Plant Total Nitrogen Content Research Articles

UAV Multisensory Data Fusion and Multi-Task Deep Learning for High-Throughput Maize Phenotyping.

Recent advances in unmanned aerial vehicles (UAV), mini and mobile sensors, and GeoAI (a blend of geospatial and artificial intelligence (AI) research) are the main highlights among agricultural innovations to improve crop productivity and thus secure vulnerable food systems. This study investigated the versatility of UAV-borne multisensory data fusion within a framework of multi-task deep learning for high-throughput phenotyping in maize. UAVs equipped with a set of miniaturized sensors including hyperspectral, thermal, and LiDAR were collected in an experimental corn field in Urbana, IL, USA during the growing season. A full suite of eight phenotypes was in situ measured at the end of the season for ground truth data, specifically, dry stalk biomass, cob biomass, dry grain yield, harvest index, grain nitrogen utilization efficiency (Grain NutE), grain nitrogen content, total plant nitrogen content, and grain density. After being funneled through a series of radiometric calibrations and geo-corrections, the aerial data were analytically processed in three primary approaches. First, an extended version normalized difference spectral index (NDSI) served as a simple arithmetic combination of different data modalities to explore the correlation degree with maize phenotypes. The extended NDSI analysis revealed the NIR spectra (750-1000 nm) alone in a strong relation with all of eight maize traits. Second, a fusion of vegetation indices, structural indices, and thermal index selectively handcrafted from each data modality was fed to classical machine learning regressors, Support Vector Machine (SVM) and Random Forest (RF). The prediction performance varied from phenotype to phenotype, ranging from R2 = 0.34 for grain density up to R2 = 0.85 for both grain nitrogen content and total plant nitrogen content. Further, a fusion of hyperspectral and LiDAR data completely exceeded limitations of single data modality, especially addressing the vegetation saturation effect occurring in optical remote sensing. Third, a multi-task deep convolutional neural network (CNN) was customized to take a raw imagery data fusion of hyperspectral, thermal, and LiDAR for multi-predictions of maize traits at a time. The multi-task deep learning performed predictions comparably, if not better in some traits, with the mono-task deep learning and machine learning regressors. Data augmentation used for the deep learning models boosted the prediction accuracy, which helps to alleviate the intrinsic limitation of a small sample size and unbalanced sample classes in remote sensing research. Theoretical and practical implications to plant breeders and crop growers were also made explicit during discussions in the studies.

Plant DNA methylation is sensitive to parent seed N content and influences the growth of rice

BackgroundNitrogen (N) is an important nutrient for plant growth, development, and agricultural production. Nitrogen stress could induce epigenetic changes in plants. In our research, overexpression of the OsNAR2.1 line was used as a testing target in rice plants with high nitrogen-use efficiency to study the changes of rice methylation and growth in respond of the endogenous and external nitrogen stress.ResultsOur results showed that external N deficiency could decrease seed N content and plant growth of the overexpression line. During the filial growth, we found that the low parent seed nitrogen (LPSN) in the overexpression line could lead to a decrease in the filial seed nitrogen content, total plant nitrogen content, yield, and OsNAR2.1 expression (28, 35, 23, and 55%, respectively) compared with high parent seed nitrogen (HPSN) in high nitrogen external supply. However, such decreases were not observed in wild type. Furthermore, methylation sequencing results showed that LPSN caused massive gene methylation changes, which enriched in over 20 GO pathways in the filial overexpression line, and the expression of OsNAR2.1 in LPSN filial overexpression plants was significantly reduced compared to HPSN filial plants in high external N, which was not shown in wild type.ConclusionsWe suggest that the parent seed nitrogen content decreased induced DNA methylation changes at the epigenetic level and significantly decreased the expression of OsNAR2.1, resulting in a heritable phenotype of N deficiency over two generations of the overexpression line.

Diagnosis of Nitrogen Nutrition in Sugar Beet Based on the Characteristics of Scanned Leaf Images

Sugar beet is an important economic crop in Northwest China. In this area, efficient use of nitrogen (N) fertilizer has become crucial due to decreased profits associated with both under- and oversupply relative to sugar beet requirements. Thus, fast and non-destruction diagnostic tools for estimating plant N status have an important role in reducing N inputs while maintaining sugar beet yield and qualify. The objective of our study was to quantify leaf color characterization of sugar beet with an inexpensive scanner and establish the relationship with yield, leaf nitrogen content (LNC), plant total nitrogen content (PTNC), chlorophyll content (CC), soil nitrate nitrogen content (SNNC) and soil plant analysis development (SPAD) readings in sugar beet. In 2017 and 2018, field experiments were conducted with five N treatments ranging from 0 to 180 kg N ha−1. The main results showed the following: The SPAD readings (SPR) and CC exhibited a significant or highly significant correlation (maximum = 0.70, P < 0.01), both of which reflected well the N nutrient status of the entire plant. Furtherly, a detailed association analysis revealed that there was a close relationship (maximum = − 0.63, P < 0.01) of LNC, SPR, PTNC, CC and yield with leaf color parameter Red/Blue (R/B), which was recommended as leaf color parameters for N diagnosis in sugar beet. In addition, based on the distribution of R/B value under different N rate, the yield was low with greater R/B value than 1.36 indicating an insufficient N supply, and with the R/B value was lower than 1.36, the theoretical yield reached its peak indicating an adequate supply of N fertilizer. To summarize, compared to the complicated and expensive of hyperspectral and other remote sensing technologies, scanned leaf image (SLI) processing technique was a simple, inexpensive and reliable method of determining sugar beet N status that has potential as a diagnostic tool for determining crop N requirement.

Preparation and Properties of Immobilized Particles Containing Highly Efficient Nitrogen-Fixing Klebsiella variicola GN02 Cells Isolated from the Pennisetum giganteum z. x. lin Roots

The biological properties, structural characterization, and performance of Klebsiella variicola GN02 isolated from the roots of P. sinense and embedded in sodium alginate supplemented with 10% sterile skim milk were investigated. The results showed that the immobilized K. variicola GN02 particles were more stable and had a higher survival rate than free bacteria. Infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis showed that immobilized K. variicola GN02 particles had the peaks associated with sodium alginate and K. variicola GN02 cells, indicating that K. variicola GN02 cells were successfully embedded in the sodium alginate. Compared with free bacteria, the immobilized K. variicola GN02 cells revealed slower but a longer growth period during the 40 h culture period. The OD600 and ammonia secretion of immobilized K. variicola GN02 particles were 0.87 and 18.45 mg/L, respectively. A solution incubated with immobilized K. variicola GN02 exhibited a growth-promoting effect on corn than free K. variicola GN02. Root length, plant height, fresh weight, and total nitrogen content of plants subjected to immobilized K. variicola GN02 increased by 15.3, 16.3, 8.9, and 32.3%, respectively. The number of viable K. variicola GN02 in soil also increased significantly to 20.86 × 105 CFU/g. Therefore, immobilized K. variicola GN02 has promising application value, and this study provides a theoretical basis and reference for developing a biological fertilizer with new nitrogen-fixing bacteria.

Interaction between CO2 elevation and nitrogen metabolism in two varieties of Guar (Cyamopsis tetragonoloba) plants

The aim of the experimental study is to analyse the consequence of carbon dioxide elevation on activity of nitrate reductase (NR; EC 1.6.6.1), nitrite reductase (NiR; EC 1.7.7.1), glutamate synthetase (GOGAT; EC 1.4.1.13) in leguminous Cyamopsis tetragonoloba leaves. Plants were exposed to different atmospheric carbon dioxide concentrations 300 ppm (ambient) and 490 ppm (an elevated) conditions. A decrease in activity of Nitrate Reductase (NR), Nitrite Reductase (NiR), Glutamate Synthetase (GOGAT) was found in elevated condition when compared to ambient condition. Plant nitrogen on dry weight basis was found to decrease under elevation with no significant change in soil nitrogen. Soil pH was found to change significantly under elevation, thus showing a decline in pH and promoting soil acidiosis. Total plant fresh weight (FW) and total plant dry weight (DW), Leaf area/cm2 were found increased in elevated condition. Thus, in Cyamopsis tetragonoloba plant it can be concluded that under carbon dioxide elevation Nitrate reductase, Nitrite reductase and Glutamate synthetase activity is suppressed due to a reduced amount of nitrate translocation and NADH availability for reduction in plant which is correlated with reduction in plant total nitrogen content where as plant growth and biomass is enhanced due to higher carbon fixation.

Endophytic bacteria improve nodule function and plant nitrogen in soybean on co-inoculation with Bradyrhizobium japonicum MN110

The potential of bacterial endophytes to improve symbiotic efficiency through synergistic interactions with rhizobia can help to improve nodulation and nitrogen fixation in legume plants. In the present study, we compared the effect of endophytic plant growth-promoting bacteria on nodulation and effective rhizobial symbiosis in soybean. Nodule endophyte Bacillus megaterium LNL6 isolated from root nodules of Lesperdeza sp. and plant endophyte Methylobacterium oryzae CBMB20 isolated from rice leaves were selected as endophytic co-inoculants. Treatment of Bradyrhizobium japonicum MN110 along with B. megaterium LNL6 and M. oryzae CBMB20 exhibited an increase in nodule number in pots at 35 days after sowing compared to single inoculation of MN110. Additionally, both the co-inoculation treatments showed significant increase in nodule activity which was measured in terms of nodule leghemoglobin content, nodulated root ARA and total plant nitrogen content compared to solitary inoculation of B. japonicum MN110. Though ACCD activity of the co-inoculated strains can be attributed to increase in nodule number, the observed increase in root nitrogenase activity and leghemoglobin content in the nodules is understood as due to plant growth promotion traits of the specific endophytic strains. High levels of IAA produced by B. megaterium LNL6 can be considered to have aided development of mature nodules which thereby improved the nodular nitrogen fixation. Thus, endophytic lifestyle combined with plant growth-promoting traits, such as IAA production, ACC deaminase, cellulase and nitrogenase activity by B. megaterium LNL6 and M. oryzae CBMB20, contributes to the improvement of overall symbiotic nitrogen fixation by the plant.

Pea growth and symbiotic activity response to Nod factors (lipo-chitooligosaccharides) and soil compaction

Growth and symbiotic activity of legumes are reduced by high soil compaction and mediated by Nod factors (LCO, lipo-chitooligosaccharides) application. Our objective was to assess the combined effects of soil compaction and Nod factors application on growth and symbiotic activity of pea. The experiment was two factorial and included soil compaction (1.30gcm−3 – not compacted (control) and 1.55gcm−3 – compacted soil), and Nod factors concentration (control without addition of Nod factors and use of 260nM Nod solution) for each soil compaction. The soil (Haplic Luvisol) was packed into pots, pea (Pisum sativum L.) seeds were soaked with Nod factors solution or water and then plants were grown for 46 days. This study has shown that soil compaction and treatments of pea seeds with Nod factors influenced pea growth and symbiotic activity. Soil compaction significantly reduced pea growth parameters, namely plant height, dry mass, leaf area, root mass and root length and symbiotic parameters, namely mass of nodules, dry mass of an individual nodule, nitrogenase activity and total nitrogen content in plant in comparison to the non-compacted treatment. Treatment of seeds with Nod factors generally improved nearly all of the above parameters. Nitrogenase activity per pot and total plant nitrogen content were significantly reduced by soil compaction and increased by application of Nod factors in plants grown in not compacted soil. Our results demonstrate that increased symbiotic activity resulting from Nod factors addition may mitigate adverse effect of soil compaction on plant growth.

Different Nitrogen Sources Affect Biomass Partitioning and Quality of Potato Production in a Hydroponic System

Crop production systems should reduce nitrogen application costs and assure that the appropriate form of nitrogen is used. Thus, three potato cultivars in a hydroponic system were supplied with two different nitrogen sources to determine the effect on biomass accumulation and partitioning, and total plant nitrogen content. Cultivars Agata, Atlantic and Bintje received, on alternate days, nutritive solutions differing only in either calcium nitrate or urea. Urea stimulated biomass accumulation and total nitrogen in shoots. Moreover, urea reduced the ratios tuber:shoot and tuber:root, and increased the ratio shoot:root, indicating competition for biomass partitioning between shoots and tubers. Urea stimulated greater tuber volume in the Atlantic cultivar, and increased tuber protein content, which is undesirable for industry. These results suggested that salts containing nitrate could be more appropriate for hydroponic potato cultivation, since urea compromised tuber quality and biomass partitioning in all cultivars studied.

Isotopic evidence of significant assimilation of atmospheric-derived nitrogen fixed by Azospirillum brasilense co-inoculated with phosphate-solubilising Pantoea dispersa in pepper seedling

The contribution of plant growth-promoting bacteria (PGPB) of the genus Azospirillum to the plant N budget through biological nitrogen fixation (BNF) is still controversial. The aim of this study was to determine the contribution of BNF by Azospirillum brasilense on pepper grown at different N levels, attained using the 15N natural abundance method. To this end, pepper plants were grown in a growth chamber and treated with A. brasilense combined with Pantoea dispersa and then irrigated at four different N levels (0, 1, 3 and 7 mM NO 3 −). The assimilation of fixed N was clear from the lower δ 15N values observed in bacteria-treated plants compared with those of non-bacteria treated plants. The percentage of BNF-derived N decreased with decreasing NO 3 − levels in the growth medium. BNF contribution to the total nitrogen content of plants was found to be as high as 46%. The results suggest that the bacteria have a potential to supply a considerable amount of N to pepper seedlings, as well as to stimulate plant growth and N uptake when Azospirillum– Pantoea treatment is combined with low NO 3 − levels.

Ontogenetic shift in the scaling of dark respiration with whole‐plant mass in seven shrub species

Summary 1. Recent evidence suggests that metabolic scaling exponents should shift from ≈ 1 to ∼¾ as plants grow from seedlings to mature trees. This study examines whether there is an ontogenetic shift in the scaling exponent of dark respiration with whole‐plant biomass and whether the allometry of dark respiration vs. plant total nitrogen content is consistent with these metabolic scaling relationships. 2. We examined seedling mass, dark respiration, biomass allocation, water and nitrogen contents, and relative growth rates for 351 seedlings of seven shrub species that span three orders of magnitude in total plant mass (i.e. &lt;1 mg to &gt;1 g). 3. Dark respiration increased with increasing seedling mass in each of three growth stages for each species. The scaling exponents for dark respiration vs. plant mass were c. 1·0 during the earliest stage of seedling development (&lt;60 days after germination) but declined in the later two growth stages (&gt;90 and &lt;120 days after seed germination) for five of the seven species studied. However, the metabolic scaling relationship was isometric when the data were pooled for each species across all size classes. 4. With increasing plant size, the biomass allocated by each species to the metabolically active organ (leaf) generally scaled against whole plant biomass with a slope smaller than 1·0 but significantly larger than ¾. 5. Water and nitrogen contents declined with increasing seedling mass and whole plant dark respiration increased disproportionally (i.e. scaling slope &gt;1) with increasing total plant water or nitrogen content, possibly because small seedlings have a lower water and nutrient‐use efficiency compared to larger ones in water‐ and nutrient‐ unlimited habitats. 6. The change in relative growth rate paralleled the ontogenetic shift in the dark respiration vs. mass relationship, which may explain the isometric metabolic scaling relationship if growth efficiency is inversely proportional to seedling mass. 7. We therefore demonstrate an ontogenetic shift in the metabolic scaling during plant ontogeny. Although the proximate mechanisms underlying the shift are not fully understood, we speculate that a contributing factor is the accrual of less metabolically active tissues or organs with increasing total body mass in the form of secondary tissues with high cell wall volume fractions (e.g. wood and phellum).

Does the exception prove the rule? (Reply)

Enquist . 1 raise several points that they claim cast doubt on our findings and interpretation2 regarding whole-plant relations of respiration, R, with plant mass, M, and total plant nitrogen content, N. We agree with Enquist et al. that R does not scale isometrically with M across all plants. However, their assertion that we claim that isometric scaling (R ∝ Mθ, with θ = 1) is universal in plants of all sizes is incorrect — in fact, we conclude the opposite2, noting that there is isometric scaling within individual experiments, non-isometric scaling of respiration versus mass across all data pooled, and no common relation across all data2.

Effects of wild rice (Zizania palustris) straw on biomass and seed production in northern Minnesota

Wild rice ( Zizania palustris L.) litter accumulation may inhibit plant growth and production both by physically suppressing seedling emergence and by nitrogen immobilization in fresh litter. This latter mechanism could reduce nitrogen availability to plants early in the growing season at a period when more than half of the annual uptake occurs. To test the importance of these mechanisms, we planted wild rice in mesocosms. Half the tanks were planted with seeds sown below the litter and half were planted with seedlings grown to a height taller than litter thickness. One-third of the tanks were treated with fresh (nitrogen immobilizing) litter, one-third were treated with litter that had been incubated for 26 d and was mineralizing nitrogen, and one-third did not receive litter. These treatments resulted in a fully crossed factorial design, with nine replicates for each treatment combination, totaling 54 tanks. We measured plant growth, vegetative, root, and seed biomass, total plant N, and available N at 2.5 cm sediment depth. The presence of litter and its stage of decay caused plant, root, and seed biomass, and seed and total plant nitrogen content to increase. We found no physical inhibition of litter on the potential growth of plants started as seeds. Therefore, the timing of litter nitrogen immobilization or mineralization affects the potential growth of wild rice.

Composition of Casuarina leaf litter and its influence on Frankia-Casuarina symbiosis in soil.

Plant needles of Casuarina equisetifolia were collected and analyzed in parallel with soil analysis. In three strains of Frankia--symbionts of Casuarina--their infectivity and plant performance was determined in vitro after soil amendment with different leaf litter concentrations. Only one strain was able to nodulate the plant at all litter concentrations (0.5, 3 and 5%) although the nodules were very small. However, all treated plants grew poorly; their growth was reduced by approximately 90% (for 5% litter concentration) compared to plants grown on untreated soil, on the basis of total dry mass. Inhibition of nodulation can be attributed to high concentrations of some elements and compounds that were either found in C. equisetifolia litter or originally found in soil (i.e. chloride, cyanide, copper, manganese and phenols). In general, plant growth decreased as more litter was added. Plant total nitrogen content was also reduced after increasing the litter concentration. The inhibitory effect of high litter concentrations was mainly on plant growth and to a lesser extent on plant nodulation by Frankia strains.

Response of Soybean [Glycine max (L.) Merr.] Cultivars to Genistein‐Preincubated Bradyrhizobium japonicum: Nodulation and Dry Matter Accumulation under Canadian Short‐Season Conditions

The addition of genistein, a plant‐to‐bacteria signal molecule, to Bradyrhizobium japonicum cells prior to use as inocula has been shown to increase nodule number and promote soybean N2 fixation at low root zone temperatures. Previous greenhouse and field experiments involving only two cultivars have indicated that soybean [Glycine max (L.) Merr.] cultivars can vary in their response to genistein application. The objective of this study was to evaluate a range of soybean cultivars for response to genistein application under short‐season cool‐spring Canadian conditions. A 2‐year field study was conducted in 1997 and 1998 with a range of soybean cultivars recommended for Quebec. The 11 cultivars tested represented a range of yield potentials and maturity groups. They were inoculated with genistein‐preincubated B. japonicum inocula or regular inocula, applied into the furrow at the time of planting. The results of these experiments indicated that neither maturity nor yield was correlated with increases in nodulation, biomass, and plant total nitrogen content resulting from genistein treatment and that all maturity groups responded to genistein application in essentially the same way. Thus, response of soybean cultivars to genistein addition is regulated by genotype characteristics other than maturity or yield level.

Preincubation of B. japonicum cells with genistein reduces the inhibitory effects of mineral nitrogen on soybean nodulation and nitrogen fixation under field conditions.

Genistein is the major root produced isoflavonoid inducer of nod genes in the symbiosis between B. japonicum and soybean plants. Reduction in the isoflavonoid content of the host plants has recently been suggested as a possible explanation for the inhibition of mineral nitrogen (N) on the establishment of the symbiosis. In order to determine whether genistein addition could overcome this inhibition, we incubated B. japonicum cells (strain 532C) with genistein. Mineral N (in the form of NH4NO3) was applied at 0, 20 and 100 kg ha-1. The experiments were conducted on both a sandy-loam soil and a clay-loam soil. Preincubation of B. japonicum cells with genistein increased soybean nodule number and nodule weight, especially in the low-N-containing sandy-loam soil and the low N fertilizer treatment. Plant growth and yield were less affected by genistein preincubation treatments than nitrogen assimilation. Total plant nitrogen content was increased by the two genistein preincubation treatments at the early flowering stage. At maturity, shoot and total plant nitrogen contents were increased by the 40 μM genistein preincubation treatment at the sandy-loam soil site. Total nitrogen contents were increased by the 20 μM genistein preincubation treatment only at the 0 and 20 kg ha-1 nitrate levels in clay-loam soil. Forty μM genistein preincubation treatment increased soybean yield on the sandy-loam soil. There was no difference among treatments for 100-seed weight. The results suggest that preincubation of B. japonicum cells with genistein could improve soybean nodulation and nitrogen fixation, and at least partially overcome the inhibition of mineral nitrogen on soybean nodulation and nitrogen fixation.

Gas exchange and growth responses to elevated CO2 and light levels in the CAM species Opuntia ficus‐indica

ABSTRACTGas exchange and dry‐weight production in Opuntia ficus‐indica, a CAM species cultivated worldwide for its fruit and cladodes, were studied in 370 and 750 μmol mol−1 CO2 at three photosynthetic photon flux densities (PPFD: 5, 13 and 20 mol m−2 d−1). Elevated CO2 and PPFD enhanced the growth of basal cladodes and roots during the 12‐week study. A rise in the PPFD increased the growth of daughter cladodes; elevated CO2 enhanced the growth of first‐daughter cladodes but decreased the growth of the second‐daughter cladodes produced on them. CO2 enrichment enhanced daily net CO2 uptake during the initial 8 weeks after planting for both basal and first‐daughter cladodes. Water vapour conductance was 9 to 15% lower in 750 than in 370 μmol mol−1 CO2. Cladode chlorophyll content was lower in elevated CO2 and at higher PPFD. Soluble sugar and starch contents increased with time and were higher in elevated CO2 and at higher PPFD. The total plant nitrogen content was lower in elevated CO2. The effect of elevated CO2 on net CO2 uptake disappeared at 12 weeks after planting, possibly due to acclimation or feedback inhibition, which in turn could reflect decreases in the sink strength of roots. Despite this decreased effect on net CO2 uptake, the total plant dry weight at 12 weeks averaged 32% higher in 750 than in 370 μmol mol−1 CO2. Averaged for the two CO2 treatments, the total plant dry weight increased by 66% from low to medium PPFD and by 37% from medium to high PPFD.

Radiometric estimation of biomass and nitrogen content of barley grown at different nitrogen levels†

Abstract Field measurements of red (655 nm) and near-infrared (NIR: 805 nm) canopy reflectance from barley grown at different nitrogen levels are related to changes in biomass accumulation and total nitrogen content of the plant material. Crop biomass and the NIR reflectance or the NIR/red index are highly correlated. The variation in reflectance and index accounted for by the biomass is between 93 and 99 per cent. In the different nitrogen treatments the percentage nitrogen content of the crop is negatively correlated with the biomass accumulation, and the nitrogen content declines in a exponential manner. The correlation coefficient between plant nitrogen content and biomass declines from −0·99 to −0·92 with increasing nitrogen application rates. However, at any given chronological age the total plant nitrogen content and the accumulated biomass are strongly correlated in a curvilinear manner. Hence on each sampling date the NIR and NIR/red reflectance are closely related to percentage plant nitrogen in...

Symbiotic effectiveness of strains of Rhizobium leguminosarum biovar phaseoli isolated from soils of Rwanda

We have isolated 48 strains of Rhizobium leguminosarum biovar phaseoli from nodules of Phaseolus vulgaris L. cultivated on 32 different soils at 22 various locations in Rwanda, Central Africa. The symbiotic effectiveness of the strains was appraised in the greenhouse by measuring shoots dry matter and total plant nitrogen content after six weeks of growth. Of the strains tested 19%, 58% and 23% were rated very effective, effective and ineffective, respectively. A very significant correlation (r=0.96, P<0.01) was observed between shoots dry matter and total N content. By using the total nitrogen balance method, it was estimated that in the presence of a very effective strain, up to 86% of the N present in the shoots comes from N2 fixation. No significant correlations were observed between the symbiotic effectiveness of the strains and the pH of the soils from which they originated, the tolerance of the strains to acidity or their ability to produce organic acids. The nine very effective strains selected were highly competitive against two ineffective strains with the two P. vulgaris cultivars Rubona-5 and Kiryumukwe.

Wild Oat (Avena fatua) and Spring Barley (Hordeum vulgare) Growth and Development in Monoculture and Mixed Culture

Barley (Hordeum vulgareL. ‘Advance’) and wild oat (Avena fatuaL. # AVEFA) were grown in the field in monoculture and mixed culture (additively) to compare their seasonal growth and development. Barley and wild oat tiller and tiller head production were reduced by the interference (higher density) of the other species. Plant height of either species was not affected by interference of the other. Wild oat biomass was reduced more and at an earlier growth stage (two to three tillers) than was barley biomass (heading) in mixed culture. Barley and wild oat grown in monoculture had similar total plant nitrogen content throughput the growing season. Gas exchange and water potential of barley and wild oat in monoculture and mixed culture were similar. All measurements indicated that barley and wild oat grown in monoculture had growth and development patterns that were similar. In mixed culture, however, barley was more competitive with wild oat than wild oat was with barley. Wild oat reduced barley yield component quality and grain yield.

Uptake hydrogenase in fast‐growing strains of Rhizobium sp. (Sesbania) in relation to nitrogen fixation

Eight of 104 fast‐growing strains of Rhizobium sp. (Sesbania) tested possessed a hydrogen recycling system. Depression of uptake hydrogenase occurred in poor as well as in rich carbon media. A statistically significant increase (&gt; 22%) in total plant nitrogen content and dry matter yield was observed by the inoculation of hup+ strains over hup‐ strains.