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UNITED STATES DEPARTMENT OF AIGRICULEURE

shea from the Bureau of Plant Industry
WM. A. TAYLOR, Chief

Washington, D. C. PROFESSIONAL PAPER June 27, 1917

EFFECT OF FALL IRRIGATION ON CROP YIELDS AT
BELLE FOURCHE, S. DAK.

By F. D. Farrew., Agriculturist in Charge of Demonstrations on Reclamation Projects,
and Beyer AUNE, Farm Superintendent, Western Irrigation Agriculture.

CONTENTS.

Page Page
NE ROMUCHIOM pes). ea ies yee yes aye a 1 | Results of the experiments—Continue%
VITA es estes SG <lecrns Pere cisereratee e eerie 2 i CHRO Oy UG KS i ag ce are ree ae Pe 6
SOU le See fee Se Ce Ra ean ea ee 3 Soillinoistuness et. A eer SO ee eh ee 8
Methods used in the experiments..........---- 4 | Character of soil the determining factor........ 10
Results of the experiments........-.--.-....-- Deal Mes UIT a oyenaeerarers acts ites Gotta aioe states ae Gate oe A 12

INTRODUCTION.

One of the conspicuous features of the climate of the Great Plains
area 1s the lhght precipitation received during the winter months.
Throughout most of the Plains region, about three-fourths of the
annual precipitation occurs during the six months from April to
September, inclusive,'so that the winter months are, comparatively,
very dry. As a result, it is commonly found that after producing a
crop the land remains dry from harvest time until the rainy season
of the following year. The soil on such land during this period may
be deficient in moisture not only near the surface but throughout
the zone of action of the roots of crop plants. It has been assumed
that this soil-moisture deficiency might have an unfavorable influence
on the growth of crops, both by hindering the germination of spring-
sown seed and by retarding or preventing the desired movement of
the water received as precipitation or applied in rrigation during the
growing season.

The practice of fall irrigation—the application of water to the
land in the fall of the year—has been advocated as a corrective of
this condition in irrigated regions. Various writers on irrigation
have suggested the desirability of fall irrigation, and a few investi-

1 Briggs, L. J., and Belz, J. O. Dry farming in relation to rainfall and evaporation. U.S. Dept. Agr.,
Bur. Plant Indus. Bul. 188, 71 p., 23 fig.,1 pl. 1910.

85963°—Bull. 546—17

ye BULLETIN 546, U. S. DEPARTMENT OF AGRICULTURE.

gators have made field studies of the subject. Knorr; experimenting
for three years on the North Platte Reclamation Project in western
Nebraska with wheat, oats, barley, potatoes, sugar beets, and corn,
found that the fall irrigation of the land on which these crops were
to be grown increased the yield an average of 16 per cent. The
yield increases secured in these experiments were ascribed to the
fact that fall irrigation resulted in more moisture in the surface soil
at seeding time in the spring and also in a better absorption of
moisture by the soil to a depth of 6 feet during summer irrigation.
These experiments were conducted on a sandy loam soil at the
Scottsbluff Experiment Farm, a field station of the Bureau of Plant
Industry. |

The favorable results secured at Scottsbluff suggested the advis-
ability of repeating the experiments at another point in the Great
Plains area where the soil conditions are different from those at
Scottsbluff. Accordingly, in the autumn of 1913 a series of fall-
irrigation experiments involving oats, sugar beets, flax, potatoes,
barley, corn, and wheat was inaugurated at the Belle Fourche E:xperi-
ment Farm on the Belle Fourche Reclamation Project in western South
Dakota, The experiments with these seven spring-planted crops were
‘continued through 1914, 1915, and 1916. The results secured are
reported in this bulletin.?

RAINFALL.

During the nine years, 1908 to 1916, inclusive, the annual rainfall

cat the Belle Fourche Experiment Farm ranged from 6.64 inches, in
-19141, to 21.02 inches, in 1915, the mean for the 9-year period being
-14:05 inches. In connection with the problem of fall irrigation it is
-important to consider the distribution of the rainfall with reference to
‘thetall period—the period between the beginning of harvest and the
time of fall irrigation—and to the winter period. The mean rain-
fall of these periods during the nine years of record and the actual
rainfall during the time in which the fall-irrigation experiments were
conducted are shown in Table I.

“TasLe I.—Precipitation at the Belle Fourche Experiment Farm, 1908 to 1916, inclusive.

Mean, Period of experiment.

Period covered. years, |

5 | |
108 +0) 191s" | 1914. Pa orS: leelole

‘Aotalannuall: 2 \25o5 oe eae Bea HES paca degboe - ccabies a2 14. 05
Fall period (August to October, inclusive)........-..--.----- our

Winter period (November to March, inclusive)......-.------ 2.15 1.84 | 2.52 | 1.99

1 Knorr, Fritz. Experiments with crops under fall irrigation at the Scottsbluff Reclamation Project
Experiment Farm. U.S. Dept. Agr. Bul. 133, 17 p., 5 fig. 1914.

2The writers desire to acknowledge their indebtedness to Mr. O. R. Mathews, Assistant, Dry-Land
Agriculture Investigations, for assistance in the conduct of these experiments.

EFFECT OF FALL IRRIGATION ON CROP YIELDS. o

The table shows the lght precipitation which occurs during the
winter months, from November to March, inclusive. During two of
the three winters included in the period of experiment there was
somewhat less than the mean winter rainfall for the period of record,
2.15 inches, and during the other there was slightly more than the ©
mean. Likewise, two of the three fall periods affecting the experi-
ments were drier and one was wetter than the mean for this fall
period, 3.75 inches. From this it would appear that if fall irrigation
were desirable at Belle Fourche, its benefits would have been empha-
sized during the period of these experiments.

SOIL.

The soil on which these experiments were conducted is an extremely
heavy clay of the class popularly known as ‘‘gumbo.”’ Soils of this
general character cover wide areas in the northern Great Plains. This
particular soil has been classified by the Bureau of Soils as Pierre
clay, of which the average mechanical composition is reported! as
follows:

Per cent.
JES OYS) CASRN) seen: DISSE fee poet eee att INR ase oor oer Nash Peg ate aan rare ian B 0. 2
Coarse'sande eet . 30 bee ieee... Pieris eee He
Mrecinmmigean Gia shy Rc et re te ORR ee cas Fe 1.4
TETAS) (SPM Ue 2 a a GM RI OP A SA ee MN i eg ese Rh (Otic eran tae DeD
Meryfine san Gown nee te aes toes see eee eas Ue 13.0
SLU Hp deel ese Ch RIES ALL, RY AIRS ah, ica ee Sue a NR ge eae Ff Nat 43.2
OL aya Pe Se ee ieysl. fo ae. EE he ce iua Los A £2 35. 0

According to the same authority, the Pierre clay covers about one-
third of the area of the Belle Fourche Reclamation Project and
occurs on this area to a uniform depth of about 6 feet. It has been
formed through the weathering of the underlying beds of Pierre
shale. According to a report? of a reconnoissance soil survey made
by the Bureau of Soils, the Pierre clay covers an area of nearly
eight million acres in the western half of South Dakota.

Important characteristics of this soil are its great water-carrying
capacity, its high water retentivity, and the extreme changes of
volume which accompany changes in its moisture content. Mathews?
found that this soil will carry about 30 per cent of water and that
about half of this is available to crops. The latter do not begin to
suffer from lack of water unless the soil moisture content approaches
17 per cent, which is approximately the wilting coefficient of this
soil. The importance in fall irrigation of the extreme changes of
volume accompanying changes in moisture content of this soil will
be discussed later.

1Strahorn, A. T., and Mann, C. W. Soil survey of the Belle Fourche area, South Dakota. In U.S.
Dept. Agr., Bur. Soils, Field Oper. 1907 [9th Rpt], p. 898. 1909.

2Coffey, G. N., and others. Reconnoissance soil survey of western South Dakota. In U.S. Dept. Agr.,
Bur. Soils, Field Oper. 1909 [11th Rpt.], p. 1401-1476, illus., pl. 9-15. 1912.

3 Mathews, O. R. Water penetration in the gumbo soils of the Belle Fourche Reclamation Project.
U.S. Dept. Agr. Bul. 447, 12 p., 4 fig. 1916.

4 BULLETIN 546, U. S. DEPARTMENT OF AGRICULTURE.

METHODS USED IN THE EXPERIMENTS.

The experiments were conducted in field P, Series I, II, I,
and IV, seven tenth-acre plats being used in each series. A
diagram of these plats is shown in figure 1. The land was first
broken in August, 1911, and it produced oats in 1912 and again
in 1913. It is uniform in topography and soil. The crops of 1912
and 1913 were harvested from the field as a whole, no record having
been secured of the production of the different series of plats. Series
II and IV were irrigated on November 11, 1913, November 11, 1914,
and November 10, 1915. Except for this fall irrigation, the treat-

= 13

suke ko [SS ip

Fic, 1.—Diagram ofa part of field P, Belle Fourche Experiment Farm, showing the location of the plats
used in the fall-irrigation experiments. The arrows indicate the direction of the flow of the water in
the irrigation laterals supplying these plats.

ments applied to Series II and IV were uniform with those applied
to Series I and III. : 3

The fall irrigation was applied each year after the plats were
plowed, except that in the autumn of 1914 the plats which that year
had produced intertilled crops were not plowed. Low earth dikes
were thrown up at the lower side of the plats to impound the water
sufficiently to insure a complete covering of the land. The water
was then applied by flooding and allowed to run on each plat from
three to four hours. The summer irrigation of each crop was uni-
form on all four series as to both time and method of application.
No attempt was made to measure the water applied, but the meth-
ods of irrigation recognized in the locality as good-farming methods
were followed. The sugar beets and potatoes were irrigated by the
furrow method and the other crops by field flooding.

EFFECT OF FALL IRRIGATION ON CROP YIELDS. 5

The experiments were conducted in duplicate each year, the seven
plats in Series I duplicating those in Series III, while the plats in
Series II and IV were duplicates. The following crop varieties were
used: Oats, Great Dane in 1914 and Swedish Select in 1915 and 1916;
sugar beets, South Dakota No. 40 in 1914 and Kleinwanzleben in
1915 and 1916; flax, Minnesota No. 25; potatoes, Eureka in 1914
and 1915 and U. S. No. 4452 in 1916; barley, Minnesota No. 6 in
1914, Himalaya (Guy Mayle) in 1915, and Chevalier in 1916; corn,
Payne White Dent in 1914 and 1916 and Martens White Dent in
1915; and wheat, Defiance in 1914, Pringle Champlain in 1915, and
Marquis in 1916. The positions occupied by the crops on each of
the four series each year, the crop sequence on each plat during the
3-year period, and the number of summer irrigations applied are
shown in Table II.

TABLE I1.—Sequence of crops and number of irrigations applied to each in the fall-irrigation
experiments at the Belle Fourche Experiment Farm in 1914, 1915, and 1916.

1914 1916

Plat. Nun Num-

er of ber of

Crop. irriga Crop. irriga-

tions tions.
Ho 7 ASE. SO ee Oe ee 3 Gaisti ste es 1
ONO Sh ee Wass Beets ies eee 3 Rotatoes:2-0 = 2222 1
NOS oe rer eitlenxe sts eet 2 | Béctonghiee sy 2
INGOs ee ee iPotatoess os = so | 4 | Wiest. 22" 1
INO Li eee Le | Barley 2: 5:28). .7] 2 | Barley-rs2 see S 1
TN Te Ty Wai Ae Gorn eos ee | 3 Gorn 2s sete eee 1
INOF NS aVWWihe@atinse eee | 2 dE Eb cae Sees ae 1

As shown in Table II, an intertilled crop followed a close-planted
crop on each plat except No. 13 in 1915 and 1916 and No. 10in 1916.)
More irrigation was necessary in 1914 than in either 1915 or 1916, as
the growing season of 1914 received somewhat less rainfall than either
of the others. The variations in both crop sequence and summer,
irrigation were the same on all four series.

All cultural operations on the four series were uniform as to both
character and time of performance throughout the period of experi-
ment. These included the ordinary operations incident to the pro-
duction of the seven field crops involved. The land was manured
from October 6 to 10, 1915, when 12 tons per acre of well-rotted
barnyard manure were applied uniformly to all the plats.

RESULTS OF THE EXPERIMENTS.

in the conduct of these experiments attention was directed chiefly
to the crop yields secured on fall-irrigated land as compared with
those of land not so irrigated and to the soil-moisture conditions on
the two groups of plats, particularly before the first summer irri-
gation each season. It was to be expected that any important,

.

6 BULLETIN 546, U. S. DEPARTMENT OF AGRICULTURE.

differences in the yields of the crops on the several plats would be
associable with soil-moisture differences in the spring, as the only
variation in the treatment of the land was the irrigation applied to
half the plats in the fall of each year.

CROP YIELDS.

Two plats of each of the seven crops were grown each year on the
fall-irrigated land, and the same number were grown on check series,

the latter receiving no fall irrigation. The yields are reported in
detail in Table III.

Tas_eE III.— Yields of crops in the fall-wrrigation experiments at the Belle Fourche Experi-
ment Farm in 1914, 1915, and 1916.

Plats and year. Series. | Wheat. Oats. Barley. Flax. Corn. Beets. | Pastas

Fall-irrigated plats: Bushels. | Bushels. | Bushels. | Bushels. | Bushels. Tons. | Bushels.
1914 II 31.5 47.8 29.1 17.0 53. 4 8.9 172
MSO SERS SES Sia IV 28. 5 39.0 26.8 10.5 45. 8 7.3 127
1915 { IT 24.0 70. 9 35. 7 18.8 29.3 5.1 108
BOGE Sigs Meret IV 19.3 60. 6 34.8 16.3 29.0 3.6 77
1916 { II 15.5 80. 6 39. 2 10. 4 50. 4 13. 2 | 267
Plat Cae AUC as IV 13.8 72. 2 38.3 9.1 45.4 12.2 254
Average, three |
Yeats ee ee 22.1 61.9 33.9 13.7 42.2 8.4 167
Check plats:
ie { 24.6 40.0 28.7 17.4 47.2 9.5 173
Sciaiy taker abinsoas 7 Til 19.3 47.8 26.0 14.8 51.4 dene: 158
1915 { I 22.7 80.0 43.2 16.3 29.3 5.9 105
i Ill 24.5 80.3 33.5 19.1 33. 7 5.7 100
1916 { I 14.3 73.9 41.8 12.1 47.9 13.5 225
Dg ett Ill 15.3 84.7 43.6 11.8 53.9 13.9 272
Average, three |
VCars... 2. Seat ek 20.1 67.8 36.1 15. 2 43.9 9.2 | 172

In order to facilitate comparisons of the yields shown in Table III,
‘the figures have been calculated in percentages, and the relative yields
are shown in Table IV, in which the yields of the check plats are repre-
sented as 100 per cent. The yield shown for each crop is the average
of duplicate plats.

\TasLe 1V.—Relative yields (expressed in percentages) of crops in the fall-arrigation expert-
ments at the Belle Fourche Experiment Farm in 1914, 1915, and 1916.

Ve | |
1914 1915 1916 3-year average.
: an A = 4 Oy E Dt
be Ke) SS fey ass: joe oO co
Crop. 8 kell bes s| 2 olny os ans
8 rm 8 a=) CS — fas} —
&0 Ho | bo Ps | bo Be 3] bo ne
— i Oa & = y te) S — os ct — os c
> ad sip Ae ae oO E ad ES ek = av =
= 9 |Seal = S Haileh |e 2 bo| = g =
=| 2 28 3 |2/185| 3 | 8 bas] s ges
& Sy Ne: I oO = & Oo |S = Ci AS
RD eee ENE Gs. | ee ; anbecel acre
\Witreat= G5) el 2a ee 137 | 100 | +37 92; 100;— 8}; 98}; 100] — 2] 110} 100; +10
HOSES =o Sao apie ees aoe 9951003) a 82| 100] —18 96} 100] — 4 91} 100} —9Q
Barley is 345 Ss acke ee cess 102} 100) + 2 92} 100} — 8 91} 100} — 9 94} 100} —6
MUA Keven a cacao rere ecto 85} 100] —15 99} 100; —1 88 | 100 | —12 90} 100} —10
WOOL “i eiceic tase wee ahr 101} 100; +1 94} 100] —6 94} 100] — 6 96} 100} —4
NB COtS 2. wee aee eee seco 98 | 100} — 2 7 100 | —26 93 | 100] —7 91} 100} —9
Potatoes. ce recenenc eee eae 90 | 100} —10 $0} 100} —10; 105] 100}]+ 5 97} 100} —3

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EFFECT OF FALL IRRIGATION ON CROP YIELDS. (&

The figures in Table IV show that in 1914 the yields of wheat,
barley, and corn were higher on the fall-irrigated plats than on the
check plats, the increases being 37, 2, and 1 per cent, respectively,
while the yields of the four other crops were lower on the fall-irrigated.
land, and that the average yield increase of the seven crops in that.
year was 2 per cent in favor of fall irrigation. In 1915 the yields of
all the crops were lower on the fall-irrigated land, the average decrease
being 11 per cent. In 1916 all the crops yielded less on the fall-
irrigated plats than on the checks, except potatoes, which yielded 5 per
centmore. In the 3-year average, wheat on fall-irrigated land showed
an increase of 10 per cent, while all the other crops showed decreases
ranging from 3 to 10 per cent, the average yield decrease of the seven
crops on fall-irrigated land for the 3-year period being 4 per cent of
the average yield of the check plats.

The fact that of the 42 duplicate plat averages secured in the 3-year
period only four were in favor of fall irrigation would support a pre--
sumption that fall irrigation on this soil was detrimental. However,
since not all the yields were against fall irrigation, it is possible that.
the yield variations were accidental. In order to determine whether :
these differences were significant, the probable errors of the average
yields have been calculated. The results are shown in Table V, in_
which the yields secured during the 3-year period are summarized.
TasLE V.—Summary of the yields secured in the fall-irrigation experiments at the Belle

Fourche Experiment Farm in 1914, 1915, and 1916, showing the probable errors of the
averages.

Fall-irrigated plats. Check plats.
: Difference
Cr Unit of | Num- Num- in favor
op- yield. | berof| Average | berof| Average of fall
plats yield per plats yield per irrigation...
aver- acre. aver- acre.
aged aged
Wihtea tae eee ere etn ee | Bushels 6 22.14 2.2 6 20.14 1.4 +2.04 2.6
OSTS ee geseas ee ae ss ee a Becks so 6 61.9+ 5.0 6 67.8+ 6.0 —5.9+ 7.8:
iaytig Gi ee fea, © Ga oe Se Petedowe tl te: 6 330992195 6| 36.14 2.5 2G
BY axe tis Som 5 [Rd ORs 6 13.74 1.4 6 15.24 .9 —1.54+ 1.7
COR ee epee fad oe Sek ead Ouse 5: 6 42.2+ 3.3 6 43.9+ 3.1 —l.7+ 4.5
HB CGiSeet eee ee ees en & Monsels. 6 | 8.44 1.1 6 | 2e et |e Seo
EP ORMLOCS sete wee es. Soe iyes oe Bushels... 6 | 167 +23.0 6 | 172 +19.0| —5.0+30.0

The figures in the last column in Table V show for each of the seven.
crops the difference between the average yield of the fall-irrigated —
plats and that of the check plats during the 3-year period. None of.
the differences was as great as the probable error, so that all must:
be regarded as insignificant. A similar tabulation of the yields of
straw and stover (which are not shown here) produces a like result,
there being no significant differences in the average yields of these
products. .

The explanation of the somewhat lower average yields secured on
the fall-irrigated land lies in the relatively low productivity of Series.

8 BULLETIN 546, U. S. DEPARTMENT OF AGRICULTURE.

IV, one of the two fall-irrigated series. The 3-year average yield of
the crops on Series [V was 16 per cent lower than the corresponding
average of Series II, while the 3-year averages of the two check
series, | and III, were identical. The relatively low productivity of
Series IV may have. been associated with a heavy infestation of
gumbo weed (iva azillaris). This weed was more abundant on
Series IV than on any of the other series throughout the period of
experiment. At any rate, there is nothing in the data to indicate
that fall irrigation influenced the crop yields.

SOIL MOISTURE.

When the experiments were planned, it was the intention to make
soil-moisture determinations shortly after the fall irrigation each
year and also during the early part of the growing season. It was
found, however, that because of cold weather the soil remained wet
so long after the fall irrigation that fall sampling was impracticable.
All the soil-moisture data available, therefore, were secured during
the spring and early summer of each of the three years of the period
of the experiment. In each sampling two cores were taken on each
plat and composited to a single sample for each foot section.

Soil moisture in 1914.—Three samplings were made in 1914, on
May 5, June 18, and June 27. The samples secured on May 5 were
taken from the plats seeded to oats, barley, and wheat, two plats
of each crop on the fall-irrigated land and the same number of
check plats, a total of six plats representing each fall treatment.
These samples were taken 34 days before the first irrigation. The
second set of samples, taken June 18, was from the same plats as
the May 5 samples and from the two flax plats, a total of eight
plats representing each fall treatment. This sampling was done 10
days after the first irrigation of the oats, wheat, and barley and one
day after the flax was irrigated. The samples secured on June 27
were from the same plats as those taken on June 18, and no irrigation
water was applied between the two sampling dates. These moisture
determinations were made to a depth of 4 feet. A summary of the
results is given in Table VI, which also shows the probable errors of
the averages of moisture content.

Table VI shows that on May 5 the average moisture content of the
upper 3 feet of soil on the fall-irrigated plats was higher than that of
the corresponding depths on the check plats, the greatest difference
being in the second foot, where it amounted to 8.3+0.5 per cent.
The soil of all the plats, however, contained an abundance of mois-
ture, the moisture content being well above the wilting coefficient,
which is approximately 17 per cent. The difference in the moisture
content of the fourth foot on the same date, 2.2+1.2 per cent, was
insignificant. On June 18, after the plats had been irrigated, the only
significant differences were found in the second and third feet, where
the soil of the fall-irrigated plats contained about 5 per cent more

EFFECT OF FALL IRRIGATION ON CROP YIELDS. 9

moisture than that of the check plats. On June 27 there were no
significant differences in moisture content, all differences being less
than their probable errors. It will be noted that the moisture con-
tent of the fourth foot was practically the same on each of the three
sampling dates. The results of the moisture determinations made
in 1914 showed that while the soil of the fall-irrigated plats contained
more moisture than that of the check plats early in the season, when
-all the plats had abundant moisture, the differences decreased as the
season advanced and disappeared before the end of June.

TasLE VI.—Summary of the results of soil-moisture determinations made in 1914 in the
fall-wrrigation experiments at the Belle Fourche Experiment Farm.

|
| Fall-irrigated plats. Check plats.

fe x | Diteeace
Date. Depths|) ose Nee Be e@s
‘ eet Moisture bey of | Moisture - iipeation
aan content. ene content.
aged. aged. |
Feet. | Per cent. Per cent. Per cent.
UBF eta os Ae I i eR AS oie 1 6 28.7+0.4 6 25.1+0.6 +3.6+40.7
DD) Qh speek esi b ees eae 2 6 28.8+ .4 6 | 20.5+ .3 +8.34 .5
ID YG ices nee aye mie A an 3 6 26.6+ .3 6 21.0+ .3 +5.6+ .4
IDX OLS ame Bie Ste ee Sk dee Seen nn deel ee 4 6 21.7+1.0 6 19.5+ .7 +2.241.2
AOE TCS ea sje pak SS NR oe A ae Rie arc 1 8 23.14 .6 8 21.54 .7 +1.6+ .9
TD YG) 87 A GIES Heer Senta Raed ee year a 2 8 25.34 .7 8 20.3+ .9 +5.0+1.1
1D) Qe es a. res SR ON MERON 3 8 26.54 .6 8 20.9+ .5 +5.6+ .8
LB AG ye 5 ee ese, ecto ae Oe a Se oe a 4 8 21.54 .8 8 20.2+ .9 +1.3+41.2
TUTOR One em Mtoe ee Pe 1 | 8 22.34 .6 8 22.1+ .7 + .2+ .9
1B Xa ya Ayres Rema 8 eRe tI Bi 11 2 | 8 25.84 .4 8 25.04 .7 + .8+ .8
TD) a eg AE Ey tee ee ESS 3 | 8 26.4+ .6 8 | 26.3+ .9 + .141.1
SDD Re oe OI ren ay 4 | 8 .8 8 | 20.74 .9 ao TEI?

no
=
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Soil moisture 1n 1915.—The sampling in 1915 was done on May 24
and June 10. Ail the plats in Series I and II were sampled on the
first date and those in Series III and IV on the second. No irriga-
tion water was applied to any of the plats in 1915 until July 14, so
that the moisture determinations were made five and seven weeks,
respectively, before the first irrigation. The samples were taken to
a depth of 3 feet. Table VII gives a summary of the results of the
moisture determinations, together with the probable errors of the
averages of moisture content.

‘Taste VII.—Summary of the results of soil-moisture determinations made in 1915 in the
fall-wrrigation experiments at the Belle Fourche Experiment Farm.

Fall-irrigated plats. Check plats.
: . ie Difference
N - - in favor
Date. Depth: | yee pie me
ber of | Moisture | P&T Of! Moisture as
Me a content. aah content. 8 :
aged. aged.
Feet. Per cent. Per cent. Per cent.
MB ga NES CEE SY OLR ETS 1 7 29.2+0.3 7 30. 440.2 —1.2+0.3
Bee PANE ee in ye yk 2 7 29.44 .4 7 29.44 .4 0
TO eso eR eee ore Lee a EY 3 7 28.14 .2 7 26.0+ .9 +2.1+ .9
ay Ue lel Oe eed Magee a ee 1 7 30.04 .3 a 30.3+ .6 — .3+:.7
1D O18 SPA CS Ra Me oa 0A ae 2 7 29.84 .2 7 29.4+ .6 + .4+ .6
1D Voy Esa = 0 age Ae A APR (OI Ctr a 3 a 27.94 .3 7 27.6- .7 + .31 .8

10 BULLETIN 546, U. S. DEPARTMENT OF AGRICULTURE.

Except for a very slightly lower average moisture content in the
first foot of the fall-irrigated plats sampled May 24, the moisture
determinations made in 1915 disclosed no differences large enough to
be considered significant between the fall-irrigated plats and the
checks. Asin the spring of 1914, the soil on all the plats sampled con-
tained an abundant supply of moisture. As the moisture content of
all the plats before the first irrigation was found to be substantially
the same, no further moisture determinations were made during the
season.

Soil moisture wn 1916.—The first irrigation in 1916 was applied
July 6. Soil-moisture determinations were made to a depth of 2 feet
on all the plats in oats, wheat, and barley on June 10, and the plats in
potatoes, beets, corn, and flax were sampled to the same depth on
June 30. The results of the two samplings are summarized in Table
VIII, which also shows the probable errors of the averages of mois-
ture content.

TasLeE VIII.—Summary of the resulis of soil-movisture determinations made in 1916 in
the fall-irrigation experiments at the Belle Fourche Experiment Farm.

Fall-irrigated plats. Check plats.
=< | - Ditterenes
Date. Depth. | Um | um anaes
Pa | Moisture Pe Moisture eeeaaae
awee | content. Pane content.
aged. aged
|
|
Feet | Per cent. Per cent. Per cent.
SIME 0 He ae ee ee 1 6 27.7+0.6 6 27.4+1.0 +0.3+1.2
Dog oA Sas 8s Oe CS OE TE 2 6 29.24 .8 6 99.24 .9 0 +1.2
TURES Os Sa ee a ae 1 8 29.7+ .6 8 | 29.9+1.2 — .241.3
D 2 8 30.24 .3 | 8 30.14 .4 Lie pgnss

The results of the soil-moisture determinations made in 1916 were
practically the same as those secured in 1915. The soil on all the
plats contained an abundance of moisture at the time of sampling,
and there was no significant difference between the moisture content
of the fall-irrigated plats and that of the checks.

The results of the determinations made during the three years may
be summarized by the statement that any higher soil-moisture con-
tent resulting from fall irrigation was found only at times when the
soil on both the fali-irrigated plats and the check plats was well sup-
plied with water and that all significant differences in soil moisture
disappeared early in the growing season, so that the crops showed no
effects of fall irrigation.

CHARACTER OF SOIL THE DETERMINING FACTOR.

The fact that fall irrigation produced no effect on crop yields at
Belle Fourche while it resulted in decidedly higher yieids at Scotts-
bluff makes it desirable to compare the rainfall and the soil con-
ditions at the two places. The comparison is shown in Table IX.

EFFECT OF FALL IRRIGATION ON CROP YIELDS. 11

TaBLE IX.—Ratnfall and soil conditions of the Scottsbluff and Belle Fourche Experiment

Farms.
Items of comparison. Scottsbluff. |BelleFourche.
Mean precipitation (inches):
NTNU See re Vt I NG A SOS Re A Re a I 14. 47 14. 05
Fall period (August to October, inclusive)....................----------- 4. 96 Bald
Winter period (November to March, inclusive)..........-...-------.---- 1.35 PN
a otal Ckugust tofMarch meclusive) = 32-52-65. 2- ese ease ncaece ec ses = 6. 31 5. 90
oil:
AD OL Soci SORTA PO HLS AUS INR Na SC Na a a Ro Sandy loam.} Pierre clay.
Field moisture-carrying capacity............--....-------.-. per cent !.. 13 27
Wailtin ge iCoeih Clem tis ein ik mares mratanie cei uy Aco TaN oa a Edoiee 6 17

1 These figures, which represent average conditions at the two field stations, were obtained from the
Office of Dry-Land Agriculture.

It will be noted that the precipitation at Scottsbluff does not differ
materially from that at Belle Fourche, either as to the total quantity
or as to the quantities received during the fall and winter periods.
The soils represent the essential difference between the two places in
relation to fall irrigation. The figures showing moisture-carrying
capacity and wilting coefficient mdicate something of the wide
dissimilarity of the two types of soil. The sandy loam, being coarse
grained, has a low moisture-carrying capacity and a low wilting co-
efficient. On the other hand, the extremely fine-grained Pierre clay
has more than double the moisture-carrying capacity of the sandy
loam and its wilting coefficient is nearly three times as high.

The soil at Scottsbluff is readily pervious to water to a depth of at
least 6 feet, and its permeability is higher when the soil is moist than
when it is dry. Knorr: found with this soil that water applied
during the regular irrigation season pereolated deeper on the plats
on which the moisture content was relatively high as a result of fall
irrigation than on the check plats where the soil moisture content.
was comparatively low. This fact, together with the greater quan-
tity of moisture available in the fall-irrigated plats at planting time,
is believed to explain the beneficial effects ot fall irrigation at Scotts-
bluff.

The moisture relationships of the soil at Belle Fourche are very
different from those at Scottsbluff. At Belle Fourche the soil is
practically impervious except when it is dry, and the depth of water
percolation depends chiefly upon the extent to which the soil is
cracked as a result of dryness. The addition of moisture causes the
soil to expand rapidly, and as expansion increases permeability de-
creases. After making an extensive study of water penetration in
these soils, Mathews ? states that ‘‘On a dry soil, penetration takes
place rapidly to a depth of about 2 feet because of the cracked con-

1 Knorr, Fritz. Experiments with crops under fall irrigation at the Scottsbluff Reclamation Project.
Experiment Farm. U.S. Dept. Agr. Bul. 133,17 p., 5 fig. 1914.

2 Mathews, O.R. Water penetration in the gumbo soils of the Belle Fourche Reclamation Project-
U.S. Dept. Agr. Bul. 447, p.11. 1916.

days BULLETIN 546, U. S. DEPARTMENT OF AGRICULTURE.

dition of the soil near the surface. After the layer of easily pene-
trated soil becomes wet, it becomes so swollen and compact that it
is nearly impervious, and further water movement is very slow.”

The results secured in the fall-irrigation experiments at Belle
Fourche are in accord with these observations. The application of
irrigation water in the autumn filled the surface soil to its moisture-
carrying capacity, but apparently had no effect beyond the third
foot. Irrigation water applied uniformly to all plats during the
growing season, together with the natural precipitation, equalized
the moisture content of the soil in these plats, irrespective of their
treatment the previous fall. It is important to note also that an
abundance of moisture was present in all the plats at the time of
sampling in the spring and early summer and that after this time
moisture was supplied by irrigation.

These facts account for the absence of significant differences be-
tween the average yields of crops on the fall-irrigated plats and
those secured on the check plats. It is possible that if an adequate
supply of moisture had not been maintained by irrigation during
the growing season the soil-moisture content of the fall-irrigated
land would have been higher in the spring than that of the check
plats. It seems certain, however, that where crops are properly
irrigated during the growing season fall irrigation on this soil will
eee no material effect.

SUMMARY.

The light precipitation received during the winter months in the
Great Plains area commonly causes soil to remain dry from the time
crops are harvested until the rainy season the following year. In
some soils this deficiency of moisture may have an unfavorable in-
fluence on the growth of crops, both by hindering the germination
of spring-sown seed and by retarding or preventing the desired
movement of the water received as precipitation or applied in irri-
gation during the growing season.

Fall irrigation has been advocated as a corrective of this condi-
tion in irrigated regions. It has been found efficacious on sandy
loam soil in western Nebraska, where it resulted in increased soil
‘ moisture in the spring and in greater moisture absorption by the
soil throughout the irrigation season.

In order to test the practice of fall irrigation on a heavy clay soil,
experiments were conducted at the Belle Fourche Experiment
Farm, in western South Dakota, in 1914, 1915, and 1916. These
experiments included wheat, oats, barley, flax, potatoes, sugar
beets, and corn, each crop being grown each year in duplicate tenth-
acre plats both on fall-irrigated land and on land which received no
fall irrigation.

‘sina

EFFECT OF FALL IRRIGATION ON CROP YIELDS. 13

There were no significant differences between the average yields
secured on the fall-irrigated plats and those on the check plats.

Soil-moisture determinations were made in the spring and early
summer each year. In 1914 they disclosed no significant differ-
ences in the moisture content of the soil resulting from fall irriga-
tion except that in the first two of the three samplings more moisture
was found in the first 3 feet of the fall-irrigated plats than in the cor-
responding depths of the check plats. No effect was noted beyond
the third foot. The difference found in the upper 3 feet existed
at a time when all the plats contained abundant moisture, and it
disappeared before the end of June. No significant differences were
found in 1915 or 1916.

The failure of fall irrigation to increase crop ylelds in these ex-
periments seems to be attributable to the character of the soil at
Belle Fourche. This soil is a heavy clay, which will absorb water
only when dry and which expands rapidly when moisture is added
to it. This expansion so compacts the soil as to make it imper-
vious, so that the storage of water in the lower depths for the use of
crops is not practicable.

PUBLICATIONS OF THE U. S. DEPARTMENT OF AGRICULTURE ON
RELATED SUBJECTS.

AVAILABLE FOR FREE DISTRIBUTION BY THE DEPARTMENT.

Experiments With Crops Under Fall Irrigation at the Scottsbluff Reclamation Project
Experiment Farm. (Department Bulletin 133.)

Sugar-beet Growing Under Irrigation. (Farmers’ Bulletin 567.)

Irrigated Pastures for Northern Reclamation Projects. (Bureau of Plant Industry,
DE 2:)

FOR SALE BY THE SUPERINTENDENT OF DOCUMENTS, GOVERNMENT PRINTING
OFFICE, WASHINGTON, D. C.

Progress Report of Cooperative Irrigation Experiments at California University Farm,
Davis, Cal., 1909-1912. (Department Bulletin 10.) Price, 5 cents.

The Flow of Water in Irrigation Channels. (Department Bulletin 194.) Price, 25
cents.

The Drainage of Irrigated Land. (Department Bulletin 190.) Price, 10 cents.

Drainage of Irrigated Lands. (Farmers’ Bulletin 371.) Price, 5 cents.

Potato Culture on Irrigated Farms of the West. (Farmers’ Bulletin 386.) Price, 5
cents.

Trrigation of Sugar Beets. (Farmers’ Bulletin 392.) Price, 5 cents.

The Use of Windmills in Irrigation in the Semiarid West. (Farmers’ Bulletin 394.)
Price, 5 cents.

Irrigation of Grain. (Farmers’ Bulletin 399.) Price, 5 cents.

Trrigation of Orchards. (Farmers’ Bulletin 404.) Price, 5 cents.

Timothy Production on Irrigated Land in the Northwestern States. (Farmers’ Bul-
letin 502.) Price, 5 cents.

Suggestions to Potato Growers on Irrigated Lands. (Bureau of Plant Industry Cir-
cular 90.) Price, 5 cents. |

Irrigation in South Dakota. (Office of Experiment Stations Bulletin 210.) Price,
10 cents.

Storage of Water for Irrigation Purposes: Part I. Earth-fill Dams and Hydraulic-fill
Dams. (Office of Experiment Stations Bulletin 249, Part I.) Price, 30 cents.

15

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