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Oxygation of rhizosphere with subsurface aerated irrigation water improves lint yield and performance of cotton on saline heavy clay soil

Surya P. Bhattarai and David J. Midmore

Plant Sciences Group, School of Biological and Environmental Sciences, Central Queensland University, Rockhampton, QLD 4702, Australia. www.cqu.edu.au
Email s.bhattarai@cqu.edu.au , d.midmore@cqu.edu.au

Abstract

Salinity in agricultural soils has large impact on plant performance. Waterlogging and anoxia due to poor soil structure is a major problem for crop production in saline heavy clay soils. Inadequate oxygen concentration in the rhizosphere exacerbates the effect of salt and leads to poor plant performance. An experiment in the screen house was conducted to investigate growth and yield performance of cotton (Gossypium hirsutum L.) supplied with subsurface aerated water or non-aerated water to soil with four different salinity (ECe) levels of 2, 8, 14, 20 dS/m. The interaction between salinity and aeration was found to be non-significant for the variables measured. Cotton produced a significantly higher dry matter and lint yield with aerated water, irrespective of soil salinity level. The increase in yield was accompanied by an increase in root mass, canopy light interception and harvest index.

Media summary

Subsurface irrigation with aerated water improved cotton growth and yield in saline soils. Lint yield increased by 26 percent with aeration compared with the control in saline heavy clay soils.

Key Words

Aeration, salinity, subsurface drip irrigation, cotton, air injection, water use efficiency

Introduction

Salinity of agricultural soils is a major environmental threat in many parts of the world. Excess of salt in the soil on its own, or in combination with waterlogging, has severe consequences for plant production including cotton (Kahlow and Azam, 2002). Overcoming salinity, therefore, has become a major challenge to sustainable and productive primary industries. Many saline soils are also subjected to waterlogging as such soils experience raised water tables and reduced infiltration of applied water. Salinity in clay soil is often associated with sodicity, which reduces the porosity in the soil, thereby reducing the soil oxygen (Richards, 1969).

Plant roots require adequate oxygen for root respiration as well as for sound metabolic function of the root and the whole plant. Barrett-Lennard (2003) reported that transfer of roots from well drained to water logged conditions could decrease ATP production by about 95 % in the root. Hypoxia- or anoxia- induced low ATP can be detrimental for the survival of plants in the saline soils. Hypoxia or anoxia of saline soils has a range of adverse effects on the plant performance. Firstly it affects the growth, namely of the roots, followed by shoot growth (Kafkafi and Bernstein, 1996); secondly it impairs the process of solute moments across the membranes; and thirdly, the effects of anoxia are expressed in terms of reduced stomatal conductance and/ or leaf water potential, reflecting symptoms resembling water stress (Rhodes and Loveday, 1990). Amelioration of the hypoxic root zone in order to improve effective soil aeration, therefore, is crucial in order to improve plant performance under saline conditions.

Aeration of the crop root zone can be accomplished by injection of air alone, irrigating the crop with aerated water, or injection of hydrogen peroxide in the root zone. Injection of air alone could be quite expensive and the injected air can move away from the root zone due to the chimney effect. Earlier studies (Bhattarai et al., 2004) show promise in the use of aerated water with sub surface drip irrigation to improve crop performance in heavy clay soils in a range of crops including cotton. We examined the effect of aerated subsurface irrigation water on the performance of cotton over a range of salinity levels in a heavy clay soil and report that oxygation of the rhizosphere increased root weight, leaf weight, biomass, and lint yield. Increases in plant height, leaf area; number of nodes, light interception, and harvest index were related to the enhanced performance due to aeration in saline heavy clay soil.

Methods

Crop details

The study was conducted in the screen-house (67 % of full sunlight) at Rockhampton, Australia (230, 22’, 0.345’’S latitude, 150o, 31’, 0.53’’E Longitude) from September 2003 to February 2004 on cotton (Gossypium hirsutum L.) variety- 289 I. The crop was grown in white 20 L plastic containers (40 cm x 25-27.5 cm) lined with a black polyethylene and filled with 26 kg of heavy clay soil, classified as vertosol. Containers were fitted with Netafim pot drippers placed at 25-30 cm below the soil surface, without a drain hole, were filled to a bulk density of 1.3 g cm-3. The dripper delivery was 1 L h-1 and was operated under the pressure of 62-76 Kpa (9-11 PSI) at the return to the water pump. The use of pot drippers was to mimic the SDI system in the field. Soil water was measured daily in one pot per plot using a calibrated Micro Gopher system (Soil Moisture Technology, Australia), the probe of which consists of a capacitance sensor. Irrigation was imposed on a 1-3 day interval, between 700 h to 1200 h, based on the readings from the Micro Gopher; refill was when the soil moisture reached 32 mm per 100 mm of soil depth. Seeds were sown at 1 m between and 10 cm within rows (containers within the row were in contact with each other. Experimental plots comprised five containers with a total of 15 plants. The nutrient requirement of the crop was supplied through fertigation using a Peter’s Professional general-purpose water-soluble fertilizer (20:8.7:16.6 NPK and 0.01%B, 0.004%Cu, 0.05%Fe, 0.03%Mn, 0.001%Mo, 0.003%Zn) at the rate of 0.5 g L-1 continuously throughout the crop season. Seeds were sown into the containers at a depth of 5 cm on 1 September 2003, prior to the imposition of treatments.

Experimental design and treatments details

The experimental design was a Randomized Complete Block. This factorial experiment consisted of four salt levels (made up through addition of sodium chloride, were equivalent to ECe of 2, 8, 14 and 20 dS/m) with and without aeration with three replicates. The salt was introduced to the pots 15 days after emergence as three installments, at three days intervals. Mazzei model air injector injected 12 % air by volume of water on aeration treatment and the non-aerated control received no additional air. The oxygen concentration in the soil was monitored using PSt3 oxygen sensitive fibre optic minisensors with a fibox-3 oxygen meter (PreSens GmbH, Germany).

Data recording

Weather data were recorded from an adjacent weather station. Performance of cotton in terms of phenology, growth and development and yield was recorded from ten bordered plants (i.e. three pots) per experimental plot. Root samples (one core sample per pot - collected 145 days after sowing) were obtained by coring with a 3 cm diameter soil corer to the entire depth of the pot. The collected core samples were soaked in 1% solution of ground breaker (active constituent 10 g L-1 buffered polylignosulfonate) for 2-3 hours and roots were separated from soil using a 45-micrometer sieve following the floatation technique. The living roots were separated manually by discarding the dead based on visual observation of tissue color as described by Caldwell and Virgina (1991), and the root length and diameter of the former was determined using a Hewlett Packard scanner and Delta-T software. The washed root samples were oven-dried for 48 hours at 70 o C for the determination of dry mass. Fortnightly light interception by the canopy was measured with two samples per plot using an AccuPAR Ceptometer (Decagon, USA) and the leaf chlorophyll concentration on one fully expanded leaf per plant using the Minolta SPAD-502 meter that provides a non-destructive determination of relative chlorophyll concentration. At final harvest lint yield and its components was measured on ten bordered plants per treatments. Leaves were then dried at 70oC for 48 h, bolls for 3 days and stem for 7 days for above-ground biomass determination.

Data analysis

The data collected were subjected to analysis of variance (ANOVA) using GLM for a factorial randomised complete block design employing SYSTAT version 9. Where interactions were not significant, main effects only are presented. As the interaction effects between salinity and aeration were not significant for most of the parameters except for canopy light interception and number of nodes per plant, only main effects due to salinity and aeration are presented.

Results

Environmental parameters and applied water to the crop

The daily mean air temperature measured outside the screen house ranged from 22-30°C representing a gradual increase in temperature over the crop period. The relative humidity ranged from 28 % to 67 %. Light averaged 17.47 MJ m-2 d-1, with a minimum of 6.6 to a maximum of 21.5 MJ m-2d-1. Season mean rhizosphere oxygen concentration decreased with salinity and increased with aeration treatment [8.75±1.98 mg/L (range 2.1-10.3) in 2 dS/m aeration against 5.95±2.07 mg /L (range 0.02-8.51) in 2 dS/m control and 6.55±0.56 mg/L (range 5.44-7.55) in 14 dS/m aeration against 4.66±2.61 mg/L (range 0.02-9.18) in 14 dS/m control]. The soil temperature during the period of rhizosphere oxygen monitoring ranged between 21 to 31°C. In general, rhizosphere O2 concentration was observed highest at night and lowest at mid day. Water applied to the crop over crop season for different treatments are presented in Figure 1. Crop water use tended to be higher throughout the crop season with aeration and lower salt concentration compared with the non-aerated control and higher salinity treatments.

Figure 1. Water used (L/m2) by cotton over season in different salinity levels with and without aeration (□- 2 dS/m with air, ■- 2 dS/m without air, ∆- 8 dS/m with air, ▲-8 dS/m without air, ◊- 14 dS/m with air, ♦-14 dS/m without air, ○- 20 dS/m with air and ●-20 dS/m without air).

Phenological parameters

A number of measured parameters did not differ significantly between treatments. These included location of the lowermost flowering nodes, days to squaring, flowering, and first boll open, and crop maturity. However, plant height and number of nodes per plant decreased significantly (p<0.05) with increasing salinity and increased significantly (p<0.05) with aeration compared with the respective controls (Table 1 and 2). Likewise, stem diameter increased with aeration but decreased with increasing salinity compared with the control (Table 1).

Yield and yield components

The difference between the control and aeration treatments was significant (P<0.05) for lint yield (a 26 % increase with aeration) and the difference between salinity treatments were also significant. A significant decrease in cotton lint yield was observed with increasing salinity. Averaged over aeration treatments, the lint yield was reduced by 10, 41 and 51 % respectively for 8, 14 and 20 ECe compared with the control. Similar trends for the effects of aeration and salinity were also observed for above ground biomass (Table 1). Although non-significant, there was a tendency for aeration to increase yields proportionally more at the higher salinity (12, 8, 62 and 52 % at 2, 8, 14, and 20 dS/m respectively). The increase in the lint yield due to aeration was associated with an increase in fruits set and therefore number of bolls, and boll individual weight (Table 2). The number of bolls and mean boll weight decreased significantly with increasing salinity.

Physiological responses

Light interception was enhanced in the aeration treatment compared with the control, and decreased with increasing salinity above 8 dS/m (Table 1). The beneficial effect of aeration was greater at higher salinity (data not presented). Leaf dry weight increased with aeration by 13 percent compared with non-aeration and decreased significantly with increasing salinity, but mean leaf chlorophyll concentration measured over the crop season did not differ significantly due to aeration and salinity treatments. Root weight per plant increased with aeration but decreased significantly with increasing levels of soil salinity. However, the root: shoot ratio was not affected by treatments

Table 1. Effect of salinity and aeration on yield components, lint yield and harvest index of cotton

Variable

Levels

Plant height (cm)

Node per plant
(No.)

Branch per
plant (No.)

Boll per
plant (No.)

Boll weight
(g)

Fruit set
(%)

Root
per
plant
(g)

Chlorophyll (SPAD unit)

Lint yield
(g/m2)

HI

Salinity

2 dS m-1
8 dS m-1
14 dS m-1
20 dS m-1

LSD

134
119
112
98

12.0

23.6
22.7
22.2
21.0

1.28

16.3
15.6
15.5
14.9

n.s.

16.8
14.4
10.4
9.3

3.03

5.67
5.90
5.31
5.07

0.51

47
44
35
34

9.8

43
32
32
19

10.2

48.0
47.6
46.9
45.1

n.s.

325
291
192
160

57.2

0.17
0.18
0.16
0.15

0.01

Irrigation
Water

Aerated
Control

LSD

(df =14)

121
112

8.5

22.8
22.1

0.90

15.9
15.3

n.s.

13.9
11.7

2.14

5.67
5.29

0.36

42
38

6.9

36
31

7.21

46.6
47.2

n.s.

272
215


40.5

0.17
0.16

0.00

Table 2. Effect of salinity and aeration on phenology, biomass, root and shoot properties and light interception.

Variables

Levels

Lowest flower node

First square
(days)

First flower (days)

First boll open
(days)

Harvest
(days)

Leaf weight
(g/m2)

Biomass
(g/m2)

Stem diameter
(mm)

Root: shoot
ratio

Light intercept-tion
(%)

Salinity

2 dS m-1
8 dS m-1
14 dS m-1
20 dS m-1

LSD

6
6
6
6

n.s.

46
47
48
47

n.s.

63
68
67
65

n.s.

113
114
113
114

n.s.

145
146
145
146

n.s.

342
296
228
216

56

1920
1653
1662
1043

312

10.7
10.4
9.1
9.0

0.79

0.23
0.20
0.28
0.24

n.s.

73
73
66
61

3.22

Irrigation
Water

Aerated
Control

LSD

(df =14)

6
6

n.s.

47
47

n.s.

66
65

n.s.

113
113

n.s.

145
145

n.s.

288
257

39

1571
1333

220

10.2
9.5

0.56

0.23
0.25

n.s.

70
66

2.28

Conclusion

Lint yield of cotton decreased progressively with increase in soil salinity. Soil aeration enhanced yield across all salinity treatments, somewhat more so at higher salinity, and hence through enhanced tolerance to salinity stemmed the yield reduction. Averaged over the salinity treatments, aeration increased cotton lint yield by 26 percent compared with the non-aerated treatment. This result warrants intensive research of oxygation technology to address commercial applications for productive use of saline land for crop production.

References

Barrett-Lennard EG (2003). The interaction between waterlogging and salinity in higher plants: causes, consequences and implications. Plant and Soil 253, 35-54.

Bhattarai SP, Huber S and Midmore DJ ( 2004). Aerated subsurface irrigation water gives growth and yield benefits to Zucchini, vegetable soybean and cotton in heavy clay soils. Annals of Applied Biology 144, 285-298

Caldwell MM, Virginia RA (1991). Root systems. In: Plant Physiological Ecology: Field Methods and Instrumentation, pp. 367-392. Eds. RW Pearcy, JR Ehleringer, HA Mooney and PW Rundel. London, Chapman and Hall.

Fowler JL (1986). Salinity and Fruiting. In: Cotton physiology pp.107-111. Eds JR Mauney and JM Stewart. Memphis, Tennessee, USA: The cotton foundation.

Kafkafi U, Bernstein N (1996). Root growth under salinity stress. In: Plant Roots: The Hidden Half. pp. 435-451. Eds. Y Waisel, A Eshel and U Kafkafi. New York, Marcel Decker.

Kahlown MA and Azm M (2002). Individual and combined effect of waterlogging and salinity on crop yields in the Indus basin. Irrigation and Drainage 51, 329-338.

Rhoades JE and Loveday J (1990). Salinity in irrigated agriculture. In: Irrigation of agricultural crops.pp.1089-1142. Eds. BA Stewart and DR Nielsen. No. 30 in the series Agronomy. ASA, CSSA, SSSA, Madison, Wisconsin, USA.

Richards LA (1969). Diagnosis and improvement of saline and alkali soils. Agriculture Handbook No. 60, United Sated Department of Agriculture, Washington, D. C. http://www.ussl.ars.usda.gov/hb60/hb60.htm

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