Abstract: Effects of Azotobacter application either individually or in combination with the use of organic and chemical fertilizers on the growth and yield of transplant amen rice and nutrient status of post-harvest soil were evaluated. Increased growth in terms of leaf area index and tiller number/plant was recorded from Azotobacter application both individually and in combination with the use of organic and chemical fertilizers. Considering both grain and straw yields, Azotobacter exhibited significant influence along with all levels of organic and chemical fertilizers. But overall best performance regarding growth and yield was observed from Azotobacter application along with the use of three-fourths of the recommended dose of chemical fertilizers. Analysis of post-harvest soil showed that Azototiacter along with the use of three-fourths of the recommended dose of chemical fertilizers performed the best in maintaining organic matter and available P status in soil.
Introduction
Depletion of soil organic matter is one of the most important factors of deterioration of crop productivity, as soil organic matter plays an important role in preserving the fertility and productivity of soils. Introduction of high yielding fertilizer responsive crop varieties coupled with intensive cropping in Bangladesh have thrusted tremendous pressure on the soil organic matter and soil nutrients. Moreover, farmers rarely add sufficient amount of organic manures to the soil against their removal. As a result, the natural nutrient reserve in soil has been steadily declining which is alarming for sustaining the crop productivity in Bangladesh. Karim et al. (1994) reported that soil organic matter in Bangladesh has been depleted by 945% during the period from 1969-70 to 1989-90. Under this situation, the integration of organic and inorganic fertilizers may facilitate the utilization of nutrients for crop growth and productivity and help replenish the organic matter status in soli. The long-term research at BRRI indicates that the addition of cowdung at 5 t/he/year can improve the rice productivity with no degradation of soil fertility (Bhuiyan, 1994). As the organic fertilizer is very limited in production, the feasibility of using bio-fertilizer in rice may be explored. A study was, therefore, undertaken to evaluate the effects of Azotobacter application on the growth and yield of transplant amen rice and nutrient status of post-harvest soil.
Materials and Methods
A field trial was conducted during amen season of 1996 at the Agronomy Field Laboratory of Bangladesh Agricultural University, Mymensingh, Bangladesh to see the effects of Azotobecter application on the growth and yield of rice and nutrient status of postharvest soil. The experiment included following treatments: two levels of Azotobacter application (Arotobeeter inoculation (A1) and no inoculation (A0)), three levels of cowdung (control, 5 Wet and 10 t/ha) and five levels of chemical fertilizers (control, one-fourth of the recommended dose, half of the recommended dose, three-fourths of the recommended dose and full of the recommended dose). Treatment combinations for chemical fertilizers and cowdung have been presented in Table 1. Recommended dose of chemical fertilizers used in the experiment was 80-60-40-30-5 kg of N-P205-K10-S-Zri, respectively (BRRI, 1995). Chemical fertilizers namely urea, TSP, MP, zinc sulphate and gypsum were applied as the source of N-P205-K20-S-Zrt, respectively. Split-plot design was followed in laying out the experiment with three replications assigning organic and chemical fertilizers in main plot and Azotobacter in sub-plot. Rice variety BR11 developed by Bangladesh Rice Research Institute was used as the planting material. Roots of rice seedlings were inoculated with Azotobacter by dipping them in Azotobacter solution (10 ml of Azotobacter inoculant with 1 L of water) for 20 minutes before transplanting. Full dose of cowdung was given at seven days before land preparation while full dose of TSP, MP, zinc sulphate and gypsum and one-third of urea were applied at the time of final land preparation. The rest of urea was top-dressed at maximum tillering stage and prior to panicle initiation stage. All the necessary intercultural practices were done as and when necessary.
Regarding the growth study of the crop data were collected on leaf area index (LAI) and number of tillers/m2 measured at 15 days interval. Ten hills from each plot were selected randomly and tagged from which data on aforementioned growth parameters were recorded. LAI was calculated by using the leaf non-removing technique (IRRI, 1972). After harvesting of the crop plot-wise grain and straw yields were recorded at 12% moisture level. For soil nutrient analysis, initial soil sample before final land preparation and soil samples from each plot after harvesting of the crop were collected. Organic matter and total N were measured by wet oxidation method and micro kjeldahl method, respectively (Page et al., 1982) and available P by the technique described by Black (1965).
Results and Discussion
Growth and yield: Leaf area index (LAO of transplant amen rice was significantly influenced by the inoculation of rice seedlings with Azotobacter (Fig. 1). The figure shows that LAI increased with the progress of the growth processes of the crop up to 80 days after transplanting (DAT) and declined afterwards. At the earlier stages of crop growth (up to 30 DAT) the rate of increment was slower, but it was rapid from 30 DAT and afterwards and reached the peak at 60 DAT. From this figure it is evident that in both the treatments LAI increased upto 60 DAT, but the rate of increment was much higher in Azotobactor inoculated treatment than that of uninoculated one.
| Table 1: | Treatment combinations far chemical fertilizers and cowdung |
| Table 2: | Effects of Azatobartar application along with the use of organic and chemical fertilizers on leaf area index of transplant amen rice |
| In a column, figures having similar letter(s) do not differ significantly whereas figures bearing dissimilar letters differ similarly (as per DMRT) | |
Almost a similar growth trend of LAI was also noticed in case of tiller number/m2 due to Azorobacrer inoculation (Fig. 2). However, it is interesting to note that both LAI and tiller number/m2 declined after 60 OAT much more sharply in uninoculated plot than those of inoculated one. Probably Azorobactar could supply N throughout the life cycle of the crop, especially at the later stages which was responsible for this slower declination of LAI and tiller number/m2 after BO DAT in Azotobanter inoculated plot. Venkatararnan (1902) also stated that Azorobacrer accelerated the growth of crops by supplying nitrogen and growth stimulating substances. LAI was also influenced significantly when Azorobacter was applied along with organic and chemical fertilizers (Table 2). LA's were much lower at lower level of organic and chemical fertilizers while these were significantly higher with medium to high levels of chemical fertilizers. It can be seen from the table that LAI increased with the increasing levels of chemical fertilizers in combination with A2atobacter. But LAI declined when cowdung was added with Azotobacter and chemical fertilizers in most of the cases which indicated that application of Azotobacter along with chemical fertilizers was sufficient to achieve the best performance in producing Led. Purushothamon et al. (1977) also found increased growth of rice crop due to interaction of Azorobacrer with chemical fertilizers NPK.
| Table 3: | Effects of Azotabacter application along with the use of organic and chemical fertilizers on grain and straw yields of transplant aman rice |
| Table 4: | Effects of Azotobacter application along with the use of organic and chemical fertilizers on nutrient status ofpost-harvest soil |
| In case of initial sell-organic matter content was 1.15; total N content wee 0.070 and available P content was 25pprn | |
| Fig. 1: | Effects of Azorobacter application on leaf area |
| Fig. 2: | Effects of Azotobacter application on tiger nurnberirn2 index (LA1) of transplant amen rice of transplant amen rice |
Table 3 represents the grain end straw yields of rice including their increment over control as influenced by Azotobsofer inoculation along with the application of organic and chemical fertilizers. Azotobacter application increased both grain end straw yields along with almost all levels of organic and chemical fertilizers. In case of grain yield, the highest 44.65% increment over control was recorded with the application of 10t cowdungtha and full dose of chemical fertilizers without Azotobacter application. On the other hand, Azorobacrer application along with the use of three-fourths of the recommended dose of chemical fertilizers produced the highest 57.31% increased grain yield over control. Azotobecter application also resulted notable increment overall In straw yield over control, though the highest straw yield increment (53.03%) was obtained from the application of 10t cowdung/ha and full dose of chemical fertilizers.
Nutrient status of post-harvest soil: Date in Table 4 presents the status of organic matter, total N and available P in the post-harvest soil as influenced by interaction of Azotobacrer with cowdung and chemical fertilizers. By Azatobecter inoculation total N remained unaffected while organic matter and available P showed significant changes. Azotobacter inoculation exerted significant effect in maintaining organic matter content and available P of the post-harvest soil. Although organic matter content and available P of postharvest soil declined from their respective initial, the rate of depletion on Azotabacter inoculated treatments was very minimum compared to those of uninoiulated treatments. However, Azotobacter inoculation along with three-fourths of the recommended dose of chemical fertilizers performed the best in maintaining organic matter and available P status of post-harvest soil probably because of increased enzymatic activities in soil resulting more availability of plant nutrients. The results of this study revealed that Azotobacter applicatian increased plant growth in terms of LAI and tiller number/m2 and ultimately grain and straw yields of rice irrespective of levels of organic and chemical fertilizers. But the highest performance was achieved from Azotobacter application in combination with the use of three-fourths of the recommended dose of chemical fertilizers, On the other hand, Azotobacter application in combination with the use of same level of chemical fertilizer also helped in reducing nutrient depletion from soil.