Nitrogen cycling in tree plantations grown on a poor sandy savanna soil in Congo

doi:10.1016/0929-1393(96)00096-0

Applied Soil Ecology

Volume 4, Issue 2, September 1996, Pages 161-172

https://doi.org/10.1016/0929-1393(96)00096-0 Get rights and content

Abstract

Fast growing Eucalyptus trees are grown in Congo for industrial purposes, on a very poor sandy savanna soil. The sustainability of such land use is questionable, particularly regarding nutrient availability. Among the lacking nutrients, nitrogen (N) deserves special attention as N status is supposed to be improved by N-fixing trees. To assess N changes in tree plantations, N cycling was studied in Eucalyptus and Acacia stands and compared to the native savanna.

Nitrogen accumulation in vegetation and soil, together with N flows in the ecosystem, were estimated. It was assumed that the difference between N amounts in Acacia stands and in Eucalyptus stands was an estimate of the amount of N fixed symbiotically in the former.

The results showed that 800–1000 kg N ha⁻¹ were accumulated during 7 years in Acacia stands. Nitrogen fixation was higher in Acacia auriculiformis than in Acacia mangium.

Nitrogen cycling through litter fall was high in Acacia stands, up to 170 kg ha- I per year, and low in Eucalyptus and Pinus stands. However, in Eucalyptus stands, slow litter decay and reduced N release from decaying litter resulted in a relative accumulation of organic N in the forest floor.

Decrease in N content was observed in organomineral fractions under the trees. In top-soil (0–10 cm) N mineralization was higher in tree stands than in savanna and total N decreased significantly under 7-year-old Eucalyptus. Under older Eucalyptus, decreasing N content of organic matter was shown by the increase in $C N$ ratio. Under Acacia, soil N increase was significant in the older stands studied but not in the younger ones, and fixed N accumulated in trees and in the forest floor first. The implications of these observations are discussed.

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This result was different from those of several previous studies, which reported that soils in acacia stands emitted a larger amount of N2O than soils in eucalyptus stands (Dick et al., 2006; Li et al., 2010; Zhang et al., 2014). Studies have reported that eucalyptus stands generally have lower N input from litterfall (Bernhard-Reversat 1996; Forrester et al., 2005), slower N mineralization (Li et al., 2001; Tchichelle et al., 2017), and a smaller N pool in the litter (Voigtlaender et al., 2012; Tchichelle et al., 2017) than acacia stands, which should provide a smaller amount of N resources for N2O production in eucalyptus stands. In the present study, the N input from litterfall in the eucalyptus stands was much lower than that in the acacia stands (Table 1).
Tropical monoculture leguminous tree plantations are important nitrous oxide (N₂O) sources, especially in the Asian tropics. We evaluated the effect of conversion from leguminous Acacia mangium to non-leguminous Eucalyptus pellita on N₂O emissions. A 4-year monitoring experiment was conducted in three areas in South Sumatra, Indonesia. In each area, we established acacia and eucalyptus plantation sites adjacent to one another after the harvest of acacia trees. In contrast to our expectation, the averaged N₂O flux at the eucalyptus stands (1.07 mg m⁻² day⁻¹ of N) was not significantly different from that at the acacia stands (0.96 mg m⁻² day⁻¹ of N). This result was attributable to the higher soil NO₃ content in the eucalyptus stands than that in the acacia stands, which was due to the lower N requirement of eucalyptus than that of acacia. In conclusion, converting leguminous acacia to non-leguminous eucalyptus was not an effective option to mitigate N₂O emissions in the short term.
Litter and topsoil in Alnus subcordata plantation on former degraded natural forest land: A synthesis of age-sequence
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Alder (Alnus subcordata C. A. M.), as N-fixing tree, are preferred plantation species that may change soil microbial community and play a vital role in nutrient cycling. Litter and topsoil in different ages of alder plantation by focusing on microbial and enzyme activities have not yet been studied. This study is aimed at examining the effect of 15, 20 and 25 years old of alder plantation compared to without tree cover (WTC) area in northern Iran. Thirty samples per site were collected from the litter and soil (20 × 20 × 10 cm) layers. Following variability of litter quality, soil physicochemical and biological properties, the microbial activities which related to soil C and N has been changed. Basal respiration (BR), substrate inducted respiration (SIR), microbial biomass carbon (MBC), metabolic quotient (qCO₂), microbial entropy (MBC:C), carbon availability index (CAI), carbon management index (CMI), particle organic carbon (POC) and dissolved organic carbon (DOC) were reported to be significantly higher in 25 years old plantation than in 20 and 15 years old plantation and WTC area. Also, NH₄⁺, NO₃⁻, and N mineralization, microbial biomass nitrogen (MBN), particle organic nitrogen (PON) and dissolved organic nitrogen (DON) were significantly higher in older plantations. Enzymes activities (i.e., urease, acid phosphatase, arylsulfatase and invertase) were significantly higher in alder plantation compared to WTC area with an increase in 25 years old plantation. Our findings highlight the importance of monitoring the plantation effects on C and N cycling that can be involved with global warming phenomena.
Nitrogen dynamics in a nutrient-poor soil under mixed-species plantations of eucalypts and acacias
2017, Soil Biology and Biochemistry
Citation Excerpt :
Faster rate of litter decomposition, thus higher nitrogen release from decaying litter through mineralisation, may result in lower accumulation of soil organic N under acacia trees than under eucalypt trees (Bernhard-Reversat, 1996). Higher rate of N mineralisation under acacia trees than under eucalypt trees is commonly observed in tropical plantations (Bernhard-Reversat, 1996; Parrotta, 1999; Li et al., 2001; Voigtlaender et al., 2012). Faster turnover rate of N is thus expected in stands where acacia is planted either alone or in mixture.
Introducing nitrogen-fixing species (NFS) in eucalypt plantations is a useful practice to compensate nitrogen loss at harvest, reduce fertilizer inputs, improve soil fertility and sustain forest productivity in low input systems. Nitrogen (N) and carbon (C) were evaluated in the active part of soil organic matter (SOM) i.e., the particulate organic matter (POM), which was obtained after soil (0–0.05 m) physical fractionation at the end of a first 7-year rotation (R1Y7) and at year 2 of a second rotation (R2Y2) in pure acacia (100A), pure eucalypt (100E) and mixed-species (50A50E) stands in an experimental plantation established on an Arenosol in the Congolese coastal plains. N concentration (in g kg⁻¹ of soil) was higher in coarse POM (cPOM, 4000–250 μm) in 100A and 50A50E compared to 100E at 2YR2, while no difference was found in fine POM (fPOM, 250–50 μm) and in the organo-mineral fraction (OMF, < 50 μm). N content in cPOM was more than 3 times higher at R2Y2 than at R1Y7. A slight increase was also observed in fPOM, while no difference was observed in OMF between R1Y7 and R2Y2. Lower C:N ratios in the two POM fractions in 100A and, to a lesser extent, in 50A50E compared to 100E suggests an improved soil N status after acacia trees have been introduced in eucalypt plantations. The lack of difference in N content of coarse POM between 100A and 50A50E at R1Y7, despite higher amount of N in the forest floor and N returning to the soil (harvest residues and litterfall) in 100A than in 50A50E, suggests a faster cycling of nitrogen under acacia than under eucalypt.
Changes in above- and below-ground nitrogen stocks and allocations following the conversion of farmland to forest in rocky desertification regions
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In other words, the top-soil in karst areas of SW China constitutes the main reservoir for N in the overall ecosystem budget while the soil is vulnerable to natural or human-induced erosion and disturbance. Therefore, best management practices in plantations, as outlined in the GGP, need to be implemented to improve the soil quality and promote N storage (Bernhard-Reversat, 1996). The biomass nitrogen storage (both above-ground and below-ground parts) in Z. bungeanum plantations rapidly increased from 0.94 kg N ha⿿1 for the 1-year-old stand to 262.12 kg N ha⿿1 for the 10-year-old stand (Table 5).
Afforestation of degraded land is one of the principal strategies for preventing soil erosion and promoting ecosystem recovery in fragile regions, especially in rocky desertification areas. In China, millions of hectares of farmland have been converted into forest in order to arrest and reverse rocky desertification under the Grain for Green Program (GGP). This study evaluated implications of land-use change from annual maize cultivation to perennial Zanthoxylum bungeanum plantations (1-, 4-, 7-, and 10-year-old) in the karst region of Guizhou province, southwest China. The study analyses the variations of biomass and nitrogen (N) storages as well as N distributions in biomass components and soil depths. Results showed that the N content in components of Z. bungeanum ranged from 0.31% to 3.24% with a mean value of 1.75%, which was lower than that of maize (2.13%) in the same region. The biomass N storage measured for the maize cropland was 210.59 kg ha^⿿1, while this value increased linearly with stand ages for the four Z. bungeanum plantations (0.94, 108.31, 212.20, and 262.12 kg ha^⿿1, respectively). The average amount of soil N storage in the Z. bungeanum plantations (9.33 t ha^⿿1) was significantly lower than in the adjacent intensively managed maize cropland (10.04 t ha^⿿1). This is mainly due to long-term organic and inorganic fertilizer inputs in the farmland stage. Total ecosystem N storage averaged 10.25 t ha^⿿1 in the maize cropland, and 9.38, 9.82, 9.05, and 9.67 t ha^⿿1 in the 1-, 4-, 7- and 10-year-old Z. bungeanum plantations, respectively. Soils accounted for 97% of total ecosystem N storage in both land-use systems. This study suggests that the reduction of surface soil disturbance during plantation management practices plays a crucial role in improving the N storage. Data of annual plantation area and biomass N accumulation rates under the GGP indicate that Guizhou province was a net N sink with 2.35 ÿ 10⁸ kg N in 2010, corresponding to 41.45% of N (NO_X-N and NH₃-N) emissions in that year. Besides increasing N sequestration over time (as these forest mature), the large-scale plantations of Z. bungeanum have the potential to restore severely degraded soils in the karst region of SW China.
Effects of tree species on topsoil properties and nitrogen cycling in natural forest and tree plantations of northern Iran
2016, Catena
Citation Excerpt :
Scott and Binkley (1997) found that the net N mineralization was controlled by the forest litter fall quality by influencing the SOM quality. Increase in N mineralization has been ascribed by some authors to higher soil nutrient content and resulting lower tannin levels (Reversat, 1996). The results of this study showed that there is negative correlation between C and N mineralization.
After 15 years, the effects of Alnus subcordata (AS), Populus deltoides (PD), Taxodium distichum (TD) plantations and a mixed natural forest dominated by Quercus castaneifolia, Carpinus betulus and Parrotia persica (QC-CB-PP) on litter quality and soil fertility were assessed in northern Iran. Sixteen samples per stand were taken from the forest floor and top 10 cm of soil. Litter quality differed among the tree species, showing the highest N concentration (1.85%) and lowest C (39.43%) in the AS stand. Sand, clay and water content did not differ for the tree species, but soil bulk density were highest in AS (1.59 g cm^− 3) ≈ PD (1.56 g cm^− 3) and silt content peaked in QC-CB-PP (47%). Soil pH (7.16), EC (0.29 dS m^− 1), total N (0.34%), available P (24.6 mg kg^− 1), available K (337.4 mg kg^− 1), available Ca (256.3 mg kg^− 1), available Mg (57.4 mg kg^− 1), earthworm density (3.5 individuals m^− 2), earthworm biomass (42 mg m^− 2) and microbial respiration (0.48 mg CO₂-C g soil^− 1 day^− 1) were significantly higher in the AS stand. In contrast, higher contents of soil organic C (2.58%) and C/N ratio (28.70) were found in the TD stand. The fine root biomass varied among the study sites in the ranked order of QC-CB-PP (94.2 g m^− 2) > PD (65.1 g m^− 2) ≈ AS (64.6 g m^− 2) > TD (36.9 g m^− 2). Negative nitrification rates were observed in all forest types. Net soil ammonification and N mineralization rates were significantly higher in the AS (0.46 and 0.31 mg kg^− 1 d^− 1, respectively) than in the PD (0.22 and 0.08 mg kg^− 1 d^− 1, respectively), QC-CB-PP (− 0.07 and − 0.24 mg kg^− 1 d^− 1, respectively), and the TD (− 0.07 and − 0.26 mg kg^− 1 d^− 1, respectively) sites. Our study reveals the differential impacts of tree species on the physical, chemical, and biological properties of the topsoil. In particular, planting N₂-fixing Alnus subcordata can help increase soil fertility in northern Iran.
Nutrient leaching and deep drainage under Eucalyptus plantations managed in short rotations after afforestation of an African savanna: Two 7-year time series
2013, Forest Ecology and Management
African savannas developed an efficient strategy of nutrient uptake and control of nitrification making it possible to avoid large losses of nutrient by drainage. The conversion of native savanna into commercial forest plantations is an important global change driver that potentially impacts element cycles.
Afforestation of native Congolese savannas by Eucalyptus started 30 years ago. Large amounts of nutrients are removed through biomass harvesting every 6–7 years. Losses of nutrients by deep drainage might be a serious threat for the sustainability of these plantations, established on sandy soils with high hydraulic conductivities.
We compared the soil N-mineralisation, the nutrient fluxes and deep drainage beneath savanna and Eucalyptus plantation in Congo. Then, we discussed the strategy of nutrient recycling.
The water fluxes at a depth of 400 cm were approximately 20% higher in the savanna than in Eucalyptus plantation.
Although the nitrification rate and solution chemistry exhibited strong modifications during the first year following both savanna afforestation and the harvesting of the Eucalyptus stand, the losses of nutrients by deep drainage remained unexpectedly low. The largest fluxes of drainage at a depth of 6 m were found for ${NH}_{4}^{+} -N$ , which reached a maximum of 0.4 g m⁻² yr⁻¹ in the second year following savanna afforestation and 1 g m⁻² yr⁻¹ in the first year after clear cutting. The deep drainage of ${NO}_{3}^{-} -N$ , Mg²⁺, Ca²⁺ and K⁺ did not exceed 0.2 g m⁻² yr⁻¹ in the savanna and at any stage of plantation development. These results are discussed regarding (i) the roots distribution in the soil of each ecosystem and (ii) the nutrient accumulation in biomass.
The limited changes between the nutrient fluxes in both ecosystems were the result of fast root growth in the deep soil layers after planting, combined with an intense uptake of the tree roots to satisfy the large nutrient and water requirements for the development of tree crowns.
Intense uptake and cycling of nutrients mitigated the risk due to clear cut and N fertilisation in this forest plantation. Nevertheless, forest managers must carefully fit fertilisation regimes to the nutrient requirements of new clone selected by breeding programmes and reduce as much as possible the delay between harvesting and re-planting to avoid high losses by deep drainage.

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¹: Present address: Laboratoire d'Ecologie des Sols Tropicaux, ORSTOM, Centre d'lle de France, 32 Avenue Henri Varagnat, 93143 Bondy Cedex, France.

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Nitrogen cycling in tree plantations grown on a poor sandy savanna soil in Congo

Abstract

Zentralbl. Bakteriol. Abt. II

For. Ecol. Manage.

Soil Biol. Biochem.

Soil Biol. Biochem.

For. Ecol. Manage.

For. Ecol. Manage.

Sci. Total Environ.

Soil Biol. Biochem.

Soil Biol. Biochem.

Soil Biol. Biochem.

Soil Biol. Biochem.

Carbon and N mineralization and denitrification in a humid savanna of West Africa (Lamto Côte d'lvoire).

Acta Oecol.

Nitrogen accretion and soil biomass production by three Prosopis species

Agrofor. Syst.

L'azote du sot et sa participation au cycle biogéochimique en foret ombrophile de Côte d'Ivoire

Rev. Ecol. Biol. Sol.

Biogeochemical cycle of N in a semi-arid savanna

Oikos

Le recyclage des éléments minéraux par la strate herbacée dans un peuplement naturel à Acacia seyal et dans une plantation d'Eucalyptus au Sénégal

Acta Oecol. Oecol. Gen.

Litter incorporation to soil organic matter in natural and planted tree stands in Senegal

Pedobiologia

Dynamics of litter and organic matter at the soil-litter interface in fast-growing tree plantation on sandy ferallitic soils (Congo)

Acta Oecol.

Biomasse, minéralomasse et productivité en plantation d' Acacia mangium et A. auriculiformis au Congo

Bois Forets Trop.

Inhibition de la nitrification par des extraits acqueux de litière de Teck (Tectona grandis) et de Niaouli (Melaleuca leucodendron)

Rev. Ecol. Biol. Sol

Inorganic forms of N.

The fate of nutrients during fires in a tropical savanna

Aust. J. Ecol.

Biological N fixation in trees in agro-ecosystems

Plant Soil

Recherches sur la minéralisation de l'azote dans les sols de savanes de Lamto (Côte d'Ivoire)

Rev. Ecol. Biol. Sol

Potential for N fixation in tropical legumes and grasses

Nitrogen fixation by trees

Une méthode de fractionnement granulometrique de la matière organique des sots. Application aux sots tropicaux a textures grossiès très pauvres en humus

Cah. ORSTOM Set. Pédol.