| 1. |
- Dahlin, Sigrun, et al.
(författare)
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Allanblackia – a tree crop under current domestication: What are the soil requirements and symbionts?
- 2012
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In order to improve livelihoods and enhance food security and resilience of rural communities, diverse and multifunctionalagricultural systems are promoted. There has long been a lack of investment in domestication of plant species that arespecifically suited to African farmers' circumstances, but there is now a growing demand for commercialization and use of localcrops and trees. One example is the indigenous tree Allanblackia which seeds contain high-value edible oil. Traditionally,Allanblackia seeds have been collected from wild stands by rural communities, but more recently access to wild stands isthreatened by deforestation. During the last decade, Allanblackia oil has further received attention from industry as raw materialin the production of spreads and soaps, increasing the demand for Allanblackia seeds. In response to this ICRAF in 2002launched a research program aiming for the domestication of Allanblackia tree species on smallholder farms. Up to now,research activities have focused on selection of highly productive plant materials and propagation methods. However, to fullyoptimize the harvest potential of domesticated Allanblackia, the trees´ requirements for nutrients and water must be met, butknowledge on this is largely lacking. Work carried out on management of Allanblackia seedlings at the nursery has preliminarilyshown that incorporation of soil collected from native Allanblackia stands in the potting medium enhances growth of seedlings,indicating a positive plant-microbial interaction. Symbiotic relationships between plants and micro-organisms are very commonand often stimulate nutrient and water uptake from the soil. However, in this case it remains to clarify if such interaction existsand, if so, which organisms are involved and how they can be promoted in the nursery and on farm-land. The purpose of thisstudy is to obtain information about the environmental requirements of Allanblackia and it has two main objectives. The generalsoil chemical and physical parameters of natural A. stuhlmannii stands will be determined and will with information on climaticconditions and the soil water regime be used to characterise the abiotic requirements of the species. Biological enhancing factorswill be sought, with a particular focus on mycorrhizal symbionts. The fieldwork will be carried out during August-September2012, in the Eastern Arc Mountains, Tanzania. Together with local expertise and researchers at ICRAF, native Allanblackiastands will be localised and site characteristics, such as elevation, slope and drainage assessed. In addition, soil samples will becollected for characterisation of chemical and physical properties, such as soil pH, major plant nutrients, soil organic carbon, soiltexture, bulk density and water holding capacity. The root systems will also be traced from the tree and root fragments collected,bleached and stained. These will subsequently be examined for occurrence of arbuscules and vesicles in the search for possiblesymbionts, and degree of colonisation determined. The study will provide knowledge on the environmental requirements andbiological relationships essential for understanding the tree's biology and appropriate cultivation practices and thus contribute tothe domestication process. Preliminary results will be presented at the conference.
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| 2. |
- Dahlin, Sigrun, et al.
(författare)
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Cutting regime affects the amount and allocation of symbiotically fixed N in green manure leys
- 2010
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Ingår i: Plant and Soil. - : Springer Science and Business Media LLC. - 0032-079X .- 1573-5036. ; 331, s. 401-412
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Tidskriftsartikel (refereegranskat)abstract
- Cutting strategy effect on N(2) fixation and distribution of fixed N above and below ground in red clover (Trifolium pratense L.) and mixed red clover/perennial ryegrass (Lolium perenne L.) green manure leys was quantified in field experiments including in situ mezotrons and microplots. Symbiotically fixed N in clover, transfer of fixed N to grass in the mixed stands and the fate of (15)N contained in mulch were estimated by isotope dilution. Below ground clover-derived N was estimated by leaf labelling. Total N(2) fixation was estimated by correcting fixed N in plant shoots with plant-derived N below ground and recycled N from mulch. The total N(2) fixation was larger in harvested and mulched stands (average 45 g m(-2)) than in the intact stands (32 g m(-2)). Of the fixed N, 53% (intact), 46% (harvested) and 60% (mulched) was found below ground. The average recycling of N in mulch was 21% and contributed 13.7% (pure clover) and 2.2% (mixed) of the clover N in the regrowth. Recycling of N did not decrease N(2) fixation in the mulched compared with harvested stands. The results indicate that cutting regime should be considered when estimating total amounts of N fixed by green manure leys.
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| 3. |
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| 4. |
- Dahlin, Sigrun, et al.
(författare)
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Mulch N recycling in green manure leys under Scandinavian conditions
- 2011
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Ingår i: Nutrient cycling in agroecosystems. - : Springer Science and Business Media LLC. - 1385-1314 .- 1573-0867. ; 91, s. 119-129
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Tidskriftsartikel (refereegranskat)abstract
- Nitrogen (N) recycling to the regrowth of mulched red clover (Trifolium pratense L.) and mulched mixed red clover/perennial ryegrass (Lolium perenne L.) leys was determined in field experiments during three consecutive years using (15)N-labelled shoot material. Nitrogen recycling was greater in the pure clover stands than in the mixed stands in the beginning of the growing season, but increased successively in the mixed stands so that it was similar (14-15.5%) in both stands at the end of the season. This recycling of N from the mulch led to increased biomass accumulation but did not alter stand composition in the mixed stands. Mulch-derived N was incorporated into the soil organic N in both pure clover and mixed stands which thus contributed to building up soil fertility. An approximately similar proportion of N remained unaccounted for in mulched pure clover and mixed stand leys and presumably represented gaseous losses. To exploit the benefits of green manure leys in the humid temperate zone while minimising the negative environmental impact, these should be harvested rather than mulched.
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| 5. |
- Dahlin, Sigrun, et al.
(författare)
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N release pattern from green manures can be modified through species composition
- 2012
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Ingår i: Acta Agriculturae Scandinavica, Section B - Soil and Plant Science. - : Informa UK Limited. - 0906-4710 .- 1651-1913. ; 62, s. 659-665
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Tidskriftsartikel (refereegranskat)abstract
- This study examined whether the N release pattern during decomposition of plant materials used as green manures can be modified in the short term through mixing plant materials with different levels of easily degradable compounds. In a lysimeter study, white clover shoots were mixed with perennial ryegrass shoots or chicory roots. Leaching of clover N was decreased more by inclusion of chicory than by ryegrass. However, decreased leaching losses over the non-growing season did not lead to enhanced N uptake by the crop during the following growing season.
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| 6. |
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| 7. |
- Dahlin, Sigrun, et al.
(författare)
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Recycled by-products can make positive contributions to the yield and nutritional composition of grass-clover leys
- 2013
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Four selected by-products (biogas digestate, pot ale, wood ash and rockdust) were tested for their fertiliser value to a mixed perennial ryegrass-red clover crop in terms of crop performance (yield and botanical composition) and mineral quality. To render the results relevant to production systems on marginal land, two inherently low-fertility soils were used for the 14 months pot experiment. A number of nutrients of interest in high-yielding dairy production were determined in plants and soils: N, P, K, Ca, Mg, Na, Co, Cu, Mn, Mo, Ni and Zn. All tested by-products increased overall yield and affected nutrient concentrations of the individual plant species. The effects differed between the grass and clover, though, which lead to changes in botanical composition indirectly affecting the nutrient concentrations of the mixed crop. Individual by-products increased concentrations of Cu, Mg, Na and/or Zn to close to or over the recommended minimum concentrations. There is thus potential to enhance agricultural productivity on marginal land through improved forage production and quality by matching of by-products, soils and forage species/mixtures. However, to secure sustainable use of by-products as fertilisers or soil amendments, soil quality must be considered and monitored in addition to crop quality, e.g. by using element balances.
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| 8. |
- Dahlin, Sigrun
(författare)
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Review of interventions and technologies for sustainable intensification of smallholder crop production in sub-humid sub-Saharan Africa : with an assessment of effectiveness of selected options on differently endowed case study farms : a working paper
- 2014
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Besides low soil fertility, climate variability has often been identified as the major constraint to agricultural productivity in Sub-Saharan Africa (SSA), with rainfall variability (both within and across seasons) being the most critical. Traditionally, reasonable yields could be achieved in spite of constant or smaller resource inputs by expanding the cropped area, but this is no longer a viable option. Crop production intensification is required to produce more food per unit of input and land, while maintaining or rebuilding soil fertility. However, most smallholder farmers lack access to resources such cash, fertiliser and technological expertise to address constraints caused by the biophysical environments in which they operate. The objective of this review was to collate and appraise the range of crop production intensification options that have been developed for smallholder farmers in SSA. A case study from central Mozambique was included to illustrate the impact and relevance of locally feasible options to farmers who own different resources. The study has revealed that sustainable intensification of crop production requires that multiple constraints are addressed simultaneously, in this case primarily soil fertility/plant nutrient supply and weed management. Success of crop intensification options will also depend on proper targeting to different farm types as well as field soil fertility gradients. Although smallholder farmers in SSA have limited assets, the case study revealed the occurrence of local opportunities to increase current crop productivity which in some cases do not need substantial capital inputs by the farmers, but more efficient use and targeting.
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| 9. |
- Dahlin, Sigrun, et al.
(författare)
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Revisiting herbage sample collection and preparation procedures to minimise risks of trace element contamination
- 2012
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Ingår i: European Journal of Agronomy. - : Elsevier BV. - 1161-0301 .- 1873-7331. ; 43, s. 33-39
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Tidskriftsartikel (refereegranskat)abstract
- A renewed interest in trace elements (TE), as micronutrients as well as potentially toxic elements, and new options for multi-element analysis has led to an increased number of scientists engaging in TE studies. Accreditation, certification and quality control of TE analyses often applies only to the last step in the sample chain when prepared samples are sent to the laboratory for digestion/extraction and subsequent analysis. However, all stages of the chain from initial sampling to final analysis require an understanding of the specific challenges involved in TE studies and an awareness of the contamination risks as well as approaches to limit these. Contamination can potentially be introduced during all stages of handling and preparation of plant samples, e.g. through dust and the materials that make up the different work surfaces, tools and containers used. Milling devices originally used during preparation of two sets of archived herbage samples were tested to indicate the degree of contamination that can arise from milling. For example, some of the milling devices tested showed effects on several TE concentrations while also increasing the variability between samples. A titanium knife mill which was included for comparison gave the best results, showing no measurable contamination by TE of primary interest, while it allowed a high throughput of samples. To enhance the quality of data on TE in bulky plant material such as herbage and to ensure future usability of newly archived samples, we suggest that field handbooks and sample preparation protocols (where needed) are revised to include precautions against TE contamination in all handling steps. This will ensure reliable data on concentrations of micronutrients and potential toxic TE in plant material. (C) 2012 Elsevier B.V. All rights reserved.
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| 10. |
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