Effect of Salts Stress on the Growth and Yield of Wheat ( Triticum aestivum L . )

In order to study the effect of salts stress on the growth and yield of wheat (cv. Inqalab), a pot experiment was conducted in the wire-house of the Department of Soil Science, Sindh Agriculture University Tando Jam. The soil was artificially salinized to a range of salinity levels i.e. EC 2.16, 4.0, 6.0, 8.0 and 10.0 dS∙m with different salts (MgCl2 + CaCl2 + Na2SO4). The salinized soil used for the experiment was sandy clay in texture, alkaline in reaction (pH > 7.0) and moderate in organic matter (0.95%) content. The results showed that with increasing salinity there was an increase in the ECe, Na, Ca, Mg and Cl and decrease in the K, SAR and ESP values of the soil Increasing salinity, progressively decreased plant height, spike length, number of spikelets spike 1000 grain weight and yield (straw and grain). Adverse effects of salts on plants were associated with the accumulation of less K and more Na and Cl in their flag leaf sap, grains and straw. This resulted in lower K:5Na ratio in flag leaf sap, grains and straw of wheat plants. These results indicated that the effects of salts stress were greater at 10 than at 8, 6 and 4 EC dS∙m.

staple foods for more than one third of the world population.Wheat played a vital role in the development of civilization.The king of cereals wheat is the principal source of food and is extensively grown, consumed and preferred in Pakistan.It contains approximately 60% -80% protein, 2% -2.5% glucose, 1.5% -2% fat and 2% -3% mineral matter [1].However, these may vary in proportion from variety to variety and locality to locality.Wheat crop is cultivated in all provinces of Pakistan as a bumper winter crop.The average yield of wheat in Pakistan is about 23888 kg•ha −1 which is comparatively very low to the other wheat growing countries of the world.The factors behind the low yield include poor fertility status of soil, less and imbalance use of fertilizers, unawareness and utilization of modern technology by the farmers, environment and climatic condition of the area, deficiency of macro and micronutrients and availability of required irrigation water at proper time [2].
Besides the above factors, soil salinity is the major problem, which affects the yield of this important crop.It is commonly observed in arid and semi-arid regions of the world [3].It is considered as a serious soil problem of Pakistan.About 6.3 m ha land is affected by salinity.Whereas in Sindh 2.3 m ha land is affected by different types of salts, mostly slats of chlorides and sulfates of sodium, calcium and magnesium [4].The soil which contains inorganic salts, also supplies necessary nutrients to the plant but when the concentration of these salts reaches such a level that is harmful for plant growth [5].
Excess amount of salts in the soil affects plant from germination to harvesting [6].It may affect the plants in two ways: a) by decreasing the rate of water entry in to plants, b) promoting the entry of toxic ions [7].Generally, salinity problem increase with increasing salt concentration in irrigation water.Crop growth reduction due to salinity is generally related to the osmotic potential of the root-zone soil solution.This will lead to certain physiological changes and substantial reduction in crop production [8].Plants in salt stress condition require a tight nutrition dose to maintain their normal physiology and to face the condition were they locate.In these circumstances they require a balanced nutrition of both macro and micronutrient elements to boost up their growth and development.Generally macronutrients N, P, K are supplied extensively but micronutrients are often ignored.However, their essentiality cannot be neglected for better crop yield especially under tough conditions.
The relative salt tolerance of wheat crop is 7.0 dS•m −1 and its yield decrease is 25% at 9.0 dS•m −1 [9].The reduction in growth and yield varies between cultivars and salt concentrations of the medium [10].The recently developed cultivars form a much diversed genetic base and may therefore possess a wider range of salts stress tolerance.Keeping in view the above facts, this study was planned to see the growth and yield response of Inqalab wheat variety to salts (MgCl 2 + CaCl 2 + Na 2 SO 4 ) stress.

Materials and Methods
In order to assess the effect of salts stress on the growth and yield of wheat variety Inqabab, a pot experiment was conducted in the wire-house of the Department of Soil Science, Sindh Agriculture University Tando Jam.The following methodology was adopted.

Experimental Design
Fertile soil (plough layer) was collected from the arable land of latif Experimental Farm of Sindh Agriculture University, Tando Jam.The soil was air dried ground and passed through 4 mm garden sieve.The air dried soil was placed in plastic containers with drainage holes in bottom.The 9 kg pots were arranged on wooden benches in RCBD with three replications.

Seed Sowing, Fertilizer and Irrigation
Seeds of wheat variety Inqalab were at 4 cm plant to plant distance.Few days after emergence, 7 seedlings were allowed to grow in each pot up to maturity.In order to reduce losses by evapotranspiration, the pots were regularly irrigated by normal irrigation water.The recommended does of NPK was applied in the form of NPK (10:23:15) and urea (46%N) to each pot.Nitrogen was applied at the rate 136 kg N ha −1 in the form of NPK and urea in three splits, first at the time of sowing, second at the 1 st irrigation and the remaining at the 2 nd irrigation.Phosphorus and K were applied at the rate 67 kg 2 5 P O − ha −1 and 44 kg K 2 O ha −1 in the form of NPK at the time of sowing.

Preparation of Saline Soil
Different saline soil treatments were prepared artificially by mixing different salts.The quantity of different salts (MgCl 2 , CaCl 2 and Na 2 SO 4 ) required for the preparation of saline soil treatments was calculated using the method described by Rowell [11].The salinity levels developed for the experiment were:

Plant Analysis 2.5.1. Flag Leaf Sampling, Sap Extraction and Chemical Analysis
The flag leaf of three plants from each replication of all the treatments was detached, placed in Eppendorf tubes and stored in a freezer at −10˚C.The lamina of the flag leaves were removed and the sap was extracted and analyzed for Na + , K + using the method of Gorham [12].K + /Na + ratio was also determined by using the values of K + and Na + (Table 1).

Preparation of Straw and Grain Samples for Chemical Analysis
Straw and grain samples from all the replications of each treatment were prepared for analysis of Na + , K + , Ca 2+ and Mag 2+ .

Soil Analysis
The soil samples were collected before sowing from each treatment.Samples were prepared and analyzed for soil texture, pH, ECe (dS•m −1 ), O.M%, cations (Na + , K + , Ca 2+ and Mg 2+ ) and anions ( CO − , 3 HCO − and Cl − ), Soil samples were also collected after harvest of the crop for the analysis of above properties with the exception of OM% and soil texture (Table 2).

Calculations
Sodium adsorption ratio (SAR), exchangeable sodium ratio (ESR) and exchangeable sodium percentage (ESP) were calculated using the following formula suggested by Rowell [11].

Statistical Analysis
All plant data were analysed by performing ONEWAY-ANOVA using Minitab-12 statistical package.Standard Error for Different between Means (S.E.D) was calculated using the following formula: SED = (2EMS/n) 1 /2Least Significant Different (LS.D.) = S.E.D × edf t value at 5% probability level.

Soil Properties
Physico-chemical properties of soil before sowing and after harvesting of wheat crop   [17] are summarized in Table 3 and Table 4.

Plant Height (cm) at Flag Leaf Stage
The effect of salts stress on plant height is shown in Table 4 plant height recorded at flag leaf stage was significantly (P < 0.05 (decreased by increasing salinity.Plants grown in all salt treatments were significantly (P < 0.05) shorter than in the control soil treatment.Increasing salinity decreased the plant height.There was larger decrease in plant height at high salinity (EC 10 dS•m −1 ) levels.

Spike Length (cm)
The effect of salts stress on spike length is shown in Table 5 the plants grown in saline

Number of Spikelets Spike −1
The effect of salts stress on number of spikelets spike −1 is shown in Table 6.The number of spikelets spike −1 was significantly (P < 0.05) decreased by increasing salinity level The Plants grown in saline soil treatments had significantly lower number of spikelets spike −1 than the plants grown in the control soil treatment.Increasing salinity had decreasing effect on the number of spikelets spike −1 .The larger decrease in number of spikelets spike −1 was recorde on the plants grown at high EC (EC 10 dS•m −1 ) than at low (EC 6 dS•m −1 ) and medium EC (EC 8 dS•m −1 ) levels.

Straw Yield (Mg•Plant
The effect of salts on straw yield is shown in Table 7. Increasing salts stress significantly (P < 0.05) decreased the straw yield of wheat.The plants grown in saline soil treatments  produced significantly lower straw yield than in the control.Increasing salinity decreased the straw yield.The decrease in straw yield was greater at high EC (EC 10 dS•m −1 ) than at low (EC 6 dS•m −1 ) and medium EC (EC 8 dS•m −1 ) levels.

Grain Yield (Mg•Plant
The effect of salts stress on grain yield is shown in Table 8.The results revealed that grain yield (mg•plant −1 ) decreased significantly (P < 0.05) with increasing salts concentration.The plants grown in salt treatments had significantly lower grain yield than in the control soil treatment.Increasing salinity also decreased grain yield per plant.

1000 Grain Weight (g)
The effect of salts stress on 1000 grain weight is shown in Table 9.The results revealed that 1000 grain weight decreased significantly (P < 0.05) with the progressive increase in salts stress.The plants grown in saline soil treatments had significantly lighter grains than in the plants grown in the control soil treatment.The effect of increasing salinity on 1000-  grain weight was decreasing.These grain were significantly lighter in weight at low (EC 6 dS•m −1 ), medium (EC 8 dS•m −1 ) and very high at high salinity (EC 10 dS•m −1 ) levels.

Na + , K + , and K + /Na + Ratio in Flag Leaf Sap of Wheat
The effect of salts stress on Na + , K + , and K + /Na + ratio in flag leaf sap of wheat is presented in Tables 10-12.The effect of increasing soil salinity was to increase Na + and decrease K + concentration in the flag leaf sap.This was resulted in lower K + /Na + ratio.
The increase in Na + and decrease in K + were more marked in the flag leaf sap of the plants grown in high salinity treatment than in the control and other sol treatments.

Na + , K + , Cl − and K + / Na + Ratio in Grains of Wheat
The effect of salts mixture on ion concentration in the grains of wheat is shown in Tables 13-16.Salinity significantly increased Cl − and Na + but decreased K + and K + / Na + ratio contents in the grains at all salinity levels.Plants grown at moderate and high salinity levels had significantly higher Cl − and Na + but lower K + /Na + ratio than the plants grown at the control and low salinity level.and decreased the concentration of K + and K + /Na + ratio in the straw at all levels.At high salinity level plants accumulated more Na + and Cl − but less K + and hence they ex habited lower K + /Na + in their straw.

Ca 2+ and Mg 2+ Content in Grains and Wheat Straw
The effect of salts stress on Ca 2+ and Mg 2+ contents in grains and straw of wheat are shown in the Tables 21-24.The results indicated that with the increasing concentration of soluble salts in soil (Table 1, Table 2) the concentration of Ca 2 and Mg 2+ increased both in grains and straw of wheat.Plants in high salinity treatments accumulated more Ca 2+ and Mg 2+ than in other soil treatments.
The soil used in this experiment was sandy clay with 37.5% clay and 0.95% organic matter.When this soil was treated with salts it showed properties typical to those of saline soils of Sindh (Ghafoor, 2004).The results obtained in this experiment showed that salinity had adverse effects on almost all growth and yield parameters.The effects of high salinity on soot height (Table 3), spike length (Table 4), number of spilelets spike −1 (Table 5), straw yield (Table 6), grain yield (Table 7) and 1000 grain weight (   [21] have also pointed out that the yield of wheat crop decreased significantly with increasing salinity levels.The decrease in grain yield under highly saline soil treatments was due to the fewer tillers, lighter grains.It has also been reported by others workers  [20] that decreased tillering is the main cause for lower crop yield in salt-affected soils of arid and semi arid regions. The greater effects of salinity on plants were associated with larger effects on ions (Tables 9-23).As was expected, the effects of salinity on plants was to increase Na + , Cl − , Ca 2+ and Mg 2+ and decrease K + and K + /Na + ratio compared to control plants.The increase in Na + , Cl − , Ca 2+ and Mg 2+ contents may be attributed to the increase amount of sodium, calcium and magnesium in soil solution due to the addition of salts (MgCl 2 + CaCl 2 + Na 2 S0 4 ) when soils were prepared.Similar effects of salinity on wheat plants for ions content have been reported by many workers [22] [23] [24] [25] [26].

Conclusions
A pot experiment was conducted in the wire-house of the department of Soil Science, Sindh Agriculture University Tando Jam to see the effects of salts stress on the growth and yield of wheat (Cv.Inqalab).
The soil used in the experiment was clay loam in texture, alkaline in reaction (pH > 7.0), moderate in organic matter (0.95%).The soil was artificially salinized to different salinity levels i.e.ECe 2.16, 4.0, 6.0, 8.0 and 10.0 dS•m −1 with different salts (MgCl 2 + CaCl 2 + Na 2 SO 4 ).The plant data were subjected to statistical analysis.
Following key points have been observed during this study.
1) Increasing salinity increased the ECe, Na + Ca 2+ , Mg 2+ and Cl − content and decreased the K + , SAR and ESP values in the soil.
2) Increasing salinity significantly decreased plant height, spike length, number of spikelets Spike −1 , 1000 grain weight, and straw and grain yields plant −1 .Increasing salinity significantly increased Na + concentration but decreased K + concentration and K + /Na + ratio in the flag leaf sap.
3) Increasing salinity increased Na + , Ca 2+ , Mg 2+ and Cl − content while decreased K + and K + /Na + ratio in straw and grains.
It was concluded from the present study that salts stress (MgCl 2 + CaCl 2 + Na 2 SO 4 ) adversely affects the growth and yield of cultivar Inqalab.Due to the osmotic and ionic toxicity effects, its yield immediately decreased as salinity level increased.
the chemical properties of soil before sowing and after harvesting of wheat crop showed ECe, pH soluble cations and anions, SAE and ESP values were typical of that an agricultural soils of Sindh.However, when the same soil was treated with different proportions of MgCl 2 , CaCl 2 and Na 2 SO 4 salts that showed an increase in ECe and very small decrease in SAR and ESP.The pH of treated soil was alkaline in reaction before sowing and it decreased slightly in all treatments after harvest of the crop.With increasing concentrations of salts there was rise in Na + , Ca 2+ , Mg 2+ and Cl − in all soil treatments.During the course of the experiment pH and soil salinity in almost all treatments (T2 = 5.91, T4 = 9.2 and T5 = 10.3 dS•m −1 ) decreased slightly possibly due to leaching and uptake of soluble salts by the plants.
soil treatments had significantly (P < 0.05) shorter spikes than the plants grown in the control soil treatment.Increasing salinity significantly (P < 0.05) decreased the length of spikes.These decreases were greater at high salinity (EC 10 dS•m −1 ) level than at low (EC 6 dS•m −1 ) and medium (EC 8 dS•m −1 ) salinity levels.

3. 3 . 3 .
Na + , K + , Cl − and K + /Na + Ratio in Wheat Straw The effects of different salinity levels on ion concentrations in the straw are shown in the Tables 17-20.Salinity significantly (P < 0.05) increased the toxic ions (Na + and Cl − )
[14]paration and Analysis of straw for Na + and K + Acid wet digestion EEL-flame photometer Rowell[11]3 Preparation and Analysis of straw and grain samples for Cl − Dry ash method Muffle Furnace Methods Manuals Soils[14]

Table 3 .
Physicochemical properties of soil before sowing.

Table 8
) were greater than low and medium salinity.The plants grown at high salinity level were 20.56% smaller in height, produced 23.73% smaller spikes, showed 20.56% fewer spikelets.High salinity