Abstract: An experiment was conducted at Students Farm, Sindh Agriculture University, Tandojam, Pakistan to assess the NP requirement (0-0, 50-25, 75-37.5 and 100-50 NP kg ha-1) for soybean varieties (Bossier and Pelican). The highly significant differences for varieties and fertilizer combinations for plant height, index and seed yield per hectare were observed. Whereas, non-significant differences were recorded under number of pods per plant. The variety Pelican under 100-50 kg NP ha-1 produced taller plants (66. 25 cm) and more number of pods (55.00 plant-1). However, the seed index (14.00 g) and seed yield (3007 kg ha-1) were superior in variety Bossier with the application of 75-37.5 kg NP ha-1.
INTRODUCTION
Soybean, being a leguminous crop, fixes atmospheric nitrogen (N) with the help of the nitrogen-fixing bacteria Bradyrhizobium japonicum, which are present in nodules of soybean roots. Nodulation begins within a week after emergence (Bergersen, 1958) and N-fixation begins at about 14 days (Hardy et al., 1971). Thus, in the seedling stage N uptake is high and N deficiency is observed during the first two weeks of plant growth, before symbiotic N-fixation begins. Therefore, a starter application of N not exceeding 25-30 kg N ha-1 is recommended (Beg, 1984; Hussain, 1989; Quresh and Khan, 1985). The application of N fertilizer, aside from the starter dose mentioned above, is not advisable, as the amount of N fixed through bacteria is inversely proportional to the amount of N applied. Addition of N through fertilizers, FYM, or green manure simply replaces N-fixation and grain yield remains similar to that obtained only with inoculum. The total amount of N fixed by nodules ranges from 65 (Alexander, 1977) to 450 kg ha-1 (Hardy and Havekla, 1975), depending upon the method of estimation and environmental conditions. The crop can fix 300 kg N ha-1, depending upon its yield potential, the availability of soil N and genetic interaction between the host genotype and the Rhizobium japonicum strain (Cassman et al., 1981). Generally, about one-third of the total N requirements of the plant are met through N-fixation and the other two-thirds from soil sources. The amount of N fixed is enough to produce a grain yield of 3000-4000 kg ha-1. Intensive soybean production seldom includes application of N fertilizer, but rather relies on N fixation to supplemental uptake of residual N from the soil (Pepper, 1982). In an other study, it was reported that soybeans are highly susceptible to fertilizer burn, so care should be taken to avoid sowing the seed with the fertilizer. Soybeans can e susceptible to manganese deficiency; this can be corrected by applying up to 8 kg ha-1 manganese sulphate (Devine et al., 1998). Work in North Dakota found that grain soybeans had a residual N yield of 100 kg N ha-1 for subsequent crops. This may be higher for forage soybeans as it has not transferred much N from the nodules to grain by the time of harvest (Devine and Hatley, 1998). Thus, looking the above research, much work has been done on various agronomic aspects of soybean cultivation for assessing high yielding varieties with appropriate fertilizer doses.
MATERIALS AND METHODS
The field experiment was conducted at Students Farm, Sindh Agriculture University, Tandojam, Pakistan in RCBD. The details of the treatments used are as under:
| Varieties | Two | ||
| V1= | Bossier | ||
| V2= | Pelican | ||
| Fertilizer Rates | Four | ||
| F1 = | Control | ||
| F2 = | 50-25 NP kg ha-1 | ||
| F3 = | 75-37.5 NP kg ha-1 | ||
| F4 = | 100-50 NP kg ha-1 |
Seedbed preparation: Land was ploughed thrice by crosswise plowing with the help of tractor followed by clod crushing and leveling to facilitate uniform distribution of irrigation water. Thus, a good seedbed was prepared.
Seed sowing and fertilizers: The seed of soybean varieties viz: Bossier and Pelican was drilled by single coulter hand drill keeping the recommended distance of 30 cm between rows. The fertilizer doses applied are integrated in the treatments. Full dose of phosphorus and half of nitrogen was applied at sowing time and remaining half dose of nitrogen was given at second irrigation.
Irrigation: Soybean is very sensitive to heavy irrigation and care was taken to avoid the over irrigation. First irrigation was given after three weeks and subsequent irrigations were given as per need of the crop.
Care and maintenance: Crop was kept free from weeds and interculturing was performed to loosen the soil and to eradicate the weeds.
Data analysis: The data obtained was statistically analyzed for mean discrimination through Duncan’s Multiple Test and for significant level by analysis of variance following the procedures of Gomez and Gomez (1984).
RESULTS AND DISCUSSION
Plant height (cm): Plant height differed significantly for varieties and fertilizer combinations. Maximum plant height (58.96 cm) was recorded from variety Pelican, whereas 100-50 kg NP ha-1 produced taller plants (61.87 cm) (Table 1). The interaction (VxF) showed that variety Pelican x 100-50 kg NP ha-1 produced taller plants (66.25 cm) as compared to other varieties and fertilizer combinations Achakzai et al. (2002) suggested that plant height significantly and positively increased by added fertilizer over control. However, Menaria et al. (2003) reported that plant height responded upto 40 kg P ha-1. These results are also supported by Akhtar et al. (1988) they reported that application of nitrogen improved vegetative growth of plant.
| Table 1: | Plant height (cm) of soybean varieties as affected by different fertilizer combination and their interactions |
| *Mean values withen same letter(s) are not significantly different | |
Pod number plant-1: Statistically results for number of pods plant-1 were non-significant. However, variety Pelican recorded maximum number of pods plant-1 (53.00) as compared to Bossier. Fertilizer level of 75-37.5 kg NP ha-1 recorded maximum (54.00) number of pods plant-1 (Table 2). The Interaction (VxF) showed maximum number of (55.00) pods plant-1 under variety Pelican in the plots where 75-37.5 kg NP ha-1 was incorporated. Similar results were reported by Gan et al. (2002) that nitrogenous and phosphorus fertilizers significantly produced more number of pods in soybean crop.
Seed index (g): The seed index showed statistically different results for fertilizer combination, however, varieties and its interaction (VxF) were non-significant. More seed index (12.40 g) values were obtained under variety Bossier. Fertilizer level 75-37.5 kg NP ha-1 produced maximum seed index (13.87 g) (Table 3). The interaction, variety Bossier x 75-37.5 kg NP ha-1 recorded maximum seed index (14.00 g). Gurkirpal Singh et al. (2001), they reported that NPK at 90-60-35 kg ha-1 produced highest 100 grain weight.
Seed yield (kg ha-1): The results were statistically highly significant for varieties, fertilizer combination and their interaction (VxF). Individually, the variety Bossier produced maximum (1685 kg ha-1) and fertilizer combination of 75-37.5 kg NP ha-1 recorded higher (2704 kg ha-1) seed yield.
| Table 2: | Pods plant-1 of soybean varieties as affected by different fertilizer combinations and their interactions |
| *Mean values withen same letter(s) are not significantly different | |
| Table 3: | Seed index (1000 seed weight, g) of soybean varieties as affected by different combinations fertilizer and their interactions |
| *Mean values withen same letter(s) are not significantly different | |
| Table 4: | Seed yield kg ha-1 of soybean varieties as affected by different fertilizer combinations and their interactions |
| *Mean values withen same letter(s) are not significantly different | |
The over all results showed that variety Bossier under 75-37.5 kg NP ha-1 produced more seed yield as compared to variety Pelican and other fertilizer combinations (Table 4). Similar results were reported by Stefanesu and Palanciuc (2000); Achakzai et al. (2002) reported that grain yield increased with the application of 50-50 kg NP ha-1. Further, Chorey et al. (2001) reported that 60-30 kg NP ha-1 recorded comparatively higher seed yield. Gan et al. (2002) revealed that yield increased at N and P supply and was mainly associated with more seeds, greater pod number plant-1 which confirm the results.
CONCLUSIONS
It was concluded that variety Pelican produced greater plant height and number of pods plant-1 under 75-37.5 kg NP ha-1, where as variety Bossier produced heavy seed index and more grain yield per hectare with the incorporation of 75-37.5 kg NP ha-1.