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Selenium is essential for human health and mainly delivered via terrestrial foodstuffs. An advanced characterization of selenium chemical forms shows that organic matter increases its accumulation in soils but could limit its supply to plants

Drained cultivated peatlands have been an essential agricultural resource for many years. To slow and reduce the degradation of these soils, which increases with drainage, the use of plant-based amendments (straw, wood chips, and biochar) has been proposed. Literature on the effects of such amendments in cultivated peatlands is scarce, and questions have been raised regarding the impact of this practice on nutrient cycling, particularly nitrogen (N) dynamics. By means of a six-month incubation experiment, this study assessed the effects of four plant-based amendments (biochar, a forest mix, willow, and miscanthus) on the release kinetics of water-soluble N pools (mineral and organic) in two histosols of differing degrees of decomposition (Haplosaprist and Haplohemist). The amendment rate was set at 15 Mg ha−1 on a dry weight basis. The N release kinetics were significantly impacted by soil type and amendment. Miscanthus and willow were the amendments that most reduced the release of soluble organic N (SON) and mineral N (minN). The addition of plant-based amendments reduced the total amount of released N pools during the incubation (cumulative N pools) by 50.3 to 355.2 mg kg−1, depending on the soil type, the N pool, and the type of amendment. A significant relationship was found between microbial biomass N, urease activity, and the cumulative N at the end of the incubation. The results showed that the input of plant-based amendments in cultivated peatland decreases N release, which could have a beneficial impact by decreasing N leaching; however, it could also restrict crop growth. Further research is needed to fully assess the impact of such amendments used in cultivated peatlands on N and on C fluxes at the soil–plant and soil–atmosphere interfaces to determine if they constitute a long-term solution for more sustainable agriculture.

Abstract Background An aquaponic system couples cultivation of plants and fish in the same aqueous medium. The system consists of interconnected compartments for fish rearing and plant production, as well as for water filtration, with all compartments hosting diverse microbial communities, which interact within the system. Due to the design, function and operation mode of the individual compartments, each of them exhibits unique biotic and abiotic conditions. Elucidating how these conditions shape microbial communities is useful in understanding how these compartments may affect the quality of the water, in which plants and fish are cultured. Results We investigated the possible relationships between microbial communities from biofilms and water quality parameters in different compartments of the aquaponic system. Biofilm samples were analyzed by total community profiling for bacterial and archaeal communities. The results implied that the oxygen levels could largely explain the main differences in abiotic parameters and microbial communities in each compartment of the system. Aerobic system compartments are highly biodiverse and work mostly as a nitrifying biofilter, whereas biofilms in the anaerobic compartments contain a less diverse community. Finally, the part of the system connecting the aerobic and anaerobic processes showed common conditions where both aerobic and anaerobic processes were observed. Conclusion Different predicted microbial activities for each compartment were found to be supported by the abiotic parameters, of which the oxygen saturation, total organic carbon and total nitrogen differentiated clearly between samples from the main aerobic loop and the anaerobic compartments. The latter was also confirmed using microbial community profile analysis.

Yam (Discorea spp.) is a staple food crop in Africa that requires fertile soils and an annual rainfall of about 1,500 mm. However, in the semi-arid North-West of Burkina Faso, farmers produce yam in continuous rotation on degraded soils with annual rainfall of 610–960 mm. Understanding this local know-how can help improve yam cultivation in other regions and cropping systems in Africa. This study evaluated the productivity of this yam farming system in an interdisciplinary manner involving agronomic and economic analyses. We studied the cropping practices and socio-economic conditions of 67 households in 12 villages. We questioned farmers about their yam management schedule and inputs and we measured the yam fresh tuber yields in their fields. We sampled soils, manure and yam tubers for chemical analyses. Then, we calculated soil surface nutrient balances for N, P, and K. We found that the cropping system was characterized by densely planted ridges and relatively small size of harvested tubers. The farmers coped with degrading soils and increasing market demand by applying in average 16.2 t ha−1 of manure. About 31% of the farmers applied an average of 435 kg ha−1 of NPK fertilizer and another 24% applied an average of 300 kg ha−1 of urea. The average yam yield was 16.2 t ha−1, well above the West African average yield of 10.7 t ha−1.The yam had high value (0.59 USD kg−1) at relatively low production expenditure (0.04 USD kg−1), providing farmers the opportunity to increase and diversify incomes. Our results suggest that the development of this intensified yam production may be limited by farmer's low purchasing power of yam seed tubers, fertilizers and labor.

Manure and sewage sludge are known to add significant amounts of zinc (Zn) and other metals to soils. However, there is a paucity of information on the fate of Zn that derives from complex organic fertilizers in soil–plant systems and the contribution of these fertilizers to the Zn nutrition of crops. To answer these questions, we grew Italian ryegrass in the presence of ZnSO4, sewage sludge, and cattle and poultry manure in an acidic soil from Heitenried, Switzerland, and an alkaline soil from Strickhof, Switzerland, where the isotopically exchangeable Zn had been labeled with 67Zn. This allowed us to calculate the fraction of Zn in the shoots that was derived from fertilizer, soil, and seed over 4 successive cuts. In addition, we measured the 67Zn:66Zn isotope ratio with the diffusive gradients in thin films technique (DGT) on soils labeled with 67Zn and incubated with the same fertilizers. After 48 days of growth, the largest fraction of Zn in the ryegrass shoots was derived from the soil (79–88%), followed by the Zn-containing fertilizer (11–20%); the least (

Phosphomonoesterases play an important role in the soil phosphorus (P) cycle since they hydrolyze P monoester to phosphate. Their activity is generally measured in soil extracts, and thus, it remains uncertain how mobile these enzymes are and to which extent they can be translocated within the soil profile. The presence of phosphomonoesterases in soil solutions potentially affects the share of labile dissolved organic P (DOP), which in turn would affect P leaching. Our study aimed at assessing the production and leaching of phosphomonoesterases from organic layers and topsoil horizons in forest soils and its potential effect on dissolved P forms in leachates obtained from zero-tension lysimeters. We measured phosphomonoesterase activities in leached soil solutions and compared it with those in water extracts from litter, Oe/Oa, and A horizons of two beech forests with a contrasting nitrogen (N) and P availability, subjected to experimental N × P fertilization. In addition, we determined phosphate and DOP. In soil solutions leached from litter, Oe/Oa, and A horizons, phosphomonoesterase activities ranged from 2 to 8 μmol L–1 h–1 during summer, but remained below detection limits in winter. The summer values represent 0.1–1% of the phosphomonoesterase activity in soil extracts, indicating that enzymes can be translocated from organic layers and topsoils to greater soil depths. Activities of phosphomonoesterases obtained by water extracts were greater in the organic layer of the P-poor site, while activities of those in soil solutions were similar at the two sites. Nitrogen addition increased phosphomonoesterase activities in leached soil solutions of the organic layer of the N- and P-poor soil. Using a modeling approach, we estimated that approx. 76% of the initial labile DOP was hydrolyzed to dissolved inorganic P within the first 24 h. Back calculations from measured labile DOP revealed an underestimation of approx. 15% of total dissolved P, or 0.03 mg L–1. The observed leaching of phosphomonoesterases implies that labile organic P could be hydrolyzed in deeper soil horizons and that extended sample storage leads to an underestimation of the contribution of DOP to total dissolved P leaching. This has been neglected in the few field studies measuring DOP leaching.

Yam (Dioscorea spp.) is a staple food crop and a source of income for millions of people in West Africa. Traditionally, in West Africa, yams are grown without any external inputs, leading to low tuber yields. The rapid decrease of tuber yield observed after the first yam cropping season has been ascribed to nutrient depletion and/or to the accumulation of yam-specific pests and diseases. This has led farmers to grow yam on new surfaces under fallow each year. Using a transdisciplinary approach, we identified different yam-based rotations and fertilization regimes that could stabilize yam production in rotational cropping systems and improve water yam (D. alata) productivity. These innovations were tested in researcher-managed field trials established along an environmental gradient crossing four yam growing zones spanning from the Humid Forest (Liliyo in Côte d’Ivoire) to the Derived Savanna/Forest Transition (Tiéningboué in Côte d’Ivoire), the Southern Guinean Savanna (Midebdo in Burkina Faso), and the Northern Guinean Savanna (Léo in Burkina Faso) between 2016 and 2018. The fertilization factor implemented at each site included a control with no fertilization (NON), sole mineral fertilization as NPK (MIN), combined organic and mineral fertilization (MINORG) and sole organic fertilization as manure (ORG), while the rotation factor included water yam in rotation with cereal (YamCer), legume (YamLeg), and white yam (YamYam). The average water yam tuber yields were 32.8, 20.3, 2.7, and 2.5 t fresh matter ha−1 in 2016, and 16.4, 10.7, 8.9, and 5.2 t fresh matter ha−1 in 2018 in Liliyo, Tiéningboué, Midebdo, and Léo, respectively. The most important determinants of tuber yields were the total amount of rainfall recorded during the yam growing period and between tuber initiation and maximum canopy development, and the soil carbon stocks in the 0–30-cm layer. We confirmed in this study that soil surface coverage measured between 70 and 98 days after planting was an early indicator of tuber yield. Fertilization impacted positively the soil surface cover but had a weak impact on tuber yields. Rotation had no impact on either the soil surface cover or tuber yields. This lack of observable impacts was partly due to the very large variability of tuber yields, to the variable rainfall, and to an anthracnose attack in two sites in 2018. The impacts of fertilization and rotation on yam yields should be studied over longer periods. This is, to our knowledge, the first publication showing the relative impacts of site-specific properties (rainfall and soil carbon stocks) versus management practices on water yam yield along an environmental gradient going across the West African yam belt.

While there are estimates of the abiotic processes contribution to soil phosphorus (P) availability, less is known about the contribution of biological processes. Two main enzymatic processes involved in soil P cycling are known to alter the oxygen isotopic composition of phosphate (δ18O-P), each in a different way, through the cleavage of the P–O bond: the intracellular P turnover and the organic P hydrolysis. The former induces isotopic equilibration between phosphate and water and is considered the major process affecting soil available P via microbial P release. The latter induces depleted δ18O-P in the phosphate released from the mineralization of organic P. We studied P dynamics in organic horizons of two contrasting soils (low- and high-P availability) from temperate beech forests. We labeled the soil with 18O-enriched water and followed changes in the δ18O-P of different soil P pools in the presence or absence of added leaf litter during 3 months of incubation. δ18O-P values of almost all P pools progressively increased indicating oxygen incorporation from the enriched soil water into phosphate via the above-mentioned enzymatic processes. δ18O-P of available P increased more in the P-rich soil than in the P-poor soil and approached the isotopic equilibrium between phosphate and water, revealing the impact of microbial P release into the available P pool. However, in the P-poor soil, the available P brought the isotopic signature induced by phosphatase enzymes, indicating that it was mostly originated from the hydrolysis of organic P. Therefore, under P-limiting conditions, the isotopic effect of organic P hydrolysis can outweigh the isotopic equilibrium effect. Finally, two independent isotopic approaches with 33P and δ18O-P provided very similar estimates of P exchanged between the available P and other inorganic soil pools. This suggests that δ18O-P can be successfully used to trace P fluxes, provided that the underlying processes do not break the P–O bonds of the phosphate molecule.

Forests dominated by beech (Fagus sylvatica L.) cover large parts of Europe where they occupy a broad ecological niche in terms of soil fertility. This indicates a large potential to adapt to different soil conditions over long time periods. Recent changes in tree mineral nutrition across Europe raise the question to what degree beech can acclimate to changing soil conditions in the short term. In this study, we aimed at assessing the plasticity of root traits and rhizosphere properties of young beech trees from populations that are adapted to either high or low nutrient supply, when growing in soils differing in their fertility. We sampled beech saplings from two forest sites of contrasting nutrient supply, most distinctly in terms of phosphorus. We grew them for 2 years in rhizoboxes in mineral soil either from their own site or from the other site. We assessed the influence of the factors “plant origin” and “current soil” on root traits and rhizosphere properties. Fine root traits related to growth (biomass, length), architecture (branching), and morphology (diameter) responded strongly to the factor “current soil.” Provenance (factor “plant origin”) modified the response. The modifying effect was consistent with an influence of the plant status in those nutrients, which were not in sufficient supply in the soil. An additional genotypic difference in the sensitivity of the beech saplings to different soil nutrient supply could not be excluded. Fine root parameters normalized for length, mass, or volume (root tip density and frequency, specific root length and area, and root tissue density) did not differ among the treatments. Differences in percentage of mycorrhizal root tips and rhizosphere parameters related to phosphorus mobilization potential (pH, abundance of organic acid anions, and phosphatase activity) were small and mainly determined by the “current soil.” Provenance had only a minor modifying effect, possibly due to differences in the ability of the plants to transfer carbon compounds from the shoot to the root and the fungal partner. Our results indicate a high plasticity of young beech trees to adapt their root system to different soil nutrient supply, thereby also taking into account internal nutrient reserves.

Many mineral P fertilizers contain toxic uranium (U) in high concentrations. When the fertilizers are applied to agricultural sites, U can either accumulate in the soil or leach to ground and surface waters. We analyzed the U fluxes at three arable and three grassland agricultural sites on the Swiss plateau for 1 year. We calculated all inputs and outputs to the soils, modeled the speciation of U in the soil solution and investigated the possible leaching of U along preferential flow paths. We found that all sites showed positive U budgets (+0.9–6.6 g ha–1 y–1), indicating an accumulation of U. However, the accumulation of U was low and a doubling of U concentration in the surface soil would need 850–2,660 years assuming today’s U fluxes. Mineral P fertilizers were the quantitatively most important input, followed by manure application and mineral weathering (only important in the soils developed on limestone). While at sites with slightly acidic pH only little U (

Our understanding of phosphorus (P) cycling in soils, a basis for many ecosystem services, has been limited by the complexity of P forms and processes. Here the authors use spectroscopic and isotopic techniques to estimate turnover times of P pools and tease apart biologically-driven and geochemically-driven P fluxes.

Abstract Background Changing the phosphorus (P) nutrition leads to changes in plant metabolism. The aim of this study was to investigate how these changes are reflected in the distribution of 33P and the isotopic composition of oxygen associated to P (δ18OP) in different plant parts of soybean (Glycine max cv. Toliman). Two P pools were extracted sequentially with 0.3 M trichloroacetic acid (TCA P) and 10 M nitric acid (HNO3; residual P). Results The δ18OP of TCA P in the old leaves of the − P plants (23.8‰) significantly decreased compared to the + P plants (27.4‰). The 33P data point to an enhanced mobilisation of P from residual P in the old leaves of the − P plants compared to the + P plants. Conclusions Omitting P for 10 days lead to a translocation of P from source to sink organs in soybeans. This was accompanied by a significant lowering of the δ18OP of TCA P in the source organs due to the enzymatic hydrolysis of organic P. Combining 33P and δ18OP can provide useful insights in plant responses to P omission at an early stage.

Exploiting the natural variability of Brachiaria forage germplasm to identify forage grasses adapted to infertile acid soils that contain very low available phosphorus (P) is an important research objective for improving livestock production in the tropics. The objective of this study was to determine the differences in the release of root biochemical markers, i.e. carboxylates and acid phosphatases (APases), during the development of P deficiency in signalgrass and ruzigrass. We used the hydroxyapatite pouch system in hydroponics to simulate conditions of low P supply in acid soils to test the response of well-adapted signalgrass (Brachiaria decumbens cv. Basilisk, CIAT 606) and less-adapted ruzigrass (B. ruziziensis cv. Kennedy, CIAT 654). We monitored shoot and root growth and other physiological and biochemical components that are important for root functionality at weekly intervals for 3 weeks. We found that monocarboxylate exudation was not associated with the plant’s physiological P status, while exudation of oxalate and secreted-APases increased with declining plant P concentrations in both grasses. Ruzigrass showed higher exudation rates and grew faster than signalgrass, but could not maintain its initial fast growth rate when P concentrations in plant tissue declined to 1.0 mg P/g dry matter. Oxalate was the dominant exuded carboxylate for signalgrass after 21 days of growth and this response might confer some eco-physiological advantages in signalgrass when grown in low-P acid soils.

Organic fertilizer applications can contribute to Zinc (Zn) biofortification of crops. An enriched stable isotope source tracing approach is a central tool to further determine the potential of this biofortification measure. Here, we assessed the use of the widely available quadrupole single-collector ICPMS (Q-ICPMS, analytical error = 1% relative standard deviation) and the less accessible but more precise multicollector ICPMS as reference instrument (MC-ICPMS, analytical error = 0.01% relative standard deviation) to measure enriched Zn stable isotope ratios in soil–fertilizer–plant systems. The isotope label was either applied to the fertilizer (direct method) or to the soil available Zn pool that was determined by isotope ratios measurements of the shoots that grew on labeled soils without fertilizer addition (indirect method). The latter approach is used to trace Zn that was added to soils with complex insoluble organic fertilizers that are difficult to label homogeneously. To reduce isobaric interferences during Zn isotope measurements, ion exchange chromatography was used to separate the Zn from the sample matrix. The 67Zn:66Zn isotope ratios altered from 0.148 at natural abundance to 1.561 in the fertilizer of the direct method and 0.218 to 0.305 in soil available Zn of the indirect method. Analysis of the difference (Bland–Altman) between the two analytical instruments revealed that the variation between 67Zn:66Zn isotope ratios measured with Q-ICPMS and MC-ICPMS were on average 0.08% [95% confidence interval (CI) = 0.68%]. The fractions of Zn derived from the fertilizer in the plant were on average 0.16% higher (CI = 0.49%) when analyzed with Q- compared to MC-ICPMS. The sample matrix had a larger impact on isotope measurements than the choice of analytical instrument, as non-purified samples resulted on average 5.79% (CI = 9.47%) higher isotope ratios than purified samples. Furthermore, the gain in analytical precision using MC-ICPMS instead of Q-ICPMS was small compared to the experimental precision. Thus, Zn isotope measurements of purified samples measured with Q-ICPMS is a valid method to trace Zn sources in soil–fertilizer–plant systems. For the indirect source tracing approach, we outlined strategies to sufficiently enrich the soil with Zn isotopes without significantly altering the soil available Zn pool.

A greater diversity of crops grown in homegardens in Sri Lanka is thought to be positively associated with increased nutritional diversity of the diet of members of households and their improved nutritional status and health. However, no studies have been made to evaluate the quantitative contribution of homegardens to people's food and nutrient intake and security. Here we report three studies to test an improved homegarden production system, with agricultural and extension interventions, designed for the mid-country wet zone in Sri Lanka. The study assessed the impact of the improved system on crop type diversity, on dietary intake and diversity and food and nutritional security of the households. In Study 1, 100 households with homegardens were evaluated for their household characteristics and homegarden practices. Study 2 was on a sub sample of 20 households each with organized homegardens (OHG); households were provided with planting material, agricultural inputs and advice, and were regularly monitored by a field officer for methodical farming. These improved home gardens were contrasted with non-organized homegardens (NOHG; without intervention) to measure crop diversity through a simple species count. Study 3 assessed 25 sample households with OHG and 20 households with NOHG: dietary nutrient intake and diversity and household food security were quantified. Family food consumption was assessed using a 5-day diet diary. Perceived household food security status was determined using United States Department of Agriculture Food Security Module. Nutrient intakes, dietary adequacy, and contribution to dietary diversity from produce derived from homegarden were calculated. A total of 149 crop species were recorded in the homegardens with a 14% greater diversity in OHG than NOHG. Household food security was not significantly associated with organized or non-organized homegardens. The improved, organized home gardens provided diets with a greater contribution of energy, carbohydrates, fat, calcium, iron, zinc, folate, thiamin, niacin, vitamin C, and vitamin A compared with NOHG. The study demonstrates that households with OHG had greater dietary diversity from homegarden produce compared with that of households with NOHG leading to better food and micronutrient intake and nutritional security.

Decreasing phosphorus (P) concentrations in leaves of beech (Fagus sylvatica L.) across Europe raise the question about the implications for forest health. Considering the distribution of beech forests on soils encompassing a broad range of nutrient availability, we hypothesized that this tree species exhibits high phenotypic plasticity allowing it to alter mass, and nutrient allocation in response to local nutrient availability. To test this, we grew two groups of 12–15 year old beech saplings originating from sites with high and low soil P availability for 2 years in mineral soil from their own site and in soil from the other site. After two growing seasons, P concentrations in leaves and stem, as well as mass allocation to leaves and fine roots were affected by both soil and plant origin. By contrast, relative P allocation to leaves and fine roots, as well as P concentrations in fine roots, were determined almost entirely by the experimental soil. Independent of the P nutritional status defined as average concentration of P in the whole plant, which still clearly reflected the soil conditions at the site of plant origin, relative P allocation to leaves was a particularly good indicator of P availability in the experimental soil. Furthermore, a high plasticity of this plant trait was indicated by a large difference between plants growing in the two experimental soils. This suggests a strong ability of beech to alter resource allocation in response to specific soil conditions.

New management practices must be developed to improve yam productivity. By allowing non-destructive analyses of important plant traits, image-based phenotyping techniques could help developing such practices. Our objective was to determine the potential of image-based phenotyping methods to assess traits relevant for tuber yield formation in yam grown in the glasshouse and in the field. We took plant and leaf pictures with consumer cameras. We used the numbers of image pixels to derive the shoot biomass and the total leaf surface and calculated the ‘triangular greenness index’ (TGI) which is an indicator of the leaf chlorophyll content. Under glasshouse conditions, the number of pixels obtained from nadir view (view from the top) was positively correlated to shoot biomass, and total leaf surface, while the TGI was negatively correlated to the SPAD values and nitrogen (N) content of diagnostic leaves. Pictures taken from nadir view in the field showed an increase in soil surface cover and a decrease in TGI with time. TGI was negatively correlated to SPAD values measured on diagnostic leaves but was not correlated to leaf N content. In conclusion, these phenotyping techniques deliver relevant results but need to be further developed and validated for application in yam.

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 surfaces while the mean yield remained around 10 t tuber ha−1. In West Africa, yam is traditionally cultivated without input as the first crop after a long-term fallow as it is considered to require a high soil fertility. African soils, however, are being more and more degraded. The aims of this review were to show the importance of soil fertility for yam, discuss barriers that might limit the adoption of integrated soil fertility management (ISFM) in yam-based systems in West Africa, present the concept of innovation platforms (IPs) as a tool to foster collaboration between actors for designing innovations in yam-based systems and provide recommendations for future research. This review shows that the development of sustainable, feasible, and acceptable soil management innovations for yam requires research to be conducted in interdisciplinary teams including natural and social sciences and in a transdisciplinary manner involving relevant actors from the problem definition, to the co-design of soil management innovations, the evaluation of research results, their communication and their implementation. Finally, this research should be conducted in diverse biophysical and socio-economic settings to develop generic rules on soil/plant relationships in yam as affected by soil management and on how to adjust the innovation supply to specific contexts.

Home gardens are considered as vital units for enhancing food security particularly in developing nations of South Asia, such as Sri Lanka. Although the yam crop Dioscorea spp. constitute a popular but still minor component in Sri Lankan home gardens, they have the potential of producing large quantities of edible material with minimal inputs. However, their real value in South Asian home gardens is not yet reported. Hence, this study was carried out to get insights into home garden characteristics, gardener demography as well as current management practices within 300 Sri Lankan home garden systems that are located along a climatic gradient. By using interviews and field observations, gardeners, who cultivated in particular Dioscorea species, were studied within 10 of the 25 administrative districts distributed in the wet, intermediate and dry climatic zone of Sri Lanka. Furthermore, current management practices of yams cultivation were analyzed on local scale and compared afterwards with management recommendations published in the year 2006 by the Department of Agriculture. Dioscorea species were found in a majority of home gardens, especially in wet and intermediate zones of Sri Lanka. D. alata was the most prominent species and was managed at a subsistence level and not as per recommendations developed by the Department of Agriculture. Our results revealed that Dioscorea alata is an essential component of Sri Lankan home gardens in rural areas and can yield substantial quantities of edible tubers with low input, especially during times of food scarcities, and has therefore the potential to enhance food security and rural development.

Zinc (Zn) nutrition is of key relevance in India, as a large fraction of the population suffers from Zn malnutrition and many soils contain little plant available Zn. In this study we compared organic and conventional wheat cropping systems with respect to DTPA (diethylene triamine pentaacetic acid)-extractable Zn as a proxy for plant available Zn, yield, and grain Zn concentration. We analyzed soil and wheat grain samples from 30 organic and 30 conventional farms in Madhya Pradesh (central India), and conducted farmer interviews to elucidate sociological and management variables. Total and DTPA-extractable soil Zn concentrations and grain yield (3400 kg ha-1) did not differ between the two farming systems, but with 32 and 28 mg kg-1 respectively, grain Zn concentrations were higher on organic than conventional farms (t = -2.2, p = 0.03). Furthermore, multiple linear regression analyses revealed that (a) total soil zinc and sulfur concentrations were the best predictors of DTPA-extractable soil Zn, (b) Olsen phosphate taken as a proxy for available soil phosphorus, exchangeable soil potassium, harvest date, training of farmers in nutrient management, and soil silt content were the best predictors of yield, and (c) yield, Olsen phosphate, grain nitrogen, farmyard manure availability, and the type of cropping system were the best predictors of grain Zn concentration. Results suggested that organic wheat contained more Zn despite same yield level due to higher nutrient efficiency. Higher nutrient efficiency was also seen in organic wheat for P, N and S. The study thus suggests that appropriate farm management can lead to competitive yield and improved Zn concentration in wheat grains on organic farms.

RESUMEN Se evaluaron en invernadero en un suelo de Matazul, Meta, Colombia durante 6 semanas, 2 genotipos de Brachiaria (uno mejor adaptado a bajo P, B. decumbens y otro menos adaptado, B. ruziziensis) y 8 progenies del cruzamiento entre ellos ( mejores adaptados: H-7, H-40, H-28, H-58; menos adaptados: H-190, H-94, H-82, H-179). Los genotipos mejor adaptados presentaron mayor biomasa aérea, explicada por mayor área foliar, mayor absorción de P en el tallo y mayor volumen de raíz. Las características morfológicas de las raíces, principalmente longitud, peso seco y contenido de P, permiteron mejor adaptación a bajo P disponible en el suelo. El periodo de evaluación fue suficiente para observar diferencias entre progenies.

Zinc (Zn) deficiency is a major problem for many people living on wheat-based diets. Here, we explored whether addition of green manure of red clover and sunflower to a calcareous soil or inoculating a non-indigenous arbuscular mycorrhizal fungal (AMF) strain may increase grain Zn concentration in bread wheat. For this purpose we performed a multifactorial pot experiment, in which the effects of two green manures (red clover, sunflower), ZnSO4 application, soil γ-irradiation (elimination of naturally occurring AMF), and AMF inoculation were tested. Both green manures were labeled with 65Zn radiotracer to record the Zn recoveries in the aboveground plant biomass. Application of ZnSO4 fertilizer increased grain Zn concentration from 20 to 39 mg Zn kg-1 and sole addition of green manure of sunflower to soil raised grain Zn concentration to 31 mg Zn kg-1. Adding the two together to soil increased grain Zn concentration even further to 54 mg Zn kg-1. Mixing green manure of sunflower to soil mobilized additional 48 µg Zn (kg soil)-1 for transfer to the aboveground plant biomass, compared to the total of 132 µg Zn (kg soil)-1 taken up from plain soil when neither green manure nor ZnSO4 were applied. Green manure amendments to soil also raised the DTPA-extractable Zn in soil. Inoculating a non-indigenous AMF did not increase plant Zn uptake. The study thus showed that organic matter amendments to soil can contribute to a better utilization of naturally stocked soil micronutrients, and thereby reduce any need for major external inputs.

Maize growth, root colonization by arbuscular mycorrhizal fungi (AM fungi) and by non-AM fungi, and soil properties were studied on a field of Humic Andosol in 1998. The field had been tilled with different intensities since November 1997.A plot was minimum-tilled with a rotary tiller (MT) and the other plot was tilled with a moldboard plow and disc-harrowed(T). The least-squares fit of cubic or quadratic surfaces to the data collected from 9-100 locations in each plot clarifiedthat the dry weight of maize shoot and root colonization by fungi showed a clear spatial variability in the area of 17.5mx25 m. Inverse spatial variability patterns between AM fungi and non-AM fungi in both MT and T indicated that there was an apparent competition between them in colonizing maize roots. Maize growth showed a spatial variability pattern similar to that of AM fungal organs, in particular in T. This suggested that the spatial variability pattern of maize in T wasmoreaffected by the relationship between AM fungi and non-AM fungi. Site-specific control of AM fungal infection for improvingmaize growth in small fields was discussed.

BACKGROUND: Arbuscular mycorrhizal fungi (AMF) are known for their beneficial effects on plants. However, there is increasing evidence that some ruderal plants, including several agricultural weeds, respond negatively to AMF colonization. Here, we investigated the effect of AMF on the growth of individual weed species and on weed-crop interactions. METHODOLOGY/PRINCIPAL FINDINGS: First, under controlled glasshouse conditions, we screened growth responses of nine weed species and three crops to a widespread AMF, Glomus intraradices. None of the weeds screened showed a significant positive mycorrhizal growth response and four weed species were significantly reduced by the AMF (growth responses between -22 and -35%). In a subsequent experiment, we selected three of the negatively responding weed species--Echinochloa crus-galli, Setaria viridis and Solanum nigrum--and analyzed their responses to a combination of three AMF (Glomus intraradices, Glomus mosseae and Glomus claroideum). Finally, we tested whether the presence of a crop (maize) enhanced the suppressive effect of AMF on weeds. We found that the growth of the three selected weed species was also reduced by a combination of AMF and that the presence of maize amplified the negative effect of AMF on the growth of E. crus-galli. CONCLUSIONS/SIGNIFICANCE: Our results show that AMF can negatively influence the growth of some weed species indicating that AMF have the potential to act as determinants of weed community structure. Furthermore, mycorrhizal weed growth reductions can be amplified in the presence of a crop. Previous studies have shown that AMF provide a number of beneficial ecosystem services. Taken together with our current results, the maintenance and promotion of AMF activity may thereby contribute to sustainable management of agroecosystems. However, in order to further the practical and ecological relevance of our findings, additional experiments should be performed under field conditions.

Fertilization is an important management strategy of yams (Dioscorea spp.) especially when grown in degraded soils. A field study evaluated the leaf numbers, leaf area indices, crop growth, yields, and nitrogen (N) and potassium (K) use efficiencies of D. alata and D. rotundata in Côte d'Ivoire when grown in two contrasting soils with and without fertilizer. D. alata had a lower number of leaves per vine, although leaf area indices were higher, and the leaves were retained for a longer period than in D. rotundata. In all situations, the yields of D. alata were significantly higher, and fertilizers promoted growth of shoots, roots, tubers, and, thus, final yields especially in the low fertile savanna soil. The beneficial impact of fertilizer on yields was significantly lower in the fertile forest soils. The nutrient use agronomic efficiencies indicated the impact of both N and K in promoting yields especially under nonfertilized conditions.

Isotope source tracing enables to accurately determine the fate of nutrients that are applied with fertilizers to soils. While this approach is well established for major nutrients such as nitrogen, it is not yet established for trace metals. Here, we aimed to determine the fate of the micronutrient zinc (Zn) and the contaminant cadmium (Cd) that were applied with an organic fertilizer to a soil–wheat system. A pot study was conducted in which wheat was grown on an alkaline soil. The soils received green manure and/or soluble Zn fertilizer and were compared with non-fertilized control treatments (n = 4 experimental replicates). The green manure was labelled with the stable isotopes 67Zn and 111Cd. For an efficient sample throughput, a method was provided and validated to determine enriched stable isotope ratios (67Zn:66Zn and 111Cd:110Cd) and the Zn and Cd concentrations in one analytical run. To this end, single collector ICP-MS analyses and stable isotope mass balances calculations were combined. Applying this method revealed that the addition of green manure increased neither Zn nor Cd concentrations in wheat grains due to biomass dilution effects. Isotope source tracing showed that the largest fraction of these metals in the wheat shoots derived from the soil in all treatments (Zn 87–99 %, Cd 94–98 %). Moreover, the addition of green manure increased the transfer of Zn and Cd from soil to wheat by a factor 1.9 for both elements. This increased transfer was likely related to a nitrogen fertilization effect that increased root and shoot biomass and thereby the soil exploration of the wheat. This study demonstrated how the fate and dynamics of multiple trace metals can be efficiently determined in soil–fertilizer–crop systems using isotope source tracing. [ABSTRACT FROM AUTHOR]