Effects of conservation agriculture on soil quality and productivity in contrasting agro‐ecological environments of Zimbabwe

Abstract

Experimentation by farmers with conservation agriculture (CA) is increasing in southern Africa, but local longer term data on these new production systems are scarce. This study focuses on CA research at two contrasting on‐farm sites and one on‐station long‐term trial in Zimbabwe. The on‐farm trials were conducted at Chikato village on a sandy soil at Zimuto Communal Area with low rainfall and at Hereford farm near Bindura on a clay‐rich soil in a high rainfall area. The on‐station trial was at Henderson Research Station near Mazowe where more in‐depth soil studies were possible. Results of CA systems from the on‐station site show on average 38 and 65% greater water infiltration on ripline‐seeded (RS) and direct‐seeded CA treatments compared with conventionally ploughed control treatments. Results from on‐farm sites show a 123 and 168% greater aggregate stability at Hereford and 11 and 24% lower dispersion ratio at Chikato on the two CA compared with the conventionally ploughed control treatments. Soil carbon increased by 46% in the first 20 cm on the sandy soils at Chikato in RS and by 104% in direct‐seeded CA treatments in four cropping seasons from 2004 to 2008, while it stayed at low levels on the conventionally tilled control treatment. Yields on CA plots were higher on the sandy soils in dry seasons, but lower in very wet seasons because of waterlogging. Yields on clay soils were less affected by the rainfall season. Crop productivity from CA systems increased at all sites over time owing to better management although significant differences between CA and conventional treatments on the three sites were apparent only after several cropping seasons. Conservation agriculture offers practical solutions to small‐scale farmers threatened by future soil degradation and fertility loss, but its successful use will depend on weed control and adequate application of fertilizers. The results indicate that there is no immediate increase in maize (Zea mays L.) yield when changing from a tilled to a CA system, but there is gradual improvement in some soil quality indicators over time.

Conservation agriculture in Southern Africa: Advances in knowledge

“…Similarly, studies conducted under the semi-arid conditions of Zimbabwe showed that over time CA practices improved hydraulic properties (unsaturated hydraulic conductivity and capillary sorptivity) of a clay loam soil 65 . However, studies also showed that the effect of CA on water infiltration was dependent on soil type, with the potential negative effect of waterlogging on granitic sandy soils, which have a tendency to accumulate too much water 23,30 . Water balance studies over a 5-year period (1994/5-1998/9) on clay soils at Hatcliffe, Zimbabwe by Nyagumbo 59 , allowed water losses through runoff and evapotranspiration to be compared between a CA system in the form of mulch ripping (MR) and conventional moldboard plowing (CMP) (Fig.…”

“…However, there are also conflicting results from the region 28 and elsewhere 29 that show no causal relationship between intensive tillage and carbon loss. Limited retention of surface crop residues adds to the decline in soil carbon in conventional systems 30 . Furthermore, accelerated soil erosion in tilled systems decreases the amount of important plant nutrients (e.g.…”

Assessment of Ecological Assets for Sustainable Regional Development: A Case Study of Deqing County, China

“…Following the division of 2nd grade areas, Deqing County, in the region with mid-subtropical hilly red soil, is mainly influenced by water erosion. The revised universal soil loss equation (RUSLE) [46][47][48] takes comprehensive account of rainfall, slope, vegetation, soil texture and human disturbance and estimates the average level of annual soil erosion through quantifying these five factors as rainfall erosivity (R), soil erodibility (K), topography (slope length and gradient LS), vegetation coverage factor (C) and water and soil conservation measures (P).…”

On the Ground or in the Air? A Methodological Experiment on Crop Residue Cover Measurement in Ethiopia

“…Thus, all measurement methods collected during the survey (LT and M1 to M5) refer to the same time as remote sensing measurements. Following the contribution of van Deventer et al (1997), the NDTI was calculated using the formula:…”

“…In order to achieve increases in agricultural productivity, a better and more sustainable use of land is advocated (sustainable intensification) by proponents of conservation agriculture. Thus, conservation agriculture has received considerable attention among scholars and policy makers (Kassam et al 2009;Erenstein et al 2012;Thierfelder and Wall 2012;Tesfaye et al 2015). The CGIAR-a global partnership on international agriculture research-has invested significantly into conservation agriculture research over the last decades (Renkow and Byerlee 2010) and a growing number of development organizations have been promoting conservation agriculture, with recent efforts focusing on smallholder farming systems in sub-Saharan Africa and Asia (Stevenson et al 2014).…”