Consistent data on tropical peat forest disturbances and associated greenhouse gas (GHG) emissions remain limited. We quantified and compared driver-specific GHG emissions from aboveground biomass (AGB) loss, peat decomposition and fire from peat forest disturbances in Indonesia, Peru, and Democratic Republic of Congo (DRC) over 2020-2021. Direct drivers were identified through visual interpretation of Planet (4.77 m) and Sentinel-2A (10 m) imagery for 1000 randomly sampled disturbance events per country. We estimated CO2 emissions from AGB loss using pre-disturbance data from the Climate Change Initiative Biomass product. Emissions (CO2, CH4 and N2O) from peat decomposition were calculated using driver-specific emission factors. We computed emissions from fire applying refined values for prescribed peat fires. Large-scale agriculture was the primary driver of emissions in Indonesia (48%), followed by smallholder agriculture (26%), and grassland (10%). Conversely, smallholder agriculture was the dominant driver of emissions in Peru (59%) and DRC (94%). Logging contributed to emissions across all countries, while mining, road development, and river meandering were relevant mainly in Indonesia and Peru; windstorms played a minor role in Peru. Fire accounted for half of emissions and was predominantly linked to agriculture (80% in Indonesia, 75% in Peru, and 95% in DRC). Overall, CO2 was the dominant GHG (72%), followed by CH4 (20%) and N2O (8%). Across countries, combined emissions from AGB loss, peat decomposition and fire in the disturbance year (2020) exceeded post-disturbance peat decomposition emissions in 2021 by 19-20 times. Nevertheless, cumulative peat decomposition over two decades will eventually reach the massive emissions released from all sources in the disturbance year. Our analysis provides the first systematic cross-country comparison of driver-specific GHG emissions in tropical peat forests, underscoring the major role of fire associated with agricultural expansion and the long-term importance of post-disturbance peat decomposition. These findings offer key insights to inform (inter) national emission reduction policies and strengthen reporting of peat forest emissions under frameworks such as the Paris Agreement.
Tag: decomposition
Resource capture and utilization in intercropping: water
The capture and utilization of water by sole and intercrops are compared by decomposing crop production/unit area into uptake/unit area (capture) and production/unit uptake (utilization efficiency). Data are from published studies. Comparisons are made by contrasting data from the intercrops against weighted means from the sole crops, with weights based on the proportion of each species in the intercrop. Water capture by intercrops differs from water capture by sole crops only slightly (usually between 6 and +7%). Water-utilization efficiency by intercrops, however, greatly exceeds water-utilization efficiency by sole crops, often by more than 18% and by as much as 99%. Four mechanisms that may account for the consistent increases in water-utilization efficiency by intercrops are postulated on the basis of crop water relations theory but empirical data from intercropping studies are not adequate to test them. The water-utilization efficiency response by intercrops to increased levels of seasonably available water differs from the response by sole crops. Variation in plant density often affects water-utilization efficiency.
Production and decay of structural root material of winter wheat and sugar beet in conventional and integrated cropping systems
Production of structural root material of sugar beet and winter wheat was quantified by analysis of root growth and decay in a time series of minirhizotron images, combined with a single auger sampling. Cumulative root production of winter wheat was about 1700 kg ha1 for conventional crp management and 1960 kg ha1 for integrated (less pesticides and mineral fertilizer, less intensive soil tillage and more organic manure) crop management; in 1990 the difference between the two management systems was statistically significant. At harvest time 85% and 68% (in 1986 and 1990, respectively) of this structural root production remained as intact roots in the soil in both management systems. For sugar beet total fine root production was estimated at 1150 kg ha1 in 1987 and 1989, with a significantly lower amount on the field on which minimum tillage was introduced in 1986; on average 47% of total root production remained as intact roots at harvest.Winter wheat root decay was studied with litter pots after crop harvest and in the following growing season. Initially, the N concentration in remaining roots increased while dry weight decreased. No net immobilisation or mineralisation of N and P during autumn was evident. During the next growing season net mineralisation was proportional to loss of root weight in an exponential decay with a half-life of 600 degree days (daily temperature sum). This N release pattern during the next growing period thus contributes to the synchrony between N demand and supply, but no difference between the two management systems was found.
Integrating leguminous trees and shrubs in cropping systems of Southern Africa
Soil and water management is an essential element in food security, agriculture sector growth and sustainable land management of sub-Saharan Africa (SSA). The increased land degradation and declining fertility of SSA soils contribute to food insecurity and poverty. Previously, agroforestry researchers tended to focus mostly on soil nutrient replenishment as being solely responsible for post-fallow crop yield dynamics. Missing from many studies on soil fertility issues is the recognition of the important role of soil physical properties in agricultural productivity. However, many factors affect soil fertility and some agroforestry measures taken to correct soil nutrient deficiencies can also produce desirable soil physical effects. We hypothesized that planted tree fallows can potentially increase soil N status and improve soil physical properties, thus increasing subsequent crop yields. Field studies were conducted on infertile sandy clay loams at Msekera and Kagoro, Zambia, to determine the effect of contrasting fallows (natural fallow, planted non-coppicing and coppicing tree fallows) and no-tree no-fallow [maize (Zea mays L.) with and without fertilizer] on soil fertility and maize yields. This study attempted to address agricultural productivity by viewing soil fertility in terms of both chemical and physical properties. Hence, this report discusses the implications of improving the nutrient status of soils without correcting soil physical constraints. Data from both tree-(agroforestry) and non-tree-based systems have been used to illustrate important physical and chemical changes that occur in soils as a consequence of varying management regimes or cropping systems. Such data show that the concept of soil productivity refers to more than replacement of the lost nutrients. Other aspects include soil structure, soil water retention, water storage, infiltration and soil penetration resistance. The results imply that standard inputs such as mineral or organic fertilizers can maintain only some elements of soil productivity. Therefore, a broader view that incorporates the role of soil physical properties and water in influencing productivity is appropriate. This research does not attempt to provide a comprehensive treatment of all aspects of soil fertility in agroforestry systems. For example, it does not address the role of soil biota diversity in soil productivity.
Litter-derived nitrogen reduces methane uptake in tropical rainforest soils
Litter comprises a major nutrient source when decomposed via soil microbes and functions as subtract that limits gas exchange between soil and atmosphere, thereby restricting methane (CH4) uptake in soils. However, the impact and inherent mechanism of litter and its decomposition on CH4 uptake in soils remains unknown in forest. Therefore, to declare the mechanisms of litter input and decomposition effect on the soil CH4 flux in forest, this study performed a litter-removal experiment in a tropical rainforest, and investigated the effects of litter input and decomposition on the CH4 flux among forest ecosystems through a literature review. Cumulative annual CH4 flux was −3.30 kg CH4-C ha−1 y−1. The litter layer decreased annual accumulated CH4 uptake by 8% which greater in the rainy season than the dry season in the tropical rainforest. Litter decomposition and the input of carbon and nitrogen in litter biomass reduced CH4 uptake significantly and the difference in CH4 flux between treatment with litter and without litter was negatively associated with N derived from litter input. Based on the literature review about litter effect on soil CH4 around world forests, the effect of litter dynamics on CH4 uptake was regulated by litter-derived nitrogen input and the amount soil inorganic nitrogen content. Our results suggest that nitrogen input via litter decomposition, which increased with temperature, caused a decline in CH4 uptake by forest soils, which could weaken the contribution of the forest in mitigating global warming.
Soil-mediated filtering organizes tree assemblages in regenerating tropical forests
Decomposition: driven by nature or nurture?
Although the carbon flow involved in decomposi- tion is approximately equal to that in primary pro- duction, the amount of research is far less. A recent symposium under the title “Driven by Nature” re- viewed the role of plant litter quality in determining decomposition in terrestrial ecosystems, both in the tropics and in the temperate region (Cadisch and Giller, 1996). In as far as decomposition of plant residues is indeed fully ‘driven by their nature’, i.e. determined by the physical, chemical and biological qualities of the organic residue, a fairly small re- search attention might be justified. In practice, how- ever, the biotic and abiotic environment in which decomposition takes place (the ‘nurture’) has a con- siderable modifying effect both on the rate at which decomposition occurs and on the end-products formed (CO 2, CH 4, humus, charcoal). The role of cell and tissue structure as well as ‘secondary’ metabolites during the life of the plant can now be connected to their effects during decomposition after death of the plant (or its parts).
Multipurpose tree prunings as source of nitrogen to maize under semi-arid conditions in Zimbabwe: 3. Interactions of pruning quality, time and method of application. Agroforestry Systems
Decomposition- and N-mineralization rates of multipurpose tree prunings applied as a source of N to annual crops in agroforestry systems are affected by the chemical composition and method and time of application of the prunings and the soil type. In a greenhouse study undertaken on two contrasting Zimbabwean soils, there was a significant interaction of pruning quality with time and method of pruning application on nitrogen recovery by maize and residual effects on a subsequent maize crop on both soil types. Incorporating prunings in the soil at planting gave higher nitrogen recovery compared to surface application at two or four weeks after planting for all three MPT species used.Flemingia macrophylla showed prolonged N immobilization on an Alfisol (sandy clay loam) but not on the Psamment (sandy soil). Nitrogen recovery by the second maize crop (residual effect) was influenced by pruning quality, time of application, and soil type. Low-quality prunings such asFlemingia macrophylla andAcacia angustissima applied four weeks after planting gave higher residual effect on N recovery on the Alfisol than on the Psamment (3% vs. 6%).
Alley cropping of maize with calliandra and leucaena in the subhumid highlands of Kenya: Part 2. Biomass decomposition, N mineralization, and N uptake by maize
A major challenge in developing agroforestry approaches that utilize tree-leaf biomass for provision of N to crops is to ensure synchrony between the N released from decomposing prunings and N demand by crops. A study was conducted in the subhumid highlands of Kenya to assess the rate of decomposition and mineralization of soil-incorporated Calliandra calothyrsus Meissner (calliandra) and Leucaena leucocephala (Lam.) de Wit (leucaena) tree biomass and maize roots (Zea mays L.) both in an alley cropping and a sole cropping system. The amount of mineralized N peaked four weeks after planting (WAP) maize in all the treatments during both seasons of 1995. Cumulative mineralized N at week 20 ranged from 114 to 364 kg N ha1 season1, the absolute control treatment giving the lowest and the prunings-incorporated treatments giving the highest amounts in the two seasons. Total N uptake by maize, ranging from 42 to 157 kg ha1 season1, was lowest in the ‘alley-cropped, prunings-removed’ treatments, and highest in the ‘non alley-cropped-prunings-incorporated’ treatments. The apparent N recovery rate by maize was highest in the fertilizer applied treatments in the two seasons. Decomposition rate constants (kD) ranged from 0.07 to 0.21 week1, and the rates among the different plant residues were as follows: leucaena < calliandra < maize roots. Nitrogen release rate constants (kN), ranging from 0.04 to 0.25 week1, followed a similar pattern as the rate of decomposition with leucaena releasing the highest amount of N followed by calliandra and lastly by maize roots
Carbon, nitrogen and phosphorus mineralization from tree leaves and manure
Farmers in developing countries cannot afford inorganic fertilizers. Multipurpose tree leaves or livestock manure are major sources of nutrients for soil fertility replenishment. Nutrient release from these organic inputs depends on their chemical composition and on soil properties. This study determined the chemical composition of leaves of four African browse species and manure from goats fed leaves as protein supplements, and their mineralization of C, N and P. Cumulative evolved CO2 was significantly correlated with the initial N content of the organic inputs (r 0.83, P<0.05) and the C:N ratio (r 0.80, P<0.05), and was negatively correlated with the lignin:N ratio (r–0.71, P<0.05). Cumulative P released was negatively correlated with the C:P ratio (r 0.76, P<0.05) and positively correlated with initial P content of the organic amendments (r 0.76, P<0.05). Cumulative N mineralized was not significantly correlated with initial N, lignin or P concentrations of the organic inputs. Leaves from Acacia karro and Acacia nilotica had high concentrations of polyphenols, which may have caused immobilization of N in both leaves and manure. Gliricidia sepium leaves had low amounts of soluble polyphenols, a high N content and a high rate of N mineralization, but the manure from goats fed Gliricidia leaves immobilized N. The leaves of all browse species immobilized P, but the manure released P. The results suggested that some browse leaves cannot meet the N and P requirements of crops due to their low P content and prolonged N and P immobilization. However, the manures had higher P contents and rates of P mineralization, which suggested that manure is a good source of P for crops. The implications of these results for nutrient cycling in mixed farming systems is discussed.