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  • Soil Fertility
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  • 1
    Language: English
    Description: In many tropical regions, slash-and-burn agriculture is considered as a driver of deforestation; the forest is converted into agricultural land by cutting and burning the trees. However, the fields are abandoned after few years because of yield decrease and weed invasion. Consequently, new surfaces are regularly cleared from the primary forest. We propose a reclamation strategy for abandoned fields allowing and sustaining re-cultivation. In the dry region of south-western Madagascar, we tested, according to a split-plot design, an alternative selective slash-and-burn cultivation technique coupled with compost amendment on 30-year-old abandoned fields. Corn plants (Zea mays L.) were grown on four different types of soil amendments: no amendment (control), compost, ashes (as in traditional slash-and-burn cultivation), and compost + ashes additions. Furthermore, two tree cover treatments were applied: 0% tree cover (as in traditional slash-and-burn cultivation) and 50% tree cover (selective slash-and-burn). Both corn growth and soil fertility parameters were monitored during the growing season 2015 up to final harvest. The amendment compost + ashes strongly increased corn yield, which was multiplied by 4-5 in comparison with ashes or compost alone, reaching 1.5 t/ha compared to 0.25 and 0.35 t/ha for ashes and compost, respectively. On control plots, yield was negligible as expected on these degraded soils. Structural equation modeling evidenced that compost and ashes were complementary fertilizing pathways promoting soil fertility through positive effects on soil moisture, pH, organic matter, and microbial activity. Concerning the tree cover treatment, yield was reduced on shaded plots (50% tree cover) compared to sunny plots (0% tree cover) for all soil amendments, except ashes. To conclude, our results provide empirical evidence on the potential of recultivating tropical degraded soils with compost and ashes. This would help mitigating deforestation of the primary forest by increasing lifespan of agricultural lands.
    Keywords: Crop Yield ; Deforestation ; Microbial Activity ; Organic Matter ; Soil Fertility ; Structural Equation Model
    ISSN: 20457758
    E-ISSN: 20457758
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  • 2
    Language: English
    In: Soil Biology and Biochemistry, December 2014, Vol.79, pp.117-124
    Description: Crop production in subsistence agriculture in tropical Africa is still sustained mainly by short-to medium-term fallows to recuperate natural fertility of the soils. Microbes play a pivotal role both in the process of soil fertility restoration and in nutrient acquisition by the crops. Here we ask the question how the duration of fallow affects the composition of indigenous arbuscular mycorrhizal fungal (AMF) communities and their contribution to maize nutrition and growth, in acidic, low P soils of southern Cameroon. This question has been addressed in a bioassay where soils collected from continuously cropped fields, short-term fallows dominated by and long-term fallows (secondary forests) have been sterilized and back- and cross inoculated with living soils from the different land-use systems. Particular microbes larger than the pore size of the filter paper (mainly the fungi including the AMF) contained in the cropped and short-fallowed soils caused greater growth and P uptake stimulations to the maize as compared to the forest soil. By using molecular profiling, we demonstrated a shift in the composition of AMF communities along a gradient of fallow duration, changing from dominance by in the forest fallow soil, to dominance by under cropland. Our results contradict the hypothesis that deterioration of quality of root symbiotic communities would be responsible for a rapid yield decline following deforestation, and indicate a positive feedback of cropping on mycorrhizal functioning under conditions of shifting agriculture in tropical Africa.
    Keywords: Arbuscular Mycorrhiza ; Bioassay ; Chromolaena Odorata ; Fallow ; Maize ; Phosphorus ; Quantitative Real-Time Pcr ; Southern Cameroon ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 3
    Language: English
    In: Agriculture, Ecosystems and Environment, 30 January 2011, Vol.140(1-2), pp.155-163
    Description: ▶ We describe how legume proportion modifies N acquisition from different sources. ▶ Symbiotic N fixation was stimulated in mixtures compared to monocultures. ▶ Uptake of N from soil N pools was stimulated in mixtures compared to monocultures. ▶ The acquired N was used more efficiently by mixtures for biomass production. Concerted use of legumes and of functional diversity in grassland forage systems can provide major contributions to the challenges of agricultural systems being productive yet environmental friendly. Acquisition and transformation of nitrogen (N) resources by legumes and grasses were studied in a temperate grassland experiment near Zurich (Switzerland) to investigate mechanisms driving effects of functional diversity in mixed swards and to optimise mixtures for efficient resource use. Grass–legume interactions and N availability were varied by manipulating legume percentage of the sward (0–100%) and N fertiliser application (50, 150 or 450 kg of N ha year ). N technology quantified N derived from symbiotic (Nsym) and non-symbiotic (Nnonsym) sources. Generally, acquisition of Nsym by the entire mixture was stimulated by grasses. As a result, strong overyielding of Nsym occurred (e.g. 75 and 114% for year 1 and 2 at N150) and mixtures with only 60% and 37% legumes (year 1 and 2) already attained the same Nsym yield as pure legume stands. Legumes stimulated Nnonsym acquisition by the entire mixture, largely via increased uptake by the grass component. Thus, overyielding of Nnonsym of 31% occurred in year 1 (N150). Mutual grass–legume interactions stimulated acquisition of Nsym, acquisition of Nnonsym and efficient transformation of N into biomass compared to either monocultures. These effects of functional diversity can substantially contribute to productive and resource efficient agricultural grassland systems and were maximised in mixtures with 40–60% legumes.
    Keywords: Competition ; Cost 852 ; Facilitation ; N Uptake ; Symbiotic N2 Fixation ; Transgressive Overyielding ; Agriculture ; Environmental Sciences
    ISSN: 0167-8809
    E-ISSN: 1873-2305
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  • 4
    Language: English
    In: Plant and Soil, 2010, Vol.334(1), pp.391-407
    Description: Organic farming largely depends on animal manure as a source of phosphorus (P) and the recycling of animal manure globally is becoming increasingly important. In a pot experiment, using radioactive P labeling techniques, we studied ryegrass uptake of P applied with animal manure and water soluble mineral fertilizer to soils that had been cropped for 22 years according to organic or conventional farming practices. The soils differed in P status and microbial activity. Labeling soil-available P also allowed assessing the uptake from residual P that remained in the soils because of their different fertilization histories. On each soil, recovery of fresh manure P in four harvests of ryegrass shoots was lower than recovery of mineral P. It ranged from 24% to 35% for manure P and from 37% to 43% for mineral P. Recovery of fresh manure P was affected by soil-available P contents. It was lower at a higher available P in a conventional soil. Different levels in microbial activity among soils were of lesser importance for the recovery of fresh manure P in plants. The recovery of residual P ranged from 9% to 15%. Residual P contained in organic cropped soils contributed less to P nutrition of ryegrass than the residual P contained in conventional cropped soils, probably due to their lower residual P contents being composed of stable P forms. The indirect isotope dilution technique is useful in assessing manure P uptake by plants, but attention must be given to added P interactions, i.e., the potential impact of organic amendments on P uptake from non-labeled soil and residual P.
    Keywords: Phosphorus ; Animal manure ; Residual phosphorus ; Isotope techniques ; Phosphorus uptake ; Organic and conventional farming
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 5
    Language: English
    In: Soil & Tillage Research, March 2016, Vol.156, pp.99-109
    Description: In view of the importance of soil carbon (C) and the scarce data on how conservation agriculture might influence its accumulation in Southern Africa this study presents data from 125 on-farm validation trials across 23 sites in Malawi, Mozambique, Zambia and Zimbabwe. These validation trials are paired plot comparisons of conventional agricultural practice and conservation agriculture that had been established between 2004 and 2009. Traditional cropping systems vary across the study area although they all are tillage based and maize is the main crop grown. The treatments proposed on the validations trials reflect this variability in conventional practice and propose an adapted conservation agriculture option. The sites are thus grouped into four specific treatment comparisons. Bulk density and soil C concentrations were measured from samples collected at four depth layers (0–10 cm, 10–20 cm, 20–30 cm and 30–60 cm), thereafter C stocks were calculated. On the basis of the stover biomass harvest C inputs were assessed. No consistent differences in bulk density and soil C concentrations were found. Carbon stocks were found to be positively influenced by conservation agriculture only when a mouldboard ploughed maize-legume rotation was compared to a direct seeded maize legume rotation (with residue retention). Even when increases were significantly greater under conservation agriculture the order of magnitude was small (∼2 Mg ha ). Limited C inputs, ranging between 0.1 and 1 g C kg soil yr , are likely to be the major bottleneck for C increase. These results, based on on-farm validation trials indicate that there is a limited potential for conservation agriculture to significantly increase soil C stocks after up to 7 years of conservation agriculture practices, in the studied systems.
    Keywords: Residue Retention ; Soil Fertility ; Carbon Sequestration ; Agriculture
    ISSN: 0167-1987
    E-ISSN: 1879-3444
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  • 6
    In: Journal of Applied Ecology, June 2009, Vol.46(3), pp.683-691
    Description: 1 Increasing plant species richness often increases biomass production in nutrient‐poor semi‐natural grasslands. If such positive diversity–productivity effects also apply to nutrient‐rich agricultural grasslands, mixtures could improve resource‐use efficiency in the vast area used for forage production. We therefore quantified the diversity–productivity effects in nutrient‐rich agricultural grasslands using four‐species grass–legume mixtures. 2 The sown overall density and species proportions of Lolium perenne, Dactylis glomerata, Trifolium pratense and Trifolium repens were varied in a 3‐year field experiment to investigate the effects of species richness (1, 2, 4 species) and species proportion (0, 3, 10, 25, 40, 50, 70, 90, 100% sowing proportion) on productivity under a nitrogen fertilization of 50, 150 or 450 kg N ha−1 year−1. 3 The four‐species mixtures reached up to twice the yield of the average of the four species’ monocultures (overyielding up to 106%), predominantly due to combining grass and legume species. Mixtures were up to 57% more productive than the most productive monoculture (transgressive overyielding). Both these diversity–productivity effects appeared across a broad range of species proportions and persisted at the two lower levels of N fertilization for 3 years. 4 Mixtures fertilized with 50 kg N ha−1 year−1 produced yields comparable to grass monocultures fertilized with 450 kg N ha−1 year−1, if the legume proportion was about 50 to 70%. Diversity–productivity effects were reduced at the highest level of N fertilization, where they virtually disappeared in the third year. Increased N fertilization also accelerated the observed general trend towards D. glomerata dominated and legume‐poor swards. 5 Synthesis and applications. Diversity–productivity effects led to consistent transgressive overyielding in intensively managed grasslands, suggesting a highly increased resource‐use efficiency in mixtures. Performance better than monocultures can be achieved with grass–legume mixtures that have a low number of species, across a wide range of species proportions and in nutrient‐rich conditions. Processes such as niche complementarity and positive interspecific interactions leading to diversity effects proved to be highly relevant and widely applicable for intensive forage production. Such diversity–productivity effects could allow reduced inputs of N fertilizer without loss of productivity in different grassland production systems.
    Keywords: Cost 852 ; Diversity–Ecosystem Function ; Diversity–Productivity Effects ; Grass–Legume Mixtures ; Monocultures ; Rgrd ; Simplex Design ; Species Proportions ; Yield
    ISSN: 0021-8901
    E-ISSN: 1365-2664
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  • 7
    Language: English
    In: Nutrient Cycling in Agroecosystems, 2010, Vol.88(3), pp.447-462
    Description: Canavalia brasiliensis (canavalia), a drought tolerant legume, was introduced into the smallholder traditional crop-livestock production system of the Nicaraguan hillsides as green manure to improve soil fertility or as forage during the dry season for improving milk production. Since nitrogen (N) is considered the most limiting nutrient for agricultural production in the target area, the objective of this study was to quantify the soil surface N budgets at plot level in farmers fields over two cropping years for the traditional maize/bean rotation and the alternative maize/canavalia rotation. Mineral fertilizer N, seed N and symbiotically fixed N were summed up as N input to the system. Symbiotic N 2 fixation was assessed using the 15 N natural abundance method. Nitrogen output was quantified as N export via harvested products. Canavalia derived in average 69% of its N from the atmosphere. The amount of N fixed per hectare varied highly according to the biomass production, which ranged from 0 to 5,700 kg ha −1 . When used as green manure, canavalia increased the N balance of the maize/canavalia rotation but had no effect on the N uptake of the following maize crop. When used as forage, it bears the risk of a soil N depletion up to 41 kg N ha −1 unless N would be recycled to the plot by animal manure. Without N mineral fertilizer application, the N budget remains negative even if canavalia was used as green manure. Therefore, the replenishment of soil N stocks by using canavalia may need a few years, during which the application of mineral N fertilizer needs to be maintained to sustain agricultural production.
    Keywords: N natural abundance method ; Canavalia brasiliensis ; Forage legume ; Nicaraguan hillsides ; Nitrogen budget ; On-farm trials
    ISSN: 1385-1314
    E-ISSN: 1573-0867
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  • 8
    Language: English
    In: Environmental science & technology, 20 February 2018, Vol.52(4), pp.1919-1928
    Description: The application of mineral phosphate (P) fertilizers leads to an unintended Cd input into agricultural systems, which might affect soil fertility and quality of crops. The Cd fluxes at three arable sites in Switzerland were determined by a detailed analysis of all inputs (atmospheric deposition, mineral P fertilizers, manure, and weathering) and outputs (seepage water, wheat and barley harvest) during one hydrological year. The most important inputs were mineral P fertilizers (0.49 to 0.57 g Cd ha yr) and manure (0.20 to 0.91 g Cd ha yr). Mass balances revealed net Cd losses for cultivation of wheat (-0.01 to -0.49 g Cd ha yr) but net accumulations for that of barley (+0.18 to +0.71 g Cd ha yr). To trace Cd sources and redistribution processes in the soils, we used natural variations in the Cd stable isotope compositions. Cadmium in seepage water (δCd = 0.39 to 0.79‰) and plant harvest (0.27 to 0.94‰) was isotopically heavier than in soil (-0.21 to 0.14‰). Consequently, parent material weathering shifted bulk soil isotope compositions to lighter signals following a Rayleigh fractionation process (ε ≈ 0.16). Furthermore, soil-plant cycling extracted isotopically heavy Cd from the subsoil and moved it to the topsoil. These long-term processes and not anthropogenic inputs determined the Cd distribution in our soils.
    Keywords: Soil ; Soil Pollutants
    ISSN: 0013936X
    E-ISSN: 1520-5851
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  • 9
    Language: English
    In: Frontiers in Plant Science, 01 November 2017, Vol.8
    Description: Yam (Dioscorea spp.) is a tuber crop grown for food security, income generation, and traditional medicine. This crop has a high cultural value for some of the groups growing it. Most of the production comes from West Africa where the increased demand has been covered by enlarging cultivated...
    Keywords: Dioscorea Spp ; Soil Fertility ; Interdisciplinarity ; Transdisciplinarity ; Innovation Platforms ; Botany
    E-ISSN: 1664-462X
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  • 10
    Language: English
    In: Environmental science & technology, 16 April 2019, Vol.53(8), pp.4140-4149
    Description: The supplementation of Zn to farm animal feed and the excretion via manure leads to an unintended Zn input to agricultural systems, which might compromise the long-term soil fertility. The Zn fluxes at three grassland sites in Switzerland were determined by a detailed analysis of relevant inputs (atmospheric deposition, manure, weathering) and outputs (seepage water, biomass harvest) during one hydrological year. The most important Zn input occurred through animal manure (1076-1857 g ha yr) and Zn mass balances revealed net Zn accumulations (456-1478 g ha yr). We used Zn stable isotopes to assess the importance of anthropogenic impacts and natural long-term processes on the Zn distribution in soils. Soil-plant cycling and parent material weathering were identified as the most important processes, over the entire period of soil formation (13 700 years), whereas the soil pH strongly affected the direction of Zn isotopic fractionation. Recent anthropogenic inputs of Zn only had a smaller influence compared to the natural processes of the past 13 700 years. However, this will probably change in the future, as Zn stocks in the 0-20 cm layer will increase by 22-68% in the next 100 years, if Zn inputs remain on the same level as today.
    Keywords: Soil ; Soil Pollutants
    ISSN: 0013936X
    E-ISSN: 1520-5851
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