Conservation agriculture and slope position effect on selected soil physical properties of a Vertisol at Tshivhilwi in Limpopo Province

Abstract

Conservation agriculture (CA) is a production system that involves three principles which are minimal or zero tillage, crop rotation and mulching with plant residues. CA improves soil physical properties resulting in soil fertility improvement. However, there are relatively few studies that have documented the benefits of CA on soil physical properties of vertisols. A study was conducted to determine the influence of CA and slope position on soil bulk density (BD), total soil porosity (Vf), soil aggregate stability (AS), soil water holding capacity (WHC), soil organic carbon (SOC), soil electrical conductivity (EC), infiltration rate (IR) and cumulative infiltration (CI) of a vertisol, at Mutanga Wa Ndodzi Agricultural Co-operative at Tshivhilwi village where CA has been in practice since 2013. The farm practices CA with crop rotation. The field used for CA was tilled once in 2013 using a mouldboard plough. Mulching is done using maize stalks. After planting fertilizer was applied based on crop requirement. One set of soil samples were collected from a field under CA while another set was collected from a field under natural grass (control) which is located directly opposite the CA field. Soil samples were collected 10 m apart from 0-10 and 10-20 cm depths along the transects which were at, 10 m apart. A core of diameter of 5 cm and height of 5 cm was collected to determine soil BD. SOC was determined using the modified Walkley-Black wet oxidation procedure. EC was measured with glass electrode professional EC meter in 1:5 ratio soil water suspension. Soil AS was determined using wet sieving method. Soil particle density was determined using a pycnometer bottle after which the bulk density and particle density of the soil were used to calculate soil porosity. Soil WHC was determined by saturating with water 25 g of oven-dried soil in a glass funnel and its water holding capacity determined by gravimetric method. Management and slope position interaction had a significant effect at 0-10 cm and 10-20 cm soil depth with lower BD at the CA site lower slope position at 0-10 cm soil depth. SOC was significantly higher on lower and middle slope of CA than natural grassland (NG) site. The CA site x recorded higher EC at the middle and lower slope positions compared to NG site. Higher AS was observed at the CA site than NG at all slope position at 0-10 cm soil depth, at 10-20 cm CA site recorded higher AS at the lower and middle slope. Vf was significantly higher at the CA site than NG site at all slope positions, CA lower slope was associated with higher Vf followed by middle and summit slope. CA site exhibited a higher WHC than NG site at all slope positions, CA middle lower slope positions had the highest WHC. Interaction effect was observed on final IR however, the significant difference between the two-management system was observed at lower and middle slope. Conservation agriculture and slope position interaction in this research resulted in significantly higher BD, SOC, EC, AS, vf and WHC but had no effect on BD middle slope and summit slope positions at 0-10 cm, SOC summit and lower slope positions at 10-20 cm soil depth, EC summit slope at 0-10 cm, vf at summit and middle slope at 10-20 cm soil depth and WHC lower slope lower slope position at 10-20 cm soil depth. According to the findings of this study, practicing conservation agriculture in various slope positions could be recommended to improve soil properties (bulk density, soil organic carbon, soil electrical conductivity, aggregate stability, total soil porosity, water holding capacity and infiltration rate) of a Vertisol.