salt-tolerant forage cultivation on a saline-sodic field for biomass production and soil reclamation

LAND DEGRADATION & DEVELOPMENT, VOL. 7.11-18 (1996)

SALT-TOLERANT FORAGE CULTIVATION ON A SALINE-SODIC FIELD FOR BIOMASS PRODUCTION AND SOIL

RECLAMATION

M. QADIR AND R. H. QURESHI Department of Soil Science, University of Agriculture, Faisalabad, Pakistan

AND N. AHMAD

Department of Crop Physiology, University of Agriculture, Faisalabad, Pakistan AND

M. ILYAS University College of Agriculture, Rawalakot, Azad Kashmir, Pakistan

ABSTRACT Chemical reclamation of sodic and saline-sodic soils has become cost-intensive. Cultivation of plants tolerant of salinity and sodicity may mobilize the CaC03 present in saline-sodic soils instead of using a chemical approach. Four forage plant species, sesbania (Sesbania aculeata), kallar grass (Leptochloa fusca), millet rice (Echinochloa colona) and finger millet (Eleusine coracana), were planted in a calcareous saline-sodic field (EC, = 9.6-11.0 dS m-', SAR = 594-72.4). Other treatments included gypsum (equivalent to 100 per cent of the gypsum requirement of the 15 cm soil layer) and a control (no gypsum or crop). The crops were grown for 5 months. The performance of the treatments in terms of soil amelioration was in the order: Sesbania aculeata = gypsum > Leptochloa j ima > Echinochloa colona > Elusine coracana > control. Biomass production by the plant species was found to be directly proportional to their reclamation efficiency. Sesbania aculeata produced 32.3 Mg forage ha-', followed by Leptochloa fusca (24.6 Mg ha-'), Echinochloa colona (22.6 Mg ha-') and Eleusine coracana (5.4 Mg ha-'). Sesbania aculeata emerged as the most suitable biotic material for cultivation on salt-affected soils to produce good-quality forage, and to reduce soil salination and sodication processes.

KEY WORDS salt-tolerant plants; soil salination; soil sodication; forage yield; soil reclamation

INTRODUCTION

Salt-affected soils in Pakistan and elsewhere in the world have very low productivity because of the dominance of soluble salts (salinity) and/or exchangeable Na' (sodicity). The world has about 955 x lo6 ha of salt-affected area (Szabolcs, 1991), of which about 6-3 x lo6 ha are in Pakistan (Khan, 1993). Approximately 23 and 37 per cent of the cultivated land is saline and saline-sodic/sodic, respectively (Tanji, 1990), and a ratio of about 40:60 between these two categories of salt-affected soils indicates the greater severity of the sodicity problem.

The normal reclamation procedure for saline-sodidsodic soils increases Ca2' on the soil's cation exchange sites at the expense of Na'. The replaced Na', along with the excess soluble salts, is removed from the root zone in infiltrating water. Reclamation of these soils by chemical amendments that supply soluble Ca2', directly or indirectly, is an established technology. Over the years, this approach has become cost-intensive. The majority of subsistence farmers cannot afford the high initial investment to purchase the chemical amendments to start reclamation of the affected lands. On the other hand, many sodic/saline-sodic soils contain lime (CaC03) at varying depths (Choudhri, 1972; Kovda et al., 1973). This Ca2+ source does not participate in ion exchange reactions with Na' owing to its negligible solubility. The

CCC 1085-3278/96/010011-08 0 1996 by John Wiley & Sons, Ltd.

Received 20 February 1995 Revised 8 August 1995

12 M. QADIR. ET AL.

CaCOl in sodic/saline-sodic soils could be mobilized to release CaZ+ through the root action of certain plant species which are more tolerant to salinity/sodicity than most field crops (Robbins, 1986; Qadir, 1994). The plant roots release organic compounds and complex energy sources (Dormaar, 1988) and increase COz partial pressure (Robbins, 1986), as well as decrease soil pH (Mashali, 1991). and all these combine to increase the dissolution of soil CaC03 and cause a decrease in soil salinity/sodicity with time (Abrol et al., 1988; Ahmad er a)., 1990). The plant roots also physically act upon the soil to improve its permeability (Elkins, 1985). The above-ground plant parts provide shade to the host soil, lower the soil temperature, have a mulching effect, decrease evaporation from the soil surface and thus check upward movement of salts through capillaries (Sandhu and Qureshi, 1986). In addition, the plant biomass can be used as forage.

Plants growing in a saline and/or sodic environment may face certain limitations, particularly in terms of root establishment and biomass production. Therefore, the plant species that are able to colonize salt- affected soils without the need to apply any chemical amendments are important for the stabilization and reclamation of the growth medium (Lauchli and Epstein, 1990). The ability of some plant species to grow in a wide range of stress conditions has greatly increased their adaptability and utility (Evans and Rotar, 1987). Research conducted on various aspects of plant salt-tolerance found that some forage species, such as Sesbania aculeata and Leptochloa fusca, are tolerant to salinity, sodicity or both (Aslam et al., 1979; Sandhu et at., 1981; Yaseen et al., 1990). These species have also been tried to a limited extent for the reclamation of sodic and saline-sodic soils (Hamid et al., 1990; Qadir et ul., 1992). How- ever, their effectiveness compared with chemical amendments and other salt-tolerant plant species has rarely been evaluated.

This paper reports the results of a field experiment where in addition to Sesbania aculeata and Leptochloa fusca, two more species, Echinochloa colona and Eleusine coracana, were grown on a calcareous saline-sodic soil with the following specific objectives:

(1) to evaluate the effectiveness of the plant species as compared with gypsum (taken as a standard

(2) to compare the plant species for biomass production from a saline-sodic soil. chemical amendment) and simple leaching for soil reclamation;

MATERIALS AND METHODS

A field experiment was carried out on a calcareous saline-sodic soil (pHs = 8.4-8.8, EC, = 9.6-11.0 dS m-', SAR = 59.4-72.4, CEC = 98-107 mmol, kg-', CaC03 = 7.3-8.1 %, texture = sandy-clay loam for the upper 15 cm layer). Preliminary classification defines that soil as coarse loamy, mixed, calcareous, hyper- thermic, Fluventic Camborthids. The following treatments, four cropped and two non-cropped, were arranged in a randomized complete block design with three replications, using a plot size of 6 m x 3 m.

( 1 ) Control (simple leaching with no gypsum or plant species). (2) Gypsum at 100 per cent gypsum requirement (GR) of the 15 cm soil depth, i.e. 14.8 Mg ha-' (no

(3) Sesbania (Sesbania aculeata); the common name in Pakistan is dhancha. (4) Kallar grass (Leptochloa fusca); the common name in Pakistan is also kallar grass. ( 5 ) Millet rice (Echinochloa colona); the common name in Pakistan is swank. (6) Finger millet (Eleusine coracana); the common name in Pakistan is mandal.

After the experiment had been set out, composite soil samples were collected from each plot for 0-15 cm and 15-30 cm depths. Particle-size analysis was carried out using the method of Bouyoucos (1962). Determinations of the pH of the saturated soil paste (pH,), the electrical conductivity of the saturation extract (EC,), soluble CaZ++Mg2+ (titration with standard versinate solution), soluble Na' (flame photo- meter), gypsum requirement (Schoonover's method), lime percentage and cation exchange capacity (CEC) were done according to the methods outlined by Page et al. (1982).

In the plots under gypsum treatment, agricultural-grade gypsum powder (passed through a 70-mesh

crop).

SALT-TOLERANT FORAGE ON A SALINE-SODIC SOIL 13

Table I. Effect of forage plant growth and gypsum application on the EC of the soil

Treatment EC, (dS m-')

Original soil After harvest of plant species

0-15 cm soil depth Control Gypsum Sesbania aculeata Leptochloa fusca Echinochloa colona Eleusine coracana


Control Gypsum Sesbania aculeata Leptochloa fusca Echinochloa colona Eleusine coracana

0-30 cm soil depth

10.8 9.9

10.1 9.7

11.0 9.6

7-8 8.9 8.0 8.4 7.5 8.1

9.3 9.4 9.1 9.1 9.3 8.9

9-8 a (09.3)* 8.0 b (19.2) 6.0 c (40.6) 6.7 c (30.9) 7.8 b (29.1) 8-4 b (12.5)

7-6 a (02.6) 7.4 a (16.8) 5.2 c (05.0) 5-9 c (29-8) 6.2 b (17.3) 7.6 b (06.2)

8.7 a (06.5)

5.6 e (38-5) 7-7 b (18.1)

6.3 d (30.8) 7.0 c (25.5) 8.0 b (10.1)

Notes: Means followed by different letters for individual soil depth differ significantly at P = 0.05. *Figures in parentheses indicate a percentage decrease over the original level.

sieve and having 90 per cent purity) was broadcast on the soil surface and mixed with the surface soil. Leptochloa fusca was grown by transplanting stem cuttings of the plants, while the other species were sown by the broadcast method. Sowing/transplanting was completed during the first week of July. All plots, including the control and gypsum treatments, were irrigated with water of low electrolyte concen- tration (EC = 0.28 dS m-') to a depth approximating that required by the plants grown. The plant species were grown for 5 months. During this period, two cuttings of each crop were taken. The harvested material was weighed just after cutting. After the final cutting of the plant species, composite soil samples were collected from each plot from the same depths as mentioned above. These were analysed for pH,, EC, and soluble Ca2++MgZ' and Na'.

RESULTS AND DISCUSSION

Soil salinity (EC,) A decrease in soil EC, was observed in all the treatments, with crops (except Eleusine coracana) being more effective than non-cropped treatments (Table I). The efficiency of the treatments in lowering the EC, of the respective original soils was in the order: Sesbania aculeata > Leptochloa fusca > Echinochloa colona > Eleusine coracana = gypsum > control. The reduction in EC of the cropped treatments may have been hastened by the root action, which improved soil permeability (Elkins, 1985). This helped leach soluble salts from the root zone (Abrol et al., 1988). The above- ground plant parts also made a contribution by providing shade to the soil and lowering the soil tem-

14 M. QADIR, E T A L .

Table 11. Effect of forage plant growth and gypsum application on the SAR of the soil

Treatment SAR (rnmol 1K1)”*


&15 cm soil depth Control 68.1 58.3 a (14.4)* Gypsum 72.4 29.1 e (5943) Seshania aculeata 59.4 33.9 de (42.9) Leptochloa fusca 60.3 37.7 d (37.5) Echinochloa colona 62.1 44.1 c (29.0) Eleusine coracana 64.1 50.1 b (21.8)

15-30 cm soil depth Control 52.2 48.1 a (07-8) Gypsum 49.9 27.3 a (45.3) Seshania aculeata 50.1 3 3 . 0 ~ (34.1) Leptochloa fusca 50.9 36.1 c (29.1) Echinochloa colona 52.1 41.0b (21.3) Eleusine coracana 53.1 46.0 a (13.4)

Control 60.2 53-2 a (11.8) Gypsum 61.2 28.2 e (53.9) Sesbania aculeata 54.8 33.5 e (39.9)

0-30 crn soil depth

Leptochloa fusca 55.6 36.9d (33.6) Echinochloa colona 57.1 4 2 . 6 ~ (25.4) Eleusine coracana 58.6 48.1 b (17.9)

~ ~ _ _ ~ ~ ~ ~ ~

Nores: Means followed by different letters for individual soil depth differ significantly at P = 0.05. *Figures in parentheses indicate a percentage decrease over the original level.

perature, thus having a mulching effect. This helped to decrease evaporation from the soil surface and thus the capillary rise of soluble salts was reduced (Sandhu and Qureshi, 1986). Some fraction of salts could have been taken up by the plants (Ahmad et al., 1990). In the plots under Eleusine coracana, a patchy plant population was observed. That is why this treatment was less efficient than the other cropped treatments.

In the gypsum-treated soil, the improvement in soil conditions with respect to salinity was due to floc- culation of the dispersed soil matrix (Oster, 1982), a typical characteristic when Ca2+ is supplied through gypsum. This improved soil permeability and hence leaching of soluble salts (Shainberg et al., 1989). In the control treatment (simple leaching without gypsum or plant species), a small decrease in EC was due to the inadequate leaching of salts by rain and irrigation waters.

The applied treatments were more efficient in lowering the EC, of the upper 15 cm layer of soil than of the lower layer (15-30 cm). This was because the original soil had more salts in the upper layer. Further, the leaching water carrying salts from the upper layer might have become concentrated as it moved down the profile, and thus could not leach all of its soluble contents below the 15-30 cm layer.

Soil sodicity (SA R) The sodium absorption ratio (SAR) indicates the sodicity hazard of soils. For the desodication process, replacement of exchangeable Na’ from the soil colloids followed by its removal in the infiltrating water is necessary. Analysis of soil samples, taken after the final harvest of the plant species, indicates that the desodication process was operative in all the treatments (Table 11). Gypsum treatment was the most


effective, while the simple leaching (control) was the least efficient. The greater decrease of SAR in the gypsum-treated soil at both soil depths was due to an increase of dissolved Ca" in the soil followed by displacement of the exchangeable Na+ by Ca2+ and subsequent leaching by applied water under conditions of improved soil aggregation (Oster, 1982; Shainberg el al., 1989). A small decrease in SAR with simple leaching might be due to 'valence dilution', as demonstrated by Reeve and Bower (1960). In the soil-water system where mono- and divalent cations in solution are in equilibrium with the adsorbed cations, the addition of water to the system alters the equilibrium condition. The dilution of the soil solution favours the adsorption of divalent cations such as CaZ+ at the cost of monovalent cations such as Na'. The reverse is true when the soil solution is concentrated owing to evaporation. The decrease in SAR was also due to the Ca2+ in the applied water.

The reclamation efficiency of the cropped treatments was in between that of the gypsum and the control treatments. Sesbania aculeata and Leplochloa fusca, followed by Echinochloa colona, were better than Eleusine coracana owing to better growth of the above- and below-ground plant parts. The decrease in SAR in the plots under different plant species confirmed their role in improvement of the soil chemical environment. The probable factors involved in SAR decrease by the root action could be: (1) dissolution of soil lime to supply Ca2+ via reaction of the naturally occurring CaC03 with H2CO3 formed from COz-released by root respiration; (2) H' ion release from the roots by an active electro- genic transport mechanism followed by Na+-H exchange at the soil-colloid surfaces; (3) Na' uptake by the plant species. Apart from root action, Ca2+ supplied in irrigation water and lime dissolution through soil microbial activity also contributed to the decrease in SAR.

The treatments had a greater effect on the desodication process in the upper soil layer than in the lower one. This may be due to the decreasing Ca2+:Na+ ratio in water as it moved down (Ghafoor, 1984). Since the Na' replaced from the upper layer of soil also moved downward, it increased the SAR of the downward-moving water. Hence somewhat less Ca2+ was available to replace Na+ at the lower soil depth.

Soil reaction (pH) A significant decrease in the pH of the upper soil layer was observed in all treatments except the control (Table 111). The effects of the gypsum and the crop treatments were statistically similar. The decrease in pH of the gypsum-treated soil may be due to the replacement of exchangeable Na' during Na+-Ca*+ exchange and subsequent leaching. This pH decrease has sometimes been associated with the degree of soil reclamation, and especially with a decrease in the soil sodication process (Ghafoor, 1984; Kumar and Abrol, 1984). The decrease in pH of the cropped treatments may be due to the release of acidic root exudates (Dormaar, 1988). Another possible reason for the decrease in soil pH may be deduced from the work of Robbins (1986), who found a tremendous increase in C 0 2 partial pressure in a calcareous sodic soil sown with sordan (Sorghum biolor x Sorghum Sudanese).

All the treatments decreased the pH of the lower soil depth. However, the treatment differences were statistically non-significant. The greater decrease in pH of the upper soil layer as compared with the lower layer may be attributed to the removal of Na' from the upper layer to a greater extent than from the lower layer. Moreover, the soil was calcareous in nature and had more CaC03 in the lower soil layer than in the upper layer. The colloidal ciliate CaC03 acts as a buffer and resists any appreciable change in soil pH in the alkaline range (Deverel and Fujii, 1990). Therefore, the pH of the lower layer was less affected because it had more CaC03 as compared with the upper layer.

Forage yield Transplanting of Leptochloa fusca and sowing of other plant species were done in the first week of July. The weather was hot and dry. Finger millet completely failed to germinate at the first attempt. However, in the next attempt the crop was established in patches. The establishment of other plant species was generally not affected. As regards forage (fresh biomass weight) production, the above-ground plant material was harvested twice during the 5 months for which the plant species were grown.

At the time of first cutting, the maximum plant biomass (22.1 Mg ha-') was harvested from the Sesbuniu aculeata plots, followed by Echinochloa colona (18.3 Mg ha-') and Leptochloa fuscas (16.2 Mg ha-'). The

16 M. QADIR, ETAL.

Table 111. Effect of forage plant growth and gypsum application on the pH of the soil

Treatment PH




Control Gypsum Sesbania aculeata Leptochloa fusca Echinochloa colona Eleusine coracana

0-30 cm soil depth

8.7 8.8 8.6 8.8 8.4 8.5

8.5 8.3 8.1 8.5 8.5 8.3

8.6 8.6 8.4 8.7 8.5 8.4

8.7 a (It O.O)* 8.1 b (-7.9) 8.2 b (-4.6) 8.1 b (-7.9) 8.3 b (-1.2) 8.3 b (-2.3)

8.3NS (-2.4) 8.2 (-1.2) 8.2 (+1.2) 8.3 (-2.3) 8.5 (M.0) 8.3 (i0.0)

85NS (-1.2) 8.2 (-4.6) 8.2 (-2.4) 8.2 (-5.7) 8.4 (-1.2) 8.3 (-1.2)

Nores: Means followed by different letters for individual soil depth differ significantly at P = 0.05. *Figures in parentheses indicate a percentage decrease(-)/increase(+) over the original level. NS = Non-significant.

Table IV. Biomass (fresh weight of above-ground part) produced by different plant species

Plant species First Second Total cutting cutting biomass

(Mg ha-') (Mgha-I)

Sesbania aculeata 22.la 10.2 a 32.3 a Leptochloa fusca 16.2 c 8.4 a 24.6 b Echinochloa colona 18.3 b 4.3 b 22.6 b Eleusine coracana 3.9 d 1.5 c 5.4 c

Note: Means followed by different letters in a column differ significantly at P = 0.05.

minimum yield was obtained from Efeusine coracana, and was only 3.9 Mg ha-'. During the second cutting, a similar trend in biomass production was observed except for Leptochloa fusca, which had better yield than Echinochloa colona (Table IV).

The combined performance of the plant species for both harvests was in the order: Sesbuniu aculeatu > Leptochloa fusca = Echinochloa colona > Eleusine coracana. As was expected from its patchy growth, Eleusine coracana produced almost five times less biomass as compared with the most productive Ses- bania aculeatu. Therefore, the latter species seems to be a better choice owing to its higher fodder yield,


vigorous and deeper root system, which opens up the soil for leaching of salts, and ability to fix nitrogen in the soil for subsequent crops. On the other hand, Leptochloa fusca may be better under salt-affected waterlogged conditions because of its tolerance to waterlogging.

CONCLUSIONS

The efficiency of biological reclamation (growing of salt-tolerant forage species on saline-sodic soils) was comparable to chemical reclamation, which needs a good deal of initial investment to purchase gypsum or other chemical amendments.

Among the plant species tested, Sesbania aculeata and Leptochloa fusca emerged as potential biotic materials, followed by Echinoahloa colona. The species not only produced a good quantity of biomass, but also caused a significant decrease in soil salination and sodication processes. The reclamation efficiency of the plant species was found to be proportional to their biomass production capacity. Ses- bania aculeata seems to be a better choice owing to its higher fodder yield, vigorous and deeper root system, and ability to fix nitrogen for subsequent crops. However, Leptochloa fusca may be suitable for saline-sodic/sodic soils having periodic inundation (waterlogging).

ACKNOWLEDGEMENTS

This work was funded by USAID and the Government of Pakistan through the Irrigation Systems ManagemenVResearch Project (Biotic and Chemical Reclamation of Sodic Soils).

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salt-tolerant forage cultivation on a saline-sodic field for biomass production and soil reclamation

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