A. T. M. A. Choudhury

Prospects and potentials for systems of biological nitrogen fixation in sustainable rice production

The N requirement of rice crops is well known. To overcome acute N deficiency in rice soils, this element is usually supplied to the rice crop as the commercially available fertilizer urea. But unfortunately a substantial amount of the urea-N is lost through different mechanisms causing environmental pollution problems. Utilization of biological N fixation (BNF) technology can decrease the use of urea-N, reducing the environmental problems to a considerable extent. Different BNF systems have different potentials to provide a N supplement, and it is necessary to design appropriate strategies in order to use BNF systems for efficient N supply to a rice crop. Research has been conducted around the world to evaluate the potential of different BNF systems to supply N to rice crops. This paper reviews salient findings of these works to assess all the current information available. This review indicates that the aquatic biota Cyanobacteria and Azolla can supplement the N requirements of plants, replacing 30–50% of the required urea-N. BNF by some diazotrophic bacteria like Azotobacter, Clostridium, Azospirillum, Herbaspirillum and Burkholderia can substitute for urea-N, while Rhizobium can promote the growth physiology or improve the root morphology of the rice plant. Green manure crops can also fix substantial amounts of atmospheric N. Among the green manure crops, Sesbania rostrata has the highest atmospheric N2-fixing potential, and it has the potential to completely substitute for urea-N in rice cultivation.

Nitrogen Fertilizer Losses from Rice Soils and Control of Environmental Pollution Problems

Abstract Nitrogen (N) requirements of rice crop are met from both the soil and fertilizers. Because of acute N deficiency in most rice soils, fertilizer N must be applied to meet the crop demand. N fertilizer applied to rice crops is partially lost through different mechanisms, including ammonia volatilization, denitrification, and leaching. These losses may cause environmental problems such as polluting the atmosphere, aquatic systems, and groundwater. These problems cannot be alleviated completely. However, they can be reduced a considerable extent by various techniques. Research has been conducted around the world to minimize N fertilizer losses. This paper reviews this information on N fertilizer losses, indicating management practices for minimizing these losses from the soil‐water system.

Phosphorus Adsorption in Some Australian Soils and Influence of Bacteria on the Desorption of Phosphorus

Abstract Seven Australian soil samples were collected from different locations (Camden, Griffith, Narrabri, Rutherglen, Wagga Wagga, Wee Waa (Ivanhoe), and Yanco) to measure their phosphorus (P) adsorption rates. Soils were collected from the top 0–15 cm, and P was added at 0, 100, 200, 300, 400, and 500 µg P g−1 soil. Results indicated that P adsorption increased significantly with increasing levels of added P. In subsequent studies, soils from Griffith and Narrabri and two bacteria Pantoea spp. known as FA001 and FA010 were tested for P mobilization at 100 µg P g−1 soil concentration. The rate of P mobilization [P extracted by 0.01 M calcium chloride (CaCl2)] in the Narrabri soil showed significant differences between treatments, but with and without bacteria, this was not the case for the Griffith soil. In Narrabri soil, the highest extractable P (0.492 µg g−1) was obtained with the treatment containing the strain FA001 after bacterial lysis with trichloromethane (CHCl3), and the lowest P (0.236 µg g−1) was measured in the treatment without bacterial amendment and without CHCl3 treatment, indicating the P‐mobilizing ability of the strain FA001. It was found that the minimum P‐adsorption capacities (revealed from the Langmuir and Temkin adsorption isotherms) of the Narrabri and the Griffith soils are 357 and 500 µg g−1, respectively; the buffering capacities of the Narrabri and the Griffith soil are 71.7 and 93.7 µg g−1, respectively. These findings indicate that soils with high P adsorption and buffering capacities are less likely to respond to the P‐mobilizing bacteria. Therefore, the application of the Langmuir and Temkin adsorption isotherms for estimating soil P‐adsorption and buffering capacities can be used to predict the potential usefulness of biofertilizer application.

EFFECTS OF A MULTISTRAIN BIOFERTILIZER AND PHOSPHORUS RATES ON NUTRITION AND GRAIN YIELD OF PADDY RICE ON A SANDY SOIL IN SOUTHERN VIETNAM

Field experiments during two successive rainy seasons were conducted in southern Vietnam to evaluate the effects of a commercial inoculant biofertilizer (‘BioGro’) and fused magnesium phosphate (FMP) fertilizer on yield and nitrogen (N) and phosphorus (P) nutrition of rice. Inoculation with BioGro containing a pseudomonad, two bacilli and a soil yeast significantly increased grain yield in the second season and straw yield in both seasons by 3–5%. The FMP fertilizer significantly increased grain yield from 1.72–2.33 t ha−1 to 2.99–3.58 t ha−1 along with total N and P accumulation at all rates in both cropping seasons. In the first season the difference in grain yield between BioGro treated and untreated plots was marginal but in the second season BioGro out-yielded the control at all the rates of added P. Overall, BioGro application did not compensate for low P fertilizer application to the same extent previously demonstrated for low N fertilizer applications.

Utilization of BNF Technology Supplementing Urea N for Sustainable Rice Production

The critical nitrogen (N) requirement of rice crops for maximum yields is well known. To overcome acute N deficiency in rice soils as a result of an increasing yield per unit area in the past 50 years of almost three-fold, this element has been usually supplied to the rice crop as the chemical fertilizer ‘urea’. Unfortunately a substantial amount of the urea-N is lost through different mechanisms, causing environmental pollution problems. In principle, utilization of biological nitrogen fixation technology can supplement the use of urea-N, reducing the environmental problems to a considerable extent by improving nitrogen use efficiency. Different biological nitrogen fixation (BNF) systems have different potentials to provide an N supplement. It is necessary to design appropriate strategies to obtain more sustainable N supply to the rice crop. This paper reviews research to evaluate the potential of different BNF systems to supply N for the rice crop, assessing the current information.

BioGro: A Plant Growth-Promoting Biofertilizer Validated by 15 Years’ Research from Laboratory Selection to Rice Farmer’s Fields of the Mekong Delta

Since their original isolation from rice paddies near Hanoi, the set of microbial strains comprising the biofertilizer BioGro have been subjected to extensive and intensive experimentation in both laboratory and the field. Based on a hypothesis that such strains inoculated onto rice and other plants could significantly reduce the need for chemical fertilizers, this has been successfully tested using numerous procedures, documented in a series of peer-reviewed papers. The BioGro strains have been examined by a range of molecular and biochemical techniques, also providing means of quality control of inoculants. A positive response by rice plants to BioGro strains has been confirmed by proteomics. More than 20 randomized block design field experiments conducted in Vietnam or Australia have confirmed their effectiveness under a range of field conditions, reviewed here. Interactions with different rice cultivars have also been examined. While the response to inoculation is complex, the hypothesis of increased nutrient efficiency has been amply confirmed as consistent with observations. Finally, an extensive participatory research project over 3 years in the Mekong Delta showed reductions in fertilizer needs as high as 52 % as rice farmers learned to apply the technology. This result shows the importance of such adaptive practices for successful application of this biofertilizer technology in field condition.

Effects of bacterial inoculant biofertilizers on growth, yield and nutrition of rice in Australia

ABSTRACT Inoculant biofertilizer application increased fertilizer nitrogen (N) use efficiency in Vietnam in some previous field experiments. Similar results may be obtained in Australia. With this view in mind, a greenhouse experiment and two field experiments were conducted using a Vietnamese inoculant biofertilizer (BioGro) and several other plant growth promoting (PGP) bacteria. In the greenhouse trial, bacterial inoculations increased shoot and root weights of rice plants significantly. In the field experiments, particularly with Rhizobium leguminosarum, similar effects including significant differences in nitrogen uptake in vegetative matter were observed at the panicle initiation (PI) stage. However, these effects were not significant on grain yield at harvest and it is concluded that the much longer period of growth for Australian rice may allow compensation between treatments. Re-inoculation of plants at the PI stage, and lower application rates of N fertilizer in at least two splits are suggested for future field experiments.

Field Application Strategies for the Inoculant Biofertilizer Biogro Supplementing Fertilizer Nitrogen Application in Rice Production

Biofertilizer research for rice in Vietnam has focused on the isolation and selection of strains that can fix nitrogen, solubilize inorganic phosphates, stimulate plant growth, and breakdown soil organic matter. This paper assesses the consistent positive effect of BioGro on grain yield and agronomic parameters, including the rates and times for its application, the need for continued inoculation of crops grown in the same site, varietal differences, and nitrogen (N), phosphorus (P), and potassium (K) combinations on the effectiveness of BioGro. The commercial biofertilizer, BioGro, consists of four strains, one formerly considered as nitrogen fixing, Pseudomonas fluorescens, a soil yeast strain, Candida tropicalis is P-solubilizing, and two other bacilli, Bacillus amyloliquefaciens and Bacillus subtilis, potentially breaking down cellulose, protein, and starch. All four strains contribute to plant growth promoting rhizobacteria (PGPR) effect as shown by enhanced root growth. BioGro can be produced in local factories providing there is technical backup in the supply of starter culture and quality control of the final product.

Effects of bacterial inoculants and sources of phosphorus on yield and phosphorus uptake of wheat

ABSTRACT Phosphorus (P) mobilizing bacteria play an important role in the availability of soil and fertilizer P for all crops including wheat. Two greenhouse experiments were conducted to evaluate the effects of six P mobilizing bacterial strains and three P sources tricalcium phosphate {[Ca3(PO4)2], calcium hydrogen phosphate [CaHPO4.2H2O] and rock phosphate} on yield and P uptake of wheat. All the bacterial inoculants increased grain yield significantly over control in one greenhouse experiment while only three strains produced significantly higher grain yield over control in a second experiment. Difference among P sources were not significant in acquiring grain yield in experiment 1 while Ca3(PO4)2 and CaHPO4.2H2O produced significantly higher grain yield over rock phosphate in experiment 2. The differential pattern in results in two experiments might be due to difference in growth conditions. More greenhouse studies as well field experiments are recommended to confirm the beneficial effects of these P mobilizing bacterial strains on wheat.

Evaluation of Phosphorus Mobilization Potentials of Six Bacterial Strains from Four Insoluble Phosphorus Sources

A laboratory experiment was conducted to evaluate the P mobilization potentials of six bacterial strains isolated from three wheat-growing soils of Australia. Four different forms of insoluble phosphorus (P) were used in this experiment. Two strains (Pantoea ananatis and Pantoea sp.) mobilized more P from calcium phosphate [Ca3(PO4)2] when ammonium sulfate [(NH4)2SO4] was used as a source of nitrogen (N) compared to ammonium nitrate (NH4NO3) as the N source. The remaining four strains showed increased P-mobilizing ability with nitrate as sources of N. Cultures containing Burkholderia sp. showed a greater net increase in soluble P from rock phosphate compared to Ca3(PO4)2. Mobilization of P from aluminium phosphate (AlPO4) and iron phosphate (FePO4) was much lower than from calcium P sources in cultures containing all the bacterial strains tested. Pantoea ananatis and Pantoea sp. were significantly better than other strains in mobilizing P from AlPO4 whereas Pantoea sp. was identified as a minor P mobilizer from FePO4.