Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Sustaining conservation values in selectively logged tropical forests: the attained and the attainable
    Putz, F.E. ; Zuidema, P.A. ; Synnott, T. ; Peña Claros, M. ; Pinard, M.A. ; Sheil, D. ; Vanclay, J.K. ; Sist, P. ; Gourlet-Fleury, S. ; Griscom, B. ; Palmer, J. ; Zagt, R. - \ 2012
    Conservation Letters 5 (2012)4. - ISSN 1755-263X - p. 296 - 303.
    rain-forest - southeast-asia - impact - biodiversity - disturbance - management - diversity - biomass - borneo - carbon
    Most tropical forests outside protected areas have been or will be selectively logged so it is essential to maximize the conservation values of partially harvested areas. Here we examine the extent to which these forests sustain timber production, retain species, and conserve carbon stocks. We then describe some improvements in tropical forestry and how their implementation can be promoted. A simple meta-analysis based on >100 publications revealed substantial variability but that: timber yields decline by about 46% after the first harvest but are subsequently sustained at that level; 76% of carbon is retained in once-logged forests; and, 85–100% of species of mammals, birds, invertebrates, and plants remain after logging. Timber stocks will not regain primary-forest levels within current harvest cycles, but yields increase if collateral damage is reduced and silvicultural treatments are applied. Given that selectively logged forests retain substantial biodiversity, carbon, and timber stocks, this “middle way” between deforestation and total protection deserves more attention from researchers, conservation organizations, and policy-makers. Improvements in forest management are now likely if synergies are enhanced among initiatives to retain forest carbon stocks (REDD+), assure the legality of forest products, certify responsible management, and devolve control over forests to empowered local communities.
    Flood occurence mapping of the middle Mahakam lowland area using satelite radar
    Hidayat, H. ; Hoekman, D.H. ; Vissers, M.A.M. ; Hoitink, A.J.F. - \ 2012
    Hydrology and Earth System Sciences 16 (2012). - ISSN 1027-5606 - p. 1805 - 1816.
    forested wetlands - river basin - inundation - kalimantan - indonesia - patterns - example - borneo - palsar - model
    Floodplain lakes and peatlands in the middle Mahakam lowland area are considered as ecologically important wetland in East Kalimantan, Indonesia. However, due to a lack of data, the hydrological functioning of the region is still poorly understood. Among remote sensing techniques that can increase data availability, radar is well-suitable for the identification, mapping, and measurement of tropical wetlands, for its cloud unimpeded sensing and night and day operation. Here we aim to extract flood extent and flood occurrence information from a series of radar images of the middle Mahakam lowland area. We explore the use of Phased Array L-band Synthetic Aperture Radar (PALSAR) imagery for observing flood inundation dynamics by incorporating field water level measurements. Water level measurements were carried out along the river, in lakes and in peatlands, using pressure transducers. For validation of the open water flood occurrence map, bathymetry measurements were carried out in the main lakes. A series of PALSAR images covering the middle and lower Mahakam area in the years 2007 through 2010 were collected. A fully inundated region can be easily recognized on radar images from a dark signature. Open water flood occurrence was mapped using a threshold value taken from radar backscatter of the permanently inundated river and lakes areas. Radar backscatter intensity analysis of the vegetated floodplain area revealed consistently high backscatter values, indicating flood inundation under forest canopy. We used those values as the threshold for flood occurrence mapping in the vegetated area.
    Soils on exposed Sunda Shelf shaped biogeographic patterns in the equatorial forests of Southeast Asia
    Slik, J.W.F. ; Aiba, S.I. ; Bastian, M. ; Brearley, F.Q. ; Cannon, C.H. ; Eichhorn, K.A.O. ; Fredriksson, G. ; Kartawinata, K. ; Laumonier, Y. ; Mansor, A. ; Marjokorpi, A. ; Meijaard, E. ; Morley, R.J. ; Nagamasu, H. ; Nilus, R. ; Nurtjahya, E. ; Payne, J. ; Permana, A. ; Poulsen, A.D. ; Raes, N. ; Riswan, S. ; Schaik, C.P. ; Sheil, D. ; Sidiyasa, K. ; Suzuki, E. ; Valkenburg, J.L.C.H. van; Webb, C.O. ; Wich, S. ; Yoneda, T. ; Zakaria, R. ; Zweifel, N. - \ 2011
    Proceedings of the National Academy of Sciences of the United States of America 108 (2011)30. - ISSN 0027-8424 - p. 12343 - 12347.
    last glacial maximum - carbon stocks - vegetation - east - sea - environments - biodiversity - indicators - climate - borneo
    The marked biogeographic difference between western (Malay Peninsula and Sumatra) and eastern (Borneo) Sundaland is surprising given the long time that these areas have formed a single landmass. A dispersal barrier in the form of a dry savanna corridor during glacial maxima has been proposed to explain this disparity. However, the short duration of these dry savanna conditions make it an unlikely sole cause for the biogeographic pattern. An additional explanation might be related to the coarse sandy soils of central Sundaland. To test these two nonexclusive hypotheses, we performed a floristic cluster analysis based on 111 tree inventories from Peninsular Malaysia, Sumatra, and Borneo. We then identified the indicator genera for clusters that crossed the central Sundaland biogeographic boundary and those that did not cross and tested whether drought and coarse-soil tolerance of the indicator genera differed between them. We found 11 terminal floristic clusters, 10 occurring in Borneo, 5 in Sumatra, and 3 in Peninsular Malaysia. Indicator taxa of clusters that occurred across Sundaland had significantly higher coarse-soil tolerance than did those from clusters that occurred east or west of central Sundaland. For drought tolerance, no such pattern was detected. These results strongly suggest that exposed sandy sea-bed soils acted as a dispersal barrier in central Sundaland. However, we could not confirm the presence of a savanna corridor. This finding makes it clear that proposed biogeographic explanations for plant and animal distributions within Sundaland, including possible migration routes for early humans, need to be reevaluated.
    Current and future CO2 emissions from drained peatlands in Southeast Asia
    Hooijer, A. ; Page, S. ; Canadell, J.G. ; Silvius, M. ; Kwadijk, J. ; Wösten, H. ; Jauhiainen, J. - \ 2010
    Biogeosciences 7 (2010). - ISSN 1726-4170 - p. 1505 - 1514.
    peat swamp forest - tropical peat - indonesia - malaysia - ecology - fluxes - borneo
    Forested tropical peatlands in Southeast Asia store at least 42 000 Million metric tonnes (Mt) of soil carbon. Human activity and climate change threatens the stability of this large pool, which has been decreasing rapidly over the last few decades owing to deforestation, drainage and fire. In this paper we estimate the carbon dioxide (CO2) emissions resulting from drainage of lowland tropical peatland for agricultural and forestry development which dominates the perturbation of the carbon balance in the region. Present and future emissions from drained peatlands are quantified using data on peatland extent and peat thickness, present and projected land use, water management practices and decomposition rates. Of the 27.1 Million hectares (Mha) of peatland in Southeast Asia, 12.9 Mha had been deforested and mostly drained by 2006. This latter area is increasing rapidly because of increasing land development pressures. Carbon dioxide (CO2) emission caused by decomposition of drained peatlands was between 355 Mt y-1 and 855 Mt y-1 in 2006 of which 82% came from Indonesia, largely Sumatra and Kalimantan. At a global scale, CO2 emission from peatland drainage in Southeast Asia is contributing the equivalent of 1.3% to 3.1% of current global CO2 emissions from the combustion of fossil fuel. If current peatland development and management practices continue, these emissions are predicted to continue for decades. This warrants inclusion of tropical peatland CO2 emissions in global greenhouse gas emission calculations and climate mitigation policies. Uncertainties in emission calculations are discussed and research needs for improved estimates are identified.
    Secondary succession after fire in Imperata grasslands of East Kalimantan Indonesia
    Yassir, I. ; Kamp, J. van der; Buurman, P. - \ 2010
    Agriculture, Ecosystems and Environment 137 (2010)1-2. - ISSN 0167-8809 - p. 172 - 182.
    rain-forest - tropical lowlands - new-guinea - vegetation - cylindrica - borneo - plantation - biomass - island - soils
    Regeneration of grassland areas is becoming increasingly important, not only to create new secondary forest and recover the original biodiversity, but also recover for agriculture. We studied an early succession in Imperata grasslands in East Kalimantan, Indonesia, using plots that last burned 3 years, 4 years and 9 years previously on, secondary and primary forest. The species coverage data were analyzed using CANOCO. While Imperata decreases, the average percentage of shrubs and young trees clearly increases with time. In the burned plots, Melastoma malabathricum, Eupatorium inulaefolium, Ficus sp., and Vitex pinnata L. strongly increase with the age of regeneration, but these species were rare in the secondary forest. Texture strongly influenced regeneration: soils with more than 50% sand had a slower development towards secondary forest. The number of species was lower in the more sandy soils. The latter showed a stronger increase with time of Pteridium aquilinum L., which appears to slow down the subsequent vegetation development. Canonical correspondence analysis (CCA) of the environmental gradient and vegetation showed that pH, bulk density, sand and clay are the factors influencing the distribution of species. CCA showed also that soil properties had a strong influence on vegetation composition. M. malabathricum, V. pinnata L., Lycopodium cernum, Vernonia arborea Buch.-Ham., Dicranopteris linearis are all species associated with high levels of exchangeable Al and low pH. Imperata grasslands are not a final and stable stage of land degradation, but, when not maintained by frequent fires and human disturbances, regenerate spontaneously and rapidly to secondary forest. The introduction of native shrubs and trees will speed up this process. Recovery for agriculture has not been studied but should not pose major problems under management system without fire
    Soil carbon changes upon secondary succession in Imperata grasslands (East Kalimantan, Indonesia)
    Kamp, J. van der; Yassir, I. ; Buurman, P. - \ 2009
    Geoderma 149 (2009)1-2. - ISSN 0016-7061 - p. 76 - 83.
    forest - vegetation - biomass - borneo - fractions - storage - fire
    Soil carbon changes upon secondary succession in Imperata grasslands are important both for their effect on potential production and for possible implications of forest degradation and regeneration on global climate change. We studied the effect of forest regeneration after fire in Imperata (speargrass) grasslands of East Kalimantan on soil properties, using 47 plots that last burned in 2004, 94 plots that last burned in 2003, 126 plots last burned before 2003, 43 plots of secondary forest, and 28 plots of primary forest. Although soil carbon stocks increase upon natural regeneration from grassland to secondary forest, highest carbon stocks are found in the later regeneration phases and lowest under primary forest. This is contrary to the situation in other forest systems. Low C stocks under primary forests may be due to extremely low fertility, combined with shallow soils and low root mass in the topsoil. Root density¿as observed in the field¿is much higher under the grass vegetation. The effects of regeneration on soil are strongest in the A-horizon, where soil carbon content increases with 14%, from 14.5 g kg¿ 1 in Imperata grassland to 16.5 g kg¿ 1 in secondary forest, while carbon stocks in the A-horizon increase from 16.51 ton C ha¿ 1 to 18.70 ton C ha¿ 1. This is accompanied by a decrease in pH and an increase in bulk density. The total soil carbon stocks in Kalimantan (fixed mass, approximate depth section 40 cm) are 36.19 ton ha¿ 1 in Imperata grassland, 38.98 ton ha¿ 1 in secondary forest and 33.19 ton ha¿ 1 in primary forest, which is considerably lower than in Sumatra. Above-ground C/below-ground C ratios are higher in Kalimantan primary forest but lower in Kalimantan secondary forest than in Sumatra. Soil carbon stocks in Imperata grassland could be lower than previously thought. This has important consequences for carbon sequestration projects in East Kalimantan, because carbon storage potentials could be higher
    Allometric equations for estimating the above-ground biomass in tropical lowland Dipterocarp forests
    Basuki, T.M. ; Laake, P.E. van; Skidmore, A.K. ; Hussin, Y.A. - \ 2009
    Forest Ecology and Management 257 (2009)8. - ISSN 0378-1127 - p. 1684 - 1694.
    net primary production - wood density - temporal variability - carbon storage - central amazon - tree biomass - brazil - borneo - stocks
    Allometric equations can be used to estimate the biomass and carbon stock of forests. However, so far the equations for Dipterocarp forests have not been developed in sufficient detail. In this research, allometric equations are presented based on the genera of commercial species and mixed species. Separate equations are developed for the Dipterocarpus, Hopea, Palaquium and Shorea genera, and an equation of a mix of these genera represents commercial species. The mixed species is constructed from commercial and non-commercial species. The data were collected in lowland mixed Dipterocarp forests in East Kalimantan, Indonesia. The number of trees sampled in this research was 122, with diameters (1.30 m or above buttresses) ranging from 6 to 200 cm. Destructive sampling was used to collect the samples where diameter at breast height (DBH), commercial bole height (CBH), and wood density were used as predictors for dry weight of total above-ground biomass (TAGB). Model comparison and selection were based on Akaike Information Criterion (AIC), slope coefficient of the regression, average deviation, confidence interval (CI) of the mean, paired t-test. Based on these statistical indicators, the most suitable model is ln(TAGB) = c + ¿ln(DBH). This model uses only a single predictor of DBH and produces a range of prediction values closer to the upper and lower limits of the observed mean. Model 1 is reliable for forest managers to estimate above-ground biomass, so the research findings can be extrapolated for managing forests related to carbon balance. Additional explanatory variables such as CBH do not really increase the indicators¿ goodness of fit for the equation. An alternative model to incorporate wood density must be considered for estimating the above-ground biomass for mixed species. Comparing the presented equations to previously published data shows that these local species-specific and generic equations differ substantially from previously published equations and that site specific equations must be considered to get a better estimation of biomass. Based on the average deviation and the range of CI, the generalized equations are not sufficient to estimate the biomass for a certain type of forests, such as lowland Dipterocarp forests. The research findings are new for Dipterocarp forests, so they complement the previous research as well as the methodology of the Good Practice Guidance for Land Use and Land Use Change and Forestry (GPG-LULUCF)
    Wood Density as a Conservation Tool: Quantification of Disturbance and Identification of Conservation-Priority Areas in Tropical Forests
    Slik, J.W.F. ; Bernard, C.S. ; Breman, F.C. ; Beek, M. van; Salim, A. ; Sheil, D. - \ 2008
    Conservation Biology 22 (2008)5. - ISSN 0888-8892 - p. 1299 - 1308.
    tree species composition - rain-forest - dipterocarp forests - central-america - el-nino - diversity - borneo - kalimantan - indonesia - fire
    Inventories of tree species are often conducted to guide conservation efforts in tropical forests. Such surveys are time consuming, demanding of expertise, and expensive to perform and interpret. Approaches to make survey efforts simpler or more effective would be valuable. In particular, it would be good to be able to easily identify areas of old-growth forest. The average density of the wood of a tree species is closely linked to its successional status. We used tree inventory data from eastern Borneo to determine whether wood density can be used to quantify forest disturbance and conservation importance. The average density of wood in a plot was significantly and negatively related to disturbance levels, with plots with higher wood densities occurring almost exclusively in old-growth forests. Average wood density was unimodally related to the diversity of tree species, indicating that the average wood density in a plot might be a better indicator of old-growth forest than species diversity. In addition, Borneo endemics had significantly heavier wood than species that are common throughout the Malesian region, and they were more common in plots with higher average wood density. We concluded that wood density at the plot level could be a powerful tool for identifying areas of conservation priority in the tropical rain forests of Southeast Asia.
    Climate regulation of fire emissions and deforestation in equatorial Asia
    Werf, G.R. van der; Dempewolf, J. ; Trigg, S.N. ; Randerson, J.T. ; Peters, W. - \ 2008
    Proceedings of the National Academy of Sciences of the United States of America 105 (2008)51. - ISSN 0027-8424 - p. 20350 - 20355.
    modis - vegetation - indonesia - peat - algorithm - dataset - borneo - policy
    Drainage of peatlands and deforestation have led to large-scale fires in equatorial Asia, affecting regional air quality and global concentrations of greenhouse gases. Here we used several sources of satellite data with biogeochemical and atmospheric modeling to better understand and constrain fire emissions from Indonesia, Malaysia, and Papua New Guinea during 2000¿2006. We found that average fire emissions from this region [128 ± 51 (1¿) Tg carbon (C) year¿1, T = 1012] were comparable to fossil fuel emissions. In Borneo, carbon emissions from fires were highly variable, fluxes during the moderate 2006 El Niño more than 30 times greater than those during the 2000 La Niña (and with a 2000¿2006 mean of 74 ± 33 Tg C yr¿1). Higher rates of forest loss and larger areas of peatland becoming vulnerable to fire in drought years caused a strong nonlinear relation between drought and fire emissions in southern Borneo. Fire emissions from Sumatra showed a positive linear trend, increasing at a rate of 8 Tg C year¿2 (approximately doubling during 2000¿2006). These results highlight the importance of including deforestation in future climate agreements. They also imply that land manager responses to expected shifts in tropical precipitation may critically determine the strength of climate¿carbon cycle feedbacks during the 21st century.
    Strategies for implementing sustainable management of peatlands in Borneo
    Wösten, J.H.M. - \ 2003
    Wageningen : Alterra - 9
    veengebieden - veengronden - bodembeheer - borneo - maleisië - indonesië - peatlands - peat soils - soil management - borneo - malaysia - indonesia
    Practical use of a hydrological model for peatlands in Borneo; modelling the Sungai Sebangau catchment in Central Kalimantan, Indonesia
    Vries, F.T. de - \ 2003
    Wageningen : Alterra (Alterra-rapport 797) - 87
    hydrologie - modellen - veengebieden - borneo - kalimantan - indonesië - hydrologie van stroomgebieden - hydrology - models - peatlands - borneo - kalimantan - indonesia - catchment hydrology
    The value and vulnerability of tropical peatlands is nowadays widely recognised. To increase knowledge of the hydroloy of peat swamp forests and to promote sustainable management model studies can be a useful tool. In this study the Sebangau catchment in Kalimantan, Indonesia, is modelled in SIMGRO. By means of model input geohydrological data for the area were integrated. Model calculations give an impression of the spatial distrubution of groundwater levels and of fluctuations throughout the years. Further refining of the model however is a requisite to make the model suitable for simulation of landuse scenarios.
    The effect of shoot length of Gliricidia cuttings on survival rate and rooting ability
    Tolkamp, G.W. ; Saweni, - \ 1997
    Balikpapan : International MOF Tropenbos-Kalimantan Project - 5
    bosbouw - vegetatieve vermeerdering - scheutstekken - bomen - wortels - plantenontwikkeling - groene zones - heggen - kalimantan - borneo - gliricidia sepium - forestry - vegetative propagation - shoot cuttings - trees - roots - plant development - green belts - hedges - kalimantan - borneo - gliricidia sepium
    Rooting ability of Shorea leprosula cuttings in relation to wounding of tissue and hormone application
    Tolkamp, G.W. ; Priadjadi, A. - \ 1997
    Balikpapan : International MOF Tropenbos-Kalimantan Project - 12
    bosbouw - vegetatieve vermeerdering - bomen - wortels - plantenontwikkeling - plantengroeiregulatoren - kalimantan - borneo - forestry - vegetative propagation - trees - roots - plant development - plant growth regulators - kalimantan - borneo
    Non-timber forest products of East Kalimantan : Potentials for sustainable use.
    Valkenburg, J.L.C.H. van - \ 1997
    Wageningen : Tropenbos Foundation - ISBN 9789051130300 - 202
    bosbouw - bosproducten - bosbedrijfsvoering - theorie - duurzaamheid (sustainability) - opbrengsten - flora - plantengeografie - kalimantan - borneo - ericaceae - sierplanten - bosproducten anders dan hout - forestry - forest products - forest management - theory - sustainability - yields - flora - phytogeography - kalimantan - borneo - ericaceae - ornamental plants - non-wood forest products
    Inventarization, classification and evaluation of (potential) acid sulphate soils, survey component : report of the third research coordination mission, October 26 - November 25, 1988
    Andriesse, W. - \ 1988
    Wageningen : LAWOO (Research on acid sulphate soils in the humid tropics ) - 19
    zure gronden - kattekleigronden - onderzoek - kalimantan - borneo - rapporten - acid soils - acid sulfate soils - research - kalimantan - borneo - reports
    Bodemkundige informatie Stiboka zure gronden; LAWOO onderzoek
    Set up field experiments to study physical and chemical processes in acid sulfate soils in the Pulau Petak area, South-Kalimantan, Indonesia
    Bronswijk, J.J.B. ; Consten, C.J.M. ; Nugroho, K. - \ 1988
    Wageningen : ICW (ICW nota 1901) - 24
    zure gronden - kattekleigronden - proefvelden - experimenteel veldonderzoek - proeven - kalimantan - borneo - acid soils - acid sulfate soils - experimental plots - field experimentation - trials - kalimantan - borneo
    Foliar diagnosis, nutrition and yield stability of black pepper (Piper nigrum L.) in Sarawak
    Waard, P.W.F. de - \ 1969
    Wageningen University. Promotor(en): A.C. Schuffelen. - Amsterdam : Koninklijk Instituut Voor de Tropen - 149
    piper nigrum - maleisië - sarawak - borneo - piper nigrum - malaysia - sarawak - borneo

    Until 1942 cultivation of pepper P. nigrum L. in Sarawak produced relatively small but regular yields. High demands after 1945 and restricted use of "burnt earth" compelled farmers to abandon the application of this traditional fertilizer. Instead, "fool proof" manufactured fertilizers of mainly organic origin were successfully applied in massive volumes and large yields were obtained. In 1954 and following years a sharp fall in price induced a decline in production, in part owing to much reduced applications of fertilizer. As a result the economic crop cycle of some 16 years was limited to some 1-3 years; the bulk of the total yield was obtained in the first year of production.

    An initial survey on leaf symptoms and die-back indicated unbalanced and inadequate mineral nutrition of the crop. The current system induced severe deterioration of plant appearance in the period of monsoon rains, which coincide with berry expansion. During this time no fertilizers are applied as a rule.

    A method has been worked out to diagnose the nutritional demands of N, P, K, Ca and Mg by chemical foliar analysis. Major aspects involved in the establishment of a sampling procedure were systematically studied. The effect on chemical concentrations was investigated of the portion of the vine, the presence of fruit, the branch, the age of the leaf, the presence of the petiole, leaf size, leaf thickness, sunshine, different stems on a plant, location of fertilizer dressings and the number of leaves to be sampled per vine. Similarly, the influence of the mode of cleaning of the leaves, of the drying temperature on loss of N and the effect of length of storage on the content of N were studied.

    Studies on the error of bulk sampling and the effect of appropriate stratification of the different leaves in the canopy on the reduction of this error showed that suitable division into strata reduced the number of vines to be included in a bulk sample up to 16 times as compared with random sampling, assuming the same degree of precision. Furthermore the inclusion Of 4 appropriately stratified leaves from each of 60-70 vines in each bulk sample obtained from homogeneous areas, would represent chemical concentrations with a precision of 10% of the population mean (P = 0.05) irrespective of physiological condition.

    Data on seasonal variation indicated declining levels of N and K within the monsoon; this was accompanied by gradually rising levels of leaf P and leaf Ca. Leaf Mg tended towards constancy. Bivariate ratios showed, on most occasions, a regular relationship with time, but constant values were observed only occasionally.

    A sand experiment on deficiencies of nutrients showed characteristic discolourations due to nutrient shortage. Concurring foliar concentrations and ratios associated with full nutrients, partial or complete deficiency of a single element allowed tentative registration of normal, fair, critical and deficient threshold values in the leaves for each element (table 18). Single and multiple deficiencies could be recognized by using an appropriate grouping of concentrations and their ratios. Application of these values to random field data showed a satisfactory power of discrimination. The ratio values gave a good indication of the order of importance in the case of multiple deficiencies.

    The influence was studied of dressings of NPK fertilizers on leaf concentrations and ratios. It was observed that increasing dressings of N, P, and K were directly reflected in risising concentrations of leaf N, leaf Pand leaf K, respectively. Simultaneously, N- P "antagonism" and "antagonism" between bases was also operative. Apparently, considered balancing of applications of different fertilizers is essential. The ratios between elements gave some indication of priorities of different dressings. It was also observed that under the influence of the very heavy, early applications leaf concentrations of N, K and Mg fall to deficiency levels. This indicates that the distribution in time also requires adjustment.

    The development of physiological exhaustion could be attributed to an inadequate net supply of N, K and Mg to the leaves during translocation processes of nutrients in the period of fruit development. Stability of yield at a high level of production can be maintained by preventing development of nutrient shortages and ensuring fair to normal concentrations of N, P, K, Ca and Mg in the leaves throughout the year. Threshold values, independently obtained from field vines corroborate the tentative values for the normal levels found in the pot experiment. The latter may therefore be considered as fundamentally correct. Rather complicated interactions of "antagonisms" and "synergisms" may become operative if foliar levels fall below these normal levels. The data have also shown convincingly that the values for log N/P can be used as a satisfactory control for abundance of flowers at a specific potential for flowering.

    Finally, the agricultural implications of these findings are discussed in Ch. 10. The data allowed a plausible interpretation of crop behaviour and crop performance under the traditional system of cultivation before 1942 and that in the period after 1945. By integrating the leaf data of this work with information concerning factors affecting the supply of nutrients to the plant, it was shown that foliar diagnosis furnished a suitable foundation to devise an appropriate fertilizer policy for pepper.

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