Current knowledge gaps are identified and new lines of research for improving our understanding of the processes that drive deep root growth and functioning are proposed. This ultimately leads to a reflection on an alternative paradigm that could be used in the future as a unifying framework to describe and analyse deep rooting. Despite the many hurdles that pave the way to a practical understanding of deep rooting functions, it is anticipated that, in the relatively near future, increased knowledge about the deep rooting traits of a variety of plants and crops will have direct and tangible influence on how we manage natural and cultivated ecosystems.

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Fine root dynamics is a main driver of soil carbon stocks, particularly in tropical forests, yet major uncertainties still surround estimates of fine root production and turnover. This lack of knowledge is largely due to the fact that studying root dynamics in situ, particularly deep in the soil, remains highly challenging. We explored the interactions between fine root dynamics, soil depth, and rainfall in mature rubber trees (Hevea brasiliensis Müll. Arg.) exposed to sub-optimal edaphic and climatic conditions. A root observation access well was installed in northern Thailand to monitor root dynamics along a 4.5 m deep soil profile. Image-based measurements of root elongation and lifespan of individual roots were carried out at monthly intervals over 3 years. Soil depth was found to have a significant effect on root turnover. Surprisingly, root turnover increased with soil depth and root half-life was 16, 6–8, and only 4 months at 0.5, 1.0, 2.5, and 3.0 m deep, respectively (with the exception of roots at 4.5 m which had a half-life similar to that found between depths of 1.0 and 2.5 m). Within the first two meters of the soil profile, the highest rates of root emergence occurred about 3 months after the onset of the rainy season, while deeper in the soil, root emergence was not linked to the rainfall pattern. Root emergence was limited during leaf flushing (between March and May), particularly within the first two meters of the profile. Between soil depths of 0.5 and 2.0 m, root mortality appeared independent of variations in root emergence, but below 2.0 m, peaks in root emergence and death were synchronized. Shallow parts of the root system were more responsive to rainfall than their deeper counterparts. Increased root emergence in deep soil toward the onset of the dry season could correspond to a drought acclimation mechanism, with the relative importance of deep water capture increasing once rainfall ceased. The considerable soil depth regularly explored by fine roots, even though significantly less than in surface layers in terms of root length density and biomass, will impact strongly the evaluation of soil carbon stocks.

Climate change is viewed as a cause in accelerating the rate of invasion by alien species in addition to the globalization of anthropogenic activities. Ecological niche modeling has become an instrument in predicting invasion from natural or invaded ranges to uninvaded ranges based on the presence records of organisms and environmental parameters. This study explored the changes in the distributions of globally noxious alien species (Aegratina adenophora, Ageratum conyzoides, Chromolaena odorata, Lantana camara, Mikania micrantha, and Parthenium hysterophorus) in Bhutan, to provide evidence that even a mountain environment is under the threat of invasion given the change in climatic conditions. With fairly high accuracy, the model results suggest that there will be a potential increase in the areas of invasion among most of the species, except Parthenium hysterophorus, which will experience a northerly shift and decline in distribution. The results also indicate changes in patterns of invasion, some becoming more concentrated toward a given direction, while others become more dispersed over time. This study provides a framework that can be used in the strategic control of the species, future detection surveys, and further research.Agronomy 2019, 9, 442 2 of 16 recreational amenities for ecotourism, deforestation, and upland agriculture adoption [19], compounded by climatic change, have exposed vulnerable mountains to disturbance [20][21][22][23][24]. The warming climate has resulted in an altitudinal upward shifting of cold-temperate species (e.g., Fagus sylvatica) and Mediterranean species (Quercus ilex) in Catalina, Spain [25]. In Bhutan, farmers have reported that due to climate change, invasive plants have started to colonize highland pasture, preventing the regeneration of fodder grasses [26]. Given a change in climatic conditions, adjacent lowland flora heavily influence species composition in mountain communities [27]. Mountain environments are rated as highly sensitive to climate change due to a short growing season and limited niches for resident species [28][29][30][31][32]. Human activities and climate change has led to invasions in mountainous areas in Europe, Australia, South Africa, Kashmir, Hawaii, the United States Pacific Northwest, and Chile [20]. Furthermore, alien invasive weeds are habitat generalists, with high plasticity to adapt to wide ranges of climatic conditions [33][34][35][36][37]. Species tolerant of wider environmental conditions are frequently associated with the following physiological traits: an efficient use of nutrients in low nutrient soils, higher root-shoot ratio in arid systems and a lower root-shoot ratio in light-limited systems for resource acquisition, lower leaf construction costs and higher photosynthetic energy use efficiency as well as early phenology in arid systems [38,39].With its inhospitable terrain and strong conservation strategies (maintaining 60% or more forest cover, with more than 51% designated as protected areas and with a rigid forest management rule...

Weeds represent a significant problem in Thailand’s sugarcane production. The various cycles of sugarcane cultivation result in degrees of weed severity in which each species requires a different weed control method, the most popular of which is the post-emergence herbicide method. However, sugarcane farmers often use incorrect rates, and operators’ safety is missing or applications are not selective, causing toxicity and interrupted growth of sugarcane. The effects of post-emergence herbicide types, time, and application rates are presented herein, through an experiment in Northeast Thailand, conducted in a randomized complete block design (RCBD) with four replications. The herbicides paraquat and ametryn were evaluated, with paraquat being more effective, yet resulting in higher toxicity and lower yield components. We may conclude through our experiments that ametryn and paraquat can be applied only once for sugarcane at the tillering stage and at rates of 540 and 2400 g ai ha−1, respectively. These rates were lower than the recommended rates, which represented the minimum doses necessary to control Thailand’s dominant weed species like Brachiaria distachya (L.) Stapf., Dactyloctenium aegyptium (L.) P.B., Praxelis clematidea R.M King & H. Rob and Pennisetum polystachion (L.) Schult. Consequently, the adequate control of weeds is a rather case-specific situation and therefore each weed species should be taken into account.

International audienceUnderstanding better the interactions between root systems in associated crops is significant for basic knowledge in plant science and to help designing cropping systems. Current research on inter-specific root interactions concentrates on static descriptions of the horizontal extension of root systems or on the dynamics of provoked root encounters. This study considers detailed observations of the dynamics of inter-specific root interactions, in the vertical plane, at both the whole root system and the individual root levels. Corn and young rubber trees were grown in association in artificial conditions that excluded the possibility of competition for resources, using rhizoboxes, i.e. thin containers with a transparent wall. The paper presents novel approaches, such as the study of root system growth trajectories, to document root system development in terms of overall growth rate, colonization of soil space and individual root growth patterns. It was found that (i) corn roots developed towards rubber roots until a contact was established, (ii) rubber roots expanded faster and more vertically in association with corn, (iii) the expansion rates of both root systems varied concomitantly and (iv) inter-specific root encounters resulted in reduced elongation rates in both species. Implications of these results for corn/rubber intercropping are discussed. This work advocates in favour of a better understanding of under-ground facilitative effects between species. If understood enough to be manipulated, such knowledge might become a powerful tool for the design of more sustainable and efficient cropping systems

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Background: Chemical fertilizer is very expensive for most smallholder farmers in northeastern Thailand. Grain legumes can be grown in dry season to provide cash income and residues for green manure for succeeding crop. The current study was to evaluate the effect of groundnut stover incorporation to the soil integrated with chemical fertilizer on growth and yield of succeeding rice crop grown under rainfed conditions. Methods: Groundnut planted in dry season by supplemental irrigation. At harvest time, groundnut stover were sampled to determine the dry weight and analysis for nutrients content, as well as calculated the amount of nutrients return to the soil. Incorporation of groundnut stover combined 50% dose of chemical fertilizer was compared with 100% dose of chemical fertilizer treatment using by the farmer at two locations. Growth and yield of succeeding rice crop were evaluated at harvest. Result: Incorporation of groundnut stover combined 50% dose of chemical fertilizer had similar grain yields of rice to that of using 100% dose of chemical fertilizer alone as use by the farmers. This indicates that groundnut grown in dry season provided not only cash income, but also for green manure to the succeeding rice crop.