Air-Drying Effect on Soil Reaction and Phosphorus Extractability From Upland-Lowland Tropical Soils as Related to Their Colloidal Stability

Abstract

Abstract. Although air-drying is a universally accepted practice for preserving soils before analyses, it can irreversibly affect certain soil processes and, hence, results of soil analyses. Reports about such effects on extractable/available phosphorus (P av ) are conflicting and are scanty for low-P av tropical soils. Moreover, little is known about its relative effects for well and poorly drained soils or about any underlying role of soil colloidal stability. In this study, soil samples from well-drained uplands and adjoining poorly drained lowlands in four locations in southeastern Nigeria were analysed field-moist and air-dried for pH and P av . The soils are mostly medium-textured. A trend existed of drying-induced decreases in soil pH for both uplands (4.8-5.8) and lowlands (4.6-5.6); whereas this effect was consistently non-significant in the former (unless tested for irrespective of location, 5.35 vs 5.53), it was location-specific in the latter. Airdrying tended to increase and decrease P av in upland soils (0.62-12.75 mg kg -1 ) and lowland soils (0.93-20.52 mg kg -1 ), respectively, with a reverse effect in one lowland with values exceeding 15 mg kg -1 . However, these effects were non-significant except in one upland soil with evidence of appreciable organic matter. Correlations between soil pH and P av were positive and non-significant, but strongest for field-moist lowland soils. Soil colloidal stability indices of water-dispersible clay and clay flocculation index proved useful in understanding the results for soil pH and P av , respectively, with the effect of the former being more distinct than that of the latter. Air-drying is still recommended only for upland soils while we explore fully the interrelationships among drying-induced differences and colloidal stability for soils of contrasting drainage status.

The potential of fermented cottonseed oil-mill effluent as inexpensive biofertilizers and its agronomic evaluation on medium-textured tropical soil

“…That of available phosphorus was unexpected, considering the fact that the soil was only slightly acidic. This observation thus highlights the well-known low status of phosphorus availability in tropical soils (Owusu-Bennoah et al 1995;Obalum and Chibuike 2017).…”

Comparative assessment of temporal changes in soil degradation under four contrasting land‐use options along a tropical toposequence

“…For Sawah , soil pH was the only parameter that showed appreciable decline. Though this has been attributed to excessive leaching (Ali et al, ; Darmawan et al, ) and air drying effect on soil pH in lowland soils (Obalum & Chibuike, ), it should be noted that bunds demarcating Sawah basins serve as barriers against surface runoff and erosion known to be the major processes contributing to soil degradation in the study area. Such bunds also make for efficient management and use of water and nutrient resources, hence the 'slight' change in soil quality under Sawah .…”

“…Also, because the lowland Sawah soil was seasonally always puddled and submerged, greater dispersibility of clay would be expected under Sawah compared with TRF, for instance. The reductive effect of the routine preanalyses air drying on soil pH has been reported to increase with increase in water‐dispersible clay content of upland‐lowland soils (Obalum & Chibuike, ), hence the observation under Sawah .…”

How Air-Drying Affects DGT P Results in Calcareous Soils

“…The slope was larger than 1, illustrating that the air-drying process decreased extractable P from soils using the Olsen P method. Obalum and Chibuike [37] reported that the process of soil air-drying increased and decreased the available P in upland and lowland soils respectively, and attributed the reason to the release of mobilized P by Fe (III) oxyhydroxides via the redox reaction in soils [38,39]. Soinne et al [40] reported that drying changed P distribution in soil particles with different sizes.…”