Fallow System Research Articles

Weed biomass dynamics in planted fallow systems in the humid forest zone of southern Cameroon

Interest in planted fallow systems has focused on soil fertility improvement, neglecting other potential benefits of such systems. It is important to quantify other processes responsible for crop yield increases under planted fallows, such as weed control. The suppressive potential on weeds of Flemingia macrophylla [(Willd.) Merrill] and Pueraria phaseoloides (Roxb.) Benth, planted fallows was evaluated in field trials in three villages in southern Cameroon. In each village, experiments were set up in 4–5 year-old bush fallow dominated by Chromolaena odorata (L.) R. M. King & H. Rob. and 20 year-old secondary forest. Total aboveground biomass production of P. phaseoloides was 7.45 Mg ha−1, 4.2 times higher than F. macrophylla (1.78 Mg ha−1 ; P < 0.05). The high biomass of P. phaseoloides resulted in a significantly greater reduction in total weed biomass compared to Flemingia macrophylla in both wet and dry seasons. In the wet season (11 and 18 MAP), there were significant fallow system × land use and fallow system × village interactions for total weeds and broadleaf weeds. P. phaseoloides in bush (0.55 Mg ha−1), and P. phaseoloides at Ngoumou (0.09 Mg ha−1) had the lowest total weeds in the wet seasons. After the dry season, the lowest total weed mass was consistently recorded in P. phaseoloides while the highest was in the natural regrowth. The population of grasses was always higher in the F. macrophylla system than in P. phaseoloides system throughout the wet and dry seasons. Grass biomass in the P. phaseoloides-forest LUS was the least (0.01 Mg ha−1), 58 times lower than in F. macrophylla-bush (0.58 Mg ha−1). Biomass production of P. phaseoloides was highly significantly correlated with total weed biomass (r = −0.64; P = 0.004) while no relationship was found between biomass production of F. macrophylla and total weed biomass (r = −0.08, P = 0.747). It was concluded that P. phaseoloides was a suitable leguminous species for weed control. But for F. macrophylla, its low biomass production coupled with a compact plant architecture compromised it as an appropriate species for weed control in a planted fallow system.

Performance of an improved fallow system in the Peruvian Amazon—modelling approach

As traditional slash-and-burn systems with prolonged fallow periods are no longer feasible in most parts of the tropics, improved agroforestry systems have high potential to increase the productivity of farming systems and sustain continuous crop production. Our objective was to assess biophysical and economic performance of planted leguminous tree fallow (using Inga edulis) compared to the traditional slash-and-burn farming system, practiced by farmers on fields infested with noxious weedy grass Imperata brasiliensis around the city of Pucallpa, Peru. An existing agroforestry model SCUAF was used to predict biophysical factors, such as changes in soil characteristics and farm outputs (crop and tree yield). While a cost-benefit analysis spreadsheet, which uses the output from SCUAF and economic data on input/output levels and prices, calculates economic performance of the systems. The Inga fallow system can provide improvements to a range of soil biophysical measures (C, N, P content). This enables higher levels of farm outputs to be achieved (higher cassava yields). However, for smallholders the improved system must be more economically profitable than the existing one. At prices currently encountered, the Inga fallow system is more profitable than the Imperata fallow system only in the long-term. In adopting the Inga fallow system, smallholders will incur lower profits in the first years, and it will take approximately 10 years for smallholders to begin making a profit above that achievable with the Imperata fallow system. Unless smallholders are capable of accepting the lower profitability in first years, they are less likely to adopt the new system.

A Janus-faced biodiversity change and the partiality of ecological knowledge in a world biodiversity hotspot in Ghana: Implications for biodiversity rehabilitation

The Gyamfiase–Adenya–Obom cluster of villages in the forest-savanna region of Ghana is located within one of Conservation International’s 34 “World Biodiversity Hotspots” of the most biodiversity-threatened regions of the world. In collaboration with local farmers in this area since 1993, the People, Land Management and Ecological Change Project in Ghana (PLEC-Ghana) has been working on promoting biodiversity rehabilitation to address problems of biodiversity change. This goal is expected to be achieved through agrobiodiversity or biodiversity-friendly agricultural practices. However, farmers’ employment of these practices has been lackluster, even while they acknowledge biodiversity changes, dominated by Chromolaena odorata and other herbaceous species, that are driving the decline in forests and their biodiversity. In interpreting the difficulties of biodiversity rehabilitation in Gyamfiase–Adenya–Obom, this study outlines the diverging ecological knowledge of non-residents/outsiders and local farmers about biodiversity change, which it describes as Janus-like with two diverging faces. One face of biodiversity change shows the detrimental impacts on biodiversity and its observers—non-residents/outsiders—insist on biodiversity rehabilitation that nurtures forests, and the growth and domination of tree species. The other face of biodiversity change shows its agronomic advantages and its observers—the local farmers—are skeptical of current biodiversity rehabilitation practices. Farmers see agronomic benefits in biodiversity change, in particular the benefit of faster soil regeneration within the predominant bush fallow system of farming. And as a result of this observation, farmers continue with practices that sustain a decline in forests and biodiversity. Based on social and ecological research that explores three biodiversity-friendly practices promoted by PLEC-Ghana (fallow management, mulching, and intensive weeding to protect tree seedlings), this article discusses the partiality of ecological perspectives that emphasize either face of biodiversity change but not both, and the implications for biodiversity rehabilitation.

Daytime, Temporal, and Seasonal Variations of N2O Emissions in an Upland Cropping System of the Humid Tropics

Nitrous oxide (N2O) contributes to global climate change, and its emission from soil–crop systems depend on soil, environmental, and anthropogenic factors. Thus, we evaluated the variability of N2O emissions measured by microchambers (cross section: 184 cm2) from a groundnut–fallow–maize–fallow cropping system of the humid tropics. The crops received inorganic nitrogen (N) plus crop residues (NC), inorganic N alone as ammonium sulfate (RN), and half of the inorganic N along with crop residues and chicken manure (N1/2CM), amounting for the crop rotation to 322, 180, and 400 kg N ha−1 yr−1, respectively. The N2O fluxes during the groundnut–maize crop rotation were log‐normally distributed, and the frequency distributions were positively skewed. Daytime changes in N2O fluxes were inconsistent, and the 50% of total N2O emission during the 12 h measurement periods was attained earlier under maize (∼11∶00 h) than groundnut covers (∼13∶00 h). Spatial variability in each treatment with eight gas chambers was large but smaller during the cropping periods than the fallow, indicating masking efficiency of crop covers for the soil heterogeneity that was accelerated presumably by antecedent climatic variables. The temporal variability of N2O emissions was also large (coefficients of variation, CV, ranged from 60 to 81%), involving both input differences between treatments and measurement periods. As such, the relative deviation from the annual mean of total N2O emission was high during the period after a large N application with a maximum of +480%, due to addition of chicken manure. The seasonal contribution of summer and monsoon to N2O emissions was insignificant. However, intensive rainfall negatively (−0.65**) and the amount of added N from either source positively (0.83***) correlated with the integrated N2O emissions, and those were exponential. Results suggest that around noon (12∶00 h) gas collection could represent well the daily N2O fluxes, increasing the number or size of the gas chambers could minimize the large variability, and mainly the rainfall and N inputs regulated its emissions in the humid tropics of Malaysia.

Effect of Mucuna Fallow on Weed Dry Matter and Composition in Succeeding Maize

ABSTRACT Weeding requires a major proportion of labour in farming of smallholders in Africa. Any technology that can effectively reduce the weeding requirement increases the productivity of the household. Studies were conducted on farmers' fields in the Sunyani District (2°8' to 2°31′W latitude, 7°7' to 7°36' N longitude), located in the Forest-Savannah Transitional Zone of Ghana in 1999 and 2000 to assess the impact of two different slash-and-mulch Mucuna fallow systems on weed dry matter (DM), weed density and frequency in succeeding maize compared with the prevailing slash-and-burn natural fallow system. Late maturing Mucuna pruriens (L.) DC var. utilis (Wright) Burck reduced weed DM by 58% in 1999 and 68% in 2000. The system with the local early maturing Mucuna variety did not reduce weed DM significantly. On the whole, 58 weed species from 27 families were identified. The most dominant species were Chromolaena odorata (L.) R.M. King & Robinson, Centrosema pubescens Benth., Euphorbia heterophylla Linn, and Mucuna spp. volunteer seedlings. The M. pruriens system reduced eight persistent weeds (frequency of occurence < 20%) both in frequency and average density compared with the short season natural fallow treatment. In contrast, only two persistent weed species were affected in the same way by the system with the local Mucuna variety, while six persistent weeds increased in frequency of occurence and seedling density. Poaceae species were negatively affected by the Mucuna systems. While in the natural fallow treatment Poaceae comprised 27.8% of all species identified, their proportions were reduced to 23.1% and 21.7% after fallow with the local Mucuna variety and M. pruriens, respectively. The greater weed suppressing effect of M. pruriens is considered to be a result of its longer life span than the early maturing local variety.

A Study of Act to Green Manure Fallow System in Upland farming

A Study of Act to Green Manure Fallow System in Upland farming

Weed Control In Peanut Grown in a High-Residue Conservation-Tillage System

Information is needed on the role of cover crops as a weed control alternative due to the increase in adoption of conservation-tillage in peanut production. Field experiments were conducted from autumn 1994 through autumn 1997 in Alabama to evaluate three winter cereal cover crops in a high-residue conservationtillage peanut production system. Black oat (Avena strigosa Schreb.), rye (Secale cereale L.), and wheat (Triticum aestivum L.) were evaluated for their weed-suppressive characteristics compared to a winter fallow system. Three herbicide systems were utilized: no herbicide, preemergence (PRE) herbicides followed by (fb) postemergence (POST) herbicides, and PRE fb sequential POST herbicides. The PRE fb POST herbicide input system consisted of pendimethalin at 1.12 kg ai/ha fb an additional early POST application of paraquat at 0.14 kg ai/ha plus bentazon at 0.56 kg ai/ha. The PRE fb sequential POST herbicide input system contained the aforementioned herbicides fb 2,4-DB at 0.22 kg ai/ha plus chlorimuron at 0.14 kg ai/ha applied late POST. No cover crop was effective in controlling weeds without a herbicide program. However, when black oat or rye was utilized with PRE fb POST herbicides, weed control was similar to the high input system in two out of three years. Yield increased in 14 of 27 comparisons following conservation-tilled peanut using the Brazilian cover crop management system, compared to a winter fallow system. Yields never decreased following a winter cover crop compared to winter fallow. The winter fallow, high herbicide input system yielded between 7 and 26% less peanut compared to the highest yielding system that included a winter cover crop. The Brazilian system using black oat or rye cover crop has potential to increase peanut productivity and reduce herbicide inputs for peanuts grown in the Southeast.

Rapid decay of dolichos [Lablab purpureus (L.) Sweet] residue leads to loss of nitrogen benefit to succeeding maize (Zea mays L.)

The traditional natural fallows are no longer practicable in sub-Saharan Africa and technologies to replace them are being popularised through management of short fallow systems. Dolichos [Lablab purpureus (L.) Sweet] is among the legumes used to improve such fallows and its residues are incorporated to improve yield of succeeding cereal. Two field studies were conducted to determine dolichos residue mineralisation schedule and response of maize to timing of the residue incorporation, to establish if the current residue incorporation practice maximises nutrient benefit to succeeding cereal. Dolichos residue was applied at 2 t/ha in litterbags, buried in the field at 15-cm depth and retrieved after 1, 2, 4, 8 and 16 weeks, and the remaining debris analysed for loss of weight, N, P and K. A parallel split-plot experiment was set up to determine response of maize to time of residue incorporation, with or without fertiliser nitrogen supplementation. The main plot treatments were nitrogen fertiliser applied at 0, 30 and 60 kg/ha at sixth fully opened leaf in maize. The subplot treatments were residue management regimes, which included four residue incorporation times of 2, 4, 6, and 8 weeks before sowing maize, residue removal off the field, residue mulched on surface and traditional weedy fallow. Results show rapid loss of N, with 50% being released within the first 2–4 weeks after burying. Residue incorporated at 2 and 4 weeks before sowing improved maize yield, while residue removal off-field reduced yield comparably with the traditional weedy fallow. However, there were no statistical differences among the timing of the dolichos residue incorporation. These results reflect poor synchrony of mineralised N and uptake by succeeding maize as currently practiced and suggest residue incorporation closer to sowing maize to benefit the cereal.

Effects of tillage practices combined with mucuna fallow on soil erosion and water dynamics on Ishigaki Island, Japan

This study was conducted on a sloping field at the Japan International Research Center for Agricultural Sciences, Okinawa Subtropical Station, Ishigaki Island, Okinawa Prefecture, Japan, to evaluate the effects of zero tillage farming combined with mucuna fallow as a cover crop on soil erosion and water dynamics. Two fallow systems (natural and mucuna) in combination with two soil tillage treatments (zero tillage and conventional tillage) were imposed on three sloping fields (2.0°, 3.5° and 5.0°). A sorghum crop (Sorghum bicolor (L) moench) was planted after the soil tillage treatment. Soil loss for zero tillage farming combined with mucuna fallow was equivalent to only 3% of that for the conventional tillage farming with natural fallow. Runoff water was also reduced by between 74% and 77% when compared with the conventional tillage system with natural fallow. These results indicate that zero tillage with mucuna fallow is a very effective measure for the control of soil erosion and water runoff. Moreover, this farming system improved water infiltration during both the fallow and the sorghum cropping periods. For the zero tillage plot, water loss as deep percolation increased 1.6-fold compared with that for the conventional farming under heavy rainfall conditions. It is expected that under less rainfall areas or seasons, the effects of zero tillage farming combined with the mucuna cover crop may be more pronounced on water runoff control and, therefore, may greatly improve soil water conditions.

Can earthworms be used as bio-indicators of land-use perturbations in semi-deciduous forest?

The potential of tropical earthworms as bio-indicators of forest degradation by human-induced activities was assessed at a landscape level in the Ivory Coast. The study site covered 400 ha and was characterized by a set of land-use types along a gradient of perturbation from semi-deciduous forest, through reforestation, fallow systems to cultivated annual crops. Samples were taken on a grid at each sampling point and earthworms were hand-sorted from a 25 × 25 × 30-cm soil monolith. Results showed a potential increase in relative populations (number: +53.1%, biomass: +94.8%) of species in the earthworm communities following forest conversion. Furthermore, the impact of land-use change was higher in relation to land-use intensification in terms of earthworm populations and diversity in intermediate-disturbed systems (Multispecies plantations, old fallows). Earthworm diversity was the most sensitive response to land-use change. The species Dichogaster saliens Beddard 1893, Hyperiodrilus africanus Beddard 1891, Millsonia omodeoi Sims 1986, Dichogaster baeri Sciacchitano 1952, Dichogaster ehrhardti Michaelsen 1898, Agastrodrilus sp., Stuhlmannia palustris Omodeo and Vaillaud 1967 and, to some extent, Millsonia sp. appeared to be most sensitive to land-use change. More field and laboratory investigations are needed to find out the most efficient species to be used in bio-monitoring programmes aimed at preventing ecosystem degradation due to anthropogenic activities in the forest areas of Ivory Coast.

Simulated long-term effects of different soil management regimes on the water balance in the Loess Plateau, China

A soil management regime that improves water use efficiency (WUE) is urgently required to increase the sustainability of the winter wheat-summer fallow system in the Loess Plateau, China. However, the long-term partitioning of the water balance must be understood in order to evaluate the viability of possible soil management regimes. Therefore, an ecosystem model (CoupModel) was used to explore the effects on components of the water balance of five types of soil management regimes: conventional practice, wheat straw mulching, incorporation of high organic matter contents, compaction, and use of a harvested fallow crop. Three variants of the fallow crop approach were also considered, in which the crop was harvested 15, 30 and 45 days before sowing the wheat (designated Fallow-15d, Fallow-30d and Fallow-45d, respectively). Simulations were used to identify the relative magnitude of soil evaporation, wheat transpiration and deep percolation and to elucidate the temporal variability in these components for a selected location using climate records spanning 45 years. However, the soil management regime significantly influenced the magnitude of every component of the water balance (in terms of minimum, maximum and mean values) over the long periods considered. Consequently, wheat yield and WUE differed significantly among the simulated treatments. Mulching led to significantly lower soil evaporation, higher transpiration, and more frequent and extensive deep percolation than other regimes, thereby improving fallow efficiency (percentage of rainfall stored in the soil during the fallow period at the end of the fallow period), wheat yields and WUE. In contrast, soil compaction gave the opposite results, leading to the most unfavourable partitioning of the water balance reflected in the lowest wheat yield and WUE values of all the regimes. In 90% of the years no deep percolation occurred in the soil compaction simulations. Use of a fallow crop with optimal harvest timing (Fallow-30d) improved partitioning of the water balance (decreased soil evaporation) and did not significantly reduce wheat yield compared with conventional practice. High organic matter contents in the soil also had a positive influence on the water balance and improved wheat yield and WUE relative to conventional practice. Therefore, mulching appears to be the best management practice for the winter wheat-summer fallow system in the Loess Plateau, according to the simulations. Increasing soil organic matter may be the best option if mulching cannot be implemented. The ideal time for harvesting a fallow crop for use as green manure or fodder appears to be ca. 30 days before sowing the winter wheat.

Evaluation of weed control provided by three winter cereals in conservation-tillage soybean

Information is needed on the role of cover crops as a weed control alternative due to the high adoption of conservation tillage in soybean [Glycine max (L.) Merr.] production. Field experiments were conducted from fall 1994 through fall 1997 in Alabama to evaluate three winter cereal cover crops in a high-residue conservation-tillage, soybean production system. Black oat (Avena strigosa Schreb.), rye (Secale cereale L.), and wheat (Triticum aestivum L.) were evaluated for their weed-suppressive characteristics compared to a winter fallow system. Three herbicide systems were utilized: no herbicide, a mixture of two pre-emergence (PRE) herbicides, or PRE plus post-emergence (POST) herbicides. The PRE system contained pendimethalin plus metribuzin. The PRE plus POST system contained pendimethalin plus a prepackage of metribuzin and chlorimuron ethyl applied PRE, followed by an additional chlorimuron ethyl POST application. No cover crop was effective in controlling weeds without a herbicide. However, when black oat or rye was utilized with only PRE herbicides, weed control was similar to the PRE plus POST input system. Thus, herbicide reductions may be attained by utilizing cover crops that provide weed suppression. Rye and black oat provided more effective weed control in the PRE only herbicide input system than wheat in conservation-tillage soybean. The winter fallow, PRE plus POST herbicide input system yielded significantly less soybean one out of three years when compared to systems that included a winter cover crop.

Carbon Sequestration in Dryland Soils and Plant Residue as Influenced by Tillage and Crop Rotation

Long-term use of conventional tillage and wheat (Triticum aestivum L.)-fallow systems in the northern Great Plains have resulted in low soil organic carbon (SOC) levels. We examined the effects of two tillage practices [conventional till (CT) and no-till (NT)], five crop rotations [continuous spring wheat (CW), spring wheat-fallow (W-F), spring wheat-lentil (Lens culinaris Medic.) (W-L), spring wheat-spring wheat-fallow (W-W-F), and spring wheat-pea (Pisum sativum L.)-fallow (W-P-F)], and Conservation Reserve Program (CRP) planting on plant C input, SOC, and particulate organic carbon (POC). A field experiment was conducted in a mixture of Scobey clay loam (fine-loamy, mixed, Aridic Argiborolls) and Kevin clay loam (fine, montmorillonitic, Aridic Argiborolls) from 1998 to 2003 in Havre, MT. Total plant biomass returned to the soil from 1998 to 2003 was greater in CW (15.5 Mg ha(-1)) than in other rotations. Residue cover, amount, and C content in 2004 were 33 to 86% greater in NT than in CT and greater in CRP than in crop rotations. Residue amount (2.47 Mg ha(-1)) and C content (0.96 Mg ha(-1)) were greater in NT with CW than in other treatments, except in CT with CRP and W-F and in NT with CRP and W-W-F. The SOC at the 0- to 5-cm depth was 23% greater in NT (6.4 Mg ha(-1)) than in CT. The POC was not influenced by tillage and crop rotation, but POC to SOC ratio at the 0- to 20-cm depth was greater in NT with W-L (369 g kg(-1) SOC) than in CT with CW, W-F, and W-L. From 1998 to 2003, SOC at the 0- to 20-cm depth decreased by 4% in CT but increased by 3% in NT. Carbon can be sequestered in dryland soils and plant residue in areas previously under CRP using reduced tillage and increased cropping intensity, such as NT with CW, compared with traditional practice, such as CT with W-F system, and the content can be similar to that in CRP planting.

Forage Yield Response to Water Use for Dryland Corn, Millet, and Triticale in the Central Great Plains

Forages, with greater water use efficiency (WUE) than grain and seed crops, could be used to diversify reduced and no‐till dryland cropping systems from the traditional wheat (Triticum aestivum L.)–fallow system in the semiarid central Great Plains. However, farmers need a simple tool to evaluate forage productivity under widely varying precipitation conditions. The objectives of this study were to (i) quantify the relationship between crop water use and dry matter (DM) yield for corn (Zea mays L.), foxtail millet (Setaria italica L. Beauv.), and winter triticale (X Triticosecale Wittmack); and (ii) determine the range and distribution of expected DM yields for these three crops in the central Great Plains based on historical precipitation records. The three crops were grown in a dryland no‐till corn–millet–triticale sequence from 1998 through 2004 at Akron, CO. Dry matter production was linearly correlated with water use for all three crops, with regression slopes ranging from 24.2 (corn) to 33.0 kg ha−1 mm−1 (millet). Water use efficiency varied widely from year to year (0–32.2 kg ha−1 mm−1) for the three crops, as influenced by growing season precipitation and time of year in which the crops were grown. Millet and triticale produced similar amounts of DM for a given water use, while corn produced less. Precipitation use efficiency for the millet–triticale–corn forage system was 8.7 kg ha−1 mm−1, suggesting this as an efficient forage system for the region.

Abundance of insect pests and their effects on biomass yields of single vs. multi-species planted fallows

Indigenous and exotic leguminous shrubs that are promising for planted fallow for soil fertility replenishment in east and southern Africa have been found to harbour many herbivorous insects, giving suspicion that widespread adoption of fallow systems may aggravate insect pests. Studies were conducted on farms in western Kenya from 1999 to 2001 to monitor the abundance of herbivorous insects and assess their effects on biomass yields of pure and mixed fallows. The treatments tested were single and two-species mixtures of Tephrosia vogelii, Sesbania sesban and Crotalaria grahamiana and a natural fallow in a split plot design, with the fallow systems in the main plots and protection vs. no protection against insects in sub-plots spread over six farms. Eighteen insect species belonging to seven orders and 14 families were identified as pests of␣the fallows with varied abundance and infestation level across the sites. While Hilda patruelis and Amphicallia pactolicus were most damaging to C. grahamiana, Mesoplatys ochroptera was detrimental to S.␣sesban. T. vogelii hosted fewer insects than others. Nevertheless the pest infestation did not cause significant biomass yield reduction during the study period. Pest attack was generally greater in villages that had been testing the planted fallows for some years compared with villages that took up the fallows recently. This indicates the potential for increased pest infestation with increased adoption of the system by farmers. Multi-species fallows did not indicate any advantage over single species fallows in terms of either reduced pest incidence or increased biomass production.

Factors controlling decomposition of soil organic matter in fallow systems of the high tropical Andes: A field simulation approach using 14C- and 15N-labelled plant material

Abstract N-rich (C:N=27) and N-poor (C:N=130) wheat straw, labelled with 14C and 15N, was incubated for 2 yr in two major ecosystems of the upper elevation belt of cultivation in the high Andes: the moist Paramo (precipitation=1329 mm, altitude=3400 m asl, Andes of Merida, Venezuela) and the dry Puna (precipitation=370 mm, altitude=3800 m asl, Central Altiplano, Bolivia). The experiment was installed in young (2 yr) and old (7 yr) fallow plots. The following soil analyses were performed at nine sampling occasions: soil moisture, total-14C and -15N, and Microbial Biomass (MB)-14C and -15N. The measured data were fitted by the MOMOS-6 model (a process based model, with five compartments: labile and stable plant material, MB, and labile (HL) and stable humus (HS)) coupled with the SAHEL model (soil moisture prediction) using daily measured and/or predicted meteorological data. The aim was to understand how (1) the climatic conditions, (2) the quality of plant material, (3) the fallow age and (4) the soil properties affect the cycling of C and N within the soil organic matter system. The fallow age (2 and 7 yr) did not affect the measured data or the model predictions, indicating that in these systems the decomposition potential is not affected by fallow length. During the short initial active decomposition phase, the labile plant material was quickly exhausted, enabling a build up of MB and of HL. During the low activity phase, that covered 4/5 of the time of exposure, the MB size decreased slowly and the HL pool was progressively exhausted as it was reused by the MB as substrate. The HL compartment was directly or indirectly the major source for the inorganic 15N production. If the C:N ratio of the added plant material increased, the model predicted (1) a reduction of the decomposition rates of the plant material (essentially the stable plant material) and (2) an increased mortality of the MB which increased the production of HL (microbial cadavers and metabolites). Thus the essential effect of the slower decomposition due to the N-poor plant material was a higher accumulation of C and N in the HL and its slower recycling by the MB during the low activity phase. The labelling experiment allows to understand the higher soil native organic matter content in Paramo soils compared to Puna. The large sequestration of organic matter generally observed in the Paramo soils can be explained by two abiotic factors: the unfavourable soil microstructure and the accumulation of free aluminium linked to the climatic and acid soil conditions, inhibiting the microbial activity physically and chemically.

Indigenous livelihoods, slash-and-burn agriculture, and carbon stocks in Eastern Panama

Improved crop–fallow systems in the humid tropics can simultaneously sequester atmospheric carbon emissions and contribute to sustainable livelihoods of rural populations. A study with an indigenous community in eastern Panama revealed a considerable biophysical potential for carbon offsets in small-scale slash-and-burn agriculture through longer fallow periods, improved fallow management, secondary forest development, and agricultural intensification. Based on soil and biomass carbon measurements, estimated annual sequestration rates amount to 0.3−3.7 t C ha − 1 yr − 1 . Despite such potential, the economic benefits of initiatives aimed at sequestration of carbon in the community are likely to be rather unequally distributed within the community. Heterogeneity in livelihood strategies and uneven asset endowments among households – factors often overlooked in the ongoing carbon and sustainable development debate – are expected to strongly affect household participation. Indeed, only the better-endowed households that have also managed to diversify into more lucrative farm and non-farm activities are likely to be able to participate in and thus benefit from improved crop–fallow systems that capture carbon. Economic, ethical, institutional, and technical concerns need to be taken into account when designing community carbon management and investment plans.

Stable isotopes for characterisation of trends in soil carbon following deforestation and land use change in the highlands of Madagascar

The impacts of human land use in the highlands of Madagascar are often equated with land degradation and decreasing soil fertility. The practice most often focused on is deforestation through slash-and-burn cultivation ( tavy), and shifting cultivators are often portrayed as being ignorant, poverty-stricken peasants felling trees for fields and food. However, there is uncertainty whether soil degradation is related to recent tavy or earlier forest clearance, and whether some highland areas were ever forested. In this paper we use stable isotopes ( δ 13C) and diffuse reflectance spectroscopy (DRS) to study the impacts of deforestation and various other land use changes on ecosystem properties, soil organic carbon (SOC) dynamics and soil quality (fertility) in the highlands of Madagascar. Land cover transitions (between C 3 and C 4 systems) are defined and quantified in the study area. Historical land use had greater effect on soil organic carbon concentrations than current land use, with cultivated areas previously under C 3 and C 4 systems having 37.3 and 14.8 g SOC kg − 1 , respectively. Grasslands previously under C 3 had approximately 124% more SOC than grasslands previously under C 4, while SOC concentrations were 65.3 and 54.9 g C kg − 1 under natural forest and in mixed fallow systems, respectively. A soil fertility index developed for the study area based on diagnostic soil spectra was compared with findings related to SOC dynamics and land use change.

A Study on the Farm Condition for the Extension of Green Manure Fallow System to the Large Scale Upland Farming in Tokachi District

A Study on the Farm Condition for the Extension of Green Manure Fallow System to the Large Scale Upland Farming in Tokachi District

The analyses of physiological and morphological attributes of 10 tree species for early determination of their suitability to afforest degraded landscapes in the Aral Sea Basin of Uzbekistan

The establishment of woody fallow systems is an option for the improvement of degraded agricultural landscape within the ecologically deteriorated Aral Sea area in northwest Uzbekistan. Growth and development of ten tree species, differing in tolerance to drought and salinity, were studied over 24 months. To determine species suitability for afforestation, conventional diameter and height measurements were compared to Relative Growth Rate (RGR) and its underlying components, Net Assimilation Rate (NAR), Specific Leaf Area (SLA) and Leaf Weight Ratio (LWR), as well as the Crop Growth Rate (CGR) as a function of NAR and Leaf Area Index (LAI). RGRs varied between 0.46 and 2.16 mg g −1 day −1 and showed highly significant differences among species, but also between years, which reduces the parameter's suitability for species selection. The same is true for NAR and SLA. CGR values ranged from 0.01 to 0.71 g m −2 day −1, increased with age of the trees, and showed significant species differences. CGR correlated better with NAR ( r = 0.89) and SLA ( r = 0.86) than RGR. Overall CGR correlated highly with the RGRs in height and diameter (in 80% and 71% of all cases, respectively). Thus, CGR appears to be a suitable indicator complementing RGR, NAR and SLA estimates to decide on species suitability for afforestation. The intensive measurements for RGR should be done later, rather than earlier in the tree life cycle. At an early age, CGR and diameter measurements are more meaningful. A combination of estimates, not a single factor, best assesses the long-term sustainable growth under natural conditions and allows early selection of species suitable for afforestation of degraded patches in the agricultural landscape. Ranking of all parameters concurrently showed the high potential of Elaeagnus angustifolia and Populus euphratica, which matched previous rankings based on total biomass production and financial added value.