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Universiteit Gent (2009)

The effect of conservation farming on soil physical properties in Malawi

Kamwendo Medrina

Titre : The effect of conservation farming on soil physical properties in Malawi

Auteur : Kamwendo Medrina

Université de soutenance : Universiteit Gent

Grade : Master of Science (MS) Physical Land Resources 2009

Résumé
Changes in soil physical and hydraulic properties in soils under conservation agriculture have been less documented, especially with semi-arid soils, for which the technique has been promoted. The objectives of this study were to assess and compare selected soil physical and hydraulic properties under two management systems ; conventional tillage (CT) and conservation agriculture (CA) on sandy loam soils on the Lilongwe Plain in Central Malawi. Six small scale farmer fields at four locations practicing CA for 2 and 4 years respectively, and adjacent fields under (CT) with similar soil type and maize (Zea mays, L.) - based crop rotation were selected. Conservation agriculture, particularly after 4 years, consistently showed lower values towards optimal soil salt content for plant growth while pH (H20) and pH (KCl) were significantly higher under CA than CT. CA after either 2 or 4 years of practice significantly showed higher total soil nitrogen (N) and phosphorous (P) at both soil depths compared to CT. Further, N and P were significantly higher after 4 years compared to 2 years of CA. Higher levels of potassium were obtained under CT than CA in both layers of the soil. Soils after 4 years of CA significantly subtended more soil organic carbon (SOC) than 2 years of CA or CT at both soil depths. Bulk density did not significantly differ amongst soil management practices at 0-15 cm soil depth. However, at the 1530 cm soil depth, bulk density under 4 years of CA was significantly (P<0.05) higher than under 2 years of practice and CT, respectively. CA after 4 years produced soils with significantly higher aggregate stability compared to 2 years of CA at 0-15 cm soil depth or to CT at 15-30 cm soil depth. Macroporosity after 2 and 4 years of CA, was significantly higher at ψ = -1 kPa, -5 kPa and -10 kPa in the top soil layer compared to the sub-layer unlike under CT. However, no significant differences in matrix porosity were observed amongst practices. No significant differences in soil water content at saturation between CA and CT nd between the two durations of CA were observed. However, CA after 4 years of practice significantly subtended more water at field capacity in the top soil layer and at permanent wilting point in the sub-layer than CA after 2 years. There were no significant differences in hydraulic conductivity (KS) among the practices. However, KS value for soils under CA was higher than for soils under CT. No significant differences in the parameter S among soil management practices in the top soil layer were observed. However, the value of S for CA after 4 years was higher than for either 2-year CA or CT fields, respectively. Volumetric soil water content at different suction levels significantly distinguished the practices showing CA after 4 years with greater soil water retention. Soil organic carbon, aggregate stability, macroporosity, volumetric soil water content at field capacity and permanent wilting point, and soil water retention appeared to be the most useful indicators of soil physical and hydraulic quality even in the early stages (2-4 years) of CA because they significantly responded to soil management practices encountered in this study

Source : Pedon 21 - Physical Land Resources - Universiteit Gent

Page publiée le 26 décembre 2015, mise à jour le 24 janvier 2018