Long-term Effects of Pre-harvest Burning and Nitrogen and Vinasse Applications on Yield of Sugar Cane and Soil Carbon and Nitrogen Stocks on a Plantation in Pernambuco, N.E. Brazil

Abstract

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.

Soil and crop residue CO2-C emission under tillage systems in sugarcane-producing areas of southern Brazil

“…Given that sugarcane C concentration of 40 % was about 15 Mg ha -1 , we estimated short term loss to be 3 % of total C associated with sugarcane residues. Our result is consistent with that reported by Resende et al (2006), who found that part of the C stored and associated with crop residues in soil was lost after tillage during the replanting period, which usually occurs every six years in sugarcane areas. Changes in SOC emission due to tillage incorporation have previously been reported by Adiku et al (2008) and Al-Kaisi and Yin (2005).…”

Efeito da queima da palhada da cana-de-açúcar e de aplicações de vinhaça e adubo nitrogenado em características tecnológicas da cultura

“…Assim, a queima prévia dos canaviais passou a ser praticada em larga escala (Ceddia et al, 1999). No entanto, com a queima, são perdidos cerca de 10 t ha -1 ano -1 de palha, que contém diversos nutrientes, dentre os quais se destacam N (40-60 kg ha -1 ), S (15-30 kg ha -1 ) e C (4.500 kg ha -1 ) (Urquiaga et al, 1997;Resende et al, 2006). O impacto desta prática a longo prazo em características tecnológicas da cultura de cana não vem sendo descrito na literatura.…”

Quantifying soil carbon stocks and greenhouse gas fluxes in the sugarcane agrosystem: point of view

“…However, several authors have emphasized the need to investigate soil C stocks at deeper layers when assessing the impact of management changes in sugarcane, preferably down to one meter (Resende et al, 2006), from various depth intervals since soil C has not a linear behavior along soil profile. Samples could be sampled from the following soil layers: 0-0.1, 0.1-0.2, 0.2-0.3, 0.4-0.5, 0.7-0.8 and 0.9-1.0 m for three out of nine pits and 0-0.1, 0.1-0.2, 0.2-0.3 m in the other 6 pits ( Figure 2).…”