A quantitative review of the effects of biochar application to soils on crop productivity using meta-analysis

Sugarcane straw represents, under Brazilian conditions, approximately one third of the total primary energy of sugarcane in the field. Today, its use for energy is incipient and it is mostly wasted by either burning in the pre-harvest or left on the ground to decay. Besides its potential use as feedstock for energy production, there are several possible agronomic benefits of the straw blanket left on the ground such as soil protection against erosion, increase of soil organic carbon content, inhibition of weed growth, nutrient recycling and reduction of soil water losses, to name a few. The balance of the impacts and the economic and energetic value of the straw indicate that the amount of the straw left on the ground that could be considered optimal is dependent on the local conditions, agricultural practices, characteristics of the straw and intended final use. This work is meant to shed some light into this subject to help the understanding of the importance of the various impacts of the straw blanket on the ground, the availability and quality of the straw, the economics of straw recovery and use and the main criteria for determining the amount of straw that can be recovered for bioenergy or biofuels production.

Sugarcane straw availability, quality, recovery and energy use: A literature review

Brazil is a major sugarcane producer and its production more than doubled over the last decades to meet global bioenergy demands for reducing crude oil dependency and mitigating climate change. Nevertheless, the adverse effects of this growth on jeopardizing the sustainability of sugarcane production are not known, especially when environmental impacts of agricultural inputs and production processes are not judiciously managed. This article is a comprehensive review of the state-of-the-knowledge and the main advances made thus far in the sugarcane sector. Here, we review the major environmental impacts of rapidly expanding sugarcane plantation on the land use change and its competition with food production, as well as those associated with sugarcane cultivation in Brazil. Our main finding are that sugarcane plantation did not contribute to direct deforestation, and its expansion on degraded pastures with the attendant increased yields of food crops and livestock intensification decreased land competition between food and sugarcane. Non-burning sugarcane harvesting is a win-win strategy because of its benefits involving agronomic and environmental aspects, but soil compaction is among the main issues in sugarcane cropping systems. Sugarcane is highly efficient in terms of nitrogen use efficiency, which is an important factor for its high energy balance. But, special attention should be given regarding emissions of nitrous oxide when straw mulching is combined with application of nitrogen fertilizer and vinasse. Recent advances in the sugarcane sector also show significant reductions in water consumption, making sugarcane ethanol one of the most favorable options in terms of water footprint. Growing realization of a vast potential indicates the need to further enhance the environmental benefits of sugarcane ethanol by optimizing the agricultural production chain. Based on this improved knowledge, the adoption of best management practices is among researchable priorities that can be developed to consolidate the large potential of sugarcane production towards greater sustainability.

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Sustainability of sugarcane production in Brazil. A review

Soil degradation, caused by land misuse and soil mismanagement, has plagued humanity since the dawn of settled agriculture. Many once thriving civilizations collapsed due to erosion, salinization, nutrient depletion and other soil degradation processes. The Green Revolution of the 1960s and 1970s, that saved hundreds of millions from starvation in Asia and elsewhere, by-passed Sub-Saharan Africa. This remains the only region in the world where the number of hungry and food-insecure populations will still be on the increase even by 2020. The serious technological and political challenges are being exacerbated by the rising energy costs. Resource-poor and small-size land-holders can neither afford the expensive input nor are they sure of their effectiveness because of degraded soils and the harsh, changing climate. Consequently, crop yields are adversely impacted by accelerated erosion, and depletion of soil organic matter (SOM) and nutrients because of the extractive farming practices. Low crop yields, despite growing improved varieties, are due to the severe soil degradation, especially the low SOM reserves and poor soil structure that aggravate drought stress. Components of recommended technology include: no-till; residue mulch and cover crops; integrated nutrient management; and biochar used in conjunction with improved crops (genetically modified, biotechnology) and cropping systems, and energy plantation for biofuel production. However, its low acceptance, e.g. for no-till farming, is due to a range of biophysical, social and economic factors. Competing uses of crop residues for other needs is among numerous factors limiting the adoption of no-till farming. Creating another income stream for resource-poor farmers, through payments for ecosystem services, e.g., C sequestration in terrestrial ecosystems, is an important strategy for promoting the adoption of recommended technologies. Adoption of improved soil management practices is essential to adapt to the changing climate, and meeting the needs of growing populations for food, fodder, fuel and fabrics. Soil restoration and sustainable management are essential to achieving food security, and global peace and stability.

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Soils and food sufficiency. A review

article i nfo Soil water erosion and shallow landslides depend on aggregate stability and soil shear strength. We investigated the effect of vegetation on both soil aggregate stability and shear strength (through direct shear tests) in former croplands converted to vegetated erosion protection areas within the context of China's sloping land conversion programme. Four treatments were analysed in plots comprised of (i) 4 year old crop trees, Vernicia fordii, where understory vegetation was removed; (ii) V. fordii and the dominant understory species Artemisia codonocephala; (iii) only A. codonocephala and (iv) no vegetation. Soil samples were taken at depths of 0-5 cm and 45-50 cm. Root length density (RLD) in five diameter classes was measured, soil organic carbon (SOC), hot water extractable carbon (HWEC), texture and Fe and Al oxides were also measured. We found that mean weight diameter after slow wetting (MWDSW) in the A-horizon, was significantly greater (0.94-1.01 mm) when A. codonocephala was present compared to plots without A. codonocephala (0.57- 0.59 mm). SOC and RLD in the smallest diameter class (b0.5 mm), were the variables which best explained variability in MWDSW. A significant positive linear relationship existed between MWDSW and soil cohesion but not with internal angle of friction. As herbaceous vegetation was more efficient than trees in improving aggregate stability, this result suggests that the mechanisms involved include modifications of the cohesive forces between soil particles adjacent to plant roots and located in the enriched in SOC rhizosphere, thus also affecting shear strength of the corresponding soil volume. Thus, vegetation stabilised soil under different hierarchical levels of aggregate organisation, i.e. intra- and inter-aggregate. Our results have implications for the efficacy of techniques used in land conversion programs dedicated to control of soil erosion and shallow landslides. We suggest that mixtures of different plant functional types would improve soil conservation on slopes, by reducing both surface water erosion and shallow substrate mass movement. Planting trees for cropping or logging, and removing understory vegetation is most likely detrimental to soil conservation.

Effects of vegetation type on soil resistance to erosion: Relationship between aggregate stability and shear strength

Texture and sesquioxide effects on water-stable aggregates and organic matter in some tropical soils

Effect of sugarcane residue management (mulching versus burning) on organic matter in a clayey Oxisol from southern Brazil

Brazil is the world's largest sugarcane producer, so changes in sugarcane management in Brazil can affect the environment to a great extent. During almost one century, studies were carried out in cropping systems involving pre-harvest burning of aerial sugarcane residues. Nowadays the green trash management of sugarcane residues has become a common practice, although the effects are still poorly documented. The objective of this work was to compare topsoil carbon and nitrogen stocks, aggregation and bulk density in Brazilian sugarcane plantations where aerial residues were either burned (Cq) or left on the soil surface (Sq) after harvest. The study was carried out in three plantations, one on a clayey soil (Latossolo Vermelho, LVdf, i.e. Typic Hapludox) and two on sandy soils (Argissolo Vermelho-Amarelo, PVAd, i.e. Typic Hapludult, and Neossolo Quartzarenico, RQo, i.e. Quartzpsamment). On each plantation, the experimental design included six replications per treatment. After three crops, the accumulated aerial residue biomass in Sq treatment amounted to 40 t ha-1 of DM from which 4.5 and 3.6 t ha-1 of DM (i.e. 11 and 9 %) were still present at the soil surface in LVdf and RQo, respectively. This represented 1.60 and 1.35 t ha-1 of C and 0.022 and 0.021 t ha-1 of N, respectively. As a result, soil carbon at a 0-20 cm depth increased by 6.3 and 4.7 t ha-1 in LVdf and RQo, respectively. Over the three-year period, the rate of carbon sequestration in the litter and topsoil in the Sq treatment was 2.63 and 2.02 t ha-1 yr-1 in LVdf and RQo, respectively. Topsoil content of stable macroaggregates was also higher with Sq than with Cq: 814 vs. 693 g kg-1 in LVdf, and 516 vs, 420 g kg-1 in RQo, respectively. On the other hand, Sq caused topsoil compaction (PVAd and RQo) due to the mechanized harvest system. In the Brazilian soils under study, green trash management of sugarcane residues improved the topsoil properties and promoted carbon and nitrogen sequestration in the litter and topsoil.

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Avaliação de atributos físicos e estoques de carbono e nitrogênio em solos com queima e sem queima de canavial

Effect of conversion from sugarcane preharvest burning to residues green-trashing on SOC stocks and soil fertility status: Results from different soil conditions in Brazil

Edgar F. de Luca

Papers

Texture and sesquioxide effects on water-stable aggregates and organic matter in some tropical soils

Effect of sugarcane residue management (mulching versus burning) on organic matter in a clayey Oxisol from southern Brazil

Avaliação de atributos físicos e estoques de carbono e nitrogênio em solos com queima e sem queima de canavial

Effect of conversion from sugarcane preharvest burning to residues green-trashing on SOC stocks and soil fertility status: Results from different soil conditions in Brazil