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Alnus acuminata Kunth. (alnus) has been widely promoted under climate change mitigation and adaptation programs in the East African highlands. However, information is lacking on the impact of its pruning management and green manure (GM) application on soil health and the productivity of associated crops. Using a large suit of soil quality indicators, crop growth and yield measurements, this study identified appropriate combinations of alnus pruning levels and GM application for sustainable intensification of potato (Solanum tuberosum) and wheat (Triticum aestivum) production. This study compared six treatments, namely, (1) sole crops of potato or wheat (control), (2) sole crop + GM, (3) 75% pruning, (4) 75% pruning + GM, (5) 90% pruning and (6) 90% pruning + GM. The best treatments were the 75% pruning + GM and 90% pruning + GM, which significantly differed from the control in soil pH, soil organic carbon (SOC), total nitrogen (TN), total phosphorus (P), exchangeable calcium (Ca) contents, the N:P and C:P stoichiometric ratios and the soil structural stability index (SSI). These treatments increased soil pH by 5–6%, SOC by 74–82%, TN by 58–68%, exchangeable Ca by 76–81%, total P by 17–21%, the N:P ratio by 40%, C:P ratio by 43–51%, the SSI by 71–79%, potato tuber yields by 17–21% and wheat yields by 21–32% over the control. Therefore, it is concluded that pruning and application of alnus green manure have the potential to significantly improve soil health and crop productivity on degraded soils in the study area.

Assessing effects of climate change on agricultural systems and the potential for ecological intensification to increase food security in developing countries is essential to guide management, policy-making and future research. 'Push-pull' technology (PPT) is a poly-cropping design developed in eastern Africa that utilizes plant chemicals to mediate plant-insect interactions. PPT application yields significant increases in crop productivity, by reducing pest load and damage caused by arthropods and parasitic weeds, while also bolstering soil fertility. As climate change effects may be species-and/or context-specific, there is need to elucidate how, in interaction with biotic factors, projected climate conditions are likely to influence future functioning of PPT. Here, we first reviewed how changes in temperature, precipitation and atmospheric CO2 concentration can influence PPT components (i.e., land use, soils, crops, weeds, diseases, pests and their natural enemies) across sub-Saharan Africa (SSA). We then imposed these anticipated responses on a landscape-scale qualitative mathematical model of maize production under PPT in eastern Africa, to predict cumulative, structure-mediated impacts of climate change on maize yield. Our review suggests variable impacts of climate change on PPT components in SSA by the end of the 21st century, including reduced soil fertility, increased weed and arthropod pest pressure and increased prevalence of crop diseases, but also increased biological control by pests' natural enemies. Extrapolating empirical evidence of climate effects to predict responses to projected climate conditions is mainly limited by a lack of mechanistic understanding regarding single and interactive effects of climate variables on PPT components. Model predictions of maize yield responses to anticipated impacts of climate change in eastern Africa suggest predominantly negative future trends. Nevertheless, maize yields can be sustained or increased by favourable changes in system components with less certain future behaviour, including higher PPT adoption, preservation of field edge density and agricultural diversification beyond cereal crops.

Increasing areas of agricultural land in high rainfall areas of Sub-Saharan Africa (SSA), where crop production used to be reliable, are affected by soil acidity. This review focuses on the extent, causes and effect of soil acidity on soil properties and crop yield and its management from the context of SSA. Studies showed that the detrimental effects of soil acidity can be mitigated through liming, integrated acid soil management and the use of acid-tolerant germplasms. Application of lime resulted in yield increments of 34–252% in wheat, barley and tef, 29–53% in faba bean and soybean, and 42–332% in potato in Ethiopia, 111–182% in maize in Kenya, and 45–103% in Mucuna in Nigeria under moderate to severe acid soil conditions. This was accompanied by a corresponding increase in soil pH up to 1.9 units and a decrease in exchangeable acidity and aluminum up to 2.1 cmol kg−1. Use of acid-tolerant crop varieties such as maize expressing superior tolerance to Al toxicity resulted in a yield increase of 51% under low soil pH in Cameroon and Kenya. Overall, soil acidity covering ∼35% of SSA should be reclaimed with lime and integrated acid soil management interventions, which could significantly increase crop yield and enhance the resilience of the tropical agroecosystems.

Globally, belowground biomass (BGB) accounts for 20–26% of total biomass, and as such it is an important carbon (C) pool for many vegetation types. However, large uncertainty exists for belowground...

Tea (Camellia sinensis) is often grown under a canopy of trees forming a distinctive agroforestry system covering an estimated area of 3.94 million ha of land globally. Although, tea is a major commercial crop in many countries in tropical and sub-tropical regions, including China, India and Sri Lanka, tea agroforestry systems (TAFS) have remained little studied for their role in carbon management and climate change adaptation/mitigation actions. We, therefore, undertook a detailed study on the storage of organic carbon in above- and below-ground vegetation and soil under age chronosequence of TAFS in North East India. The specific aim of this study was to quantify variations in soil physical and chemical properties, carbon storage in shade trees and tea bushes, and ecosystem carbon stocks under the chronosequence of TAFS. This study has established significant variations in soil properties and carbon storage in different aged TAFS. One of the salient findings is the decrease in soil bulk density and increase in water holding capacity with the age of TAFS in the 0–50 cm depth. The total vegetation C stock (shade trees + tea bushes + litter biomass) increased with increase in the age of TAFS, and the increase was as high as 25% in > 20 years compared to younger (

Agarwood (Aquilaria malaccensis Lam.) (Thymelaeaceae) is valued in many cultures because of its distinctive fragrance and its use in incense, perfumery, and traditional medicine. Large-scale harvesting from natural populations caused rapid depletion of the species in the wild, and the species is now listed as “Critically Endangered” and almost extinct in the wild. The promotion of this species in agroforestry systems may pave the way for its conservation. The present study aimed to quantify the growth and coppicing ability of agarwood under monoculture and polyculture stands. Monoculture stands aged more than 20 years, and stem girth (1.37 m above ground) of 60–70 cm had the highest growth increment of 3.73 cm yr−1. Monoculture stands (>10 years old) also recorded higher number of coppicing stocks than polyculture stands. The highest coppice growth increment (4.07 cm yr−1) was recorded in the 70–80 cm stem girth in monoculture stands. Based on the results, we recommend the promotion of agarwood trees with good coppice management in forestry programs to conserve the species while also meeting the economic needs of rural communities.

Summary Although soybean is emerging as an important commercial crop in sub-Saharan Africa (SSA), its productivity on smallholder farms is very low. Soybean requires application of phosphorus (P) fertilizer and inoculation with the right rhizobium strains to achieve optimum biological nitrogen fixation and higher yields. However, subsistence farmers in SSA rarely invest in P fertilizers and inoculants due to lack of knowledge of their use and benefits. Most of the early reports on soybean in SSA have been based on work on research stations; hence, information is lacking on the profitability of fertilizer and inoculant use on smallholder farms in SSA. The main hypothesis of the present study was that the combined application of P and inoculants significantly reduces yield risks and increases P use efficiency and profitability compared with P fertilizer alone under smallholder farm conditions. We analyzed a data set of over 2,800 observations from on-farm demonstrations across Ghana, Kenya, Malawi, Rwanda, Tanzania, Uganda, and Zambia. Soybean yields, the partial factor productivity of P (PFPP), agronomic efficiency of P (AEP), and the value cost ratio (VCR) were significantly improved by the combined application of P fertilizer with inoculants than with P fertilizer alone. Combining P and inoculants increased yields over P alone by 17.3% in Kenya, 21.4% in Zambia, 25.7% in Ghana, 56.4% in Tanzania, and 57.1% in Malawi. However, soil organic matter was an important determinant of yield response and P use efficiency. The VCR increased linearly with increasing AEP in P + inoculant (R2 = 0.829) and less so with P fertilizer alone (R2 = 0.672). Net present values were positive in all countries, indicating that investments in P fertilizer and inoculants will generate profits over time. In order to increase uptake of fertilizers and inoculants among subsistence farmers and make soybean production more profitable, appropriate policies and market incentives need to be created.

Summary Nutrient deficiency is a major constraint in tef (Eragrostis tef (Zucc.) Trotter) production in Ethiopia. In the past, a blanket recommendation of nitrogen (N) and phosphorus (P) fertilizers has been applied regardless of the diversity of agroecological zones and soil types. As crop responses declined with widespread deficiencies of nutrients, farmers have lost interest in applying the recommended fertilizer rates. The present study was conducted with the objective of quantifying the response of tef to different rates of N, P, potassium (K) and sulphur (S) fertilizers under balanced application of the nutrients other than the one under investigation. In each region, the same set of trials was implemented on farmers’ fields for three years. All trials were implemented on Vertisols across four agroecological zones (AEZs). The treatments were seven rates of N, six rates each of P and S and eight rates of K with a basal application of zinc (Zn) and boron (B). The results showed that the most limiting nutrient is N followed by P in each agroecological zone on the Vertisols. There was clear evidence of increases in grain yield with increasing rates of N and P, but the responses to K and S rates did not follow clear trends across AEZs. With balanced application of the other nutrients, 23–92 kg N ha−1 increased grain yield by 11–92%, while 10–40 kg P ha−1 increased yields by 12–33% over the control in the different AEZs. Based on results from dose–response models, it is concluded that the agronomic optimum rates for tef production are 69 kg N, 20 kg P, 30 kg K and 10 kg S ha−1 in the cool sub-moist mid-highlands and the tepid sub-humid mid highlands; 92 kg N, 30 kg P, 15 kg K and 10 kg S ha−1 in tepid moist mid highlands but 69 kg N, 10 kg P, 15 kg K and 10 kg S ha−1 in the tepid sub-moist mid highlands. On Vertisols not covered by this study, these recommendations should be subject to appropriate soil and plant analysis. We also recommend further studies on the nutrient requirement of tef on other soil types and AEZs.

The use of fertilisers in maize production has been the focus for many years of agronomic studies on research stations in East Africa. However, information on production risks and profitability of fertiliser use on smallholder farms is generally lacking because most of the early studies have focused on mean yields and yield components on research stations. This study applied rigorous analyses to determine conditions under which (1) production risks are low; (2) the recommended nitrogen (N) and phosphorus (P) fertiliser rates achieve a yield target of ≥3 t ha−1 believed to be a necessary condition to kick start a smallholder-led ‘green revolution’ in Africa and (3) N and P fertiliser use is profitable on smallholder farms in East Africa. Analysis of data from 464 on-farm trials in Kenya, Rwanda, Tanzania and Uganda revealed significant variations in production risks and nutrient use efficiency with season and soil type. On most sites, except in Uganda, production risks were lower with the recommended N and P fertilisers than the control during both the short and long rains. Production risks were three to four times higher with N and P fertiliser relative to the control on Lixisols and Ferralsols, but such risks were much lower on Nitisols, Leptosols, Vertisols, Plinthosols and Cambisols. The probability of exceeding grain yields of 3 t ha−1 with the recommended N and P rates was over 0.60 on Nitisols and Leptosols, but less than 0.20 on Lixisols and Plinthosols. The agronomic use efficiencies of N (AEN), P (AEP) and value cost ratios (VCR) were highest on Cambisols and lowest on Plinthosols. The VCR increased linearly with increase in AEN (R2 = 0.92) and AEP (R2 = 0.87) and less so with increase in grain yields (R2 = 0.47–0.60). Net present values indicated profitably of N and P fertiliser over the long term in only 30% of the site by season combinations in Uganda compared with 69% in Kenya, 81% in Rwanda and 84% in Tanzania. Patterns of N use efficiencies were different from P use efficiencies across soil types. Therefore, we recommend that N and P fertilisers should be appropriately targeted to soils where applied nutrients are used efficiently by maize crops.

Summary A number of studies across sub-Saharan Africa have recently reported poor crop responses and low agronomic use efficiencies of applied nitrogen (AEN), phosphorus (AEP) and potassium (AEK). However, the conditions under which non-responsiveness occurs, its underlying causes and its probability of occurrence on different soil types are not well understood. Using data from 542 sites and 14 soil types in 23 African countries, we provide novel insights into the linkage between lack of response to applied N, P and K, the mineralogy of soils and their resilience to erosion. We estimated mean responses as well as the probabilities (ϕ) of no response in terms of response ratio (RR), yield gain (YG) and agronomic efficiency. Here we defined ‘no response’ as zero agronomic response to fertilizer inputs in a given site and year indexed by either RR ≤ 1, AEN ≤ 0, AEP ≤ 0 or AEK ≤ 0. The highest risks of no response were recorded on the iron-rich Plinthosols (ϕ = 0.26) followed by the aluminium-rich Alisols (ϕ = 0.16) and the erosion-prone Lixisols (ϕ = 0.16) and Leptosols (ϕ = 0.13). In terms of yield gains, the highest risk of low response (i.e., YG ≤ 0.5) was recorded on Alisols (ϕ = 0.47) and the lowest on Fluvisols (ϕ = 0.05). Cambisols, Fluvisols, Luvisols and Nitisols were deemed highly responsive to NPK fertilizer. The risks of no response were significantly higher on soils derived from siliceous than mafic parent materials, soil types with low resilience to erosion, soils with low-activity clays and high P fixation capacity. It is concluded that maize grain yields can exceed 3 t ha-1 with high probability (ϕ > 0.80) on Andosols, Nitisols and Vertisols, but with very low probability (ϕ < 0.30) on Alisols and Arenosols. It is also concluded that across soil types and agroecological zones, the risk of no response is up to two times more on farmers’ fields than on research stations. Here, we discuss the implications of these finding for the design and location of future agronomic trials. We also provide insights to guide the targeting of fertilizer subsidies where nutrients can be more efficiently used.

Summary Optimisation of fertiliser use and site-specific nutrient management are increasingly becoming critical because of the growing need to balance agricultural productivity with the growing demand for food and environmental concerns. Trials to determine responses of crops to fertilisers have been widely conducted in sub-Saharan Africa (SSA) with increasing emphasis on the development of economically optimum rates (EORs). Computation of EORs depends on accurate estimation of both the optimum nutrient rate and the agronomic maximum yield response; however, estimation of nutrient-response parameters and EORs is beset by a number of problems. Therefore, the objectives of this paper were to (1) point out common problems in the development and use of nutrient dose-response models and (2) provide corrective measures to facilitate future trial design and data analysis. This review outlines the underlying assumptions, strengths and limitations of the various response functions in order to facilitate informed choices by practitioners. Using specific examples, it also shows that (1) the commonly used trial designs do not allow examination of interactions between two or more nutrients and (2) trial designs with ≤5 nutrient levels and wide spacing between the levels result in large uncertainty in dose-response parameters. The key recommendations emerging from the review are as follows: (1) factorial designs and response surface models should be used more widely to address interactions between nutrients; (2) a minimum of six carefully spaced nutrient levels should be used to correctly estimate dose-response parameters; and (3) when locating field trials, Reference Soil Groups and cropping history should be carefully considered to produce site-specific EORs.

Increasing barley production in the face of declining soil fertility on smallholder farms is a critical challenge in Ethiopia. The objectives of this study were to (1) determine the optimum rates of nitrogen (N), phosphorus (P), potassium (K), and sulfur (S) fertilizers under a balanced fertilization of other macro- and micronutrients (zinc and boron) and (2) quantify the agronomic efficiency of N and P on Cambisols and Vertisols. The trials were conducted for three consecutive years (2014–2016) on farmers’ fields on 83 sites under rain-fed conditions. On each farm, six rates of N, P, K, and S with a balanced application of the other nutrients were laid out separately in a randomized block design with three replicates. Balanced fertilization resulted in yield increments of 26–59% on Cambisols and 18–74% on Vertisols, as compared with the control (0 N). Application of P increased grain yield from 11% to 30% and from 7% to 14% due to the interaction of P by soil type as compared with the control. The application of K and S, however, had no significant effect on barley yields on either soil type. The highest agronomic efficiency of N (AEN) was obtained from 46 kg N ha−1, with AEN increasing by 117% on Cambisols and 33% on Vertisols, as compared with the highest N rate of 230 kg N ha−1. The maximum agronomic efficiency of P (AEP) was recorded with 10 kg P ha−1 on Vertisols, with AEP increasing by 73% on Cambisols and 452% on Vertisols, as compared with the application of 50 kg P ha−1. With balanced application of other nutrients, use of 230 kg N and 20 kg P ha−1 was recommended for tepid sub-moist mid-highlands and Vertisols. For tepid sub-humid mid-highlands, application of 46 kg N and 20 kg P ha−1 with balanced application of other nutrients was recommended. For Cambisols, application of 230 kg N and 40 kg P ha−1 was recommended with balanced application of the other nutrients. Similarly, application of 230 kg N, 40 kg P, and 10 kg S ha−1 was tentatively recommended for cool sub-most mid highlands. However, response to K was inconsistent and therefore a firm recommendation could not be proposed for the study sites. Further research needs to be conducted on more soil types and locations.

Plant biomass is an integral part of the global carbon cycle and a renewable energy source that can deaccelerate the rising global temperature. India has 71 million ha (M ha) of land under forests represented by tropical to alpine ecosystems. Numerous direct and indirect species-specific and mixed-species equations have been used for biomass estimation in India. Biomass estimation equations that facilitate the prediction of aboveground biomass (AGB) stocks non-destructively across India are still lacking. Therefore, the objective of this review is to (i) assess the existing species-specific biomass estimation equations for trees, bamboos, palms, and bananas in India, (ii) assess and identify the most appropriate multi-species biomass estimation equations for AGB estimation across India, and (iii) define the critical research gaps in biomass estimation in India. The literature search found 85 species-specific and six multi-species AGB estimation equations reported from India. It was also found that a 50% of these equations were based on the power-law function using diameter at breast height (D) as the predictor variable. We carried out a multi-fold validation to compare the multi-species equation's compatibility by comparing the root mean square error (RMSE). The estimated RMSE values of the six reported multi-species equations showed that the following two equations could be effectively used for estimation of AGB: (i) lnAGB= 0.349+1.316 lnGBH and (ii) AGB= (0.18D2.16) × 1.32. These are adequate for predicting biomass of any woody species across a range of conditions in India.

Alien invasive insect and mite species (AIS) represent a major challenge for agriculture, food production, and biodiversity in Africa. However, the lack of awareness and appreciation of AIS threats continues to hinder the development of appropriate policies and practices for their management in sub-Saharan Africa. The objectives of this review are to (1) provide a synthesis of current and future threats to food production and the economic impacts of AIS, (2) identify challenges to their management at national and regional levels, and (3) propose a strategy for a concerted pan-African response. The review identifies a total of 16 alien invasive insect and mite pests, affecting all categories of food crops, causing combined losses in excess of US$ 1 billion annually across Africa. Various models predict that AIS threats will continue to increase due to expansion of the geographic distribution and host range of existing invasions, thus threatening the already tenuous food situation on the continent. The review also reveals that only 16.7% of the countries have adequate border control procedures, while over 66.7% do not have comprehensive AIS management strategies. Therefore, we propose development of a pan-African strategy for effectively responding to AIS threats, and achieving the continental visions of free trade and collective food security. We recommend that biosecurity be considered as a food security intervention complementing yield improvement technologies, and implemented as a core element of national and regional strategies.

Parkia timoriana (DC.) Merr. is an economically important agroforestry tree species grown in home gardens and shifting cultivation areas throughout the North-eastern states of India. This s...

Although soil degradation is a major threat to food security and carbon sequestration, our knowledge of the spatial extent of the problem and its drivers is very limited in Southern Africa. Therefore, this study aimed to quantify the risk of soil structural degradation and determine the variation in soil stoichiometry and nutrient limitations with land use categories (LUCs) and climatic zones. Using data on soil clay, silt, organic carbon (SOC), total nitrogen (N), available phosphorus (P), and sulfur (S) concentrations collected from 4,468 plots on 29 sites across Angola, Botswana, Malawi, Mozambique, Zambia and Zimbabwe, this study presents novel insights into the variations in soil structural degradation and nutrient limitations. The analysis revealed strikingly consistent stoichiometric coupling of total N, P, and S concentrations with SOC across LUCs. The only exception was on crop land where available P was decoupled from SOC. Across sample plots, the probability (φ) of severe soil structural degradation was 0.52. The probability of SOC concentrations falling below the critical value of 1.5% was 0.49. The probabilities of soil total N, available P, and S concentrations falling below their critical values were 0.95, 0.70, and 0.83, respectively. N limitation occurred with greater probability in woodland (φ = .99) and forestland (φ = .97) than in cropland (φ = .92) and grassland (φ = .90) soils. It is concluded that soil structural degradation, low SOC concentrations, and N and S limitations are widespread across Southern Africa. Therefore, significant changes in policies and practices in land management are needed to reverse the rate of soil structural degradation and increase soil carbon storage.

Schizostachyum dullooa is a semelparous, thin walled bamboo that grows in the moist forests of India, Bangladesh and Myanmar. The species has great potential in upliftment of socioeconomic conditions of the rural areas of North East India. The long flowering interval in S. dullooa has hindered documentation of its demography and its influence on regeneration of canopy trees. We hypothesized that mass flowering and death of S. dullooa opens a window of opportunity creating space for the regeneration of canopy tree seedlings. We studied the flowering pattern and seedling demography of this species between the years 2010 and 2015 in the Barak Valley, and evaluated if seedling abundance of canopy tree species increased after the flowering event. We followed five successive seedling cohorts to determine variation in survival of canopy tree seedlings, seedling attributes [i.e., maximum height (cm), diameter (cm) and density (individuals per 0.01 ha)]. At the local scale, mast flowering extended over 4 years in small patches of about 100 m2 where flowering and non-flowering culms were often mixed. At the landscape scale, sites with mast flowering stands were interspersed with sites that did not have flowering stands indicating spatially discontinuous flowering patterns. Mortality rate of bamboo seedlings was high during the first year. At the end of the study, 15–26% of the initial bamboo seedlings in each cohort survived and S. dullooa was able to re-colonize sites it previously occupied. Mass flowering significantly increased seedling density and growth of canopy trees compared to non-flowering sites. It is concluded that flowering and death of S. dullooa facilitates the regeneration of canopy trees, with implications for the structure and function of the forest ecosystem.

The combined application of cattle manure and inorganic fertilizer has been widely recommended in the context of integrated soil fertility management (ISFM) on smallholder farms in sub-Saharan Africa (SSA). However, the conditions under which this combination (hereafter ISFM) improves nutrient and water use efficiency and crop yields have not been systematically studied. Therefore, we undertook a meta-analysis of studies conducted in rain-fed maize production systems across SSA with the objective of (1) quantifying the magnitude of improvement in grain yield, rain use efficiency (RUE), agronomic efficiency of nitrogen (AEN) and phosphorus (AEP) due to ISFM; (2) determining conditions under which ISFM achieves greater yield response, RUE, AEN and AEP; and (3) compare yield responses to the substitutive and additive approaches of ISFM with sole application of cattle manure. Application of high rates of cattle manure in combination with high N fertilizer rates increased yield response only by 27.5%, but it achieved 47% lower AEN and 27% lower AEP relative to a combination of low manure and low N fertilizer rate. The substitutive approach of ISFM achieved 54% greater AEN and 16% greater AEP than the additive ISFM approach. Yield response and AEN also significantly varied with soil type. On most soil types, AEN was 2–195% lower under sole manure than under ISFM or sole fertilizer. We recommend application of moderate rates of cattle manure (5–10 t ha−1) combined with moderate doses of N fertilizer (

Fire and overgrazing reduce aboveground biomass, leading to land degradation and potential impacts on soil organic carbon (SOC) and total nitrogen (TN) dynamics. However, empirical data are lacking on how prescribed burning and livestock exclusion impact SOC in the long-term. Here we analyse the effects of 19 years of prescribed annual burning and livestock exclusion on tree density, SOC and TN concentrations in the Sudanian savanna ecoregion at two sites (Tiogo and Laba) in Burkina Faso. Results revealed that neither livestock exclusion nor prescribed burning had significant impact on SOC and TN concentrations. The results at both sites indicate that 19 years of livestock and fire exclusion did not result in a significant increase in tree density compared to grazing and annual prescribed burning. The overall mean (± SEM) of SOC stocks in the 0–50 cm depth increment in the unburnt (53.5 ± 4.7 Mg C ha−1) and annually burnt (56.4 ± 4.3 Mg C ha−1) plots at Tiogo were not statistically different. Similarly, at Laba there was no significant difference between the corresponding figures in the unburnt (37.9 ± 2.6 Mg ha−1) and in the annually burnt plots (38.6 ± 1.9 Mg ha−1). Increases in belowground inputs from root turnover may have countered changes in aboveground biomass, resulting in no net change in SOC and TN. We conclude that, contrary to our expectation and current policy recommendations, restricting burning or grazing did not result in increase in SOC stocks in this dry savanna ecosystem.

Agarwood (Aquilaria malaccensis Lam.) is highly valued for its medicinal, incense and perfumery properties. Due to the illegal harvest and trade in its wood, this species is critically endangered in the wild. Managing the agarwood on farmland is believed to enhance the economic security of smallholder farmers while also contributing to the conservation of the species. However, information is scanty on the cultivation of agarwood in smallholder farmlands and the effect of stand density and managements on the associated vegetation and soil properties. Therefore, the objectives of this study were to quantify (i) the diversity, density distributions and importance values, (ii) functional diversity and (iii) soil carbon and nitrogen contents, and C:N stoichiometry under different agarwood management regimes on smallholder farms. A total of 40 farms were selected for this study, and these were categorised into four management regimes based on the proportion of agarwood trees as: pure stand (100 % agarwood trees), dominant (61–99%), moderate (30–60 %) and non-dominant (

Shifting cultivation is a globally important form of agriculture covering over 280 million hectares in the tropics, but it has often been blamed for deforestation and forest degradation. In North East India (NEI) it has been practiced for millennia and it is an important element of the cultural identity of indigenous communities. It is often practiced on slopping lands with fragile soils (mostly Acrisols), which are prone to rapid degradation with cultivation. The shortened fallow cycle as practised currently is ecologically unsustainable and economically not viable. This study aimed to quantify (i) changes in soil bulk density, aggregate stability and compaction in relation to chronosequence and soil depth, (ii) changes in the proportion of macro, meso, and micro aggregates and associated soil organic carbon (SOC) content in relation to soil depth and fallow chronosequence, and (iii) determine the minimum fallow length that achieves SOC stocks comparable with adjacent intact forest land. The proportion of soil macro-aggregates and meso-aggregates significantly varied with land-use and soil depth as well as their interactive effects. Across all soil depths, forest land had the highest proportion of macro-aggregates (75.6%), while the currently cultivated land had the least proportion (51.1%). The SOC contents in macro-aggregates increased with fallow age and decreased with soil depth; the highest (1.95%) being in the top 10 cm soil of 20 years old fallows and the lowest (0.39%) in 21–30 cm depth of 5 years old fallows. Multivariate analysis identified bulk density and porosity as the most important variables to discriminate between land use practices. The analysis provided evidence for significant changes in soil compaction, aggregate stability and SOC content with the transition from undisturbed forest to slash-and-burn cultivation and fallow phases. It is concluded that a minimum of 20 years of fallow period is required to achieve SOC content and C stocks comparable with intact forest land.

Understanding the impacts of fire and grazing on soil carbon dynamics is critical for designing savanna management strategies. Fire and grazing are generally thought to degrade land by inducing loss of soil carbon. However, empirical data are lacking on the long-term effects of prescribed burning and livestock exclusion on soil organic carbon (SOC). We analysed the effects of 19 years of prescribed burning and livestock exclusion on SOC on two sites (Tiogo and Laba) in the Sudanian savanna ecoregion of Burkina Faso. On both sites, prescribed burning slightly increased SOC over the control in the 0-50 cm soil depth across exclosure treatments; the relative increase being 1.8% and 5.4% on the Tiogo and Laba sites, respectively. However, livestock exclusion did not significantly increase tree densities, soil total nitrogen, and SOC content. The overall mean ( SEM) of SOC stocks in the 0-50 cm depth were 53.5  4.7 Mg ha-1 in the unburnt plots and 56.4  4.3 Mg ha-1 in annually burnt plots on the Tiogo site, while the corresponding figures on the Laba site were 37.9  2.6 Mg ha-1 in the unburnt and 38.6  1.9 Mg ha-1 in annually burnt plots. Neither exclosure nor prescribed burning had a statistically significant effect on SOC stocks in the 0-20 cm and 20-50 cm soil depths. We conclude that restricting burning or grazing did not increase the soil carbon sequestration potential of this dry savanna ecosystem contrary to our expectation.