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Adequate measurements of the nitrogen (N) concentration in the aboveground biomass of sugarcane throughout the growth cycle can be obtained using the critical N dilution curve (CNDC) concept, which provides an N-nutrition index (NNI). The aim of this work was to determine the CNDC value for Brazilian sugarcane variety SP81-3250, establish the critical concentration of N, and determine the NNI in the aboveground biomass throughout the cane plant and first ratoon crop cycles. The study was performed in three experimental areas located in São Paulo, Brazil, during the crop cycles of 2005/2006 (18-month cane plant) and 2006/2007 (first ratoon). The plant cane crop was fertilized with treatments of 40, 80, or 120 kg N ha-1 and a control treatment without N. After the plant cane harvest, rates of 0, 50, 100, or 150 kg N ha-1 were applied to the control plot and the 120 kg N ha-1-treatment plot in a split-plot experimental design with four repetitions. Throughout both sugarcane cycles, measurements of aboveground biomass were used to determine the dry-mass (DM) production and N concentration for each treatment. CNDC varied between the growth cycles, with a higher N concentration observed in the initial stages of the first ratoon and a lower N dilution observed throughout the plant cane cycle. The NNI value indicated excessive N storage in the initial stages and limiting concentrations at the end of the growth cycle. CNDC and NNI allow for the identification of the N-nutrition variation rate and the period in which the nutrient concentration limits the production of aboveground biomass. The equations for the critical N (Ncr) level obtained in this study for plant cane (Ncr = 19.0 DM-0.369) and ratoons (Ncr = 20.3 DM-0.469) can potentially be used as N-nutritional diagnostic parameters for sugarcane N nutrition. [ABSTRACT FROM AUTHOR]

Abstract: Nitrogen (N) fertilization of sugarcane crops is a common practice used to reach sustainable levels of productivity, both for plant cane and especially for the ratoon. However, when evaluating the amount of N in the plant derived from fertilizer (NDDF) at harvest, this contribution is approximately 20% of total plant biomass N, which raises questions regarding the efficiency of N fertilization. The goal of this study was to evaluate the N derived from fertilizer (NDFF) during the sugarcane crop development, for both plant cane and first ratoon crop cycles. Two field experiments were performed in São Paulo State, Brazil, in Arenic Kandiustults and in Typic Eutrustox. The sugarcane was mechanically harvested without burning. N fertilizer for both the plant cane (doses of 40, 80 and 120kgha−1 of N as urea) and the first ratoon (doses of 50 and 100kgha−1 of N as ammonium sulfate) was labeled 15N. The results showed that NDFF contributed up to 40% of the total N in the plant cane at initial stages of development. The magnitude of this contribution decreased during stages of maturity to approximately 10% of total N at harvest. In the first ratoon, application of N fertilizer was more effective for crop nutrition, constituting up to 70% of total N in initial stages of development and decreasing through the cycle, reaching approximately 30% at harvest. Therefore, studies that evaluate NDDF only at harvest can lead to underestimating the role of N fertilizer for sugarcane nutrition. The higher NDFF in ratoon explains why this crop cycle presents a more consistent response to N fertilization than plant cane, as observed in several studies developed under Brazilian conditions in the last decades. [Copyright &y& Elsevier]

• N fertilization in sugarcane ratoon cycles causes small changes in soil C-N stocks. • Cover crop increases soil N stock and microbial biomass C, but not C stocks. • Cover crop reduces sugarcane response to N fertilization over four crop cycles. • Cover crop increases sugarcane yield 9–15% over four years without additional N. • Cover crop replaces N fertilizer by 9 and 15 kg ha−1 yr−1 in sandy and clayey soils. Sugarcane production for biorenewables demands substantial inputs of nitrogen (N) fertilizer that can lead to environmental consequences, and no clear effect has been reported on soil organic carbon (SOC) and N stocks. The use of a previous legume crops cultivation to add N to soil is a promising strategy to reduce the dependence in synthetic N fertilizer, having an international appeal for sustainable production of bioenergy crops. This study investigates a four-year impact of N fertilization on SOC and N stocks and sugarcane ratoon yields in a sandy and clayey soils, while considering the effects of a legume cover crop cultivated during the renovation period on decreasing N fertilizer requirements. Treatments with N fertilizer rates were arranged in a randomized block design after plant-cane harvest: 60, 120, 180 kg N ha−1 and control (without N) in two paired areas previously managed with Crotalaria spectabilis and bare fallow. Soil samples for SOC and N stocks were quantified at the beginning of the trial, and measured again along with microbiological attributes after four consecutive years, while sugarcane yield was assessed annually. SOC and N stocks were unaffected by N fertilizer rates, whereas the cultivation of cover crop increased soil N storage and microbial biomass carbon. There was limited responsiveness of sugarcane ratoons to additional N supplied by inorganic fertilizer under cover crop, whereas positive responses occurred under bare fallow. Considering the average of four-harvest yields, cover crop increased sugarcane yield by 9 % (5 Mg ha−1) at sandy soil and 15 % (16 Mg ha−1) at clayey soil relative to bare fallow. Cover crop provided an annual N fertilizer replacement of 9 and 15 kg ha−1 in the sandy and clayey soils. The long-lasting historical effect of cover crop in increasing sugarcane yield per area without the need for extra N from fertilizer opens a new possibility to increase the sustainability and alleviate associated greenhouse gas emissions of sugarcane fields by allowing savings in synthetic N fertilizer. [ABSTRACT FROM AUTHOR]

Ethanol production is expected to increase to 54 billion litres in 2030. Two alternatives from an agronomic point of view could be increasing the amount of area under sugarcane cultivation and/or narrowing the yield gaps. Precision agriculture (PA) approach and technologies for that are a feasible strategy to boost yields without the need for any further expansion of sugarcane areas. Through life cycle assessment (LCA), this study addressed the economic and environmental suitability of production expansion based on four scenarios in South-Central Brazil. Current production, expansion of area and yield, and PA technology adoption (fertiliser management and systematisation) are the scenarios assessed. The results showed that if no yield gain is achieved, an expansion of 4.5 million hectares of cultivated area will be required to reach those targets. To maintain stable cropping areas, the average yield of sugarcane should be increased from 76.2 Mg ha−1 to 122.4 Mg ha−1 in 2030. Such an increase could potentially reduce production costs by 26% and greenhouse gas emissions by 14% compared to those in the current scenario. However, the findings suggest that the adoption of site-specific management alone is not enough to address the necessary production to reach the goals by 2030. So, conclusions drawn from this study suggest that it will be necessary adopting strategies to increase sugarcane production, either through site-specific management or the expansion of cultivated area. The improved management of spatial–temporal variability through PA technologies is a win–win strategy to promote yield gains, reduce production costs and further ensure environmental benefits of sugarcane-based ethanol. • Area and yield increase would be required to reach ethanol goalsby 2030. • Site-specific management alone is not enough to reach Ethanol goals by 2030. • Fertiliser management and field systematisation reduced production costs. • Spatial–temporal variability management is a win–win strategy. [ABSTRACT FROM AUTHOR]

Large amounts of straw are remained in the sugarcane fields after the crop to be mechanically harvested. Straw is pointed out as a feedstock to attend high bioenergy production demand. However, either indiscriminate straw removal or high amount of straw kept on the field may impair several soil functions and thereafter decreases plant tillering and crop yield. Better nutrients cycling and soil physical protection due to Leguminosae species grown within the sugarcane renewal period may offset implications of straw managements across the crop cycles. Thus, does Crotalaria sp. grow within the sugarcane renewal period can offset the undesirable implications of unsustainable straw management on soil and crop yield? To address this research question, a two-year experiment was carried out in Quirinópolis, Chapadão do Céu, Iracemápolis and Quatá, first two sites are in Goiás state, while the other sites are in São Paulo state, Brazil. Soil and plant parameters under straw retention rates (i.e., 0%, 50% and 100% of straw retention) were assessed. This management was coupled with fallow (F) and Crotalaria sp. (CR) grown within the sugarcane renewal period. Soil parameters evaluated included, carbon (C) and nitrogen (N) stocks, while stalk yield was plant parameters assessed. The straw retention implications on soil and plant were site-specific. Carbon and N stocks in the upper 0.4 m soil layer were, respectively, 3.5 and 3.1 time higher at the fine-textured soil than the stocks of those elements at the coarse-textured soil. Regardless of Crotalaria sp. grown, stalk yield increased (ranged from 3 to 16 Mg ha−1) under total straw retention rate for most sites, while in the coolest site 50% and 100% straw retention reduced stalk yield in 13 and 14 Mg ha−1, respectively. In addition, Crotalaria sp. grown within the sugarcane renewal period does not seem able to avoid reduction on soil N availability due to straw retention along the ratoon cycles. Overall, straw removal for bioenergy should be judiciously performed, according to local edaphoclimatic conditions. • Stalk yield was increased due to straw retention in the most sites. • Sugarcane straw retention reduces plant tillering and yield in the coolest site. • Crotalaria sp. promotes the soil nutrient cycling (mainly K and P). • Straw retention increases C sequestrated and stocks. • Crotalaria sp. grown in the sugarcane renewal period increases soil N. [ABSTRACT FROM AUTHOR]