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Seed germination studies are often used to predict the potential of plants to extend their global distribution. In this research, the effect of gibberellic acid (G[A.sub.3]) concentrations, pre-chilling, temperature, water and salt stresses, pH, high-temperature pretreatment, planting depth, and flooding on seed germination and seedling emergence of three Amaranthus retroflexus L. populations was investigated. G[A.sub.3] concentration significantly affected seed germination of all three A. retroflexus populations grown under light/dark conditions. All three populations germinated under constant (10,15, 20, 25, and 30 [degrees]C) and alternating (20/15, 25/18, and 35/25 [degrees]C (day/night)) temperatures. The optimum alternating temperature for germination of all three populations was 18/25 [degrees]C day/night. Seed germination was severely reduced under moisture and salt stresses. Seedling emergence was reduced on the soil surface by increasing the planting depth from 2.5 to 7.5 cm, and no seedlings emerged when the planting depth of seeds was more than 10 cm. The results of this research help us to understand the germination capacity and requirements of A retroflexus in different environments and also provide information to help better control the weed. Key words: alternating and constant temperatures, pH, planting depth, seed germination, water stress, Introduction Amaranthus retroflexus L. is a summer annual weed belonging to the Amaranthaceae (Holm et al. 1997). It is native to central and eastern north America and recognized as one [...]

Context: Seed germination and seedling emergence are affected by many environmental factors. Knowledge regarding factors affecting seed germination of spiny cocklebur (Xanthium spinosum L.) and common cocklebur (X. strumarium L.) could help determine their potential distribution and control strategies. Aims: The present study was conducted to investigate the effect of key environmental factors on seed germination and seedling emergence of spiny cocklebur and common cocklebur. Methods: Seed germination of spiny cocklebur and common cocklebur was tested at various constant and alternating temperatures, pH, salinity and moisture stress. The effect of flooding height, burial depth and soil type on seedling emergence was also investigated. Key results: The optimum constant temperature for germination of spiny cocklebur was 25°C, and 35°C and higher for common cocklebur. Under alternating temperature, maximal germination was at 25/15°C and 35/15°C for spiny cocklebur and common cocklebur, respectively. Maximum germination of both spiny cocklebur and common cocklebur was at neutral pH. Spiny cocklebur germination was not suppressed as much by lower and higher pH or by an increasing salinity as was common cocklebur germination. Conclusions: Common cocklebur appears to be better adapted to warmer environments than is spiny cocklebur, but less so to a broad range of soil pH and salinity stress. Implications: The different germination responses of common cocklebur and spiny cocklebur to the environmental factors of temperature, pH and salinity imply that the two species may occupy different niches across the landscape. Our knowledge of these responses can help in identifying potential areas for invasion for increased monitoring and management. Information on factors affecting spiny cocklebur (Xanthium spinosum) and common cocklebur (X. strumarium) seed germination could help us determine their potential distribution in different regions and their effective control strategies. Maximum germination of both spiny cocklebur and common cocklebur was at neutral pH. Spiny cocklebur germination was less sensitive to high and low pH, salinity, flooding and surface burial than was common cocklebur germination, indicating that it may be better adapted to the broader range of conditions. Image by Faezeh Zaefarian. [ABSTRACT FROM AUTHOR]

Conservation agriculture (CA) is being promoted as an energy efficient and cost-effective farming system that conserves soil and water and improves crop yields. Adoption of this farming system can contribute to attainment of Sustainable Development Goal (SDG) 2: end hunger, achieve food security and improved nutrition, and promote sustainable agriculture. However, the adoption rate of this new farming technique by smallholder farmers in sub-Saharan Africa (SSA) is low. The trade-offs and synergies related to the three pillars that anchor CA have not, however, been investigated in the context of Botswana. Farmers are faced with trade-offs in the use of crop residue in CA as mulch with traditional use as feed for livestock. This paper reviews the components of CA with a view to contribute to the development of CA strategies for Botswana. We show that adoption of CA in SSA is challenged by lack of weed control measures, the lack of a market for grain legumes and competing uses of crop residue. The paper highlights the discrepancy between CA methods and current government subsidies, issues that may restrain the adoption of CA in Botswana. The paper concludes by making recommendations for research and policy development for sustainable CA practices in Botswana. [ABSTRACT FROM AUTHOR]

BACKGROUND Low rainfall is a major limitation to expanding the dairy industry in semi-arid environments in East Africa. In such dry areas, plants need to keep their tissues hydrated and stomata open for carbon exchange and to grow. On this basis, we assessed the productivity of 10 lines of Napier grass ( Pennisetum purpureum Schum.), which formed three yield clusters: low yielding ( LYC), moderate yielding ( MYC), and high yielding ( HYC), in a wet highland (Muguga) and semi-arid lowland (Katumani) of Kenya. Stomatal conductance ( gs), leaf water potential ( LWP) and relative water content ( RWC) were monitored, and water use simulated, over four growth cycles in 2012. These were used with measurements of leaf area index ( LAI) and plant dry weight to explore the possible use of these physiological parameters for assessing productivity potential of Napier grass accessions. RESULTS The plants were less stressed at Muguga, where gs was 700-1000 mmol m−2 s−1, LWP −0.4 to −0.9 MPa and RWC was 82-95%; these values at Katumani were 450-750 mmol m−2 s−1, −0.7 to −1.4 MPa and 74-93%, respectively. Total water use at Katumani was of the order HYC ≈ MYC (390 mm) > LYC (370 mm), and water use efficiency ( WUE, kg ha−1 mm−1) followed the same order HYC (34.3) > MYC (32.6) > LYC (24.9); whereas at Muguga water use averaged 710 mm for HYC and MYC, greater than 676 mm for LYC, and WUE (kg ha−1 mm−1) averaged 29.2 for HYC and MYC, and 19.4 for LYC. CONCLUSIONS The three water stress indices were poor, whereas vigorous early canopy development (determined as LAI) was a more reliable predictor of productivity potential of Napier grasses. In these dry environments, therefore, early rapid canopy development can be an effective indicator of yield potential and a credible selection criterion. © 2016 Society of Chemical Industry [ABSTRACT FROM AUTHOR]