Growth‐promoting diazotrophs can enhance the growth and development of associated crops by transferring fixed N or by improving nutrient uptake through modulation of hormone‐linked phenomena in inoculated plants. Six rhizobial diazotrophs isolated from a wide range of legume hosts were investigated to determine their growth‐promoting activities in lowland rice (Oryza sativa L.) during 1997. Seeds and seedlings of rice Pankaj were inoculated with different rhizobia and grown in potted soil supplemented with varied amounts of mineral N. Inoculation with Rhizobium leguminosarum bv. trifolii E11, Rhizobium sp. IRBG74, and Bradyrhizobium sp. IRBG271 increased rice grain and straw yields by 8 to 22 and 4 to 19%, respectively, at different N rates. Nitrogen, P, and K uptake were increased by 10 to 28% due to rhizobial inoculation. Nitrogen‐15‐based studies indicated that the increased N uptake was not due to biological N2 fixation (BNF). Inoculation also increased Fe uptake in rice by 15 to 64%. Indole‐3‐acetic acid (IAA) accumulated in the external root environment of rice plants when grown gnotobiotically with rhizobia. The results indicate that certain strains of rhizobia can promote rice growth and yield, most likely through mechanisms that involve changes in growth physiology or root morphology rather than BNF.

and Leong, 1986), thereby suppressing the diseases they cause. Other mechanisms of GPA include the induction Rice (Oryza sativa L.) is one of the world's most important crops.of host systemic disease resistance (Maurhofer et al.,The present investigation was designed to assess the range of growthpromoting activities of various diazotrophic bacteria on rice seedling 1994), N 2 fixation (Burton, 1976), solubilization of previgor, its carryover effect on straw and grain yield, and the persistence cipitated mineral nutrients (Subba Rao, 1982), and/or of an inoculant strain on rice roots under greenhouse conditions. production of plant growth regulators (Tien et al., 1979; Growth responses to inoculation exhibited bacterial strain-rice variety Bashan et al., 1990) that induce additional root hairs specificity that were either stimulatory or inhibitory. Growth reand/or lateral root formation (Tien et al., 1979), thereby sponses included changes in rates of seedling emergence, radical elonenhancing the plant's ability to take up nutrients from gation, height and dry matter, plumule length, cumulative leaf and root soil and increase yield. areas, and grain and straw yields. Most notable were the inoculation Rhizobial inoculation of legume seed is well studied, responses to Rhizobium leguminosarum bv. trifolii E11 and Rhizoand exploitation of this beneficial N 2 -fixing root-nodule bium sp. IRBG74, which stimulated early rice growth resulting in a symbiosis represents a hallmark of successfully applied carryover effect of significantly (P ϭ 0.05) increased grain and straw yields at maturity, even though their culturable populations on roots agricultural microbiology. However, much less informadiminished to below detectable values at 60 d after planting. The test tion is available regarding the association and GPA of strains were positive for indole-3-acetic acid production in vitro, but rhizobia with nonlegumes. In nature, rhizobia do associonly some reduced acetylene to ethylene in association with rice under ate with roots of nonlegumes without forming true nodlaboratory growth conditions. These studies indicate that certain ules (Ladha et al., 1989; Yanni et al., 1997), but their strains of nonphotosynthetic diazotrophs, including rhizobia, can propopulations decrease in number in the absence of lemote growth and vigor of rice seedlings, and this benefit of early gume-host plants (Ladha et al., 1989; Chabot et al., seedling development can carryover to significantly increased grain 1996b). Direct growth promotion of nonlegumes by rhiyield at maturity.

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Rice crops uptake large amounts of potassium (K), which is mainly supplied from inorganic fertilizer. Alternate K sources are essential to preserve natural reserves and to recycle unused K containing stubbles. We have evaluated the performance of rice straw (RS) in farmers' field following integrated plant nutrient system (IPNS) for supplementing K requirement of rice and compared with agro-ecological zone (AEZ )-based chemical fertilizer and farmers' practice in Tista Meander Floodplain soils of Bangladesh during 2013-2015. Application of RS @ 4.5 t ha −1 + IPNSbased fertilizer replaced full dose of chemical K fertilizer without significant reduction in grain yield of Boro rice. The K uptake with RS incorporation was similar to AEZ-based chemical fertilizer use. Considering soil health and environmental issue, RS + IPNS-based fertilizer management was the best option for growing wetland rice. INWASCON

in promoting growth of nonlegumes following inoculation (Fyson and Oaks, 1990;Haque and Ghaffar, 1993; Rhizobial inoculation increases grain yield in rice (Oryza sativa L.), a nonlegume plant, but little is known about the mechanism(s) involved. This study was conducted to determine whether inoculation but little is known about the mechanism(s) involved. with rhizobia could influence leaf photosynthesis of rice plants underProbable mechanisms were increased root growth that greenhouse conditions. Rice seeds and pot soil were inoculated with favored higher nutrient uptake (Chabot et al., 1996; three rhizobial strains with or without added N fertilizer. Single-leaf Yanni et al., 1997), disease control (Haque and Ghaffar, net photosynthetic rates were measured with portable photosynthesis 1993), and production of a phytohormone (Chabot et systems (LI-6200 and LI-6400) at several growth stages. Stomatal al., 1996). Recently, Volpin and Phillips (1998) reported conductance, chlorophyll fluorescence, specific leaf weight, and leaf N content were also measured. Grain yield and yield components that inoculated rhizobia influence the physiological stawere determined at maturity. A significant increase in single-leaf net tus of inoculated plants by increasing root respiration. photosynthetic rate by rhizobial inoculation was observed in all three Biswas et al. (2000a) reported that rhizobial inoculation independent experiments. The effect of rhizobial inoculation on phosignificantly increased uptake of N, P, K, and Fe by tosynthesis was greater in zero-N than in 90 kg N ha Ϫ1 treatment. rice plants compared with the uninoculated control. In The increase in photosynthetic rate by rhizobial inoculation was 12% another study, Biswas et al. (2000b) observed a signifiaveraged across all treatments in the three experiments. The effects of rhizobial inoculation on stomatal conductance, specific leaf weight, cant increase in vigor of rice seedlings following rhizoand leaf N content were relatively small and less consistent than bial inoculation. This benefit of early seedling developphotosynthetic rate. Chlorophyll fluorescence data suggest that the ment could carry over to significantly increase grain increase in photosynthetic rate following rhizobial inoculation was not yield at maturity. associated with conversion efficiency of light energy in photosystem II.

Purpose Information on carbon dioxide (CO 2 ) emission from different organic sources and their temperature sensitivity to decomposition is scarce in Bangladesh. Therefore, this study quantified the rates of CO 2 emission and carbon (C) degradation constants from different organic material mixed soils at variable temperatures in two laboratory experiments. Methods The first experiment was conducted at room temperature for 26 weeks to study CO 2 emission and C mineralization using vermicompost, chicken manure, cow dung, rice straw, and rice husk biochar. Weekly CO 2 emission was measured by alkali absorption followed by acid titration. The second experiment comprised two factors, viz. four organic materials (vermicompost, chicken manure, cow dung, and rice straw) and six temperature regimes (25, 30, 35, 40, 45, and 50°C). Organic materials at 2.5 g C kg -1 soil were mixed in both experiments. Results CO 2 emission reached the peak at 5th weeks of incubation and then decreased with irregular fashion until 21st week. The C emission loss followed in the order of chicken manure [ rice straw [ vermicompost [ cow dung [ rice husk biochar, and C degradation constants indicated the slower decomposition of rice husk biochar compared to cow dung, vermicompost, chicken manure, and rice straw. Temperature positively enhanced the mineralization of organic materials in the order of 50 [ 45 [ 40 [ 35 [ 30 [ 25°C, which contributed to higher availability of soil phosphorus. Conclusions High temperature increased mineralization of tested organic materials. Because of slower decomposition rice husk biochar, cow dung and vermicompost application can be considered as climate-smart soil management practices that might help in reducing CO 2 emission from soil.