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.

Following completion of research experiments on common bean in Uganda, five rainy seasons of community-based field trials enabled farmers to learn about and evaluate improved management practices and technologies for adoption. A multistakeholder bean Innovation Platform continues to develop in membership size, diversity, enthusiasm and capability, with 10 value chain member organizations and 1000+ farmers. In Mozambique, field experiments were completed mid-2017 by IIAM. Two SAWBO video animations were released on research-based farmer-validated bean production recommendations in Uganda and Mozambique and one on jerry can storage for Mozambique. IIAM created and is field testing its first App, focused on bean production recommendations. Project team members presented 14 papers/posters at the Grain Legume Research Conference in Burkina Faso. One M.S. student graduated and two are near completion. One M.S. student and one Ph.D. student are progressing well. Research results are published in peer-reviewed journal articles and a book chapter, with others being prepared. Some will be disseminated in regional/national practitioner and policy outlets in Africa. Training methods and media are ready for dissemination to intermediate and end users. Capacity strengthening through applied research-based training has been successfully conducted.

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.

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.