Macro- and microscale gaseous diffusion in a Stagnic Luvisol as affected by compaction and reduced tillage

Intensification of mechanical agriculture has increased the risk for soil compaction and deformation. Simultaneously, reduced tillage practices have become popular due to energy saving and environmental concerns, as they may strengthen and improve the functioning of structured soil pore system. Soil aeration is affected by both compaction and reduced tillage through changes in soil structure and in the distribution of easily decomposable organic matter. We investigated whether a single wheeling by a 35 000 kg sugar-beet harvester in a Stagnic Luvisol derived from loess near Göttingen, Germany, influenced the gas transport properties (air permeability, gaseous macro- and microdiffusivities, oxygen diffusion rate) in the topsoil and subsoil samples, and whether the effects were different between long-term reduced tillage and mouldboard ploughing. Poor structure in the topsoil resulted in slow macro- and microscale gas transport at moisture contents near field capacity. The macrodiffusivities in the topsoil under conventional tillage were slower compared with those under conservation treatment, and soil compaction reduced the diffusivities by about half at the soil depths studied. This shows that even one pass with heavy machinery near field capacity impairs soil structure deep into the profile, and supports the view that reduced tillage improves soil structure and aeration compared with ploughing, especially in the topsoil

Allocation of added selenium in lettuce and its impact on roots

Allocation of selenium (Se) in lettuce and its impact on root morphology were studied to better understand the growth responses of plants to added Se. Lettuce was grown in vermiculite under controlled growing conditions for seven weeks, and the allocation in the shoots and roots of selenate added in increasing dosages (0, 1, 10, 100, 500 and 1000 µg Se per 3.5-litre pot) as well as morphological variables of the roots were determined. The intermediate additions of 100 and 500 µg Se per pot seemed to produce the highest biomasses, although this was nearly masked by large scatter in the data. The Se contents both in roots and shoots increased roughly proportionally to the amount of Se added. However, at small additions Se was preferentially allocated to roots, whereas at larger additions the contents in roots and shoots (mg kg-1 dry matter) were roughly equal. Se treatments did not change the morphology of hypocotyls. On the contrary, the specific length and area of basal and lateral roots were smallest at intermediate Se additions, whereas the specific volume was largest at the largest Se addition. These effects of Se on root morphology were, however, not unambiguously related to plant growth. As the Se contents in roots increased, the roots grew thicker and the specific volume of lateral roots increased in agreement with a hypothesis of increased endogenous ethylene production

Recycling lake sediment to agriculture : Effects on plant growth, nutrient availability, and leaching

Sediment removal from eutrophicated shallow lakes may not only be an effective method for lake restoration but also provides the potential for recycling nutrients from sediments to crop production. However, finding a suitable strategy for sustainably reusing the sediment remains a challenge. Therefore, current study focused on the best practices in applying the sediment from a shallow eutrophicated lake to the soil in terms of grass yield, nutrient uptake, and nutrient leaching. During a nine-month lysimeter experiment, 100-cm high columns were filled with six combinations of soil, sediment, and biochar, with or without meat bone meal organic fertilizer. Aboveground biomass, root mass distribution in soil, nutrient concentration, phosphorus (P) uptake of perennial ryegrass (Lolium perenne L.) along with easily soluble nutrients in the growing medium, and leached mineral nitrogen (N) and P levels were measured. Plant growth conditions were improved by sediment additions, as the yield and P uptake of ryegrass nearly doubled in treatments containing sediment compared to the control soil. While the sediment was richer in macro and micronutrients (e.g. P and N) compared to the soil, the leached N and P levels from both treatments were almost equivalent (N < 830 mg m−2 and P < 3 mg m−2). In addition, applying a 2-cm layer of biochar between the sediment and soil reduced P and N leaching by 50%. According to the results, applying a 75-cm thick layer of sediments on agricultural sandy loam soils surrounding the lake seems a promising practice for improving plant yield and soil nutrient status without increasing of P and N leaching from soil.Peer reviewe

Internal phosphorus loading in a small shallow Lake: Response after sediment removal

Mankind is taking advantage of numerous services by small shallow lakes such as drinking water supply, irrigation, and recreational function; however, many of these lakes suffer from eutrophication. Given the key role of phosphorus (P) in eutrophication process, one of the effective restoration methods especially for small shallow lakes is removal of sediments enriched with nutrients. In our study, we used interannual, seasonal, and spatial data to examine the changes in sediment P mobility after removal of sediments in 2016 from a 1-ha highly eutrophic lake. We measured the sediment redox potential, analyzed soluble reactive P (SRP) in the pore water and P fractional composition of the surface sediments, and calculated the P diffusive flux in three locations in two continuous years (2017 and 2018) after the excavation. Similar measurements were done before sediment removal at central site of the lake in 2015. Removing nutrient-rich sediment also removed 6400 kg of P, and thus the potential for release of P from sediments decreased on a long-term scale. However, a large pool of releasable P was rebuilt soon after the sediment removal due to high external P loading, resulting in extensive anoxia of sediment surface and associated internal P loading as high as 1450 mg m−2 summer−1. Moreover, the Fe-P and labile P fractions were the most important sources of P release, as evidenced by their considerable seasonal and interannual changes after the sediment removal. The sediment total Fe negatively correlated with sediment P diffusive flux, pore water SRP, and near-bottom water total P and SRP concentrations which indicated a strong linkage between sediment P dynamics and Fe after the restoration. Sediment removal could be a beneficial restoration approach, but the effects on lake water quality remain only short-term unless there is an adequate control on external loading to the lake.Peer reviewe

Effects of liming on oxic and anoxic N2O and CO2 production in different horizons of boreal acid sulfate soil and non-acid soil under controlled conditions

In acid sulfate (AS) soils, organic rich topsoil and subsoil horizons with highly variable acidity and moisture conditions and interconnected reactions of sulfur and nitrogen make them potential sources of greenhouse gases (GHGs). Subsoil liming can reduce the acidification of sulfidic subsoils in the field. However, the mitigation of GHG production in AS subsoils by liming, and the mechanisms involved, are still poorly known. We limed samples from different horizons of AS and non-AS soils to study the effects of liming on the N2O and CO2 production during a 56-day oxic and subsequent 72-h anoxic incubation. Liming to pH >= 7 decreased oxic N2O production by 97-98 % in the Ap1 horizon, 38-50 % in the Bg1 horizon, and 34-36 % in the BC horizon, but increased it by 136-208 % in the C horizon, respectively. Liming decreased anoxic N2O production by 86-94 % and 78-91 % in Ap1 and Bg1 horizons, but increased it by 100-500 % and 50-162 % in BC and C horizons, respectively. Liming decreased N2O/(N2O + N2) in anoxic denitrification in most horizons of both AS and non-AS soils. Liming significantly increased the cumulative oxic and anoxic CO2 production in AS soil, but less so in non-AS soil due to the initial high soil pH. Higher carbon and nitrogen contents in AS soil com-pared to non-AS soil agreed with the respectively higher cumulative oxic N2O production in all horizons, and the higher CO2 production in the subsoil horizons of all lime treatments. Overall, liming reduced the proportion of N2O in the GHGs produced in most soil horizons under oxic and anoxic conditions but reduced the total GHG production (as CO2 equivalents) only in the Ap1 horizon of both soils. The results suggest that liming of subsoils may not always effectively mitigate GHG emissions due to concurrently increased CO2 production and denitrification.Peer reviewe

Sustainable bioenergy cropping: growing reed canarygrass in acid suphate soils

The response of reed canary grass to water logging, acidity and dissolved metals will be studied in the field as well as in a controlled environment using large monoliths of undisturbed acid suphate soil taken into PVC tubes

Effect of persistent subsoil compaction on N2O emissions from arable soils

Compaction occasionally increased N2O in soil air. No large differences in soil air composition, N2O emissions or moisture content were found between the treatments. The N2O concentrations at 15, 30, 50 and 70 cm depths correlated positively with the emission of N2O from the soil in both fields (r=0.4-0.7***). The subsoil O2 concentrations correlated negatively with N2O emission, but only at the Finnish site. The results suggest that subsoil compaction does not significantly increase N2O emissions from these soils 15-30 years after compaction. This may indicate a minor role of subsoil in the production of N2O compared with topsoil

Factors limiting microbial N2O and CO2 production in a cultivated peatland overlying an acid sulphate subsoil derived from black schist

Factors limiting the production of the greenhouse gases nitrous oxide (N2O) and carbon dioxide (CO2) were investigated in three incubation experiments conducted with soil from top- and subsoil horizons of a peatland which had an acid sulphate mineral subsoil derived from black schists. The effect of moisture was investigated by equilibrating undisturbed soil samples from three horizons (H-2, Cg and Cr) at -10, -60 or -100 cm matric potential and measuring the gas production. In the second experiment, the effects of temperature and various substrates were studied by incubating disturbed soil samples in aerobic conditions at 5 or 20 degrees C, and measuring basal respiration and N2O production before and after adding water, glucose or ammonium into the soil. In the third experiment, the effects of added glucose and/or nitrate on the denitrification in soil samples from four horizons (H1, H2, Cg and Cr were investigated by acetylene inhibition and monitoring of N2O production during a 48-h anaerobic incubation. The production of CO2 in the topmost peat horizon was largest at -10 cm matric potential, and it was larger than those in the mineral subsoil also at -60 and -100 cm potentials. In contrast, drainage seemed to increase N2O production, whereas in the wettest condition the production of N2O in the mineral subsoil was small and the peat horizon was a sink of N2O. Lowering of temperature (from 20 degrees C to 5 degrees C) decreased CO2 production, as expected, but it had almost no role in the production of N2O in aerobic conditions. Glucose addition increased the aerobic production of CO2 in peat, but it had a minor effect in the mineral horizons. Lack of C source (glucose) was limiting anaerobic N2O production in the uppermost peat horizon, while in all other horizons, nitrate proved to be the most limiting factor. It is concluded that peatlands with black schist derived acid sulphate subsoil horizons, such as in this study, have high microbial activity in the peaty topsoil horizons but little microbial activity in the mineral subsoil. These findings are contrary to previous results obtained in sediment-derived acid sulphate soils.Peer reviewe

Voiko peltobioenergiatuotanto vähentää happamilta sulfaattimailta tulevaa vesistökuormitusta?

Peltoviljelyssä olevista happamista sulfaattimaista purkautuu vesistöihin ajoittain hyvin hapanta jarunsaasti metalleja sisältävää kuivatusvettä. Vähäistä kuivatussyvyyttä vaativan ruokohelven viljelybioenergiatuotantoon saatttaisi olla yksi ratkaisu tähän ongelmaan näillä alueilla.Tutkimus kuivatussyvyyden vaikutuksesta ruokohelven tuotantoon happamilla sulfaattimaillasekä kuivatussyvyyden ja kasvin vaikutuksesta valumaveden laatuun aloitettiin kesällä 2007 osanamaatalousmetsätieteellisentiedekunnan yhteistutkimushanketta "Peltobioenergiaketjut raaka-aineentuotanto ympäristöllisesti ja taloudellisesti kestävällä tavalla" esikokeilla, joissa selvitettiin, voidaankohappamilta sulfaattimailta otettuja suuria maanäytelieriöitä käyttää pelto-olojensimulointiin.Esikokeissa pyrittiin luomaan toimiva mittausjärjestelmä ennen laajemman kokeen aloittamista jakasvullisten jäsenten mukaanottamista. Käytännön toteutukseen kehitettiin häiriintymättömiensuurten maapatsaiden ottamisen tekniikka, vedensäätöjärjestelmä ja jatkuvatoimisten mittausteninstrumentointi kahden suuren maanäytelieriön avulla.Isot maalieriöt otettiin Viikin koetilan pellolta, joka on hapanta sulfaattimaata. Samallepeltolohkolle asennettiin pohjavesiputkia pohjaveden laadun ja korkeuden seuraamiseksi. Pohjavedenkorkeuden vaihtelun aiheuttamia muutoksia maanäytelieriöissä verrattiin kasvukauden aikana pelloltamitattuihin pohjaveden laadun muutoksiin.Maanäytelieriöistä mitattiin maan redox-potentiaaliasekä vesipitoisuutta, lämpötilaa jasähkönjohtavuutta jatkuvatoimisesti 10 minuutin välein muokkauskerroksesta, hapettuneestakerroksesta ja pelkistyneestä kerroksesta. Aineiston keräämiseen käytettiin dataloggereita (Agilent34980A) ja (Degacon Em50), josta tulokset siirrettiin tietokoneelle. Maan pH-arvoaja huokosvedenkoostumusta seurattiin määräajoin.Redox-mittaustentoteutus käyttämen suolasillan avulla toteuttua yhteistä referenssielektrodiakaikille Pt-elektrodeilleantoi luotettavia tuloksia. Jatkuvatoimisen ja manuaalisen redox-mittauksenkeskimääräinen ero oli pienin pelkistyneessä kerroksessa (38 mV) ja hapettuneissa kerroksissa hiemanisompi (100 mV). Pohjaveden pH:n, sähkönjohtavuuden ja redox-potentiaalinmuutokset pohjavedenkorkeuden funktiona pellolla ja maanäytelieriöissä olivat samansuuntaisia. Pohjaveden pinnan nousulaski redox-potentiaaliaja sähkönjohtavuutta ja nosti veden/maan pH-arvoamolemmissa.Esikokeesta saadut alustavat tulokset viittaavat siihen, että maanäytelieriöllä voidaan simuloidapellolla tapahtuvia pohjaveden muutoksia ja seurata pohjaveden korkeuden vaikutusta maanominaisuuksiin. Pohjaveden nostolla oli esitutkimuksessa pH-arvoanostava vaikutus, kuten aiemmissahappamilla sulfaattimailla tehdyissä tutkimuksissa on havaittu. Ruokohelven kasvu pohjaveden pinnanollessa korkealla ja kasvin vaikutus maan ominaisuuksiin ja valumaveden laatuun on tutkimuksenseuraava vaihe