Effect of nitrogen and sulphur on growth, yield and chemical composition of maize grown under saline soil conditions

Salinity is the major problem in agricultural land. It is a major factor reducing plant growth (Batool et al., 2014). The direct effect of salts on plant growth have three broad categories: (i) increasing the osmotic potential of the soil solution that reduces plant available water, (ii) a deterioration in the physical structure of the soil such that water permeability and soil aeration are diminished, and (iii) increase in the concentration of certain ions that have an inhibitory effect on plant metabolism(Nishma et al., 2014).  Excess salt may affect plant growth either through osmotic inhibition of water uptake by roots or specific ion effects, which may cause direct toxicity (Saqib et al., 2012 and Abbas and Akladious, 2013).

Variation in nitrogen availability can affect plant development and grain production in maize. Maize grain yield is linked to both higher nitrogen uptake and higher ability to utilize nitrogen accumulated in the plant and yield pro­duction (Luque et al., 2006). The beneficial effects of nitrogen on crop production are well documented. However, nitrogen mining by crops for optimum productivity widely varies on account of different agro-climates, soils, plant cultivars, management practices and other factors. Maize responds more favorably to plant densities because of higher leaf area index at silking, which results in more interception of photo synthetically active radiation and have higher radiation use efficiency during grain filling. The yield potential of maize can be realized only when if it is grown with adequate fertilization and optimum plant population (Singh and Singh, 2006).

Nitrogen fertilization plays significant role in improving soil fertility and increasing crop productivity (Ogola et al., 2002; Cheema et al., 2010 and Karasu, 2012). Likewise, sulfur is recognized as the fourth major nutrient after N, P and K. On an average maize crop absorbs as much S as it absorbs P. When S is deficient in soil, full yield potential of the crop cannot be realized regardless of other nutrients even under good crop husbandry practices. Kaya et al. (2009) showed that applications of elemental S and S-containing waste resulted in a decrease of soil pH and general increase in nutrient concentrations for both plants and in residual available nutrient concentration in the experimental soils. Soils have become deficient in S due to cultivation of high yielding varieties, use of high grade S free fertilizers and lack of industrial activity (Scherer, 2009). Sulfur fertilizers are known to enhance crop yield and uptake of macronutrients especially nitrogen (Islam et al., 2012). Chaghazardi et al. (2014) showed that the yield, soil pH, and micronutrients, including copper, iron, and zinc were significantly affected by sulfur and organic manure levels and their interaction. Dhage et al. (2014) reported that available S in the soil increased with increasing levels of applied sulphur. Grain yield per hectare can be increased significantly by application of nitrogen and sulphur (Rasheed et al., 2003).

This study suggested that utilization of proper application of nitrogen and sulphur to the maize might be a promising approach to obtain higher grain yield on salt affected soil. Also, the chemical composition of maize plants was examined. The main objectives of the present work were to evaluate the effect of nitrogen and sulphur on yield and chemical composition of maize grown under saline soil condition.

Materials and Methods

Field experiment was carried out at the Experimental Research Station, Faculty of agriculture, Saba Basha, Alexandria University, Abees region during May to September, 2015. The Physical and Chemical Properties of the experimental soil are presented in Table 1.

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

      *(1:2) Soil: water suspension       **(1:1) Soil: water extract

The used plant was corn (Zea mays,L) Individual hybrid K 130 cultivar. The area of experimental plot was 10.50 m² (3.5 m length x 3 m width), with 5 ridges 60 cm apart and 25 cm between hills. The experiment included 20 treatments which were the combination of four nitrogen rates (0, 30, 60 and 90 kg N/fed) as urea, and five sulphur rates (0, 50, 100, 200 and 300 kg S/fed). The recommended dose of phosphorus (36 kg P₂O₅) was applied as superphosphate (15% P₂O₅) to the soil in a single dose during land preparation. Also, potassium as potassium sulphate (48% K₂O) was applied (9 kg K₂O/fed) to the soil in three doses. The first dose was on Jun. 21, 2015 and the second dose was on August 11, 2015 and the third dose was on 29 August 2015. Four nitrogen rates (0, 30, 60 and 90 kg N/fed.) as urea (46.5%N) were used. The Nitrogen fertilizer was added in two equal doses.  The first dose after three weeks from sowing and the second dose after two weeks from the first dose. Five sulphur rates (0, 50, 100,200 and 300 kg S/fed) as elemental sulphur were applied to the soil in a single dose during land preparation.

At maturity, plants were harvested and the grain yield (ton/fed) of corn was recorded. Soil samples were collected, air dried, ground to pass through a 2 mm sieve and soil pH was determined in 1:1 (w/v) soil to water suspension using glass electrode (Jackson, 1973). The available sulphur was determined using the method of turbidmetrically with barium chloride as described by (Jackson, 1973). For available nitrogen, the soil samples were extracted by 2 M KCl, and available N was determined colorimetrically by Nesselers method (Chapman and Pratt, 1961). Available phosphorus was extracted with 0.5 M NaHCO3 solution adjusted to pH 8.5 according to Olsen et al., (1954). The extraction was done by ammonium acetate (1 N of pH 7.0) and potassium was measured according to (Jackson, 1973) by Jenway PFP-7 flame photometer.

Samples of plant leaves were collected, washed with tap water then by distilled water, oven dried at 65°C for 48 hours and the oven-dried weight was recorded. The oven-dried plant material was ground using stainless steel mill. A portion of 0.5g powdery oven-dried plant material was wet-digested with H₂SO₄-H₂O₂ (Lother,1980) and the following determinations were carried out in the digested solution. Potassium was measured flame photometer, total phosphorus were determined clorimetrically by vanadomolby date using spectrophotometer, (Chapman and Pratt, 1961) and total nitrogen was determined colorimetrically by Nesselers method (Chapman and Pratt,  1961) and total suphur wet digested using 0.5g powdery oven-dried plant material with HNO₃- H₂O₂ (Zheljazkov and Nielson, 1996).

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, simple regressing and quadratic polynomial calculations were carried out using CoHort software (1995).

Results and Discussion

Grain yield of maize

Tables (2 and 3) indicated that S application has significant effect on the grain yield. The grain yield was increased by 22.77, 48.38, 75.35 and 104.74% with S application at 50, 100, 200 and 300 kg /fed, respectively relative to the control (without S). The increase of yield at higher S rates may be due to increasing the efficiency of nitrogen and other elements in soil.

Nitrogen rate significantly affected the grain yield (Table 2) because the highest grain yield was obtained with application of 90 kg N /fed. and accounted as 4.711 ton /fed. This increase corresponding to 30.48% over the control treatment.

Table (2). The grain yield of maize plant as influenced by sulphur and nitrogen application rates

Table (3). Mean effects of sulphur and nitrogen application rates on grain yield of maize plants

Jayakumar et al. (2008) concluded that with increasing rates of applied nitrogen, the grain yield has increased up to a certain level. Hammed et al. (2011) demonstrated that without application of N, grain yield and quality was greatly reduced. Also, the interaction between sulphur and nitrogen rates significantly affected the grain yield (Table 2 and Fig 1). The highest values of grain yield were produced due to application of 300 kg S /fed with 90 kg N /fed. Other reports confirmed that the grain yield per hectare can be increased significantly by the application of both nitrogen and sulphur (Rasheed et al., 2004).

Fig. (1). The relation between sulphur rates and nitrogen rates on grain Yield of maize plants

Desta (2015) reported that the maximum grain yield was recorded in plots treated with 90 kg N ha^-1 and in plots treated with 15 kg S ha^-1. This might be probably due to the important role of N and S for growth and development which led to higher photosynthetic activities that resulted in the production of enough assimilate for subsequent translocation for higher yield. Sulphur and nitrogen relationships were established in terms of dry matter and yield for several crops in many studies (Ahmed et al., 1998; Jamal et al., 2005; 2006, 2010). The utilization of nitrogen depends in a high degree on the balancing of nitrogen dose with the dose of sulphur (Wyszkowski 2000 and 2001; Grzebisz and Gaj, 2007).

The grain yield of maize (Y) was regressed against the sulphur rate (X₁) and nitrogen rate (X₂). The grain yield of maize was positively correlated with the two variables (R² = 0.956**). The regression equation for this relationship was:

                   y = 0.4014 + 0.0031x₁ + 0.0121x₂ 

                      R² = 0.956 (P < 0.01)

Thus, the efficiency of S rate: N rate would be equal to 0.0031: 0.0121 or 1: 4.This equation can be used to predict sulphur application rate and nitrogen application rate to attain the optimum grain yield of maize plants when growth under soil conditions. 

Elemental composition

Elemental composition of maize plants as affected by sulphur application and nitrogen rates are presented in Table (4). Table 5 shows the main effects of sulphur application and nitrogen rates. Increasing sulphur application from zero to 300 kg S /fed showed significant effect on leaves N, K, P and S contents. Nitrogen, K, P and S contents were relatively increased to 10.95, 25.51, 39.15 and 56.77% for N; 27.74, 43.72, 97.08 and 142.86% for K; 12.10, 25.42, 43.25 and 60.71% for P and 12.12, 21.21, 32.07 and 40.40%  for S at  rates of 50, 100, 200, and 300 kg S /fed respectively over the control treatment (without S application).

Sulphur fertilizer application could also increase N, P, K accumulation and plant requirements for sulphur are closely linked to nitrogen availability (Xie et al., 2004). It has been reported that application of sulphur fertilizer significantly increased potassium and sulphur content in the straw of both spring and winter rapeseed (Jankowski et al., 2015).

Table (4). The effects of sulphur and nitrogen rates on N, K, P and S content in leaves of maize plants 

Table (5). Mean effect of sulphur and nitrogen rates on nitrogen concentration in maize plant leaves 

Table (5) showed that N, K, P and S contents are significantly affected by nitrogen rates. Increasing N application rate up to 90 kg N/fed increased N , K, P and S contents in maize plant leaves by about 74.22%, 39.42%, 68.68%, and 51.04%, respectively over the control treatment (without N).

The interaction between S rates and N rates had significant effect on elemental composition (N, P, K and S) as shown in Table 4. The relationship between N contents in leaves andN-applicationrates was expressed by a straight line equation at each soil S level (Table 6). A significant positive relationship was found between N leaf content and N application rates at the five soil S levels. The obtained values of R² were high and the comparison of the slopes of the five equations gives quantitative expression of the efficiency of N at the different levels of S application.

Table (6) shows that at the S rates of 50, 100, 200 and 300 kg S/fed, the efficiency of N increased to 100, 100, 128.60 and 142.86% as compared with the efficiency ofthe control (i.e. at zero kg S/fed), respectively. It could be concluded from these results that the efficiency of N application for increasing N contents was increased as the S soil level was increased.

Table (6). Simple regression equation for relating N content of maize plants with N application for the different rates of S application

                Y = N content (g /kg)

                  X = N application (kg /fed)

Soil pH and Available S

Tables (7and 8) show the pH of the soil cultivated with maize plants as affected by sulphur application and nitrogen levels. Table (8) showed decreasing in pH value of soil as a result of increasing S rate. The highest value of pH was obtained through zero sulphur, while the lowest value of pH was produced through 300 kg S/fed. Also, the pH values were decreased with increasing the levels of applied nitrogen to the soil (Table 8). It is clear that the pH values ranged between 8.04 and 8.01.it is clear that the interaction between sulphur and nitrogen was not significant on pH at 75 days after planting and at harvest (Table 7).

Table (7). The effects of sulphur and nitrogen rates on pH and available S in soil

Table (8). Mean effect of sulphur and nitrogen rates on pH and available S in Soil

Table (7) shows the S-availability in soil cultivated with maize plants as affected by sulphur application rates and nitrogen application rates. The effect of sulphur rates on available S in soil increased with increasing sulphur rates since the highest level was 245.5 mg /kg soil attained at the rate of 300 kg S /fed, while the lowest value 162.7 mg /kg soil was produced without sulphur application. The S-availability ranged between 180.7 and 272.9 mg/kg soil at 75 days after planting and between162.7 and 245.5 mg/kg soil as sulphur rates increased from zero to 300 kg S/fed. (Table 8).

Application of nitrogen rates to the soil indicated significant increase in elemental availability of S as compared to the control treatment (without N) as shown in Table (8). The highest values of elemental S in soil was obtained with 90 kg N/fed, while the lowest values were obtained in the absence of applied N. The interaction between sulphur rates and nitrogen rates had significant effect on elemental S in soil (Table 7). The highest value of elemental S in soil were obtained through application of 300 kg S/fed with 90 kg N/fed, while the lowest elemental S value in soil was obtained through the absence of both sulphur and nitrogen.