The paper provides an overview of institutions, scientists, and practitioners involved over the years in the various ways in which participatory plant breeding (PPB) is implemented, with indication of the crops involved and the countries in which it took place, or is still taking place. This might help creating a better awareness of the scope (both geographical and crop wise) of the different methodologies as well as of their advantages, disadvantages, applicability, and limitations. Through a literature survey, we found 254 publications showing that over a period of 36 years participatory approaches in plant breeding have been used in 69 countries (10 developed and 59 developing) with 47 crops including self-pollinated, cross-pollinated, and vegetatively propagated crops, by several Institutions including CGIAR centers, universities, and NGOs. We argue that there are no obvious scientific or technical reasons limiting the use of PPB, and we interpret the limited institutionalization as a difficulty to accept the paradigm shift that participation implies.

Cowpea bean (Vigna unguiculata) is usually submitted to pre-harvest burndown with herbicides aiming to an early harvest. We aimed to quantify the residues of paraquat, diquat, glufosinate-ammonium and glyphosate in cowpea grains subjected to two timings of pre-harvest burndown. Three identical experiments were installed in Dourados (Lat. 22° S), Sinop (Lat. 11° S) and Teresina (Lat. 05° S), Brazil, comprising the pre-harvest burndown of cowpea bean with these herbicides, applied either with 50 or 75% of the pods dry and ready for harvest. As hotter and drier the location as slower the herbicide dissipation. Glyphosate should not be used for pre-harvest burndown of cowpea. Herbicide residues were above the maximum levels stated by the Brazilian legislation when applied with 50% dry pods. Burndown herbicides aiming to speed harvest should be applied with at least 75% dry pods in cowpea to ensure safe herbicide residue levels in grains.

Soil alkalinity imposes important limitations to lupin productivity; however, little attention has been paid to investigate the effects of soil alkalinity on plant growth and development. Many lupins are sensitive to alkaline soils, but Lupinus albus material from Egypt was found to have tolerance to limed soils. The aim of this study was to compare the growth response of two cultivars of L.albus L. – an Egyptian cultivar, P27734, and an Australian cultivar, Kiev Mutant, to different soil pH levels and to understand the physiological mechanisms underlying agronomic alkalinity tolerance of P27734. Plants were grown under three pH levels (5.1, 6.7, and 7.8) in a temperature-controlled glasshouse. For both cultivars, the greatest dry mass production and carboxylate exudation from roots were observed at alkaline pH. The better performance of the Egyptian cultivar at high pH was entirely accounted for by its greater seed weight. From a physiological perspective, the Australian cultivar was as alkaline-tolerant as the Egyptian cultivar. These findings highlight the agronomic importance of seed weight for sowing, and both cultivars can be used in alkaline soils.

Landowners can engage in voluntary conservation with the help of incentive programs. Recommended conservation practices are selected based on management intentions as well as the contribution of those practices to the overall net returns. However, conservation motives are heterogeneous and based on individual risk behavior. Existing cost-share programs might either under-fund or over-fund conservation, which could lead to inefficient management of natural resources. The current analysis evaluates the economic feasibility of variable cover crop strategies, multiple seeding rates, within a soybean production system in silt loam and clay soils. The study utilizes stochastic efficiency with respect to a function, referred to as SERF, for determining the preferred strategies under various risk preferences. The SERF method accounts for the heterogeneity of individual decision-making with regards to conservation adoption. Results indicate that most risk-averse farmers chose tillage radish with medium seeding rate as their preferred strategy. However, as the risk-bearing capacity of an individual increases, the current level of incentives does not motivate to implement conservation. The most preferred plan for risk-neutral farmers is the fallow system in both silt loam and clay soils. The economic and risk assessment framework can improve understanding of the temporal dynamics of different practices and inform policy on conservation structure that promotes agricultural systems that are economically, environmentally, and socially sustainable.

Breeding for drought tolerance using novel genetic resources possessing relevant agronomic and adaptive traits is a key to enhance productivity and food security in wheat growing areas. Herein, the main objectives were (i) to use a combination scoring index (multiple scoring index, (MSI)) for selection of durum wheat genotypes under different drought stress intensities (SIs) (ii) to examine repeatability of the scoring index through bootstrap re-sample method, and (iii) to study the relationship of MSI with some drought-adaptive traits. Sixteen durum wheat genotypes were grown under rainfed and irrigated conditions during three cropping seasons (2012–2015), resulting in different drought SIs, that is, mild (SI < 0.3), moderate (0.3 < SI < 0.6), and severe (SI > 0.6). The average grain yields among test environments varied between 708 and 3631 kg ha−1. The validation of the methodology of scoring index was confirmed by the correlation coefficients between score indices and their original values across different drought SIs. According to MSI, the genotypes G16, G1, and G3 had the best combination of high productivity and high resilience to mild, moderate, and severe drought stress conditions, respectively. These results indicated that the ranking of genotypes varied among different drought SIs, which support the high potential of durum wheat for adaptation to different drought stress conditions. Based on the bootstrap samples, non-repeatable correlations were observed between the estimates of MSI from different levels of stress. The significant correlation between MSI with grain yield and 1000-kernel weight (TKW) under severe drought condition provides evidence that MSI ultimately be considered as a tool for effective selection of drought-tolerant genotypes. The MSI selected genotypes based on high productivity and resilience, to each level of drought SI, and favorable adaptive traits useful for breeding.

Combined use of lime, animal manure and inorganic fertilisers is effective in replenishing the fertility of degraded acid soils. However, many smallholder farmers lack access to sufficient amounts of these inputs to improve the fertility and reduce the aluminium toxicity of Ferralsols. Organic manures are available but often have low nutrient content, which limits their ability to supply nutrients to soils. In a two-factor field experiment over four seasons on an Anthropic Ferralsol in Southern Province, Rwanda, we assessed (i) the effect of cattle manure on soil properties at a reduced rate affordable to smallholder farmers compared with that of NPK fertiliser applied, with and without lime also at a reduced rate, and (ii) the effect of supplementing grass in a basal cattle diet with legume leaves on manure quality and its effect on soil properties. Manure from cattle fed only the grass Chloris gayana (grass-only manure) and from cattle fed C. gayana supplemented with Acacia angustissima leaves (grass+legume manure) was applied at 5 t dry matter ha-1 (25% of the recommended rate) at the beginning of each growing season. NPK was applied as split doses supplying a total rate of 70 kg N ha-1. Lime was applied annually at a rate of 2.0 t CaO ha-1, which was 25% of the rate required to neutralise total acidity at the site. All amendments were applied only to the soil surrounding the maize plants (planting stations), which is estimated at 25% of the plot area. Maize stover was left on plots after harvest and planting stations were retained over all growing seasons. All treatments altered soil properties at the planting stations. Lime generally increased pH but there was no significant difference between lime plus manure treatments and non-limed manure treatments. Soil organic carbon concentration and cation exchange capacity were higher in manure and NPK treatments than in non-fertilised treatments. The manure treatment increased soil water-holding capacity compared with the NPK and non-fertilised treatments. There was no significant difference in total N, Ca2+, Mg2+ and K+ between the NPK and manure treatments. Micro-dosing animal manure can thus replace mineral fertiliser plus lime for soil fertility replenishment in smallholder farming. Grass+legume manure contained higher concentrations of total N, Ca, Mg, K and Na than grass-only manure, but its effect on soil properties did not differ significantly from that of grass-only manure.

Understanding the genetic variability, heritability and genetic advance (GA) of traits in any plant population is an important pre-requisite for variety development. The objectives of the study were to assess the level of genetic variability among vegetative growth traits and yield, assess the relationship among the growth traits and yield and predict GA for the most heritable traits among Robusta coffee full-sib families. The trial was established in June 2009 at the experimental fields of the Cocoa Research Institute of Ghana with 62 full-sib families planted in a randomized complete block design with six replications. Significant (p < 0.05) variation was observed among the full-sib families evaluated for all traits, except for span (canopy diameter). Span and number of laterals were genetically correlated (p < 0.001) with cumulative yield (2013–2017), with span being the vegetative growth trait most strongly related to cumulative yield (rg = 0.60, p < 0.001). The most heritable vegetative growth and yield traits were, respectively, number of laterals (H2 = 0.59) and cumulative yield (H2 = 0.41). The top 10 families (BP40, BP41, BP9, BP36, BP34, BP28, BP37, BP14, BP4 and BP10) in terms of cumulative yield are proposed for multi-location evaluation and possible release as hybrids for coffee farmers in Ghana.

White yam (Dioscorea rotundata) is an important tuber crop in a number of countries, but especially in West Africa where it serves as a food staple as well as a cash crop as excess production is sold in local markets. But the availability of quality planting material, most notably seed yams, for yam production remains an important constraint for farmers. Techniques have been developed to help address this limitation by cutting yam tubers into pieces (minisetts), treating them with the pesticide either via a seed dressing dust or pesticide ‘dips’ and planting to grow seed yams of the required size and quality. But while there have been many studies on the agronomy and adoption by farmers of these techniques, there have been fewer studies on their economic performance. Indeed, to date there have been no studies that compare the economic performance of treating setts compared to leaving them untreated, and neither has there been any analysis of the environmental impact of treating setts. This paper reports the results of a study designed to address these two gaps in knowledge and is based upon results from a series of farmer-managed seed yam plots established in the middle belt of Nigeria over 4 years (2013–2016). Results suggest that revenue and gross margin were higher for treated versus untreated setts although the latter still performed relatively well. Using the Field Use Environmental Impact Quotient (EIQ), the commonly recommended pesticide sett treatments were estimated to have a low-to-moderate environmental impact, and further research is needed to see how far pesticide use can be reduced to still be effective and minimise any environmental impact.

Cocoa (Theobroma cacao) farmers in Sulawesi, Indonesia typically use subsidised, ammonium-based rice fertilisers that in combination with poor agricultural practices have resulted in soil acidification, loss of organic matter, aluminium toxicity and lower soil fertility. As a result, these soils are only marginally appropriate for replanting cocoa to boost production. A field experiment was performed to test alternative soil amendments for successful replanting of cocoa on these deficient soils. In a trial with a randomised block design, 6-month old seedlings, top-grafted with the local MCC02 clone, were planted under light Gliricidia sepium shade and after 3 months treated quarterly with two options of mineral fertilisers: either a customised fertiliser, consisting of Nitrabor (a combination of calcium nitrate and boron), dolomite, rock phosphate and KCl or a NPK/urea mix used by farmers, each supplied with or without ‘micronutrient’ rock salt, organic fertiliser and beneficial microorganisms or their culture medium, a mixture of chitin and amino acids (a total of 20 treatments). Over a 4-year period, the marginal mean rates of stem diameter increment and flowering score were higher in customised fertiliser than NPK/urea treatments. The average growth rate was highest in the first year and was increased by supplying organic fertiliser. A significant correlation (r = 0.22, p < 0.05) occurred between growth and available P, but concentrations of available P were higher in the NPK/urea plots, which also had lower mean growth rates. Combined supply of organic fertiliser and microbes increased available P, as well as growth rates, in both the customised and NPK/urea treatments. In contrast, NPK/urea-treated plots without these amendments demonstrated very low growth rates. The customised formulation was more effective with or without added organic fertiliser or inoculated microbes. Micronutrient supply stimulated flowering. Growth rates in trees supplied with NPK/urea were also promoted by micronutrients. Leaf flush production occurred in regular cycles and was unaffected by the nutrient amendments. After 3 years, the customised and organic fertiliser application increased soil pH and exchangeable Ca and Mg concentrations, although they remained below recommended levels for cocoa production. These treatments had little impact on soil C content (about 1.3%) which was also deficient. Exchangeable Al and total Zn concentrations were higher in soils amended with NPK/urea. The results of the trial provide evidence that utilisation of organic fertiliser in combination with customised nitrate-based formulations improves cocoa establishment, growth and soil properties and should be recommended as a replacement for the NPK/urea fertilisers traditionally used by farmers.

The perennial forage peanut is a stoloniferous, perennial tropical legume with potential for use in pastures. Based on the hypothesis that under intermittent stocking herbage accumulation would follow a similar pattern to that described for tropical forage grasses, the objective of this study was to evaluate canopy characteristics and herbage accumulation of forage peanut subjected to strategies of rotational grazing management. Treatments corresponded to all possible combinations of two grazing frequencies (regrowth interrupted at 95% and maximum canopy light interception – LI95% and LIMax) and two grazing severities (post-grazing canopy heights (CHs) equivalent to 40 and 60% of the pre-grazing heights). Treatments were imposed to experimental units during an adaptation period (from November 2014 to January 2015) and the subsequent experimental period lasted from February 2015 to April 2016, comprising two consecutive pasture growing seasons with no interruption between them (summer I to summer II). The pre-grazing targets of LI95% and LIMax corresponded to CHs of 13 and 18 cm, respectively. Forage peanut showed high grazing tolerance as pre-grazing leaf area index (except during summer I and autumn/winter), total herbage, and leaflet dry matter accumulation varied only with seasons. Higher rates of herbage production were recorded during summer I and summer II, followed by those during late and early spring and autumn/winter. Since there was no difference in the pattern of herbage accumulation between LI95% and LIMax and stolons predominated at the bottom of the canopies, forage peanut may be rotationally grazed with greater flexibility than most tropical forage grasses. Recommended pre-grazing CHs are within 13 and 18 cm, and post-grazing heights between 40 and 60% of the pre-grazing height.

Modification of the existing cropping practice is needed to maintain rice (Oryza sativa L.) productivity and reduce irrigation water input. A 2-year field experiment was conducted during the dry rice growing season of 2016 and 2017 at the Asian Institute of Technology, Pathum Thani, Thailand, to investigate the effects of establishment method and irrigation level on growth, yield, and water productivity of irrigated lowland rice. The treatments consisted of two Thai rice cultivars (Pathumthani 1 and RD57), two establishment methods (dry direct seeding [DDS] and transplanting [TP]), and three irrigation levels (continuous flooding [CF], 15 cm threshold water level below the soil surface for irrigation [AWD15], and 30 cm threshold water level below the soil surface for irrigation [AWD30]). Overall, the performance of RD57 was better than Pathumthani 1 under DDS with 50% higher grain yield and 90% higher water productivity at AWD15. RD57 also had higher shoot dry matter, number of tiller m–2, and number of panicle m–2 across establishment methods and irrigation levels. Grain yield and water productivity of RD57 were similar under two establishment methods across irrigation levels, whereas the performance of TP was better than DDS for Pathumthani 1 irrespective of irrigation levels. The highest grain yield and water productivity of Pathumthani 1 was observed at AWD15 under TP and that of RD57 under both establishment methods at the same irrigation level. AWD15 saved 26 and 32% irrigation water under TP and DDS, respectively, compared with TP-CF treatment combination. AWD15 irrigation level could be recommended for greater water productivity without compromising yield when Pathumthani 1 is cultivated through TP and RD57 is cultivated through either DDS or TP. Although water-saving potential was higher compared with CF, AWD30 is not recommended for irrigated lowland rice cultivation due to significant yield reduction.

The most important objective of lentil breeding programs is to develop new genotypes that are genetically more productive. Besides, it is necessary that the varieties obtained have short flowering cycles to allow the later sowing of summer crops. Selection is based through phenotypic means; however, we argue it should be based on genetic or breeding values because quantitative traits are often influenced by environments and genotype–environment interactions. The objectives of this study were to: (i) identify genotypes with the highest merit; (ii) estimate genetic parameters to know the genetic control of morphological traits in macrosperma and microsperma lentil types using best linear unbiased prediction (BLUP). Twenty-five recombinant inbred lines (RILs) from six F4 families selected on the basis of precocity and high yields were tested in four environments for important quantitative traits. The analysis of variance showed significant differences between genotypes, environments, and genotype–environment interactions for all the traits. Seven macrosperma- and two microsperma-type RILs were selected. Based on average ranking from breeding values and molecular data obtained with sequence-related amplified polymorphism (SRAP), the same genotypes were selected. Genotypic coefficients of variation, heritability across and by environment, and genetic correlation coefficients using BLUP were obtained. According to our results BLUP could replace molecular analysis methods because the selection process was simpler, more cost-effective, and more accurate. The breeding value of parents would give a better ranking of their genetic value than would their phenotypic value; therefore, the selection efficiency would be enhanced and the genetic gain would be more predictable. The selected genotypes could become potential commercial varieties or be used as parental lines in future hybridization programs.

On low-input smallholder farms of Kenyan upland landscapes, erosion of nutrient-rich topsoil strongly affects crop yields. Where maize (Zea mays) is intercropped on erosion-prone slopes, intercropping can potentially reduce soil erosion. The objective of this research was to quantify the contribution of crops and crop mixtures of different growth habits to erosion control and their influence on above-ground biomass and earthworm abundance as indicators of soil function in smallholder farming systems under a bimodal rainfall pattern in Western Kenya. The experiment involved five treatments, namely maize (Z. mays)/common bean (Phaseolus vulgaris) intercrop (maize intercrop), maize/common bean intercrop plus Calliandra (Calliandra calothyrsus) hedgerows and Calliandra mulch (Calliandra), sole Lablab (Lablab purpureus), sole Mucuna (Mucuna pruriens) and groundnut (Arachis hypogaea) intercropped with maize (during the short rains). The experiment was conducted over three consecutive cropping seasons and the cropping system had significant effects on soil loss, runoff, water infiltration, earthworm abundance and above-ground biomass and crop grain yield. The Calliandra treatment had the lowest runoff (11.6–17.2 mm ha−1) and soil erosion (31–446 kg ha−1 per season) in all the seasons, followed by the Mucuna treatment. Lablab was affected by disease and showed the highest soil erosion in the last two seasons. Infiltration was highest in Calliandra treatment, and earthworm abundance was higher under Mucuna and Calliandra treatments (229 and 165 earthworms per square metre, respectively) than under other crops. Our results suggest that including sole crops of herbaceous species such as Mucuna, or tree hedgerows with mixtures of maize and grain legumes has the potential to reduce runoff and soil erosion in smallholder farming. Additionally, these species provide a suitable habitat for earthworms which stabilise soil structure and macropores and thus potentially increase infiltration, further reducing soil erosion.

In cotton–wheat cropping system of Pakistan, wheat (Triticum aestivum L.) is harvested in late April; however, the optimum sowing time of Bt cotton is mid-March. This indicates a time difference of 4–6 weeks between the harvest of wheat and cotton sowing. It is hypothesized that this overlapping period may be managed by transplanting cotton seedlings (30–45 days old) in late April, after the harvest of wheat due to better performance of already established seedlings. To this end, this study was conducted to evaluate the allometric traits and fiber quality of transplanted Bt cotton after harvesting wheat in the cotton–wheat cropping system. The Bt cotton–wheat cropping systems were flat sown wheat (FSW)–conventionally tilled cotton, FSW–zero tilled cotton, ridge sown wheat–ridge transplanted cotton using 30- and 45-days-old seedlings, and bed sown wheat (BSW)–bed transplanted cotton (BTC) also using 30- and 45-days-old seedlings. The study was conducted at Vehari and Multan in Punjab, Pakistan. Bt cotton in BSW–BTC with 45-days-old seedlings showed better performance for allometric (leaf area index; (LAI), net assimilation rate; (NAR), and crop growth rate; (CGR)), seed cotton yield, and fiber traits (fiber uniformity, fiber length, fiber strength, and fiber fineness) in comparison to other treatments. Most of the fiber quality traits were positively correlated with allometric traits and biological yield (dry matter yield at maturity) at both locations, except correlations of CGR and LAI with fiber fineness and fiber length and NAR with fiber length. As plant growth and fiber quality of transplanted cotton was significantly higher than conventionally grown cotton, our data indicate transplanting is an interesting management practice for improving productivity in wheat–cotton cropping systems.

Sweetpotato (Ipomoea batatas, Convolvulaceae) is an important food crop in Sub-Saharan Africa (SSA). Lack of access to quality sweetpotato planting material after sweetpotato limits utilization of market oriented improved clones and new varieties. Obtaining clean planting material in the right quantity and quality is a challenge in the SSA region. Farmers often obtain planting materials from their own sources with multiple rooting, drawn from a previous crop or neighbors and face the risk of it being infected with sweetpotato viruses. The objective of this study was to examine the economic and physical yield performance of sandponics multiplication method by comparing with conventional soil method using optimal N-nutrient inputs. The performance of five sweetpotato cultivars (Irene, Delvia, Tanzania, Gweri, and Kabode) in the modified prototype sweetpotato nutrient media was evaluated. Vine production utilizing modified sandponics nutrient media with trellised plants was compared to the conventionally used soil media. Analysis of variance indicated that the main effects of cultivar and substrate were highly significant (p < 0.0001) for nodes produced, vine multiplication rate (VMR), number of cuttings produced, and vine length. In addition, cultivar by substrate interaction was highly significant at 0.01 probability level for nodes produced, VMR, and vine length. Vine multiplication rate was 33% higher in the sandponics system compared to the conventional soil method of multiplying sweetpotato vines. Among the cultivars studied, Irene was the most favorable cultivar with a VMR of 65.2 in sand and 45.5 in soil. The cost-effectiveness analysis indicates that the cost per cutting (i.e., 3–4 nodes) produced from sandponics method was 4.6 KSH (US$ 0.046) as compared to 3.1 KSH (US$ 0.031) per cutting produced from conventional method. Sandponics system is competitive due to its capability of increased VMRs. However, the optimal number of ratooning needs to be investigated to understand the economies of scale in future research.

Resilient cropping systems are required to achieve food security in the presence of climate change, and so several long-term conservation agriculture (CA) trials have been established in southern Africa – one of them at the Chitedze Agriculture Research Station in Malawi in 2007. The present study focused on a longitudinal analysis of 10 years of data from the trial to better understand the joint effects of variations between the seasons and particular contrasts among treatments on yield of maize. Of further interest was the variability of treatment responses in time and space and the implications for design of future trials with adequate statistical power. The analysis shows treatment differences of the mean effect which vary according to cropping season. There was a strong treatment effect between rotational treatments and other treatments and a weak effect between intercropping and monocropping. There was no evidence for an overall advantage of systems where residues are retained (in combination with direct seeding or planting basins) over conventional management with respect to maize yield. A season effect was evident although the strong benefit of rotation in El Niño season was also reduced, highlighting the strong interaction between treatment and climatic conditions. The power analysis shows that treatment effects of practically significant magnitude may be unlikely to be detected with just four replicates, as at Chitedze, under either a simple randomised control trial or a factorial experiment. Given logistical and financial constraints, it is important to design trials with fewer treatments but more replicates to gain enough statistical power and to pay attention to the selection of treatments to given an informative outcome.

This study identified decision variables influencing fertilizer adoption and optimal fertilizer rates among smallholder farmers in the Ethiopian highlands. The fertilizer adoption and fertilizer use were examined in four regional states using a questionnaire survey, which was administered to 2880 farm households. A double hurdle model was used to analyze factors influencing the two independent decisions of adoption of fertilizers and use of fertilizers. The model estimates of the first hurdle revealed that the probability of fertilizer adoption increased by 1.2% as household education status improved, by 1.4% for an increased number of active family members, by 5.6% with improved access to credit, by 3.4% with cooperative membership, by 3.3% with an increase in farm size, by 4.6% when soil and water conservation practices are employed, and by 3.4% when agroecology of the farm is located in the medium to highland zone. Conversely, the probability of fertilizer adoption reduced by 0.9% for an increase in family size, 0.6% with 1 km distance from all-weather road, 1.6% for a kilometer further to farm plots, and 0.9% for an increase in number of parcels. The intensity of use of fertilizers was influenced by education status of the household head, family size, access to credit, membership to cooperatives, use of crop rotation, annual income, number of farm plots owned, use of soil and water conservation, and agroecology. Therefore, a concerted effort is needed to encourage fertilizer adoption and optimum fertilizer use intensity by improving households’ resource endowment, institutional capacity to deliver services, and infrastructure development.

The area of individual leaves in oil palm has been conventionally estimated from a regression equation that is based on the size and number of leaflets. The aim of the present study is to verify the accuracy of this equation, which became standard in oil palm research. Therefore, true leaf area, measured with a video camera, was estimated from the product of number of leaflets per leaf (n) with mean length (l) times mid-width (w) of six of the longest leaflets (nlw). The database was assembled, annually for the first 4 years after planting, from 2961 leaves of dura × pisifera testcrosses descending from six distinct pisifera origins. The regression coefficients of the regression lines of nlw plotted against true area did not show a trend with age of the palms or a difference among pisifera origins. The common regression equation fitted through all data of this study accurately estimated true leaf area of the testcrosses and also the areas of 2- to 3.5-year-old dura palms of three distinct origins as well as 18-year-old tenera palms. These outcomes are at odds with the conventional regression equation that overestimates the true leaf areas by about 24%. A more recently-developed variant underestimates true area of the young tenera and dura palms by 28%, while overestimating true area of old tenera palms by 19%. Possible causes for these deviations from true area are discussed. The paper argues that parameters depending on leaf area of previous physiological studies need to be reassessed.

In response to the extensive development of upland rice on the hillsides of the Malagasy highlands, alternative cropping systems have been designed based on conservation agriculture (CA). As the promotion of CA in smallholder farming systems is still the subject of debate, its potential benefits for smallholder farmers require further assessment. In the context of resource-poor farmers and low-input production systems, nitrogen (N) is a major limiting nutrient. The effects of contrasted cropping systems have been studied on upland rice yield and N uptake in rainfed conditions: conventional tillage (CT) and CA with a mulch of maize or a legume (Stylosanthes or velvet bean). Decision Support Systems for Agrotechnology Transfer (DSSAT) crop growth model was used to quantify the soil N balance according to the season and the cropping system. The lowest yields were obtained in CA with a mulch of maize and were also associated with the lowest crop N uptake. Upland rice yields were higher or equivalent under CA with a legume mulch than under CT cropping systems. The supply of N was considerably higher in CA with a legume mulch than in CT, but due to higher leaching and immobilization in CA, the final contribution of N from the mulch to the crop was reduced although not negligible. DSSAT has been shown to be sufficiently robust and flexible to simulate the soil N balance in contrasting cropping systems. The challenge is now to evaluate the model in less contrasted experimental conditions in order to validate its use for N uptake and yield prediction in support to the optimization and design of new cropping systems.

Parthenium hysterophorus is a prolific invasive weed species, which infests many crops in over 40 countries around the world. A 2-year field study was carried out to quantify the potential impacts of this weed on direct-seeded rice. Parthenium weed was allowed to compete for 2, 4, 6 or 8 weeks after crop emergence, while full season weedy and weed-free plots were maintained as controls. Parthenium weed plants grew taller and attained more biomass as the competition duration prolonged. The yield and yield-related attributes of rice were negatively affected with increasing competition duration. The season-long competition caused the highest reductions in panicle number (28–34%), panicle length (26–27%), grains per panicle (22–23%) and grain yield (33 and 38%) of rice in both years. Weed competition for 2–8 weeks caused 5–34% and 6–33% losses in rice grain yield during both years, respectively. Importantly, Parthenium weed control after 8 weeks of competition did not improve rice yield significantly. The results suggested that Parthenium weed should be controlled in rice fields between 4 and 8 weeks after crop emergence under direct-seeded conditions to avoid over 10% yield losses.