Conservation agriculture can provide a low-cost competitive option to mitigate global warming with reduction or elimination of soil tillage and increase soil organic carbon (SOC). Most studies have evaluated the impact of zero till (ZT) only on surface soil layers (down to 30 cm), and few studies have been performed on the potential for C accumulation in deeper layers (0-100 cm) of tropical and subtropical soils. In order to determine whether the change from conventional tillage (CT) to ZT has induced a net gain in SOC, three long-term experiments (15-26 years) on free-draining Ferralsols in the subtropical region of South Brazil were sampled and the SOC stocks to 30 and 100 cm calculated on an equivalent soil mass basis. In rotations containing intercropped or cover-crop legumes, there were significant accumulations of SOC in ZT soils varying from 5 to 8 Mg ha À1 in comparison with CT management, equivalent to annual soil C accumulation rates of between 0.04 and 0.88 Mg ha À1 . However, the potential for soil C accumulation was considerably increased (varying from 0.48 to 1.53 Mg ha À1 yr À1 ) when considering the soil profile down to 100 cm depth. On average the estimate of soil C accumulation to 100 cm depth was 59% greater than that for soil C accumulated to 30 cm. These findings suggest that increasing sampling depth from 30 cm (as presently recommended by the IPCC) to 100 cm, may increase substantially the estimates of potential CO 2 mitigation induced by the change from CT to ZT on the free-draining Ferralsols of the tropics and subtropics. It was evident that that legumes which contributed a net input of biologically fixed N played an important role in promoting soil C accumulation in these soils under ZT, perhaps due to a slow-release of N from decaying surface residues/roots which favored maize root growth.

ABSTRACT:The objective of this study was to evaluate the performance of two genotypes of elephant grass, fertilized with and without N, for biomass production for energy use under the edaphoclimatic conditions of the Cerrado. The genotypes Roxo and Paraíso, grown in a field experiment in a Latosol in the Cerrado region were evaluated for biomass yield, nitrogen accumulation, C:N and stem:leaf ratios, fibre, ash and P and K contents and calorific value. The accumulated dry biomass ranged from 30 to 42 Mg ha -1 and showed no response to nitrogen fertilization with the lowest biomass obtained by the genotype Paraíso and the highest by Roxo. The total N accumulation followed the same pattern as for dry matter, ranging from 347 to 539 kg N ha -1 . C:N and stem:leaf ratio of the biomass produced did not vary with treatments. The fibre contents were higher in genotype Paraíso and the highest levels of ash in the genotype Roxo. The K content in the biomass was higher in genotype Roxo and P did not vary between genotypes. The calorific value averaged 18 MJ kg -1 of dry matter and did not vary with the levels of N in leaves and stems of the plant. Both genotypes, independent of N fertilization, produced over 30 Mg ha -1 of biomass under Cerrado conditions.

No abstract

This chapter is a review about sugarcane, one of the most important energy crops. It will describe some aspects of the production system, like varieties, pests and diseases, nutrients requirements, mechanical harvest, residue management and water use. After, sugarcane products and co-products are presented, followed by an energy balance of the production of sugarcane ethanol in Brazil. To finish, an analysis of the land use changes in sugarcane areas is made. About varieties, in the last years, beyond traditional cross breeding, molecular marker techniques and genetic engineering have also been used in genetic improvement programmes. Current improvement faces new challenges, where the objective is to use all parts of the plant that are not normally used to produce energy, as straw, leaves, and the residues and not only the juice extracted in grinding. As a result of these genetic programmes the sugarcane sector is a model in the gain of production (tons per hectare; litres per ton) and in the employment of technologies that reduce the use of chemical defensives, as, for instance, the biological control of pests. Those programs were successful in introducing materials resistant or tolerant to the main pests and diseases that affect sugarcane. In addition, it is expected that the use of transgenic cultivars will result in a greater reduction in the use of defensives, though environmental impacts should be better defined. In spite of the success, new pests and diseases, like Telchin licus licus and orange rust, have appeared, posing new challenges. Sugar cane cultivation culture is considered relatively efficient in using nutrients – the mean dose of mineral fertilizer used is 408 kg/ha, similar to that of several other crops with much smaller productions of biomass per area. One important aspect for this rational use of fertilizers is nutrient recycling, common in sugarcane agroindustry, by returning solid and liquid residues, such as filter cakes, ashes, straw, and, especially, vinasse. Also, the biological nitrogen fixation (BNF) has an important role in the nitrogenous nutrition of sugarcane in Brazil, and in the world. In the industry, rational water use has been adopted. The industry requirement for water has dropped from 5 m3 per ton to 1.83 m3 per ton of sugarcane; reaching 1.23 m3 of water per ton. Mills with the best management practices replace only 500 litres of water in the industrial system, with a recycling rate of 96.67 %. The sugarcane production system and the processing of its main products, sugar and alcohol, generates a significant number of co-products that have high added value. In addition to vinasse and filter cake, the bagasse is the co-product most used in the agroindustrial system of sugarcane. It is mainly used to produce energy. Basically all the thermal energy, and about 95% of the electric energy, is produced at the mill with co-generation systems using the bagasse. The estimation of the total fossil energy used in the field operations is 12329.7 MJ ha−1 year−1. Considering that one litre of ethanol produces 21.45 MJ of energy in the combustion, one hectare of sugarcane currently producing an average 6510 L of ethanol could generate 139639.0 MJ of energy, approximately 11 times the fossil energy invested in the agricultural operations. In addition to the energy balance, analysis of the process of land use change must be made. Studies recently conducted show that, in Brazil, sugarcane production is localized and expanding in areas that have been designated for agricultural production since long ago. The projections indicated that sugarcane expansion will continue in those areas. This means that there is no sugarcane expansion in the agricultural frontier. An Agroecological Zoning analysis for Sugarcane showed that the country has about 64.7 million hectares of land that is suitable for the expansion of sugarcane cultivation. And, to supply the market for the conditions in the year 2020, the additional area needed for the production of sugarcane will be of approximately 5.1M ha. Also, it is expected for the year 2020 that there will be a net reduction of approximately 100 kg CO2 eq m−3 of ethanol, in the emissions associated with the land use change in Brazil. Combining these facts, it is observed that sugarcane expansion in Brazil has a great chance of being conducted in a way that is less harmful to the environment, with land use changes that allow for a smaller emission of greenhouse gases and greater sustainability of the adopted production systems.

The use of legumes in pre-cultivation on the common bean has the possibility of providing atmospheric N to the soil, making it available to this crop, and may cover part of its N demand and increase grain yield. The objective of present study was to evaluate the effect of hyacinth bean and jack bean as green manures on the production of common bean grown in two seasons. Cover crops were evaluated for fixed N 2 , dry matter yield, nitrogen (N) and carbon (C) concentrations, C:N ratio and N accumulation in the shoot. The jack bean accumulated higher biomass and more total N than hyacinth bean and spontaneous vegetation (control). However, both legume species, when used as green manure, resulted in an increase in the N concentration of common bean. Compared to the spontaneous vegetation, hyacinth bean residue increased yield of common bean by 32% and jack bean residue increased the bean yield by 46%. These yields were recorded when common bean was cultivated a few weeks after residues incorporation into the soil and about seven months later, thus showing a flexibility to family farmers for making their decisions on the best cropping season.

No abstract

Purpose: Soybean is the most important grain crop in Brazil with a mean N accumulation of over 250 kg N ha-1, principally from biological N2 fixation. The residual N benefit depends heavily on the quantity of the belowground N at harvest, much which cannot be directly recovered in roots. The purpose of this study was to investigate different aspects of the 15N leaf-labelling technique to quantify non-recoverable root N (NRRN) derived from senescent roots and nodules (rhizodeposits). Methods: Soybean plants were grown in pots of soil and at 27 days after planting (vegetative stage V4) cut or whole leaves were exposed to highly enriched 15N-labelled urea or glutamine. Seven sequential harvests of the plants and soil were taken until the final grain harvest at 70 days after labelling.Results: After only 48 h, the plants labelled with 15N urea transferred approximately 5% to the soil, while only 1% was found in the roots. Leakage of 15N label was even more pronounced when the leaves were labelled with 15N glutamine. After this initial leakage, the excess 15N deposited in the soil only increased by a further 2.6% of applied label, which suggested that only part of this N represented senescence of roots or nodules.Conclusions At the final harvest, N in roots separated from the soil amounted to 6.4% of total plant N. Discounting the early rapid deposition of 15N-enriched N to the soil, our calculations indicated that at final harvest the total NRRN was 2.8% of total plant N.

No abstract