Nitrogen (N) is an essential macronutrient for plant growth and productivity, but deficient in most Zimbabwean soils and its dynamics under conservation tillage are not well documented. The objective was to determine the effects of fertilizer application on mineral N dynamics and yield of maize (Zea mays L) and soybean (Glycine max (L) Merr) under conservation tillage in sub-humid tropical conditions of North Western Zimbabwe. Soil N mineralization was measured using in-situ incubation of undisturbed soil cores and soil N was determined using the method of extraction with 0.5M K2SO4. Nitrogen in aboveground plant tissue and grain was determined using spectrophotometry after Kjeldhal digestion. Soil N mineralization steadily increased as the growing season progressed and soil mineral N was 6.9% higher under conventional tillage compared to conservation tillage. The effects of mineral fertilizer application on soil N mineralization were highest in mulched plots and lowest in maize monocropping. Similar to N uptake at 5 weeks after planting (wap), grain and stover N uptake were highest when a combination of reduced tillage and mulching practices were used and lowest under conventional tillage. Highest soil N mineralization, maize N uptake, soybean N uptake and grain yield are achievable when all the three practices of conservation agriculture are applied compared with application of one or two practices as currently adopted by smallholder farmers in sub-Saharan Africa. Combining mineral fertilizer application with conservation agriculture results in higher soil N mineralization, N uptake and grain yield when compared with fertilizer application under conventional tillage.

Maize demand in Sub-Saharan Africa is expected to increase 2.3 times during the next 30 years driven by demographic and dietary changes. Over the past two decades, the area cropped with maize has expanded by 17 million hectares in the region, with limited yield increase. Following this trend could potentially result in further maize cropland expansion and the need for imports to satisfy domestic demand. Here, we use data collected from 14,773 smallholder fields in the region to identify agronomic practices that can improve farm yield gains. We find that agronomic practices related to cultivar selection, and nutrient, pest, and crop management can double on-farm yields and provide an additional 82 million tons of maize within current cropped area. Research and development investments should be oriented towards agricultural practices with proven capacity to raise maize yields in the region. Maize demand in Sub-Saharan Africa is expected to increase. Here, the authors use data collected by One Acre Fund on 14,773 smallholder fields in the region and determine that maize production can be increased with minimal cropland expansion by improving management practices.

ContextAgronomic data such as applied inputs, management practices, and crop yields are needed for assessing productivity, nutrient balances, resource use efficiency, as well as other aspects of environmental and economic performance of cropping systems. In many instances, however, these data are only available at a coarse level of aggregation or simply do not exist.ObjectivesHere we developed an approach that identifies sites for agronomic data collection for a given crop and country, seeking a balance between minimizing data collection efforts and proper representation of the main crop producing areas.MethodsThe developed approach followed a stratified sampling method based on a spatial framework that delineates major climate zones and crop area distribution maps, which guides selection of sampling areas (SA) until half of the national harvested area is covered. We provided proof of concept about the robustness of the approach using three rich databases including data on fertilizer application rates for maize, wheat, and soybean in Argentina, soybean in the USA, and maize in Kenya, which were collected via local experts (Argentina) and field surveys (USA and Kenya). For validation purposes, fertilizer rates per crop and nutrient derived at (sub-) national level following our approach were compared against those derived using all data collected from the whole country.ResultsApplication of the approach in Argentina, USA, and Kenya resulted in selection of 12, 28, and 10 SAs, respectively. For each SA, three experts or 20 fields were sufficient to give a robust estimate of average fertilizer rates applied by farmers. Average rates at national level derived from our approach compared well with those derived using the whole database ( ± 10 kg N, ± 2 kg P, ± 1 kg S, and ± 5 kg K per ha) requiring less than one third of the observations.ConclusionsThe developed minimum crop data collection approach can fill the agronomic data gaps in a cost-effective way for major crop systems both in large- and small-scale systems.SignificanceThe proposed approach is generic enough to be applied to any crop-country combination to guide collection of key agricultural data at national and subnational levels with modest investment especially for countries that do not currently collect data.

The abilities of grain legumes to fix atmospheric nitrogen are well documented, but the non-N effects of incorporating legumes into cereal-based systems are poorly understood. Continuous cropping of maize is assumed to increase maize fungal root pathogens, but few studies have documented this in sub-Saharan Africa. In this study, it was hypothesized that maize pathogen densities of F. oxysporum, F. verticillioides, F. equiseti, F. graminearum, F. chlamydosporum, C. eragostidis, M. phaseolina, Trichoderma spp., Pythium spp, Phoma spp, R. solani and E.pedicellatum are lower under legume-maize rotations than under continuous maize cropping, while fertilisation also affects pathogen densities. Field measurements were taken during the 2017/18 and 2018/19 summer growing seasons at two sites in South Africa to investigate the effect of crop rotation and fertilisation on densities of soil-borne fungal pathogens in maize. Densities of 12 pathogens on maize roots and crowns were investigated 110 days after planting using a modified DNA extraction method and qPCR technology. Maize following a legume had lower densities of F. graminearum, F. oxysporum, E. pedicellatum, and C. eragostidis at both localities. However, no consistent rotation effects were observed on densities of M. phaseolina, Trichoderma spp., Pythium spp., R. solani, Phoma spp., F. verticillioides and F. equiseti. Impacts of fertilisation on pathogen densities were also inconsistent depending on the site and season. This warrants for an integrated approach to fungal pathogen control in maize production.

Maize demand in sub-Saharan Africa will increase 2.3 times during the next 30 years driven by demographic and dietary changes. Over the past two decades, the area cropped with maize has expanded by 17 million hectares in the region, with little improvement in farmer yields. If these trends persist, massive increase in maize area and/or imports will be needed to meet domestic demand. Here we used data collected from 13,364 smallholder fields to identify agronomic practices that can promptly deliver large on-farm yield gains. We show that good agronomic practices regarding nutrient, crop management, and cultivar selection can more than double on-farm yields and provide an additional 93 million tons of maize within current cropland. Given the magnitude and urgency of the challenge ahead, agricultural research and development investments must be re-oriented towards agricultural practices with proven capacity to raise yields in farmer fields.

The use of herbicides for weed control in arable crop production is known to be fast and effective. However, there is paucity of information on the safety of commonly used grass herbicides on emergence, growth, and productivity of sesame (Sesamum indicum L.) genotypes currently being grown in Zimbabwe. A study was carried out in Zimbabwe during the 2017/18 cropping season in Gokwe South to evaluate the effect of alachlor, metolachlor, propaquizafop, and fluazifop-p-butyl on seed germination, growth, and yield of three sesame genotypes, namely, IETC, Lind 02, and Ziada 94. A laboratory experiment was laid in a completely randomised design with genotype and herbicide type as the factors. Seed germination, radicle, and plumule length were recorded at the end of the experiment. In the pot studies, two separate experiments were carried out to evaluate the effect of pre and postemergence herbicides on 50% emergence, plant height, number of branches, 50% flowering, number of pods, and yield of three sesame genotypes. The laboratory experiment results revealed significant ( p < 0.05 ) interactions among varieties and preemergence graminicides for germination percentage, radicle length, plumule length, and germination vigor index. Alachlor and metolachlor differentially reduced all germination parameters in the sesame genotypes used in the study. In the preemergence pot studies, there were significant ( p < 0.05 ) interactions on 50% emergence, plant height, and number of branches but not on number of pods and yield. Metolachlor significantly reduced all the measured parameters in IETC and Ziada 94. In the postemergence pot study, propaquizafop significantly ( p < 0.05 ) reduced plant height, number of pods, and yield of sesame more than fluazifop-p-butyl and hand pulling. It can be concluded that metolachlor and propaquizafop are not safe for use in these sesame genotypes at dosage rates that were used in this study. There is need for further screening of more sesame genotypes for tolerance to these and other commonly used genotypes to avoid unintentional phytotoxic damage on sesame.

Smallholder agriculture is an important source of livelihoods in South Asia and sub-Saharan Africa. In these regions the highest concentrations of nutritionally vulnerable populations are found. Agricultural development needs to be nutrition-sensitive, and contribute simultaneously to improving household nutrition, farm productivity and environmental performance. We explored the windows of opportunities for farm development and the potential of crop diversification options for meeting household dietary requirements, whilst concurrently improving household economic performance in contrasting smallholder farm systems in Kenya and Vietnam. Farm and household features and farmer perspectives and priorities were integrated into a farm-household model that allowed quantification of a diverse set of nutritional, labour and productive indicators. Using a multi-objective optimization algorithm, we generated ‘solution spaces’ comprising crop compositions and management configurations that would satisfy household dietary needs and allowed income gains. Results indicated site-specific synergies between income and nutritional system yield for vitamin A. Diversification with novel vegetables could cover vitamin A requirements of 10 to 31 extra people per hectare and lead to greater income (25 to 185% increase) for some households, but reduced leisure time. Although the Vietnamese sites exhibited greater nutrient system yields than those in Kenya, the household diets in Kenya had greater nutrient adequacy due to the fact that the Vietnamese farmers sold greater proportions of their on-farm produced foods. We conclude that nutrition-sensitive, multi-method approaches have potential to identify solutions to simultaneously improve household income, nutrition and resource management in vulnerable smallholder farming systems.

During a workshop and field visit in December 2019 in South Africa we discussed the Role soil C of Conservation Agriculture and carbon sequestration for climate mitigation. The insights of the workshop comprised of: (i) Integrating livestock into crop systems to achieve circularity, (ii) Economic and environmental sustainability is possible without subsidy, (iii) The transition towards sustainable farming can also be slow: Every step into the direction of sustainability if a good one, (iv) Vision and love for the land: a good farmer is a steward of the land; and (v) Ways to find hands-on local, but holistic solutions for every farm.

Understanding drivers of weed density and diversity is essential for the development of weed management strategies. Here, we compared temporal changes in weed density and diversity under no-till (NT) and conventional (CONV) tillage systems in cotton-maize rotations on loam, clay loam and sandy loam soils immediately after transition to NT in Kadoma, Zimbabwe. The effect of tillage system on weed density varied through the growth season and was dependent upon soil type and species composition of the weed community. Although weed responses to tillage system varied amongst species, we identified general trend effects on weed density on specific soils. At 3 weeks after crop emergence (WACE), weed density on loam soils was 76% and 96% higher in NT than in CONV during the 2009/2010 and 2010/2011 seasons, respectively, and on clay loam soils it was 37% and 33% higher in NT than CONV, respectively. Weed densities in NT and CONV were similar across all soil types at 6 WACE during the 2009/2010 and 2010/2011 seasons and at 9 WACE in 2009/2010. Tillage system did not affect weed density during the growth season on sandy loam soils. Weed diversity (Shannon index) was at least 75% higher in NT than CONV on loam and clay loam soils at 3 WACE during both seasons. It is likely these increases in weed densities following conversion to NT will exacerbate already prevalent weed management problems in the smallholder sector. Earlier weeding is recommended to suppress weed emergence and reduce likely associated crop yield losses.

Food insecurity and malnutrition are challenges in rural Rwanda that are presumed to be affected by differential household socioeconomic status, but the relationship between food and nutrition security and socioeconomic status is not well-understood. We used a participatory and multidisciplinary study comprising nutrition survey, focus group discussion (FGD), detailed household/farm characterization, and interviews to construct a participatory household typology and to determine differences in the socioeconomic, food, and nutrition security status of 17 households representing the identified household types in Nyabihu District of Western Province. Strategies to improve household food and nutrition security were identified by the case study households themselves. During the FGDs, it was hypothesized that financial, physical, and natural capitals varied, resulting in high, medium, and low resource endowed households, abbreviated as HRE, MRE, and LRE, respectively. The HRE households had the most educated household heads, largest landholdings (similar to 1 ha), and highest agricultural biodiversity and total farm income per annum. This probably resulted in better diets for women, children higher household food consumption relative to the other households. In contrast, the LRE households were the least food-secure, with poor household food consumption and low dietary diversity across seasons, probably due to limited physical and economic access to food. However, anthropometry of women and children did not differ with household type. Half of the children were stunted, including some from the more food-secure HRE households. Undiversified, nutritionally inadequate diets and bouts of illness likely contributed to chronic malnutrition in children. Making agricultural programs more nutrition-sensitive, creating diverse employment opportunities, and sensitizing communities to nutrition and adequate feeding practices of children could complement the interventions identified by households to improve their food and nutrition security.

Purple nutsedge (Cyperus rotundus) is an invasive weed in tropical cultivated lands and propagates through tubers, rhizomes, seed and corms. Weedy invasive plants have unique functional traits that enable their invasiveness. The objectives of this study were to determine the drivers of the purple nutsedge invasion in the Zimbabwe's agricultural systems among allelopathy, dispersal and dormancy-breaking mechanisms. Three experiments were carried out each in the laboratory, greenhouse and field. All the experiments were in completely randomised design replicated six times. Results showed that purple nutsedge leaf, stem and tuber extracts successfully (P < 0.001) inhibited germination and radical extension of Sorghum bicolor. Cutting the seed, which mimics the plough action on tubers gave the highest (P < 0.05) sprouting compared to exposure to freezing temperatures. There was a direct relationship between dispersal distance and wind speed (R-2 = 0.907). The purple nutsedge plants attached to the plough were related (R-2 = 0.515) to the number of plough passes. This study confirmed that allelopathy, easiness for dispersal and dormancy-breaking by the cutting action of the plough were the drivers of the weed's invasiveness. Therefore, allelopathy, ploughing, dispersal by wind and plough contribute to invasiveness of the weed.

Integrated systems research is one of the pillars in the nutrition-sensitive landscapes (NSL) approach that is being implemented in case-study sites in Zambia and Kenya. This chapter describes systems and systematically explores windows of opportunity for sustainable redesign and innovation in landscape and farm systems for improved nutrition using whole-farm and landscape models for each site. It discusses the strengths and challenges of systems approaches in agricultural research based on interactions with smallholder communities from the three diverse settings. The NSL approach investigates how improved land-use and management of resources in farms and landscapes can improve the livelihoods of rural people, their nutritional status and the ecosystem services that landscapes provide. To address and include the culture, values and priorities of people in nutrition-sensitive landscapes during the investigation and support of the envisioned development pathways, an inclusive approach to learning cycles is used.

Conservation agriculture (CA) is thought to reduce weed pressure from the third year of adoption, when recommended practices are followed. Weed growth and crop yield were assessed during the third and fourth year of maize–cowpea–sorghum rotation, second and third year of maize–cowpea rotation and first and second year of maize monocropping on a clay loam soil at Matopos Research Station (annual rainfall, 573 mm) following recommended CA management practices. Each experiment had a split‐plot randomized complete block design with mouldboard plough (CONV), minimum tillage (MT) with ripper tine and planting basins as main‐plot factor and maize residue mulch rate (0, 2 and 4 t/ha) as a subplot factor, with threefold replication. All subplots were surface mulched and weeded by hoe at the same time. We hypothesized that under MT weed growth would be considerable with maize monocropping but from year 3 of CA, weed growth would decrease and crop yield increase relative to values from unmulched CONV. Minimum tillage increased weed growth in 2nd year of maize monocropping. Under the maize–cowpea rotation, the considerable weed growth in planting basins was likely due to the large intrarow spacing and poor light competiveness of the cowpea variety. Mulch contributed to weed growth being suppressed by up to 36% under CA in the maize–cowpea–sorghum rotation relative to unmulched CONV. When planted on the same date, crop yield did not differ between CA and unmulched CONV. Maize–cowpea–sorghum rotation grain yield (3143 kg/ha) was double that under monocropping, probably due to improvements in soil physical and chemical conditions.

Sustainable intensification is proposed as a promising way to increase the productivity of agricultural systems while reducing pressure on ecosystems, safeguarding equitable relations among societal groups, and supporting the economic viability of households, enterprises, and communities. In sub-Saharan Africa, the identification and dissemination of options for sustainable intensification is hampered by the large diversity within and between farming systems, and their complexity arising from the interactions among different farm components and external factors. This study therefore uses an integrated farming systems approach to identify and assess context-specific improvements that can then be implemented and tested on-farm to foster experiential learning and facilitate adoption. We conducted a farming systems analysis for nine Africa RISING intervention sites across four countries, based on rapid and detailed farm characterizations, followed by model-supported diagnosis, and exploration of options for sustainable intensification. Farm diversity was described and analyzed by means of typologies and cross-site comparisons. Identified constraints varied depending on site and farming system type, but commonly included low input availability, climatic variability, poor soil fertility, sub-optimal livestock feeding, biotic stresses, and poor access to training and technical advice, all impairing farm productivity, returns to labor and capital inputs, income generation and food security. We investigated entry points that tackle the above constraints by exploring alternative farm configurations, technologies and practices for representative farms. By assessing potential impact of these changes on indicators beyond productivity, trade-offs were identified and assessed, for instance between profitability and household food self-sufficiency, and between nitrogen availability for crop uptake and increased nutrient losses. Taking a systems perspective during the entry point evaluation allowed differentiating potential effects on indicators at the field level versus the farm and household level. The exploration of options for specific farming system types now enables more targeted testing of promising innovations with farmers in the second project phase.

•Reduced tillage plots planted 12–18 days earlier than conventional tillage plots.•Weeding frequency was 42.1–58.9% higher in reduced tillage plots.•Labor demand was 119.7% higher under reduced tillage.•Returns to investment were 42.7% higher under reduced tillage.

SUMMARY Globally, a range of agronomic factors have been reported to have an impact on the performance of conservation agriculture (CA) and often determine its performance in relation to conventional agriculture (CONV). To assess this performance in Zimbabwe, 48 CA experiments were conducted by the International Crops Research Institute for the Semi-Arid Tropics in the semi-arid areas of southern Zimbabwe from 2004 to 2010, to calculate the weighted mean difference (WMD) through meta-analytical methods. The two CA practices, planting basins (Basins) and ripper tillage (Ripper), were compared with CONV. It was hypothesised that CA results improved yield compared with CONV and that the effect of CA practices on yield is affected by soil type, rainfall amount and distribution and selected management practices, which included rates of inorganic fertilisers and manures and mulching. Basins were superior to CONV in 59% of the experiments and the overall effect was significant ( p < 0.001). The effect of Ripper was non-significant. The hypothesis that CA practices result in improved maize grain yield over CONV was accepted for Basins. The WMD for experiments conducted on sandy soils was 0.365 t ha −1 for Basins and 0.184 t ha −1 for Ripper, and in both cases was significant ( p < 0.05). For clay soils, only the WMD for Basins was significant. A higher rainfall regime (500–830 mm) resulted in a lower WMD for Basins (0.095 t ha −1 ) and Ripper (0.105 t ha −1 ) compared with 0.151 t ha −1 for Basins and 0.110 t ha −1 for Ripper under lower rainfall (320–500 mm). The overall effect of Basins under the higher rainfall regime was not significant. There was better yield performance for Basins when the rainfall was well distributed; the reverse was noted for the Ripper. The application of 10–30 kg ha −1 of N (micro-dose range) resulted in a higher WMD for Basins than zero N application. Without N application, the WMD of Basins was not significant. For zero manure application in Basins, the WMD was 0.043 t ha −1 compared with 0.159 t ha −1 when manure was applied. The application of mulch depressed the WMD in Basins by 44% and Ripper by 89%. The hypothesis that yield performance under CA is influenced by soil type, rainfall amount and distribution, inorganic fertiliser and manure application was accepted.

SUMMARY Although the application of small quantities of nitrogen (N) fertiliser has improved cereal yields on low-input farms in semi-arid Zimbabwe, the practice is reported to be laborious and time-consuming by farmers. In an effort to make micro-dosing less labour-intensive and more precise, an ammonium nitrate (AN) tablet, the equivalent of a micro-dose of prill AN (28 kg N ha−1) applied per maize plant, was developed by International Crops Research Institute for the Semi-Arid Tropics in collaboration with Agri-Seeds, Zimbabwe. This study characterized the physical stability, chemical (N% and solubility) and agronomic performance of AN tablets compared with prill AN. Only 10% of tablets broke when dropped from 2 m, showing that they are physically stable and can handle rough treatment. The N content in the tablets (33.3%) was comparable to that in prill AN (34.6%). However, the tablet formulation took twice as long to dissolve than prill AN when placed on a wet soil. Despite this difference in solubility, simple leaching column experiments suggest that less than 2% of the total AN applied was lost due to leaching. Agronomic trials were superimposed on the paired-plot demonstrations used to promote micro-dosing and the conservation agriculture tillage technique of planting basins from 2005 to 2008. Each tillage (plough and basins) plot was subdivided into three sub-plots on which no AN, prill AN and tableted AN treatments were superimposed. Maize was planted and management of plots was left to farmers. Micro-dosing with either prill or tableted AN significantly (p < 0.001) increased maize grain yield by over 40% in all seasons for planting basins. However, on the ploughed plot there was no yield benefit to using either AN formulation in the season with the lowest rainfall (2006–2007). There was no significant difference in grain yield and agronomic N use efficiency between prill and tableted AN formulations except for the 2005–2006 season in planting basins. During this season, in planting basins, tableted AN had significantly (p < 0.001) higher rainwater productivity than prill AN, which translated into greater grain yield. In addition, the maximum benefit to micro-dosing was observed to accrue when combined with water harvesting techniques such as planting basins. An observation supported by the host farmers, who in the second and third seasons chose to apply available basal soil fertility amendments to the basin plots over the flat plots. Thus, AN tablets if available at an affordable price can be used by smallholder farmers to more precisely apply N fertiliser. Future work should focus on the labour issues of micro-dosing, and making cost-effective tablets available to resource-poor farmers and also addressing other limiting soil nutrients.