On the Canadian prairies, organic production generally includes the use of annual green manure (GrM) crops, which are terminated using tillage to add nutrients and organic matter to the soil. However, in a GrM plough-down year, farmers face loss of income. As an alternative to growing traditional GrM crops, legumes can be grown alone or intercropped with cereals and harvested as green feed forage (GF) for use on-farm or for sale to other producers without depleting soil nitrogen (N) for the subsequent crop. We hypothesized that the GF system would have similar biomass, and N yield, and ultimately would return N into the soil. Furthermore, by intercropping a legume with a cereal, biological N2-fixation will be enhanced in the legume.<p> Field experiments, conducted over two years, were established at Vonda and Delisle, Saskatchewan, Canada. The experiment was conducted using a randomized complete block design (RCBD) with 16 treatments and four replicates in which field pea (<i>Pisum sativum</i> cv 40-10 silage pea), oat (<i>Avena sativa</i> L.cv AC Morgan), and triticale (X <i>Triticosecale</i> Wittmack cv Pika) were grown alone or in combination and managed as GrM or GF. Wheat and tillage fallow served as cropped and uncropped controls, respectively. The tillage fallow-control system was tilled twice in the growing season using a small tractor disc. The intercropped oat was seeded at three densities (50, 100, and 150 plants m-2) to determine whether increasing cereal density stimulated N2-fixation in the field pea.<p> The GrM system was sampled and incorporated (when the field pea was at full bloom) two weeks earlier than the GF system. Consequently, at both sites, all treatments in the GF system consistently yielded more dry matter and accumulated more N than treatments in the GrM system. At the Delisle site, where percent nitrogen derived from the atmosphere (%Ndfa) was compared, increasing cereal density did not increase N2-fixation in both management systems. However, pea in the GF system accumulated more than twice the amount of N (kg ha-1) from fixation as compared to pea in the GrM system, presumably because of the longer growth period.<p> Wheat grown following the GrM treatments produced more biomass and accumulated more N than wheat following the GF treatments. Wheat grown after the monoculture field pea as a GrM had greater yield than all treatments. As well, the GrM system returned more N to the soil than did the GF system. The extra two weeks of growth in the GF system resulted in the extraction of significant amounts of nutrients and probably moisture from the soil, which adversely affected yield and nutrient composition of the following wheat crop.<p> Although organic farmers may lose income in the plough-down year, on a longterm soil sustainability basis, the GrM system is a better option than the GF system as it returns nutrients to the soil, thus providing improved plant biomass, and N accumulation of subsequent crops. However, organic farmers growing GF for hay may benefit from the increased productivity of this system on a short-term basis. Thus, farmers pursuing GF options may need to adopt other means of sustaining soil productivity on a longer term. The tilled fallow-control system resulted in high amounts of biomass and N accumulation by the subsequent wheat crop, probably due to the fact that there were no nutrients taken up in the previous year and moisture was conserved in these treatments. However, this system may have less long-term benefits compared to the GrM regime, as no nutrients are returned through ploughing down a crop.

Many multicellular cyanobacteria produce specialized nitrogen-fixing heterocysts. During diazotrophic growth of the model organism Anabaena (Nostoc) sp. strain PCC 7120, a regulated developmental pattern of single heterocysts separated by about 10 to 20 photosynthetic vegetative cells is maintained along filaments. Heterocyst structure and metabolic activity function to accommodate the oxygen-sensitive process of nitrogen fixation. This dissertation focuses on my research on heterocyst development, including morphogenesis, transport of molecules between cells in a filament, differential gene expression, and pattern formation. We using microarray experiments we found that conR (all0187) gene is necessary for normal septum-formation of vegetative cells, diazotrophic grow, and heterocyst morphogenesis. In our studies we characterized the expression of sigma factors genes in Anabaena PCC 7120 during heterocyst differentiation, and we found that the expression of sigC, sigG and sigE is localized primarily in heterocysts. Expression studies using sigE mutant showed that nifH is under the control of this specific sigma factor.

Diss. (sammanfattning) Umeå : Sveriges lantbruksuniversitet, 2009. / Härtill 4 uppsatser.

In the soybean nitrogen fixing symbiosis, suboptimal root zone temperatures (RZTs) inhibit the inception and development of nodules, leading to reduced nitrogen fixation and soybean yield. The purpose of this thesis was to evaluate the effects of selected with potential low temperature tolerant strains, originating from the northern areas of the USA, and mutants made from Bradyrhizobium japonicum USDA 110, on soybean nodulation, nitrogen fixation and yield in a short season area with cool spring conditions. Among the 40 B. japonicum strains evaluated, only USDA 30, USDA 31, 532 C and USDA 110 grew well at 15°C. USDA 30 and USDA 31 grew better than 532 C and USDA 110 at 15°C. Mutants Bj 30050--Bj 30059 could not produce lipo-chito-oligosaccharide (LCO) at measurable levels in the absence of genistein. All mutants produced more LCOs than 532 C and USDA 110 at the same temperature and genistein concentration. Temperature and genistein concentration did not affect LCO production dynamics for the following: mutant Bj 30055, 532 C and USDA 110. Both mutant production and identification of low temperature tolerant strains achieved the general objective of improved soybean nitrogen fixation in a cool climate. Inoculation with low temperature tolerant strains (USDA 30, USDA31), or mutants (Bj 30055 and Bj 30058) improved soybean development (increases in leaf area and shoot nitrogen content), nodulation (increases in nodule number and nodule weight), nitrogen fixation and yield relative to inoculation with B. japonicum strain 532 C, the strain currently included in most Canadian soybean inocula.

Whole farm nutrient budgets (WFNB) enable producers to link dairy herd management with traditional field nutrient management plans. The objective of this study was to calculate WFNBs of nitrogen, phosphorus, and potassium (N, P, and K) at a commercial farm in New Brunswick and in Prince Edward Island. Reliable estimates of N fixation from alfalfa and red clover on the farms were obtained with adjustments to the Høgh-Jensen et al. (2004) dry matter conversion models. The farms had surpluses of N, P, and K. Both farms imported feed as well as nutrient inputs for crop production. Surpluses of all nutrients were typical in comparison to WFNBs of similar dairy farms; however, the nutrient use efficiencies were low. The imported manure and fertilizer used in the crop production components contributed to surpluses of N and P which could likely be reduced to improve overall farm nutrient use efficiency.

The effect of Ascophyllum nodosum extracts on the nodulation and growth of alfalfa was investigated. Plant growth assay revealed that alfalfa treated with 2 g L-1 ANE exhibited a significant increase in leaf area. Under salt stress, alfalfa treated with 0.5 g L-1 ANE exhibited a significant increase in total length compared to controls. A root hair deformation assay indicated that ANE 0.5 g L-1 stimulated the synthesis of Nod factors secreted by rhizobia thus accelerate root hair deformation of alfalfa. Similarly, ANE 0.5 g L-1 caused an increase in nodC gene expression suggesting that ANE may act similarly to flavonoids in the rhizobium-legume symbiosis. Under field conditions, ANE increased the total number of functional nodules, total root length and total leaf area. Taken together, the results suggest that ANE may contain compound(s) that promote specific metabolic pathway both in alfalfa and bacterium thus enhance the symbiotic relationship.

Glutamine (Gln) is a critical intermediate in nitrogen metabolism in all organisms. Here, a whole cell biosensor (GlnLux) for Gln was constructed by transforming a bacterial Gln auxotroph with a constitutive lux reporter. The biosensor was optimized for sensitivity, linearity, efficiency, specificity and robustness to permit detection of Gln in vitro and in vivo. The optimized GlnLux biosensor achieved nanomolar sensitivity with Gln standards. Extracts from only 1 mg of maize (Zea mays L.) leaf tissue were sufficient for Gln detection by GlnLux. Measurements of Gln in leaf extracts by GlnLux correlated with quantification by high performance liquid chromatography (Spearman r = 0.95). GlnLux permitted indirect in planta imaging of Gln using a CCD camera, enabling identification of plants that had been fertilized with nitrogen. Imaging using GlnLux also resolved predicted spatial differences in leaf Gln concentration. In a second application, it was demonstrated that GlnLux embedded into agar permits non-destructive screening of co-inoculated bacterial colonies for biological nitrogen fixation (BNF). GlnLux agar was able to distinguish a Bradyrhizobium japonicum wild type strain (nif+) from a mutant strain defective in nitrogenase (nif-) following ≥8 h of co-incubation. The technology was used to screen a bacterial endophyte diversity library cultured from Zea mays (L.) seeds for biological nitrogen fixation. / OMAFRA

In this study, six annual legumes and the perennial, red clover (Trifolium pratense L.) were monocropped (MC) and intercropped (IC) with barley in a field study with three N levels, 0, 30 and 60 kg N ha$ sp{-1}$. At O kg N ha$ sp{-1}$, N$ sb2$-fixation and N transfer were estimated by the $ sp{15}$N isotope dilution (ID) method. At 60 kg N ha$ sp{-1}$, a direct $ sp{15}$N labelling method was employed to study N transfer. The hypotheses were that the annual species would be more productive within one growing season than red clover, that increased N levels would increase herbage dry matter (DM) and crude protein (CP), that the proportion of N derived from N$ sb2$-fixation in IC-legumes would be higher than that of MC-legumes and that within intercrops there would be evidence of N transfer. In neither year was the total DM yield of red clover, MC or IC, less than the rest of the legumes. In 1991, the total DM yield of intercrops responded to 30 kg N ha$ sp{-1}$; in neither year did the estimated total CP yield of MC-legumes or intercrops respond to N levels. Only in 1992 was there evidence of N$ sb2$-fixation and the proportion of N derived from fixation by IC-legumes was 145% higher than that of MC-legumes. Only the $ sp{15}$N direct labelling method gave evidence of N transfer, to associated legume and barley plants in 1991, and to associated legume plants in 1992.

Soybean (Glycine max (L.) Merr.) is a subtropical legume that requires root zone temperatures (RZTs) in the 25 to 30$ sp circ$C range for optimal symbiotic activity. The inability of soybean to adapt to cool soil conditions limits its development and yield in short season areas. In particular, nodulation and N$ sb2$ fixation by this subtropical crop species is sensitive to cool (RZT). The objectives of this thesis were to determine whether or not PGPR could be used to help overcome the low RZT inhibition of soybean nodulation, to improve soybean nitrogen fixation and yield under field conditions and to determine the methods by which such increases occurred. The work reported in this thesis has demonstrated that PGPR can increase early season nodulation and total seasonal nitrogen fixation and yield of soybean growing in an area with cool spring soils. The ability of PGPR to stimulate soybean nodulation and growth was shown to be related to their ability to colonize soybean roots, and this was shown to be related to RZT. All steps in early nodulation were stimulated by the presence of PGPR. The beneficial effects of PGPR are exerted through a diffusible molecule excreted into the growth medium. The addition of genistein, a plant-to-bacteria signal molecule already shown to stimulate soybean N$ sb2$ fixation at low RZT, plus PGPR causes increases in soybean nodulation, N$ sb2$ fixation, and growth that were greater than those caused by the addition of PGPR alone, but only at 25 and 17.5$ sp circ$C, and not at 15$ sp circ$C RZT.

Maximum wheat (Triticum aestivum L.) yields in Zambia were obtained with weekly irrigation at 85% of class A pan evaporation during the whole irrigation interval and split application of urea N of which the initial portion of the fertilizer was either broadcast and incorporated or broadcast after the crop had established itself. This corresponded with maximum utilization of fertilizer N. The proportion of N derived from fertilizer was independent of fertilizer placement at various water regimes and N utilization was primarily a function of water availability. / Two nonnodulating soybean (Glycine max L.) cultivars, Clark RJ1 and N77, or in their absence Pearl millet (Panicum glaucum L.) were judged to be appropriate reference crops for estimating N$ sb2$ fixation by soybeans using $ sp{15}{ rm N}$ isotope dilution techniques. A local soybean cultivar, Magoye, was rated highest among three cultivars tested for its ability to support N$ sb2$ fixation by Bradyrhizobium japonicum and contributed biologically fixed N$ sb2$ to a subsequent wheat crop.