The use of crop residues as a bioenergy feedstock is considered a potential strategy to mitigate greenhouse gas (GHG) emissions. However, indiscriminate harvesting of crop residues can induce deleterious effects on soil functioning, plant growth and other ecosystem services. Here, we have summarized the information available in the literature to identify and discuss the main trade-offs and synergisms involved in crop residue management for bioenergy production. The data consistently showed that crop residue harvest and the consequent lower input of organic matter into the soil led to C storage depletions over time, reducing cycling, supply and availability of soil nutrients, directly affecting the soil biota. Although the biota regulates key functions in the soil, crop residue can also cause proliferation of some important agricultural pests. In addition, crop residues act as physical barriers that protect the soil against raindrop impact and temperature variations. Therefore, intensive crop residue harvest can cause soil structure degradation, leading to soil compaction and increased risks of erosion. With regard to GHG emissions, there is no consensus about the potential impact of management of crop residue harvest. In general, residue harvest decreases CO₂ and N₂O emissions from the decomposition process, but it has no significant effect on CH₄ emissions. Plant growth responses to soil and microclimate changes due to crop residue harvest are site and crop specific. Adoption of the best management practices can mitigate the adverse impacts of crop residue harvest. Longterm experiments within strategic production regions are essential to understand and monitor the impact of integrated agricultural systems and propose customized solutions for sustainable crop residue management in each region or landscape. Furthermore, private and public investments/cooperations are necessary for a better understanding of the potential environmental, economic and social implications of crop residue use for bioenergy production.

To enhance global bioenergy production, the Brazilian industry's interest in using sugarcane (Saccharum officinarum) straw as a feedstock for electricity and cellulosic ethanol production has increased recently. However, indiscriminate straw removal may negatively affect key soil functions related to water infiltration, retention, and availability to plants. Therefore, a microlysimeter system with a 0.2 m soil column was built to evaluate the effects of straw removal rates on water drainage and water storage in a sandy clay loam soil from a commercial sugarcane field in southeastern Brazil. The experiment was conducted in an open area where the lysimeter system was subjected to rainfall. After assembly, the treatments consisting of four straw amounts of 0, 3, 6, and 12 Mg ha⁻¹ were applied, representing straw removal rates of 100% (bare soil), 75%, 50%, and 0%, respectively. The water drainage was quantified and collected for 17 months, and the soil water storage was measured over a two-month period. The soil water holding capacity was calibrated by an inverse modeling approach minimizing the differences between soil water storage measured in the field and simulated by a water balance model. Our results reveal that the amount of water drained from bare soil was 30% lower than no removal treatment. Bare soil had the lowest water storage for most of the days, indicating a greater susceptibility to losing water through evaporation and drying. The long-term simulation for early, mid, and late sugarcane harvest seasons suggests longer periods of water restriction to crop growth under higher straw removal rates (i.e., 100% and 75%), potentially impairing sugarcane growth and thus yield. Also, the findings suggest that partial residue maintenance, up to 6 Mg ha⁻¹ of straw (50% removal) on the soil surface, seems to be sufficient to prevent excessive water losses and daily variations of soil water content, sustaining soil water storage rates above the critical point for sugarcane growth.

Maize is one of the main staple crops of the world but needs large amounts of nitrogen (N) to achieve a high yield. Mineral N fertilization is one of the main production costs to cultivation and organic N sources could be a cost-effective alternative to mineral sources. We hypothesized that organic N sources could replace mineral fertilizer whilst maintaining high yields. Therefore, our study examined the effect of N supplied through organic sources on the yield of maize and its components and evaluated the economic viability of using organic N sources in terms of cost savings of energy resources. A field experiment was carried out in the Southeastern region of Brazil (São Paulo state) on a Typical Acrudox soil with a clay texture. The experiment was set out in a complete randomized block design, with six treatments (five N sources + control) and four replicates. The treatments were: (A) mineral source (urea - Ur); (B) a by-product from the food industry (Fby); (C) biofertilizer from swine manure (Bs); (D) poultry bedding (Pb); (E) cattle manure (Cm); and (F) control (Co - without N). The maize yield components evaluated were plant height (V6 and R2 stages), root dry mass and morphoanatomy (R2 stage) and, at harvest, grains in ears, thousand kernel weight (TKW), productivity and crop residues dry mass. Economic viability was assessed by considering the cost of each N source in relation to gross economic revenues from the sale of corn. Overall, the results showed that only Fby produced better yield components and was more productive than urea. This source also provided the highest economic revenue and the lowest fertilizer cost for each unit produced. The Pb and Cm sources were less productive than the mineral source, but were better than Bs, which was slightly better than the control (without N application). The same pattern of results was found for economic revenue and fertilizer cost. Bs was the most expensive N source and consequently gave the lowest economic returns to farmers. In summary, the N efficiency of the organic sources as an alternative to mineral sources for high-yield maize was ranked as follows: Fby >Ur> Pb > Cm > Bs > Co.