{"id":9727,"date":"2026-04-08T11:41:47","date_gmt":"2026-04-08T11:41:47","guid":{"rendered":"https:\/\/www.proefschriftmaken.nl\/portfolio\/niharika-rahman\/"},"modified":"2026-04-23T07:58:21","modified_gmt":"2026-04-23T07:58:21","slug":"niharika-rahman","status":"publish","type":"us_portfolio","link":"https:\/\/www.proefschriftmaken.nl\/en\/portfolio\/niharika-rahman\/","title":{"rendered":"Niharika Rahman"},"content":{"rendered":"","protected":false},"excerpt":{"rendered":"","protected":false},"author":8,"featured_media":13122,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_acf_changed":false,"footnotes":""},"us_portfolio_category":[45],"class_list":["post-9727","us_portfolio","type-us_portfolio","status-publish","has-post-thumbnail","hentry","us_portfolio_category-new-template"],"acf":{"naam_van_het_proefschift":"Environmental efficiencies and controversies","samenvatting":"Er is geen Nederlandse samenvatting beschikbaar. De Engelse samenvatting vind je <a href=\"https:\/\/www.proefschriftmaken.nl\/en\/portfolio\/niharika-rahman\/\">hier<\/a>.","summary":"Palm oil from oil palm (Elaeis guineensis Jacq.) is one of the most important vegetable oils in terms of production and trade. The continuous rise in the global demand for palm oil has resulted in the large-scale expansion of oil palm monoculture in the world\u2019s tropical regions. Tropical rainforests have provided most of the land for these newly established oil palm plantations, particularly in major producing countries such as Indonesia and Malaysia. This expansion has led to the conversion of carbon-rich land-use types to oil palm plantations with a range of negative environmental impacts, including the loss of carbon stock. However, studies investigating the long-term environmental\/carbon loss effect of conversion of forest into a forest are scarce. Thus, there is a considerable risk that further expansion will contribute to future deforestation (Fitzherbert et al., 2008), contributing to environmental degradation. However, there is scope for increasing oil palm production through sustainable intensification of existing plantations rather than continuing ongoing area expansion. Intensification through best management practices (BMP) was introduced to increase production in oil palm plantations through the efficient use of production-related inputs and resources (Donough et al., 2009). One of these is a soil moisture and nutrient management scheme that, among other things, involves the application of more organic residues such as pruned fronds, empty fruit bunches (EFB) and palm oil mill effluent (POME) to close the nutrient loop. Residue management of BMP can play an important role in conserving soil moisture as well as adding plant nutrients, and may also contribute to the SOC pool. Sequestration of soil organic carbon (SOC) in existing oil palm plantations is an important strategy to limit carbon losses. However, residue incorporation in the plantation can be a potential source of N2O and CH4 emissions from oil palm plantations in addition to the large chemical fertilisers commonly used on the plantations, and this has not been investigated. Thus, the identification of strategies that can reduce dependence on chemical fertilisers by increasing the use of recycled organic residues that can not only enhance SOC stock but also reduce GHG emissions without impacting yield is imperative for the sustainability of the oil palm production system. This thesis was therefore written to understand the effect of conversion of forest to oil palm plantations on SOC stock and how, through BMP, it is possible to improve environmental efficiency to focus on an environmental friendly approach.\n\nThe overall objective of this thesis was to identify the effect of the conversion of forest to oil palm plantations on SOC stock, and identify the best possible environmentally sustainable management option for the oil palm production system. The specific research questions of this thesis research were: (i) What are the effects of conversion from forest to oil palm plantations on SOC stocks over different time scales? (Chapter 2) (ii) What are the effects of inorganic fertilisers and organic amendments applied in oil palm management systems on N2O and CH4 emissions? (Chapter 3) (iii) How do different waste management practices influence SOC stocks in the different management systems of oil palm plantations? (Chapter 4) and (iv) What is the carbon debt associated with conversion from forest to large-scale commercial oil palm plantations and how can this debt be reduced by different management systems, e.g. best management practices, commercially-managed and smallholder-managed oil palm production systems? (Chapter 5). This thesis contains four research chapters plus an introduction (Chapter 1) and a general discussion (Chapter 6).\n\nIn the study in Chapter 2, soil samples were collected from the forest and nearby oil palm plantations of different age groups with a different conversion period from a soil depth of 0-70 cm. The results showed that SOC stocks reduced by 42 %, 24 % and 18 % after 29, 39 and 49 years of conversion respectively. SOC stocks under oil palm plantations were found to build up slowly during the second rotation the longer it had been since conversion (39 and 49 years) with the help of better organic residue management. Significant differences in SOC stocks were found among different management zones in the oil palm plantations. The practice of chipping of the old oil palms during plantation re-establishment is likely to play a vital role in SOC gain in the second rotation cycle. Organic residue management is likely to have contributed to the development of distinctly higher SOC stocks under certain management zones over time where pruned fronds were used. The greatest differences between SOC stocks in the reference forest and the converted plantations were found in the topsoil (0-15 cm depth), but differences were also found in the subsoil (>30 cm). These results indicate that the improved management practices applied in the oil palm plantations under investigation facilitated a partial recovery of SOC loss the longer it had been since the forest was converted to oil palm plantations.\n\nChapter 3 described four field-based measurements of soil nitrous oxide (N2O) and methane (CH4) emissions from commercial oil palm plantations in North Sumatra, Indonesia. One experiment investigated the effects of soil-water saturation on N2O and CH4 emissions from inorganic fertilisers and organic amendments by simulating 25 mm rainfall per day for 21 days. The experiment was conducted using urea and enriched mulch (EMU) with and without water. EMU is a partially decomposed organic amendment that is a mixture of pressed empty fruit bunches (EFB) and palm oil mill effluent. The results demonstrated that all the treatments with simulated rainwater showed significantly higher CO2-eq. GWP than their respective treatments without water. This study confirmed that soil moisture (precipitation) was a major driver of N2O emission from oil palm plantations. Therefore, the timing of fertiliser application is an important management decision that has implications for reduction of N2O emissions from oil palm plantations by avoiding periods of heavy rainfall. Three year-long experiments focused on N2O and CH4 emissions from (a) inorganic fertiliser (urea), (b) a combination of EMU with urea and (c) organic amendments (EFB, EMU and pruned fronds) applied in different doses and spatial layouts. The result showed that a higher dose of urea led to significantly higher N2O emissions, with emission factors ranging from 2.4 % to 2.7 %, which is considerably higher than the IPCC standard of 1 %. CH4 emissions were found to be negligible. The application of organic amendments only also significantly affected both N2O and CH4 emissions. N2O emissions from organic amendments were 66-86 % lower than those from urea fertiliser, while a significant amount of CH4 was emitted from the application of organic amendments. GHG emissions depended both on the type (EFB and EMU) and dose of organic amendments. The results showed that N2O and CH4 emissions from organic amendments increased with greater doses. With twice the dose of EFB, cumulative emissions were up to three times greater. Being partially decomposed, EMU had a lower global warming potential (GWP) value than EFB. GWP was higher for a high dose of fresh EFB treatments followed by a high dose of urea application. An improved management practice with the application of a lower dose of urea with EMU resulted in 50 % lower GWP (CO2-eq. ha-1) than using urea alone. Therefore this study suggests that the combined application of inorganic fertilisers and organic amendments could be an effective fertiliser management strategy for oil palm plantations.\n\nIn the study in Chapter 4, soil samples were collected from three different management systems, i.e. best management practices (BMP), current management practices typical of large-scale plantations (CMP) and smallholder management practices (SHMP) in North Sumatra, Indonesia. The results showed that SOC stocks of plantations under BMP were 18 % and 31 % higher than under CMP and SHMP systems respectively. In the BMP system, soils under the interrow zone that received enriched mulch and frond stack positions that received pruned fronds stored significantly more SOC than the harvesting path. BMP also had a 33 % higher fresh fruit bunch yield than the SHMP system. This study shows that residue incorporation or retention as a part of BMP could be an effective strategy for increasing SOC stocks of oil palm plantations and confirms that these management practices could improve yields from SHMP systems.\n\nIn Chapter 5, a modelling approach, the simulation model FIELD, was combined with experimental data to evaluate the carbon debt in the forest to oil palm conversion and the possibility of mitigating net total carbon losses by improved management systems. After initialisation of the FIELD model with the observed data, the model was able to describe long-term SOC dynamics. The results showed that land-use change from forest to oil palm plantations contributed to the CO2 emissions and resulted in a carbon debt. The magnitude and rate of SOC losses greatly depended on the initial SOC stock in the converted forest soil. SOC stock initially declines following the conversion of forest to oil palm plantation but recovers part of it as the stand age increases. Different management systems (BMP, CMP and SHMP) showed different carbon accumulation capacities and GHG emissions depending on their management practices. SOC stock could be increased slowly over time from 3.6 to 8 t ha-1 by better agronomic practice, depending on the growth rate and organic waste management and fertilisation practices, leading to a time-averaged C stock that helps reduce the carbon debt. Zero burning techniques and returning mill residues (EMU and EFB) to the soil in the BMP systems in particular can substantially increase SOC stocks in the long term, which reduces the carbon debt. BMP with EMU application was identified as the best option in terms of higher C accumulation, with the lowest fertiliser-induced GHG emissions and net CO2-eq. emission per ha land area in oil palm plantations. The efficient use of nutrients and land and restoration of soil carbon pools through BMP with the EMU system are recommended for oil palm plantations to partially offset atmospheric CO2 and long-term environmental sustainability.\n\nThe general discussion (Chapter 6) addressed the main findings of the research and their implications in a broader context. The thesis demonstrates that SOC stocks reduced by 42 %, 24 % and 18 % after 29, 39 and 49 years of oil palm conversion from forest respectively. SOC stocks under oil palm plantations slowly built up again during the second rotation as time since conversion increases. This indicates that the improved management practices applied in the oil palm plantations under investigation facilitated a partial recovery of SOC loss with increasing time from conversion. The practice of chipping the old oil palms during replanting is likely to play a vital role in SOC gain in the second rotation cycle. Organic residue management, which is an integral part of the BMP approach, is likely to have contributed to the development of much higher SOC stocks where pruned fronds were used. SOC stocks in plantations under BMP were 31 % higher than under SHMP. BMP practice also increased yield by 33 % compared with the SHMP systems. A better management approach that includes residue incorporation or retention could be an effective strategy for increasing SOC stocks as a means of mitigating the effects of oil palm cultivation on climate change in oil palm plantations. The practice of partly replacing inorganic fertiliser with the various organic amendments, as practised in the BMP approach, showed that the higher dose of urea led to significantly higher N2O emissions, with emission factors ranging from 2.4 to 2.7 % in the long-term experiment, which is considerably higher than the IPCC standard of 1 %. Organic amendments were a significant source of both N2O and CH4 emissions, but N2O emissions from organic amendments were 66-86 % lower than those from inorganic fertilisers. Among the various organic amendments available, the application of EMU could be the best option due to its greater GHG mitigation potential. An improved combined management practice, which involves replacing some of the urea with recycled organic materials (EMU), would reduce net GWP by 50 % compared with practices where only inorganic fertilisers were applied. Therefore, N2O and CH4 emissions could be decreased to a greater extent by combining inorganic fertilisers and organic amendments, and could therefore be an effective fertilisation strategy for oil palm plantations. The outcomes presented in this thesis could serve as a baseline for a better understanding of GHG emissions and their dynamics in mineral soils in order to reduce environmental losses, which can increase the economic benefits and agro-ecological efficiency of oil palm management systems. Finally, the perspectives and future research directions section offers inspiration and guidance for researchers in future. Long-term research is essential in order to understand the yield response curve for N and evaluate the trade-offs between yield and GHG emissions in oil palm plantations. Long-term research is also required on smallholders\u2019 plantations using the BMP approach in relation to GHG, SOC stocks, soil quality and yield in one integrated study in various different geographic and climatic locations. Finally, a socioeconomic study should be carried out to investigate the level of adoption of BMP practices and associated barriers among independent smallholder farmers.","auteur":"Niharika Rahman","auteur_slug":"niharika-rahman","publicatiedatum":"5 oktober 2022","taal":"EN","url_flipbook":"https:\/\/ebook.proefschriftmaken.nl\/ebook\/niharikarahman?iframe=true","url_download_pdf":"","url_epub":"","ordernummer":"FTP-202604081138","isbn":"978-94-6447-352-0","doi_nummer":"","naam_universiteit":"Wageningen University","afbeeldingen":13122,"naam_student:":"","binnenwerk":"","universiteit":"Wageningen University","cover":"","afwerking":"","cover_afwerking":"","design":""},"_links":{"self":[{"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/us_portfolio\/9727","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/us_portfolio"}],"about":[{"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/types\/us_portfolio"}],"author":[{"embeddable":true,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/users\/8"}],"replies":[{"embeddable":true,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/comments?post=9727"}],"version-history":[{"count":1,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/us_portfolio\/9727\/revisions"}],"predecessor-version":[{"id":9728,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/us_portfolio\/9727\/revisions\/9728"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/media\/13122"}],"wp:attachment":[{"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/media?parent=9727"}],"wp:term":[{"taxonomy":"us_portfolio_category","embeddable":true,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/us_portfolio_category?post=9727"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}