Monitoring of the humus status of soils of the Ingulets irrigation system

The results of long-term studies (1957–2007) of the changes in the morphology of soil profiles and in the reserves and fractional composition of the humus in the soils of the Ingulets irrigation system are discussed. After 50 years of irrigation, the boundaries of the genetic horizons shifted downward by 15–30 cm. The redistribution of the humus took place: its content decreased to a low level in the plow layer of the irrigated and rainfed soils and significantly increased in the layer of 60–100 cm so that the reserves of humus in the layer of 0–100 cm somewhat increased and corresponded to a moderate level. The distribution of humus in the soil profiles was characterized by the gradual lowering down the soil profile. The concentration of nitrogen in the humus of the irrigated southern chernozems was very low. The degree of humification of the soil organic matter was high. The humus was of the humate type in the upper horizons and of the fulvate-humate type in the lower horizons.     

Salinization dynamics in irrigated soils of the Svetloyarsk irrigation system,Volgograd oblast

On the basis of soil surveys performed by the Volgograd hydrogeological reclamation expedition in 1998 and 2006, published data, and original materials obtained by the authors, the dynamics of soil salinization within the Svetloyarsk irrigation system in Volgograd oblast during the irrigation and post-irrigation periods have been traced. It is found that high irrigation rates under conditions of poor drainage and closed drainage basins upon both shallow (within the Caspian Lowland) and relatively deep (on the Ergeni Upland) occurrence of saline groundwater and the presence of natural salts in the soils and subsoils lead to the rise in the groundwater level above the critical level and the development of secondary salinization in the previously surfacesaline, deeply saline, and even nonsaline soils. During the post-irrigation period (15–18 years) under modern climatic conditions, the groundwater level has been descending to a depth of more than 3 m, and the degree of salinity in the upper meter of light chestnut and meadow-chestnut soils has decreased owing to the leaching of salts with atmospheric precipitation.     

Nitrogen regime of soils with different macrosymbiont genotypes

The specificity of the nitrogen regime in gray forest and meadow-chernozemic soils under the effect of different genotypes of peas (Pisum sativum L.) was shown under field and optimal hydrothermal conditions. The dynamics of the nitrogen form ratios in soils with and without symbiotic nitrogen fixation was studied. The role of the macrosymbiont type genotype in the accumulation of ammonium, nitrate, and microbial nitrogen in soils was revealed.     

Lessivage and its relation to the hydrological regime of soils

By the examples of four typical catenas in the East European Plain, the role of lessivage in the development of automorphic and hydromorphic loamy and clayey soils with light-colored acid eluvial horizons and with different degrees of gleyzation has been studied. It is found that characteristic features of lessivage are often observed in the soils without hydrological barriers hampering or preventing the vertical migration of soil water and mass transfer processes. The hydrological barriers may be represented by the shallow horizons of temporarily perched water, or by the ascending capillary fringe of the ground water, or by the water-saturated horizons, in which the volume of free pores does not exceed 2–4%. It is shown that light-colored acid eluvial horizons may be formed in the profiles of loamy and clayey soils without any signs of lessivage. The development of strongly gleyed soils (gleyed soddy-podzolic soils and pseudogley soils (Stagnosols)) is not related to colmatage (silting of their illuvial horizons through lessivage); it is conditioned by the actual hydrological regime of these soils. The role of lessivage, podzolization, and gleyzation in the development of clay-differentiated soils is discussed.     

On the dynamics of salts in solonetzic soil complexes of the Pallas irrigation system in relation to fluctuations in the groundwater level and changes in the regime of irrigation

Changes in the salt status of solonetzic soil complexes within the Pallas irrigation system were estimated for a field surveyed in 1990 and 2003. The irrigation of this field was stopped in 2000. In 2003, the depth of the groundwater table lowered by 1 m, and the groundwater salinity decreased considerably in comparison with the corresponding values obtained in 1990. The concentrations of Na⁺ and SO ₄ ^2? ions in water extracts, as well as the ESP values in the upper horizons of solonetzes, became lower. In meadow-chestnut soils, dealkalization processes were active in the entire profile.     

Temperature regime of agrosoddy-podzolic soils on slopes of different steepness

Soil temperature regime at the depth of 20 cm may vary considerably on different parts of a given slope. This variation may be related to the position of the particular site on the slope and to the geomorphic features of the slope, including its surface inclination. The soils of the upper steep part of the slope of southern aspect are subjected to more active warming in the spring. They are characterized by higher cumulative temperatures above 10°C. The degree of this difference depends on the particular weather conditions. The differences in the soil temperature regimes may be the reason for the unequal crop yields on the different parts of the slope.     

Hydrothermic regime,dynamics of organic matter and nitrogen in drained peaty soils at different sanding modes

The rate of biochemical decomposition of organic matter in drained peaty soils has been studied for the black, sand‐mixed, and sand‐mantled farming systems with a concurrent analysis of hydrothermic conditions. The maximum depletion of peat was observed in the plow horizon for the black system and in the plow and subplow horizons for the mixed system. For the sand‐mantled system, two maximums were found for the biochemical decomposition of organic matter (in the plow horizon and in the zone of the open capillary fringe). Sand‐mixed and sand‐mantled cultures enhance the biochemical depletion of peat. An accelerated decomposition of the peat organic matter after addition of sand results in increasing the content of mobile nitrogen in soil and ground waters. Protection against the degradation is associated with control of the ground water table.     

Modern state of the soils of flood irrigation systems in the semidesert zone

The data of two soil and vegetation surveys of flood basins of the Mamai irrigation system performed in 1987 and 2012 are compared. This irrigation system is found within the Caspian Lowland in Western Kazakhstan oblast of Kazakhstan. The thickness of the humus horizon decreased by 4 cm on the average attesting to the first-second stages of soil degradation. The humus content in the A + B1 horizons decreased by 0.3% on the average with variations corresponding to the first-third degradation stages. From 1987 to 2012, the area of saline soils and the content of exchangeable sodium in them also increased attesting to the development of desertification in the studied zone. The flooded portion of flood basins decreased from 84% in 1987 to 69% in 2012, and the groundwater level rose from 3.6–4.0 to 1.8–3.1 m. Soil degradation processes, together with adverse anthropogenic impacts, resulted in a decrease in the projective cover of valuable plant species and the productivity of herbs grown in flood basins.     

Effect of irrigation methods on urea phosphate reactions in calcareous soils

Abstract

Urea phosphate (17–44–0) (UP) was injected in surface placed drip irrigation lines, subsurface placed drip irrigation lines (15 cm below soil surface), or band under furrow irrigation on a calcareous soil. In drip irrigation, UP was split in two applications, two weeks apart, to give a total rate of 50 kg P₂O₅/ha. The furrow rate was 100 kg P₂O₅/ha in a single application. Soil analysis one month after the first injection of UP showed high levels of available P (NaHCO₃ extractable) around the drip emitters. Considerable P mobility in the soil was detected within 20 cm from the emitters. Banding UP under the furrow did not leave any measurable levels of available P by the end of the experiment. Soil NO₃‐N levels were comparable in all fertilized irrigation treatments, and were higher than the levels under an unfertilized furrow. Soil pH was reduced by 0.5 units around the drip emitters, but no change was measurable under furrow irrigation. Soluble salts (ECe) were concentrated in the top 10 cm of the soil surface in all the fertilized irrigation methods. Split application of UP in subsurface drip irrigation provided the longest residual and best distribution of available P in a calcareous soil.     

Salt mineral distribution patterns in soils of the Otjomongwa pan, Namibia

The deposits of the Otjomongwa pan, southwestern Kalahari, Namibia, contain halite, thenardite and minor amounts of calcium-bearing sulfate minerals. The deposits show vertical variations in salt content, evaporite mineralogy and thenardite morphology, with similar patterns throughout the basin. The salt minerals were formed by evaporation of groundwater, within a groundmass of lacustrine deposits that did not contain synsedimentary evaporites. Lateral variations in total salt content are related to the direction of groundwater flow during a period with high groundwater levels following the end of lacustrine sedimentation in the pan basin. This was followed by a period without any groundwater influence that continues to the present. During this stage, leaching by rainwater occurred, resulting in changes in evaporite mineralogy, morphology and distribution.     

Thermal regime of tundra soils under reclamation and restoration of natural vegetation

This paper covers the specifics of the temperature regime in reclaimed tundra soils under a sown perennial herb meadow and a restored (secondary) ecosystem as compared to the small-shrub yernik (birch)-willow-moss and shrub yernik-willow-moss tundra types. The taxonomic position of the anthropogenic soils and those of the secondary (restored) biogeocenosis is discussed as related to the transformation or regeneration of the biotic and thermal components of the biogeocenosis. The soil development causes profound changes in the freezing-thawing regime, which gives grounds to distinguish the developed soils as an individual soil type.     

Effects of vegetation regime on denitrification potential in two tropical volcanic soils

Effects of vegetation and nutrient availability on potentail denitrification rates were studied in two volcanic, alluvial-terrace soils in lowland Costa Rica that differ greatly in weathering stage and thus in availability of P and base cations. Potential denitrification rates were significantly higher in plots where vegetation had been left undisturbed than in plots where all vegetation had been removed continuously, and were higher on the less fertile of the two soils. The potential denitrification rates were correlated strongly with respiration rates, levels of mineralizable N, microbial biomass, and moisture content, and moderately well with concentrations of extractable NH _inf4 ^sup+ , Kjeldahl N, and total C. In all plots, denitrification rates were stimulated by the removal of O₂ and by the addition of glucose but not by the addition of water or NO _inf3 ^sup- .This is Paper 2772 of the Forest Research Laboratory, Oregon State University     

Effect of irrigation on nematode population dynamics and activity in desert soils

Summary The nematode community in litter and soil was examined for a year in the Chihuahuan desert, before and after supplemental rainfall application. Proportions of nematode-active or anhydrobiotic forms and population densities were determined for 3 treatments: control (natural rainfall), a single, large (25-mm) monthly irrigation pulse, and 4 smaller (6-mm) irrigations spaced at weekly intervals. In litter the greatest nematode abundance was in the 6 mm week^–1 treatment (48 nematodes 20 g^–1 litter). Bacteriovores and fungivores accounted for approximately 95% of the numbers and biomass in all treatments. In soil, water amendments had no significant effect (P < 0.05) on annual mean densities of total nematodes, fungivores, bacterivores, or omnivore predators. Phytophage densities were greater on both irrigation treatments, with highest densities (9268 m^–2) in the 6 mm week^–1 soils, which was 5.9% of the total soil nematode density. Total densities of individual trophic groups were not significantly different before or after rainfall. Soil nematode densities fluctuated independently with trophic group, month, and season. Bacterial feeders and omnivore predators were the largest contributor to total soil nematode density and biomass. Prior to irrigation, there were no differences in the percentage of anhydrobiotes on the three treatments. Anhydrobiotes decreased after irrigation in all treatments, and were significantly lower in soils of the larger, monthly irrigation. Nematodes were inactive (anhydrobiotic) and decoupled from decomposition processes when soil water matric potentials reached –0.4 MPa.Dedicated to the late Prof. Dr. M.S. Ghilarov     

Influence of carbon substrates and moisture regime on nitrogen fixation in paddy soils

The influence of several carbon sources on heterotrophic N₂ fixation in four paddy soils under flooded and nonflooded conditions was investigated by ¹⁵N-tracer technique. Greater N₂ fixation occurred in submerged soils amended with cellulose and rice straw, the former being superior. Addition of sucrose, glucose and malate in that order stimulated N₂ fixation in submerged alluvial soil, while sucrose alone enhanced N₃ fixation in laterite soil. In submerged acid soils none of these C sources stimulated N₂ fixation. Nonflooded conditions favoured N₂ fixation in alluvial and acid saline soils amended with cellulose, sucrose and glucose.     

Changes in the temperature regime of podzolic soils in the course of natural forest restoration after clearcutting

The results of temperature monitoring in podzolic soils under the middle-taiga bilberry spruce forest and secondary mixed forest of the Komi Republic performed in 2008–2014 are presented. The changes in characteristics of soil temperature in the litter horizon and in the mineral horizons at the depths of 20 and 50 cm are outlined. It is shown that soil temperature regimes differ under the native spruce forest, young growth, and middle-aged secondary mixed forest. The soils of secondary phytocenoses are warmed up to a greater depth and are characterized by the higher heat supply. The differences are seen in a number of temperature parameters, such as the accumulated temperatures above 5°C and above 10°C at the depths of 20 and 50 cm. The most significant differences between the studied plots manifest themselves in the values of temperature amplitudes during the warm season. Maximum values of daily temperature amplitudes were obtained on the plot under young growth, whereas the soil under the middle-aged mixed forest was characterized by minimum values of daily temperature amplitudes.     

Physical properties and hydraulic regime of alluvial soils in floodplains of rivers in the Sikhote-Alin Mountains

The particle-size distribution, density, porosity, and water yield of soils in the floodplains in the Sikhote-Alin Mountains are characterized. The principal soil-hydrological constants are determined, and the mode of their variation upon different river discharge is shown. It is found that the vertical heterogeneity of the soil profiles’ density may be one of the reasons for the formation of a high water level in minor river basins in the Sikhote-Alin in the summer.     

Pyrogenic disturbances of the hydrothermic regime of cryogenic soils under light coniferous forests in southeastern Siberia

Pyrogenic transformations of the physical state of cryogenic soils in the southern and middle taiga were investigated. The long-term dynamics of the microclimate on burns and the soil temperature and moisture to the depth of 120 cm were studied. Data on the postfire restoration of the ground cover are presented. Experiments on artificial sprinkling of burned areas differing in the degree of the burning out of the forest litter, the slope gradient, etc., have been performed. An experimental model demonstrating the relationships between the surface runoff and five environmental factors has been proposed. The pyrogenic destruction of the ground cover and the lower phytocenosis layers was accompanied by significant disturbances of the microclimate and anomalous thawing of the permafrost on the burns. In the pine stand on the colluvial fan after the intense fire, the soil temperature at the depth of 10 cm (in the summer) exceeded the control value by 3–5°C; in the larch forest on the southern slope of the Stanovoi Ridge, it increased by 1.5–2.0 times after the fire of medium intensity. On the mountain slopes, the surface runoff was significantly intensified, which resulted in drastic environmental and silvicultural consequences.     

Subsurface drip irrigation and urea phosphate fertigation for vegetables on calcareous soils

Drip irrigation lines installed at 5 cm (shallow) or 15 cm (deep) below the soil surface and furrow irrigation were compared for vegetables grown on calcareous desert soils. Urea phosphate (UP) fertilizer (17–44–0) was injected twice in the drip irrigation lines during the growing season. Yields were compared to preplant fertilized and unfertilized furrows. Fall cabbage (Brassica oleracea var. capitata L.) gave comparable yields under the different irrigation treatments with the drip treatments using half the water used by the furrow treatment. Cabbage yield increased in all fertilized treatments as compared to the unfertilized furrow. Petiole P and NO₃‐N concentrations were higher from the drip than from the furrow treatments. Zucchini squash (Cucurbita pepo L.) had the highest yields under deep drip and fertilized furrow treatments, with the deep drip using half the water and P rate used by the furrow treatment. The deep drip increased squash yield by 34% over the shallow drip. The unfertilized furrow gave the lowest yield. Leaf tissue concentrations of P and NO₃‐N were comparable under deep drip and fertilized furrow treatments and were higher than the concentrations achieved from shallow drip and unfertilized furrow treatments.     

Impacts of irrigation methods on greenhouse gas emissions/absorptions from vegetable soils

Journal of Soils and Sediments - Recently, N2O, CO2, and CH4 have been gaining attention as major greenhouse gases (GHGs) that contribute to global warming. Agricultural water-saving irrigation...