In discussions on root research methods, so far the choice of sampling schemes seem to have been neglected topics. I this paper sampling schemes are discussed for various situations. it is shown that the schemes used traditionally for raw crops such as serials may give a bias of upto 30% on total root dry weight. More reliable sampling schemes are presented, as well as possibilities for correction of data from traditional sampling.available data of variation is root mass per auger sample are summerised to calculate the number of replicate samples required to detect differences (of given magnitude) between two means. The coefficient of variation of root weight per auger sample seem to be fairly constant at around 40% in grassland, with slightly higher value to deeper layer of soil.
Tag: roots
Global change and root function
Global change includes land-use change, elevated CO2 concentrations, increased temperature and increased rainfall variability. All four aspects by themselves and in combination will influence the role of roots in linking below- and above-ground ecosystem function via organic and inorganic resource flows. Root-mediated ecosystem functions which may be modified by global change include below-ground resource (water, nutrients) capture, creation and exploitation of spatial heterogeneity, buffering of temporal variations in above-ground factors, supply and storage of C and nutrients to the below-ground ecosystem, mobilization of nutrients and C from stored soil reserves, and gas exchange between soil and atmosphere including the emission from soil of greenhouse gases.The theory of a functional equilibrium between root and shoot allocation is used to explore predicted responses to elevated CO2 in relation to water or nutrient supply as limiting root function. The theory predicts no change in root:shoot allocation where water uptake is the limiting root function, but substantial shifts where nutrient uptake is (or becomes) the limiting function. Root turnover will not likely be influenced by elevated CO2, but by changes in regularity of water supply. A number of possible mechanisms for root-mediated N mineralization is discussed in the light of climate change factors. Rhizovory (root consumption) may increase under global change as the balance between plant chemical defense and adapted root consuming organisms may be modified during biome shifts in response to climate change. Root-mediated gas exchange allows oxygen to penetrate into soils and methane (CH4) to escape from wetland soils of tundra ecosystems as well as tropical rice production systems. The effect on net greenhouse gas emissions of biome shifts (fens replacing bogs) as well as of agricultural land management will depend partly on aerenchyma in roots
Agricultural concepts of roots: from morphogenetic to functional equilibrium
Concepts of the importance of root growth and function for plant production have changed gradually over the past century from a ‘morphogenetic equilibrium’ between root and shoot growth, which can be summarized as ‘the more roots the better shoot growth’, to a ‘functional equilibrium’ which puts emphasis on the water and nutrient uptake by the root system and not on the size of the root system as such. In fact, separate optima for root growth and shoot growth (dependent on root function) can often be distinguished. To obtain maximum crop production, relatively small root systems can be sufficient, provided the supply of water and nutrients is continuously high. Agricultural interventions aimed at increasing rooting depth by lowering the water-table or by deep soil tillage may be counterproductive for plant growth. Larger root systems may, however, reduce risks under rapidly changing environmental conditions and may increase nutrient use efficiency and hence reduce nutrient losses to the environment. Concepts are discussed in a historical perspective and examples are given of the empirical evidence to support or refute them.
Loss of dry matter and cell contents from fibrous roots of sugar beet due to sampling, storage and washing
To obtain correction factors for estimating root dry weight from washed samples and to test the efficiency of various procedures for storing root samples, dry matter losses were determined by simulating root washing methods with roots obtained from a nutrient culture. For sugar beet dry matter losses were higher than values previously found for wheat and ryegrass: about 30% for the procedure normally used and about 40% for samples pretreated with sodium pyrophosphate. The largest share of water-soluble sugars was lost from root samples within one day of storing roots. The N content of roots expressed on the basis of remaining dry matter rose first during handling of the root samples and decreased in samples stored for a longer period. In most cases no cell wall material (cellulose and lignin) is lost from the root samples; expressed on the basis of remaining dry weight the contents consequently rose.
Farmer-led community institutions: key to reversing land degradation in the 21st century
Reversing global land degradation is about better and simpler technologies, better national policies and much more. But ultimately it is about rural people and their institutions. The greatest prospect for reversing land degradation in the next century is the evolution of real farmer-led community institutions that take charge and transform the way research and extension in land management are done. Broad-based evidence for this is emerging. This paper will examine this as part of a process of people taking back greater control of their furures through decentralization, democracy and local leadership. Examples of locally-led processes in natural resource conservation suggest two successful streams: (1) institutions that are developed independently by local communities and managed by them, whose subsequent activities may not be assisted by outside stakeholders, and (2) local conservation institutions that are initiated and guided by the public sector.
Mathematical models on diffusion of oxygen to and within plant roots, with special emphasis on effects of soil-root contact: II. Applications
In relation to explanations of anaerobiosis in the field, mathematical models pre- sented in part I are evaluated in the light of the disparity between the low oxygen pressure required by plant roots in well-stirred nutrient solutions and the rather high values apparently required in the field. Water film and rhizosphere respiration do not fully explain this dis- parity. Soil-root contact as described in part I is shown to considerably affect the partial pressure of oxygen required for unrestricted aerobic respiration.
Theory and description of the 3D Hi-sAFe agroforestry model
Auger sampling, in-growth cores and pin board methods
This chapter outlines those methods for assessing root systems structure and function in the field which are based on washing roots free from the soil in which they grew. Some of these methods are included in previous reviews (Kolesnikov 1971; Böhm 1979). The methods are either disruptive or totally destructive to the root system being studied and to the immediate environment (Taylor et al. 1991).
Ecological interactions, management lessons and design tools in tropical agroforestry systems
During the 1980s, land- and labor-intensive simultaneous agroforestry systems (SAFS) were promoted in the tropics, based on the optimismon tree-crop niche differentiation and its potential for designing tree-crop mixtures using high tree-densities. In the 1990s it became clearer that although trees would yield crucial products and facilitate simultaneous growing of crops, they would also exert strong competitive effects on crops. In the meanwhile, a number of instruments for measuring the use of growth resources, exploratory and predictive models, and production assessment tools were developed to aid in understanding the opportunities and biophysical limits of SAFS. Following a review of the basic concepts of interspecific competition and facilitation between plants in general, this chapter synthesizes positive and negative effects of trees on crops, and discusses how these effects interact under different environmental resource conditions and how this imposes tradeoffs, biophysical limitations and management requirements in SAFS. The scope and limits of some of the research methods and tools, such as analytical and simulation models, that are available for assessing and predicting to a certain extent the productive outcome of SAFS are also discussed. The review brings out clearly the need for looking beyond yield performance in order to secure long-term management of farms and landscapes, by considering the environmental impacts and functions of SAFS.
Effect of field establishment methods on root-knot nematode (Meloidogyne spp) infection and growth of Sesbania sesban in western Kenya
Pot studies indicated that root-knot nematode (Meloidogyne javanica) infection reduces sesbania (Sesbania sesban) growth and planting methods modify the nematode damage, but their effects on sesbania biomass production at the field scale are not known. A field study was conducted in western Kenya for 2 yr, comparing direct seeding of sesbania with transplanting of bare-rooted seedlings in pure stands, with and without nematicide application in the field and in the nursery. In moist conditions, neither planting method nor nematicide had any influence on seedling survival and early growth. When early season rainfall was low and erratic, transplanted seedlings survived and grew better than seedlings from direct sowing, and nematicide application in the field and/or nursery improved seedling survival. Direct seeded sesbania had significantly less nematode galling and smaller nematode populations in the roots than transplanted sesbania. Both the establishment methods produced similar quantities of biomass, but direct seeded sesbania produced significantly greater biomass than the transplanted crop, if seedlings were already infected with nematodes in the nursery. Nematode infection on average reduced total sesbania biomass by 19%. Where sesbania cover crops have to be established by transplanting for socio-economic reasons, it is essential to use healthy seedlings free from nematodes for a good plant stand and early growth. Nematode-free seedlings can be produced on farms by at least one month of solarization of seedbeds. Neither field establishment method, nor nematicide application altered the soil nematode populations over a 12-month period. This means that the potential threat of increased Meloidogyne populations to nematode-susceptible crops following sesbania cover crops remains the same irrespective of how sesbania is established.