Nitrogen (N) losses in agroecosystems are a major environmental and economic issue. This issue is particularly pronounced in oil palm cultivation because oil palm production area is expected to increase to 12 Mha by 2050. N fertilization in oil palm plantations is mainly provided by mineral fertilizers, palm oil mill by-products, and biological fixation using legume cover crops. N loss has a major environmental impact during cultivation. For instance, 48.7 % of the greenhouse gases emitted to produce 1 t of palm oil fruit are due to N fertilization. Actually, there is little comprehensive knowledge on how to calculate N budgets in oil palm plantation in order to optimize fertilization, taking into account N leaching and N gases emissions. Here we modeled knowledge about all N fluxes in an oil palm field following standard management practices of industrial plantations, on a mineral soil, from planting to felling after a 25-year-growth cycle. The largest fluxes are internal fluxes, such as oil palm uptake, with 40-380 kg N ha, and the decomposition of felled palms at the end of the cycle, with 465-642 kg N ha

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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. (Résumé d'auteur

Potassium is the main nutrient in oil palm nutrition. On oil palm estates, potassium fertilization is usually adjusted based on leaflet K content. However, in the Magdalena river valley in Colombia where the soils are deficient in Cl, KCl has always caused a drop in leaflet K content, sometimes to deficiency levels, yet yields remain high. To elucidate this paradox, we conducted a multi-annual trial on 11-year-old oil palms by comparing unfertilized plots and plots receiving KCl or NaCl. We analysed the physico-chemical characteristics of the soils and the K, Ca, Mg, Na, and Cl contents of different organs: leaflets, rachises, petioles, stems, roots, and fresh fruit bunches. Our results showed that Cl stimulated the uptake of K, Ca, and Mg cations in aerial parts and that K was primarily stored in the stem (72% of the K in aerial vegetative organs). Our results also showed that the soils were rich in K easily accessible to the crop, a fact that conventional extraction of exchangeable cations did not reveal, and that the richness was probably of volcanic origin. Lastly, analysis of rachis K content was seen to be a good potential indicator of K taken up by the plant, and could thus replace leaflets for monitoring potassium fertilization in oil palm plantations.

SUMMARYIn the oil palm plantations of Ecuador, two factorial trials (namely CP06 and CP08) were used to assess the effects of N, P and K fertilization on the soil chemical characteristics after 10 years of fertilizer application. The use of ammonia-based fertilizers has resulted in a drop in soil pH, which has reached 1.2 units in one of the two trials. A drop in cation exchange capacity (CEC) was also found, and a loss of exchangeable cations that probably reflected leaching of excess N as nitrates. The use of KCl enriched the soil in K, which contributed to impoverishment in Ca and Mg. In both trials, the highest N and K application rates had no significant effect on yield in comparison with an intermediate fertilization rate; however, their effects on the fertilized soil significantly increased the risk of N and cation leaching towards the deep soil layers. We also compared the effects of the N, P and K factors on soil properties outside the fertilizer application zone. In both trials, the mineral reserves played a major role in meeting the needs of the control palms, which had not been fertilized for 10 years, as no significant yield drop has been observed except in trial CP06 when no KCl was applied. However, uptake of nutrient in the control plots did not lead to significant impoverishment of the soil.

Predicting the fertilizer requirements of an oil palm plantation has long been a difficult task. Two main methods have emerged. Leaf analyses (LA) were used for fertilization management as early as the 1950s. Leaf contents are compared to optimum references, making it possible to adjust the fertilizer rates applied in each block. Another approach, based on the nutrient balance (NB), is to evaluate and replace nutrients that are exported from the field, or immobilized by the plant. Plantations must adopt environmentally friendly practices; in particular, fertilizer inputs must be estimated with sufficient precision to achieve the highest possible yields, without applying excessive amounts of nutrients in relation to plant demand and the storage capacity of soils. We questioned the relevance of each method for achieving these objectives. We did so using some long-term fertilization trials to compare the optimum N and K rates recommended by each method in the adult phase. It appeared that LA led to moderate rates compared to NB. It also appeared that calculating a precise nutrient balance on a field scale was hampered by a lack of precise information (i) about the biomasses produced and their composition and (ii) about the highly variable outputs of the environmental losses. On the other hand, LA provided a simple indicator of the ability for each block to achieve its potential yield. We believe that this perfectible method is more protective of the environment, without the risk of a significant decrease in yields or a decrease in soil mineral reserves.

Sanguinet lake is separated from the Atlantic Ocean by a wide Holocene coastal dunes system in SW France. The present day lake level is 21 m above mean sea level (msl). It formed when aeolian sand closed the mouth of the small La Gourgue river which gradually became a lagoon and then a lake. Dated sub-lacustrine archaeological remains (human settlements, canoes, and wooden architectural structures), as well as paleoenvironmental evidence (drowned tree stumps and lagoonal deposits exposed on the beach) are used to interpret the formation and chronology of lake level rise during the past 4000 years.Around 2000-1650 B.C., the river flowed into a lagoon or an estuary which connected with the ocean west of the present Sanguinet Lake. Its level was affected by the tide, which ranged between 2 m below and 3 m above msl. The accumulation of aeolian sand before 1500-1000 B.C. began to close the connection with the sea. At this time, the elevation of the surface of the lake water was approximately 5 m above msl, but it still remained connected to the ocean. Around 1000 B.C., the lake level rose quickly by 1 to 2 m during a period of renewed mobility of the coastal aeolian sand, and continued to rise slowly until about 100 A.D. when there was a gradual closure of the lake outlet. This rise forced people who were living on the lake shore and along the rivers to move to higher land along the valley. The nearby Gallo-Roman site of Losa was settled at the end of the 1st century B.C.; then the final blocking of the outlet occurred because of spit growth as a result of north-south littoral drift accompanied by the deposit of aeolian sand. This led to the lake level rising rapidly. Consequently, Losa was abandoned in the 3rd century A.D. and ruins of its temple (at 17 m above msl) were submerged in the 6th century. Further oscillations of the lake level probably correspond to water table fluctuations before it became stable at around 1000 A.D.The highest lake level (23.35 m) was reached during the 18th century as a consequence of modern dune formation, and thus was artificially reduced to 21 m in 1840 by construction of an overflow channel.

SUMMARYPotassium chloride (KCl) is the most widely used fertilizer in oil palm (Elaeis guineensis) plantations and the rates applied are based on interpretation of leaf K contents. When no positive response on leaf K contents can be detected, no optimum content can be established whatever the yield response to KCl rates. We used data from 13 fertilization trials conducted on several continents to study the responses of leaf K, leaf Cl, leaf Ca and yield to KCl rates as a function of the soil properties of each site. We found that the abundance of exchangeable Ca in the soil expressed as a percent of the cation exchange capacity (CEC) was the best soil variable to predict if leaf K content would increase with KCl rates. In addition, we found that the leaf K contents of unfertilized controls at the end of the trials were also correlated with Ca/CEC. This ratio thus appears to be a better index of soil K reserves than soil exchangeable K content.