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VI. Fertilization and Water-Use Efficiency with Limited Moisture Supply

VI. Fertilization and Water-Use Efficiency with Limited Moisture Supply

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well-disseminated was greater than 26 atmospheres when the soil had

reached its “minimum point” of water content. Kmoch et al. (1957) and

Ramig (1959) also show significant moisture depletion below the 15atmosphere percentage by wheat in Nebraska. Fifteen-atmosphere tension

is usually regarded as the lower limit of available moisture for most

practical purposes.

Therefore, one of the problems of dryland agriculture and range

management is to determine whether there are favorable moisture

interludes in the cycle of plant development when the soil cannot supply

sufficient nutrients for maximum growth. If, in these periods, fertilizers

can increase the net assimilation rate or growth without exhausting

water at a faster rate, then total yield and water-use efficiency can be

increased. If fertilizers accelerate the rates of both growth and water

use, the yield and water-use efficiency will depend on the total supply

of water and the status of the crop when the moisture supply becomes

exhausted. Thus accelerated water use through fertilization can be

disastrous for grain crops if the soil moisture supply is exhausted and

rains do not come before the grains are filled. This timing of moisture

use, total moisture supply, and plant development is much less critical

for crops that are grown for their vegetative parts and need not complete

their life cycle through seed production.

Forage grasses. Holmen et al. (1961) studied the Y vs. ET relationships of smooth bromegrass grown without irrigation and simultaneously

studied relationships in irrigated bromegrass, as shown in Fig. 3. Nitrogen

was applied at rates of 0, 40, or 80 pounds per acre. Fertilization

increased hay yields and had no significant effect on total evapotranspiration; water-use efficiency increased linearly with yield. Similar

results were obtained when grass was cut twice as often to simulate

pasturing. Whether comparisons are made on the basis of hay or pasture

yields, the water-use efficiency was higher on dryland than on irrigated

land for a comparable rate of nitrogen application. Burton et al. (1957)

found marked reductions in the water required to produce a pound of

dry matter by three varieties of Bermudagrass, Pensacola Bahiagrass,

and Pangolagrass when 50, 100, or 200 pounds of nitrogen per acre

was applied in each of 2 years. These studies were conducted on a deep

sand at Tifton, Georgia. The authors assumed that all precipitation from

April 1 through October 31 was consumptively used and none was lost

by percolation beyond the root zone or by runoff. Moisture depletion

in the profile between start and end of the season was assumed to be

4 inches. This was added to rainfall. In 1953 water use was then stated

to be 49.66 inches and in 1954,17.68inches. Even in dry 1954, fertilization

about doubled water-use efficiency for all grasses except Pangola.



Studies were conducted under more droughty conditions than those

noted above: Sneva et al. (1958) found that fertilization with NH4N03

reduced the pounds of water required to produce a pound of crested

wheatgrass hay in dry central Oregon where precipitation comes mainly

in the winter. With 0, 10, 20, 30, or 40 pounds of nitrogen applied per

acre to different plots in each of 3 years, the respective average “water

requirements” for the year of application were 2800, 2400, 2000, 1900,

and 1900, respectively. Mean annual hay yields increased from 711 to

1176 pounds per acre. Water used was taken as precipitation from

November 1 to June 1 and was not actual consumptive use. Fertilization

increased the percentage of the total yield produced before June 1. This

more rapid growth depleted the soil moisture at the 6- and 15-inch

depths more rapidly the greater the quantity of fertilizer used. The

fertilized grass cured earlier as a result of the earlier exhaustion of soil

moisture, which appeared to be complete at those depths by early July.

Plots were 15 by 15 feet in an area where advection is probably great.

Thomas and Osenbrug ( 1959) reported marked increases in efficiency

of use of seasonal precipitation through nitrogen fertilization of smooth

brome-crested wheatgrass grown for hay on Pierre clay in western South

Dakota. Replicated plots 8 by 35 feet were fertilized annually for 4

years. Hay yields were taken each year and for a subsequent 4 years.

Seasonal precipitation was rainfall between March 30 and June 22,

these dates corresponding to initiation of annual growth and harvest,

respectively. Seasonal precipitation vaned from a low of 3.06 to a high

of 9.82 inches, the mean being 5.72 inches for the period of study.

Fertilization with 255 pounds of nitrogen an acre more than doubled

mean yields and efficiency of rainfall use, as shown in Table VII. Lower

rates of nitrogen produced smaller, but still highly significant, increases.

The regression coefficients of yield on seasonal precipitation within a

fertility level showed a marked increase as fertilizer application was


Haise et al. (1960) reported unpublished data of J. R. Thomas which

show marked increases in water-use efficiency of a smooth brome-crested

wheatgrass mixture from fertilization of Pierre clay in both 1956 and

1957 in western South Dakota. Pounds of hay per acre-inch of water

consumptively used increased linearly with yield, fertilization having

little or no effect on evapotranspiration under these dryland conditions.

Similar unpublished data of J. J. Bond obtained with blue gramagrass

(Bouteloua gracilis) and Sudangrass in the Texas Panhandle are also

cited. Haise et al. (1960) plotted water-use efficiency against yield for

all these data. Within a grass species for a particular year, these functions

were linear, but the regression lines of different species and of different



years for a species had different slopes. Nevertheless all water-use

efficiency vs. yield functions were linear and can be extrapolated to the

origins of both axes, thus conforming to model D in Fig. 1.

Wheat. Koehler (1960) measured the effect of nitrogen fertilization

on the consumptive use (April 29-July 23) and yield of Omar winter

wheat on summer fallow in the 15-inch rainfall area of Washington.

Growth was accelerated by nitrogen applied at each of five rates from

0 to 160 pounds per acre. Plants getting 80 or 160 pounds reached

maximum growth considerably earlier than the others. Difference in


The Effect of Fertilizer on Yields and Efficiency of Use of Seasonal Precipitation for

an 8-Year Period by Smooth Bromegrass-Western Wheatgrass in

Western South Dakotaa

Total fertilizer


per acre


32 Tons of manure

32 Tons of manure and

85 pounds of N

85 Pounds of N

170 Pounds of N

255 Pounds of N

170 Pounds of N and

255 pounds of P,O,








hay yield


Yield vs.



(lb./acre-in. )





















From Thomas and Osenbrug ( 1959).

total consumptive use between the unfertilized wheat and that getting

160 pounds of nitrogen per acre was 0.7 inch, the maximum use being

about 12.5 inches. All the difference in consumptive use was due to

greater moisture extraction in the 6-, 7-, and 8-foot depths. The top

5 feet had no available water when the wheat matured. Koehler used

the statistical procedure of Leggett (1959), which predicts that 4 inches

of water is needed just to produce a wheat plant, and then calculated

that 6.4 bushels of wheat was produced per acre-inch of water without

fertilizer and 7.2 bushels was produced per acre-inch with 80 pounds

of nitrogen. This gain in efficiency is not outstanding, but then fertilization increased yield only from 58 to 68 bushels on this Walla Walla

silt loam summer-fallowed the previous year.

Power et aZ. (1960) found that RESCUE spring wheat in northeastern

Montana produced more dry matter and grain per inch of soil moisture

and precipitation used when the wheat was fertilized with phosphorus.




Dry matter was increased by phosphate application at seeding at each

of the following stages: tillering, heading, dough stage, and harvest;

yield was raised about 4 bushels, or 16 per cent. Phosphorus fertilization

and the resultant accelerated growth did not increase total evapotranspiration or the rate of soil moisture depletion on the four moisture

regimes employed (see Section VII). The plots were 8 by 20 feet.

Ramig (1959) measured the effects of stored soil moisture at

planting and nitrogen fertilization on the yields and evapotranspiration

of Cheyenne winter wheat on plots 64 inches by 13 feet on Holdrege silt

loam at North Platte, Nebraska. Soil was wet to about 0, 2, 4, and 6 feet

by preplanting irrigation. Evapotranspiration was taken at rainfall plus

change in soil moisture content to the 6-foot depth between planting

and harvest. No runoff occurred. Average data for 2 years and the two

moisture extremes as shown in Table VIII. When the soil was dry at


Average Evapotranspiration and Water-Use Efficiency of Cheyenne Winter Wheat

Grown after Wheat at North Platte, Nebraska, for 1954 and 1955a

Approximate inches of available water in 6-foot

profile at seeding time
























( in. )

( bu./acre-in. )



(bu./acre-in. )





























From Ramig (1959).

F and S are fall and spring applications, respectively.

planting, nitrogen fertilization had no effect on yield, evapotranspiration,

or water-use efficiency. When the soil was wet to field capacity 6 feet

deep ( approximately 8.1 inches of available moisture) nitrogen fertilization increased yield and total water used. but the water-use efficiency

increased from 1.12 bushels per acre-inch to a maximum of 2.04 bushels.

On the plots with a full profile at seeding, nitrogen fertilization increased

the use of water at tensions above 15 atmospheres. This amounted to as

much as 2 inches for the profile. On the dry soil, extraction at tensions

above 15 atmospheres could not contribute to total water use because

these plots were drier than the 15-atmosphere tension at time of seeding.

Near Amarillo, Texas, Jensen and Sletten got significant increases



in yield and water-use efficiency by nitrogen fertilization of Concho

winter wheat in normal 1957 and wet 1958,but not in dry 1956. Data

are shown in Table IV as the MI moisture treatment that got only a

preplanting irrigation. The yields and consumptive-use data show that

this treatment was definitely moisture-limited compared to the M4

treatment. The M1,however, was not typical of nonirrigated land.

Corn. Carlson et al. (1959) studied the effect of nitrogen fertilization

at two stand densities of corn on nonirrigated plots concurrent with their

studies on irrigated corn. The data are shown in Table V. On dryland,

nitrogen fertilization did not affect yields, water use, or water-use

efficiencies significantly in either year. Forage produced per acre-inch

of water was higher without irrigation than with irrigation unless a high

nitrogen rate and thick stand were used together. As mentioned earlier,

this points up the fact that water-use efficiency is frequently greater on

dryland than on irrigated land. Further, the interaction of nitrogen and

stand shown in these data demonstrates the need for the best combination

of soil and crop management practices if water is to be used efficiently.

Grain sorghum. Jensen and Sletten (see Table 111, M1 moisture

treatment ) got no significant differences in yield, evapotranspiration,

or water-use efficiency of hybrid grain sorghum getting one preplanting

irrigation only when nitrogen fertilization varied from none to 240

pounds per acre. Comparison of yields and evapotranspiration data of

the M 1 vs. M 4 moisture treatments shows that water was certainly

limiting on the M1treatments.

Cereal crops in Nebraska. Olson et al. (1960 with additions from

personal communication) reported that nitrogen fertilization increased

yields, soil moisture extraction, and water-use efficiency of four nonirrigated crops grown at many locations in Nebraska. In 29 experiments

with wheat, nitrogen increased average yields from 31 to 37 bushels an

acre, water use by 0.9 inch, and water-use efficiency by 12 per cent. In

16 experiments with oats, yields were increased from 46 to 66 bushels,

water extraction by 0.8 inch, and water-use efficiency by 38 per cent.

With corn in 12 experiments, yields were raised from 70 to 112 bushels

an acre, water use went up 1.3 inches, and water-use efficiency increased

by 44 per cent. Grain sorghum in nine experiments showed a yield

increase of 15 bushels an acre over a check yield of 60 bushels. Water

use was up 1.4 inches and water-use efficiency by 11per cent. Olson also

states that even under very dry conditions water-use efficiency was

increased by fertilization and that it was higher under dry conditions

than when moisture supply was more plentiful. He also reports reductions

in water-use efficiency when nitrogen was used on wheat grown on

fallowed land that produced high yields without fertilizers even though



adequate water was left in the profile at harvest. Consumptive use was

taken as the difference in soil moisture content to a depth of 6 feet

between planting and harvest plus 90 per cent of the precipitation, the

other 10 per cent assumed to have run off. Differences in consumptive

use induced by fertilization were due to differences in moisture extraction

in the upper 4 feet of profile by oats and wheat and throughout the

6-foot profile for corn and sorghum.

VII. Fertilization and Moisture Extraction by Roots

The favorable effects of fertilizers, when nutrients are deficient, on

the mass and distribution of roots have been reported many times and

are generally well known. In general, fertilization promotes top growth

faster than root growth, leading to an increased top : root ratio. However, there are only a few reports on the concurrent effects on total

water extraction and on vertical and horizontal changes in the extraction

pattern. Whether these would be expected to change would depend, at

least in part, on whether the evaporative demand of the tops were

changed. Changes in depth of rooting or ramification of roots in the

soil would be of particular importance under conditions of limited

water supply where full exploitation of soil water would be of greatest


Two studies with wheat show no effect of fertilization on soil

moisture extraction. Perhaps many studies with similar results have been

conducted but have not been published because of the negative findings.

Zubriski and Nonim (1955) in 12 North Dakota trials showed that

there was only 7.8 inches of total water, not available water, remaining

in the soil profile to a depth of 5 feet whether the wheat without

fertilizer yielded 13.1 bushels per acre or with fertilizer yielded 17.9

bushels per acre. Power et al. (1961) found that fertilization of dryland

spring wheat with phosphorus on Williams silt loam in northeastern

Montana had no consistent effect on cumulative soil moisture use or

total moisture use from seeding to tillering, to heading, to dough stage,

or to harvest, respectively. Phosphorus application increased dry weight

production compared to nonfertilization at all growth stages and raised

average grain yields about 4 bushels per acre, or 16 per cent. This

experiment had two levels of preplant moisture ( 2 and 4 feet of wet

soil) and two levels of seasonal moisture attained by irrigation or by

covering some plots during rains (see Section VI).

Several investigators have reported that fertilization does affect the

rate of depletion and/or total extraction of soil moisture. Koehler (1960)

found no differences in soil moisture content to a depth of 4 feet of a

deep Walla Walla silt loam at harvest due to fertilization of wheat, but



he found that the differences in total water use of 0.7 inch between

unfertilized plots and those fertilized with 160 pounds of nitrogen per

acre occurred in the 5-, 6-, and 7-foot depths. Kmoch et al. (1957)

studied the distribution and weight of wheat roots, and available soil

moisture content at three dates on plots adjusted to four levels of soil

moisture by irrigation before planting, with and without the application

of 80 pounds of nitrogen per acre. The soil was a deep Holdrege very

fine sandy loam at North Platte, Nebraska. Samples taken in June, 4

weeks before harvest, showed about 50 per cent greater root weight due

to nitrogen fertilization regardless of the depth to which the soil was

wet at planting. Soil wet to zero or 2 feet at planting contained less roots

than that wet to 4 or 6 feet. Soil samples showed that the nitrogen

fertilizer had increased the moisture extraction by 1.5, 0.9, 1.2, and

5.0 inches for the 10-foot profile on the plots having 0, 2, 4, and 6 feet

of wet soil, respectively, as compared to the unfertilized plots. Extraction

of moisture at tension values over 15 atmospheres occurred. Thus nitrogen

fertilization increased total root weight and soil moisture depletion, but

appeared to have little effect on rooting depth. As part of this study,

Ramig (1959) showed that nitrogen fertilization resulted in less available

water in the 6-foot profile at all times of sampling from April 11 to

harvest on July 12, 1956, where the profile at seeding had been wet to

6 feet. With 80 pounds of fall-applied nitrogen, water extraction of as

much as 1.08 inches in excess of the 15-atmosphere percentage for the

6-foot profile had occurred. Since there was no runoff, these effects of

fertilizers were effects on evapotranspiration, not on runoff. Where the

profile was dry at seeding, nitrogen fertilization had no effect on soil

moisture content as the profile was always dry and the soil moisture

content for the 6-foot profile was always less than that for the 15atmosphere percentage. Thus the wheat yields of about 5 bushels per

acre obtained on this soil moisture regime were due to quick interception

and use of surface moisture from rains. Sneva et al. (1958) found that

nitrogen-fertilized crested wheatgrass in semiarid central Oregon depleted the soil moisture at the 6- and l5inch depths more rapidly than

unfertilized grass. This earlier depletion of soil moisture caused the

grass to cure earlier, but the hay yields were also increased. Smika et

al. (1961) showed that fertilization of mixed native grass at Mandan,

North Dakota, with 30 or 90 pounds of nitrogen per acre annually had

increased the moisture extraction to a depth of 6 feet compared with

unfertilized grass in the 3 years between the start of the experiment

and the inception of soil moisture sampling in 1954 and that these differences in soil moisture in the subsoil persisted through 1958. The

plots were 5 feet wide and 20 feet long.

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VI. Fertilization and Water-Use Efficiency with Limited Moisture Supply

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