The ‘acid rain’ problems in forests in The Netherlands are largely due to excessive aerial inputs of NH3 and NH4 from intensive livestock farms. Nitrification is slow under acid soil conditions, so a large part of the V available to the trees is in the ammonium form. In pot experiments the response of Douglas-fir to various NH4:NO3 ratios was tested, using a nitrification inhibitor. Rhizosphere pH was measured with microelectrodes. If nitrate contributed less than 20% to total N uptake, net carboxylate production was insufficient for internal pH control and the tree died. If more than 65% of the N absorbed was taken up as nitrate, net OH excretion by the roots occurred, leading to alkalization of the rhizosphere at the root tip and at the root growth zone. Thus, root growth can continue in strongly acid soils.
Tag: growth
Phosphorus and liming effects on early growth of selected plant species grown on an ultisol
A series of pot experiments were conducted to test the effect of phosphorus (P) application and liming on early growth performance of Zea mays, Mucuna pruriens and nine woody species (Albizia ferruginea, Cajanus cajan, Dactyladenia barteri, Dalbergia sissoo, Enterolobium cyclocarpum, Flemingia macrophylla, Gliricidia sepium, Leucaena leucocephala, and Pentacletra macrophylla) on an Ultisol. Low reponse to liming and high response to P application were observed in this trial. Early top growth of the eleven species was correlated to seed size and seed nitrogen (N), P, and calcium (Ca) contents. Highest correlation was observed with seed P content (r = 0.896). Large seeded size species (D. barteri, E. cyclocarpum, M. pruriens, and P. macrophylla) showed the least reponse to P application, while the remaining small seeded size species showed significant responses to P application. The large seeded species also showed relatively less increases in N, P and Ca uptakes with P application and liming. The pot test can be used in prescreening of woody species for use on low P and acid soils. The results also emphasize the need for seed size consideration in multipurpose trees and shrubs selection for establishment in low P and on degraded soils
Resource use and growth in semi-arid agroforestry systems
The work reported here aimed to provide a comprehensive database of core information to support the development and validation of process-based models of resource capture and growth in the semi-arid overstorey agroforestry systems. Intensive field studies were carried out in Kenya over a 30 month period and the results obtained were combined with data from a previous project to produce a dataset spanning a 4.5 year period. This dataset was then used to verify output from the HyPAR model. Allometric procedures developed from the pipe model theory (Lott et al., 1998) were used to estimate tree growth non-destructively throughout the observation period. Significant differences in tree size between the sole (Td) and dispersed agroforestry (CTd) treatments were established during the first 130 days after planting, probably because of competition with the associated crops. The above-ground biomass and trunk length and taper characteristics of the CTd trees remained inferior to those of Td trees throughout the observation period, seriously undermining the economic potential of this agroforestry system. Comparison of output from the HyPAR model against the observed results provided information pertinent to future model development. The model proved to be insufficiently flexible for end-users wishing to simulate the growth of different crops during the same simulation cycle, or to use model output to aid management decisions such as the timing of pruning. The allometric procedures used by the model to estimate canopy size from trunk diameter at breast height also proved incapable of accounting for reductions in canopy size resulting from pruning. Estimates of tree height are rounded to the nearest metre within the model, representing a potentially serious loss of resolution when annual increments often do not exceed 2 m. In addition, the numerous parameters required by the model would force most end-users to rely heavily on published information, potentially undermining the reliability of simulations.
Comparative growth of some multipurpose trees and shrubs grown at Machakos, Kenya
Growth rates of 29 multipurpose trees grown in an agroforestry arboretum for six years at a sub-humid to semi-arid climatic zone are presented. Exotic species such as Grevillea robusta, Sesbania grandiflora, Leucaena leucocephala, Cassia siamea and Sesbania sesban, some of which were outside their traditional climatic zones, had higher diameters, heights and bole volumes/tree (upto 130% more in certain cases) than of the indigenous species. However, poor performance of several species (both exotic and indigenous) would limit their agroforestry potentials at the evaluation site or other similar areas.
Reconstructing pre-agricultural expansion vegetation cover of Ethiopia
Landscape reconstructions can be used to define a reference condition from which to assess the magnitude of land changes caused by human influence. Since the beginning of the last century, the population of Ethiopia has increased drastically with large effects on the natural vegetation and biodiversity. However, the original land cover patterns in Ethiopia have not been precisely mapped, which hinder the identification of the biophysical and socio-economic factors that contributed to the current landscape patterns. The objective of this study was to reconstruct the past century vegetation landscapes of Ethiopia (i.e. vegetation cover before agricultural expansion) and identify which ecosystems have been most affected by land changes. First, the net primary productivity (NPP) was modelled based on the climatic constraints of natural vegetation growth (water availability, solar radiation and minimum temperature) derived from remote sensing and climate data. This analysis showed that water availability is the most critical constraint for vegetation growth for all regions and land cover types in Ethiopia. Then, the past vegetation was mapped based on predicted NPP. Our results show that i) the extent of broadleaved evergreen or semi-deciduous forest, open broadleaved deciduous forest, closed to open shrubland, mosaic forest-shrubland/grassland, sparse vegetation and grassland was 18.8%, 12.4%, 20.6%, 31.5%, and 16.8%, respectively, and ii) current agricultural landscapes were previously covered mainly by broadleaved evergreen and deciduous forest, which encompassed 38.9%. The least affected by agricultural expansion were sparse vegetation and grassland. Our study provides novel insights on pre-agricultural expansion landscapes in Ethiopia with critical information for scientists and other stakeholders working on the restoration and rehabilitation of degraded areas.
Effect of organic fertilizer on the growth and fruit yield of six paprika (Capsicum annum L.) cultivars in Malawi
The production of paprika (Capsicum annum L.) under small-scale farm conditions in southern Africa is constrained by low soil fertility and lack of appropriate cultivars. The objective of this study was to determine the growth responses and fruit yields of six cultivars of paprika to organic and inorganic nutrient sources. The study was conducted in 2007 and 2008 at Chitedze Agricultural Research Station in Malawi. A combination of six paprika cultivars and four nutrient sources, namely (1) organic input from Gliricidia, (Gliricidia sepium) biomass, (2) inorganic fertilizer, (3) integrated nutrient input (Gliricidia biomass + inorganic fertilizer), and (4) control (no nutrient input) were compared. Each combination was replicated five times. A split-plot design was used where nutrient sources formed the main plot and cultivars the sub-plots. Plant height differed due to nutrient source in 2007 and 2008, while differences due to cultivar were minor. The control plots produced the shortest plants (height 60 cm). Numbers of branches and fruits per plant differed due to nutrient source and cultivar during most of the study period. Plants receiving either organic inputs (Gliricidia biomass) alone or the integrated nutrient input alone had significantly higher stem, leaf and fruit weight compared with the control. Average fruit yield was lower in control plots than in plots receiving the organic input alone or the integrated nutrient input. Among cultivars, Papri-King, Papri-Supreme and Papri-Queen produced higher dry fruit yield. The ASTA and RAL colour rating was within the internationally accepted range for fruit from the treatments.
Climate change and tree genetic resource management: maintaining and enhancing the productivity and value of smallholder tropical agroforestry landscapes. A review
Anthropogenic climate change has significant consequences for the sustainability and productivity of agroforestry ecosystems upon which millions of smallholders in the tropics depend and that provide valuable global services. We here consider the current state of knowledge of the impacts of climate change on tree genetic resources and implications for action in a smallholder setting. Required measures to respond to change include: (1) the facilitated translocation of environmentally-matched germplasm across appropriate geographic scales, (2) the elevation of effective population sizes of tree stands through the promotion of pollinators and other farm management interventions; and (3) the use of a wider range of plastic species and populations for planting. Key bottlenecks to response that are discussed here include limitations in the international exchange of tree seed and seedlings, and the absence of wellfunctioning delivery systems to provide smallholders with better-adapted planting material. Greater research on population-level environmental responses in indigenous tree species is important, and more studies of animal pollinators in farm landscapes are required. The development of well-functioning markets for new products that farmers can grow in order to mitigate and adapt to anthropogenic climate change must also consider genetic resource issues, as we describe.
Albizia procera – white siris for reforestation and agroforestry
Albizia is a large fast-growing tree that occurs on many different sites. It occurs in forests and savanna woodlands, but prefers moist sites. This species provides wood for a variety of purpose, nutrition, fodder for livestock and shade for tea plantations. This article gives a brief account of this multipurpose tee and how it can be used for reforestation and agroforestry systems.
Uses and vulnerability of ligneous species exploited by local population of northern Burkina Faso in their adaptation strategies to changing environments
Background: Arid and semi-arid areas of West Africa are highly subject to climate change effects. This is combined to other drivers such as population growth and livestock number increase. To cope with such changing environment, endogenous adaptation strategies of poor local communities rely on the use of natural resources through empirical knowledge. Unfortunately, these knowledge and practices are insufficiently known to policy makers, and this hampers their consideration in the elaboration of adaptation strategies. A household survey was conducted in the Sillia village in northern Burkina Faso using semi-structured interviews. This study identified most used (preferred) species in this changing environment together with their ethnobotanical use value (VUET). Results: Overall, 86 ligneous species were listed in seven (7) use categories: human nutrition, fodder, fuel, traditional medicine, handicraft, construction and trade. From the 86 species, 11 appeared the most preferred by local population (VUET 6). Except Piliostigma reticulatum and Boscia senegalensis, all these species were part of the 21 very vulnerable species as revealed by the study. Tamarindus indica, Balanites aegyptiaca, Lannea microcarpa and Vitellaria paradoxa are the first most preferred species (VUET 7) and also most vulnerable (IV > 2.5). In this changing environment, Cassia sieberiana, Combretum micranthum, Balanites aegyptica have, for instance, become the main species used in traditional medicine replacing Ximenia americana, Coclospermum tinctorim, Maytenus senegalensis and Securidaca longepedunculata, formerly used for this need. Also, Piliostigma reticulatum is the main species used in farm lands to combat low soil fertility. Pterocarpus lucens and Adansonia digitata are the main fodder species both during dry and rainy seasons. Apart from the household surveys, vegetation survey was conducted on 96 plots in Sillia. The results showed that 25 species cited in the household surveys had locally disappeared, 22 were rare, 5 were abundant and the others were relatively abundant. Certain collection practices of given species in many use categories increase their vulnerability. Conclusion: This study documented preferred species in the adaptation strategies to changing environments and also assessed their vulnerability status under human influence; it is therefore of great use for designing sustainable management. © 2017 The Author(s).
Antimicrobial Drimane Sesquiterpenes Contribute to Balanced Antagonism but Do Not Structure Bacterial and Fungal Endophytes in the African Pepper Bark Tree Warburgia ugandensis
The African pepper bark tree, Warburgia ugandensis, accumulates antimicrobial drimane sesquiterpenes in all of its organs. One hypothesis states that plant defense compounds determine endophyte community structure. Another hypothesis suggests that they just facilitate the endophytic lifestyle by exerting a balanced antagonism. To explore this, a representative selection of endophytic bacterial and fungal isolates from this tree species was assayed together with six non-endophytic strains to determine their tolerance and susceptibility to the root and leaf extract fraction containing high and low drimane sesquiterpene amounts respectively. Inhibitory effects were explored by assessing both growth and growth efficiency, the latter of which relates respiratory activity to growth. The susceptibility of the tested strains showed considerable variation and the obtained patterns did not allow a clear distinction between root and leaf endophytes as well as endophytes and non-endophytes. In addition, all strains were also assayed against juglone, an antimicrobial and redox-active aromatic naphthoquinone. A comparison of differential pulse voltammograms and efficacy in variants of the deoxyribose degradation assay revealed that drimane sesquiterpenes possess anti- and pro-oxidant activities that compare to those of juglone. Leaf endophytes showed higher resistance to oxidative stress than root endophytes, quite contrary to the actual exposure. The obtained results support the notion that structural diverse plant defense compounds can contribute to a balanced antagonism against but not to structuring of endophyte communities. Oxidative stress seems to be involved in generating this effect albeit it cannot explain it alone.