Ciclos de carbono y nitrógeno en plantaciones de palma de aceite: claves para la productividad y la sostenibilidad / Carbon and nitrogen cycling in oil palm plantations: the keys to yield and sustainability

[Spanish] El alto rendimiento y la rentabilidad de las inversio nes en palma de aceite dependen de la fijación de carbono producto de la fotosíntesis en las ojas, la cual está limitada por la radiación, la temperatura y la disponibilidad de gua y nutrientes, en particular el nitrógeno. Los ciclos de carbono y nitrógeno también son factores determinantes para la condición del suelo en particular, la materia orgánica, la acidez y la actividad biológica), la salud de los ecosistemas acuáticos y las emisiones de gases de efecto invernadero. Aunque la productividad y los efectos am bientales del cultivo se han estudiado extensamente, es difícil predecir cómo podrían verse afectados por los cambios en el genotipo, en las condiciones ambientales o en las prácticas de manejo, dada la complejidad de las interacciones entre los ciclos de carbono y nitrógeno, y los factores antes mecanísticos, la integración de nuestro conocimiento a modelos mecanicistas predictivos es esencial para avanzar. Dicha integración se ha logrado recientemente para la palma de aceite utilizando el marco APSIM (www.apsim.info), el cual integra modelos de fisiología de cultivos y de ciclos de agua, carbono y nitrógeno. El modelo ha demostrado tener la capacidad de predecir el crecimiento vegetativo y el rendimiento aropiadamente, y de manera consistente en Papúa Nueva Guinea, en donde fue desarrollado. Ahora debe ser ensayado en un mayor rango de entornos. APSIM Oil Palm tiene un potencial considerable como herramienta para predecir el rendimiento y generar eficiencia al explorar escenarios cuya evaluación experimental no es plausible, tales como los efectos probables de una gestión de fertilizantes distinta, los efectos del tipo de clima y suelo en la productividad, la condición del suelo y el entorno. [English] High yields and return on investment in oil palm all depend on the fixation of carbon by photosynthesis in the leaves, which is limited by radiation, temperature and the availability of water and nutrients, especially nitrogen. The carbon and nitrogen cycles are also key determinants of soil condition (particularly soil organic matter, acidity and biological activity), aquatic ecosystem health and greenhouse gas emissions. Although productivity and environmental effects of cultivation are well studied, it is difficult to predict how they might be affected by changes in genotype, environmental conditions or management practices, because of complex interactions between the carbon and nitrogen cycles and these factors. Integrating our knowledge into mechanistic predictive models is essential to move forward. Such integration has recently been achieved for oil palm using the APSIM framework (www.apsim.info), which integrates models of crop physiology and cycling of water, carbon and nitrogen. The model has been shown to predict vegetative growth and yield consistently well in Papua New Guinea, where it was developed. It now needs to be tested in a wider range of environments. APSIM Oil Palm has considerable potential as a tool for predicting yield and for efficiently exploring scenarios that are not feasible to assess experimentally, such as the likely effects of different fertilizer management, climate or soil type on productivity, soil condition and the environment

Soil fertility changes following conversion of grassland to oil palm

Impacts of palm oil industry expansion on biodiversity and greenhouse gas emissions might be mitigated if future plantings replace grassland rather than forest. However, the trajectory of soil fertility following planting of oil palm on grasslands is unknown. We assessed the changes in fertility of sandy volcanic ash soils (0–0.15 m depth) in the first 25 years following conversion of grassland to oil palm in smallholder blocks in Papua New Guinea, using a paired-site approach (nine sites). There were significant decreases in soil pH (from pH 6.1 to 5.7) and exchangeable magnesium (Mg) content following conversion to oil palm but no significant change in soil carbon (C) contents. Analyses to 1.5 m depth at three sites indicated little change in soil properties below 0.5 m. There was considerable variability between sites, despite them being in a similar landscape and having similar profile morphology. Soil Colwell phosphorus (P) and exchangeable potassium (K) contents decreased under oil palm at sites with initially high contents of C, nitrogen, Colwell P and exchangeable cations. We also assessed differences in soil fertility between soil under oil palm (established after clearing forest) and adjacent forest at two sites. At those sites, there was significantly lower soil bulk density, cation exchange capacity and exchangeable calcium, Mg and K under oil palm, but the differences may have been due to less clayey texture at the oil palm sites than the forest sites. Cultivation of oil palm maintained soil structure and fertility in the desirable range, indicating that it is a sustainable endeavour in this environment

Soil physicochemical properties impact more strongly on bacteria and fungi than conversion of grassland to oil palm

The conversion of grassland to oil palm is expected to increase throughout tropical regions where oil palm grows. Given the extent of land use change, there are concerns associated with impacts on ecosystem function and nutrient cycling. For this work, soil samples were collected in Papua New Guinea from 15 sites with oil palm (planted on grassland) and adjacent remnant grassland. Using DNA-based approaches, bacterial and fungal community composition was assessed in each sample, along with abundance of genes involved in key nitrogen cycling steps: nitrification (bacterial and archaeal amoA genes), nitrite reduction (nirS gene), and nitrous oxide reduction (nosZ gene). Across all microbial properties measured, variation among sites was greater than variation due to land use change. This was driven by among-site variation in soil physicochemical properties, particularly total soil organic carbon content and d13C, electrical conductivity, exchangeable calcium, potassium and magnesium content, and extractable phosphorus content. The results suggest that in this environment, routinely measured soil properties such as soil pH, organic carbon, and exchangeable cation contents may serve as indicators for the effects of land use and management on soil microbial community composition and functioning

Soil carbon balance following conversion of grassland to oil palm

Oil palm (Elaeis guineensis Jacq.) crops are expanding rapidly in the tropics, with implications for the global carbon cycle. Little is currently known about soil organic carbon (SOC) dynamics following conversion to oil palm and virtually nothing for conversion of grassland. We measured changes in SOC stocks following conversion of tropical grassland to oil palm plantations in Papua New Guinea using a chronosequence of plantations planted over a 25-year period. We further used carbon isotopes to quantify the loss of grassland-derived and gain in oil palm-derived SOC over this period. The grassland and oil palm soils had average SOC stocks of 10.7 and 12.0 kg m⁻², respectively, across all the study sites, to a depth of 1.5 m. In the 0–0.05 m depth interval, 0.79 kg m⁻² of SOC was gained from oil palm inputs over 25 years and approximately the same amount of the original grass-derived SOC was lost. For the whole soil profile (0–1.5 m), 3.4 kg m⁻² of SOC was gained from oil palm inputs with no significant losses of grass-derived SOC. The grass-derived SOC stocks were more resistant to decrease than SOC reported in other studies. Black carbon produced in grassfires could partially but not fully account for the persistence of the original SOC stocks. Oil palm-derived SOC accumulated more slowly where soil nitrogen contents where high. Forest soils in the same region had smaller carbon stocks than the grasslands. In the majority of cases, conversion of grassland to oil palm plantations in this region resulted in net sequestration of soil organic carbon

Methods to account for tree-scale variability in soil- and plant-related parameters in oil palm plantations

Background and aims: Lateral tree-scale variability in plantations should be taken into account when scaling up from point samples, but appropriate methods for sampling and calculation have not been defined. Our aim was to define and evaluate such methods. Methods: We evaluated several existing and new methods, using data for throughfall, root biomass and soil respiration in mature oil palm plantations with equilateral triangular spacing. Results: Three ways of accounting for spatial variation within the repeating tree unit (a hexagon) were deduced. For visible patch patterns, patches can be delineated and sampled separately. For radial patterns, measurements can be made in radial transects or a triangular portion of the tree unit. For any type of pattern, including unknown patterns, a triangular sampling grid is appropriate. In the case studies examined, throughfall was 79% of rainfall, with 95% confidence limits being 62 and 96% of rainfall. Root biomass and soil respiration, measured on a 35-point grid, varied by an order of magnitude. In zones with steep gradients in parameters, sampling density has a large influence on calculated mean values. Conclusions: The methods defined here provide a basis for representative sampling and calculation procedures in studies requiring scaling up from point sampling, but more efficient methods are needed

Environmental sustainability indicators for oil palm in Papua New Guinea – conceptual framework for a research and development project

Palm oil producers participating in the Round Table on Sustainable Palm Oil (RSPO), which includes all producers in Papua New Guinea (PNG), require measurable and auditable indicators of environmental sustainability to underpin the RSPO Principles and Criteria and inform their management decisions. This paper describes the conceptual basis of a project being carried out in 2010-2013 to provide indicators of the state of soil and water resources in all oil palm production areas of PNG, excluding mill activities. \ud \ud Considering the complexity of environmental sustainability issues, it is useful to categorise them into issues that have different types of impacts, and thus require different types of indicators: Planning and biodiversity (not considered in this project); Balances of water, nutrients, C, greenhouse gases and soil (ie. erosion); Health of aquatic ecosystems; and Health of soil. Indicators must provide a meaningful assessment of these issues, and must be derived from data inputs that are already recorded or are simple to measure. The research component of this project aims to choose the best possible indicators, data inputs, and means of linking them. The research will be integrated with a pilot implementation scheme run by industry staff and growers, to help attain the goal of a workable indicator package that is sustained by the industry. \ud \ud For nutrient balances to be sustainable, inputs and losses should be balanced and minimised. The main issue of concern is leaching loss of N, and factors that are difficult to estimate include N leaching, gaseous losses of N, and biological N fixation. The C balance has vulnerable periods during initial establishment of plantations and during replant. The greenhouse gas balance is linked to the C and N cycles, with N2O emissions being the largest unknown. Net soil erosion from fields is generally small, but appears to be significant from bare connected areas on moderate slopes. Health of soil is influenced by net acid addition rate (largely related to fertiliser use), return of organic residues, and traffic. Health of aquatic ecosystems may be affected by N inputs leached from fields and poor riparian vegetation. Assessing health of estuaries will provide information on the responses to stresses, as well as indicating likely impacts offshore.\ud \ud It is proposed that indicators be estimated using input data such as visual scores of ground cover, simple vegetative measurements, and fish counts, linked to controlling factors (eg. net primary productivity) through desk top studies and field research (on some key unknowns regarding erosion, C and nutrient cycling, aquatic ecology) and modelling.\u

IN‐Palm: An agri‐environmental indicator to assess nitrogen losses in oil palm plantations

International audienceOil palm (Elaeis guineensis Jacq.) is currently cultivated on 19 million ha, and palm oil represents more than one‐third of the global vegetable oil market. Addition of nitrogen (N) via legume cover crop and fertilizers is a common practice in industrial oil palm plantations, however, there is a tendency for N loss, thus contributing significantly to environmental effects. To improve the sustainability of palm oil production, it is crucial to determine which management practices minimize N losses. Continuous field measurements would be cost‐prohibiting as a monitoring tool, and in the case of oil palm, available models do not account for all the potential nitrogen inputs and losses or management practices. In this context, we developed IN‐Palm, a model to help managers and scientists estimate N losses to the environment and identify best management practices. The main challenge was to build the model in a context of knowledge scarcity. Given these objectives and constraints, we developed an agri‐environmental indicator, using the INDIGO method and fuzzy decision trees. We validated the N leaching module of IN‐Palm against field data from Sumatra, Indonesia. IN‐Palm is implemented in an Excel file and uses 21 readily available input variables to compute 17 modules. It estimates annual emissions and scores for each N‐loss pathway and provides recommendations to reduce N losses. IN‐Palm predictions of N leaching were acceptable according to several statistics, with a tendency to underestimate nitrogen leaching. Thus, we highlighted necessary improvements to increase IN‐Palm precision before use in plantations