Jephita Gotosa

Characterisation of a sodic soil catena for reclamation and improvement strategies

Abstract A study to characterise the physical, chemical and morphological properties of a sodic soil on a gneissic granite catena was conducted in the Shangani Ranches. Soil profiles were sited in the main topographic zones at a distance of 135 m apart from the crest to the stream. A non-sodic profile (control) dug on the crest was also examined in order to compare properties. Results of this study and their relevance to reclamation and improvements are presented. All soils of the sodic catena exhibited a high degree of compaction, poor drainage status and restricted permeability and contained varying amounts of calcium carbonates (0.1–6.1%). A marked increase in clay content was noted in profiles of the mid to upper catena compared to those in lower catenal positions. Soil pH ranged between 7.5 and 10.1. Phenomenal increase in exchangeable sodium percentage (ESP) ranging from 36.9 to 98.9 was recorded in the subsoil horizons of the profiles in upper catenal positions. There was a slight drop in ESP values in soils of the lower catena. Final infiltration rates of 0.01 cm/min were recorded in representative sodic profiles compared to 0.33 cm/min in the control profile. Electrical conductivity values of all soils of the catena were less than 4.0 dS m −1 . Bulk densities of the sodic soils were generally high (>1600 kg m −3 ).

Characteristics and management options of crusting soils in a smallholder farming area of the Zambezi metamorphic belt in northern Zimbabwe

Crusting and surface-sealing soils present productivity challenges to smallholder farmers despite their high inherent fertility. Crop production on crusting soils is costly due to unfavourable conditions such as surface capping and compaction, which hinder crop emergence. A study was conducted at Bruton farm in Zimbabwe to characterise crusting soils and assess options for their management. Soil crusting was characterised using crust thickness, crusting susceptibility index, bulk density, infiltration rates, soil aggregate stability and clay mineralogy. Structured and semi-structured interviews were also conducted to capture methods used by farmers to control the crusting. The relationship between crust thickness and soil physical and chemical properties and management practices were assessed using stepwise regression analysis. Soil crusting was largely related to soil aggregation, infiltration, fine sand fraction, cotton monocropping and crop residue incorporation. Crop residue incorporation and crop rotation could be adopted to mitigate soil crusting at the scheme.