Scientific registration nº : 409 Symposium nº : 29 Presentation: poster Surge-flow irrigation in a reclaimed salt-affected soil of SW Irrigation par submersion en vue de la récupération d’un sol salé du sud-ouest de l’Espagne

ANDREU Luis (1), MORENO Félix (2), CABRERA Francisco (2), VAZ Rosario (1)

(1) Escuela Universitaria de Ingeniería Técnica Agrícola, University of Seville, Carretera Km 1. 41013 Seville. Spain. (2) Instituto de Recursos Naturales y Agrobiología de Sevilla (IRNAS-CSIC), P.O. Box 1052, 41080 Seville, Spain.

Introduction

The Guadalqivir river marshes (Marismas del ) in SW Spain cover an area of 140,000 ha. The materials forming the Guadalquivir marshes are typical of sediments deposited at different levels, according to Leyva Cabello (1976). The most recent sediments, 0-2 m thick, were deposited on the lower parts, in depressions with water- logging or run-off phenomena, enriched with salts by evaporation. In most cases, soils developed in this area are clayey, mainly illite type under a very advanced degree of alteration (González Garcíaet al., 1956; Moreno et al., 1980). They are difficult to manage in agriculture due to their high clay and salt contents (Giráldez and Cruz Romero, 1975; Moreno et al., 1981) and to the presence of a shallow very saline water table. For this reason they were initially used as natural meadows. In 1970, reclamation was initiated to irrigate the zone of (15000 ha). In this zone called sector B-XII work to install and irrigation and drainage system was begun. This work terminated in 1979, the irrigated zone being divided into 12.5 ha plots for agricultural use. The study presented in this paper corresponds to this zone. In this region, in some years, water supply for irrigation is strongly limited due to scarcity of rainfall. Management of the irrigation in these conditions is very important in order to save water and to achieve efficient salt removal from the root zone. Furrow irrigation is the main method used for cotton in the area of Lebrija. Large drainage losses are produced while replenishing soil water in the plant root zone along the entire lenght of the field. This is mainly because the soil cracks offer preferential paths to the passage of water directly to the drainage system and the slow advance of water along the furrows. Surge irrigation, the application of water as series of pulses rather than conventional continuous inflow, has been proposed as means of improving the uniformity of surface methods. The surge method can increase the rate of stream advance, drecreasing differences in infiltration opportunity times across the field and improving water

1 application efficincy. The improvement in advance has been attributed to a reduction in the infiltration rate with the pulses due to the soil surface sealing by soil particles rearrangement. Since surge irrigation could be interesting for improving irrigation efficiency in these fine textured, cracking soils in SW Spain, we undertook this study for field evaluation of this irrigation method compared with the performance of continous furrows irrigation.

Material and Methods

Experiments for the present work were carried out on a 1 ha plot (40 x 250 m) situated in the marshes on the left bank of the Guadalquivir river, near Lebrija (SW Spain). The soil of the plot is of clayey texture and its general characteristics are given in Table 1.

Table 1. General characteristics of the soil

Depth Soil particle size CaCO3 O.M: E.C. SAR % w/w;mm -1 1/2 -1/2 cm >50 50-2 <2 % % dSm cmolc l 00-30 1.0 32.0 67.0 16.0 1.03 3.0 5.8 30-60 1.0 30.0 69.0 16.0 -- 7.5 20.5 60-90 1.0 30.0 69.0 19.0 -- 11.0 36.5

The mineralogical composition of the clay fraction (70% alterated illite; 15% smectite; 10% kaolinite; <1% interstratified) is very homogeneous throughout the profile. The experimental plot is situated within an area of 12.5 ha, in which a drainage system has been installed, consisting of ceramic pieces (30 cm long) forming a pipe 250 m long buried at 1 m depth and 10 m intervals, discharging into a collecting channel perpendicular to drains. This drainage system controls the water table level which remains at approximately 0.9 m depth and whose electrical conductivity is > 80 dS m-1. The plot was sown with cotton, one of the main crops in the zone. Subsoiling to 55 cm depth was applied once per year in order to improve the drainage. Traditional furrow irrigation performance during 1990 was compared with experiments with surge flow irrigation carried out during the crop season in 1991. In order to show the water and salts movement ocurring after irrigation we present detailed studies corresponding to furrow irrigation on 4-7-90 and surge flow irrigation on 26-7-91.Irrigations were carried o out in furrows 250 m in lenght and 1 /oo in slope arranged along drain directions. We used the “variable on time-constant advance distance” approach to surge management in our experiments. The constant distances used in the furrow were ¼, ½, ¾ and the total. Advance and recession were monitored by recording the arrival and disappearance of water at increments of 10 m. Several measurement sites were situated in an experimental plot in which water content profile, tensiometric profile, water table level, and salinity of soil and soil water were followed. Drainage water discharge flow was also measured and the salinity of water analysed periodically. A neutron probe was used to measure water content in the soil. Drainage water flow was measured by means of a limnigraph with a V-notch weir. Electrical conductivity (EC) was determined in drainage water and in 1:5 soil/water extracts to study soil salinity evolution between irrigations, soil water content was also determined.

2 Results and discussion. he surge advance and recession results (Fig. 1) show that water travelled rapidly over the soil wetted by previous surges but then slowed dramatically once dry soil was encountered. The application time of water was approximately 70% of the application time used in the traditional furrow irrigation (continuous flow) in 1990. Due to the fact that inflow rate was a little higher in surge flow than in continuous flow the total water applied was practically the same in both types of irrigation.

10

8 4 6 r u h (

3 e 4 m i T

surge advance 2 2 surge recession continuous advance 1 continuous recession 0 0 50 100 150 200 250 Distance (m) Fig. 1 Measured advance and recession trajectories for the four surges used. Continous advance and recession for furrows irrigation is also shown.

The hydrograph, cumulative drainage and electrical conductivity (EC) of drainage water are shown in Fig.2. In continous furrow irrigation drain discharge (Fig.2a) started half an -1) occured in the first 24 hours. In the case of surge flow irrigation the hydrograph is very similar (Fig.2b). The drain discharge started 45 min. after the beginning of irrigation. The last surge had stopped. The total drainage represents 29% of the water applied in the four surges. This represents a slight decrease in comparison with drainage during the

3 Water table: days after, in various sites in the plot for both furrow and surge flow irrigation, are represented in Fig. 3a and 3b respectively. Diferences among piezometers in a particular deeper piezometric levels correspond to the nearer the sites from the collecting drainage channel. Under continous furrows irrigation the piezometric level reached until 20 cm irrigation the water table level only rose to a maximum of 45 cm depth (Fig. 13). Several days after irrigation, the piezometric level returned to the situation prior to

This behaviour is similar to that reported by Van Hoorn (1984) and Martínez Beltrán (1988) for soils of this area with similar drain spacing and depth.

Water content in the profile, measured immediately after irrigation stoped, showed a situation near saturation in furrow irrigation (Fig. 4a). This was followed by a decrease after irrigation. Water content profile changes, after surge flow irrigation (Fig. 4b), were similar those after furrows irrigation. In contrast, observations carried out at several with surge irrigation than with the traditional furrow irrigation.

4 1.5 70 100 (a) )

) Q 60 1

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50 i ( t 1.0 Cumulative m m a e

60 l

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( n m i

Q 30

40 u a C

0.5 r C E

20 d 20 10 0.0 0 0 0 50 100 150 200 1.5 70 100

(b) ) m 60 ) Q e 1 80 v m - ) i (

t 1 EC 50 m e - a 1.0 l g h S

u Cumulative 60 a

40 d n ( m m drainage i u a m 30 C r (

40 C

E 0.5 d Q 20 20 10 0.0 0 0 0 50 100 150 200 250 Time (h) Fig. 2 Drain outflow (Q) hydrographs, cumulative drainage and electrical conductivity (EC) of drainage water: (a) after furrow irrigation; (b) after surge flow irrigation.

0 P0 Irrigation (a) 20 P1 ) P3

m P4 c

( 40 P5 h t P6 p

e 60 D 80

100 0 2 4 6 8 10 12 0 P1 ) 20 (b) P4 m c

( P5

h 40 t p e

D 60

80 Irrigation 100 0 2 4 6 8 10 12 Time (day)

Fig. 3 Change of the piezometric level: (a) after furrow irrigation; (b) after surge flo5w irrigation. Salinity of the drainage water and soil:

Figures 2a and 2b show the evolution of the EC of drain water (ECdw) during furrow and surge flow irrigation, respectively, with an irrigation water whose mean EC and SAR values are 0.96 dS m-1 and 2.0 mmol1/2 l-1/2 respectively. The evolution of the electrical conductividad of drainage water, ECdw, (Fig. 2) shows a similar pattern with both irrigation systems. The change of ECdw showed high values when the drainage started, this may be due to the leaching of salts accumulated in the surfaces of cracks. Afterwards decreased to a minimum value when the drainage outflow reached the highest value, due to a dilution effect. As the drainage outflow decreased the ECdw increased reaching the highest values when the drainage rate was again low. In contrast with traditional furrows the EC at the begining of drainage discharge, during surge flow irrigation, shows values much lower than those during sprinkling and furrow irrigation. The minimum EC value reached in surge flow (10.5 dS m-1) was lower than in furrow irrigation (18.0 dS m-1). This higher salinity of the drainage water is probably due to the contribution of the very saline water table. Total salt leached in 120 h, computed by the integration of cumulative drainage and salt concentration, was: 11,250 kg ha-1 and 2,547 Kg ha-1 for furrows and surge flow irrigation respectively. The efficiency of salt leaching calculated as quantity of salts per volume of applied water was 16 g l-1 in the case of furrow irrigation and 3 g l-1 for surge flow (Andreu, 1992). Considering the electrical conductivity of the 1:5 soil/water extract ,(EC1:5), (mean value of five sites) for the conditions of the furrows irrigation (Fig. 5a), minimum values were obtained in the upper layers immediately after irrigation, followed by an increase until the next irrigation. For the other layers EC1:5 tended to increase throughout the irrigation period depending on the changes in the soil water content. Taking into account that for the furrow irrigation the irrigation water did not seem to contribute to an increase in the soil water content of the 60-90 cm layer, the salt loss in the profile can be estimated from the loss in the 0-60 cm layer. This loss estimated by the composition of the saturated paste extract was 11,425 kg ha-1 in 96 h, similar to the salt leached in the drain water in 120 h (11,250 kg ha-1). The electrical conductivity values of the 1:5 soil/water extracts (EC1:5) from samples taken the day after irrigation and the day before the next irrigation were identical (1.2 and 1.2 dS m-1, respectively) for the soil layer 0-30 cm in depth under surge flow irrigation, but differents under furrow irrigation (0.95 and 1.2 dS m-1, respectively). For the soil layer of 30-60 cm in depth the EC1:5 increased from 2.5 to 2.9 dS m-1 under surge flow irrigation and from 1.75 to 2.95 dS m-1 under furrow irrigation. These changes were, for the soil layer 60-90 cm in depth, from 3.7 to 4.2 dS m-1 under surge and from 4.0 to 5.2 dS m-1 under furrow irrigation. These show lower increases of EC1:5 in the soil profile under surge flow than under furrow irrigation, which means lower resalinization of the soil profile, between two consecutive irrigations, for the case of surge flow than for furrow irrigation. This can be related to the rise of the water table, which is different under both irrigation systems as mentioned before.

6 Conclusions

Shrinking and swelling of the soil studied originate changes of bulk density according to the water content status, developing a network of vertical cracks horizontally interconnected. This fissure network offer preferential paths for the passage of water to deeper soil layers, being responsible for the rapid effect of the drainage system. Water infiltration is thus controlled in a first step by cracks and macropores, and is very rapid; when cracks and macropores are filled, a slow redistribution process controlled by the soil micropore matrix takes place as shown by the measured values of hydraulic conductivity.Surge irrigation accelerates water advances rates. This resulted in improved distribution of infiltrated water and consequently lower drainage volumes. This fact can be important for saving water in areas with water supply limitation or for avoiding environmental problems derivated from drainage waters. The drainage behaviour of this soil, with a rapid passage of water through the cracks only washed in a first step the salts concentrated on the crack surfaces. Efficiency of salt leaching is much higher with furrow irrigation than with surge flow irrigation.. Under surge flow irrigation the water table level remained deeper than under sprinkling and furrow irrigation. This can prevent the movement of salts from the water table to the upper soil layers.

Acknowledgements

Thaks are due to Mr. J. Rodriguez for help in the field experiments. Research carried out in the framework of the contract no. EV4V-0099-C (A) of the CEC.

References

Andreu, L. 1992. Movimiento de agua y sales en suelos recuperados a la Marisma del Guadalquivir. Ph.D. Thesis, University of Córdoba (Spain), 205 pp. Giráldez, J.V. and Cruz Romero, G. 1975. Salt movement in Guadalquivir marshy soils under field and laboratory conditions. Egypt. J. Soil Sci., 15: 79-93. González García, F., González García, S. and Chaves Sánchez, M. 1956. The alkali soils of the lower valley of the Guadalquivir: physico-chemical properties and nature of their clay fraction. Proceedings VI th Intern. Congress Soil Sci., B(I.26): 185-191. Grande Covián, R. 1967. Las marismas del Guadalquivir y su rescate. Ministerio de Agricultura, vol. 5, No. 29. Madrid (Spain). Kamphorst, A. 1988. Water and salt transport in the irrigated cracking clay soils of the Kachhi Plains, Pakistan. Part I: Vertical transport. Soil Tech., 1:271-281. Leyva Cabello, F. 1976. Memoria explicativa de la hoja geológica 1:50000, No. 1018, "El Rocio". I.G.M.E., Madrid (Spain). Martínez Beltrán, J. 1988. Drainage criteria for heavy soils with a shallow impervious layer. Agric. Water Manage., 14: 91-96. Moreno, F., Arrue, J.L., Murillo, J.M., Pérez, J.L. and Martín, J. 1980. Mineralogical composition of clay fraction in marsh soils of SW Spain. Polish J. Soil Sci., 13: 65-72. Moreno, F., Martin, J. and Mudarra, J.L. 1981. A soil sequence in the natural and reclaimed marshes of the Guadalquivir river, Seville (Spain). Catena, 8: 201-221.

7 Van Hoorn, J.W. 1984. Salt transport in heavy clay soil. Proceedings of the ISSS Symposium on Water and Solute Movement in Heavy Clay Soils (ILIR publication 37, J. Bouma and P.A.C. Raats, Eds.), 1: 229-240.

Keywords: surge-flow irrigation, saline soil, drainage, salt leaching, water table Mots clés : irrigation par submersion, sol salé, drainage, lessivage des sels, nappe

q (cm3cm-3) q (cm3cm-3)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0 0

20 20 (a) (b)

40 ) 40 ) m m c ( c

( 60 60 Surge flow

Furrow h t h t p p e

e 80 80 27/7/91 D

D 4-7-90 29/7/91 6-7-90 5/8/91 100 10-7-90 100

120 120

140 140

160 160

Fig. 4 Change of soil water content profiles: (a) after furrow irrigation; (b) after surge flow irrigation.

6 6 furrow (a) surge flow (b) 5 5

) 60-90 cm 1 )

- 60-90 cm 1 - m

4 m 4 S

d S (

d 5 ( :

1 5 30-60 cm :

30-60 cm 1 C 3 3 C E E 2 2 0-30 cm 0-30 cm irrigation 1 1 irrigation irrigation irrigation 0 0 0 5 10 0 5 10 Time (days) Time (days) Fig. 5 Evolution of the electrical conductivity of the soil/water extracts (EC ): 1:5 (a) after furrow irigation and (b) after surge flow irrigation.

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