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To detect N2‐fixing bacteria in a plant without using culture methods, nifH gene segments were amplified with degenerate primers from DNA extracted from stems of sugarcane (Saccharum officinarum L.) and leaves of pineapple (Ananas comosus [L.] Merr.). Sequences of the nifH clones were homologous to those of bacteria in the genera Bradyrhizobium, Serratia, and Klebsiella. The bacteria with nifH sequences homologous to those of the three genera may be promising candidates for predominant endophytic diazotrophs in sugarcane and pineapple, because these sequences were commonly detected in samples from different host plants, which were collected at different locations. On the other hand, no nifH sequence related to Gluconacetobacter diazotrophicus, which is an endophytic N2‐fixing bacterium and had been previously isolated from sugarcane, was detected in sugarcane. This indicates the absence or the presence of few G. diazotrophicus in the stems of the sugarcane plants used in the current study.

Sugar mill by-products compost may be a good soil amendment to promote tomato (Lycopersicon esculentum L.) growth. In addition, the compost may further promote plant growth by inoculation with N 2 -fixing bacteria. Compost from sugar-mill waste was prepared with and without the N 2 -fixing bacteria, Azotobacter vinelandii, Beijerinckia derxii and Azospirillum sp. and incubated for 50 days. Each compost type was added to 10 kg of soil in pots at rates of 0, 15, and 45 g with and without fertilizer N at rates of 0, 0.75, and 1.54 g. A blanket application of P and K was applied to all pots. Shoot and root dry weights and N content of the whole plant was measured at 55 days. Dry weight of tomato shoots was increased by 40% by addition of fertilizer N and root weight was increased by 66%. Without fertilizer N the high rate of inoculated compost increased shoot growth 180% and uninoculated compost increased shoot growth 112%. For most treatments with and without fertilizer N, inoculated compost enhanced shoot growth and nitrogen content more than uninoculated compost. Root weights were nearly doubled by addition of either compost in comparison to the 0 N treatment. At the low rate of compost addition without fertilizer N, root weight was the same for uninoculated and inoculated compost but at the high rate of compost addition root weight was 32% higher for inoculated compost. The N 2 -fixing bacteria colonized roots when inoculated compost was used. Sugar mill by-products compost proved to be an effective soil amendment for promoting the growth of tomato plants.

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Inoculation of sugar mill by-products compost with N 2 -fixing bacteria may improve its quality by increasing total N and available P. Compost was inoculated with Azotobacter vinelandii (ATCC 478), Beijerinckia derxii (ATCC 49361), and Azospirillum sp. TS8, each alone and all three together. Numbers of all N 2 -fixing bacteria in compost declined from an initial population of 5 · 10 5 cells g )1 during incubation. The population of Azotobacter declined to approximately 2 · 10 2 cells g )1 and the population of Beijerinckia and Azospirillum declined to approximately 9 · 10 3 and 3.5 · 10 4 cells g )1 respectively, at day 50. Inoculation with N 2 -fixing bacteria increased acetylene reduction, total N by 6-16% and available P by 25-30% in comparison to the uninoculated control. Increasing the N content and P availability of compost increases its value and there may be additional benefit from providing N 2 fixing bacteria.