Toward farm specific recommendations for the use of mineral fertilizers in sahelian crop-livestock systems

Low soil fertility is recognized as the major constraint to rainfed cereal production in the Sahel. Given that most farmers can not afford enough fertilizer to cover all their fields, it is important to fine-tune the recommendations to maximize the fertilizer economic return at farm level while minimizing economic risks linked to climate fluctuations. This study was designed to help draw site/year/farm specific recommendations regarding hill placed application of mineral fertilizer either combined or not with organic amendments. A three year, multi-factorial experiment was conducted on-farm on three sites from 2003 to 2005 to test the effect of hill-placed application of small doses of DAP fertilizers on three pearl millet (Pennisetum glaucum (L.) R. Br.) genotypes for a range of organic amendments. Results showed a consistent grain yield increase due to fertilizer application for the no-manure plots on 2 sites, the fertility level of the third site being good enough to mask to effect of mineral fertilizer with the exception of 2004, marked by an early drought. In normal conditions, no synergism was detected between organic and mineral fertilizer. However it became apparent in the case of re-sowing or late sowing with a larger effect of mineral fertilizer on manure plots

Modeling hydraulic properties of sandy soils of Niger using pedotransfer functions

Direct determination of soil hydraulic properties is often costly and laborious hence the use of indirect methods such as pedotransfer functions (PTFs). Despite progress made in PTF development in general, little evaluation of PTFs has been done for the sandy soils of Niger. We tested the ability of three PTFs, (Campbell, van Genuchten, and Vauclin) to determine soil water retention and unsaturated hydraulic conductivity (K) for sandy soils at two villages (Banizoumbou and Bagoua) in Niger. Modeled K was compared to K estimated from neutron probe readings at 1.4 m; and modeled moisture retention was compared to lab measurements derived from the hanging water column method and pressure plate apparatus for the following depth intervals: 0–30, 30–60, and > 60 cm at Banizoumbou; and 0–30, 30–120, and > 120 cm at Bagoua. The Campbell PTF resulted in lower root mean square error (RMSE) (0.05–0.06 m3 m− 3) for soil moisture retention for the three depth intervals at the two sites and performed better than the van Genuchten function (RMSE 0.06–0.07 m3 m− 3) for Bagoua soils which had higher sand content. The van Genuchten PTF consistently overestimated dry regime moisture retention for the three depth intervals especially at Bagoua but performed well for the wet regime. The Campbell and Vauclin PTFs underestimated K (RMSE 0.61–1.01 mm d− 1) at both sites whereas the van Genuchten model was close to field measurements (RMSE 0.26–0.47 mm d− 1). These results show that the Campbell model is a cheaper alternative to direct measurement of moisture retention and the van Genuchten function can be used to estimate K for Niger's sandy soils with modest accurac

How has the Zimbabwe mycobacterial culture and drug sensitivity testing system among re-treatment tuberculosis patients functioned during the scale-up of the Xpert MTB/RIF assay?

Background: In Zimbabwe, while the Xpert MTB/RIF assay is being used for diagnosing tuberculosis and rifampicin-resistance, re-treatment tuberculosis (TB) patients are still expected to have culture and drug sensitivity testing (CDST) performed at national reference laboratories for confirmation. The study aim was to document the Xpert MTB/RIF assay scale-up and assess how the CDST system functioned for re-treatment TB patients. Methods: We performed an ecologic study using national aggregate data. Results: Use of the Xpert MTB/RIF assay increased from 11 829 to 68 153 between 2012 and 2016. Xpert assays worked well, with successful tests in more than 90% of cases, TB detection rates at 15-17% and rifampicin resistance in <10%. During Xpert scale-up, the number of sputum specimens from re-treatment TB patients reaching national reference laboratories for CDST increased from 12% to 51%. In terms of laboratory performance, culture contamination increased from 3% to 17%, positive cultures from 13% to 17% and successful CDST from 6% to 14%: the proportion of CDST showing any resistance to rifampicin averaged 44%. From 2009 to 2016, the proportion of notified re-treatment TB patients with successful CDST increased from <1% to 7%. Conclusions: While components of Zimbabwe's CDST system for re-treatment TB patients showed some changes during the scale-up of the Xpert MTB/RIF assay, overall performance was poor. The country must either invest in improving CDST performance or in advanced molecular diagnostic technology

Participant recruitment and retention in longitudinal preconception randomized trials: lessons learnt from the Calcium And Pre-eclampsia (CAP) trial.

BACKGROUND: The preconception period has the potential to influence pregnancy outcomes and randomized controlled trials (RCTs) are needed to evaluate a variety of potentially beneficial preconception interventions. However, RCTs commencing before pregnancy have significant participant recruitment and retention challenges. The Calcium And Pre-eclampsia trial (CAP trial) is a World Health Organization multi-country RCT of calcium supplementation commenced before pregnancy to prevent recurrent pre-eclampsia in which non-pregnant participants are recruited and followed up until childbirth. This sub-study explores recruitment methods and preconception retention of participants of the CAP trial to inform future trials. METHODS: Recruiters at the study sites in Argentina, South Africa and Zimbabwe completed post-recruitment phase questionnaires on recruitment methods used. Qualitative data from these questionnaires and quantitative data on pre-pregnancy trial visit attendance and pregnancy rates up to September 2016 are reported in this paper. RStudio (Version 0.99.903 https://www.rstudio.org ) statistical software was used for summary statistics. RESULTS: Between July 2011 and 8 September 2016, 1354 women with previous pre-eclampsia were recruited. Recruitment took 2 years longer than expected and was facilitated mainly through medical record/register and maternity ward/clinic-based strategies. Recruiters highlighted difficulties associated with inadequate medical records, redundant patient contact details, and follow-up of temporarily ineligible women as some of the challenges faced. Whilst the attendance rates at pre-pregnancy visits were high (78% or more), visits often occurred later than scheduled. Forty-five percent of participants became pregnant (614/1354), 33.5% (454/1354) within 1 year of randomization. CONCLUSIONS: In preconception trials, both retrospective and prospective methods are useful for recruiting eligible women with certain conditions. However, these are time-consuming in low-resource settings with suboptimal medical records and other challenges. Trial planners should ensure that trial budgets cover sufficient on-site researchers with pre-trial training, and should consider using mobile phone and web-based electronic tools to optimize recruitment and retention. This should lead to greater efficiency and shorter trial durations. TRIAL REGISTRATION: Pan-African Clinical Trials Registry, Registration Number: PACTR201105000267371 . The trial was registered on 6 December 2016

Long-term changes in organic matter of woodland soils cleared for arable cropping in Zimbabwe

Subsistence farmers in Africa depend largely on the soil organic matter to sustain crop productivity. Long-term changes in soil organic carbon and nitrogen were measured after woodland clearance for smallholder subsistence farming or for commercial farming. The contents of organic carbon and nitrogen in soil under reference woodlands were largest (53.3 t C ha-1, 4.88 t N ha-1) in a red clay soil (~ 50% clay + silt), followed by a granitic sand (~ 12% clay + silt; 22.8 t C ha-1, 1.47 t N ha -1) and least (19.5 t C ha-1, 0.88 t N ha-1) in a Kalahari sand (~ 5% clay + silt). Organic carbon declined rapidly under cultivation to attain new equilibria within 10 years on all smallholdings. Greatest losses occurred in soils that initially contained most carbon and nitrogen in the order: red clay (22.4 t C ha-1 and 1.0 t N ha -1) > granitic sand (13.2 t C ha-1 and 0.8 t N ha -1) > Kalahari sand (10.6 t C ha-1 and 0.5 t N ha -1). On the clay soil, commercial farming with intensive use of mineral fertilizers and incorporation of maize stover led to more gradual decline: at equilibrium, contents of carbon and nitrogen were 15 t C ha -1 and 1.7 t N ha-1 greater than on smallholdings with similar soil and climate. In the Kalahari sand the ¿13C of organic C remained constant after woodland clearance, and maize contributed less than 10% of the total C even after 55 years. The ¿13C signature increased slightly with increasing duration of cultivation by smallholders in the granitic sands and red clay soil where maize contributed 29% and 35% of the C at equilibrium. Under more productive commercial farming, the carbon derived from maize accounted for 50% of the total after 10 years of cultivation and 67% at equilibrium. The persistence of woodland carbon in the sandy soil is attributed to chemical stabilization resulting from large concentrations of lignin and polyphenols in the tree litter, or as charcoal