The effect of the Danube diversion on the soil moisture conditions in Csallóköz and Szigetköz

Summary. Following the commissioning of the Gabčíkovo (Bős) hydroelectric power plant in 1992, a monitoring program was launched to assess the agricultural and forestry consequences of the diversion of the Danube into a newly built derivation channel in the Žitný ostrov (Csallóköz) and Szigetköz areas. Prior to the Danube diversion, groundwater played a significant role in the water supply of plants, therefore it is of primary importance to monitor the changes in groundwater levels and soil moisture. Correlation between the groundwater depth and soil moisture time series taken at four measurement points of Szigetköz (T-03, T-04, T-09, T-16) between 1995 and 2012 was analysed. Average and extreme water levels (quartiles 1 and 4) were examined for the 18-year time series, in which 2nd and 3rd quartiles of the groundwater levels were treated together as characteristic water level. It was found that groundwater significantly correlated with soil moisture storage below the rooting zone of field crops. Összefoglalás. A Gabčíkovo (Bős) vízerőművet 1992-ben helyezték üzembe. A dunacsúnyi duzzasztó vize a bősi erőművön átfolyva a Szlovákiában épített vízlevezető csatornából 40 km után tért vissza a korábbi Duna főmederbe. A régi Duna főmederbe emiatt az elterelt szakaszon a korábbi vízmennyiség ötöde került. Minthogy mind a szlovákiai, mind a magyarországi mezőgazdasági és erdőterületek vízellátásában a talajvíz és a dunai árhullámok jelentős szerepet játszottak, 1995-től a Duna-elterelés hatásának felmérésére talajvízszint és talajnedvesség monitoring program indult a Csallóközben és a Szigetközben. A szlovák megfigyelések publikált anyagainak megállapításait és a Szigetközből két szántóföld, egy kaszálórét és egy nyárfaültetvény 1995 és 2012 közötti mérési adatait dolgoztuk fel. A talajvízmélység és a 10 cm-es talajrétegek mért térfogatszázalékos (v.%) nedvességtartalmából számított talajvízkészletek közötti korrelációt számítottuk. A 18 éves idősoron külön vizsgáltuk a jellemző, illetve a szélsőséges vízszintek (1. és 4. kvartilisek) hatását. A jellemző vízszintek hatásának vizsgálatához a talajvízszint értékek 2. és 3. kvartilisét egyben kezeltük. Megállapítottuk, hogy szignifikáns, ill. közel szignifikáns összefüggés csupán az átlagosnál a talajfelszínhez közelebbi (Q1) talajvízmélység esetén volt kimutatható mind a mély (T-03), mind a sekély talajrétegű (T-09) szántóföld 210–300 cm-es, illetve 120–140 cm-es talajszintjében. Vagyis a szántóföldi kultúrák számára az átlagos talajvízmélység nem jelentett vízpótlást. A régi Duna főmederhez közeli kaszálóréten (T-04) a talajvízmélység helyett a dunaremetei medervízszint adatok és a talajnedvességkészlet között még a 140 cm-es mélységben található kavicsos alapkőzet fölötti 20 cm-es talajrétegben sem volt jelentős kapcsolat. A mély talajrétegű (300 cm) erdészeti mérőhely (T-16) talajvízmélység és talajnedvességkészlet korrelációja csupán a 210–300 cm-es talajréteg esetében volt közel szignifikáns. A nyárültetvények fejlődéséhez szükséges éves 700–900 mm vízigény biztosítására emiatt a régi Duna főmederbe engedett többletvízre lenne szükség. A szántóföldi kultúrák terméshozama is elsősorban az adott év csapadékmennyisége és eloszlása szerint alakul. Amennyiben az időjárási feltételek kedvezőtlenek, megoldásként öntözni szükséges. Beszámoltunk továbbá arról, hogy két éve négy mérőhely üzemel, ami a naponta óránként mért 6 órás átlag talajnedvesség-adatokat gyűjti. A folyamatos talajnedvesség-adatgyűjtés célja az időjárás, a növényi vízfelhasználás és a talajvízből történő nedvesítés nyomon követése és a talajvízforgalom-modell leírásának a kontrollja. A közeljövő feladata az évente 12-14 alkalommal az ezeken a mérőhelyeken is gyűjtött kapacitívszondás és a folyamatos nedvességmérési eredmények megfeleltetése, minthogy a bemutatott közel azonos példa mellett több helyen és mélységben időben párhuzamos módon változik ugyan a kétféle érték, azonban akár több, mint 5 v.% különbséggel.

Soil nitrogen and water management by winter-killed catch crops

Improving N cycling in agroecosystems is one of the key challenges in reducing the environmental footprint of agriculture. Further, uncertainty in precipitation makes crop water management relevant in regions where it has not been necessary thus far. Here, we focus on the potential of winter-killed catch crops to reduce N leaching losses from N mineralization over the winter and soil water management. We compared four single catch crops (white mustard, phacelia, Egyptian clover and bristle oat) and a fallow treatment with two catch crop mixtures with 4 and 12 plant species (Mix4 and Mix12). High-resolution soil mineral N (Nmin) monitoring in combination with modelling of spatiotemporal dynamics served to assess N cycling under winter-killed catch crops, while soil water was continuously monitored in the rooting zone. Catch crops depleted the residual Nmin pools by between 40 and 72 % compared to the fallow. The amount of residual N uptake was lowest for clover and not significantly different among the other catch crops. Catch crops that produce high N litter materials, such as clover and mustard leaves, showed an early N mineralization flush immediately after their termination and the highest leaching losses from litter mineralization over the winter. Except for clover, all catch crops showed Nmin values between 18 and 92 % higher on the sowing date of the following maize crop. However, only Mix12 was statistically significant. Catch crops depleted the soil water storage in the rooting zone during their growth in autumn and early winter, but preserved water later on when their residues cover the ground. The shallow incorporation of catch crop residues increased water storage capacity during the cropping season of the main crop even under drought conditions. Hence, catch cropping is not just a simple plant cover during the winter but improved the growth conditions for the following crop at decreased N losses. Mixtures have been shown to compensate for the weaknesses of individual catch crop species in terms of nutrient capture, mineralization and transfer to the following main crop as well as for soil water management. Detailed knowledge about plant performance during growth and litter mineralization patterns is necessary to make optimal use of their full potential.

Global distribution of the rooting zone water storage capacity reflects plant adaptation to the environment

The rooting zone water storage capacity (S0) extends from the soil surface to the weathered bedrock (the Critical Zone) and determines land-atmosphere exchange during dry periods. Despite its importance to land-surface modeling, variations of S0 across space are largely unknown as they cannot be observed directly. We developed a method to diagnose global variations of S0 from the relationship between vegetation activity (measured by sun-induced fluorescence and by the evaporative fraction) and the cumulative water deficit (CWD). We then show that spatial variations in S0 can be predicted from the assumption that plants are adapted to sustain CWD extremes occurring with a return period that is related to the life form of dominant plants and the large-scale topographical setting. Predicted biome-level S0 distributions, translated to an apparent rooting depth (zr) by accounting for soil texture, are consistent with observations from a comprehensive zr dataset. Large spatial variations in S0 across the globe reflect adaptation of zr to the hydroclimate and topography and implies large heterogeneity in the sensitivity of vegetation activity to drought. The magnitude of S0 inferred for most of the Earth’s vegetated regions and particularly for those with a large seasonality in their hydroclimate indicates an important role for plant access to water stored at depth - beyond the soil layers commonly considered in land-surface models.

Effect of sprinkler irrigation on the properties of leached chernozem and the yield of Bromopsis inermis Leyss. in the Southern Cis-Ural

The paper examines the effect of the long-term (10 years) low-intensity sprinkler irrigation on the properties of leached chernozem soils covered with Bromopsis inermis Leyss. (BIL) stands in the Southern Cis-Ural forest-steppe. The study analysed changes in the soil’s agrophysical and chemical properties. As a result of long-term irrigation, the humus horizon (A + AB) thickness increased by 16 ± 3 cm; the organic carbon (Corg) content and nutrients decreased in this rooting zone, in particular, Corg by 0.3%, available phosphorus by 24.8 mg/kg, exchangeable potassium by 18.4 mg/kg and the stock of Corg by 16 t/ha. The particle size distribution of irrigated soil did not significantly changed; some changes were observed for the soil’s aggregate composition. The soil’s hydrophysical properties, water and air regime worsened.

The rhizosphere responds: rich fen peat and root microbial ecology after long-term water table manipulation

Hydrologic shifts due to climate change will affect the cycling of carbon (C) stored in boreal peatlands. Carbon cycling in these systems is carried out by microorganisms and plants in close association. This study investigated the effects of experimentally manipulated water tables (lowered, raised) and plant functional groups on the peat and root microbiomes in a boreal rich fen. All samples were sequenced and processed for bacterial, archaeal (16S rDNA—V4), and fungal (ITS2) DNA. Depth had a strong effect on microbial and fungal communities across all water table treatments. Bacterial and archaeal communities were most sensitive to the water table treatments, particularly at the 10-20 cm depth—this area coincides with the rhizosphere or rooting zone. Iron cyclers, particularly members of the family Geobacteraceae, were enriched around the roots of sedges, horsetails, and grasses. The fungal community was affected largely by plant functional group, especially cinquefoils. Fungal endophytes (particularly Acephala spp.) were enriched in sedge and grass roots, which may have underappreciated implications for organic matter breakdown and cycling. Fungal lignocellulose degraders were enriched in the lowered water table treatment. Our results were indicative of two main methanogen communities: a rooting zone community dominated by the archaeal family Methanobacteriaceae and a deep peat community dominated by family Methanomicrobiaceae. Importance This study demonstrated that roots and the rooting zone in boreal fens support organisms likely capable of methanogenesis, iron cycling, and fungal endophytic association, and are directly or indirectly affecting carbon cycling in these ecosystems. These taxa, which react to changes in water table and associate with roots and particularly graminoids, may gain greater biogeochemical influence as projected higher precipitation rates could lead to an increased abundance of sedges and grasses in boreal fens.

Artificial Macropores with Sandy Fillings Enhance Desalinization and Increase Plant Biomass in Two Contrasting Salt-Affected Soils

Salt accumulation in topsoil is a widespread restricting factor that limits agricultural production and threatens food security in arid and semi-arid regions. However, whether this upward enrichment was suppressed by macropores was less documented. Therefore, artificial macropores with sandy fillings (AMSF) method was proposed in this study. Soil column experiments showed a significant improvement of saturated hydraulic conductivity (Ks) by more than 260% under artificial macropore treatment. Freshwater irrigation was conducted to monitor the short-term water and salt movement. This research aimed at evaluating the potential benefit of AMSF method on soil desalinization in coastal farmland of northern China. The results demonstrated that downward movement of soil water was stimulated in AMSF method, accordingly, washing more salt ions out of top rooting zone. Particularly, 10 cm or more macropore depth treatments of AMSF method enhanced total desalinization by 52.1% to 176.6% in 0–30 cm soil layer, in comparison to the control group without macropore. Subsequent observations for alfalfa showed higher biomass by 20.8% under 15 cm macropore depth. The results here provided an exploration demonstration to pursue these studies with the ultimate goal of optimizing application strategies for amendment in coastal salt-affected lands of northern China.

Low nitrogen retention in a Japanese cedar plantation in a suburban area, western Japan

This study aimed to evaluate nitrogen (N) leaching from Japanese cedar, the main plantation species in Japan, in response to elevated atmospheric N deposition. N leaching and possible factors, including soil nitrification, tree N uptake, and topographic steepness, were evaluated in mature (64–69 year) Japanese cedar trees planted on steep slopes (25°–40°) and neighboring Japanese oak plantations in suburban forests, which served as reference sites. N fertilization (50 kg N ha−1 year−1 as ammonium nitrate) was conducted to evaluate the response of N leaching to an elevated inorganic N pool in the surface soil. The soil water nitrate (NO3−) concentration below the rooting zone in the Japanese cedar forest (607 ± 59 μmol L−1) was much higher than that in the Japanese oak plantations (8.7 ± 8.1 μmol L−1) and increased immediately after fertilization, indicating high N leaching from the Japanese cedar plantations. The relatively low N uptake by Japanese cedar planted on the steep slopes could be an important contributor to the high N leaching. This study highlights the importance of vegetation composition for managing the water quality in headwater streams from forest ecosystems disturbed by atmospheric N deposition.

Global carbon and water exchange during drought reflects adaptation of rooting depth to climate and topography

<p>The rooting zone water storage capacity (S) defines the total amount of water available to plants for transpiration during rain-free periods. Thereby, S determines the sensitivity of carbon and water exchanges between the land surface and the atmosphere, controls the sensitivity of ecosystem functioning to progressive drought conditions, and mediates feedbacks between soil moisture and near-surface air temperatures. While being a central quantity for water-carbon-climate coupling, S is inherently difficult to observe. Notwithstanding scarcity of observations, terrestrial biosphere and Earth system models rely on the specification of S either directly or indirectly through assuming plant rooting depth.</p><p>Here, we model S based on the assumption that plants size their rooting depth to maintain function under the expected maximum cumulative water deficit (CWD), occurring with a return period of 40 years (CWD<sub>X40</sub>), following Gao et al. (2014). CWD<sub>X40</sub> is “translated” into a rooting depth by accounting for the soil texture. CWD is defined as the cumulative evapotranspiration (ET) minus precipitation, where ET is estimated based on thermal infrared remote sensing (ALEXI-ET), and precipitation is from WATCH-WFDEI, modified by accounting for snow accumulation and melt. In contrast to other satellite remote sensing-based ET products, ALEXI-ET makes no a priori assumption about S and, as our evaluation shows, exhibits no systematic bias with increasing CWD. It thus provides a robust observation of surface water loss and enables estimation of S with global coverage at 0.05° (~5 km) resolution.</p><p>Modelled S and its variations across biomes is largely consistent with observed rooting depth, provided as ecosystem-level maximum estimates by Schenk et al. (2002), and a recently compiled comprehensive plant-level dataset. In spite of the general agreement of modelled and observed rooting depth across large climatic gradients, comparisons between local observations and global model predictions are mired by a scale mismatch that is particularly relevant for plant rooting depth, for which the small-scale topographical setting and hydrological conditions, in particular the water table depth, pose strong controls.</p><p>To resolve this limitation, we investigate the sensitivity of photosynthesis (estimated by sun-induced fluorescence, SIF), and of the evaporative fraction (EF, defined as ET over net radiation) to CWD. By employing first principles for the constraint of rooting zone water availability on ET and photosynthesis, it can be derived how their sensitivity to the increasing CWD relates to S. We make use of this relationship to provide an alternative and independent estimate of S (S<sub>dSIF</sub> and S<sub>dEF</sub>), informed by Earth observation data, to which S, modelled using CWD<sub>X40</sub>, can be compared. Our comparison reveals a strong correlation (R<sup>2</sup>=0.54) and tight consistency in magnitude between the two approaches for estimating S. </p><p>Our analysis suggests adaptation of plant structure to prevailing climatic conditions and drought regimes across the globe and at catchment scale and demonstrates its implications for land-atmosphere exchange. Our global high-resolution mapping of S reveals contrasts between plant growth forms (grasslands vs. forests) and a discrepant importance across the landscape of plants’ access to water stored at depth, and enables an observation-informed specification of S in global models.</p>

Drought years of 2018 and 2019 affect CO2 balance of urban forest ecosystems in the Ruhr Metropolitan Region (Germany) differently

<p>Forests are important ecosystems for mitigating CO<sub>2</sub>. However, droughts affect the vitality of forests and alter CO<sub>2</sub> uptake. In worst cases, forest ecosystems can even turn from a carbon sink to a source in consequence of water shortage. Forest stands in urban areas are more prone to droughts because of elevated temperatures in comparison to rural land and unfavorable growth conditions such as limited rooting depth and low soil carbon content.</p><p>The drought years 2018 and 2019 in the Ruhr Metropolitan Region (Germany) were characterized by a 0.6 K higher mean annual temperature as normal and only 75 % of the normal annual precipitation. During this period, we investigated the CO<sub>2</sub> balance of urban forest ecosystems, considering annual changes in carbon stocks of tree biomass and litterfall and annual CO<sub>2</sub> effluxes from soil respiration, at eleven monitoring sites across the Ruhr Metropolitan Region by combining measuring and modelling approaches. The chosen sites represent the different urban forest types found here: old-grown semi-natural forests (beech, oak, maple), autochthon non-managed succession forests of birch, poplar or willow on brownfields and allochthone mixed forest stands planted in urban parcs and on heaps (urban greening forests).</p><p>Tree growth, leaf expansion, and CO<sub>2 </sub>efflux decreased at nearly all sites in 2019 in comparison to 2018 in consequence of the ongoing drought. While the semi-natural forests were able to increase CO<sub>2</sub> uptake by 11 % in 2019, the urban greening forests decreased their CO<sub>2</sub> uptake by 62.9 %. The succession forests were CO<sub>2</sub> sources in both years but increased the CO<sub>2 </sub>release in the second year by 85 % in comparison to the first year. Two sites turned from carbon sinks in 2018 to carbon sources in 2019. Correlation analyses showed that the soil hydraulic properties such as depth of the rooting zone, soil carbon content, and plant available water were the main influencing factors describing the decrease in tree growth and leaf development. Overall, the results indicate that, semi-natural forests on mesophilic sites are more resilient against droughts due to unlimited rooting zone, high soil carbon content, which favor the amount and accessibility of plant available water, while urban greening and succession forests are more vulnerable to droughts due to limiting rooting zone, low soil carbon content, and low plant available water. More vulnerable to droughts are also semi-natural forests on more extreme sites, like an examined Stellario-Carpinetum, which turned from a carbon sink in 2018 to a source in 2019. Furthermore, two patterns of seasonal changes in soil respiration were found in reaction to the drought. i) those of elevated soil respiration associated to elevated temperature in 2018 and decrease of soil respiration in 2019 in consequence of thermal denaturation of the microbial community, and one ii) those where, the mineralization activity was shifted to winter when the upper soil layer was rewetted, leading to larger soil respiration during the cold season.</p><p>Urban planners should ensure a deep rooting zone and carbon rich soils by establishing new urban forest stands to tackle drought periods.</p>

Superabsorbent Polymers (SAPs) Hydrogel: Water Saving Technology for Increasing Agriculture Productivity in Drought Prone Areas: A Review

To improve the soil moisture availability, by reducing the evaporation losses and retaining the moisture in effective rooting zone. The soil application of superabsorbent polymers (SAPs) is found to be the promising methodology in drought prone areas. However, very limited research work done in Indian conditions on this aspect. One of such successfully developed product is ‘Pusa hydrogel’ which is first indigenous semi-synthetic superabsorbent technology for conserving water and enhancing crop productivity and thereby increases the water use efficiency. It performs its wetting or drying cycles over a longer period of time, maintaining its very high water swelling and releasing capacity against soil pressure. Consequently evaporation, deep water percolation and nutrient leaching can be avoided. Under rainfed condition, crops can better withstand drought condition without moisture stress by using hydrogel. Systematic field studies under arid and semi-arid conditions of India are needed to develop appropriate dose, frequency and method of application of different polymers to various crops and to assess economics of use of different polymers.