沙漠研究 24-1, 153-156 (2014)
Ἃ₍◊✲ 24-1, 153 - 156 (2014)
Journal of Arid Land Studies
Journal of Arid Land Studies－ DT11 Refereed Paper －㸫DT11 Refereed Paper㸫Effective Use of Soil Water Contributed to High Yield in Wheat
in the U.S. Southern High Plains
Gautam P. PRADHAN1), Qingwu XUE*1), Shuyu LIU1), Jackie C. RUDD1) and Kirk E. JESSUP1)
Abstract: Wheat (Triticum aestivum L.) is grown in a wide range of water regimes (from dryland to limited irrigation to fullirrigation) and produces both grain and forage in the U.S. Southern High Plains. Due to the semi-arid environment in the area,drought stress is the single most important factor reducing grain and forage yields. Selection of drought tolerant wheat cultivars is a
critical strategy for wheat management under water-limited conditions. Although wheat yield and drought tolerance have been
improved over the years by the Texas A&M (TAM) Breeding Program, the physiological mechanisms of drought tolerance among theTAM cultivars have not been well understood. Our objective was to investigate the differences in soil water depletion among four
TAM cultivars. A two-year field experiment was conducted at Bushland, TX, under dryland and irrigated conditions. Cultivars
included TAM 105, TAM 110, TAM 111 and TAM 112, which were released from the late 1970’s to early 2000’s. Based on
measurement of seasonal dynamics of soil water depletion, the newer cultivars (TAM 110, TAM 111 and TAM 112) extracted morewater from the soil profile than the older cultivar (TAM 105), particularly from the deeper soil profile. However, only under extreme
water-limited conditions, varietal differences in yields were evident and were related to measured differences in soil water content.
We recommend further studies on root traits to elucidate the differential behaviors of new and old cultivars under extreme drought,
moderate drought, and irrigated conditions for SWC and yield.
Key Words: Drought tolerance, Neutron probe, Soil water depletion, Water use efficiency, Wheat

1. Introduction
Wheat is grown in a wide range of water regimes andproduces both grain and forage in the U.S. Southern High
Plains (SHP). Wheat yield and water-use efficiency (WUE:the ratio of yield to ET) are primarily limited by drought stressfrom late spring to early summer in the SHP (Musick et al.,
1994; Xue et al., 2006). Adoption of drought tolerantcultivars is a critical strategy for wheat management underwater-limited conditions. Cultivars developed by Texas
A&M AgriLife Research are grown widely in the SHP, andTAM 111 and TAM 112 were the top two cultivars in2010-2012. A previous study showed that newer cultivars,
TAM 110, TAM 111 and TAM 112, had 19-29% higher yieldthan an older cultivar, TAM 105 (Xue et al., 2014). However,the physiological mechanisms of drought tolerance among
these cultivars have not been well understood.
Under water-limited conditions, extraction and effective
use of soil water are important to increasing crop yield (Entz etal., 1992; Xue et al., 2003). The effective use of soil water isrelated to root growth and development. In the SHP, fieldstudies have been conducted on root growth and soil water
depletion (Winter and Musick, 1993; Xue et al., 2003). Xue* Corresponding Author: QXue@ag.tamu.edu
6500 Amarillo Blvd. W., Amarillo, TX 79106, USA1) Texas A&M AgriLife Research at Amarillo

et al. (2003) showed that a relatively deep root system andhigher water uptake are important for wheat to maintain higher
yield and WUE under dryland and limited irrigation conditions.
However, there is little information regarding these traits
among wheat cultivars. Therefore, the objective of this study
was to investigate the differences in soil water depletion amongfour TAM wheat cultivars.

2. Materials and Methods
A two-year field experiment was conducted at Bushland,
TX (Lat. 35°11’N, Long. 102°06’W; elevation 1170 m) in the2010-2011 (2011) and 2011-2012 (2012) winter wheat
growing seasons. Four hard red winter wheat cultivars (TAM105, TAM 110, TAM 111 and TAM 112) were used in thisstudy. These cultivars have been widely grown in the Texas
High Plains and Western Kansas (TAM 105 in 1980 to early
2000’s, TAM 110 in late 1990’s to early 2000’s, and TAM 111
and TAM 112 in the present time).
In this study, the cultivars were grown in two soil water
regimes, dryland and irrigated, which were in two different
fields. For each water regime, the experimental design was arandomized complete block design with three replications.
The soil in both fields was a Pullman clay loam (fine, mixed,
㸦Received, September 15th, 2013; Accepted, February 3rd, 2014㸧

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thermic Torrertic Paleustoll). Plot size was 5.6 m2 for drylandand 3.7 m2 for irrigated plots.
In both years, wheat was planted from the last week ofOctober to the first week of November depending on the soil
moisture condition for dryland. The seeding rate was 67 kg
ha-1 for dryland and 100 kg ha-1 for irrigated plots. Irrigatedplots generally received three to four irrigations from booting
to the middle of grain filling. The seasonal rainfall (Oct.-Jun.)was 38 mm in 2011 and 191 mm in 2012, which was below
the long term average (287 mm). As such, dryland plots
experienced moderate (2012) to extreme drought stress (2011).
The volumetric soil water content (SWC, cm3 cm-3) was
measured on five dates in 2011 (after emergence, early spring,
jointing, anthesis and maturity) and three dates in 2012
(jointing, anthesis and maturity) with a 503 DR neutron probe(CPN International, Inc., Martinez, California, USA). The
access tubes were installed at the center of each plot, and thereadings were collected at 20 cm intervals from 0-240 cm
profile. The neutron probe was calibrated in situ at Bushland,TX (Evett et al., 1993).
The amount of soil water (SW, mm) in the root zone
(0-140 cm for dryland, and 0-160 cm for irrigated) was
calculated by summation of the SWC multiplied by soil depth
at each layer. Soil water depletion (SWD) at different stages
was calculated as the difference in SW between emergence andeach stage. Rooting depth was estimated indirectly by water
depletion among measurement dates, which was defined as thelowest depth in which significant difference (p < 0.05) in SWC
occurred between sampling dates (Entz et al., 1992). Grain
yield for each plot was determined by combine harvest of thewhole plot after maturity. Evapotranspiration (ET) wascalculated using the soil water balance method, i.e ET = SWC
at planting + seasonal precipitation + total amount of irrigation- SWC at maturity (Xue et al., 2003). Since the SWC was
not measured until spring, ET was not calculated for 2012season. WUE was determined as the ratio of yield and ET.
The data were analyzed with SAS 9.2 using the PROC GLM
procedure (SAS Inc., 2008). The protected Fischer LSD at p
= 0.05 was used to separate means among the treatments.

3. Results and Discussion
There was a significant difference between years for grain
yield under both soil water regimes. The average grain yieldat 2012 was 1.6 times higher than in 2011 under both dryland
and irrigated conditions. The irrigated grain yield was 4.3 - 5times higher than the dryland grain yield in both the years(Table 1). Under dryland conditions, the three relatively
newer cultivars (TAM 110, 111 and 112) had higher yield andWUE than TAM 105 in 2011. The yield differences among

Table 1. Grain yield and WUE of four wheat cultivars. Within eachwater regime and year, means followed by the same letters are
not significantly different at p = 0.05 based on LSD test.
Cultivar

Grain yield (kg ha-1)

WUE (kg m-3)

2011

2012

2011

TAM105
TAM110

474b*
756a

861a
864a

0.36b
0.58a

TAM111

696a

875a

0.56a

TAM112
Mean676a
651

1048a
912

0.55a0.5114.98

14.94

15.85

TAM105
TAM110

3267a

4569a

0.62a

2810a

4581a

0.57a

TAM111

2922a

4665a

0.58a

TAM112
Mean2732a
2933

4478a
4573

0.55a
0.58

cv

12.41

11.55

11.97

Drylandcv
IrrigatedFig. 1. Changes of SWC along soil profile at jointing (JT), anthesis(AN), and maturity (MA) in TAM 111 in two water regimes
and two years.

cultivars were not statistically significant in 2012. Under
irrigated conditions, there were no differences among thecultivars for yield and/or WUE for either year.
Figure 1 shows the SWC along the profile at jointing (JT),anthesis (AN) and maturity (MA) in TAM 111, in two years
and two water regimes. The changes of SWC over the season
reflected the rooting depth. For dryland plots, rooting depth
was 110 cm in 2011 and 90 cm in 2012. For irrigated plots,
the rooting depth was down to 140 cm in both years. Thechanges of SWC along the profile in the other three cultivars
were similar to TAM 111 (data not shown). The rooting

155Fig. 2. Soil water content along the profile in four cultivars at anthesis (AN) and maturity (MA) in two years under dryland conditions.

Fig. 3. Soil water content along the profile in four cultivars at anthesis (AN) and maturity (MA) in two years under irrigated conditions.

depth in this study was shallower than that in a previous study(160 cm, Xue et al., 2003).
The main reason for this could be due to the relatively lateplanting date (late Oct. to early Nov.) in this study as comparedto Oct. 1 in the Xue et al. (2003) study. Winter and Musick(1993) showed that late planting (Nov.) reduced rooting depthand soil water depletion in wheat in the SHP. Lower soil
water content at planting might also have contributed to theshallower root system in this study, particularly in the 2012season.

There were significant differences in SWC among the four
cultivars along the profile at AN and MA in two years underboth dryland and irrigated conditions (Figs. 2 and 3). For
dryland wheat, in 2011, TAM 105 had higher SWC than othercultivars at both AN and MA, and TAM 110 had the lowest
SWC particularly at deeper soil layers; (Fig. 2). Further, theTAM 105 had the highest (1.5 cm3 cm-3) and TAM 110 thelowest (1.4 cm3 cm-3) averaged [(AN + MA)/2] summed rootzone water content (SrjWC). In 2012, TAM 105 and TAM
111 had higher SWC along the profile and also higher

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4. Summary
There were significant differences in SWC along the soil
profile, among four TAM cultivars in both years and underboth soil regimes. The study showed that the new cultivars
were able to extract more water from the deeper soil profile
than the older one. However, only under extreme drought
condition (i.e. under dryland condition in 2011), significant
differences in cultivars for grain yields and their relation tomeasured differences in SWC were evident. Since theeffective use of soil water is highly related to root growth anddevelopment, we recommend further studies on root traits toelucidate the differential behavior of old and new cultivars
under extreme drought, mild drought and irrigated conditions.
Fig. 4. Soil water depletion under dryland condition in four cultivars
at different growth stages (spring; jointing, JT; anthesis, AN;maturity, MA). The vertical bar is a LSD at p = 0.05.

References

averaged SrjWC (1.1 cm3 cm-3) content than TAM 110 and
TAM 112 (1.03 cm3 cm-3). For irrigated wheat, thedifferences in SWC among the cultivars were more significant
at deeper soil layers (e.g., below 120 cm) as compared to upperlayers (0-120 cm). In 2011, TAM 110 and TAM 111 hadlower SWC than TAM 105 and TAM 112. In 2012, theranking of SWC at 120-200 cm profile was TAM 105 > TAM
110 > TAM 112 > TAM 111, suggesting that newer cultivars
were able to extract more water than older cultivars fromdeeper soil (Fig. 3). It is to be noted here that the rooting
depth of irrigated wheat at Bushland is generally about 140 cm.
However, wheat plants can still extract water from deeper soil
by means of hydraulic conductivity (Xue et al., 2003). Basedon a greenhouse study (Zhang et al., 2012), the ability of newer
cultivars to extract more water from deeper soil than TAM 105
could be related to their higher aboveground and root biomass
at early stages.
Figure 4 shows the soil water depletion (SWD) under thedryland conditions in four cultivars at early spring, jointing(JT), anthesis (AN) and maturity in 2011. The cultivar TAM
110 had higher SWD than the other three from JT to MA, andTAM 111 had higher SWD than TAM 105 and TAM 112 atmaturity. The high SWD (Fig. 4) and low SWC at anthesisand maturity (Fig. 2), and also the lowest average SrjWC
indicated that TAM 110 used soil water more effectively thanthe other three cultivars under the extreme dry condition. The
better performance of a somewhat older cultivar (TAM 110) ascompared to the newest ones (TAM 111 and TAM 112) underthe extreme drought condition may be due to the presence ofrye translocation gene in it (Xue et al., 2014). However, as
the cultivar TAM 112, with the same translocation gene,performed differently, a further study is warranted.

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