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Irrigation with brackish water under desert conditions II. Physiological and yield response of maize (Zea mays) to continuous irrigation with brackish water and to alternating brackish-fresh-brackish water irrigation
Agricultural Water Management. 10 (1985) 47--60 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
47
IRRIGATION WITH BRACKISH WATER UNDER DESERT CONDITIONS II. PHYSIOLOGICAL AND YIELD RESPONSE OF MAIZE (ZEA MA YS) TO CONTINUOUS IRRIGATION WITH BRACKISH WATER AND TO ALTERNATING BRACKISH-FRESH-BRACKISH WATER IRRIGATION
D. PASTERNAK', Y. DE MALACH 2 and I. BOROVIC'
' The Rudolph and Rhoda Boyko Institute for Agriculture and Applied Biology, The Institutes for Applied Research, Ben Gurion University of the Negev, P.O. Box 1025, Beer-Sheva 84110 (Israel) 2Ramat Negev Experimental Station, Kibbutz Revivim (Israel) (Accepted 27 November 1984)
ABSTRACT Pasternak, D., De Malach, Y. and Borovic, I., 1985. Irrigation with brackish water under desert conditions. II. Physiological and yield response of maize (Zea mays) to continuous irrigation with brackish water and to alternating brackish-fresh-brackish water irrigation. Agric. Water Manage., 10: 47--60. The physiological behavior and yield response of maize under irrigation with saline water was studied in the laboratory and in the field. In the laboratory, the germination rate decreased only when the electrical conductivity (EC) of the substrate solution was above 17 dS/m. The osmotic potential of germinating maize seedlings decreased in proportion to the decrease in osmotic potential of the substrate. In the field, two maize cultivars (a field maize and a sweet maize) were irrigated alternately with saline (11 days from sowing), fresh (21 days from emergence), and saline (from day 33 to harvest) water and compared with maize irrigated with saline water continuously throughout the season. Four levels of irrigation water salinity were used (ECi = 1.2, 4.5, 7.0 and 10.5 dS/m). In the field no osmotic adjustment by the leaf sheaths of plants in response to salinity was observed. The osmotic potential of corn leaf sheaths (n) decreased with ontogeny in all treatments. The midday leaf water potential (4 L) in maize irrigated with 10.5 dS/m water was 0.75 MPa lower than in plants irrigated with 1.2 dS/m water. In the continuous treatment grain yield was reduced significantly with each increase in salt concentration, and the relationship between relative yield (y) and ECi could be expressed as y = 100--8.7 (ECi--0.84). With alternating irrigation and 7.0 dS/m treatment the grain yield was the same as in the low EC treatment (6.98 kg/m2).
INTRODUCTION
Agricultural development of the central Negev desert of Israel requires utilization of the relatively abundant saline groundwater (electrical conductivity, ECi -- 4.4--7.0 dS/m) to supplement the limited amounts of fresh water. 0378-3774/85/$03.30
© 1985 Elsevier Science Publishers B.V.
48 Bernstein and Hayward (1958) and Lunin et al. (1963) demonstrated that various plant species are sensitive to salinity only during specific short periods of their life cycles. The application of small quantities of fresh water to crops during these salt-sensitive stages of growth might permit the use of saline water for irrigation during the less sensitive stages, resulting in the economical utilization of saline water for the production of saltsensitive crops. The work reported here was planned after a previous study by the authors (Pasternak et al., 1982), which demonstrated that water with ECi of 4.4 dS/m can be used in a drip irrigation system for the production of field corn (maize) without any significant reduction in yield, and a study by Kaddah and Ghowail (1964), which demonstrated that alleviation of salinity stress during the first 3 weeks after sowing resulted in a significant increase in the salt resistance of this crop as reflected in grain yield. Yield reduction by salinity may be a result of specific ion toxicities (Eaton, 1942), of water deficit (Hoffman and Rawlins, 1971), of the creation and maintenance of low solute potentials (osmotic adjustment) by the synthesis of plant metabolites (Munns and Weir, 1981) at the expense of useful productivity, and of the diversion of energy for use in active ion transport and/or exclusion (Yeo, 1983). A limited number of physiological observations were carried out during the course of this study to identify some of the mechanisms by which corn responds to salinity. MATERIALS AND METHODS
Laboratory studies Effect of salinity on germination.
Four NaC1/CaC12 (weight ratio 3:1) solutions were prepared to give the osmotic potentials --0.04, --0.36, - 0 . 7 1 , and --1.06 MPa (ECi of 1.2, 7.8, 15.6 and 23.4 dS/m). Maize seeds (cv. KWS 752) were placed in Petri dishes lined with four layers of Whatman No. 1 filter paper, 25 seeds per dish. Each of the four salt solutions was poured into four dishes to give four replications per treatment. The Petri dishes with the seeds were placed in a 25°C incubator. When a coleoptile appeared, the seed was counted as having germinated and was discarded.
Changes in osmotic potential (~r) of maize during and following germination, as influenced by salinity. Two NaC1/CaCl~ (weight ratio 3:1) solutions were prepared, to give osmotic potentials of --0.50 and --0.85 MPa (ECi of 12.5 and 20.4 dS/m). Twenty-five maize seeds (cv. KWS 752) were placed in Petri dishes lined with filter paper soaked with one of the solutions, eight dishes per solution. Another treatment (control) entailed germinating seeds in eight dishes with water of --0.04 MPa (1.2 dS/m). Seeds in each of the three treatments were sown at 2
49 The radicles appeared in all treatments four days after the control seeds were sown. On this day, starting at time 0, and at 4, 8, 16, 24, 48 and 96 h, t w o seeds were removed from each Petri dish. The seeds were frozen by immersion in liquid nitrogen and then placed in a freezer. On the 4th day (after 96 h) the Petri dishes with the germinated seedlings were brought into the laboratory and placed under a fluorescent light at 1000 lux (~ 6 W/m2). The plants were left to grow with the three salt solutions for seven m o r e days. On the 7th day all leaves were harvested, immersed in liquid nitrogen, and placed in a freezer. The osmotic potential of the germinating seeds and of the young leaves was determined by a modification of the Shimshi and Livne (1967) method. After thawing, the sap was squeezed o u t of the seeds or leaves and a drop -was taken up into a modified syringe containing a microelectrode which measures the electrical conductivity of the sap. The total osmotic potential (~t) of the sap was measured with a Wescor 5100 B osmometer. The electrical conductivity values were converted to ne (electrolyte osmotic potential) values using the relation established by the USDA Salinity Laboratory Staff (1954). These values were subtracted from ~'t to give the metabolite potential (~m).
Field studies Experimental treatments. The experimental field was sown on 4 June 1981. Two maize cultivars were planted. A semi-dwarf European field maize cultivar -- KWS 752 -- and an American sweet corn cultivar -- 'Jubilee'. The two cultivars were germinated with water having electrical conductivities of 1.2, 4.5, 7.0, and 10.5 dS/m. After germination was complete (on 15 June 1981) half the plots were transferred to irrigation with water of ECi = 1.2 dS/m. On 5 July (21 days later) the plots were returned to irrigation with water containing the original salt levels. This will be referred to as the 'alternating' treatment. The remaining plots were irrigated throughout with water of the four salt concentrations -- the 'continuous' treatment. The experimental treatments thus comprised t w o cultivars, each irrigated with water of four salt concentrations with t w o irrigation regimes, 16 treatments altogether. Each treatment was replicated four times in a randomized split-plot design. Each plot consisted of three 12-mlong rows 1 m apart. The center row was sampled for grain or cob yield, and the t w o side rows were used for the determination of other parameters. Irrigation and salt distribution systems. A drip-irrigation system was used. The drip lines were placed on top of each maize row, 1 m apart. The distance between drippers was 50 cm and their discharge rate 2 l/h. The various salt solutions were prepared as follows. A 15% (w/v) salt brine was prepared with NaG1 and GAG12 at a weight ratio of 3:1 (the approximate ratio in the local groundwater, which has an EC of a b o u t 5.0
50 dS/m. The brine was injected into the dripper lines with a water-driven fertilizer pump through a series of discharge regulators. The regulators were set to deliver the four selected salt concentrations. Liquid fertilizer was also injected into the system with another fertilizer pump.
Management. The soil was a torrifluvent sandy loam containing 70--80% sand, 10--15% clay and 10--20% silt. Seeds were hand-sown at 10 seeds per m. Prior to sowing, the field was dressed with ammonium sulfate at 500 kg/ha and superphosphate at 600 kg/ha. Potassium nitrate was applied daily with the irrigation system at 13 kg/(ha day) together with phosphoric acid (P concentration of 20%), which was applied at a rate of 5 l/ (ha day). These somewhat excessive quantities were given to ensure an ample supply of fertilizer under the heavy leaching regime used. The quantity of irrigation water was calculated from the evapotranspiration/open pan evaporation ratio for maize established by Denmead and Shaw (1959) and from evaporation data obtained with a USWB class A pan. Approximately 30% was added to the calculated figures to ensure good leaching of salts from the r o o t zone and the maintenance of a steady-state salt concentration throughout the experimental period. The Jubilee cultivar was given a total of 710 mm of water, which was divided in the alternating treatment into 110 mm fresh water (ECi = 1.2 dS/m) and 600 mm brackish water. The field maize (KWS 752) received a total of 1050 mm of water, which was divided in the alternating treatment into 110 mm fresh and 940 mm brackish water. The difference in water use between the two varieties was because the sweet maize was harvested on 18 August and the field maize on 9 September 1981.
Measurements. The following parameters were determined during the growth period: the electrical conductivity (ECe) of the saturated extract of the soil immediately under the drippers; the production of dry matter (four times during the season); the osmotic potential of the second fully expanded leaf sheath from the top (determined with the m e t h o d mentioned above at 06.00 h, four times during the season); and the daily variation in the water potential of leaf sheaths, using a pressure b o m b (twice during the season). Ear and grain yields were determined according to c o m m o n practices.
RESULTS A N D DISCUSSION
Salinity and germination Maize is relativelyresistantto salinityduring the germination stage (Fig. 1). This finding issimilarto that described by Maas et al. (1983). An osmotic potential of --1.06 M P a in the medium delayed the beginning of coleoptile emergence by up to 2 days compared with the control, and the end of germination by up to 6 days.
51
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Fig. 1. Germination of corn (cv. KWS 752) seeds in relation to electrolyte osmotic potential of the medium ( . , --0.04; o, --0.36; o, - 0 . 7 1 ; and a, --1.06 MPa).
The osmotic potential of germinating maize seeds decreases in response to increasing salt concentration in the media (Fig. 2). The water potential (4) of the germinating seeds in the Petri dishes is assumed to be in equilibrium with the osmotic potential of the media (in this case --0.04, --0.5 and --0.85 MPa), and the turgot potential (P) of the germinating seeds can be calculated as P --- ~ -- ~t. Figure 2 shows that a more or less constant turgor potential of about 0.9 MPa was maintained in the germinating seeds at the three sal.inity levels for the whole period of germination. Turgor maintenance resulted from osmotic adjustment. Germinating maize seeds and young seedlings adjusted nt both through salt intake (~e) and through an increase in osmotically active metabolites (nm ), the latter being the more pronounced mechanism.
Salinity effects on yield and yield components. The electrical conductivity of the soil under the drippers in the continuous treatment remained constant throughout the season (Table I); there was a slight drop towards the end of the season, probably because of a higher leaching ratio at that time, due to overestimation of evapotranspiration in the saline treatments. The electrical conductivity in each of the alternating treatments changed according to the quality of water applied. Grain yield and other yield components for the cultivar KWS 752 are presented in Table II and the fresh ear yield for the Jubilee cultivar in Table III. In the continuous treatment grain yield from KWS 752 was
52
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8 16 24 48 96 264 TIME (HOURS A F T E R B E G I N I N G OF G E R M I N A T I O N ) Fig. 2. Osmotic p o t e n t i a l o f corn seedlings after co]eopti]e emergence and o f leaves 7 days after gexTnLqation as a f u n c t i o n o f osmotic p o t e n t i a l o f the m e d i u m (e, --0.04; • , --0.50; and A, --0.85 MPa). (a) t o t a l ~rt; (b) metabo]ites 7rm ; (c) electrolytes ~e-
53 TABLE I Mean electrical conductivity of the saturated soil extract, ]~'~e (dS/m), at four dates during the g~owing season (values are averages for the depth intervals 5--30 and 30-60 cm) Days after sowing
E C / o f irrigation water (dS/m) 1.2 4.5 7.0
(_)a
(+)
(_)
(+)
10.5
(_)
(+)
(_)
(+)
7.3 7.2 6.6 6.0
1.8 6.4 6.0 6.2
11.5 9.5 8.0 8.2
2.1 8.7 8.0 8.1
E----~eof soil extract (dS/m) 30 b 56 72 120
1.5 1.3 1.1 1.2
1.3 1.3 1.1 1.0
5.4 5.5 4.0 4.5
1.8 4.0 3.9 3.9
a(_), continuous treatment; (+), alternating treatment. bAverage of the 5--30 c m layer only. TABLE
II
Grain yield and yield components of the field corn cultivar K W S 752 in relation to continuous irrigation with water of four salt concentrations and to alternating irrigationwith saline--fresh--salinewater ECi (dS/m)
Grain yield e (kg/10 m 2)
No. of cobs (per m 2)
No. of kernels per cob
Kernel weight (rag)
(-):f
(+)
(-)
(+)
(-)
(+)
(-)
(+)
1.2 4.5 7.0 10.5
7.09 a 4.56 b 3.07 c 1.31 d
6.98 a 6.73 a 6.98 a 5.17 a
8.45 a 6.47 b 6.82 b 5.13 b
8.40 a 7.70 a 7.50 ab 6.53 b
294.1 a 262.0 a 187.1 b 154.9 b
291.5 a 324.9 a 352.3 a 299.5 a
292 a 268 b 243 c 218 d
291 a 269 a 269 a 260 a
Mean
4.01
6.47
6.72
7.53
224.5
317.1
255
274
a'b'C~lValues in columns denoted by similar letters do not differ at P = 5% as determined by the Duncan multiple range test. Means of continuous and alternating lzeatments for all yield parameters differ at P = 5%. eGrain weight is adjusted to 15% moisture content. f(--), continuous treatment; (+) alternating treatment. s i g n i f i c a n t l y r e d u c e d w i t h e a c h i n c r e a s e in s a l t c o n c e n t r a t i o n ( T a b l e I I ) . In the alternating treatment, the yield for the 7 dS/m treatment was the s a m e as f o r t h e c o n t r o l . A t 1 0 . 5 d S / m t h e a v e r a g e y i e l d w a s r e d u c e d b y 2 7 % , a l t h o u g h t h i s w a s n o t s t a t i s t i c a l l y s i g n i f i c a n t a t t h e 5% p r o b a b i l i t y l e v e l , d u e t o t h e h i g h v a r i a b i l i t y . T h i s is i n a g r e e m e n t w i t h r e s u l t s p r e s e n t e d b y K a d d a h a n d G h o w a i l ( 1 9 6 4 ) a n d b y M a a s e t al. ( 1 9 8 3 ) . S a l i n i t y a f f e c t e d the yield through reduction of the number of cobs per unit area and reduction of the kernel weight. It did not affect the number of kernels per cob
54 T A B L E III Yield o f fresh ears a n d yield c o m p o n e n t s o f t h e s w e e t c o r n cultivar J u b i l e e in r e l a t i o n t o c o n t i n u o u s irrigation w i t h w a t e r o f f o u r salt c o n c e n t r a t i o n s and t o a l t e r n a t i n g irrigation with saline--fresh--saline water ECi (dS/m)
Ear yield (kg/10 m s)
No. o f ears (per m s)
Ear weight (g)
(_)d
(+)
(_)
(+)
(_)
(+)
1.2 4.5 7.0 10.5
19.5 a 12.6 b 11.7 b 1.0 c
18.1 a 18.2 a 15.7 a 15.0 a
6.6 a 5.8 a 6.0 a 1.1 b
6.8 a 6.2 a 6.0 a 6.4 a
300 a 220 b 190 b 80 c
270 a 290 a 260 a 240 a
Mean
11.2
16.8
4.9
6.3
200
260
a'b~CValues in c o l u m n s d e n o t e d by similar letters d o n o t differ at P = 5% as d e t e r m i n e d b y t h e D u n c a n m u l t i p l e range test. M e a n s o f c o n t i n u o u s a n d a l t e r n a t i n g t r e a t m e n t for all yield p a r a m e t e r s d i f f e r at P = 5%. d ( _ ) , c o n t i n u o u s t r e a t m e n t ; (+), a l t e r n a t i n g t r e a t m e n t .
as significantly. There was a significant interaction between the salt concentration in the irrigation water and the irrigation regime for the number of cobs per m 2 and the number of kernels per cob, but not for the kernel weight. The yield response to salinity in the Jubilee sweet corn cultivar (Table III) was different from that of the field maize cultivar. The yield of Jubilee was linearly reduced with increasing ECi (continuous treatment) from 1.2 to 7.0 dS/m. A further increase in ECi to 10.5 dS/m resulted in a ten-fold yield reduction mainly, but not only, due to a reduction in the number of ears per unit area. Alternating application of fresh and saline water during the early growth stage prevented the yield reduction due to salinity. The relationship between relative yield and ECi or EC e was calculated using the expression suggested by Maas and Hoffman (1977): y = 100 -- b (EC -- a), where y = relative yield as a percentage of control, and b (the slope) expresses the percentage decrease in relative yield with each increase in the time-averaged EC beyond the threshold EC value of a (Table IV). The b value for grain yield (11.2) is slightly lower than the b value recently determined by Hoffman et al. (1983) for field maize in the San Joaquin Valley of California and greater than the value given by Maas and Hoffman in their 1977 review. The threshold values (Table IV) are much smaller than the values reported by them. The slope of 2.6 obtained in the alternating treatment for grain yield vs. ECi is comparable to values encountered in the literature for salt-resistant crops (Maas and Hoffman, 1977).
55 T A B L E IV T h r e s h o l d E-C a n d p e r c e n t a g e decrease in relative grain yield a n d stover weight o f cv. KWS 752 a n d in relative ear w e i g h t and fresh forage weight o f cv. Jubilee as a f u n c t i o n o f irrigation w a t e r salinity, soil w a t e r salinity, a n d irrigation regime Parameter
Threshold (dS/m)
Slope (%/(dS/m))
r~
(_)a
(+)
(_)
(+)
(_)
(+)
1.24 0.84 1.20 1.79
-2.74 -4.04
11.2 8.7 9.5 7.48
-2.6 -2.66
0.92 0.98 0.72 0.92
-0.66 -0.50
1.66 1.38 1.47 1.19
-1.77 -1.85
11.9 9.8 10.22 8.32
-4.11 -3.17
0.76 0.78 0.76 0.94
-0.86 -0.96
Field c o r n cv. KWS 752 Grain yield vs. ~ e Grain yield vs. ECi S t o v e r yield vs. L'r~e Stover yield vs ECi S w e e t c o r n cv. Jubilee Fresh Fresh Fresh Fresh
ear weight vs. ]~-Ce ear w e i g h t vs. ECi forage w e i g h t vs. E ~ e forage weight vs. ECi
a ( _ ) , c o n t i n u o u s t r e a t m e n t ; (+), alternating t r e a t m e n t .
Salinity and water relationships in the field The osmotic potential of fully expanded maize leaf sheaths (~'t) decreased during the season from a value of a b o u t --1.1 MPa 31 days after sowing to a b o u t --1.7 MPa 74 days after sowing (Fig. 3). The decrease of ~t with ontogeny was observed before by Pasternak et al. (1973, 1982) for wheat and for maize. The changes in ~t with time were effected mainly through an increased concentration of osmotically active metabolites (Fig. 3b), with very little change in r e (Fig. 3c). There were no significant differences in n t measured at 0600 h between plants in the four salinity treatments for any of the first three sampling dates. It thus appears that during vegetative growth and under field conditions, contrary to the situation during germination (Fig. 2), corn plants do not significantly adjust the morning ~t in the leaf sheaths in response to the increased ~ of the soil solution. It is most likely, however, that some adjustment in the midday ~ does occur in maize in response to salt treatment, as can be deduced from the work of Acevedo et al. (1979). Figures 4a and 4b show the variation in the ~ L of corn leaves throughout the day on t w o separate occasions. The midday ~ L values decreased with increasing salinity of the irrigation water. On the first sampling occasion the differences in midday ~ L between control plants and those irrigated with water having an ECi of 10.5 dS/m were as high as 0.75 MPa. On the second sampling occasion these differences were
56
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Fig. 3. Variation with time of osmotic potential of fully expanded corn leaves in relation to irrigation water salinity. Total 7rt (a) is separated into metabolites ~m {b) and electrolytes ~e (c). (Water ECi: o, 1.2; o, 4.5; o, 7.0; and 4 10.5 dS/m.)
much smaller. The significantly lower ~ L values in the high salinity treatments do not necessarily imply a water deficit. They could be at least partly the result of a diurnal osmotic 'adaptation' (see Acevedo et al., 1979). However, during hot days the salt-treated plants were obviously
57 "11
-I.Z
-I.|
i
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Ilii,
HOUR
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Fig. 4. Daylight variation in water potential (4 L) of corn leaves on days 47 (a) and 67 (b) after sowing in relation to irrigation water salinity. (Water ECi: o, 1.2; o, 4.5; o, 7.0; and a, 10.5 dS/m.)
wilted. More detailed measurements are needed to quantify the degree of water deficit imposed on maize by high salinity in the soil.
Effect o f salinity on dry matter Figure 5 shows the increase in dry matter in the two cultivars in relation to the salt concentration of the irrigation water and to the irrigation regime. Salinity affected dry matter production at the earlier growth stages to a much greater extent than at the later stages (Figs. 5a and 5c). This effect could be largely eliminated by irrigating the plants with fresh water during the 21 days following germination (Figs. 5b and 5d).
58
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II
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Fig. 5. Dry matter production of a field corn ¢ultivar (KWS 752) and a sweet corn cultivar (Jubilee) as affected by continuous and alternating irrigation with water of four levels of salinity. (Water ECi: e, 1.2; o, 4.5; o, 7.0; and % 10.5 dS/m.) CONCLUSIONS
This work demonstrated again that alleviation of salinity stress during the early growth stages increases the salt resistance of maize. This finding is very important for locations such as the central Negev where the abundant local saline and the expensive imported fresh water can be used alternately for irrigation of the same field. For example, it is possible to use water having an ECi of 7.0 dS/m to supply 90% of the irrigation needs of grain maize (supplemented with 10% fresh water given during the post-germination period) with no significant yield reduction. If the same field were to be irrigated throughout with 7.0 dS/m water a 50% yield reduction could be expected. The physiological responses reported here can provide explanations for
59
observations made in this study and by other workers (Kaddah and Ghowail, 1964; Maas et al., 1983) in relation to maize response to salinity. That is, the high resistance of maize to salinity during germination (Fig. 1) may be related to the capacity of germinating seeds to decrease their ~ t in proportion to a decrease in ~s, to maintain a constant and high turgor potential (Fig. 2). The higher resistance to salinity at later growth stages (Fig. 5) may be related to the observed significant increase in ~t with ontogeny (Fig. 3). If salinity indeed induces water stress in field-grown corn (Fig. 4) then perhaps frequent application of irrigation water to maintain the highest possible total soil water potential under saline conditions would be beneficial, as demonstrated experimentally by Selassie and Wagenet (1981). Further studies on the salt resistance of crops along with detailed observations on both crop physiology and mechanisms of salt resistance are imperative for the understanding and interpretation of phenomena such as observed and presented in this paper. ACKNOWLEDGEMENTS
The authors wish to thank Ms. E. Katz, Ms. H. Klotz and Mr. B. Watzke for their devoted and skilled technical help, and Dr. M.A. Tiefert for help with the manuscript. This project was supported by the German-Israel Fund for Research and Development (GIFRID) and by the Israel Vegetable Growers Association.
REFERENCES Acevedo, E., Fereres, E., Hsiao, T.C. and Henderson, D.W., 1979. Diurnal growth trends, water potential and osmotic adjustment of maize and sorghum leaves in the field. Plant Physiol.~ 64: 476--480. Bernstein, L. and Hayward, H.E., 1958. Physiology of salt tolerance. Annu. Rev. Plant Physiol., 9: 25--46. Denmead, C.T. and Shaw, R.E., 1959. Evapotranspiration in relation to the development of the corn crop. Agron. J., 51: 725--726. Eaton, F.M., 1942. Toxicity and accumulation of chloride and sulfate salts in plants. J. Agric. Res., 64: 357--399. Hoffman, G.J. and Rawlins, S.L., 1971. Growth and water potential of root crops as influenced by salinity and relative humidity. Agron. J., 63: 877--880. Hoffman, G.J., Maas, E.V., Prichard, T. and Meyer, J.L., 1983. Salt tolerance of corn in the Sacramento-San Joaquin Delta of California. Irrig. Sci., 4: 31--44. Kaddah, M.T. and Ghowail, S.I., 1964. Salinity effects on the growth of corn at different stages of development. Agron. J., 56: 214--217. Lunin, J., Gallatin, M.H. and Butchelder, A.R., 1963. Saline irrigation of several vegetable crops at various growth stages. I. Effects on yields. Agron. J., 55: 107--110. Maas, E.V. and Hoffman, G.J., 1977. Crop salt tolerance. Current assessment. J. Irrig. Drain. Div. ASCE, 103: (IR2) 115--134. Maas, E.V., Hoffman, G.J., Chaba, G.J., Poss, J.A. and Shannon, M.C., 1983. Salt sensitivity of corn at various growth stages. Irrig. Sci., 4: 45--57.
60 Munns, R. and Weir, R., 1981. Contribution of sugars to osmotic adjustment in elongating and expanded zones of wheat leaves during moderate water deficits. Aust. J. Plant Physiol., 8: 93--105. Pasternak, D., Twersky, M. and Borovic, I., 1973. Irrigation of wheat with brackish water at Ramat Hanegev. Hassadeh, 52:381--384 (In Hebrew). Pasternak, D., Borovic, I., De Malach, Y. and Berkovitch, S., 1982. High yield of corn with brackfish water irrigation. In: Water and Irrigation Review, October 1982. Water Workers Association, Tel-Aviv. Selassie, T.G. and Wagenet, R., 1981. Interactive effects of soil salinity, fertility and irrigation on field corn. Irrig. Sci., 2: 67--78. Shimshi, D. and Livne, 1967. The estimation of the osmotic potential of plant sap by refractometry and conductometry: A field method. Ann. Bot. NS, 31: 505--511. USDA Salinity Laboratory Staff, 1954. Diagnosis and Improvement of Saline and Alkali Soils. USDA Handb. 60, Government Printing Office, Washington, DC, 160 pp. Yeo, A.R., 1983. Salinity resistance: Physiologies and prices. Physiol. Plant., 58: 214-222.
47
IRRIGATION WITH BRACKISH WATER UNDER DESERT CONDITIONS II. PHYSIOLOGICAL AND YIELD RESPONSE OF MAIZE (ZEA MA YS) TO CONTINUOUS IRRIGATION WITH BRACKISH WATER AND TO ALTERNATING BRACKISH-FRESH-BRACKISH WATER IRRIGATION
D. PASTERNAK', Y. DE MALACH 2 and I. BOROVIC'
' The Rudolph and Rhoda Boyko Institute for Agriculture and Applied Biology, The Institutes for Applied Research, Ben Gurion University of the Negev, P.O. Box 1025, Beer-Sheva 84110 (Israel) 2Ramat Negev Experimental Station, Kibbutz Revivim (Israel) (Accepted 27 November 1984)
ABSTRACT Pasternak, D., De Malach, Y. and Borovic, I., 1985. Irrigation with brackish water under desert conditions. II. Physiological and yield response of maize (Zea mays) to continuous irrigation with brackish water and to alternating brackish-fresh-brackish water irrigation. Agric. Water Manage., 10: 47--60. The physiological behavior and yield response of maize under irrigation with saline water was studied in the laboratory and in the field. In the laboratory, the germination rate decreased only when the electrical conductivity (EC) of the substrate solution was above 17 dS/m. The osmotic potential of germinating maize seedlings decreased in proportion to the decrease in osmotic potential of the substrate. In the field, two maize cultivars (a field maize and a sweet maize) were irrigated alternately with saline (11 days from sowing), fresh (21 days from emergence), and saline (from day 33 to harvest) water and compared with maize irrigated with saline water continuously throughout the season. Four levels of irrigation water salinity were used (ECi = 1.2, 4.5, 7.0 and 10.5 dS/m). In the field no osmotic adjustment by the leaf sheaths of plants in response to salinity was observed. The osmotic potential of corn leaf sheaths (n) decreased with ontogeny in all treatments. The midday leaf water potential (4 L) in maize irrigated with 10.5 dS/m water was 0.75 MPa lower than in plants irrigated with 1.2 dS/m water. In the continuous treatment grain yield was reduced significantly with each increase in salt concentration, and the relationship between relative yield (y) and ECi could be expressed as y = 100--8.7 (ECi--0.84). With alternating irrigation and 7.0 dS/m treatment the grain yield was the same as in the low EC treatment (6.98 kg/m2).
INTRODUCTION
Agricultural development of the central Negev desert of Israel requires utilization of the relatively abundant saline groundwater (electrical conductivity, ECi -- 4.4--7.0 dS/m) to supplement the limited amounts of fresh water. 0378-3774/85/$03.30
© 1985 Elsevier Science Publishers B.V.
48 Bernstein and Hayward (1958) and Lunin et al. (1963) demonstrated that various plant species are sensitive to salinity only during specific short periods of their life cycles. The application of small quantities of fresh water to crops during these salt-sensitive stages of growth might permit the use of saline water for irrigation during the less sensitive stages, resulting in the economical utilization of saline water for the production of saltsensitive crops. The work reported here was planned after a previous study by the authors (Pasternak et al., 1982), which demonstrated that water with ECi of 4.4 dS/m can be used in a drip irrigation system for the production of field corn (maize) without any significant reduction in yield, and a study by Kaddah and Ghowail (1964), which demonstrated that alleviation of salinity stress during the first 3 weeks after sowing resulted in a significant increase in the salt resistance of this crop as reflected in grain yield. Yield reduction by salinity may be a result of specific ion toxicities (Eaton, 1942), of water deficit (Hoffman and Rawlins, 1971), of the creation and maintenance of low solute potentials (osmotic adjustment) by the synthesis of plant metabolites (Munns and Weir, 1981) at the expense of useful productivity, and of the diversion of energy for use in active ion transport and/or exclusion (Yeo, 1983). A limited number of physiological observations were carried out during the course of this study to identify some of the mechanisms by which corn responds to salinity. MATERIALS AND METHODS
Laboratory studies Effect of salinity on germination.
Four NaC1/CaC12 (weight ratio 3:1) solutions were prepared to give the osmotic potentials --0.04, --0.36, - 0 . 7 1 , and --1.06 MPa (ECi of 1.2, 7.8, 15.6 and 23.4 dS/m). Maize seeds (cv. KWS 752) were placed in Petri dishes lined with four layers of Whatman No. 1 filter paper, 25 seeds per dish. Each of the four salt solutions was poured into four dishes to give four replications per treatment. The Petri dishes with the seeds were placed in a 25°C incubator. When a coleoptile appeared, the seed was counted as having germinated and was discarded.
Changes in osmotic potential (~r) of maize during and following germination, as influenced by salinity. Two NaC1/CaCl~ (weight ratio 3:1) solutions were prepared, to give osmotic potentials of --0.50 and --0.85 MPa (ECi of 12.5 and 20.4 dS/m). Twenty-five maize seeds (cv. KWS 752) were placed in Petri dishes lined with filter paper soaked with one of the solutions, eight dishes per solution. Another treatment (control) entailed germinating seeds in eight dishes with water of --0.04 MPa (1.2 dS/m). Seeds in each of the three treatments were sown at 2
49 The radicles appeared in all treatments four days after the control seeds were sown. On this day, starting at time 0, and at 4, 8, 16, 24, 48 and 96 h, t w o seeds were removed from each Petri dish. The seeds were frozen by immersion in liquid nitrogen and then placed in a freezer. On the 4th day (after 96 h) the Petri dishes with the germinated seedlings were brought into the laboratory and placed under a fluorescent light at 1000 lux (~ 6 W/m2). The plants were left to grow with the three salt solutions for seven m o r e days. On the 7th day all leaves were harvested, immersed in liquid nitrogen, and placed in a freezer. The osmotic potential of the germinating seeds and of the young leaves was determined by a modification of the Shimshi and Livne (1967) method. After thawing, the sap was squeezed o u t of the seeds or leaves and a drop -was taken up into a modified syringe containing a microelectrode which measures the electrical conductivity of the sap. The total osmotic potential (~t) of the sap was measured with a Wescor 5100 B osmometer. The electrical conductivity values were converted to ne (electrolyte osmotic potential) values using the relation established by the USDA Salinity Laboratory Staff (1954). These values were subtracted from ~'t to give the metabolite potential (~m).
Field studies Experimental treatments. The experimental field was sown on 4 June 1981. Two maize cultivars were planted. A semi-dwarf European field maize cultivar -- KWS 752 -- and an American sweet corn cultivar -- 'Jubilee'. The two cultivars were germinated with water having electrical conductivities of 1.2, 4.5, 7.0, and 10.5 dS/m. After germination was complete (on 15 June 1981) half the plots were transferred to irrigation with water of ECi = 1.2 dS/m. On 5 July (21 days later) the plots were returned to irrigation with water containing the original salt levels. This will be referred to as the 'alternating' treatment. The remaining plots were irrigated throughout with water of the four salt concentrations -- the 'continuous' treatment. The experimental treatments thus comprised t w o cultivars, each irrigated with water of four salt concentrations with t w o irrigation regimes, 16 treatments altogether. Each treatment was replicated four times in a randomized split-plot design. Each plot consisted of three 12-mlong rows 1 m apart. The center row was sampled for grain or cob yield, and the t w o side rows were used for the determination of other parameters. Irrigation and salt distribution systems. A drip-irrigation system was used. The drip lines were placed on top of each maize row, 1 m apart. The distance between drippers was 50 cm and their discharge rate 2 l/h. The various salt solutions were prepared as follows. A 15% (w/v) salt brine was prepared with NaG1 and GAG12 at a weight ratio of 3:1 (the approximate ratio in the local groundwater, which has an EC of a b o u t 5.0
50 dS/m. The brine was injected into the dripper lines with a water-driven fertilizer pump through a series of discharge regulators. The regulators were set to deliver the four selected salt concentrations. Liquid fertilizer was also injected into the system with another fertilizer pump.
Management. The soil was a torrifluvent sandy loam containing 70--80% sand, 10--15% clay and 10--20% silt. Seeds were hand-sown at 10 seeds per m. Prior to sowing, the field was dressed with ammonium sulfate at 500 kg/ha and superphosphate at 600 kg/ha. Potassium nitrate was applied daily with the irrigation system at 13 kg/(ha day) together with phosphoric acid (P concentration of 20%), which was applied at a rate of 5 l/ (ha day). These somewhat excessive quantities were given to ensure an ample supply of fertilizer under the heavy leaching regime used. The quantity of irrigation water was calculated from the evapotranspiration/open pan evaporation ratio for maize established by Denmead and Shaw (1959) and from evaporation data obtained with a USWB class A pan. Approximately 30% was added to the calculated figures to ensure good leaching of salts from the r o o t zone and the maintenance of a steady-state salt concentration throughout the experimental period. The Jubilee cultivar was given a total of 710 mm of water, which was divided in the alternating treatment into 110 mm fresh water (ECi = 1.2 dS/m) and 600 mm brackish water. The field maize (KWS 752) received a total of 1050 mm of water, which was divided in the alternating treatment into 110 mm fresh and 940 mm brackish water. The difference in water use between the two varieties was because the sweet maize was harvested on 18 August and the field maize on 9 September 1981.
Measurements. The following parameters were determined during the growth period: the electrical conductivity (ECe) of the saturated extract of the soil immediately under the drippers; the production of dry matter (four times during the season); the osmotic potential of the second fully expanded leaf sheath from the top (determined with the m e t h o d mentioned above at 06.00 h, four times during the season); and the daily variation in the water potential of leaf sheaths, using a pressure b o m b (twice during the season). Ear and grain yields were determined according to c o m m o n practices.
RESULTS A N D DISCUSSION
Salinity and germination Maize is relativelyresistantto salinityduring the germination stage (Fig. 1). This finding issimilarto that described by Maas et al. (1983). An osmotic potential of --1.06 M P a in the medium delayed the beginning of coleoptile emergence by up to 2 days compared with the control, and the end of germination by up to 6 days.
51
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40
n~ LU 2O
0
I
|
.
|
4
I
I
!
8 TIME
1
|
I
!
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Fig. 1. Germination of corn (cv. KWS 752) seeds in relation to electrolyte osmotic potential of the medium ( . , --0.04; o, --0.36; o, - 0 . 7 1 ; and a, --1.06 MPa).
The osmotic potential of germinating maize seeds decreases in response to increasing salt concentration in the media (Fig. 2). The water potential (4) of the germinating seeds in the Petri dishes is assumed to be in equilibrium with the osmotic potential of the media (in this case --0.04, --0.5 and --0.85 MPa), and the turgot potential (P) of the germinating seeds can be calculated as P --- ~ -- ~t. Figure 2 shows that a more or less constant turgor potential of about 0.9 MPa was maintained in the germinating seeds at the three sal.inity levels for the whole period of germination. Turgor maintenance resulted from osmotic adjustment. Germinating maize seeds and young seedlings adjusted nt both through salt intake (~e) and through an increase in osmotically active metabolites (nm ), the latter being the more pronounced mechanism.
Salinity effects on yield and yield components. The electrical conductivity of the soil under the drippers in the continuous treatment remained constant throughout the season (Table I); there was a slight drop towards the end of the season, probably because of a higher leaching ratio at that time, due to overestimation of evapotranspiration in the saline treatments. The electrical conductivity in each of the alternating treatments changed according to the quality of water applied. Grain yield and other yield components for the cultivar KWS 752 are presented in Table II and the fresh ear yield for the Jubilee cultivar in Table III. In the continuous treatment grain yield from KWS 752 was
52
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8 16 24 48 96 264 TIME (HOURS A F T E R B E G I N I N G OF G E R M I N A T I O N ) Fig. 2. Osmotic p o t e n t i a l o f corn seedlings after co]eopti]e emergence and o f leaves 7 days after gexTnLqation as a f u n c t i o n o f osmotic p o t e n t i a l o f the m e d i u m (e, --0.04; • , --0.50; and A, --0.85 MPa). (a) t o t a l ~rt; (b) metabo]ites 7rm ; (c) electrolytes ~e-
53 TABLE I Mean electrical conductivity of the saturated soil extract, ]~'~e (dS/m), at four dates during the g~owing season (values are averages for the depth intervals 5--30 and 30-60 cm) Days after sowing
E C / o f irrigation water (dS/m) 1.2 4.5 7.0
(_)a
(+)
(_)
(+)
10.5
(_)
(+)
(_)
(+)
7.3 7.2 6.6 6.0
1.8 6.4 6.0 6.2
11.5 9.5 8.0 8.2
2.1 8.7 8.0 8.1
E----~eof soil extract (dS/m) 30 b 56 72 120
1.5 1.3 1.1 1.2
1.3 1.3 1.1 1.0
5.4 5.5 4.0 4.5
1.8 4.0 3.9 3.9
a(_), continuous treatment; (+), alternating treatment. bAverage of the 5--30 c m layer only. TABLE
II
Grain yield and yield components of the field corn cultivar K W S 752 in relation to continuous irrigation with water of four salt concentrations and to alternating irrigationwith saline--fresh--salinewater ECi (dS/m)
Grain yield e (kg/10 m 2)
No. of cobs (per m 2)
No. of kernels per cob
Kernel weight (rag)
(-):f
(+)
(-)
(+)
(-)
(+)
(-)
(+)
1.2 4.5 7.0 10.5
7.09 a 4.56 b 3.07 c 1.31 d
6.98 a 6.73 a 6.98 a 5.17 a
8.45 a 6.47 b 6.82 b 5.13 b
8.40 a 7.70 a 7.50 ab 6.53 b
294.1 a 262.0 a 187.1 b 154.9 b
291.5 a 324.9 a 352.3 a 299.5 a
292 a 268 b 243 c 218 d
291 a 269 a 269 a 260 a
Mean
4.01
6.47
6.72
7.53
224.5
317.1
255
274
a'b'C~lValues in columns denoted by similar letters do not differ at P = 5% as determined by the Duncan multiple range test. Means of continuous and alternating lzeatments for all yield parameters differ at P = 5%. eGrain weight is adjusted to 15% moisture content. f(--), continuous treatment; (+) alternating treatment. s i g n i f i c a n t l y r e d u c e d w i t h e a c h i n c r e a s e in s a l t c o n c e n t r a t i o n ( T a b l e I I ) . In the alternating treatment, the yield for the 7 dS/m treatment was the s a m e as f o r t h e c o n t r o l . A t 1 0 . 5 d S / m t h e a v e r a g e y i e l d w a s r e d u c e d b y 2 7 % , a l t h o u g h t h i s w a s n o t s t a t i s t i c a l l y s i g n i f i c a n t a t t h e 5% p r o b a b i l i t y l e v e l , d u e t o t h e h i g h v a r i a b i l i t y . T h i s is i n a g r e e m e n t w i t h r e s u l t s p r e s e n t e d b y K a d d a h a n d G h o w a i l ( 1 9 6 4 ) a n d b y M a a s e t al. ( 1 9 8 3 ) . S a l i n i t y a f f e c t e d the yield through reduction of the number of cobs per unit area and reduction of the kernel weight. It did not affect the number of kernels per cob
54 T A B L E III Yield o f fresh ears a n d yield c o m p o n e n t s o f t h e s w e e t c o r n cultivar J u b i l e e in r e l a t i o n t o c o n t i n u o u s irrigation w i t h w a t e r o f f o u r salt c o n c e n t r a t i o n s and t o a l t e r n a t i n g irrigation with saline--fresh--saline water ECi (dS/m)
Ear yield (kg/10 m s)
No. o f ears (per m s)
Ear weight (g)
(_)d
(+)
(_)
(+)
(_)
(+)
1.2 4.5 7.0 10.5
19.5 a 12.6 b 11.7 b 1.0 c
18.1 a 18.2 a 15.7 a 15.0 a
6.6 a 5.8 a 6.0 a 1.1 b
6.8 a 6.2 a 6.0 a 6.4 a
300 a 220 b 190 b 80 c
270 a 290 a 260 a 240 a
Mean
11.2
16.8
4.9
6.3
200
260
a'b~CValues in c o l u m n s d e n o t e d by similar letters d o n o t differ at P = 5% as d e t e r m i n e d b y t h e D u n c a n m u l t i p l e range test. M e a n s o f c o n t i n u o u s a n d a l t e r n a t i n g t r e a t m e n t for all yield p a r a m e t e r s d i f f e r at P = 5%. d ( _ ) , c o n t i n u o u s t r e a t m e n t ; (+), a l t e r n a t i n g t r e a t m e n t .
as significantly. There was a significant interaction between the salt concentration in the irrigation water and the irrigation regime for the number of cobs per m 2 and the number of kernels per cob, but not for the kernel weight. The yield response to salinity in the Jubilee sweet corn cultivar (Table III) was different from that of the field maize cultivar. The yield of Jubilee was linearly reduced with increasing ECi (continuous treatment) from 1.2 to 7.0 dS/m. A further increase in ECi to 10.5 dS/m resulted in a ten-fold yield reduction mainly, but not only, due to a reduction in the number of ears per unit area. Alternating application of fresh and saline water during the early growth stage prevented the yield reduction due to salinity. The relationship between relative yield and ECi or EC e was calculated using the expression suggested by Maas and Hoffman (1977): y = 100 -- b (EC -- a), where y = relative yield as a percentage of control, and b (the slope) expresses the percentage decrease in relative yield with each increase in the time-averaged EC beyond the threshold EC value of a (Table IV). The b value for grain yield (11.2) is slightly lower than the b value recently determined by Hoffman et al. (1983) for field maize in the San Joaquin Valley of California and greater than the value given by Maas and Hoffman in their 1977 review. The threshold values (Table IV) are much smaller than the values reported by them. The slope of 2.6 obtained in the alternating treatment for grain yield vs. ECi is comparable to values encountered in the literature for salt-resistant crops (Maas and Hoffman, 1977).
55 T A B L E IV T h r e s h o l d E-C a n d p e r c e n t a g e decrease in relative grain yield a n d stover weight o f cv. KWS 752 a n d in relative ear w e i g h t and fresh forage weight o f cv. Jubilee as a f u n c t i o n o f irrigation w a t e r salinity, soil w a t e r salinity, a n d irrigation regime Parameter
Threshold (dS/m)
Slope (%/(dS/m))
r~
(_)a
(+)
(_)
(+)
(_)
(+)
1.24 0.84 1.20 1.79
-2.74 -4.04
11.2 8.7 9.5 7.48
-2.6 -2.66
0.92 0.98 0.72 0.92
-0.66 -0.50
1.66 1.38 1.47 1.19
-1.77 -1.85
11.9 9.8 10.22 8.32
-4.11 -3.17
0.76 0.78 0.76 0.94
-0.86 -0.96
Field c o r n cv. KWS 752 Grain yield vs. ~ e Grain yield vs. ECi S t o v e r yield vs. L'r~e Stover yield vs ECi S w e e t c o r n cv. Jubilee Fresh Fresh Fresh Fresh
ear weight vs. ]~-Ce ear w e i g h t vs. ECi forage w e i g h t vs. E ~ e forage weight vs. ECi
a ( _ ) , c o n t i n u o u s t r e a t m e n t ; (+), alternating t r e a t m e n t .
Salinity and water relationships in the field The osmotic potential of fully expanded maize leaf sheaths (~'t) decreased during the season from a value of a b o u t --1.1 MPa 31 days after sowing to a b o u t --1.7 MPa 74 days after sowing (Fig. 3). The decrease of ~t with ontogeny was observed before by Pasternak et al. (1973, 1982) for wheat and for maize. The changes in ~t with time were effected mainly through an increased concentration of osmotically active metabolites (Fig. 3b), with very little change in r e (Fig. 3c). There were no significant differences in n t measured at 0600 h between plants in the four salinity treatments for any of the first three sampling dates. It thus appears that during vegetative growth and under field conditions, contrary to the situation during germination (Fig. 2), corn plants do not significantly adjust the morning ~t in the leaf sheaths in response to the increased ~ of the soil solution. It is most likely, however, that some adjustment in the midday ~ does occur in maize in response to salt treatment, as can be deduced from the work of Acevedo et al. (1979). Figures 4a and 4b show the variation in the ~ L of corn leaves throughout the day on t w o separate occasions. The midday ~ L values decreased with increasing salinity of the irrigation water. On the first sampling occasion the differences in midday ~ L between control plants and those irrigated with water having an ECi of 10.5 dS/m were as high as 0.75 MPa. On the second sampling occasion these differences were
56
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Fig. 3. Variation with time of osmotic potential of fully expanded corn leaves in relation to irrigation water salinity. Total 7rt (a) is separated into metabolites ~m {b) and electrolytes ~e (c). (Water ECi: o, 1.2; o, 4.5; o, 7.0; and 4 10.5 dS/m.)
much smaller. The significantly lower ~ L values in the high salinity treatments do not necessarily imply a water deficit. They could be at least partly the result of a diurnal osmotic 'adaptation' (see Acevedo et al., 1979). However, during hot days the salt-treated plants were obviously
57 "11
-I.Z
-I.|
i
-?~l
i Olin
'
Ilii,
HOUR
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I
I
,
I llIHI
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Fig. 4. Daylight variation in water potential (4 L) of corn leaves on days 47 (a) and 67 (b) after sowing in relation to irrigation water salinity. (Water ECi: o, 1.2; o, 4.5; o, 7.0; and a, 10.5 dS/m.)
wilted. More detailed measurements are needed to quantify the degree of water deficit imposed on maize by high salinity in the soil.
Effect o f salinity on dry matter Figure 5 shows the increase in dry matter in the two cultivars in relation to the salt concentration of the irrigation water and to the irrigation regime. Salinity affected dry matter production at the earlier growth stages to a much greater extent than at the later stages (Figs. 5a and 5c). This effect could be largely eliminated by irrigating the plants with fresh water during the 21 days following germination (Figs. 5b and 5d).
58
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-
IJ
15
E
2
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alternating
II
1.5
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Fig. 5. Dry matter production of a field corn ¢ultivar (KWS 752) and a sweet corn cultivar (Jubilee) as affected by continuous and alternating irrigation with water of four levels of salinity. (Water ECi: e, 1.2; o, 4.5; o, 7.0; and % 10.5 dS/m.) CONCLUSIONS
This work demonstrated again that alleviation of salinity stress during the early growth stages increases the salt resistance of maize. This finding is very important for locations such as the central Negev where the abundant local saline and the expensive imported fresh water can be used alternately for irrigation of the same field. For example, it is possible to use water having an ECi of 7.0 dS/m to supply 90% of the irrigation needs of grain maize (supplemented with 10% fresh water given during the post-germination period) with no significant yield reduction. If the same field were to be irrigated throughout with 7.0 dS/m water a 50% yield reduction could be expected. The physiological responses reported here can provide explanations for
59
observations made in this study and by other workers (Kaddah and Ghowail, 1964; Maas et al., 1983) in relation to maize response to salinity. That is, the high resistance of maize to salinity during germination (Fig. 1) may be related to the capacity of germinating seeds to decrease their ~ t in proportion to a decrease in ~s, to maintain a constant and high turgor potential (Fig. 2). The higher resistance to salinity at later growth stages (Fig. 5) may be related to the observed significant increase in ~t with ontogeny (Fig. 3). If salinity indeed induces water stress in field-grown corn (Fig. 4) then perhaps frequent application of irrigation water to maintain the highest possible total soil water potential under saline conditions would be beneficial, as demonstrated experimentally by Selassie and Wagenet (1981). Further studies on the salt resistance of crops along with detailed observations on both crop physiology and mechanisms of salt resistance are imperative for the understanding and interpretation of phenomena such as observed and presented in this paper. ACKNOWLEDGEMENTS
The authors wish to thank Ms. E. Katz, Ms. H. Klotz and Mr. B. Watzke for their devoted and skilled technical help, and Dr. M.A. Tiefert for help with the manuscript. This project was supported by the German-Israel Fund for Research and Development (GIFRID) and by the Israel Vegetable Growers Association.
REFERENCES Acevedo, E., Fereres, E., Hsiao, T.C. and Henderson, D.W., 1979. Diurnal growth trends, water potential and osmotic adjustment of maize and sorghum leaves in the field. Plant Physiol.~ 64: 476--480. Bernstein, L. and Hayward, H.E., 1958. Physiology of salt tolerance. Annu. Rev. Plant Physiol., 9: 25--46. Denmead, C.T. and Shaw, R.E., 1959. Evapotranspiration in relation to the development of the corn crop. Agron. J., 51: 725--726. Eaton, F.M., 1942. Toxicity and accumulation of chloride and sulfate salts in plants. J. Agric. Res., 64: 357--399. Hoffman, G.J. and Rawlins, S.L., 1971. Growth and water potential of root crops as influenced by salinity and relative humidity. Agron. J., 63: 877--880. Hoffman, G.J., Maas, E.V., Prichard, T. and Meyer, J.L., 1983. Salt tolerance of corn in the Sacramento-San Joaquin Delta of California. Irrig. Sci., 4: 31--44. Kaddah, M.T. and Ghowail, S.I., 1964. Salinity effects on the growth of corn at different stages of development. Agron. J., 56: 214--217. Lunin, J., Gallatin, M.H. and Butchelder, A.R., 1963. Saline irrigation of several vegetable crops at various growth stages. I. Effects on yields. Agron. J., 55: 107--110. Maas, E.V. and Hoffman, G.J., 1977. Crop salt tolerance. Current assessment. J. Irrig. Drain. Div. ASCE, 103: (IR2) 115--134. Maas, E.V., Hoffman, G.J., Chaba, G.J., Poss, J.A. and Shannon, M.C., 1983. Salt sensitivity of corn at various growth stages. Irrig. Sci., 4: 45--57.
60 Munns, R. and Weir, R., 1981. Contribution of sugars to osmotic adjustment in elongating and expanded zones of wheat leaves during moderate water deficits. Aust. J. Plant Physiol., 8: 93--105. Pasternak, D., Twersky, M. and Borovic, I., 1973. Irrigation of wheat with brackish water at Ramat Hanegev. Hassadeh, 52:381--384 (In Hebrew). Pasternak, D., Borovic, I., De Malach, Y. and Berkovitch, S., 1982. High yield of corn with brackfish water irrigation. In: Water and Irrigation Review, October 1982. Water Workers Association, Tel-Aviv. Selassie, T.G. and Wagenet, R., 1981. Interactive effects of soil salinity, fertility and irrigation on field corn. Irrig. Sci., 2: 67--78. Shimshi, D. and Livne, 1967. The estimation of the osmotic potential of plant sap by refractometry and conductometry: A field method. Ann. Bot. NS, 31: 505--511. USDA Salinity Laboratory Staff, 1954. Diagnosis and Improvement of Saline and Alkali Soils. USDA Handb. 60, Government Printing Office, Washington, DC, 160 pp. Yeo, A.R., 1983. Salinity resistance: Physiologies and prices. Physiol. Plant., 58: 214-222.