Long-term Field Trial Research Articles

Fungal community profiles in agricultural soils of a long-term field trial under different tillage, fertilization and crop rotation conditions analyzed by high-throughput ITS-amplicon sequencing.

Fungal communities in agricultural soils are assumed to be affected by soil and crop management. Our intention was to investigate the impact of different tillage and fertilization practices on fungal communities in a long-term crop rotation field trial established in 1992 in Central Germany. Two winter wheat fields in replicated strip-tillage design, comprising conventional vs. conservation tillage, intensive vs. extensive fertilization and different pre-crops (maize vs. rapeseed) were analyzed by a metabarcoding approach applying Illumina paired-end sequencing of amplicons generated by two recently developed primer pairs targeting the two fungal Internal Transcribed Spacer regions (ITS1, ITS2). Analysis of 5.1 million high-quality sequence reads uncovered a diverse fungal community in the two fields, composed of 296 fungal genera including 3,398 Operational Taxonomic Units (OTUs) at the 97% sequence similarity threshold. Both primer pairs detected the same fungal phyla (Basidio-, Asco-, Zygo-, Glomero- and Chytridiomycota), but in different relative abundances. OTU richness was higher in the ITS1 dataset, while ITS2 data were more diverse and of higher evenness. Effects of farming practice on fungal community structures were revealed. Almost two-thirds of the fungal genera were represented in all different soil treatments, whereas the remaining genera clearly responded to farming practice. Principal Component Analysis revealed four distinct clusters according to tillage practice and pre-crop. Analysis of Variance (ANOVA) substantiated the results and proved significant influences of tillage and pre-crop, while fertilization had the smallest and non-significant effect. In-depth analysis of putative phytopathogenic and plant beneficial fungal groups indicated distinct responses; for example Fusarium was significantly enriched in the intensively fertilized conservation tillage variants with the pre-crop maize, while Phoma displayed significant association with conventional tillage and pre-crop rapeseed. Many putative plant beneficial fungi also reacted differentially to farming practice with the most distinct responders identified among the Glomeromycota (arbuscular mycorrhizal fungi, AMF).

Analyzing and modelling the effect of long-term fertilizer management on crop yield and soil organic carbon in China

This study analyzes the influence of various fertilizer management practices on crop yield and soil organic carbon (SOC) based on the long-term field observations and modelling. Data covering 11 years from 8 long-term field trials were included, representing a range of typical soil, climate, and agro-ecosystems in China. The process-based model EPIC (Environmental Policy Integrated Climate model) was used to simulate the response of crop yield and SOC to various fertilization regimes. The results showed that the yield and SOC under additional manure application treatment were the highest while the yield under control treatment was the lowest (30%–50% of NPK yield) at all sites. The SOC in northern sites appeared more dynamic than that in southern sites. The variance partitioning analysis (VPA) showed more variance of crop yield could be explained by the fertilization factor (42%), including synthetic nitrogen (N), phosphorus (P), potassium (K) fertilizers, and fertilizer NPK combined with manure. The interactive influence of soil (total N, P, K, and available N, P, K) and climate factors (mean annual temperature and precipitation) determine the largest part of the SOC variance (32%). EPIC performs well in simulating both the dynamics of crop yield (NRMSE = 32% and 31% for yield calibration and validation) and SOC (NRMSE = 13% and 19% for SOC calibration and validation) under diverse fertilization practices in China. EPIC can assist in predicting the impacts of different fertilization regimes on crop growth and soil carbon dynamics, and contribute to the optimization of fertilizer management for different areas in China.

Effect of different soil cultivation methods on the emergence of Apera spica-venti

Minimum tillage, i.e. without plowing the soil, is practiced on about 40% of the arable fields in Germany. The effects on the long run of this soil cultivation are investigated in a long-term field trial. Since autumn 2007 two different soil cultivation methods are investigated in a long-term field trial, among other things, for the emergence of Apera spica-venti before herbicide control. The experimental fields are located in Germany, in the federal state of Brandenburg, about 50 km from Berlin. The crop rotation consists of winter oilseed rape, winter wheat, winter rye, winter barley, winter triticale, peas and maize. The plots were treated with herbicide since the start of the field trial in 1995. Weeds were counted before herbicide application in autumn or spring. For each plot 4 points with an area of 0.25 m² were investigated and both weed number and species were determined. The results show that the median of Apera spica-venti plants spans from 9 (year 2013) to 55 (2010) plants per m² in cereals crop plots with plowing. For the plots without plowing the median ranges between 18 (2009) and 140 (2017) Apera spica-venti plants per m². In plots without plowing the numbers of emerging Apera spica-venti plants has been rising since the year 2007.

Humic products in agriculture: potential benefits and research challenges—a review

Humic products have been used in cropland agriculture for several decades, but lack of widespread credibility has restricted their use to small proportions of farmers. To improve the credibility of humic products, we identify four knowledge gaps and propose pathways of future action to close these gaps. First, while the capacity of humic products to improve plant growth has been proven in greenhouse and growth chambers, more such work is needed in field conditions, especially to determine the modifying effects on humic product efficacy of environmental and management factors, including crop type, annual weather patterns, soil type, and fertility management. Many of the published field studies fail to address any of these factors. Second, full acceptance of humic products by the research community may first require a mechanistic explanation for plant responses to humic products. Some research groups are exploring plant-based mechanisms, but almost entirely in controlled conditions, not in field conditions. Industry often attributes yield responses to enhancement of soil nutrient availability without citing adequate evidence. Microbial-based explanations are also possible. Third, consumer trust in available humic products would be strengthened through industry-wide measures for quality control of humic product production and sale, including standard procedures for measuring their humic and fulvic acid contents and rapid bio-assays for distinguishing effective products from inert frauds. Finally, humic products are widely presumed to promote root growth, which offers the potential to increase soil C inputs and thereby improve soil health. Yet virtually, no such evidence has been presented, in part due to the absence of long-term field trials. Humic product companies in North America have organized a trade association to promote a more knowledge-based industry. To acquire a database that will support these objectives, we propose establishment of a global network of field sites that would measure crop responses to humic products across ranges of humic products, crop types, soil types, and climates. Plant and soil samples would be analyzed by cooperating specialists in advanced laboratories to identify mechanistic processes and benefits to both plant production and soil health. We believe the industry will indeed become more knowledge-based and the credibility of humic products will improve as (i) we learn more about their field efficacy across ranges of field conditions for improving crop yield and soil health, (ii) we gain further insights into possible mechanistic explanations, and (iii) the consumer gains the ability to discern genuine products from fraudulent materials.

Pine sawdust biochar reduces GHG emission by decreasing microbial and enzyme activities in forest and grassland soils in a laboratory experiment

This study investigated the effects of biochar soil amendment on greenhouse gas (GHG) emissions in soils. Pine (Pinus koraiensis Siebold & Zucc.) sawdust biochar was produced at 300 and 550°C with and without steam activation (coded as BC300-S, BC550-S, BC300 and BC550, respectively). They were applied to forest and grassland soils at 1.5% (w/w) rate in a 100-day laboratory incubation experiment. Application of BC550 significantly reduced cumulative CO2 emission from the forest soil by 16.4% relative to the control (without biochar application), but not from the grassland soil. Biochar application did not have significant effects on CH4 uptake from either soil. Application of BC550 and BC550-S reduced the cumulative N2O emission by 27.5 and 31.5%, respectively, in the forest soil and 14.8 and 11.7%, respectively, in the grassland soil, as compared to the control. The effects of BC300 and BC300-S on cumulative CO2 and N2O emission was not significant in both soils, except for the significant reduction in cumulative N2O emission from the forest soil by BC300-S. The effect of BC550 and BC550-S on N2O emission persisted until the end of the 100-day incubation indicating possible long-term effects of these biochars. We conclude that BC550 and BC550-S had the highest potential to reduce CO2 and N2O emission in the 100-day laboratory incubation experiment. These biochars should be tested in long-term field trials to confirm their potential for mitigating CO2 and N2O fluxes in real ecosystems with a relevant time frame.

Organic Amendments in a Long-term Field Trial-Consequences for the Bulk Soil Bacterial Community as Revealed by Network Analysis.

This study intended to elucidate the long-term effects of organic soil amendments on bacterial co-occurrence in bulk soil with and without addition of mineral fertiliser. Previous research mostly neglected the bacterial co-occurrence structure and focussed mainly on the parameters species diversity and abundance changes of species. Here we present a systematic comparison of two frequently used soil amendments, manure and straw, with regard to their impact on bacterial co-occurrence in a long-term field trial in Speyer, Germany. The approach involved 16S amplicon sequencing in combination with a bacterial network analysis, comparing the different fertiliser regimes. The results show an increase of bacterial diversity as well as an accumulation of bacteria of the order Bacillales in plots fertilised with manure compared to a control treatment. In the straw-amended plots neither an increase in diversity was found nor were indicative species detectable. Furthermore, network analysis revealed a clear impact of mineral fertiliser addition on bacterial co-occurrence structure. Most importantly, both organic amendments increased network complexity irrespective of mineral fertilisation regime. At the same time, the effects of manure and straw exhibited differences that might be explained by differences in their nutritional/chemical contents. It is concluded that bacterial interactions are a crucial parameter for the assessment of amendment effects regarding soil health and sustainability.

Maize and wheat root biomass, vertical distribution, and size class as affected by fertilization intensity in two long-term field trials

Root biomass is the most commonly studied root parameter to investigate below ground crop response to environmental conditions and carbon cycling in agroecosystems. Root growth is strongly regulated by site-specific growth conditions and resource availability, but only little is known about the extent to which root biomass, vertical distribution, and size class respond to fertilization intensity as compared to site. We determined coarse (>2mm) and fine (>0.5mm and≤2mm) root biomass of maize and wheat in three soil layers to 0.75m depth in different farming systems (half and full organic, full conventional) and fertilization treatments (zero, manure, full mineral N plus half mineral PK, full mineral NPK) of the Swiss long-term field trials DOK and ZOFE, respectively, and evaluated the effects of fertilization intensity and site on root biomass, vertical distribution, and size class. In DOK, total root biomass was similar in organic and conventional farming systems. In ZOFE, wheat root biomass was 1.7-times higher under full mineral N plus half mineral PK fertilization than under zero or manure fertilization and intermediate under full NPK fertilization. Vertical root distribution and size class were only marginally affected by fertilization intensity on both sites. By contrast, total root biomass of maize and topsoil root biomass of both maize and wheat were higher but subsoil root biomass of wheat and fine root proportions of both maize and wheat were lower in DOK than in ZOFE. We conclude that roots respond more to site than to fertilization intensity and that absolute inputs of root biomass carbon to soil are similar in low- and high-intensity systems. Further, root-shoot ratios were inversely related to fertilization intensity, implying that estimations of below ground carbon inputs to soil from shoot biomass need to be differentiated by fertilization intensity. Deep (below 0.5m) root biomass was 3-times higher for wheat than for maize, suggesting that crop choice is more important than fertilization intensity for carbon sequestration in deep soil.

Temperature and soil fertility as regulators of tree line Scots pine growth and survival-implications for the acclimation capacity of northern populations.

The acclimation capacity of leading edge tree populations is crucially important in a warming climate. Theoretical considerations suggest that adaptation through genetic change is needed, but this may be a slow process. Both positive and catastrophic outcomes have been predicted, while empirical studies have lagged behind theory development. Here we present results of a 30-year study of 55,000 Scots pine (Pinus sylvestris) trees, planted in 15 common gardens in three consecutive years near and beyond the present Scots pine tree line. Our results show that, contrary to earlier predictions, even long-distance transfers to the North can be successful when soil fertility is high. This suggests that present northern populations have a very high acclimation capacity. We also found that while temperature largely controls Scots pine growth, soil nutrient availability plays an important role-in concert with interpopulation genetic variation-in Scots pine survival and fitness in tree line conditions. These results suggest that rapid range expansions and substantial growth enhancements of Scots pine are possible in fertile sites as seed production and soil nutrient mineralization are both known to increase under a warming climate. Finally, as the ontogenetic pattern of tree mortality was highly site specific and unpredictable, our results emphasize the need for long-term field trials when searching for the factors that control fitness of trees in the variable edaphic and climatic conditions of the far North.

Bacterial and fungal communities respond differently to varying tillage depth in agricultural soils.

In arable cropping systems, reduced or conservation tillage practices are linked with improved soil quality, C retention and higher microbial biomass, but most long-term studies rarely focus on depths greater than 15 cm nor allow comparison of microbial community responses to agricultural practices. We investigated microbial community structure in a long-term field trial (12-years, Lincoln, New Zealand) established in a silt-loam soil over four depth ranges down to 30 cm. Our objectives were to investigate the degree of homogenisation of soil biological and chemical properties with depth, and to determine the main drivers of microbial community response to tillage. We hypothesised that soil microbiological responses would depend on tillage depth, observed by a homogenisation of microbial community composition within the tilled zone. Tillage treatments were mouldboard plough and disc harrow, impacting soil to ∼20 and ∼10 cm depth, respectively. These treatments were compared to a no-tillage treatment and two control treatments, both permanent pasture and permanent fallow. Bacterial and fungal communities collected from the site were not impacted by the spatial location of sampling across the study area but were affected by physicochemical changes associated with tillage induced soil homogenisation and plant presence. Tillage treatment effects on both species richness and composition were more evident for bacterial communities than fungal communities, and were greater at depths <15 cm. Homogenisation of soil and changing land management appears to redistribute both microbiota and nutrients deeper in the soil profile while consequences for soil biogeochemical functioning remain poorly understood.

Yield associated traits correlate with cytokinin profiles in developing pods and seeds of field-grown soybean cultivars

While lab and greenhouse based studies have long indicated that cytokinins (CK) promote yield increases in soybean (Glycine max L.), it is not known if the relationship would be valid under more complex field conditions. Thus, an ambitious CK metabolite analysis was undertaken involving long-term field trials of commercial and historical soybean varieties to determine if differences between CK profiles are related to variation in yield performance. Twenty-seven cultivars were evaluated in this study representing a wide range of performance and assessed for 12 agronomically important plant and seed parameters under field conditions. Identification and quantification of 14 forms of CK was undertaken by high-performance liquid chromatography tandem mass spectrometry (HPLC–MS/MS) at three stages of reproductive development that are critical for yield determination (R4–R6). This revealed a substantial increase in CK levels, especially the highly metabolically active free bases, in the high yielding cultivars of soybean. Significant correlations between yield components and the most active CK form, tZ (trans-Zeatin), were detected at both R4 and R5 stages. A similar trend was observed for cZ (cis-Zeatin), indicating a possible role of both zeatin isomers in pod and early seed development. Positive, significant relationships between yield and cytokinins were maintained also at R6 stage; however, a switch in hormone profiles and increased levels of isopentenyl adenine (iP) types of CK in high yielding cultivars suggested that the presence of iP derivatives allowed developing seeds to maintain their active role in sink organs and attract assimilates during the seed filling phases, when the metabolism of the maturing plant was generally slowing down. Results suggested that cytokinin metabolites or their associated genes, may serve as a valuable, early indicators of yield performance in marker-assisted breeding programs for soybean or be manipulated through gene editing techniques.

The importance of plants to development and maintenance of soil structure, microbial communities and ecosystem functions

Soil ecosystem functions depend on the development, activity and maintenance of soil biology which in turn depends on plants because they add important carbon resources through litter fall, root exudates, mucilage and root remnants, and root activity for the aggregates formation. Correspondingly, our hypothesis was that maintaining high inputs of plant-derived carbon is important to the formation and stabilisation of soil structure, and this in-turn may support a greater diversity of habitats for microbial communities thereby ensuring more robust soil ecosystem function. To test this hypothesis we measured the physical, chemical and biological characteristics of soil from a long-term field trial. The trail was initiated in Spring 2000 on a silt loam soil (Udic Dystocrept, USDA) in Canterbury, New Zealand and includes a combination of crop and tillage treatments: permanent pasture [PP], permanent fallow [PF], rotation of barley, wheat and peas under intensive [Ii], minimum [Mm] and no tillage [Nn]. Soil aggregate profiles (size class, distribution, mean weight diameter – MWD), total organic carbon and nitrogen (TOC, and TN), along with metabolic and PLFA data were analysed using a multi-phase experimental design to investigate the effect of different plants and soil management practices on soil structure, microbial metabolic diversity and activity. The PP treatment had the most complex soil structure (MWD between 3.6 and 2.8 depending on depth) with 61% of aggregates in the 8.0002.000mm size class compared with PF (MDW between 1.8 and 0.5) that had only 14% of aggregates in this size class. There was strong evidence for maintenance of good soil structure within the no tillage treatment (Nn) which had higher proportions of the 8.0002.000mm aggregates (45%) compared to Mm (40%) and Ii (35%). Similar relationships were observed in TOC and TN data. PP had superior metabolic activity with approximately 5μg CO2-Cg−1 soil (dry weight) produced in the 0–7.5cm depth for all C-source groups. These superior indicators of soil ecosystem function for PP was attributed to the lack of soil disturbance, continual supply of carbon and a stable microbial community with an enrichment of bacteria compared to fungi at the surface. We conclude that continuous growth of plants in combination with low soil disturbance promoted greater macroaggregate scale structure, added more carbon and promoted greater microbial biomass, metabolic diversity and capacity to execute soil ecosystem function.

Soil Biological Activity Contributing to Phosphorus Availability in Vertisols under Long-Term Organic and Conventional Agricultural Management.

Mobilization of unavailable phosphorus (P) to plant available P is a prerequisite to sustain crop productivity. Although most of the agricultural soils have sufficient amounts of phosphorus, low availability of native soil P remains a key limiting factor to increasing crop productivity. Solubilization and mineralization of applied and native P to plant available form is mediated through a number of biological and biochemical processes that are strongly influenced by soil carbon/organic matter, besides other biotic and abiotic factors. Soils rich in organic matter are expected to have higher P availability potentially due to higher biological activity. In conventional agricultural systems mineral fertilizers are used to supply P for plant growth, whereas organic systems largely rely on inputs of organic origin. The soils under organic management are supposed to be biologically more active and thus possess a higher capability to mobilize native or applied P. In this study we compared biological activity in soil of a long-term farming systems comparison field trial in vertisols under a subtropical (semi-arid) environment. Soil samples were collected from plots under 7 years of organic and conventional management at five different time points in soybean (Glycine max) -wheat (Triticum aestivum) crop sequence including the crop growth stages of reproductive significance. Upon analysis of various soil biological properties such as dehydrogenase, β-glucosidase, acid and alkaline phosphatase activities, microbial respiration, substrate induced respiration, soil microbial biomass carbon, organically managed soils were found to be biologically more active particularly at R2 stage in soybean and panicle initiation stage in wheat. We also determined the synergies between these biological parameters by using the methodology of principle component analysis. At all sampling points, P availability in organic and conventional systems was comparable. Our findings clearly indicate that owing to higher biological activity, organic systems possess equal capabilities of supplying P for crop growth as are conventional systems with inputs of mineral P fertilizers.

Drainage and leaching losses of nitrogen and dissolved organic carbon after introducing maize into a continuous paddy-rice crop rotation

Abstract Farmers in South Asia increasingly switch from continuous paddy-rice cropping to rotations including non-flooded crops, such as growing maize in the dry season. We hypothesized that the introduction of maize into a permanent paddy-rice cropping system boosts drainage and leaching losses of nitrogen (N) and dissolved organic carbon (DOC) in the initial years of maize establishment, due to the disturbance of the equilibrated soil conditions established under continuous paddy cropping. We tested this hypothesis in a 3.5-year field experiment using monolith lysimeters cropped with either (i) single paddy rice in the wet season and maize in the dry season (maize-paddy rice, M-MIX), or (ii) double paddy rice (R-WET) as control. Expandable and compressible pads minimized the formation of a gap at the interface between soil monolith and lysimeter casing during shrinking and swelling of the clay soil. In the first year of introducing maize, drainage (606 l m −2 yr −1 ) and leaching of total nitrogen (TN, 6.8 g N m −2 yr −1 ) and DOC (2.7 g m −2 yr −1 ) were significantly larger in M-MIX than in R-WET (water: 149 l m −2 yr −1 , TN: 0.1 g m −2 yr −1 , DOC: 0.7 g m −2 yr −1 ). However, the additional losses of water, nitrogen, and DOC caused by the introduction of maize disappeared in the following years. In the last two dry seasons of our study, drainage and leaching losses of TN, and DOC were even significantly smaller in M-MIX than in R-WET. In the dry seasons of the 2nd to 4th year after introducing maize (2013–2015), M-MIX saved on average 388 l m −2 of percolation water losses compared to R-WET and leaching losses of TN and DOC under maize were reduced on average by 0.6 g m −2 and 1.6 g m −2 , respectively. We conclude that leaching losses of water and nutrients are only transiently boosted during the first year after introducing maize in perennial rice cropping systems, so that maize cropping in the dry season could save water and reduce nutrient leaching in comparison to continuous paddy-rice cropping in the long run. Long-term field trials are necessary to validate the lysimeter results.

Long-term tillage and nitrogen fertilization: Consequences for nitrifier density and activity

Nitrification is the biological oxidation of NH3 to NO2− and then NO3−. Understanding soil management consequences for nitrifier ecology could improve nitrogen (N) fertilizer use, decrease NO3− leaching, and minimize NO and N2O emissions. This study examined how long-term N fertilization and tillage influenced nitrifier density, ratios, and nitrification rate. The study site had > 40years of continuous maize (Zea mays L.) with three nitrogen fertilization rates (0, 168, and 336kgha−1) and either no-tillage or plow tillage. The Most Probable Number (MPN) method was used to estimate the cell density of ammonia-oxidizing (AOB) and nitrite-oxidizing (NOB) bacteria and the shaken slurry method was used to measure potential nitrification rates. Tillage, fertilization, and their interaction significantly influenced the ammonia oxidizer and nitrite oxidizer cell densities and the potential nitrification rate. Nitrifier cell densities increased with increased nitrogen fertilization; nitrite oxidizer density increased more than ammonia oxidizer density leading to a decreasing AOB:NOB ratio. There were positive correlations between ammonia oxidizer and nitrite oxidizer cell densities, especial in plow tillage. The trends for nitrifier cell density and potential nitrification rate were not consistent. Fertilization increased ammonia oxidizer and nitrite oxidizer densities and potential nitrification rate, but the influence of tillage differed for different fertilization rates. This long-term field trial demonstrated that specific soil management practices differentially influence not only the cell density of nitrifiers, but their relative ratios and their response to increased inorganic nitrogen in the environment.

An unattended verification station for UF[formula omitted] cylinders: Field trial findings

In recent years, the International Atomic Energy Agency (IAEA) has pursued innovative techniques and an integrated suite of safeguards measures to address the verification challenges posed by the front end of the nuclear fuel cycle. Among the unattended instruments currently being explored by the IAEA is an Unattended Cylinder Verification Station (UCVS), which could provide automated, independent verification of the declared relative enrichment, 235U mass, total uranium mass, and identification for all declared uranium hexafluoride cylinders in a facility (e.g., uranium enrichment plants and fuel fabrication plants). Under the auspices of the United States and European Commission Support Programs to the IAEA, a project was undertaken to assess the technical and practical viability of the UCVS concept. The first phase of the UCVS viability study was centered on a long-term field trial of a prototype UCVS system at a fuel fabrication facility. A key outcome of the study was a quantitative performance evaluation of two nondestructive assay (NDA) methods being considered for inclusion in a UCVS: Hybrid Enrichment Verification Array (HEVA), and Passive Neutron Enrichment Meter (PNEM). This paper provides a description of the UCVS prototype design and an overview of the long-term field trial. Analysis results and interpretation are presented with a focus on the performance of PNEM and HEVA for the assay of over 200 “typical” Type 30B cylinders, and the viability of an “NDA Fingerprint” concept as a high-fidelity means to periodically verify that material diversion has not occurred.

Reprint of “Fast and sensitive in vivo studies under controlled environmental conditions to substitute long-term field trials with genetically modified plants”

We introduce an easy, fast and effective method to analyze the influence of genetically modified (GM) plants on soil and model organisms in the laboratory to substitute laborious and time consuming field trials. For the studies described here we focused on two GM plants of the so-called 3rd generation: GM plants producing pharmaceuticals (PMP) and plant made industrials (PMI). Cyanophycin synthetase (cphA) was chosen as model for PMI and Choleratoxin B (CTB) as model for PMP. The model genes are expressed in transgenic roots of composite Vicia hirsuta plants grown in petri dishes for semi-sterile growth or small containers filled with non-sterile soil. No significant influence of the model gene expression on root induction, growth, biomass, interaction with symbionts such as rhizobia (number, size and functionality of nodules, selection of nodulating strains) or arbuscular mycorrhizal fungi could be detected.In vitro, but not in situ under field conditions, structural diversity of the bulk soil microbial community between transgenic and non-transgenic cultivars was determined by PLFA pattern-derived ratios of bacteria: fungi and of gram+: gram− bacteria. Significant differences in PLFA ratios were associated with dissimilarities in the quantity and molecular composition of rhizodeposits as revealed by Py-FIMS analyses.Contrary to field trials, where small effects based on the transgene expression might be hidden by the immense influence of various environmental factors, our in vitro system can detect even minor effects and correlates them to transgene expression with less space, time and labour.

Long-term effects of grass-clover leys on the structure of a silt loam soil in a cold climate

Abstract Grass/legume leys are commonly included in the crop rotation in mixed farming systems in cold or humid regions in order to sustain the supply of nutrients and maintain soil fertility. Leys are also known to sequester soil organic carbon and also improve the structural stability and mechanical properties of soil. However, few studies have investigated the long-term effects of ley rotations on the architectural properties of the structural pore space in soil. We investigated the effects of grass/clover leys on soil structure in the topsoil and upper subsoil of a silt loam in a long-term field trial established in 1956 at Offer in northern Sweden. This experiment includes four treatments with varying proportions of ley (1, 2, 3 or 5 years) in 6-year rotations. We used X-ray tomography to quantify topsoil structural pore space at a resolution of 65 μm in the first year of arable cropping following the ley break, a few weeks after sowing in spring. Earthworm populations were quantified by both hand-sorting and chemical extraction, while near-saturated infiltration was measured as a proxy for soil structure in the upper subsoil. In the topsoil, the treatments with a greater proportion of ley had larger organic carbon contents, smaller bulk densities and larger porosities. However, effects of crop rotation on the pore space were limited to pores smaller than 65 μm, as no treatment effects were found for the volume, size distribution, connectivity or complexity of the X-ray imaged pore space, even though the grass-clover leys promoted larger numbers and biomass of topsoil-dwelling earthworm species. Furthermore, no positive effects of grass/clover leys on organic carbon content and soil structure were found in the subsoil. The macropore infiltration capacity in upper subsoil was generally very small (overall median value of 3 mm h−1) indicating a lack of functional macroporosity below plough depth. Consistent with these results, no individuals of deep-burrowing earthworm species were found at the site, while previous observations showed only shallow rooting, both of which are attributed to the cold climate and poor subsoil drainage.

Heavy Metal Leaching as Affected by Long-Time Organic Waste Fertilizer Application.

The recycling of urban waste products as fertilizers in agriculture may introduce contaminants such as heavy metals into soil that may leach and contaminate groundwater. In the present study, we investigated the leaching of heavy metals from intact soil cores collected in the long-term agricultural field trial CRUCIAL. At the time of sampling, the equivalent of >100 yr of urban waste fertilizers following Danish legislation had been applied. The leaching of Cu was significantly increased in the treatments receiving organic waste products compared with the unfertilized control but remained below the permissible level following Danish drinking water guidelines. The leaching of Cu was controlled primarily by the topsoil Cu content and by the leaching of dissolved organic carbon (DOC) but at the same time significantly correlated with leaching of colloids in soils that had not received fertilizer or had received an organic fertilizer with a low concentration of Cu. The leaching of Zn, Cd, and Co was not significantly increased in urban waste-fertilized treatments. The leaching of Mo was elevated in accelerated waste treatments (both agricultural and urban), and the leaching of Mo was linked to the leaching of DOC. Since leaching of Cr and Pb was strongly linked to the level of colloid leaching, leaching of these metals was reduced in the urban waste treatments. Overall, the results presented should not raise concern regarding the agricultural use of urban waste products in agriculture as long as the relevant guidelines are followed.

ASSESSING NITROGEN NUTRITIONAL STATUS, BIOMASS AND YIELD OF COTTON WITH NDVI, SPAD AND PETIOLE SAP NITRATE CONCENTRATION

SUMMARYCanopy normalized difference vegetation index (NDVI), soil plant analysis development (SPAD) reading and petiole sap NO3−‒N concentration are increasingly used as quick and non-destructive methods to monitor plant N nutrition and growth status and predict yield of crops. However, little information is available on the comparisons of these three methods in assessing N nutrition, growth and yield for cotton (Gossypium hirsutum L.). Four N rates (0, 34, 67 and 101 kg N ha−1) under two cover conditions [no cover crop and hairy vetch (Vicia villosa) crop] in a 33-year long-term field trial were used to evaluate how canopy NDVI, SPAD reading (related to chlorophyll content) and petiole sap NO3−‒N concentration (conventional method) are able to assess N nutrition and plant biomass and predict yield for cotton. Canopy NDVI and SPAD readings responded less sensitively to N rates than petiole sap NO3−‒N. The responses of NDVI and SPAD reading to N rates were generally reduced due to the winter cover crop with hairy vetch. Significant and positive correlations existed mostly among NDVI, SPAD reading, and petiole sap NO3−‒N concentration. Canopy NDVI during mid-bloom to late bloom and SPAD reading during early bloom to late bloom were effective alternative methods for assessing cotton N nutrition status. The SPAD reading at late bloom was an effective parameter to estimate cotton biomass. The NDVI at early square and SPAD reading during early square to mid-bloom were effective for cotton yield prediction.

Does long-term application of fertilizers enhance the micronutrient density in soil and crop?—Evidence from a field trial conducted on a 47-year-old rice paddy

To date, how optimized, long-term fertilizer application affects the concentration of micronutrients in the milling fractions of rice grains (bran or edible grain part) with details of their dietary exposure upon consumption has not been much explored. In this study, we report results from a 47-year-old field experiment conducted in rice paddy. Soil and rice grain samples were collected from a 47-year-old long-term fertilization field trial (treatments included NPK, compost, NPK + compost, and no fertilizer/control) conducted at Miryang, South Korea. Density of total micronutrients namely As, B, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Se, V, and Zn in soil and rice milling fractions were quantified using ICP-MS and inductively coupled plasma optical emission spectrometry (ICPOES). Concentrations of the exchangeable and water-soluble micronutrients in the soil were also determined by ICP-MS and ICPOES. Potentially bioavailable soil micronutrient levels, micronutrient transfer from soil to rice grain, and dietary intake level of micronutrients by rice consumption were calculated. The correlations between soil properties and crop micronutrient availability were analyzed. In general, long-term fertilization (NPK + compost > NPK > compost) yielded a significant effect on grain As, B, Co, Cr, Cu, Fe, Mn, Mo, Ni, Se, V, and Zn fortification and promoted bioavailable soil micronutrient density. The highest contributors to micronutrient intake could be rice grains from long-term NPK + compost fertilized plots. However, estimated levels were still lower than the recommended dietary intake levels for micronutrients established by FAO/WHO. From our study, it is important to note that 80% of total micronutrient content (Fe, Mn, Zn, Co, Ni, Se, and V) were concentrated in rice bran. This has important implications for human nutrition and health. Furthermore, correlation analysis indicates that available soil P could be considered a predictor of crop micronutrient intake. Optimized long-term application of compost with NPK fertilizers to soils is a potential grain fortification strategy. Long-term fertilization will not reasonably benefit individuals who consume only white rice, because bran with enriched micronutrients will be removed by milling. We suggest replacing the consumption of white rice by brown rice so that individuals have a better micronutrient intake.