Interest in the use of biochar in agriculture has increased exponentially during the past decade. Biochar, when applied to soils is reported to enhance soil carbon sequestration and provide other soil productivity benefits such as reduction of bulk density, enhancement of water-holding capacity and nutrient retention, stabilization of soil organic matter, improvement of microbial activities, and heavy-metal sequestration. Furthermore, biochar application could enhance phosphorus availability in highly weathered tropical soils. Converting the locally available feedstocks and farm wastes to biochar could be important under smallholder farming systems as well, and biochar use may have applications in tree nursery production and specialty-crop management. Thus, biochar can contribute substantially to sustainable agriculture. While these benefits and opportunities look attractive, several problems, and bottlenecks remain to be addressed before widespread production and use of biochar becomes popular. The current state of knowledge is based largely on limited small-scale studies under laboratory and greenhouse conditions. Properties of biochar vary with both the feedstock from which it is produced and the method of production. The availability of feedstock as well as the economic merits, energy needs, and environmental risks—if any—of its large-scale production and use remain to be investigated. Nevertheless, available indications suggest that biochar could play a significant role in facing the challenges posed by climate change and threats to agroecosystem sustainability.

Aim of study: Silvopastoral system (SPS) involving numerous indigenous trees and shrubs is a traditional land-use system in the Caatinga, but it has little been studied scientifically. Given the importance of SPS as a sustainable land-use strategy in the drylands, this paper examines the attributes of the Caatinga SPS and their relevance to other arid and semiarid regions.Area of study: Caatinga biome, with an area of 0.9 million km2 and a population of 25 million, a unique dryland ecosystem of Brazil.Materials and methods: The paper reviewed the literature on the main characteristics of SPS management of the Caatinga biome and the global perspectives of silvopastoral land-management in semiarid regions.Main results: Guidelines for sustainable SPS management of the Caatinga include maintaining up to 400 trees/ha (40% tree cover) and allowing at least 40% of the available forage to dry up to provide mulch for soil protection. Opportunities for improving the low carrying capacity of the Caatinga are thinning, coppicing, and enrichment planting with desirable tree and understory species. Establishment of fodder banks, promotion of non-conventional feed sources such as cactus, and introduction of grazing animals to orchards and plantations are some other promising interventions.Research highlights: The review highlights the importance of initiating new studies on Caatinga SPS, focusing on the role and potential of various native species and the ecosystem services they provide, in conjunction with relevant social, economic, and policy aspects to better exploit the benefits of the system and facilitate its wider adoption.

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Drylands constitute more than 40% of global land and are particularly vulnerable to the impacts of climate change. In many of these drylands, livestock activities are a major form of land-use. In Brazil, the two major dryland biomes, Cerrado and Caatinga, play a key role in the country’s livestock activities. While important economically, these activities also contribute to the emission of high amounts of greenhouse gases. One suggested strategy for mitigating the impacts of climate change is the adoption of silvopastoral systems (SPS) which combine trees, pasture, and animals simultaneously on the same unit of land. Farmers in the drylands of Brazil have a long history of practicing SPS. The practice of silvopasture is relevant to both climate change and the economy, but not necessarily to the issues of biodiversity loss and economic inequality. The lack of interdisciplinarity in rural agricultural development projects in the past, such as those related to the “Green Revolution”, resulted in the aggravation of economic inequalities and biodiversity loss. The present work, focusing on the Brazilian Drylands, reviews these issues to justify the need for interdisciplinary projects considering multiple variables like soil quality, tree density, biodiversity richness, and farmers’ perception.

Tropical soils usually lack phosphorus (P) availability due to the high P retention associated with these soils, limiting plant productivity. Brazil is the largest tropical country and worldwide exporter of beef, where overgrazing and frequent slash and burn practices resulted in large areas of degraded pastures. Land degradation and lack of releasable P could potentially be solved using a byproduct of livestock activities-bones-with high P content. The present work evaluates an industrial bonechar (obtained by the pyrolysis of bones) for its potential as a soil amendment. The bonechar's structure and chemical composition were evaluated by using x-ray diffraction, scanning electron microscopy and chemical analyses. The results showed that: i) bonechar is composed mainly of the mineral hydroxyapatite, known to bond with organic molecules of different sizes, which could increase the soil organic carbon stock, and ii) the plant available P in the bonechar is high, 2,800 mg kg -1 . Although more studies are needed on bonechar, mainly on its field application, the present work reinforces the production and agricultural use of it as a relevant soil amendment to recover degraded soils in tropical regions.