Published in: Agriculture, Ecosystems and Environment 2016, vol.228, p.101-110
Crop residues are a key livelihood resource in smallholder mixed crop-livestock systems in Sub-Saharan Africa. With expansion of arable land and resultant decline in grazing resources, crop residues are becoming an increasingly important component of livestock feeds. This demand for livestock feeds has implications for the long-term sustainability of such systems since failure to return biomass to soils has implications for soil quality and the capacity of soils to support long-term productivity. Biomass allocation patterns are likely to vary with overall level of productivity and hence availability. In this study we used a household survey to quantify crop residue allocation patterns across a gradient of productivity in Eastern Africa focusing on two sites in Ethiopia and one in Kenya. We assessed the underlying determinants of crop residue allocation patterns with a view to understanding how productivity increases through intensification will influence biomass allocation in Eastern Africa and how livelihood and natural resource management objectives could be optimized. Results showed that farmers strongly favour allocation of residues to livestock feeding but that allocation to soil increases along the productivity gradient. This reduced feeding to livestock and increased allocation to soil fertility is associated with smaller farm sizes leading to reduced animal traction needs for tillage, increased overall livestock productivity, increased use of inputs and a reduced reliance on farm-based activities in overall livelihood strategies. The implications of these trends are that productivity increases in smallholder systems are likely to reduce pressure on biomass in the long term and that measures that enhance the prospects for farmers to intensify their production systems are likely to increase soil health and sustainability objectives in general. A key conclusion of the work is that intensification of livestock production could reduce crop residue allocation to soils with long term implications for soil productivity.
Published in: PLoS One 2016, vol.11, no.6: e0157236
Quality control (QC) of germplasmidentity and purity is a critical component of breeding and conservation activities. SNP genotyping technologies and increased availability of markers provide the opportunity to employ genotyping as a low-cost and robust component of this QC. In the public sector available low-cost SNP QC genotypingmethods have been developed from a very limited panel ofmarkers of 1,000 to 1,500 markers without broad selection of the most informative SNPs. Selection of optimal SNPs and definition of appropriate germplasm sampling in addition to platform section impact on logistical and resource-use considerations for breeding and conservation applications when mainstreaming QC. In order to address
these issues, we evaluated the selection and use of SNPs for QC applications from large DArTSeq data sets generated from CIMMYT maize inbred lines (CMLs). Two QC genotyping strategies were developed, the first is a “rapid QC”, employing a small number of SNPs to identify potential mislabeling of seed packages or plots, the second is a “broad QC”, employing a larger number of SNP, used to identify each germplasm entry and tomeasure heterogeneity. The optimal marker selection strategies combined the selection ofmarkers with high minor allele frequency, sampling of clustered SNP in proportion tomarker cluster distance and selecting markers thatmaintain a uniform genomic distribution. The rapid and broad QC SNP panels selected using this approach were further validated using blind test assessments of related re-generation samples. The influence of sampling within each line was evaluated. Sampling 192 individuals would result in close to 100% possibility of detecting a 5%contamination in the entry, and approximately a 98%probability to detect a 2%contamination of the line. These results provide a framework for the establishment of QC genotyping. A comparison of financial and time costs for use of these approaches across different platforms is discussed providing a framework for institutions involved inmaize conservation and breeding to assess the resource use effectiveness of QC genotyping. Application of these research findings, in combination with existing QC approaches, will ensure the regeneration, distribution and use in breeding of true to type inbred germplasm. These findings also provide an effective approach to optimize SNP selection for QC genotyping in other species.
Published in: NJAS Wageningen Journal of Life Sciences, 2016, vol.78, p.93–101.
Relay cropping of cover crops is a strategy of increasing biomass yields and productivity of maize-based systems. However, there is need to strategically plan the relay cropping to avoid competition between the main crop and the relay cover crops while at the same time obtaining optimum yields from both crops. A study was carried out in a clay soil in a sub-humid region of Zimbabwe to investigate the effect of introducing different relay cover crops at 8, 11 and 15 weeks after planting maize (WAPM) into a standing maize crop on biomass yield of the relay cover crops, their emergence and maize yields in the 2012–13 and 2013–14 seasons. From the results of the study, it was observed that the introduction of relay cover crops late in the season compromises their emergence and hence biomass yields (as low as 0.8 kg ha−1 for blue lupins (Lupinus angustifolius var. angustifolius (L.)). In a season where longer mid-season dry spells were experienced (2013–14), biomass yields of the relay cover crops were lower than in 2012–13 season. Delays in planting of relay cover crops (i.e. from 8 to 11 and from 11 to 15 WAPM) resulted in yield reductions of around 50%. Relay cover crops introduced at different periods of the season had no significant effects on maize grain and biomass yields. However, there are relay cover crops such as the velvet bean (Mucuna pruriens (L.) DC) and common oats (Avena sativa L.) that showed better emergence even in the sub-optimal conditions (with emergence as high as 90%). Of all the investigated relay cover crops, none could contribute to significant amounts of biomass thus insignificant increases in total plot biomass. There is need to investigate on other earlier planting dates that do not compromise the biomass productivity of such relay cover crops.
Published in: In: Experimental Agriculture In press
Multilocation experiments were established to determine the best strategy for using inorganic fertilizer in conservation agriculture (CA) systems that use green manure cover crops, namely sunhemp, velvet bean and cowpea grown in rotation with maize. The objectives of the study were to determine (i) the effect of half and full rates of basal fertilizer on maize and legume biomass yields, (ii) the residual effects of unfertilized, half and fully fertilized green manure legumes on maize grown after the legumes, and (iii) the residual effect of unfertilized, half and fully fertilized green manure legumes combined with basal and topdressing fertilizer on maize yields. Experimental design was a randomized complete block with basal fertilizer as a treatment in the green manure legumes phase. Previously, in the maize phase, green manure legume species were the main treatment with basal fertilizer as a subtreatment (sunhemp, velvet bean and cowpea: 0, 75, 150 kg ha−1 and 0, 50, 100 kg ha−1, respectively). Nitrogen was applied in the maize phase at 0, 23, 46, 69 kg N ha−1 as a sub-subtreatment in Malawi. Results showed that inorganic fertilizer is the most effective when applied to the maize, not green manure legumes. Biomass of green manure legumes, sunnhemp 8084 kg ha−1, velvet bean 7678 kg ha−1 and cowpea 4520 kg ha−1, was not significantly affected by application of basal fertilizer. Maize production increased after the application of green manure legumes with maize-after-maize, maize-after-velvet bean, maize-after-sunnhemp and maize-after-cowpea, yielding 3804, 5440, 5446 and 5339 kg ha−1, respectively. Nitrogen increased maize yield regardless of the previously used green manure legumes species. Our results suggest that farmers should apply fertilizer to maize and grow green manure legumes on residual soil in CA systems. Despite growing green manure legumes, smallholders should apply nitrogen topdressing to maize grown using the green manure legumes in some agro-ecologies.
Published in: Crop Protection 2016, vol.88, p.28-36
Weeds are a major constraint to crop production, and are responsible for considerable yield losses in maize production systems throughout the world. Herbicides are widely used for weed control in maize production systems, but can have negative environmental consequences. Researchers have evaluated the use of crop competition and suppression to manage weeds in various crop combinations, including maize-based systems. Crop competition in maize may involve techniques such as reduced row spacing, increased planting density, and the use of competitive cultivars that exhibit weed suppressive potential. In this review, examination of the literature has revealed the considerable value of using crop competition in integrated weed management programs. Research has demonstrated that narrowing row spacing to half the standard distance reduced weed biomass by 39–68%, depending on weed species. Researchers have also demonstrated that increasing maize planting density by up to twice the standard rate achieved a reduction in weed biomass of 26–99%. While little research has been conducted into the use of competitive maize cultivars for weed management, several studies have documented cultivars with potential to suppress weeds. Attributes of weed competitive cultivars include high leaf area index, and other elements of leaf architecture that improve light interception by the crop, so increasing the shading of weeds. Combining crop competition methods with other agronomic practices can increase their effectiveness in controlling weeds. For example, biomass of Setaria italica (L.) Beauv was reduced by 60% when maize planting density was increased by 1.5 times the recommended spacing, and this effect was more pronounced when fertilizer was banded rather than broadcast. In summary, the strategic use of crop competition to control weeds has been a success in many regions, and is an important tool in integrated weed management. The importance of crop competition methods has particular relevance where farmers are unable to afford herbicides, as making use of crop competition is more economical.
Published in : Crop Science Society of America Crop Science 2016, vol.56, p.1-11
To aid breeding for heat-tolerant germplasm we analyzed the effects of high temperatures on the CO2 exchange rate (CER), crop growth rate (CGR), kernel number (KN), and grain yield (GY) in a 30-d period bracketing flowering. Field experiments, including three maize (Zea mays L.) hybrids with temperate (Te), tropical (Tr) and temperate × tropical (Tx) adaptation were performed in two experiments (Exp. 1 and 2). Hybrids were subjected to high temperatures induced by shelters during a 15-d period before (H1; preflowering) or after silking (H2; postflowering). Crop growth rate was measured during the 30-d period bracketing silking (CGRCP), H1 (CGRPRE), and H2 (CGRPOST). Relative to nonstressed conditions, CER was reduced by 17 and 16% in H1 and H2. Moreover, CER was associated with CGRCP (r = 0.78; p ≤ 0.001), CGRPRE (r = 0.39; p ≤ 0.05), CGRPOST (r = 0.51; p ≤ 0.01), KN (Exp. 1, r = 0.53; p ≤ 0.01; Exp. 2, r = 0.49; p ≤ 0.01), and GY (Exp. 1, r = 0.59; p ≤ 0.01; Exp. 2, r = 0.46; p ≤ 0.05). As a result of heat stress, CGRCP (H1, −17%; H2, −29%), KN (H1, −7%; H2, −45%), and GY (H1, −10%; H2, −45%) were reduced relative to the control treatment. Stronger reductions for all traits in H2 relative to H1 emphasize the importance of sufficient CER during this period. The effect of high temperature on CER differed among hybrids (Tx > Te = Tr) and is promising for future germplasm screening.
In: The International Food and Agribusiness Management Review 2016, vol. 19 (Special Issue A), p.75-92
Maize is a major staple food crop in southern Africa and stress tolerant improved varieties have the potential to increase productivity, enhance livelihoods and reduce food insecurity.
This study uses big data in refining the geospatial targeting of new drought-tolerant (DT) maize varieties in Malawi, Mozambique, Zambia, and Zimbabwe. Results indicate that more than 1.0 million hectares (Mha) of maize in the study countries is exposed to a seasonal drought frequency exceeding 20% while an additional 1.6 Mha experience a drought occurrence of 10–20%. Spatial modeling indicates that new DT varieties could give a yield advantage of 5–40% over the commercial check variety across drought environments while crop management and input costs are kept equal. Results indicate a huge potential for DT maize seed production and marketing in the study countries. The study demonstrates how big data and analytical tools enhance the targeting and uptake of new agricultural technologies for boosting rural livelihoods, agribusiness development and food security in developing countries.
Published in : Ecology of Food and Nutrition, 2016, vol.55, no.2, p.209-230
The aim of this article was to investigate the food (in)security effect of household income generated from major economic activities in rural Swaziland. From a sample of 979 households, the results of a multinomial treatment regression model indicated that gender of household head, labor endowment, education, size of arable land, and location significantly influenced the households’ choice of primary economic activity. Further results suggested that off-farm-income-dependent households were less likely to be food insecure when compared with on-farm-income-dependent households. However, on-farm-income-dependent households had a better food security status than their counterparts who depended on remittances and nonfarm economic activities.
Published in: American Phytopathological Society Phytopathology, 2016, vol. 106, no. 7, p.729-736.
Frequent emergence of new variants in the Puccinia graminis f. sp. tritici Ug99 race group in Kenya has made pathogen survey a priority. We analyzed 140 isolates from 78 P. graminis f. sp. tritici samples collected in Kenya between 2008 and 2014 and identified six races, including three not detected prior to 2013. Genotypic analysis of 20 isolates from 2013 and 2014 collections showed that the new races TTHST, TTKTK, and TTKTT belong to the Ug99 race group. International advanced breeding lines were evaluated against an isolate of TTKTT (Sr31, Sr24, and SrTmp virulence) at the seedling stage. From 169 advanced lines from Kenya, 23% of lines with resistance to races TTKSK and TTKST were susceptible to TTKTT and, from two North American regional nurseries, 44 and 91% of resistant lines were susceptible. Three lines with combined resistance genes were developed to facilitate pathogen monitoring and race identification. These results indicate the increasing virulence and variability in the Kenyan P. graminis f. sp. tritici population and reveal vulnerabilities of elite germplasm to new races.
Published in: Journal of Agricultural Science, In press.
On-farm demonstration-trials are a common strategy to introduce new technologies to farmers, while simultaneously evaluating these technologies’ performance under farmer conditions. The current study focuses on conservation agriculture (CA) technology adoption dynamics among a small group of farmers who can be considered increasingly knowledgeable, as they have hosted CA demonstration-trials for at least 7 years. Management and performance of farmers’ fields were compared with the CA demonstration-trials implemented on the same farm, focusing on yield gaps (YGs) between the two and the uptake of CA or some of its principles. Comparisons were made between demonstration-trials and farmers’ fields in three distinct land classification areas: Madziwa Communal Area (est. 1910s), Chavakadzi (est. 1980s) and Hereford (est. 2000s) Resettlement Areas. It was found that closing knowledge gaps on CA did not close YGs and that CA adoption was partial. In the Communal Area, CA principles have barely been taken up, but farmer yields were often as good as on the demonstration-trials. In the Resettlement Areas, farmers did take up reduced tillage (CA principle 1) and practised rotations (CA principle 3), but not residue retention (CA principle 2). Rather than partial CA adoption, lower fertilization rates explained the recorded YGs in the Resettlement Areas. In the three areas, farmers’ interest in CA-based increasing of yields was limited, as circumstances drove them to embark on extensification rather than a land use intensification pathway.