Effects of soil inoculation with Azotobacter and nitrogen

fertilization on the growth of Brassica rapa

 

By Charles H. Walker, II

Department of Plant Biology, Southern Illinois University, Carbondale, Illinois 62901, USA

 

 

I Introduction

 

          Nitrogen, phosphorus, and potassium are the three macronutrients required by plants.  Nitrogen is depleted from the soil by the growing of agronomic crops, especially by crops like corn (Zea mays).  The chemical nitrogen fertilizer that is commonly applied to fields is expensive.

A study in India found that 53.9% of the monocots, 53.6% of the dicots, 28.5% of the gymnosperms, and 26.1% of the Pteridophytes studied harbored nitrogen-fixing microorganisms (Sengupta et al. 1981).  When it rains, or when dew forms, nitrogen is leached from the upper leaf surface on to the surrounding ground where it becomes available for uptake by plants.  Sengupta and associates also examined 62 epiphytic plants and found that 66% of them harbored nitrogen-fixing bacteria.  This would help explain how orchids, which derive no sustenance from the plants they grow on, meet their nitrogen needs.

          Klebsiella pneumoniae, a nitrogen-fixing bacteria, has been experimentally sprayed on to the foliage of common garden vegetables.  Foliar applications doubled the yields (kg 10 m-2) of spinach, onion, tomato, and eggplant.  Nitrogen was increased by more than 30% in most crops (Nandi et al. 1983).  Chemical nitrogen application rates can be cut in half when growing Morus alba, if used in conjunction with an Azotobacter chroococcum foliage spray (Sudhaker et al. 2000).

          The second area of research has been with seed and soil inoculation.  The inoculation of wheat (Triticum aestivum) with Azotobacter chroococcum increased the grain yield by 11% and the number of tillers per plant by 16% (Ram et al. 1985).  In wheat trials in Israel, seed inoculated with Azotobacter chroococcum and Azospirillum lipoferum combined with 60 kg N/feedan produced higher yields than did 120 kg/feddan of either ammonium sulfate, ammonium nitrate or urea (El Kased et al. 1999).  Similarly corn (Zea mays) inoculated with Azospirillum had significantly higher grain % protein and leaf % nitrogen, but had lower grain yield than did plants fertilized with 10 kg N/ha (Purcino et al. 1996).

Among the dicots, seed yield of Brassica juncea was increased by 8.2% and 10.9 % when seed was inoculated with Azotobacter and Azospirillum respectively, as compared to those not inoculated (Chauhan et al. 1995).  Also B. juncea seed inoculated separately with Azotobacter and Azospirillum showed significant increase in the number of branches, pods per plant, seeds per pod, seed yield, stover, and oil (Chauhan et al. 1996).  In B. napus seed yield and total dry matter was higher when plants inoculated with Azotobacter chroococcum received no external nitrogen (Singh and Bhargava 1994).

Besides seed inoculations, the banana's sucker as well as the soil was inoculated with Azospirillum and maximum plant height and leaf size was obtained using one-half the recommended nitrogen fertilizer (Tiwary et al. 1998).  The objective of this experiment was to examine the effect of Azotobacter vinelandii and nitrogen fertilizer on the growth of Brassica rapa.  The hypotheses for this study were (1) plants inoculated with Azotobacter will exhibit more growth than plants not inoculated, and (2) plants fertilized with nitrogen will exhibit more growth than plants not fertilized.

 

II The Design - Methods and Procedures

 

          Four plates were streaked from a slant of Azotobacter vinelandii and incubated for three weeks.  A loop was used to transfer the Azotobacter vinelandii colonies to a beaker of distilled water.  An eyedropper was used to transfer 2 ml of the suspended bacteria to a small depression in the soil surface, 1 cm from where the seed was planted.  This method was employed because the distribution of Azotobacter in soil is not diffuse, but is focal (Krasilnikov 1936).

D606 com-packs were used to grow the seedlings.  They measure 17.8 cm x 13.34 cm and are divided into 6ths.The com-packs and trays were sanitized prior to the experiment to eliminate any bacterial or fungal contamination.  The soil type PRO-MIX was used throughout the experiment.  It had a pH of 6.5 and was sterilized at 77(C prior to this experiment.

Two factors were applied, inoculation of the soil with Azotobacter vinelandii (Inoc), fertilization with a 0.02g nitrogen pellet (Fert), the interaction of these 2 treatments (Inoc + Fert), and the control group (Con).  Nine of each of these were randomized within each of 3 trays, using the Latin Square design The three trays were physically separated from one another.  They were placed on different benches in the northwest, southwest, and southeast portions of the greenhouse.  The plants were grown for 33 days and were then individually dried, weighed, and their stage of growth noted (1 = leaf, 2 = bud, 3 = flower, and 4 = seed). The longest leaf on each plant was measured.

 

III Results

 

The first hypothesis was rejected, as there was no significant difference between plants growing in soil inoculated with Azotobacter and the control group.  There was a significant difference in leaf length between plants fertilized with nitrogen and the control group (F = 5.73; P < 0.05).  The fertilized group had a mean leaf length of 2.64 cm, compared to 2.28 in the control group.  However, there was no significant difference in the log of the biomass between the fertilized and the control groups.  There was a significant difference between the blocks in leaf length (F = 6.26; P < 0.01), log of the biomass (F = 100.34; P < 0.001), and stage class (F = 15.15; P < 0.001).  See Table 1.

 

Block            Leaf length (mean)                   Log of Biomass (mean)        Stage (mean)

Northwest              2.70                                               0.62                           3.54

Southwest              2.22                                               0.16                            2.17

Southeast               2.19                                               0.08                            2.08

Table 1 Block designations refer to where each of the three trays were located in the SIU greenhouse.  Means generated from S.A.S.

 

BIBLIOGRAPHY

 

Chauhan, D.R., Paroda S., & Singh D.P. 1995. Effect of biofertilizers, gypsum, and nitrogen on growth and yield of raya (Brassica juncea). Indian Journal of Agronomy 40(4): 639-642.

 

Chauhan, D.R., Parada S., & Ram, M. 1996. Response of Indian mustard (Brassica juncea) to biofertilizers, sulfur, and nitrogen fertilization. Indian Journal of Agronomy 41(4): 620-623.

 

El-Kased, F.A., Kamh, R.N., & Abd-El-Ghany, B.F. 1996. Wheat response to bio and mineral nitrogen fertilizer in newly reclaimed sandy soil. Desert Institute Bulletin 46(2): 373-386.

 

Krasilnikov, N.A. 1958. Soil microorganisms and higher plants.  Academy of Sciences of the USSR. Moscow.

 

Nande, A.S., SenGupta, B., Sen, S.P. 1983. Utility of phyllosphere N2-fixing microorganisms in the improvement of growth of some vegetables. Journal of Horticultural Science 58: 547-554.

 

Purcino, A.A.C., Paiva, E., e Silva, M.R., & de Andrade, S.R.R. 1996. Influence of Azospirillium inoculation and nitrogen supply on grain yield, and carbon- and nitrogen-assimilating enzymes in maize. Journal of Plant Nutrition 19(7): 1045-1060.

 

Ram, G., Chandrakar, B. S., & Katre, R. K. 1985. Influence of azotobacterization in presence of fertilizer nitrogen on the yield of wheat. Journal of the Indian Society of Soil Science 33: 424-426.

 

Sengupta, B., Nandi, A.S., Samanta, R.K., Pal, D., Sengupta, D.N., & Sen, S.P. 1981. Nitrogen fixation in the phyllosphere of tropical plants: occurrence of phyllosphere nitrogen-fixing microorganisms in eastern India and their utility for the growth and nitrogen nutrition of host plants. Annals of Botany 48: 705-716.

 

Singh, P. & Bhargava, S.C. 1994. Changes in growth and yield components of Brassica napus in response to Azotobacter inoculation at different rates of nitrogen application. Journal of Agricultural Science 122 (Part 2): 241-247.

 

Sudhakar, P., Chattopadhyay, G.N., Gangwar, S.K., & Ghosh, J.K. 2000. Effect of Azotobacter biofertilizer with inorganic nitrogen on leaf yield and quality of mulberry (Morus alba L.). Tropical Science 40: 75-82

 

Sudhakar, P., Chattopadhyay, G.N., Gangwar, S.K., & Ghosh, J.K. 2000. Effect of foliar application of Azotobacter, Azospirillium and Beijerinckia on leaf yield and quality of mulberry (Morus alba). Journal of Agricultural Science 134: 227-234.

 

Tiwary-D.K., Hasan, M.A., & Chattopadhyay, P.K. 1998. Studies on the effect of inoculation with Azotobacter and Azospirillium on growth, yield, and quality of banana. Indian Agriculturist 42(4): 235-240.