International audienc

Since the 1970s the area under sugarcane in Brazil has increased from 2 million to over 5 million ha (M ha), and it is expected to pass the 7 M ha mark in 2007. More than half of the cane is harvested to produce bioethanol as a fuel for light vehicles. The distilleries produce approximately 13 L of distillery waste (vinasse) for each litre of ethanol produced. In the 1980s there was considerable concern over the long-term effects of the disposal of this material (containing about 1% carbon and high in K) on cane yields if it was applied to the field. At the same time there was a growing movement to abandon the practice of pre-harvest burning and some research was showing that some Brazilian varieties of sugar cane were able to obtain significant contributions of N from plant-associated biological nitrogen fixation (BNF). For these reasons an experiment was installed on a cane plantation in the state of Pernambuco, NE Brazil to investigate the long-term effects of vinasse and N fertiliser additions and the practice of pre-harvest burning on crop and sugar yield, soil fertility parameters, N balance and soil C stocks. The results showed that over a 16-year period, trash conservation (abandonment of burning) increased cane yields by 25% from a mean of 46 to 58 Mg ha )1 . Vinasse applications (80 m 3 ha )1 crop )1 ) increased mean cane and sugar yield by 12 to 13% and the application of 80 kg N ha )1 as urea increased cane yields by 9%, but total sugar yield by less than 6% (from 7.0 to 7.4 Mg ha )1 crop )1 ). The total N balance for the soil/plant system when only the surface 20 cm of the soil was considered was positive in plots where no N fertiliser was added. However, the data indicated that during the 16 years of the study considerable quantities of soil organic matter were accumulated below 20 cm depth such that the N balance considering the soil to 60 cm depth was strongly positive, except where N fertiliser was added. The data indicated that there were considerable BNF inputs to the system, which was consistent with its low response to N fertiliser and low N fertiliser-use-efficiency. There were no significant effects of vinasse or urea addition, or trash conservation on soil C stocks, although the higher yields proportioned by trash conservation had potentially significant benefits for increased mitigation of CO 2 emissions where the main use of the cane was for bioethanol production.

No abstract

-The objective of this work was to evaluate elephant grass (Pennisetum purpureum Schum.) genotypes for bioenergy production by direct biomass combustion. Five elephant grass genotypes grown in two different soil types, both of low fertility, were evaluated. The experiment was carried out at Embrapa Agrobiologia fi eld station in Seropédica, RJ, Brazil. The design was in randomized complete blocks, with split plots and four replicates. The genotypes studied were Cameroon, Bag 02, Gramafante, Roxo and CNPGL F06-3. Evaluations were made for biomass production, total biomass nitrogen, biomass nitrogen from biological fi xation, carbon/ nitrogen and stem/leaf ratios, and contents of fi ber, lignin, cellulose and ash. The dry matter yields ranged from 45 to 67 Mg ha -1 . Genotype Roxo had the lowest yield and genotypes Bag 02 and Cameroon had the highest ones. The biomass nitrogen accumulation varied from 240 to 343 kg ha -1. The plant nitrogen from biological fi xation was 51% in average. The carbon/nitrogen and stem/leaf ratios and the contents of fi ber, lignin, cellulose and ash did not vary among the genotypes. The fi ve genotypes are suitable for energy production through combustion.Index terms: Pennisetum purpureum, ash, agroenergy, biological nitrogen fi xation, genotype, lignin. Genótipos de capim-elefante para produção de bioenergia por combustão direta da biomassaResumo -O objetivo deste trabalho foi avaliar genótipos de capim-elefante (Pennisetum purpureum Schum.) quanto ao potencial para a produção de bioenergia por combustão direta da biomassa. Avaliaram-se cinco genótipos de capim-elefante, em dois solos com baixa fertilidade. Os experimentos foram conduzidos na estação experimental da Embrapa Agrobiologia, em Seropédica, RJ. O delineamento experimental foi o de blocos ao acaso, em parcelas subdivididas, com quatro repetições. Os genótipos estudados foram Cameroon, Bag 02, Gramafante, Roxo e CNPGL F06-3. Determinaram-se a produção de biomassa, o acúmulo de nitrogênio na biomassa, o nitrogênio da biomassa proveniente da fi xação biológica, as relações carbono/nitrogênio e talo/ folha, e os teores de fi bra, lignina, celulose e cinzas da biomassa. A produção de matéria seca variou de 45 a 67 Mg ha -1 . A menor produção foi do genótipo Roxo, e as maiores, dos genótipos Bag 02 e Cameroon. O nitrogênio total acumulado na matéria seca variou de 240 a 343 kg ha -1 . Em média, 51% do nitrogênio foram provenientes da fi xação biológica. As relações carbono/nitrogênio e talo/folha e os conteúdos de fi bra, lignina, celulose e cinzas não variaram entre os genótipos. Os cinco genótipos constituem materiais adequados para produção de energia pela queima.Termos para indexação: Pennisetum purpureum, cinzas, agroenergia, fi xação biológica do nitrogênio, genótipo, lignina.

Ammonia (NH3) volatilization is one of the main pathways of N loss from agricultural cropping systems. This study evaluated the NH3–N loss from four urea‐based N sources (urea, urea–ammonium nitrate [UAN], SuperU, and ESN [polymer‐coated urea]) surface band applied at a rate of 200 kg N ha−1 to irrigated, strip‐till corn production systems for 2 yr using semi‐static chambers (semi‐open and open) to measure NH3–N loss. The efficiency of the semi‐static chambers in estimating NH3–N loss under field conditions was determined using 15N labeled urea applied at rates of 50, 100, and 200 kg N ha−1. Both chamber types had similar NH3–N recoveries and calibration factors. Immediate irrigation with 16 to 19 mm of water 1 d after N fertilization probably limited NH3–N volatilization from surface‐applied N fertilizers to a range of 0.1 to 4.0% of total N applied. SuperU, which contains a urease inhibitor, had the lowest level of NH3–N loss when compared to the other N sources. Analyzed across years, estimated NH3–N losses for the N sources were in the order: ESN = UAN > urea > SuperU. Both years the results showed that measurement time may need to be increased to evaluate NH3–N volatilization from polymer‐coated urea N sources such as ESN. The open‐chamber method was a viable, low cost method for estimating NH3–N loss from small field plot N studies.