Agricultural Water Management 98 (2011) 1687–1695 Contents lists available at ScienceDirect Agricultural Water Management j ourna l ho me page: www.elsevier.com/locate/agwat Yield and soil system changes from conservation tillage in dryland farming: A case study from North Eastern Tanzania Elin Enfors a,c,∗ , Jennie Barron b,c , Hodson Makurira d , Johan Rockström b,c , Siza Tumbo e a Department of Systems Ecology, Stockholm University, Sweden b Stockholm Environment Institute (SEI), Sweden c Stockholm Resilience Center, Stockholm University, Sweden d Department of Civil Engineering, University of Zimbabwe, Zimbabwe e Soil Water Management Research Group, Sokoine University of Agriculture, Tanzania a r t i c l e i n f o Article history: Available online 7 April 2010 Keywords: Conservation tillage Ripping Agricultural droughts In situ water harvesting Maize yields Soil health Short- and long-term effects Tanzania a b s t r a c t Yield levels in smallholder farming systems in semi-arid sub-Saharan Africa are generally low. Water shortage in the root zone during critical crop development stages is a fundamental constraining factor. While there is ample evidence to show that conservation tillage can promote soil health, it has recently been suggested that the main benefit in semi-arid farming systems may in fact be an in situ water harvest- ing effect. In this paper we present the result from an on-farm conservation tillage experiment (combining ripping with mulch and manure application) that was carried out in North Eastern Tanzania from 2005 to 2008. Special attention was given to the effects of the tested treatment on the capacity of the soil to retain moisture. The tested conservation treatment only had a clear yield increasing effect during one of the six experimental seasons (maize grain yields increased by 41%, and biomass by 65%), and this was a season that received exceptional amounts of rainfall (549 mm). While the other seasons provided mixed results, there seemed to be an increasing yield gap between the conservation tillage treatment and the control towards the end of the experiment, and cumulatively the yield increased with 17%. Regarding soil system changes, small but significant effects on chemical and microbiological properties, but not on physical properties, were observed. This raises questions about the suggested water harvesting effect and its potential to contribute to stabilized yield levels under semi-arid conditions. We conclude that, at least in a shorter time perspective, the tested type of conservation tillage seems to boost productivity during already good seasons, rather than stabilize harvests during poor rainfall seasons. Highlighting the challenges involved in upgrading these farming systems, we discuss the potential contribution of con- servation tillage towards improved water availability in the crop root zone in a longer term perspective. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The productivity of the smallholder farming systems that con- stitute the main livelihood source in sub-Saharan Africa is low (Sanchez, 2002; Conway and Toenniessen, 2003; Diao et al., 2007), with yield levels in the semi-arid and dry sub-humid regions aver- aging some 20–50% below what is achievable (Falkenmark and Rockström, 2004). Although this is a complex problem, linked to a number of biophysical and socio-economic factors (Reynolds et al., 2007), water shortage in the root zone during critical crop devel- opment stages is a fundamental issue (cf. Slegers and Stroosnijder, ∗ Corresponding author at: Department of Systems Ecology/Kräftan, Stockholm University, SE-106 91 Stockholm, Sweden. Tel.: +46 073 707 86 20; fax: +46 08 15 84 17. E-mail address: elin@ecology.su.se (E. Enfors). 2008). This is the result of a highly variable rainfall regime, lead- ing to frequent dry-spells (Barron et al., 2003), in combination with large un-productive flows in the field water balance (Rockström and Falkenmark, 2000). The latter is related to climatic factors, to soil characteristics, and to land management. As the rain typically falls as high intensity storms in these climates, run-off rates are high and infiltration rates low, and high temperatures lead to high evap- oration rates (Rockstrom, 1999). Further, conventional tillage by ploughing (and to a lesser extent hand hoeing) often cause crusting, compaction, and loss of structural stability in vulnerable dryland soils, leading to inefficient use of the water that is left (Mrabet, 2002; Roldan et al., 2003). Over the past decades, conservation tillage (CT) has been pro- moted as a way to maintain and build up soil structure and fertility in tropical agro-ecosystems (Benites et al., 1998; Bolliger et al., 2006; Hobbs et al., 2008). CT includes a range of technologies aim- ing to conserve soil and water resources in the field, by minimizing 0378-3774/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2010.02.013