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Using Selected Structural Indices to Pinpoint the Field Moisture Capacity of Some Coarse-Textured Agricultural Soils in Southeastern Nigeria Igwe, Charles Arizechukwu; Hermansah, .; Obi, Martin Eze; Wakatsuki, Toshiyuki
JOURNAL OF TROPICAL SOILS Vol 16, No 2: May 2011
Publisher : UNIVERSITY OF LAMPUNG

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.5400/jts.2011.v16i2.151-159

Over- or underestimation of field capacity (FC) of agricultural soils could misguide soil and water management and this might have negative agronomic and environmental impacts. The study sought to identify the moisture tension for reliably estimating in the laboratory the FC of some sandy soils with low-activity clay minerals and at different levels of structure development in Nsukka agroecological zone in southeastern Nigeria. Fifty-four samples of topand subsoils under contrasting vegetation cover at three locations in the zone were analyzed for texture, organicmatter contents, bulk density and total porosity. Saturated hydraulic conductivities (Ksat) of the samples were equallydetermined. Water-conducting and water-filled porosities at each of 0.06-, 0.10- and 0.33-bar tensions were implied from water retention data at the respective tensions. The soils were categorized based on their levels of structure development using a structural stability index [(organic matter: silt+clay) %] as follows: very low (< 4%), low (4-7.5%) and moderate to high (> 7.5%) stability soils. Series of simple correlation tests were run among the waterconducting porosities at the various tensions and the Ksat of the soils. In each case, the soil was assumed to have attained FC at that moisture tension which the associated water-conducting porosity showed significant positive correlation with the Ksat. Our results revealed that the 0.06-bar tension overestimated the FC of the soils. The 0.10-bar tension, the commonly used moisture tension for the purpose in the study area, proved suitable only for soils within the moderate to high structural stability category. From all indications, the 0.33-bar tension best corresponded to the FC of the less structurally developed soils in the other two categories. The level of soil structure development should therefore be considered before deciding the suitable moisture tension for the determination of FC of these and similar soils in other tropical locations.Keywords: Coarse mineral soils, field moisture capacity, saturated hydraulic conductivity, structural stability,water-conducting pores

Application of Rice-Husk Biochar to Coarse-Textured Ultisols and the Effects on Soil Fertility Indicators at Different Amendment-to-Sampling Intervals Ebido, Nancy Ekene; Awaogu, Chukwuebuka Ebuka; Akubue, Jacinta Chinonso; Ozongwu, Ogorchukwu Valeria; Unagwu, Benedict Onyebuchi; Obalum, Sunday E.; Igwe, Charles Arizechukwu
JOURNAL OF TROPICAL SOILS Vol 30, No 2: May 2025
Publisher : UNIVERSITY OF LAMPUNG

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.5400/jts.2025.v30i2.69-83

The low fertility status of the highly weathered tropical soils offers the opportunity to study the potential and optimum application rate of biochar as an organic soil amendment, especially for the dominant coarse-textured Ultisols. Despite the relatively fast mineralisation of organics in these soils and the need to synchronise nutrient release crops critical stages of nutrient requirement, the time corresponding to peak effects of biochar remains unclear. The effects of rice-husk biochar (RHB) on the soil fertility of sandy-loam Ultisols at 0, 7.5, 15, 30, and 60 Mg ha-1 equivalents in 2-kg soils were assessed at 0, 2, 4, 8, and 12 weeks of incubation (WOI). Treatments were prepared in batches to enable concurrent sampling for all five incubation intervals. The RHB enhanced soil fertility across the incubation intervals, with optimal rates as 15 Mg ha-1 for soil pH and 30 - 60 Mg ha-1 for macronutrients availability. Relative to the its non-application, RHB increased soil pH-H2O, total N, available P, exchangeable bases, exchangeable acidity, apparent CEC and base saturation by 4-30%, 43-100%, 30-202%, 13-240%, 14-675%, 21-126% and 7-82%, respectively. Soil pH tended to decrease after, while available P progressively decreased before 8 WOI, when treatment effects were generally most pronounced. At an all-encompassing optimal rate range of 30-60 Mg ha-1, RHB could reduce soil acidity and enhance the macronutrient status of coarse-textured Ultisols over at least 12 weeks, soil fertility restoration effects of which are likely to be most pronounced around 8 weeks.

Using Selected Structural Indices to Pinpoint the Field Moisture Capacity of Some Coarse-Textured Agricultural Soils in Southeastern Nigeria Igwe, Charles Arizechukwu; Hermansah, .; Obi, Martin Eze; Wakatsuki, Toshiyuki
JOURNAL OF TROPICAL SOILS Vol. 16 No. 2: May 2011
Publisher : UNIVERSITY OF LAMPUNG

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.5400/jts.2011.v16i2.151-159

Over- or underestimation of field capacity (FC) of agricultural soils could misguide soil and water management and this might have negative agronomic and environmental impacts. The study sought to identify the moisture tension for reliably estimating in the laboratory the FC of some sandy soils with low-activity clay minerals and at different levels of structure development in Nsukka agroecological zone in southeastern Nigeria. Fifty-four samples of topand subsoils under contrasting vegetation cover at three locations in the zone were analyzed for texture, organicmatter contents, bulk density and total porosity. Saturated hydraulic conductivities (Ksat) of the samples were equallydetermined. Water-conducting and water-filled porosities at each of 0.06-, 0.10- and 0.33-bar tensions were implied from water retention data at the respective tensions. The soils were categorized based on their levels of structure development using a structural stability index [(organic matter: silt+clay) %] as follows: very low (< 4%), low (4-7.5%) and moderate to high (> 7.5%) stability soils. Series of simple correlation tests were run among the waterconducting porosities at the various tensions and the Ksat of the soils. In each case, the soil was assumed to have attained FC at that moisture tension which the associated water-conducting porosity showed significant positive correlation with the Ksat. Our results revealed that the 0.06-bar tension overestimated the FC of the soils. The 0.10-bar tension, the commonly used moisture tension for the purpose in the study area, proved suitable only for soils within the moderate to high structural stability category. From all indications, the 0.33-bar tension best corresponded to the FC of the less structurally developed soils in the other two categories. The level of soil structure development should therefore be considered before deciding the suitable moisture tension for the determination of FC of these and similar soils in other tropical locations.Keywords: Coarse mineral soils, field moisture capacity, saturated hydraulic conductivity, structural stability,water-conducting pores

Application of Rice-Husk Biochar to Coarse-Textured Ultisols and the Effects on Soil Fertility Indicators at Different Amendment-to-Sampling Intervals Ebido, Nancy Ekene; Awaogu, Chukwuebuka Ebuka; Akubue, Jacinta Chinonso; Ozongwu, Ogorchukwu Valeria; Unagwu, Benedict Onyebuchi; Obalum, Sunday E.; Igwe, Charles Arizechukwu
JOURNAL OF TROPICAL SOILS Vol. 30 No. 2: May 2025
Publisher : UNIVERSITY OF LAMPUNG

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.5400/jts.2025.v30i2.69-83

The low fertility status of the highly weathered tropical soils offers the opportunity to study the potential and optimum application rate of biochar as an organic soil amendment, especially for the dominant coarse-textured Ultisols. Despite the relatively fast mineralisation of organics in these soils and the need to synchronise nutrient release crops critical stages of nutrient requirement, the time corresponding to peak effects of biochar remains unclear. The effects of rice-husk biochar (RHB) on the soil fertility of sandy-loam Ultisols at 0, 7.5, 15, 30, and 60 Mg ha-1 equivalents in 2-kg soils were assessed at 0, 2, 4, 8, and 12 weeks of incubation (WOI). Treatments were prepared in batches to enable concurrent sampling for all five incubation intervals. The RHB enhanced soil fertility across the incubation intervals, with optimal rates as 15 Mg ha-1 for soil pH and 30 - 60 Mg ha-1 for macronutrients availability. Relative to the its non-application, RHB increased soil pH-H2O, total N, available P, exchangeable bases, exchangeable acidity, apparent CEC and base saturation by 4-30%, 43-100%, 30-202%, 13-240%, 14-675%, 21-126% and 7-82%, respectively. Soil pH tended to decrease after, while available P progressively decreased before 8 WOI, when treatment effects were generally most pronounced. At an all-encompassing optimal rate range of 30-60 Mg ha-1, RHB could reduce soil acidity and enhance the macronutrient status of coarse-textured Ultisols over at least 12 weeks, soil fertility restoration effects of which are likely to be most pronounced around 8 weeks.

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