Lunnyu soils in the Lake Victoria basin of Uganda: Link to toposequence and soil type

We compared the physico-chemical characteristics of Lunnyu soils using soil type and slope position in order to explain their variability in the Lake Victoria basin of Uganda. Lunnyu patches located on four different soil types (chromic lixisol, mollic gleysols and plinthic ferralsols) were selected. At each patch, the slope was divided into shoulder, back-slope and foot-slope. Five locations along the contour of each landscape position and at distance of 20 to 30 m were located and soil samples taken at two depths (0 to 20 cm and 20 to 40 cm). The soils were analyzed for pH, available P, texture, and exchangeable bases. Lunnyu patches on chromic lixisol and mollic gleysols had higher pH, P, sand, clay and silt compared to those on plinthic ferralsols and petrifferic lixisol. Neither of the soil properties was influenced by landscape position. Soil pH, Ca, Mg, and K were higher in topsoil compared to subsoil. Neither slope position nor the type of lunnyu has showed consistent differences in all the soil properties. Results suggest a pedological explanation in which pH and texture could influence occurrence of the lunnyu soils. We recommend further studies of the pedological properties of the soils and other trace elements that this study has not investigated.Key words: Lunnyu soil, toposequence, soil type, Uganda

Study of chemical and physical properties and soil sorption of metolachlor and carbofuran in three tropical soils

The sorption of organic compounds to soil is mainly through organic matter components. The organic matter amount and type depends on soil properties such as pH, conductivity, particle size and calcium carbonate content. Therefore, organic pesticide movement-through soil strongly depends on the genesis of organic matter. Organic matter has fractions such as humic acid (HA) and fluvic acid (FA), fats and oils. For this study three tropical soils were chosen, Aguilita, Catano and Tiburones. Some of their organic matter properties, such as total acidity, UV-Vis and IR spectra were related to the sorption coefficient (Koc) of carbofuran and metolachlor. Sorption coefficients in Aguilita, Catano and Tiburones were between 34 and 1,181 ml/g for carbofuran and between 90 and 298 ml/g for metolachlor. Solutions of 100 ug/ml HAs from Aguilita, Catano, and Tiburones dissolved in 0.05N NaHC03 of pH 8.1 had E4/E6 absorption values of 5.5, 4.9 and 3.2, respectively; and those from FA in 2N HCl had values of 10.0, 6.5 and 10.4, respectively. These values suggest a highly aromatic content for HA from Tiburones (E4/E6 ~3) and mainly aliphatic for Aguilita soil. Fulvic acids from Aguilita and Tiburones soils had highly aliphatic character (E4/E6 > 8) whereas that of Catano was intermediate. Data suggest that differences in metolachlor and carbofuran Koc values for the above mentioned soils are mainly due to differences in HA and FA properties of the soils

Estimation of soil hydraulic properties of a sandy soil using capacitance probes and Guelph permeameter

Soil hydraulic conductivity (K)-water content (θ)-pressure head (h) relationships (K-θ-h) are key parameters for crop growth, irrigation, drainage, and modeling water flow and chemical transport through the soil. Several laboratory methods have been used to determine these parameters and to extrapolate to field conditions. However, it is essential to determine these parameters under field conditions to minimize the effect of spatial variability. The objective of this study was to use the Instantaneous Profile method in combination with capacitance probes, tensiometers, the Guelph permeameter, and the van Genuchten hydraulic functions to determine the hydraulic conductivity-water content-pressure head relationships of a Candler fine sand (hyperthermic, uncoated, Typic Quartzipsamments) soil. The soil was flooded for more than 2 h to achieve a constant water content through the profile and was then covered with a plastic sheet to prevent evaporative loss or addition of rain water. The capacitance probe and tensiometer readings were taken simultaneously at 0.1-, 0.2-, 0.4-, 0.7-, and 1.1-m depths. Both water content and hydraulic conductivity values decreased substantially as water redistributed through the soil profile after saturation. Saturated hydraulic conductivity, measured with the Guelph permeameter for the five soil depths, varied between 6.1 and 10.0 m day-1. More than 50% of the soil water was drained from the soil profile within 8 to 10 h following saturation. The analytical RETC (RETension Curve) model was used to extend soil water release curves beyond the limited range of tensiometer suction measurements. Results of this study demonstrate that the Sentek capacitance probe is a practical tool that can be used in combination with the Guelph permeameter and analytical fitting software (RETC) to determine in-situ soil water characteristic curves, saturated hydraulic conductivity, and k(θ) at difference soil depths

Comparative response of huanglongbing-affected sweet orange trees to nitrogen and zinc fertilization under microsprinkler irrigation

2-s2.0-85097833775Nitrogen and micronutrients have a key role in many citrus plant enzyme reactions. Although enough micronutrients may be present in the soil, deficiency can develop due to soil depletion or the formation of insoluble compounds. The objectives of this study were to (1) determine the adsorption, distribution, and availability of Zn in a sandy soil; (2) compare the effectiveness of foliar and soil application methods of Zn on Huanglongbing [HLB] affected trees; (3) compare foliar application rates of Zn for HLB-affected trees; (4) determine the effect of N rates on yield, soil inorganic N distribution patterns, and tree growth parameters. Tree rows were supplied with three N rates of 168, 224 and 280 kg·N·ha?1 and Zn at single and double recommended rates (recommended rate = 5.6 kg·Zn·ha?1) using foliar and soil application methods, in a split-plot experimental design. The results show that Zn concentration in the 0–15 cm soil depth was three times higher than the 30–45 and 45–60 cm soil depths during the study. An adsorption study revealed high Zn (KD = 6.5) sorption coefficients at 0–15 cm soil depth, while 30–45 and 45–60 cm depths showed little sorption. Leaf Zn concentration for foliar spray was two times higher than the soil application method. A nitrogen level of 224 kg N ha?1 improved canopy volume when compared to other N levels at the expense of reduced fruit weight. Foliar Zn application at 5.6 or 11.2 kg ha?1 and N rate at 224 kg ha?1 appear to be adequate for improving the performance of HLB-affected citrus trees. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.FLA-CRC-005593 U.S. Department of Agriculture, USDA: AP19PPQS, T00C116 Institute of Food and Agricultural Sciences, IFASAcknowledgments: The authors thank the UF/IFAS Citrus Initiative, USDA NIFA Hatch Project No. FLA-CRC-005593 and USDA MAC APHIS Agreement No. AP19PPQS&T00C116 for funding. The Water and Nutrient Management Lab Team at the Citrus Research and Education Center (CREC) Lake Alfred, FL is thanked for help with data collection and processing.Funding: UF/IFAS Citrus Initiative, USDA NIFA Hatch Project No. FLA-CRC-005593 and USDA MAC APHIS Agreement No. AP19PPQS&T00C116