Symbiotic dinitrogen (N2) fixation of crop and pasture legumes is a critical component of agricultural systems, but its measurement is expensive and labour intensive. Simple models which can provide approximations based on crop or pasture dry matter production would be useful for agrononomists and those interested in regional nitrogen (N) cycle fluxes. We investigate meta analysis of published data on legume shoot dry matter production, shoot %N and legume %N fixed (%Ndfa) and look for relationships among these, as a possible way of providing useful approximations of N2 fixation. We restricted our analysis to Australian studies where we have ready access to the primary data and where cultivars, management and climate are more constrained compared to a universal dataset. Regression analysis between shoot dry matter and amounts of shoot N2 fixed were strong for all crop and pasture legumes with significant differences in slope and intercept values being obtained between pastures and crops, and between chickpea (Cicer arietinium) and all other crop and pasture legumes. Annual pasture legumes showed the strongest linear relationship between N2 fixation and shoot dry matter and had the greatest slope (20.2–24.3 kg N2 fixed/t), compared to 18.7 kg N2 fixed/t for the perennial pasture legume lucerne (alfalfa, Medicago sativa), and between 10.7 to 23.0 kg N2/t for crop legumes, depending upon species. It was recognised that the use of such shoot-based relationships would underestimate the total amounts of N2 fixed since the contributions of fixed N present in, or derived from, roots and nodules are not included. Furthermore there needs to be careful consideration of the validity of an intercept term, which might reflect suppression of N2 fixation at low dry matter and high soil mineral N availability, or possibly the use of non-linear regression. For chickpea crops grown in north-eastern Australia, multiple regression indicated that N2 fixation was much more closely correlated with %Ndfa than dry matter production. Evidence presented also indicated that %Ndfa of other crops and lucerne in this region may similarly be influenced by soil mineral N. The regression approach presented provides a statistical basis to approximate N2 fixation in the first instance. This work highlights some of the dangers of fitting single regressions to aggregated datasets and using these to approximate symbiotic N2 fixation. The analysis indicates that where pasture legumes are grown in mixtures with non-legumes, and driven to high dependence on N2 fixation, simple linear regressions may be quite useful, provided that possible differences between species are investigated as the slopes of the regressions between these can be quite different. For crop legumes, where low dependence on N2 fixation can occur at higher mineral N availability, there is a need to carefully consider the intercept term, obtain estimates of mineral N availability, and/or resort to non-linear models. The gross generalisations presented in scatter plots cannot be reliably applied any more specifically, even within the datasets from which they were generated, and in some cases even within legume species between regions. They cannot substitute for direct measurement where any certainty is required under a particular set of defined conditions.

/pdf/prospects-and-problems-of-simple-linear-models-for-1ffvpv2vjo.pdf

Prospects and problems of simple linear models for estimating symbiotic N2 fixation by crop and pasture legumes

Summary


1. Tests of the effectiveness of rhizobia isolated from several common Acacia species showed significant variation among host populations in plant growth but no indication that plant performance depended on which Acacia species the rhizobial isolate was derived from. Variation in effectiveness was primarily between rhizobial isolates within a host species rather than across rhizobial isolates from different hosts. No interactions were found between host population, host origin of rhizobial strain and rhizobial isolate.



2. A study using a range of less common Acacia species showed significant variation in performance of several species (A. silvestris, A. nano-dealbata, A. trachyphloia, A. filicifolia, A. leucoclada) as a function of the inoculating rhizobial strain; two other species (A. cangaiensis, A. glaucocarpa) were marginally non-significant. For A. filicifolia and A. silvestris, growth was significantly better when plants were inoculated with their own isolates vs. those from other host species.



3. Comparisons of the performance of a third set of Acacia species found that several common species (A. melanoxylon, A. mearnsii, A. irrorata, A. binervata) varied little in their response to particular rhizobial isolates; for these species, most host–rhizobial combinations resulted in similar growth responses. Several less common species showed significant variation in performance across the rhizobial isolates tested.



4. Preliminary investigations of host specificity among legume genera showed significant variation with respect to host performance as a function of the rhizobial isolate with which plants were inoculated. Some species (e.g. A. mearnsii and Indigofera australis) were variable in their responses, while others (e.g. Hardenbergia violacea and A. melanoxylon) performed well with most isolates.



5. A comparison of the effectiveness of several Acacia-derived strains on their own hosts vs. their effectiveness on the other legume genera in the study showed that, in general, the Acacia strains performed well on other genera. However, on some host species (e.g. I. australis) the Acacia strains were less effective than the Indigofera strains, suggesting some host specificity.



6. While there was a general correlation at the among-species level in Acacia–rhizobia interactions (i.e. isolates that performed well on one host species often performed well on others), growth performance with any particular host–rhizobial combination was more difficult to predict than within-species comparisons. Our data also suggest that, at least for the genus Acacia, rare species are likely to exhibit a greater degree of host specificity than hosts that are widely distributed, and re-establishment may require special attention with respect to rhizobial strains that are used.



7. Overall, these results have clear implications for applied projects focused on the restoration of degraded habitats or abandoned farmland. Simply replanting native species into such areas may be unsuccessful unless appropriate rhizobial strains are also reintroduced. Our results suggest that when no strains for a particular host species are available, strains from its closest relative will have the highest probability of success.

Variation in the effectiveness of symbiotic associations between native rhizobia and temperate Australian legumes: interactions within and between genera

N2 fixation and N supply in organic pea (Pisum sativum L.) cropping systems as affected by weeds and peaweevil (Sitona lineatus L.)

Nitrogen balances of narrow leaf lupin (Lupinus angustifolius L.), albus lupin (L. albus L.), field pea (Pisum sativum L.), chickpea (Cicer arietinum L.), and barley (Hordeum vulgare L.) sown over a range of dates were examined in 1992 in a rotation study at Wagga Wagga, NSW. Each N budget included assessment of dependence on fixed as opposed to soil N, peak aboveground biomass N, and N removed as grain or returned as unharvested aboveground crop residues. N balances of wheat sown across the plots in 1993 were assessed similarly in terms of biomass and grain yield. Yields, N2 fixation, and crop residue N balances of the legumes were markedly influenced by sowing time, and superior performance of lupins over other species was related to higher biomass production and proportional dependence on N2 fixation, together with a poorer harvest index. Residual N balances in aboveground biomass after harvest of the 1992 crops were significantly correlated with soil mineral N at 1993 sowing and with biomass and grain N yields of the resulting wheat crop. Best mean fixation and grain N yield came from albus lupin. Wheat grain N yields following the 2 lupins were some 20% greater than after fiield pea and chickpea and 3 times greater than after barley. Net soil N balance based solely on aboveground returns of N of legumes in 1992 through to harvest of wheat in 1993 was least for narrow leaf lupin-wheat ( –20 kg N/ha), followed by albus lupin-wheat ( –44), chickpea-wheat ( –74), and field pea-wheat ( –96). Corresponding combined grain N yields (legume+wheat) from the 4 rotations were 269, 361, 178, and 229 kg N/ha, respectively. The barley-wheat rotation yielded a similarly computed soil N deficit of 67 kg/ha. Data are discussed in relation to other studies on legume-based rotations.

Nitrogen benefits of lupins, field pea, and chickpea to wheat production in south-eastern Australia

The nitrogen economies of six contrasting field pea (Pisum sativum L.) genotypes were examined at three widely separated sites in south Western Australia, using the 15N natural abundance technique to asssess proportional dependence on fixed N, harvests at peak biomass to assess total N yields and harvests at crop maturity to examine partitioning of N between seed and non harvested crop residues. The budgets for one site (Wongan Hills) included N of nodulated roots which on average comprised 12% of total plant N at peak crop biomass and 25% of recoverable plant N after harvest of seed. At this site maximum potential (residual) benefits to a following crop (peak total plant biomass N - N uptake from soil and N taken off as harvested seed) varied between genotypes from 8 to 41 g N ha-1 (mean 26; n = 6). Data for the other two sites, based solely on N budgets of above-ground parts, provided evidence of substantial site- and genotype-specific differences in N balance in terms of shoot residues (i.e. + 7 to - 24 kg N ha-1 (mean - 5) at Avondale, + 40 to - 29 (mean + 3) at Mt Barker). The results collectively indicated a general relationship between peak biomass N of a crop and its potential or otherwise to effect a net input of residue N to the ecosystem. There were, however, considerable variations between genotypes and sites due to differences in proportional dependence on fixation (range across all sites and genotypes 60-91%) and crop harvest indices for N (corresponding range 53-90%). Correlation plots were constructed from the data for N2 fixed against crop dry matter yield and residual nitrogen benefit against nitrogen harvest index. Results are discussed in relation to values for N balance of field pea and other grain legumes obtained elsewhere by other investigators.

Nitrogen Balance of Field Pea Crops in South Western Australia, Studied Using the 15N Natural Abundance Technique

Dry matter, biomass N, N2 fixation (determined by the 15N isotope dilution method), grain yield and grain N, were determined for five pea cultivars grown with three sowing times at six sites in south-eastern Australia. Earlier sowing (late April to early May) increased N2 fixation (by as much as 96 kg N/ha compared to sowing in late June to early July). Early sowing improved the probability of peas contributing to soil total N. The potential increment in soil N from the pea stubbles left after harvesting grain, averaged over the varieties, was as high as 98 kg N/ha with early sowing, and as low as -38 kg N/ha with late sowing. The benefits from earlier sowing were due to larger dry matter production with a higher N concentration and a greater proportion of plant N from N2 fixation. Varietal variation in fixed N and potential for augmenting soil total N, was generally smaller than the variation in these parameters due to different sowing dates.

Sowing Date and Varietal Effects on the N2 Fixation of Field Pea and Implications for Improvement of Soil Nitrogen

Nodulation studies on legumes exotic to Australia: the influence of soil populations and inocula of Rhizobium leguminosarum bv. viciae on nodulation and nitrogen fixation by field peas

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

I Bamforth

Author Tools

Chat about Author

Papers

Sowing Date and Varietal Effects on the N2 Fixation of Field Pea and Implications for Improvement of Soil Nitrogen

Nodulation studies on legumes exotic to Australia: the influence of soil populations and inocula of Rhizobium leguminosarum bv. viciae on nodulation and nitrogen fixation by field peas