Ap Horizon Research Articles

Impact of conventional agriculture on the concentration and quality of water-extractable organic matter (WEOM) in the surface horizons of Retisols—A case study from the Carpathian Foothills in Poland

In spite of many studies focused on the impact of land use changes on soil organic carbon (SOC) and the total nitrogen (TN) and soil organic matter (SOM) budget, less is known about the fate of water-extractable organic matter (WEOM) after the conversion of forestland to conventional farmland. The main aims of this study were: 1) to determine the concentration of water-extractable organic carbon (WEOC) and water-extractable total nitrogen (WETN) in topsoil horizons of forestland soils and cropland soils in the Carpathian Foothills in southern Poland and 2) to determine the quality of WEOM in topsoil horizons of forestland soils and cropland soils. Soil samples from topsoil horizons of forestland soils (Oi and Ah horizons) and cropland soils (Ap horizons) were collected and the concentration of WEOC and WETN was determined. In addition, the quality of WEOM was determined using ultraviolet-visible (UV–vis) spectroscopy and Fourier-transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy. The results of this comparative study clearly indicate that conventional agriculture significantly affects the concentration and quality of WEOM in surface soil horizons of Retisols in the Carpathian Foothills in southern Poland. Surface horizons of arable soils (Ap horizons) are characterized by a significantly lower mean concentration of WEOC and WETN in comparison with surface horizons of forestland soils (Oi and Ah horizons), and reflect changes in the content of bulk SOC and TN due to soil tillage. Mean concentrations of WEOC and WETN in the studied Ap horizons of arable soils are 1.98 mg l−1 and 0.15 mg l−1, respectively while the mean concentrations of WEOC and WETN in the Ah horizons of forestland soils are 15.53 mg l−1 and 0.84 mg l−1, respectively. The studied Oi horizons of forestland soils are characterized by the highest mean concentration of WEOC (44.53 mg l−1) and WETN (6.22 mg l−1). Mean specific UV absorbance values at wavelength of 254 nm (SUVA254) was the highest for WEOM from Ap horizons indicating the highest transformation of WEOM in these horizons. Mean FTIR-ATR absorption bands of WEOM obtained from Oi and Ah horizons are much more intensive than the bands of WEOM from Ap horizons, which is related to significantly lower concentration of WEOM in the latter horizons in comparison with Oi and Ah horizons of forestland soils.

Iron Stable Isotopes in Bulk Soil and Sequential Extracted Fractions Trace Fe Redox Cycling in Paddy Soils.

In paddy soils, iron (Fe) forms are highly influenced by the seasonal redox changes and leave detectable isotope signals because of fractionation between different Fe forms. Here, we present Fe concentrations and Fe isotope compositions (expressed as δ56Fe values) in a paddy soil profile from Suzhou, China. Light Fe isotopes were enriched in two iron-accumulation layers (Br3 and G1) with high Fe concentrations. In particular, large shifts in both Fe concentrations and δ56Fe values were found at the Br2 and Br3 boundaries, showing fast and efficient transformation between these horizons. With sequential extraction, we show that Fe isotopes in the short-range-ordered Fe minerals and crystalline Fe oxides were lighter than those in the residual silicate minerals. Iron enriched in light isotopes was leached from the Ap horizon and subsequently moved to Br horizon, quickly precipitating there as Fe oxides.

Model of the pression transfer apply on an alfisol from Tabuleiros Costeiros

The cohesive subsurface horizon of the Arfisol of Tabuleiros Costeiros, reduces the effective depth of these soils, compromising the yield and longevity of the perennial crops. This pedogenetic limitation can be potentiated when the pressure applied on the surface of the Ap horizon, during the traffic of agricultural machinery is transmitted to deeper horizons, AB or Bt, at higher levels the load-bearing capacity of these layers. The objective of this research was to mathematically model the transfer of pressures applied to the surface of the Ap horizon of an Alfisol for subsurface layers, relating the pressure applied to the soil profile moisture. With the experiment developed in the Laboratory of Soils and Plant Nutrition of Embrapa Tabuleiros Costeiros, it was concluded that moisture has a damping effect on the pressure transmitted from upper layers to subsurface. The pressure transmitted to the subsurface shows an exponential function with negative correlation as a function of depth, independent of the applied pressure on the surface. The increase in the contact area for the application of pressures on the soil surface, attenuates the transmission of pressure to lower layers when compared to the same pressure applied in smaller areas

Impact of agriculture on soil organic matter quantity and quality in Retisols – a case study from the Carpathian Foothills in Poland

ABSTRACT Changes in land use are very important factors affecting soil quality and especially the concentration and stock of soil organic carbon (SOC) and total nitrogen (TN). Very little is known about changes in spectroscopic properties of SOM after conversion of forestland to cropland. Therefore, the main aim of this study was to determine impact of agriculture on the concentration and stock of SOC and TN as well as spectroscopic properties of SOM in the topsoil horizons of Retisols in the Carpathian Foothills in southern Poland. Topsoil Ap horizons of arable soils are characterized by a significantly lower concentration of SOC and TN in comparison with topsoil Oi and Ah horizons of forestland soils. Topsoil Ap horizons feature higher SOC and TN stocks than topsoil Oi and Ah horizons. Significantly higher concentrations of SOC and TN in Oi horizons in comparison with Ah and Ap horizons are responsible for significantly higher mean absorbance values of all FTIR-ATR absorption bands originating from SOM in Oi horizons versus Ah and Ap horizons. Significantly higher concentrations of SOC and TN in Ah horizons of forestland soils versus those in Ap horizons of arable soils do not significantly affect mean absorbance values of FTIR-ATR bands.

Effect of organic residues on soil properties of loamy topsoil of haplic Luvisol in Northern Germany

Summary The application of organic residues should ensure a sufficient air capacity (AC) and plant available water capacity (AWC) to improve the soil aeration and water supply for plant roots, whereas the air permeability (ka) primarily depends on the number of functional and, therefore, connected pores. The objective of the study was to investigate the effect of digestates derived from maize (Zea mays L.), sugar beet (Beta vulgaris L.), and wheat (Triticum aestivum L.) in ratios of 100%, 80%, and 20%, respectively; compost of shrub debris; and sewage sludge on AC, AWC, and ka values, including the pore continuity indices (c2, c3) of a loamy Ap horizon of a haplic Luvisol. The results indicate that AC values increase from 0.142 of up to 0.191 cm3 cm−3, but pore continuities and AWC values decrease from 0.143 down to 0.111 cm3 cm−3, except for wheat-containing digestate (20w80b), which shows an opposite trend. The application of organic residues can compensate low AC values but not the AWC values. The wheat-containing digestate should be preferred for improving the water-holding capacity and, therefore, the water supply for plant roots.

The Characteristics of Poral Space as Habitat of Soybean Roots and Rhizobium Nodules

The objective of the paper was to emphasize the characteristics of the poral space (quantified according to their size and shape) of an intensely irrigated soil, representing the habitat for soybean roots and Rhizobium bacteria nodulation. The studied site is located in Southern Bărăgan Plain, Perișoru region. The soil is Vermic Chernozem (according to SRTS-2012) formed in carbonate loess like deposits. The climate is temperate continental with an average annual temperature of 10.8°C, and an average annual precipitation of 480 mm. The poral space was quantitatively evaluated at microscopic scale, using image analysis on oriented soil thin sections with the help of an image-analyzer computer. The image analysis allowed the quantitative evaluation at microscopic scale of the undisturbed structure and the adjacent porosity, in 2-D dimension (in thin sections). The pores were divided according to their shape in three classes (regular, irregular and elongated pores), and further each shape class was divided into seven size classes according to the equivalent pore diameter (ranging between 100 and >1000 µm). The result showed, unspecific conditions in the studied Chernozem, thus: Ap horizon was more compacted than the underlined Apt, consequently the total porosity was lower (0.21 m2 m-2 ) into the top Ap horizon, comparing to the underlined Apt (0.33 m2 m-2 ). In agreement with the data obtained by means of image analysis (pores quantified according to their size and shape), the oriented thin sections gave a clear representation of the genesis, location and the characteristics of the poral space. The soybeans roots developed mainly into the areas with intense biological activity. The soil macro- and mesofauna proved to be good habitat builders for soybean roots and the Rhizobium nodules, even in the conditions of a droughty period with the irrigation application delay.

Characterization, classification and fertility status of soils in semi-arid agro-ecological region of Puttur Mandal in Chittoor District, Andhra Pradesh

Seven typical pedons in semi-arid ecosystem of Puttur mandal in Chittoor district of Andhra Pradesh were studied for their morphological, physicochemical characteristics and fertility status of soils. These soils were slightly acid to moderately alkaline (pH 6.5–8.3), non-saline and deep to very deep. Texture, organic carbon (OC), cation exchange capacity (CEC) and base saturation of the soils were found to vary from sand to clay, 0.15–0.49 g kg−1, 12.80–50.52 cmol(p+)kg−1 soil and 50.0–90.6%, respectively. The soils were classified as Typic Haplustepts (pedons 1, 4, 5 and 7) and Ultic Haplustalfs (pedons 2, 3 and 6). Soils were low to medium in available nitrogen (56.2–477.7 kg ha−1), low to high in available phosphorus (7.6–90.8 kg ha−1), medium to high in available potassium (137.7–442.0 kg ha−1) and deficient to sufficient in available sulphur (1.7–40.0 mg kg−1). The DTPA extractable Zinc (Zn) was deficient (except in Ap horizon of pedons 1, 2, 3 and 5) whereas DTPA extractable copper (Cu), manganese (Mn) and iron (Fe) (except pedon 7) were sufficient.

Mineralogical Characteristics and Physico-Chemical Properties of a Newly Reclaimed Tidal Flat of Haenam Bay in the Southwestern Coast of Korea

The aim of this investigation was to identify the soil physical and chemical properties and the mineralogies of recently reclaimed tidal flat land (RTFL) consisted of five different soil series within the investigation site located in Youngsan-river Bay of Southwestern coast in Korea, that has to be only used as upland according to the policy of designated absolute agricultural land. The results show that the soil textures of the soil horizons are sandy loam and silt loam for all five soil series, with typical soil colors of yellow to pale yellow for Ap horizons containing higher clay content greater (> 18%) and greenish gray containing higher sand content (> 60%). The pHs of surface horizons for Bokchun (BC), Junbook (JB) and Poseung (PS) soil series are not only acidic (< 4.5) but also soil color is dark brown with reddish brown mottles. The X-ray diffraction (XRD) analyses represent the major minerals are illite, kaolinite and quartz for BC, JB and PS soil series while quartz and illite are major minerals for Taehan (TH) and Gwangpo (GP) soil series. Silicon and aluminum dominant in the Ap and Bg horizons are significantly higher in the soil series of BC, JB and PS than those in TH and GP. Also, we found that the kaolinite particles of varying sizes are arranged in face-to-face patterns along with the presence of spherical particles of quartz, especially in BC, JB and PS. Index map and Locations of soil profile investigation pits and soil sampling points for five soil series within the experimental site at the RTFS within the Haenam Bay. Numerous dendritic streams on the wide tidal flat and main tidal channel (maximum depth of 25 m) comprise the coastal embayment.

Biochar-assisted phytoextraction of Cd and Zn by Noccaea caerulescens on a contaminated soil: A four-year lysimeter study

Amendments of biochar, the residual solid of biomass pyrolysis, have been shown to enhance metal phytoextraction from contaminated soils with hyperaccumulating plants in specific situations. In order to investigate this phenomenon over successive harvests in field conditions, two identical undisturbed soil cylinders (1-m2 section × 1.85-m height) were excavated from a contaminated agricultural plot and monitored with instrumented lysimeters. Wood-derived biochar was added at a rate of 5% (w/w) in the first 30 cm of one of the two lysimeters. The Cd/Zn-hyperaccumulator Noccaea caerulescens was then grown for the next four years on both lysimeters. Our results showed that the hyperaccumulating plant was able to remove about 2 g m−2 of Cd and 12–16 g m−2 of Zn within four years, representing about 40% and 4% of the initial Cd and Zn soil contamination, respectively. Biochar amendment improved plant germination and survival and increased root surface density. However, no significant effect of biochar on shoot metal content of N. caerulescens was observed. Mass balances suggested that up to 10% the metal contamination moved from the disturbed Ap horizon to the deeper horizons, particularly in the biochar-amended soil profile. Furthermore, shoot Cd and Zn concentration generally decreased over the successive harvests, together with soil metal availability. Depending on the way to account for this progressive decrease in efficiency, our estimations of the time necessary to remove the excess of metals in the topsoil in these conditions ranged from 11 to 111 years for Cd and from 97 years to an infinite time for Zn. In conclusion, the simultaneous use of N. caerulescens and biochar amendment can lead to a significant removal of specific metallic elements from the topsoil, but the risk of metal movement down the soil profile and the observed decrease in phytoextraction efficiency over time deserve further investigations.

Hydrosorption and Microstructural Characteristics of Soil Horizons of Different Geneses and Their Change in Constructozems

Soil substrates used in model constructozems (artificially constructed soils) of different fabrics created on the territory of Lomonosov Moscow State University in 2012 were investigated. A layered soil construction consisting of the Ap–peat–sand–Ap horizons with a total thickness of 30 cm and a construction made of a mixture of these horizons (18 cm in thickness) underlain by a 12-cm-thick Ap horizon were studied. As a control, a variant with homogenized Ap horizon was chosen. The isotherms of water desorption from the initial soil substrates and from the samples taken from the constructions in 2016 were obtained by the method of hygroscopic equilibrium over saturated solutions of salts. We calculated approximation parameters of the isotherms and values of the total specific surface area of soil substrates according to the BET theory. A shift of water desorption isotherms towards lower values of the water content in the Ap horizon depending on the depth of its location in the profile of constructozems and on the properties of the boundary layers was revealed. It caused a decrease in the total specific surface area by 20–50% in comparison with the initial values in 2012. A sharp decrease in water sorption was noted for the peat of the layered variant of constructozems, in which the median value of the total specific surface area decreased from 560 to 162 cm2/g, and the maximum hygroscopicity decreased from 57.8 to 20.96%. By means of scanning electron microscopy, a distinct close-space microaggregation was detected in the Ap horizon that acquired a loose consistence by 2016 on the surface of variant 2. The surface of the initial peat substrate was smoothed and represented an amorphous mass of light color attesting to its organic nature. By 2016, peat samples virtually lost their amorphous coatings, so that a porous cellular surface was exposed, and its topography corresponded to the surface of plant residues. A decrease in the sorption capacity against the background of stronger roughness and complicated surface topography in most of the studied substrates attested to the high sorption capacity of surface formations of organic nature that covered the initial microaggregates, elementary mineral soil particles, and peat particles.

Fraksionasi Fosfor pada Profil Tanah Hutan, Wanatani, dan Tegalan di Jawa Barat

This study aims to evaluate the distribution of phosphorus (P) fractions within the soil horizons or profile of forest, agroforestry, and dryland in West Java and their correlations with soil chemical properties. Evaluation was based on the analytical results of soil samples taken from four soil horizons (Ao or Ap, A1 or A2, B1, and, B2) in each land use types. Fractionation of soil P was carried out using a sequential extraction method to get readily available-P (NaHCO 3 -P-inorganic (i)-P-organic (o)), rather available-P (NaOH-P i -P o ), slowly available-P (HCl-P i ), not available-P (residual-P), and total-P (HCl25%-P) fractions. The results showed that the average concentration of soil residual-P fraction in all land use types reached >99% of the total-P. The highest average concentration of residual-P fraction was measured in dryland, followed by forest and agroforestry. This indicated that soil P adsorption capacity was very high and resulted in a very low concentrations of the soil available-P fractions. The high concentrations of soil residual-P and total-P fractions were most probably related to P fertilizer application, particularly in dryland soil. Distributions of P fractions within the soil horizons at all land use types were significantly correlated with the concentration of soil organic matter content. It is therefore the concentration of soil NaOH-P o fraction was decreasing with the soil depths. The highest concentration was found at Ao or Ap horizon, although it was not the case for NaOH-P o fractions that was relatively constant.

Comparing Field Sampling and Soil Survey Database for Spatial Heterogeneity in Surface Soil Granulometry: Implications for Ecosystem Services Assessment

Lithospheric-derived resources such as soil texture and coarse fragments are key soil physical properties that contribute to ecosystem services (ES), which can be valued based on “soil” or “mineral” stocks. Soil survey data provides an inexpensive alternative to detailed field measurements which are often labor-intensive, time-consuming, and costly to obtain. However, both field and soil survey data contain heterogeneous information with a certain level of variability and uncertainty in data. This study compares the potential of using field measurements and information from the Soil Survey Geographic database (SSURGO) for coarse fragments (CF), sand (S), silt (Si), clay (C) and texture class (TC) in the surface soil (Ap horizon) for the 147-hectare Cornell University Willsboro Research Farm, NY. Maps were created based on following methods: a) utilizing data from the SSURGO database for individual soil map unit (SMU) at the field site and using representative or reported values across individual SMU; b) averaging the field data within a specific SMU boundary and using the averaged value across the SMU; and c) interpolating field data within the farm boundaries based on the individual soil cores. This study demonstrates the important distinction between mapping using the “crisp” boundary soil SSURGO databases compared to the actual spatial heterogeneity of field interpolated data. Maps of CF, S, Si, C, and TC values derived from interpolated field core samples were dissimilar to maps derived by using averaged core results or SSURGO values over the SMUs. Dissimilarities in the maps of CF, S, Si, C, and TC can be attributed to several factors (e.g., official soil series data being collected from “type locations” outside of the study areas). Correlation plot of clay estimates for each SMU showed statistically significant correlations between SSURGO and field-averaged (r = 0.823, p = 0.003) and field-interpolated clay (r = 0.584, p = 0.028) estimates, but no correlation was found for CF, S, and Si.

Factors affecting coupled degradation and time-dependent sorption processes of tebuconazole in mineral soil profiles

This laboratory degradation and adsorption study aimed to determine the tebuconazole degradation parameters for 6 profiles of Polish mineral soils and to find links between the tebuconazole degradation rate, its adsorption, soil microbial activity and other significant soil properties. The values of the adsorption distribution coefficient Kd, obtained in batch experiments after 96 h of shaking were in the range of 6.2–34.6 mL g−1. In both batch experiments and incubation experiments at 20 °C, the typical course of adsorption processes was observed, an initial rapid stage followed by a slow stage. In 3 of the 18 soils examined, adsorption was not reached within 51 days. The range of the half-life values was 201–433 days for the Ap horizon and up to 3904 days for subsoils, which were estimated using the two-site nonequilibrium adsorption model coupled with first-order degradation for dissolved and adsorbed pesticide. It was found that modeling the degradation of tebuconazole on the basis of the coefficients of microbial biomass activity for topsoil and two subsoils explained almost 96% of the variance of the estimated pore water degradation rate coefficients in examined soils. The degradation rate was also negatively correlated with the amount adsorbed in the time dependent adsorption sites. This fraction was the least available for soil microorganisms because it was strongly adsorbed in soil pores with a radius <2.5 nm, determined from the H2O desorption isotherm. The degradation rate was also affected by the ratio of the water content in soil during degradation experiments to the water content at field capacity. The results indicated that degradation occurred in the soil liquid phase only.

Efectividad de hongos micorrizo-arbusculares nativos en suelos con diferentes usos agropecuarios

Objetivo. Determinar la efectividad de hongos micorrizo-arbusculares (HMA) de suelos con diferentes usos agropecuarios, en el valle medio del río Sinú, Colombia. Materiales y métodos. Bajo condiciones de invernadero se realizó el experimento, donde se utilizó como planta indicadora Leucaena leucocephala, la cual se sembró en materos con suelo de un Andisol (horizonte B) usado como sustrato. Este sustrato, se inoculó separadamente con muestras de siete suelos (horizonte Ap), como fuente de HMA, provenientes del Centro de Investigación Turipaná de Agrosavia. Como controles se incluyeron inoculación con HMA Glomus fasciculatum y uno no-inoculado El efecto de la inoculación micorrizal se evaluó mediante el monitoreo del contenido de P foliar en las plantas de L. leucocephala, en función del tiempo hasta 64 días cuando se determinó la masa seca de su parte aérea y la colonización micorrizal. Resultados. El crecimiento de L. leucocephala y el contenido de P foliar fue significativamente superior cuando el suelo se inoculó con G. fasciculatum, en comparación a aquel observado con los demás tratamientos. De igual forma, la colonización micorrizal fue muy alta en las raíces de L. leucocephala que crecieron en el suelo inoculado con G. fasciculatum e inferior en los otros tratamientos. Conclusiones. Los resultados indican que los HMA nativos de suelos con diferentes usos, provenientes del C.I Turipaná de Agrosavia, exhibieron bajo potencial para desarrollar simbiosis micorrizal, lo que limitó el crecimiento y la concentración de P foliar en la planta hospedera.

Nitrous Oxide (N2O) Emissions from Subsurface Soils of Agricultural Ecosystems

Nitrous oxide (N2O) is a major greenhouse gas and cultivated soils are the most important anthropogenic source. N2O production and consumption are known to occur at depths below the A or Ap horizon, but their magnitude in situ is largely unknown. At a site in SW Michigan, USA, we measured N2O concentrations at different soil depths and used diffusivity models to examine the importance of depth-specific production and consumption. We also tested the influence of crop and management practices on subsurface N2O production in (1) till versus no-till, (2) a nitrogen fertilizer gradient, and (3) perennial crops including successional vegetation. N2O concentrations below 20 cm exceeded atmospheric concentrations by up to 900 times, and profile concentrations increased markedly with depth except immediately after fertilization when production was intense in the surface horizon, and in winter, when surface emissions were blocked by ice. Diffusivity analysis showed that N2O production at depth was especially important in annual crops, accounting for over 50% of total N2O production when crops were fertilized at recommended rates. At nitrogen fertilizer rates exceeding crop need, subsurface N2O production contributed 25–35% of total surface emissions. Dry conditions deepened the maximum depth of N2O production. Tillage did not. In systems with perennial vegetation, subsurface N2O production contributed less than 20% to total surface emissions. Results suggest that the fraction of total N2O produced in subsurface horizons can be substantial in annual crops, is low under perennial vegetation, appears to be largely controlled by subsurface nitrogen and moisture, and is insensitive to tillage.

Impact of land use change on organic carbon sequestration in Arenosol

Conversion of arable soils into other land uses can stabilize and increase accumulation of soil organic carbon (SOC) and in addition prevent deterioration in its properties. The data has shown changes in SOC sequestration in Ap horizon after arable land conversion (1995–2015) into managed grassland, abandoned and pine afforested. SOC in Arenosol topsoil was positively affected by long term fallow and conversion into grassland. Abandoned land and fertilised managed grassland accumulated significantly more SOC, 48% and 38% respectively compared with arable land. In unfertilised managed grassland SOC stocks decreased 2.3% during 21 years, but losses were lower than in fertilised arable land. Pine afforestation of loamy sand helped to reduce the intensity of SOM mineralization compared to arable land. The Ap horizon thickness in pine forest soil increased from 28 to 31 cm during 21 years period. However, SOC stock decreased by 1% due to reduction in carbon concentration.

Relationships between the Organic Carbon Content and Structural State of Typical Chernozem

The influence of erosion degree and slope aspect on the structural composition of typical chernozems (Haplic Chernozems) and the qualitative characteristics of organic matter in these soils were studied. We determined the organic carbon content in separate structural units of the soils under different agroecological conditions of Kursk oblast. Aggregates of 3–1 mm in size played the decisive role in the structural state of typical chernozems; their total content and the content of carbon of organic compounds in them were higher than those for the aggregates of 10–3 and <1 mm in size. The contribution of organic matter and labile humic substances to the formation of water-stable soil aggregates was also considered. A tendency for an increase in the diameter of aggregates with an increase in their organic carbon content was displayed in the soils independently from the degree of their erosion. The content of carbon of labile humic substances in water-stable aggregates of the soils on north-facing slopes was higher than that in the soils on south-facing slopes. With an increase in the portion of labile humus participating in the formation of water-stable aggregates of typical chernozems, the diameter of these aggregates increased from 0.5–0.25 to 3–1 mm. This regularity was clearly displayed in the Ap and A horizons of typical chernozems on the interfluve and on the north-facing slope and in the Ap horizon of these soils on the south-facing slopes independently from the degree of soil erosion. The results of this study may be used in methodological recommendations on regulation of the aggregate and humus states of typical chernozems in agrolandscapes with sloping topography.

Quantification of Available Water Capacity Comparing Standard Methods and a Pedostructure Method on a Weakly Structured Soil

Abstract. The purpose of this study was to evaluate the use of the pedostructure concept to determine the soil available water capacity, specifically the field capacity (FC). Pedostructure describes the soil aggregate structure and its thermodynamic interaction with water. Specifically, this work compared the calculation of soil water-holding properties based on the pedostructure concept with other standard methods for determining FC and permanent wilting point (PWP). The standard methods evaluated were the FAO texture estimate (FAO method), the Saxton-Rawls pedotransfer functions (PTFs method), and the water content at predefined soil suction (330 and 15,000 hPa) as measured with a pressure plate apparatus (PP method). Additionally, two pedostructure methods were assessed: the thermodynamic water retention curve (TWRC method) and the thermodynamic pedostructure (TPC method). Undisturbed loamy fine sand soil from a field in Millican, Texas, was analyzed at both the Ap and E horizons. The results showed that the estimated water content at FC and PWP for the three standard methods and for the TWRC method were in relative agreement. However, the TPC method used characteristic transition points in the modeled contents of different water pools in the soil aggregate and was higher for the Ap horizon, but in agreement with the other methods for the E horizon. For example, for the Ap horizon of the soil analyzed in this study, the FC estimated with the standard and TWRC methods ranged from 0.073 to 0.150 m3H2O m-3soil, while the TPC method estimate was 0.221 m3H2O m-3soil. Overall, the different methods showed good agreement in estimating the available water; however, the results also showed some variations in these estimates. It is clear that the TPC method has advantages over the other methods in considering the soil aggregate structure and modeling the soil water content within the aggregate structure. The thermodynamic nature of the TPC method enabled the use of both the soil shrinkage curve and the water retention curve in a weakly structured soil. It is expected that the TPC method would provide more comprehensive advances in understanding the soil water-holding properties of structured soils with higher clay contents. Keywords: Available water, Field capacity, Pedostructure, Pedotransfer functions, Permanent wilting point.

Temporal Dynamics of Nitrous Oxide Emission and Nitrate Leaching in Renovated Grassland with Repeated Application of Manure and/or Chemical Fertilizer

Managed grassland is occasionally renovated to maintain plant productivity by killing old vegetation, ploughing, and reseeding. This study aimed to investigate the combined effect of grassland renovation and long-term manure application on the temporal dynamics of nitrous oxide (N2O) emission and nitrate nitrogen (NO3−–N) leaching. The study was conducted from September 2013 to September 2016 in a managed grassland renovated in September 2013. In this grassland, two treatments were managed—chemical fertilizer application (F treatment) and the combined application of chemical fertilizer and beef cattle manure (MF treatment)—for eight years before the renovation. The control treatment without fertilization (CT) was newly established in the F treatment. The soil N2O flux was measured using a closed chamber method. A leachate sample was collected using a tension-free lysimeter that was installed at the bottom of the Ap horizon (25 cm deep), and total NO3−–N leaching was calculated from leachate NO3−–N concentration and drainage volume was estimated by the water balance method. In the first year after renovation, the absence of plant nitrogen uptake triggered NO3−–N leaching following rainfall during renovation and increased drainage water after thawing. NO3−–N movement from topsoil to deeper soil enhanced N2O production and emission from the soil. N2O emission in MF treatment was 1.6–2.0 times larger than those of CT and F treatments, and NO3−–N leaching in MF treatment was 2.3–2.6 times larger than those of CT and F treatments in the first year. Mineral nitrogen release derived from long-term manure application increased NO3−–N leaching and N2O emission. In the second year, N2O emission and NO3−–N leaching significantly decreased from the first year because of increased plant N uptake and decreased mineral nitrogen surplus, and no significant differences in N2O emission and NO3−–N leaching were observed among the treatments. In the second and third years, NO3−–N leaching was regulated by plant nitrogen uptake. There were no significant differences in NO3−–N leaching among the treatments, but N2O emission in MF treatment was significantly smaller than in the F treatment. Long-term manure application could be a possible option to mitigate N2O emission in permanent grassland; however, the risk of increased NO3−–N leaching and N2O emission in the renovation year induced by manure nitrogen release should be noted.

Comparative assessment of wetland and coastal plain soils in Calabar, Cross River State

The comparative assessment of wetland and coastal plain soils for agricultural productivity were studied. The investigation was carried out in two areas: Atimbo and Obufa Esuk in Calabar, Cross River State. The dominant particle size in bothcoastal and wetland soil was sandy texture. The mean bulk density values of 1.35 g/cm3 and 1.30 g/cm3 were obtained for Atimbo and Obufa Esuk coastal plain soil while 1.33 g/cm3 and 1.30 g/cm3 were obtained for Atimbo and Obufa Esuk wetland soil respectively. Total porosity in wetland soils was lower than coastal plain soil whereas moisture content in wetland soil was higher than coastal plain soil. Except Ap horizon in Atimbo coastal plain soil, the pH observed for the studied soils were all below pH of 5.0 unit which signifies high acidic condition. The mean organic carbon content in coastal plain soil was lower than wetland soil. Available phosphorus in the studied soils were high with Atimbo and Obufa Esuk coastal plain soil having a mean value of 32.10 and 32.42 mg/kg respectively, whereas those in Atimbo and Obufa Esuk wetland soils were 32.73 and 33.88 mg/kg respectively. The exchangeable calcium content obtained for both coastal and wetland soils were all below the critical limit of 5.0 cmolkg-1. Although exchangeable magnesium content was low in both soils but wetland soils was only slightly below the critical value of 1.5cmol/kg when compared to coastal plain soil. Both wetland and coastal plain soils were below (&gt;0.2 cmolkg-1) critical level of K in soils of the zone. Also, exchangeable Na in both soil were low and below 0.3 cmol/kg limit and are adequate for cultivation of arable and tree crops. ECEC in both soils were low whereas percent base saturation was high. The mean C:N ratio in Atimbo and Obufa Esuk coastal plain soil were 11.45 and 15.48 respectively. Comparatively, the C:N ratio in Atimbo and Obufa Esuk wetland soils was slightly higher having a mean value of 16.39 and 18.14 respectively. This also reflect low rate of decomposition because of anaerobic condition of the soil. The Mg:K ratio were low in both soils. The Ca:Mg ratio values were high in wetland soil when compared with a normal range of 3:1-5:1 for productive soils and was low for coastal plain soil. Per cent silt content, moisture content, and exchangeable sodium of soil sample analyzed from wetland and coastal plain soil in Atimbo were significantly different (p&lt;0.05). The result of the studied soils indicated that coastal plain soil is already losing its fertility status as typified by low values of organic carbon, total nitrogen, Exchangeable cations and high acidity couple with low moisture content; hence there is need to harnessed wetland soil for crop productivity. Wetland soils could be exploited for the cultivation of rice, oil palm, coconut, plantain, pineapple and sugar cane with judicious application of lime, and N and K fertilizers since these crops can perform well under acidic condition.Keywords: Wetland soil, coastal plain soil, soil fertility, soil properties