Inadequate supply of organic manures and S containing fertilizers have in one hand led to low S content in soil and on the other, depletion of soil fertility creating a serious constraint to higher crop production in Bangladesh. The farmers use in general 102 kg ha1 of nutrients annually against a crop removal of 200 kg (Islam et al., 1994). In addition, a significant amount of the nutrients is being lost every year through leaching from arable land of Bangladesh (Ali, 1994). Soybean (Glycine max L. Merrill) belongs to the family Leguminosae, subfamily Papilionoideae has occupied the top position in term of oil source in the world and has been placed second in respect of use as oil in Bangladesh. Soybean contains about 20-22% edible oil, 42-45% best quality protein, 20.9% carbohydrate and a good amount of other nutrients like calcium, phosphorus, iron, vitamin etc. (Gopalan, 1971). Sulphur, though a major plant nutrient, nobody thought of its application for crop production a few years back. Sulphur may enhance seed formation and protein quality through the synthesis of certain amino-acids such as cystine, cysteine, methionine and also plant hormones and some vitamins (Aulakh and Pasricha, 1988) increase nodulation (Singh and Bansal, 2000), dry matter yield (Babhulkar et al., 2000) and nutrient content (Agrawal et al., 2000) of soybean. An adequate S supply to plants is important because S deficiency can reduce yield and can effect product quality (Morris et al., 1984; Randal and Wrigley, 1986).
In Bangladesh, Zn deficiency is recurrently expanding owing to a general negligence for the use of such vital element in agricultural field. About 1.74 M ha1of land are suspected to be potentially Zn deficient in Bangladesh (Choudhury and Hore, 1989). Zinc plays an important role in many physiological functions of plants. Zinc is involved in the biosynthesis of tryptophane, a precurser of auxin which is essential for cell elongation. Zinc has been found to be essential for normal chlorophyll formation in the plants (Tisdale and Nelson, 1984). Zinc application increased nodulation efficiency and nodule nitrogenase activity (Zhang et al., 1996).
Information in relation to the effect of S and Zn on soybean in Bangladesh soil, is a meagre. Some research have been done under field conditions on the effect of S-Zn combination on wetland rice. But limited works have been performed in non-calcareous dark grey floodplain soils particularly on soybean. Thus, this research work was, therefore, undertaken to evaluate the suitable levels of S and Zn, eventually their influence on nodulation, dry matter yield and nutrient content of soybean.
Materials and Methods
The experimental location was the Horticulture Farm of Bangladesh Agricultural University, Mymensingh having a medium high land with silty loam soil, pH 6.7, 1.71% O.M., 0.09% N, 0.06 me K 100 g1 soil, available Sulphur 8 μg g1and available Zn 1.71 μg g1 soil.
The experiment was laid out in randomized complete block design (RCBD) with 3 replications. Each block was further divided into 25 unit plots for placement of 25 treatment combinations. Thus, the total number of plots under the experimental design were 75. The size of the unit plot was 4x2.5 m2. The spacing between blocks was 1 m and between plots 0.5 m. There were 5 treatments each of S and Zn including a control viz 0, 10, 20, 30 and 50 kg S ha1 and 0, 2.5, 5, 10 and 20 kg Zn ha1, respectively. Sulphur was used as gypsum (CaSO4.2H2O) and zinc as ZnSO4.H2O. In calculating the amount of S, its content in ZnSO4.H2O was reduced from that of gypsum.
The soil of each plot was uniformly fertilized with 175 kg P2O5 ha1 as triple super phosphate (TSP) and 120 kg K2O ha1 as muriate of potash (MP). Fertilizers were applied at the time of final land preparation. Basal doses of N as urea @ 60 kg ha1 was applied in 3 equal splits at final land preparation, 20 and 50 days after sowing (DAS).
Soybean seeds of cv. Shohag (Pb-1) were collected from the Department of Genetics and Plant Breeding, BAU and sown on the 13th December 2001 in line (spacing 30 cm) carefully. Each plot received 75 g (75 kg ha1) seed. Intercultural operations were done as and when needed to keep the crop free from weeds and to protect from various pests and diseases. Dry matter yield was worked out on oven dry-weight basis. Samples for estimating nodulation, dry matter yield and nutrient content of S and Zn on soybean were recorded from 10 randomly selected plants at 30, 45, 60, 90 and 110 days after sowing. The grain and straw samples were digested by di-acid mixture (Page et al., 1982) to determine the nutrient concentration of the crops. Sulphur was determined turbidemetrically following the method of Wolf (1982) and Zn was determined by atomic absorption spectrophotometer directly (Lindsay and Norvell, 1979). Data were analyzed following analysis of variance technique with the computer package programme MSTAT and mean differences were adjudged by least significant difference test (LSD) (Gomez and Gomez, 1984).
Results and Discussion
Main root nodules plant1: The results showed that the number of main root nodules plant1 was not significantly influenced neither by S nor by Zn application at all the growth stages (Table 1). The maximum number of main root nodules plant1 was obtained from S30 (2.92) and Zn20 (3.52) and the minimum from control (1.52 and 0.94, respectively). The number of nodules increased with the advancement of growth stages up to 90 DAS and then decreased. As the plants grew older, the number of nodules increased but at later stages of growth the increase was at slower rate.
The interaction effects of S and Zn were also not significant in respect of main root nodules number plant1 (Table 1). Maximum main root nodules plant1 was recorded at 90 DAS in S10Zn2.5 (6.67) treatment combination. There was no nodulation in control until 90 DAS (Table 1).
Branch root nodules plant1: The highest number of branch root nodules plant1 (3.43) was obtained from S30 treatment at 110 DAS which was statistically identical with all other treatments (Table 1), the second highest number was found in S20 treatment. It was noticed that branch root nodules were much higher than that of main root at all the growth stages which might be due to higher number of branch roots compared to single main root.
The interaction effects of S and Zn were not significant in respect of branch root nodules plant1 (Table 1). Maximum number of branch root nodules plant1 (7.67) was recorded at 90 DAS in S10Zn2.5 treatment combination and minimum (0.33) in S30Zn10 at 110 DAS.
Total nodules plant1: At 90 DAS the number of total nodules plant1 ranged from 2.996.22 (Table 1). The highest number of total nodules were found in S30 at 90 DAS and the lowest from S0 at 60 DAS. Total number of nodules increased up to 90 DAS and then decreased at 110 DAS in both the cases. The increase might be due to the growth of plant, increased levels of S application which in turn enhanced the formation of main and branch root nodules. Singh and Bansal (2000) reported that S application increased nodulation of soybean. Similar results were also observed by Ganeshamurthy and Reddy (2000), Hemantarajan and Trivedi (1997) and Singh and Chaudhari (1997).
The interaction effects of S and Zn were not significant in respect of nodulation (Table 1). Maximum number of nodules plant1 was recorded at 90 DAS in S10Zn2.5 and the minimum in S30Zn10 at 110 DAS.
Dry matter yield: Dry matter yield was significantly influenced by S fertilization at all the growth stages except at 90 DAS. The highest dry matter yield was recorded with 30 kg S ha1 and the lowest by 0 kg S ha1 at all the growth stages except 90 DAS. The dry matter yield increased with increase in S levels upto S30 beyond which it again decreased.
Dry matter yield increased with the age of plant and the increase was accelerated between 45 and 90 DAS. This might be due to quick growth of plant, increase in leaf number, plant height and increase in levels of S.
|Table 1:||Effect of sulphur and zinc on nodulation of soybean cv. Shohag (Pb-1) at different growth stages
|DAS= Days After sowing|
Interaction effect of sulphur and zinc on dry matter
yield of soybean cv. Shohag (Pb-1) at different growth stages
Similar findings was obtained by Singh et al. (1995), Hemantarajan and Trivedi (1997) who reported that dry matter production was higher with increased S application. In contrast, Wu et al. (1996) found that S alone did not significantly affect the dry matter yield of rape seed (Brassica napus L.).
Zinc showed a significant effect on dry matter yield at all the growth stages except at 90 DAS. The highest dry matter yield was obtained by Zn20 at 110 DAS and the lowest dry matter yield was obtained from control treatment. The results indicated that the application of Zn increased the dry matter up to the highest Zn dose applied (20 kg ha1) at all stages. The dry matter yield increased progressively upto 110 DAS due to application of Zn except Zn20 at 90 DAS (Table 2).
Results revealed that interaction effect of S and Zn on dry matter yield was not significant at all the growth stages except 90 DAS (Table 2). The highest dry matter yield was recorded by 30 kg S + 20 kg Zn, at 110 DAS. This treatment combination was found superior to all other treatments combination in producing dry matter at all growth stages. The lowest dry matter weight was produced by control treatment at 30 DAS. From the results, it is clear that interaction effect of increased levels of S and Zn induced increased dry matter yield due to the favourable effect of these two elements.
|Table 3:||Interaction effect of sulphur and zinc on zinc and sulphur content by soybean cv. Shohag (Pb-1) at different growth stages
The best performance in respect of dry matter production was observed with the combination of 30 kg S + 20 kg Zn ha1 (Table 2).
Sulphur and zinc content of soybean at different growth stages: Sulphur content was significantly influenced by S at 110 DAS. Sulphur content showed increasing trend with increasing growth stages. Its content at 110 DAS was higher than that of other growth stages throughout the growth period. At all the growth stages (30, 45, 60, 90 and 110 DAS) the highest S content was observed in S30 treatment and the lowest was in control (S0). The highest S content at 110 DAS might be due to the fact that during this period plants got enough time to receive adequate light, water and nutrients for their growth and development which ultimately caused to produce highest S content. These results are in good agreement with those of Agrawal et al. (2000) who explained that S application increased the concentration of S in the sunflower at different growth stages of the crop growth (Table 3).
Sulphur content of soybean was not significantly influenced by Zn at any growth stage except 60 DAS which showed an increasing trend with the advancement of growth. At all the growth stages the highest S content was observed in Zn20 and the lowest was in control. The interaction effect of S and Zn was significant on S content at all the growth stages except 30 and 45 DAS. The highest S content was found in S30Zn20 treatment and lowest in control (Table 3).
Zinc content was not significantly influenced by S at any growth stage of soybean. The highest Zn content was observed in S30 treatment and the lowest in control (S0). It was observed that the Zn content was increased upto 60 DAS and then decreased.
Zinc content was also significantly and positively influenced by Zn application at 45, 60, 90 and 110 DAS and showed an increasing trend with advanced growth stages. At all the growth stages, the highest Zn content was observed in Zn20 treatment and the lowest in control (Zn0). The interaction effect was observed significant only 90 and 110 DAS on Zn content. The highest Zn content was observed in S30Zn20 and the lowest in control (Table 3). From this discussion it is evident that the application of different levels of S and Zn accelerated nodulation, increased dry matter yield and nutrient content of soybean.
The authors want to thank and appreciations to the Departments of Horticulture, Genetics and Plant Breeding of BAU, Mymensingh; Bangabandhu Sheikh Mujibur Rahman Agricultural University, Salna, Gazipur and Bangladesh Agricultural Research Institute, Joydevpur, Gazipur for providing facilities and technical assistance.