Growth , nodulation and yield components of mung bean ( Vigna radiata ) as affected by phosphorus in combination with rhizobium inoculation

Mungbean (Vigna radiata L.) is capable of fixing atmospheric nitrogen through bacteria living in its root nodules. To study the influence of phosphorus (P) fertilization and Rhizobium inoculation on the nodulation, growth and yield of mungbean (Vigna radiata), a pot experiment was conducted in wire house, during spring season of 2010 at University of Agriculture, Faisalabad. A composite soil sample was collected from the research area and analysis of physical and chemical properties of the soil was done. Seeds of mungbean cv, NM-92 were inoculated with Rhizobium and sown in pots containing 14 kg soil. Phosphorus was applied at 1.2, 2.4 and 3.6 g per 14 kg soil in each pot alone and along with inoculation of Rhizobium phaseoli except in control pot. The source of P was single super phosphate that was mixed with soil before filling the pots. It was noted that combined use of P and inoculant enhanced the number of nodules per plant. The maximum nodules, 8.67 per plant, were recorded where 3.6 g P along with Rhizobium inoculation was applied. Phosphorus application along with Rhizobium inoculation increased the plant height significantly (13.2%) over control. Maximum increase in plant height at maturity, total number of pods and number of grains per pod were also recorded where 3.6 g of phosphorus along with Rhizobium inoculation was applied.


INTRODUCTION
Mungbean (Vigna radiate L), commonly known as green gram, is an important conventional pulse crop of Pakistan.In most of the Asian countries, the diet is cereal based.It is a rich source of protein (23%) (Hussain et al., 2010).It has the ability to fix atmospheric nitrogen (N) through Rhizobium species, living in nodules on its roots.The area sown under this crop in the year 2008-2009 was 231.1 thousand hectares with a production of 157.4 thousand tons (Govt. of Pakistan, 2009).The rate of nodulation is very low in most of the mungbean growing *Corresponding author.E-mail: drtasneem@uaf.edu.pkAuthor(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License area of Pakistan.There are numerous reasons but imbalanced nutrition appears to be one of them.Therefore, artificial inoculation of mungbean with effective Rhizobia is a useful practice for improving its yield (Guozan et al., 1985).Seed inoculation significantly increased the growth parameters of mungbean (Khan and Kounsar, 2000).Besides this, according to Gowda and Gowda (1978), due to the ability of fixing atmospheric nitrogen, mungbean requires phosphorus to improve the yield and quality of grain.Phosphorus also has favourable effects on the number and weight of effective nodules on the root system of leguminous crops (Brady, 1984).The present study was planned to determine the effect of Rhizobium in combination with different levels of P on nodulation, growth and yield of mungbean cultivar NM-92 under irrigated conditions at Faisalabad.

MATERIALS AND METHODS
Pot experiment was conducted during March -May 2010 in wire house of the Institute of Soil and Environmental Sciences, University of Agriculture, Faisalabad.Surface soil (15 cm depth) was collected from the research area and air dried, mixed thoroughly and passed through 2 mm sieve.A representative sample was taken for physical and chemical analysis of the soil.Characteristics of experimental soil are given in Table 1.
Seeds of mungbean cv, NM-92 were inoculated with Rhizobium phaseoli according to standard methods and sown in pots containing 14 kg soil in each.The inoculum was purchased from Ayub Agriculture Research Institute (AARI), Pakistan.It was sold as Nitorgen Ka Teeka.10% sugar solution was made and added with the black powder, the material provided in the standard pack, and mixed thoroughly.When the sticky paste or solution was ready it was mixed well with the seed of mungbean and sown according to different treatments immediately after drying for one hour under the shady place.The experiment was laid out in 2 factorial completely randomized design (CRD) consisted of different treatments like P 0 (control treatment that was without P and Rhizobium inoculation), P 50% of recommended P (1.2 g P), P 100% of recommended P (2.4 g P), P 150% of recommended P (3.6 g P) per pot, P 0 (Rhizobium inoculation without P), P 50% (Rhizobium inoculation+1.2 g P), P 100 % (Rhizobium inoculation + 2.4 g P), P 150% (Rhizobium inoculation + 3.6 g P).These treatments were replicated three times to minimize error.
Recommended doses of N and K fertilizers were applied at 25 and 62 kg ha -1 , by using urea of 38 g per 14 kg soil (w/w) and MOP of 72 g per 14 kg soil (w/w) for the sowing, respectively.
The pots were irrigated with fresh water, using sprinkler bucket in seven days interval.Plant height was recorded after 15 days of germination and at the time of maturity.After harvesting, length of roots, number of nodules per plant, number of pods per plant, number of grains per pod, weight of grains per plant and 1000-grain weight were recorded.NP uptake was determined by the following formulae: N uptake = {(Conc.of N in grain × Oven dry wt. of grain) + (Conc. of N in straw × Oven dry wt.straw)} / 100 P uptake = {(Conc.of P in grain × Oven dry wt. of grain) + (Conc. of P in straw × Oven dry wt.straw)} / 100 The unit is g plant -1 , for conversion of g plant -1 ; g plant -1 will be multiplied by 1000.The data collected for various characteristics were subjected to the analysis of variance and means were compared by using Duncan's Multiple Range Test (Steel and Torrie, 1997).

Plant height at maturity (cm)
The comparison of inoculated means with uninoculated revealed that average height of inoculated plants was increased by 10.19% as compared to average height of uninoculated plants (Table 1).The overall comparison of means resulted in the increase in plant height by 3.9 to 13.2% over its respective control; the interaction between graded P levels and rhizobium inoculation was significant.The maximum plant height (40.35 cm) was recorded in the inoculated plants when it was supplemented with 150 % of the recommended dose of phosphorus.These results were also supported by Thakur and Panwar (1995) who reported an increase in plant height by seed inoculation and fertilizer application.

Number of nodules plant -1
In uninoculated plants, no nodulation was observed (Table 1).The inoculated plants were infected by Rhizobium for nodulation and the average number of nodules per plant was 6.0 which further increased aggravately with application of increased P levels.The average number of nodules per plant was 11.96 in case of inoculated compared with uninoculated plants as it was 0.00 nodules plant -1 .The comparison means of different P levels with Rhizobium treatments indicated that all the three levels increased nodulation from 78-190% over their Rhizobium inoculation alone.These results were quite in line with those of Bar and Lal (1991).

Number of pods plant -1
Rhizobium inoculation along with graded levels of phosphorus significantly affected the pod formation (Table 2).In case of uninoculated plants, maximum number of pods was observed where the highest dose of phosphorus (150%) of the recommended phosphorus) was applied which further increases to 23.5% with combined application of P and rhizobium inoculation.Among the inoculated plants, the maximum pod formation (24.16 pods plant -1 ) was observed in P 100 which was 42.11% higher over its respective control.Inoculation strongly promoted the average pod formation as compared to uninoculated plants (50.32% higher than uninoculated plants).The comparison of the overall means of different P levels indicated that P rates of recommended and 150% of the recommended were statistically non significant but they were 17.59 and 22.95% higher over their respective control.Similar results were recorded by Shukla and Dixit (1996) and Ashraf et al. (2003).

Number of grains pod -1
In uninoculated plants the increasing P levels enhanced the grain formation as compared to control (without phosphorus) and P 100 and P 150 were statistically non significant (Table 2).In inoculated plants the P levels increased the grain formation as compared to control and P 100 and P 150 were statistically non significant.Overall comparison of means of P level indicated that recommended P enhanced the grain formation which was 40.08% higher than its respective control.The comparison of average of inoculated plants to uninoculated was also highly significant and it was 23.08% higher than uninoculated plants.The interaction of rhizobium inoculation and phosphorus inoculation was found non-significant.Shaheen and Rahmatullah (1996) and Perveen et al. (2002) also observed similar types of results in their findings with different treatments of Phosphorus with Rhizobium.

Weight of grains plant -1 (g)
The data (Table 3) regarding the grain weight of mungbean (g plant -1 ) as affected by various levels of phosphorus alone and in combination with Rhizobium were recorded after harvest and analysis of variance indicated the significant difference in grains' weight of mungbean due to different treatments.Among the overall means for different P levels, the maximum grain weight (3.32 g plant -1 ) was observed in P 100 and it was statistically non-significant with P 150 .Average fresh weight of grains in the inoculated plants was 105.23% greater than the average fresh weight of grains of uninoculated plants.
The interaction between phosphorus levels treatments and Rhizobium inoculation was also highly significant.These results are in accordance with Khan and Kounsar (2000) and Perveen et al. (2002).

1000-Grain weight (gm)
The analysis of variance of the data regarding the effect of phosphorus and Rhizobium inoculation on the 1000grain weight (Table 3) indicated that difference in 1000grain weight due to different phosphorus levels and inoculated treatments were highly significant but at the same time the interaction of P rates along with Rhizobium inoculums was non significant.Among the overall means for graded P levels, maximum 1000-grain weight (25.6 g) was recorded in case of P 150 which was 16.89% higher than its respective control.At the same time, this P 150 was statistically at par with P 100 .The average mean (24.8 g) for inoculated plants resulted in 5.1% greater than the average mean (26.3 g) in uninoculated plants.Interaction of both graded P levels and Rhizobium inoculums was non-significant.Response of mungbean to phosphorus along with Rhizobium inoculation was also studied by Singh et al. (1993), Khan and Kounsar (2000) and Table 3.Effect of P and Rhizobium inoculation on weight of grains plant -1 and 1000-grain weight.

Phosphorus levels
Weight of grains plant Nitrogen uptake in plant (mg plant -1 ) In inoculated plants the maximum nitrogen uptake (196.94 % higher than the respective inoculated control) was the highest dose of P (150% of the recommended P).The comparison of over all means of P treatments indicated that maximum uptake of N was at the P levels of 150% of the recommended dose and it was 157.19 % greater than the control where no P was applied.The other rest P levels P 100 and P 50 followed the P 150 .Average N uptake in inoculated plants was significantly higher than the uninoculated plants.It was 111.74% higher than its respective uninoculated plants.The interaction between P rates and rhizobium inoculation was also found highly significant.Shah et al. (1996) and Shaheen and Rahmatullah (1996) also reported that treated plots with rhizobium inoculums improved the N and P uptake by plants.

Phosphorus uptake in plant (mg plant -1 )
The analysis of variance of the data given in Table 4 showed that in uninoculated plants the highest dose of P increased the P uptake by 351.85 % over its respective control P 0 .The other rest two levels of Phosphorus, P100 and P50 followed the P150 in the inoculated plants.The comparisons of overall means of uninoculated and inoculated plants showed that P treatments had significant effect on P uptake and maximum uptake was 18.09 mg plant -1 .This was 468.86% higher than its respective control where no P was applied.Inoculation significantly promoted the average P uptake by the plants as compared to uninoculated plants which were 127.04% higher than uninoculated plants.The interaction between P levels and rhizobium inoculation was also highly significant.Bar and Lal (1991) studied the same observations in their experiments.

Conclusion
Phosphorus along with Rhizobium inoculation application increased plant height, total number of pods, number of grains per pod, and 1000-grain weight significantly.Maximum increase was noted where 150% of the recommended phosphorus along with Rhizobium inoculation was applied but it was statistically at par with the results obtained by applying 100% of the recommended phosphorus along with Rhizobium inoculation.So 100% of the recommended phosphorus along with Rhizobium inoculation is the best treatment in the experiment.

Table 1 .
Effect of phosphorus and Rhizobium inoculation on plant height and no. of nodules plant -1 .

Table 2 .
Effect of phosphorus and Rhizobium inoculation on no. of pods plant -1 and no. of grains pod -1 .

Table 4 .
Effect of phosphorus and Rhizobium inoculation on nitrogen and phosphorus uptake by plant.