This study examines three soil classification systems - Buganda, World Reference Base, and US Soil Taxonomy - in order to evaluate their relative strengths and feasibility for making linkages between them. Nine field sites and 16 pedons were considered across the soil landscapes of the Buganda catena. Each identified field pedon diagnostic horizons and characteristics were described and their soils analyzed using standard pedological techniques and measurements. To document the indigenous use of the Buganda classification system, interviews and discussions were held with farmer groups and local extension specialists. Using this local expertise, five local soil units were identified. We also identified two landscape toposequences with pedons that classified into six WRB Reference Soil Groups and five US Soil Taxonomic Suborders. While four local soil classes each mismatched with international systems' groups, Liddugavu (black) soil corresponded to Phaeozem (WRB) and Udolls (US Soil Taxonomy) and is consistently viewed as the most productive soil due to faster weed growth, diversity of crops it supports and its stable landscape location. Statistical comparisons indicated that the Buganda classes were more homogeneous and effective at separating variability of different soil properties than those of either the WRB Reference Soil Groups or US Soil Taxonomy Suborders. Integrating soil texture, pH and bases information in indigenous system methods could locally complement international classifications and linking the best of both systems would be ideal for the generation of a hybrid system. Our findings show that using the toposequence framework assists in comparing these systems in a way that is useful for scientists and local farmers.

To study the soils of Southern Highland Zone of Tanzania, four representative pedons of some landscapes were characterized. Their names and identifiers are Seatondale, Mbimba, Inyala, and Uyole, respectively TzSea 01, TzMb 02, TzIny 03, and TzUy04. The pedons were formed from the weathering of among other materials, colluvial igneous rocks, alluvium, eluvial soils, laterite, lacustrine sands and silts, andesite, pumice, aeolian deposits, and metamorphic rocks including coarse grained and strongly foliated biotite gneisses. Twenty soil samples were taken for laboratory characterization. In addition to classical horizon by horizon descriptions and laboratory analyses, 12 core samples were taken for soil-water retention characterization. The available water holding capacity was rated as very low to low. Pedon descriptions and particle size analysis showed clay eluviation-illuviation was the predominant pedogenic process in all pedons. Soil pH was rated slightly acidic to slightly alkaline. Available P ranged from 0.71 mg/kg at Mbimba to 10.67 mg/kg at Seatondale. Exchangeable bases were variable across and within the profiles; at Uyole and Inyala they were high, while at Seatondale and Mbimba they were low and medium. Values of exchangeable bases showed decreasing trends with profile depths in all sites. C/N ratios ranged between 6 and 18, total nitrogen was rated very low to low in both A and B horizons. CEC_soil ranged between 17.2 and 36.4 cmol ₍₊₎/kg. Organic carbon ranged from very low to high. The soils apparently developed from extreme and moderate weathering of parent materials. According to the USDA Soil Taxonomy, the pedons classified as Fine, Illitic, Active, Isothermic Typic Hapludult; Fine, Illitic, Active, Isothermic Andic Paleudalf; Fine, Illitic, Active, Isothermic, Mollic Paleudalf; Pumiceous, Mixed, Superactive, Isothermic, Typic Hapludand for Seatondale, Mbimba, Inyala, and Uyole, respectively. The soil depths were deep and very deep. Moisture stress and low levels of some macro-elements highly limited the productivity of the soils.

Roselle (Hibiscus sabdariffa L.) is an important tropical and subtropical crop, because of its multi uses in the medicinal purposes as well as food industries. A plot experiment was conducted in a Vertisol in Egypt over two sequential seasons (2013 and 2014) to assess the effect of silicon (Si) fertilization on roselle growth and yield. Specific growth characteristics measured were: plant heights, branching, and leaves; biomass and calyces yield; and concentrations of anthocyanin, total soluble solids (TSS), carbohydrates, N, P, and K in the calyces. The experiment compared five rates of Si fertilization (0.00, 1.75, 3.50, 5.25, and 7.00 kg Si ha-1). One-third of each rate was applied as a foliar spray at 45, 60, and 75 days after sowing, respectively. Results showed an increase in plant height, number of branches and leaves to Si fertilization rates. Similarly, anthocyanin and TSS concentration increased with increasing Si rates. Anthocyanin concentration significantly increased by 16.3% as the applied Si rate increased from 0.00 to 5.25 kg Si ha-1. However, carbohydrate content was not affected by the applied Si rates. Nutrients (N, P, and K) concentrations, in the calyces extract, increased with increasing the applied Si rate. Biomass and calyces yield increased by 23 and 33%, respectively, as the applied Si rate increased from 0.00 to 5.25 kg Si ha-1. The highest values of all of the measured properties were observed under the Si rate of 5.25 kg Si ha-1, and the lowest values were obtained from the control treatment (0.00 kg Si ha-1).

Despite a large body of scientific research that shows that soils change on relatively short time scales under different management regimes, classical pedological theory states that we should expect these changes to occur only in the surface few centimeters and that they are not of adequate magnitude to suggest fundamental changes in pedon character over short periods of time. In fact, rarely, do the scientists that make these comparisons report on any properties deeper than 30 to 45 cm in the soil profile. With this study, we evaluate soil transformation to a depth of 150 cm after 50 yr of intensive row-crop agricultural land use in a temperate, humid, continental climate (Iowa, United States), by resampling sites that were initially described by the United States soil survey between 1943 and 1963. We find that, through agricultural land use, humans are accelerating soil formation and transformation to a depth of 100 cm or more by accelerating erosion, sedimentation, acidification, and mineral weathering, and degrading soil structure, while deepening dark-colored, organic-matter rich surface horizons, translocating and accumulating organic matter deeper in the soil profile and lowering the water table. Some of these changes can be considered positive improvements, but many of these changes may have negative effects on the soils’ future productive capacity.

Corn productivity indices (CSR2T) for representative soils in the Southern Highland Zone of Tanzania were developed. The approaches used were derived from Iowa State University’s CSR2. Consistent with ISU, index points were applied to the pedon based on the USDA Soil Taxonomy subgroup, family particle size class, and available water holding capacity, solum depth and resilience to degradation characterizations. Additional index points were applied based on field conditions especially slope, erosion history and flooding or ponding risk in order to determine the inherent productivity potential of the soils in the work sites. The results were used to develop the Corn Suitability Rating in Tanzania (CSR2T) for the soil settings of Southern Highlands. Sites’ characterization results were linked with the maize field experimental results from 2003 to 2016 to determine the inherent corn productivity indices for the sites. The soils were found to have CSR2T values of 72, 56, 62 and 48 for Uyole, Mbimba, Inyala and Seatondale farms, respectively. The soils of Seatondale were observed to be more limited by water holding capacity. However, generally the study soils are observed to have good pedogenic potential for corn productivity and very minimal pedogenic limitations for corn productivity. The most serious limitation seems to be low water holding capacity.

The goal of this study was to understand better the co-play of intrinsic soil properties and extrinsic factors of climate and management in the estimation of saturated hydraulic conductivity (Ksat) in intensively managed landscapes. For this purpose, a physically-based, modeling framework was developed using hydro-pedotransfer functions (PTFs) and watershed models integrated with Geographic Information System (GIS) modules. The integrated models were then used to develop Ksat maps for the Clear Creek, Iowa watershed and the state of Iowa. Four types of saturated hydraulic conductivity were considered, namely the baseline (Kb), the bare (Kbr), the effective with no-rain (Ke-nr) and the effective (Ke) in order to evaluate how management and seasonality affect Ksat spatiotemporal variability. Kb is dictated by soil texture and bulk density, whereas Kbr, Ke-nr, and Ke are driven by extrinsic factors, which vary on an event to seasonal time scale, such as vegetation cover, land use, management practices, and precipitation. Two seasons were selected to demonstrate Ksat dynamics in the Clear Creek watershed, IA and the state of Iowa; specifically, the months of October and April that corresponded to the before harvesting and before planting conditions, respectively.

Statistical analysis of the Clear Creek data showed that intrinsic soil properties incorporated in Kb do not reflect the degree of soil surface disturbance due to tillage and raindrop impact. Additionally, vegetation cover affected the infiltration rate. It was found that the use of Kbinstead of Ke in water balance studies can lead to an overestimation of the amount of water infiltrated in agricultural watersheds by a factor of two. Therefore, we suggest herein that Keis both the most dynamic and representative saturated hydraulic conductivity for intensively managed landscapes because it accounts for the contributions of land cover and management, local hydropedology and climate condition, which all affect the soil porosity and structure and hence, Ksat.

Watershed and global-scale nitrogen (N) budgets indicate that the majority of the N surplus in anthropogenic landscapes does not reach the coastal oceans. While there is general consensus that this 'missing' N either exits the landscape via denitrification or is retained within watersheds as nitrate or organic N, the relative magnitudes of these pools and fluxes are subject to considerable uncertainty. Our study, for the first time, provides direct, large-scale evidence of N accumulation in the root zones of agricultural soils that may account for much of the 'missing N' identified in mass balance studies. We analyzed long-term soil data (1957–2010) from 2069 sites throughout the Mississippi River Basin (MRB) to reveal N accumulation in cropland of 25–70 kg ha−1 yr−1, a total of 3.8 ± 1.8 Mt yr−1 at the watershed scale. We then developed a simple modeling framework to capture N depletion and accumulation dynamics under intensive agriculture. Using the model, we show that the observed accumulation of soil organic N (SON) in the MRB over a 30 year period (142 Tg N) would lead to a biogeochemical lag time of 35 years for 99% of legacy SON, even with complete cessation of fertilizer application. By demonstrating that agricultural soils can act as a net N sink, the present work makes a critical contribution towards the closing of watershed N budgets.

Freeze-thaw (FT) cycles occur annually in soils of mesic and frigid temperature regimes. FT has profound impacts on soil aggregates yet is often difficult to document in field settings. As a result, laboratory-based FT experiments are widely used, albeit with their own limitations. Both laboratory and field-based research indicates that aggregate properties vary with rates of freezing and thawing as well as the number and amplitudes of FT cycles. In this study, we introduce a continuous freezing-to-thawing-to-freezing technique (i.e., “VTR”) and compare it to a commonly used discrete freeze-then-thaw-then-freeze method (i.e., “RTCR”) and compare both results to natural seasonal changes. Our study soil is the A horizon of the major cropped mollisol in northeastern China. We examined it under natural field soil moisture conditions as well as two controlled soil moisture contents in the laboratory. Both RTCR and VTR show a decrease in large (>1mm) aggregate content and a corresponding increase in medium (0.5 to 0.2 mm) aggregates (P>0.05) that is proportional to the number of FT cycles and soil moisture content. Wet aggregate stability (WAS) increased (P<0.05) over the time of the experiment with each method. RTCR data showed an interaction between FT cycles and soil water content. VTR was better, although certainly not with better matched field results than RTCR, which we attribute its FT cycles being matched to anactual field. These results confirm the dependability and authenticity of the VTR technique.

Management of soil salinity is an important research field around the globe, especially when associated with the limited water resources. This work aimed to improve the growth and yield of wheat (Triticum aestivum L. CV. Sakha-93) grown under salinity stress. A completely randomized design pot experiment with three replications was conducted in a loamy soil with various levels of salinity under local weather conditions. The treatments included five levels of salinity (2.74, 5.96, 8.85, 10.74, and 13.38 dSm-1) prepared by adding NaCl to the selected soil and five treatments of Si (0, 2.1, 4.2, 6.3, and 8.4 mg Si/10 plants). Silicon was applied to wheat plants as a foliar spray 30, 45, and 60 days after sowing. Results indicated that photosynthetic pigments; N, P, and K concentrations; biomass, and grain yield significantly decreased with increasing salinity concentration. For example, in the pots treated with Si rate of 0.0 mg Si/10 plants, biomass and grain yield significantly decreased by 37 and 30%, respectively, as salinity increased from 2.74 to 13.38 dSm-1. However, Na and proline concentrations increased with the increase in salinity. Supplying Si alleviated salinity stress and enhanced plant growth, e.g., at salinity concentration of 5.96 dSm-1, biomass and grain yield increased by 32 and 54%, respectively, when Si rate increased from 0.0 to 6.3 mg Si/10 plants. Similarly, under the same previous salinity and Si treatments, Na and proline concentrations decreased by 10 and 23%, respectively. Eventually, application of Si to wheat enhanced its growth and yield under salinity stress.

Afforestation trends were compared between two continentally-distinct, yet similar ecoregions to characterize similarities or differences in forest advancement due to natural and anthropogenic forcings. Temporal changes in forest cover were analyzed using high resolution aerial and satellite photographs for Southeast Iowa, USA, and satellite photographs for the western Belgorod Oblast, Russia. An increase in forested area was shown to occur over a 44-year period from 1970–2014 in Iowa where afforestation was reflected by the aggregation of smaller forest units. In the Belgorod region the opposite occurred in that there was an increase in the number of smaller forested units. The rate of forest expansion into open grassland areas, previously used as haying lands and pastures, was 14 m decade−1 and 8 m decade−1 in Iowa and the Belgorod Oblast, respectively. Based on current trends, predicted times for complete forest coverage in the study areas was estimated to be 80 years in Iowa and 300 years in the Belgorod Oblast. In both the Iowa and Belgorod Oblast, there was an increase in annual precipitation at the end of the 20th and the beginning of the 21st centuries, thus providing a contributing mechanism to forest advancement in the study regions and implications for future management practices.