at Hormigueros by the
horticulturist.1_ Nitrate of soda, ammonium sulphate, potassium
sulphate, and acid phosphate were used. In the heaviest application
these materials were applied so as to yield 75 pounds of nitrogen,
85 pounds of phosphoric acid, and 125 pounds of potash per acre.
The yield of cane on the plat receiving no fertilizer was 18.8 tons

1Porto Rico Sta. Bul. 9, p. 27.

15

per acre, that on the heavy complete fertilizer plat 21.4 tons—an
increase of about 10 per cent for heavy fertilization.

In 1911-13 an experiment with a series of 42 tenth-acre plats was
tried on the same soil, the analyses of which are given in Table I
under Nos. 448 to 451. All the plats were plowed with a steam plow
to a depth of about 2 feet in March, 1911, and again by bulls in Sep-
tember,1911. Rayada cane was planted September 20, 1911, and
cut January 7-8, 1913. All plats which received fertilizer were
fertilized at the rate of 550 pounds per acre with a mixture containing
7.3 per cent nitrogen, 3.6 per cent phosphoric acid, and 7.3 per cent
potash, derived from tankage, sodium nitrate, basic slag, and mu-
riate of potash. The fertilizer was applied in the furrow six
weeks after the cane had been planted. The following treatments
were tried on separate blocks of plats: Thorough aeration of the soil
before planting, applications of lime and stable manure, applications
of fertilizer, carbon bisulphid, stable manure, and green manuring.
The results of the different experiments are given separately.

EXPERIMENT ON THOROUGH AERATION OF THE SOIL BEFORE PLANTING.

As previous experience had indicated that this soil responded
very little to fertilizers, it was thought that possibly the trouble
was due to biological causes, in which case thorough aeration of the
soil and exposure to sunlight previous to planting might be beneficial.
The experiment comprised six plats, all of which were plowed by the
steam plow in March and plowed again by bulls in September.
Three of the six plats, however, were also plowed four times more at
intervals of about five weeks, i. e., April 12, May 20, June 30, and
August 5. All plats received the fertilizer described above. The
results are given in Table VII.

TaBLE VII.—E fect of thorough aeration of ‘‘sick”’ soil before planting.

Average .
Yield of yield of

Treatment of plats. Numbers cane per plats of
of plats. acre. like treat-
ment.
Tons. Tons
4, 17 18, 1
omimlctederilizer, DIGWeG:LWICE <..Uodec cesicdes nic cic cnccceuhedsesaxees 19 20.1 20.9
21 24.5
mt ; 16 19.5
ormplete fertilizer, plowed. SIX TIMES. oo cose cob pels boceice sUedoceas 18 21.4 21,5
20 23. 5

The yield of the three plats in each lot receiving the same treatment
vary considerably, but this is apparently due to the fact that the
soil improves from plats 16 to 21, since No. 21 is better than No. 19,

16

and No. 19 better than No. 17, also No. 20 is better than No. 18,
which is better than No. 16. As the plats were alternated in the field,
the average results are comparable and but little affected by this
inequality in the soil. It will be seen that practically no improve-
ment has resulted from frequently aerating the soil previous to
planing. This of course does not mean that good preparation of the
soil and cultivation during growth can be disregarded.

EXPERIMENT WITH LIME AND STABLE MANURE.

This experiment comprised 15 plats. The object of the experiment
was to see if the soil would be benefited by heavy applications of lime,
or lime plus stable manure. It was thought that in case the poor
condition of the soil were due to bacterial causes, a heavy application
of lime might improve the yield, since liming acid soils alters the
bacterial flora and activities.

All 15 plats were plowed six times previous to planting, the same
as plats 16, 18, and 20 of the previous experiment, and all received
550 pounds of fertilizer per acre. Burnt lime, only slightly slaked,
was used in certain plats. This was applied after the land had been
plowed by the steam plow, so it was well mixed with the soil by the
subsequent shallow plowing. The stable manure was spread just
previous to the two final plowings. The yields of the various plats
are given in Table VIII.

TaBLe VIII.—E£ fect of lime and stable manure on ‘‘sick” soil.

Yield of | yyeld of
Numbers yee meee Increase
Treatment of plats. cane per lats of 2
Pp of plats. 5 ae ie e treat- | OVeF check.
ment.
Tons. Tons. Tons
- 3 21.2
Check, Nogmine eee eas aeer aati nace ate eee tee eee | 9 26. 7 2h. DFS oo Bo cece
14 24.7
2 22.9
IONS PAGS FUETe a LE BR eR SRR oe ee eens 6 25. 1 24. 6 0.4
10 25. 7
5 25.9
NSHMNEHASLOMS PCEAGIP: 5 radon mace wc sae cones soon adenine 12 25. 0 25.5 1.3
15 25. 5
1 25. 6
Lime, 2 tons, and stable manure, 17 tons, per acre.......- a ae 24.8 6
4 PA eek
Lime, 4 tons, and stable manure, 17 tons, per acre.......- oe oe 26. 6 2. 4

The increases produced by liming at the rate of 2 and 4 tons per
acre, either alone or in conjunction with stable manure, were very
small, ranging from 0.4 to 2.4 tons of cane per acre. It is thus
evident that this treatment is of no benefit to the soil in its present
condition.

—=—=

17

EXPERIMENT WITH FERTILIZER, STABLE MANURE, CARBON BISULPHID,
AND GREEN MANURE.

This experiment included 21 plats and was designed to show
whether improvement could be produced by fertilizer alone, by
fertilizer plus stable manure, by green manuring with cowpeas, or
by application of a soil disinfectant. All the plats were plowed twice
before planting as noted on page 15. Three plats received no
fertilizer, three plats 275 pounds of fertilizer per acre, and al’ other
plats fertilizer at the rate of 550 pounds per acre. Some plats in
addition to the fertilizer received stable manure, carbon bisulphid.
or cowpeas turned under. |

The fertilizer, as in the other experiments, was applied in the
furrow six weeks after the cane was planted. The stable manure
was spread previous to the final plowmg. The carbon bisulphid
was applied two months before planting at the rate of 450 liters
per acre; three plats receiving this quantity in one application, and
three other plats receiving the same quantity in three applications
made at intervals of two weeks. The carbon bisulphid was applied
in small holes 8 to 9 inches deep and covered immediately with
earth. The cowpeas were grown and plowed under previous to
planting the cane. They made a rather poor growth and were not
well supplied with nodules. The result with cowpeas therefore can
not safely be taken as showing whether or not green manuring is
beneficial. It has since been found that better results can be secured
with sword beans on this soil. The yields of the plats are given in
Table IX.

TasLe 1X.—EKffect of fertilizer, stable manure, and carbon bisulphid on ‘“‘sick”’ soil.

Average
| Yield of | Yield of
Treatment of plats. epic | cane per Plata of Remarks.
eee: treat-
ment
| Tons. Tons.
| 24 21.0
CHEGE HOLM Rae wens one See c oe cbalcc cen 27 20.0 18.7
32 15.0
sig 35 19.0
Fertilizer, 275 pounds per acre............-. ie 18.5 | No increase over check.
7 23 21.0
Fertilizer, 550 pounds per acre.............. a ee 21.7 | 3 tons more than check.
hi 24 20.0
Cowpeas and fertilizer, 550 pounds per acre. ye ane 19.6 | 0.9 ton more than check.
Fertilizer, 550 pounds, and stable manure, a aye 93.0 ee tons more than fertilizer
17 tons per acre. 42 20. 9 : alone.
Fertilizer, 550 pounds, and carbon bisulphid a aie 95.7 |{4 tons more than fertilizer
(in 1 application), 450 liters per acre. 30 20.0 ve { alone.
Fertilizer, 550 pounds, and carbon bisulphid oe sie 99.5 |\f9-8 ton more tha- <ertilizer
(in 3 applications), 450 liters per acre. 33 16.9 oa { alone.

18

The land in which this block of plats was situated was not quite so
uniform as that in the experiment above, judged by the greater
differences between the triplicate plats. Fertilizer alone gave very
little 1f any merease of yield, 275 pounds of fertilizer yielding the
same as no fertilizer, while 550 pounds gave an increase of 3 tons of
cane. The plats with cowpeas plus 550 pounds of fertilizer gave
only 1 ton more than the checks, which show that the stand of
cowpeas secured was without effect and that probably the average
increase produced by 550 pounds of fertilizer is somewhat less than
3 tons of cane. Stable manure plus fertilizer gave about 14 tons
more cane than fertilizer alone. This confirms the results in Table
VIII, showing that stable manure was scarcely effective. The
carbon bisulphid in one application seemed to give an appreciable
increase while the carbon bisulphid im three applications gave
practically no increase, hence it is probable that this treatment is
not much more effective than any of the others.

EXPERIMENT WITH TRICRESOL,! FERTILIZER, AND STABLE MANURE.

In 1909 to 1911 a smaller experiment, carried out on the same
plantation, gave results similar to those detailed above. In this
case, however, the land had been rested two years previous to
planting.

There were eight plats of one-twentieth acre each. ‘Two check plats
received nothing, two plats a complete fertilizer, two plats a complete
fertilizer plus tricresol, and two plats stable manure. The fertilizer
used contained 9 per cent nitrogen, 6 per cent phosphoric acid,
and 6 per cent potash, derived from tankage, acid phosphate, and
potassium sulphate. This was applied to the fertilizer plats at the
rate of 500 pounds per acre. The stable manure was spread and
plowed under previous to planting. The tricresol was applied in a
0.5 per cent solution a month before planting, by sprinkling the
surface, plowing under, and sprinkling a second time. One plat
received this solution at the rate of 3,840 liters per acre, the other
plat at the rate of 7,680 liters per acre. Rayada cane was planted
December 4, 1909, and harvested January 24, 1911. The yields of
the different plats are given in Table X.

TaBLE X.—E fect of tricresol, fertilizer, and stable manure on the ‘‘sick”’ soil.

Yield of

Treatment of plats. cane per

acre.

Tons.
Ghecks mothing 3-26 ofen A ooo enschede eighind Sethe sete Ri Se eee ee eg eg eee 39.1
WO oe Lee Se wp Se hare Daweh seme eet tee oe fee Sobeen Geld oon che Aaa er 37.0
A ENES 5 UHV 75) pee ea a es eee era nets Sea eer, OER fy Ree GC ER Ee aL A i eee oe 36.9
WOR Bees fe Ae ee 5 Sie ee Se Se oS co yc er ee eee 36.1
Fertilizer and 3,840 liters 0:5 per cent trieresol peracres . <1. 22. = ob. {22a eee ee eee 35.0
BRentilizenand.7.680 liters 0.5 per centitricresol per acre: —. 2.2220 sc 5 see ee eee cae ae ee eee 33.6
Stable manure, 10 tons per acres... 522255. 500-2 Sake, 0 Pe eee eee eee eee 39.5
Stable masrure. 20 tonsyper acres. 22.32 ote fsa a oee oe ce oe Deh oe Se ee eae ee eee 40.1

ue

1 Tricresol is a nonvolatile disinfectant related to carbolic acid.

19

A comparison of the data shows that the fertilizer plats yielded prac-
tically the same as the checks; that the tricresol plus fertilizer plats
yielded slightly less than the fertilizer alone, the depression being
ereater with the larger dose of tricresol; and that the stable manure
plats yielded slightly more than the checks. All the plats were quite
uniform in yield, so it is evident none of the treatments was bene-
ficial and possibly the treatment with tricresol was slightly injurious.

EXPERIMENT WITH FERTILIZERS BY SUGAR PRODUCERS’ STATION.

In 1911-12 a fertilizer experiment on this land was carried out by
the Sugar Producers’ Station.1_ The nitrogen used was derived from
ammonium sulphate, the phosphoric acid from double superphos-
phate, and the potash from potassium sulphate. All plats except the
check received either two or all three of the elements at the rate of
60 to 90 pounds per acre. The average yield of the 16 fertilizer plats
was 21.7 tons of cane per acre, and the average yield of the four checks
was 18.2 tons, showing a gain of 3.5 tons for the fertilizer. The results
did not show that any one element was relatively more effective than

the others.
SUMMARY OF RESULTS.

A general consideration of the previous experiments seems to show
definitely that fertilizers on the ‘‘sick”’ red clay soil increase the yield
of sugar cane but little. The moderate applications of fertilizers have
not increased the yield at all, and heavy applications have increased
the yield only slightly. This shows plainly that the growth of cane
on soil in this condition is limited by some factor other than the sup-
ply of mineral nutrients.

Applications of stable manure have been as ineffective as commer-
cial fertilizers, the experiment of 1909-1911 showing an increase of
2 tons of cane per acre from an application of 20 tons of stable manure,
and the experiment of 1911-1913 showing an increase of 1.3 tons of
cane from an application of 17 tons of stable manure.

Liming has also been without results, although the land is more or
less acid in reaction to litmus. The managers of the plantation on
which the experiments were made had in previous years tried mod-
erate liming without results and the heavy applications of 2 and 4
tons of burnt lime per acre which were applied in the above experi-
ments were also without effect.

Disinfectants, which in some cases have increased the yield of cer-
tain sick soils, were not beneficial on this soil. The applications of
tricresol, a nonvolatile disinfectant, caused a slight depression rather
than increase in yield. Applications of a volatile disinfectant, carbon
bisulphid, which were much greater than could profitably be applied
in practice, were also ineffective, although possibly a slight increase
was produced.

1J, T. Crawley, Porto Rico Sugar Producers’ Sta. Bul. 3, p. 24.

20

ON THE DIFFERENCE BETWEEN THE NORMAL AND “SICK” RED
CLAY SOIL.

The normal and sick red clay soils differ greatly in their produc-
tiveness and also in their response to fertilizers and lime, as the pre-
vious experiments have shown. The unproductive soil of Hormi-
gueros in the San German Valley yields from 10 to 25 tons of cane per
acre, the normal soil in the Anasco Valley yielding from 20 to 40 and
50 tons of cane per acre.t The rainfall in the two sections, which are
about 10 miles apart, varies but little and the drainage of the land is
the same. That the chemical composition of the two soils is identical,
can be seen from Table I, analyses Nos. 448-457. Physically the two
soils are very nearly the same; if there is any difference it is in favor
of the Hormigueros soil.

The difference in the previous treatment of the two soils lies in the
more continuous cultivation of the Hormigueros soil. At Anasco
only one-third of the land on the plantation was in cane cultivation
any one year, the rest of the land being in pasture, while at Hormi-
gueros the land has been in continuous cane cultivation. With the
more intensive cultivation of the Anasco soil it is probable that the
productiveness of the two soils will become more nearly equal. That
this difference in the intensity of the previous cultivation is the cause
of the present difference in productivity seems probable, since it has
been observed at Hormigueros that the land becomes much more
productive after it has been left out of cultivation for two or three
years.

Now that fields which have been planted more continuously than
other fields should be less productive is not surprising, but it is
surprising that the fields which have been cropped most heavily
should respond least to fertilizers and other soil amendments. That
these fields have been injured by the continuous cultivation of the
same crop is apparent, but in just what the injury consists is not clear.
The trouble is not due to a mere impoverishment of the soil, for fertil-
izers and stable manure are ineffective, nor to an increase in soil
acidity, since liming is ineffective, nor to alterations in the biological
processes which could be cured by superficial disinfection, since carbon
bisulphid and tricresol are ineffective.

Recent work on the organic matter of the soil seems to show that in
certain cases crop production may be affected by organic compounds
resulting from the decomposition of crop residues left in the soil. To
see whether the organic matter of the two soils showed any differences,
100-pound samples of the productive and unproductive soil were sent
to the Bureau of Soils for examination. The report of Dr. Schreiner,
who kindly had the examination made, is as follows:

1 These are the average yields obtained from records of the plantations and not from plats. Small plats
give comparative but not absolute yields.

21

The work has been completed on the soil samples Nos. 1 and 2 which you sent to us
for examination as to organic constituents, with the view that possibly some of the
difficulties which you have noted in regard to the soils might be explained thereby.
You will recall that sample No. 1 was from Hacienda San Francisco, Hormigueros,
P. R., and that sample No. 2 was from Central Pagan, Anasco. The investigations
have been made by Dr. E. C. Shorey and Mr. Lathrop.

From soil No. 1 no crystalline material whatever could be obtained from the ether
extract at the place where we usually find dihydroxystearic acid. We must therefore
conclude that some of the constituents which we have found in this extract in other
cases, such as dihydroxystearic acid and trithiobenzaldehyde, as well as a number of
other acids, are absent from this soil. The test for creatinin, which you remember is a
nitrogenous soil constituent described in Bulletin 83,’ was likewise found to be absent
from this soil, as were also the purin bases such as xanthin or hypoxanthin. If any
of these compounds are present in the soil they are in very minute quantities only, as
no reactions whatever could be obtained therefor. The same is true of any of the
pyrimidin bases such as cytosin. Histidin, one of the protein decomposition products,
was present in this soil but the other closely associated products, arginin, lysin, and
cholin, could not be found. At this point in our investigations the sample which you
sent was exhausted and no further work could be done. You will see, therefore, that
most of the compounds tested for in this sample were found to be absent, and in this
respect the soil might be considered rather unusual from the point of view of the soils
on the continent with which we have been working.

The soil No. 2 gave in the ether extract at the place where dihydroxystearic acid is
usually found the compound trithiobenzaldehyde in good quantity. This was very
definitely identified by its melting point. This isa sulphur compound which we have
found in several soils and is more fully described in Bulletin 88.2 Associated with it
there was an aldehydelike compound and the indications were very strong that this
aldehyde is salicylic aldehyde. The salicylic aldehyde which we have found in other
soils is also described in Bulletin 88.2 * * * Ishould here say that this aldehyde is
toxic toward plants; even more so than dihydroxystearic acid. Mr. Skinner made a
test of this aldehyde from your soil on wheat seedlings and found it to be toxic.
Whether this material is also in soil No. 1, I can not say, as No. 1 was already exhausted
when we found this compound in No. 2,80 that we could not verify this point by making
plant tests or chemical tests at the proper place. No pyrimidin bases could be found.
Histidin, on the other hand, was present, but no arginin, lysin, or cholin. The purin
bases were found in this soil sample and a strong xanthin reaction was obtained, indi-
cating the presence of xanthin or guanin. No creatinin was found in this soil.

The chief points of interest between the two soils are the almost total absence of
nitrogenous compounds in soil No. 1 while such compounds were found in No. 2, and
the presence of trithiobenzaldehyde in soil No. 2, as well as the presence of what is
probably salicylic aldehyde. Ofcourse we can not draw the conclusion that the differ-
ent properties of the two soils in the field is explained by these chemical differences,
but it is indicated very strongly that the nature of the organic matter in the two soils
is different, having arisen probably as the result of different biochemical activities.
I am of the opinion that our investigations thus far do not disclose in what the real
differences in the behavior of these two soils lie, as this would require further study.

From elimination of other causes rather than direct data it appears
probable that the low productivity of the ‘‘sick”’ soil is due to the
biological condition of the soil; either to an accumulation of organisms
causing cane diseases or to some disturbance in the normal bacterial

1 Schreiner et al., U. S. Dept. Agr., Bur. Soils Bul. 83.
2 Shorey, U.S. Dept. Agr., Bur. Soils Bul. 88, p. 25.
8’ Shorey, U.S. Dept. Agr., Bur. Soils Bul. 88, p. 20.

22

life of the soil. The biological condition of the soil might affect the
plant through the formation of organic compounds by the bacteria
and fungi or through other means. There is some evidence of a
different biological condition in the ‘‘sick” and normal soil in the
report of Dr. Schreiner.

So long as this soil has to be planted continually to sugar cane it
appears as though increased yield could only come by planting new
varieties of cane which have been found to give heavier tonnage or
more sucrose than the old Rayada or Cristalina varieties. Rotation
with another crop would probably improve this soil as much as rest-
ing, but the nature of the soil and the climatic conditions are such
that it is better suited for sugar cane than almost any other crop.
Moreover, the principal commercial crops, as tobacco, pineapples,
coffee, and citrus fruit, are either not adapted for rotation or not
suited for this soil. The flooding caused by heavy rains, which some-
times occurs on this soil, renders it unsuited for many crops.

GENERAL REQUIREMENTS OF THE PORTO RICAN RED CLAY.

Certain general requirements of the Porto Rican red clay are appar-
ent from the experiments and observations that have been made thus
far. On account of its heavy nature and the flooding it is sometimes
exposed to, the maintenance of good mechanical condition and pro-
vision for good drainage are of first importance. The reasons for
this have already been pointed out in the first part of this report.
To maintain this good mechanical condition much more cultivation
is required on this type of soil than on more sandy soils.

Next in importance to cultivation and drainage are the needs for
more humus and lime. It has been pointed out that this type of soil
is uniformly acid and that much of it is low in organic matter. Addi-
tion of lime and organic matter is necessary for improving the bacte-
rial and chemical condition of this soil as well as the mechanical con-
dition. If well suppled with hme and humus, other factors being
favorable, bacterial activity will be increased and certain plant foods
be rendered more assimilable.

The importance of sufficient lime and humus in this soil, or any soil,
can best be appreciated by a newer view of soil fertility—that soil fer-
tility is not dependent so much on an absolute amount of inert mate-
rial as on a certain rate of decomposition, which is largely governed
by living and dynamic factors; that is, soil fertility is not so much
the result of a quantity as of arate.! The faster the rate, for instance,
at which plant food is rendered available, the greater will be the
fertility of a soil, other things being equal. The rate of soil decom-

1 Of course quantity will in many cases influence rate.

23

position can be increased by “‘speeding up” the bacteria through
liming and incorporation of organic matter.

The organic matter can be increased by plowing under the cane
trash instead of burning it, by green manuring, i. e., growing legu-
minous cover crops and plowing them under, or by the direct appl-
cation of organic materials, as stable manure, filter-press residue,
coffee hulls, and tobacco stems. Canavali, or sword bean, has been
found to be one of the best legumes for green manuring on this soil.
Burning the cane trash and so dissipating valuable organic matter and
nitrogen into the air is particularly disadvantageous on this soul,
which is in need of both substances. But where cane is badly
infested with insects burning the trash may be advisable.

The fertilizer experiments carried on thus far show that fair in-
creases on the normal soil can be secured by fertilization. For sugar
cane on this soil nitrogen is the most essential element and probably
gives as large mcreases as a complete fertilizer. Of course the fer-
tilizer results secured with sugar cane as a test crop do not apply to
conditions where other crops are grown. Tobacco, for instance, might
need potash on this soil as much as nitrogen. Experiments to deter-
mine the best form in which to apply the nitrogen for sugar cane on
this soil are in progress. [from the chemical composition of this soil,
1. e., the high content of iron and aluminum and the acid reaction, it
is probable that when phosphoric acid is needed basic slag would be a
good form in which to apply it. Basic slag has been found to give
good results on heavy clays and its phosphoric acid is supposed not
to be fixed by the iron and aluminum in the soil so quickly as that of
more soluble phosphates. But if a quickly available form of phos-
phoric acid is desired for a short-time crop, basic slag would hardly
give as good results as acid phosphate.

SUMMARY.

The Porto Rican red clay soil, one of the most extensive soil types
on the island, is planted chiefly to coffee and sugar cane.

It is a fairly heavy clay, often underlain by an impervious subsoil
and so requires good cultivation and drainage to be productive.

This type of soil is characterized chemically by a high percentage of
iron and aluminum, moderate amounts of nitrogen, phosphoric acid,
and potash, and no carbonates. It is almost uniformly acid and fre-
quently low in organic matter.

The experiments thus far carried on with sugar cane on this soil
show that the normal soil is benefited by liming and fertilizers.
Nitrogen is the most essential element and probably increases the
yield as much as a complete fertilizer.

1 Porto Rico Sta. Rpt. 1911, p. 25.

24

Certain areas of this soil that have long been in continuous cane
cultivation are in a ‘‘sick” or ‘‘tired”’ condition, not responding to
fertilizers, lime, stable manure, nor superficial disinfection.

In what the “‘sickness”’ consists has not been determined, but it
may be in the biological condition of the soil.

ACKNOWLEDGMENT.

The station is indebted to the Guanica Central for the land and
materials used in the conduct of many of the preceding experiments,
and thanks are due to various officials of the company who have
aided in the prosecution of the work.

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