Abstract
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
Highlights
The availability of rice in sufficient quantities can improve the economic stability
The effect of VAM inoculation on leaf potassium content showed that the dosages between 0-25 kg ha-1 K with Glomus sp. and Gigaspora sp. was effective enough in the dry season, whereas for the second wet season genus MVA cas effective in higher dosages, i.e. between 25-50 kg ha-1 K (Table 1)
Interaction effects occurred between planting seasons, K fertilizer, and mycorrhizae in influencing the ratio of shoot and root (S/R)
Summary
The availability of rice in sufficient quantities can improve the economic stability. National-scale shortage of rice has implications on the increase of import of rice. The contribution of upland rice in the procurement of the national rice production is almost no change over the last few years. The contribution of upland ice in 1995 was approximately 5.9% with the total area of 14.5% (BPTP 1997). In 1996 and 1997 upland rice contribution on the national rice production was 6% with the average yield 2.21Mg ha-1. Though the yield per unit area of upland rice increased, the national production tended to decline over the last few years
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