Effect of Potassium Sources and Rates in Relation to Nitrogen Fertilization on Barley Yield and Some Nutrient Elements Content Under Salt-affected Soil Conditions

INTRODUCTION

Barley (Hordeum vulgare L.) is one of the most important, economically valuable and widely used cereal crop, which belongs to the family Gramineae. The crop is used for preparing traditional food and beverage consumptions (Araya, 2011; Kemelew and Alemayehu, 2011). The production of barley in Egypt can be increased either by increasing more area under cultivation or by increasing yield per unit area. Currently, it is nearly impossible to increase area for barley crop due to competition with other crops and because of restricted supply of irrigation water etc.

Salinity is the major abiotic stress that reduces plant growth and crop productivity worldwide. It is resulting from excessive salinity led to reduction in photosynthesis, transpiration and other biochemical processes associated with plant growth, development and crop productivity (Tiwari et al., 2010). Furthermore, abiotic stress lead to oxidative stress in the plant cell resulting in a higher leakage of electrons towards O₂ during photosynthetic and respiratory processes which is leading to enhancement of reactive oxygen species generation (Asada., 2006).

Optimal rates of fertilizer application to salt-affected soils partially alleviate the adverse effects of salinity on photosynthesis and photosynthesis-related parameters and yield and yield components through mitigating the nutrient demands of salt-stressed plants (Sultana et al., 2001). The proper use of N fertilizer in all soil is important, but particularly so in saline soils, where N may minimize the adverse effects of salinity on plant growth and yield (Abdelgadir et al., 2005) depending on plant species, salinity level, or environmental conditions (Grattan and Grieve, 1999).Increased soil salinity decreased nitrogen uptake by inhibition of nitrate ion (Kafkafi et al. 1982). Elgharably et al. (2010) showed that N applied at 100kg ha^-1 can alleviate salinity stress on wheat.

Potassium is the third most essential nutrient element next to N and P for plant nutrition. It plays significant roles in the physiological processes of protein formation, transportation of water, nutrients and carbohydrates, photosynthesis, N utilization, stimulation of early growth and in insect and disease resistance (Lakudzala, 2013). It also promotes the transportation of assimilates, control of stomata opening, enzyme activation in plants especially those responsible for energy transfer and formation of sugars, starch and protein as well as promotion of microbial activities and the nutrition and health of man and livestock (Yawson et al., 2011).Previous studies revealed that supplying low levels of KNO₃ could alleviate the NaCl induced decreases in seed germination of certain grass species (Neid and Biesboer, 2005). As the K⁺ is involved in multiple plant activations, the K⁺/Na⁺ ratio has been proposed as an effective indicator for salinity tolerance in wheat (Zheng et al., 2008).

The benefits of silicon on the growth of a wide variety of agronomic and horticultural crops are vast and continue to increase. The beneficial effects of silicon become more evident when plants are in stressed (biotic or abiotic stress) environments than in those growing under optimal conditions (Li et al., 2007). The beneficial effects of silicon on plant growth and development are based on several mechanisms, which include the formation of a protective outer layer composed of silica deposits, the reactivity of the absorbed silicon with the heavy metals ions and other compounds within plants and the metabolic functions of silicon in stressed plant

The negative effects of salt stress on barley can be alleviated by Si and K fertilization through alleviation the carbohydrate, protein, phenolic compounds and total antioxidant activity in addition to the change in K⁺/Na⁺ ratio (Khalaf and Salih, 2014). Therefore, this study was carried out to identify the effective potassium sulphate or potassium silicate as K sources and rates of potassium application for optimum yield and plant tissue N, P, K and Si contents of barley grown on salt-affected soil in relation to nitrogen fertilization.

MATERIALS AND METHODS

Field experiment was carried out at the Experimental Resrach Station (Abis), Faculty of Agriculture, Saba Basha, Alexandria University, during the growth season of 2014/2015 using barley (Hordeum vulgare L. cv. Giza 123). Three factors were conducted in a split-split plot design with three replicates. The potassium sources (K₂SiO₄,45%K and K₂SO₄, 44%K) were applied to the main plots, potassium doses (0, 15, 30 and 45 kg K/fed.) were assigned to the sub-plots and the nitrogen doses (0, 40, 60 and 80 kg N/fed as Urea, 46%N) were assigned randomly to the sub-sub-plots. The area of each plot was 10.50 m² (3.5 m x 3 m). The usual recommended dose of phosphorus (45 kg P₂O₅/fed as Triple superphosphate) was applied to the soil before planting. The recommended cultural practices for barley were carried out the recommendation devoted to the experimental area. The main physical and chemical properties of the experimental soil are presented in Table (1). The analysis of soil was carried out according to the methods outlined by Black (1965). Available Si was determined in soil using the method of Fox et al. (1967). The soil type is alluvial which was a naturally salt-affect soil with electrical conductivity (EC) 4.8 dS/m in (1:1, soil water extract) and SAR value of 15.8

At plant harvest, five competitive plants were randomly taken, from the center of two ridges of each plot, to determine grain yield. Also, plant samples (leaves), from the middle ridge of each plot were collected. The plant samples were first washed by tap water then distilled water, plotted to remove excess adhered water then were dried in an oven at 65C^◦ for 48 hrs and ground using stainless steel mill to pass 40 mesh screen and wet-digested with H₂SO₄- H₂O₂ (Lowther, 1980) The following determinations were carried out in the digested solution: potassium by flame photometer (Jackson, 1973), total N by microkjeldehl method (Jackson, 1973) and phosphorus by  the vanadomolybidic method(Jackson,1973).Also, plant samples were digested and silicon was determined using colorimetric amino molybdate blue method according to the method described by  Elliot and Synder (1991).

Table (1). The main physical and chemical properties of the experimental soil

*measured in 1:1 soil water suspension    **measured in 1:1 soil water extract

The obtained data were statistically analyzed for ANOVA and L.S.D. The values were calculated to test the differences between the studied treatments according to Steel and Torrie (1982). Also, multiple regression equations were calculated according to CoHort Sofware(1995).

RESULTS AND DISCUSSION

 Grain yield

 Tables (2 and 3) reveal that grain yield (ton/fed) was significantly affected by application of potassium, nitrogen and by the first and second interactions except the interaction between potassium source and potassium rates. Table 3 also shows the mean effect of potassium rates on.in salts affected soils sources, levels and nitrogen levels on yield and yield attributtes n on growth, yield and chemical comp grain yield (ton /fed) of barley plants grown in salt-affected soil. The results revealed that increasing potassium rates from 0 to 45 kg /fed significantly and progressively increased the grain yield as compared with the control treatment.

The main effect of potassium application showed relative increases in grain yield by 26.47, 54.44 and 85.54% at rates of 15, 30 and 45 kg K /fed, respectively as compared with control. However, this pattern of response occurred particularly in the two sources of potassium. The highest grain yield (ton/fed) was obtained due to potassium sulfate which followed by potassium silicate. As shown in Table 3, no significant differences were observed between potassium sulphate and potassium silicate. Addition of K-fertilizer improved the growth of barley plants grown in salt-affected soils and gave a beneficial effect on the grain yield. Similar results were found by Shalaby et al. (1991), Sharma and Kamari (1996) and Sheriff et al. (1998).The insignificant difference between the grain yield of the two potassium sources may be due to the high amount of available silicon (22.6 mg/kg soil) in the experimental soil. According to Fox et al.(1967).

Table (2). Effect of potassium source, potassium rates and nitrogen rates on grain yield, N, P, K and Si concentrations in leaves of barley plants.

Table (3) also revealed that the grain yield had increased with increasing nitrogen rates up to 80 kg N /fed. These increases reflect the importance of N application in salt-affected soils. The highest grain yield (ton/fed) was found at 80 kg N /fed compared with the control. These results are in agreement with those obtained by Mugahed and Muhammed (2001),  Abd Alla(2004) , El Kadi et al. (2007) and Zeidan (2007). Alam et al. (2007) studied the influence of nitrogen fertilizer on yield and yield compositions of barley (Hordum vulgare.l). They found that most of the yield and yield compositions were significantly the highest at N rate of 120 kg N /fed. Also, Safina (2010), Shafi et al. (2011), Mousavi et al. (2012) and Alazmani (2014) reported that the grain yield was significantly affected by application nitrogen rates. The interaction between potassium sources and nitrogen rates had significant effect on the grain yield (Fig. 1). The highest grain yield was obtained through potassium silicate with 80 kg N /fed. Table (4) shows that the lowest value of grain yield was obtained through potassium silicate without nitrogen. The interaction between potassium rates and nitrogen rates had significant effect on grain yield of barley plants (Table 2 and Fig. 2).

Table (3).Mean effect of potassium source, potassium rates and nitrogen rates on yield and N, P, K and Si concentrations in leaves of barley plants.

The highest value of grain yield was obtained as result of application of 45 kg K/fed with 80 kg N /fed. The second order interaction (potassium sources, potassium rates and nitrogen rates) had significant effect on grain yield. Table (2) shows that the highest value of grain yield was obtained through potassium silicate of 45 kg K/fed with 80 kg N /fed, while the lowest grain yield was obtained through potassium sulfate without nitrogen applications.

Fig. (1). The interaction effect between potassium sources and nitrogen

              rates on barely grain yield     

Fig (2). The interaction effect between potassium rates and nitrogen rates on barely grain yield

The grain yield (ton/fed) of barley (Y) using potassium silicate was regressed with potassium rates (X₁) and nitrogen rates(X₂). The regression equation for this relationship was:

Y = 0.701 + 0.020 X₁ + 0.0073 X₂         R² = 0.942      P< 0.01

Thus, the efficiency of potassium rates and nitrogen rates would be equal to (0.020:0.0073) or (1:0.36). Also, the grain yield (Y) using potassium sulphate was also regressed against the potassium rates (X₁) and nitrogen rates (X₂). The grain yield was positively correlated with the two variables (R² =0.983). The regression equation for this relationship was:

Y = 0.816 + 0.020 X₁ + 0.0055 X₂       R² = 0. 983          P< 0.01

The comparison of the slopes of each variable in the equation (0.02:0.0055) gives a quantitative estimate for efficiency of one variable to the other. Thus efficiency of potassium rates and nitrogen rates would be equal to 0.02: 0.005 or 1:0.27.                                                 

Elemental composition

 Table (2) shows that N, P and K concentrations in plant leaves were significantly affected by potassium sources, potassium rates, nitrogen rates and all the interactions except the interaction of potassium sources and potassium rates on P and the effect of potassium sources on N and P contents. Also, a significant effect of potassium source, K-rates, N-rates and the interaction between K-source and K-rates on Si concentration was observed. Table (3) reveals that regardless of the effect of the used salt-affected soil, increasing potassium rate from 0 to 45 kg K /fed progressively and significantly increased N, P, K and Si concentrations in leaves of barley plants. The main effect of N, P,  K and Si concentrations in leaves of barley plants were 9.25, 19.45 and 25.03 % for N, 7.83, 12.92 and 19.88 % for K, 17.29, 50.93 and 81.31 % for P and  4.79, 9.57 and 24.47% for Si at harvest at 15, 30 and 45 kg K /fed, respectively as compared with the control. These data also reveal that the highest values of N, K and Si concentrations at harvest was significantly higher under potassium silicate followed by potassium sulfate. Moreover, P concentration in leaves was obtained due to potassium sulfate application rather than K-Silicate application.

Table (4). The interaction between potassium sources and potassium Levels on N, K and Si concentrations in barely leaves

Table (5). The interaction effect between potassium sources and nitrogen rates on N, P and K concentration in barely leaves

The increases in phosphorus concentration in leaves of barley plants grown on this salt-affected soil may be attributed to increasing needs of plants to phosphorus for several biological and physiological activities as stated by Maas and Hoffman (1997). It may be also due to increasing rate of photosynthesis as depicted that the rate of photosynthesis becomes enhanced by the application of potassium in stressed environment (Ali et al., 1999). Ashok et al. (2009) revealed a significant increase in grain and straw yield and uptake of N, P, K and Mn by wheat with the application of K and Mn.

Table (6).The interaction effect between potassium rates and  nitrogen rates on N, P, K concentrations in barley leaves

It has been reported that potassium is an essential plant nutrient and the growth of plant has increased in the presence of potassium fertilizer and there was more absorption of nitrogen by the plant as well as by the use of fertilizer (Tzortzakis, 2009) and Ashraf et al. (2013). Potassium is of macronutrients and its availability controls many biochemical and physiological processes in plants (Wang et al., 2013).  The presence of potassium plays essential roles in various enzyme activation, photosynthesis, protein synthesis, osmoregulation, energy transfer, stomatal movement, cation-anion balance and stress resistance (Wang et al., 2013). Potassium application as potassium sulfate increased nitrogen concentration in plant to some extent (Gupta and Haung, 2014).

Table (3) clearly showed significant differences between nitrogen concentrations in leaves at harvest. Means of nitrogen concentration increases were 6.46, 8.45 and 14.02% at harvest, phosphorus increases were 4.63, 18.92 and 30.50%, potassium increases were 9.0, 18.06 and 26.87% and silicon increases were 1.24, 2.97 and 4.25 % at 40, 60 and 80 kg N /fed, respectively, as compared with the control treatment.

Table (4) showed that the effect of interaction between potassium sources and potassium rates on N, K and Si concentration at harvest were significant. The highest values of   N, K and Si concentrations in leaves of plants were 12.00, 26.18 and 2.59 g/kg D.W, respectively, which are obtained under potassium silicate at rate of 45 kg K/ fed. However, the lowest N, K and Si concentrations in leaves of barley plants were 9.45, 20.1 and 1.88 g/kg D.W.), respectively, which was recorded to without potassium treatment.

The effect of interaction between potassium sources and nitrogen rates on N, P and K concentration in leaves of barley plants at harvest is presented in Table (5). Results revealed that this interaction had significant effect on N, P and K concentrations. The highest N, P and K concentrations were obtained under potassium silicate with 80 kg N /fed with value of 1.15, 0.35 and 2.66% respectively, while the lowest values of potassium concentration, were 0.99, 0.25 and 1.98% under the control treatment.

Table (6) showed that the effect of interaction between potassium rates and nitrogen rates on N, P and K concentrations in leaves of barley plants was significant. It is clear that the greatest potassium concentration in leaves of barley plants at harvest was recorded at 45 kg K /fed with 80 kg N /fed, (5.616, 1.218 and 2.81%, respectively). On the other hand, the lowest N, P and K concentrations in leaves of barley plants were recorded in treatment without addition of potassium and nitrogen (0.849, 0.443 and 1.775%, respectively.)The second order interaction, potassium sources, potassium rates and nitrogen rates had significant effect on N, P and K concentrations (Table 6). The highest value of N, P and K concentration in plant leaves at harvest were obtained through potassium silicate under treatment of 45 kg K /fed with 80 kg N /fed (1.218, 0.475 and 2.938%, respectively). The lowest values of N, P and K concentration (0.847, 0.194 and 1.762 % respectively) were obtained from control treatment.

The grain yield of barley increased by about 15.679% at K rates of 45kg/Fed and 80 kg N/Fed as compared with the control plants. The concentrations of nitrogen, phosphorus, potassium and silicon were significantly affected by potassium (the two sources) and nitrogen applications while that of nitrogen was not influenced by both the main effects and their interaction Table (2). In cases, a highly pronounced improvement in yield was evident under the saline soil conditions. This result contradicts other report that indicated significant promotion of plant growth at lower salinities in some halophytes, but inhibition of growth at higher salinities (Khan et al., 2000). Without potassium or nitrogen application, growth and productivity of barley plants were relatively lower as grown in saline soil. However, the trend was reversed with potassium application since response of barley to potassium was highly notable Table (2 and 3). The accumulation of K in salt stressed plants might have allowed osmotic adjustment to occur. The concentration of potassium ion in barley plants grown on saline soil increased considerably with potassium application (Tables 1 and 2), which might have contributed to better osmotic adjustment that can be explained by the higher K in leaves and better yield recorded (Table 3 ).

It is known that potassium represents the main cation in plant cells and is an important component of cell osmotic potential, which is involved in almost all physiological and biochemical processes in plants exposed to salt stress condition (Al-Karaki, 1997). The high soil salinity reduced absorption of nitrogen (Wahid et al., (2004) phosphorus (Kaya et al.,2001) and caused imbalance of mineral nutrients that resulted in a reduction or inhibition of plant growth. On the other hand, the results obtained in this experiment indicated better pattern of improvement in growth of barley under the saline soil with increasing rates of potassium application.

The agricultural benefits of silicon amendments on a soil ecosystem are well documented. Thus, Si has been shown to mitigate adverse effects of climate (Ohyama, 1985), water and mineral deficiency (Ma et al., 2001) and salinity (Matoh et al., 1986). Applications of potassium silicate can increase the quantity of mobile phosphate in the soil (O’Reilly and Sims, 1995). Application of Si-rich material has the potential to decrease P leaching by 40-70%, while retaining P in a plant-available form (Datnoff et al., 2001). In this work, no significant difference between the grain yield of potassium sulphate or that of potassium silicate because of the high amount of available silicon in the original soil than the critical value of silicon (Table 1) according to Fox et al.(1967).

Conclusion

The results of this study signify the role of K⁺ in regulating the salt stress response of barley, and suggest that potassium sulphate or potassium silicate acts as a potential growth enhancer. Potassium sulphate or potassium silicate provoked reduction in oxidative stress in plants subjected to salt stresses especially with the proper nitrogen fertilization. potassium sulphate or potassium silicate can help reduce the adverse effects of salt and may increase the barley growth, enhance antioxidant activity and K⁺ content in stressed plants and thus, protecting membrane against oxidative stress. The results obtained in this study not only confirmed, but also indicated interesting results in terms of the significant and positive crop response to potassium and nitrogen fertilization under saline soil condition, which of course demands further investigations on the pattern of crop response in relation to intensity of stress conditions.