Henrique Coutinho Junqueira Franco

Impact of sugarcane trash on fertilizer requirements for São Paulo, Brazil

The area under mechanized sugarcane (Saccharum spp.) harvesting is expanding in Brazil, increasing the return of trash to the soil. The main questions regarding this management are: (i) after adopting unburned mechanical harvesting, how long will it take to observe decreases in fertilizer requirements, (ii) what will be the magnitude of this decrease and, (iii) the impact in the short run of removing trash for energy purposes in the nutrient cycling? This study aimed to build an N prediction model for long term assessment of the contribution of sugarcane crop residues to sugarcane nutrition and to evaluate the cycling of other nutrients derived from crop residues. Keeping crop residues over the soil will increase soil N stock and N recovery by sugarcane, reaching equilibrium after 40 years with recovery of approximately 40 kg ha-1 year-1 of N. Removing trash for energy production will decrease the potential reduction in N fertilizer requirement. Of the total nutrients in the trash, 75 % of the K2O (81 kg ha-1 year-1) and 50 % of the N (31 kg ha-1 year-1) are in the tops, indicating the importance of maintaining tops in the soil to sustain soil fertility. Because the input data employed in the simulations are representative of the conditions in Southeast Brazil, these results might not be definitive for situations not represented in the experiments used in the study, but the model produced is useful to forecast changes that occur in the soil under different trash management.

Assessment of sugarcane trash for agronomic and energy purposes in Brazil

Due to new possibilities for using sugarcane (Saccharum spp.) trash for electricity generation, and the production of 2nd generation ethanol and others chemicals, the interest for its recovery has increased. However, the question of how much trash can be removed from sugarcane field still needs to be clarified. This study evaluated the amount of dry matter, nutrients content, structural compounds and efficiency of the enzymatic hydrolysis of the hydrothermal pretreated materials for tops and dry leaves in samples from sugarcane varieties. Tops and dry leaves present differences in nutrients content and moisture. Therefore, the amount of trash to be collected should not be simply based on percentages, but also should take into account the different fractions of the crop residues. For instance, around 80 % of N, P and K were derived from tops. Therein, the environmental indicators of the entire chain of sugarcane could be benefited because more nutrients would be recycled and less mineral fertilizers might be used for sugarcane production if tops are left on the field. Further, the tops have seven times more moisture than dry leaves and higher amounts of extractives (organic compounds of low molecular weight). Moreover, as the result of yield obtained in the pretreatment steps for dry leaves were superior to the tops and the glucose yields obtained in the enzymatic hydrolysis step were similar, it can be predicted that for second generation ethanol production, it is more viable to recover parts of the dry leaves fraction, leaving the tops on the field.

Produtividade da cana-de-açúcar relacionada à localização de adubos nitrogenados aplicados sobre os resíduos culturais em canavial sem queima

Knowledge about the proper management of not-burned sugar cane is still limited, particularly regarding nitrogen fertilization. A field experiment was carried out to evaluate sugar cane yield, the balance of 15N fertilizers in the soil-plant-residue system and ammonia loss by volatilization in sugarcane ratoon crop without straw burning prior to mechanical harvesting, comparing different locations of surface-applied nitrogen fertilizers. The sugar cane variety SP81-3250. Treatments were arranged in a complete randomized blocks, with four replicates. The treatments consisted of four N fertilizer sources: ammonium nitrate (AN), ammonium sulfate (AS), urea and Uran, applied over the residues in two ways: over the entire area or side dressed on both sides of the ratoon crop line, at a rate of 70 kg N ha-1. The plots treated with AS and urea were divided in microplots with 15N labeled fertilizers. The ammonia losses by volatilization were higher for urea and uran, which contain amidic nitrogen, especially when sidedressed in bands. Ammonia losses by volatilization caused a reduction in yield, whereas the location of the fertilizer-N had no influence on the sugar cane yield. Independent of the nitrogen source location, the recovery of 15N from AS in sugar cane was twice as high as from urea. The nitrogen recovered in the soil-plant-trash system was 74 and 55 % of the N applied as AS and urea, respectively.

Aproveitamento pela cana-de-açúcar da adubação nitrogenada de plantio

The 15N balance of N sources in the soil-plant system is of great value in studies of N transformation in different agroecosystems. In the sugarcane agroecosystem, the cane plant response to N fertilization for Brazilian conditions is not fully understood and the use of N fertilizer labeled with 15N can help clarify this issue. To evaluate the urea-N utilization by sugarcane at plant cane harvest, two experiments were developed with the variety SP81-3250, in commercial sugarcane fields. The experiments were carried out from February 2005 to July 2006. The experiment was a randomized complete block design and the treatments three N-urea rates (40, 80 and 120 kg ha-1) and a control without N-fertilization (0 kg ha-1 N). In the center of the plots with urea application microplots were installed and treated with 15N-labeled urea. The average recovery (%) of 15N-fertilizer by sugarcane (whole plant) was 30, 30 and 21 %, respectively, at rates of 40, 80 and 120 kg ha-1 of N. The lower urea-N recovery at higher rates, mainly for 120 kg ha-1 of N, was due to N losses from the soil-plant system. The N-urea recovery was on average 11.7 % of the total accumulated N in the whole plant. The different N rates on N from fertilizer did not influence N distribution in the different sugarcane plant parts, which were on average 50 % in the stalks, 22 % in the dry leaves, 20 % in the shoots and 8 % in the roots.

Agronomic and environmental implications of sugarcane straw removal: a major review

Large‐scale bioenergy demand has triggered new approaches to straw management in Brazilian sugarcane fields. With the progressive shift from a burned to a nonburned harvest system, most of the straw presently retained on the soil surface has become economically viable feedstock for bioenergy production. The trade‐offs between the need to preserve soil quality and produce more bioenergy have been the subject of intense discussion. This study presents a synthesis of available information on the magnitude of the main impacts of straw removal from sugarcane fields for bioenergy production and therefore represents an easily available resource to guide management decisions on the recommended amount of straw to be maintained on the field to take advantage of the agronomic, environmental, and industrial benefits. Crop residues remaining on sugarcane fields provide numerous ecosystem services including nutrient recycling, soil biodiversity, water storage, carbon accumulation, control of soil erosion, and weed infestation. Furthermore, several studies reported higher sugarcane production under straw retention on the field, while few suggest that straw may jeopardize biomass production in cold regions and under some specific soil conditions. Pest control is among the parameters favored by straw removal, while N2O emissions are increased only if straw is associated with the application of N fertilizer and vinasse. An appropriate recommendation, which is clearly site specific, should be based on a minimum mass of straw on the field to provide those benefits. Overall, this review indicates that most of the agronomic and environmental benefits are achieved when at least 7 Mg ha−1 of dry straw is maintained on the soil surface. However, modeling efforts are of paramount importance to assess the magnitude and rates of straw removal considering the several indicators involved in this complex equation, so that an accurate straw recovery rate could be provided to producers and industry toward greater sustainability.

Technical and economic assessment of trash recovery in the sugarcane bioenergy production system

Mechanized sugarcane (Saccharum spp.) harvest without burning has been increasingly adopted in Brazil, increasing trash availability on the field. This study aims at showing the importance of using an integrated framework tool to assess technical and economic impacts of integral harvesting and baling trash recovery strategies and different recovery rates as well as its implications in the sugarcane production, transport and processing stages. Trash recovery using baling system presents higher costs per unit of mass of recovered trash in comparison to system in which trash is harvested and transported with sugarcane stalks (integral harvesting system). However, the integrated agricultural and industrial assessment showed that recovering trash using baling system presents better economic results (higher internal rate of return and lower ethanol production cost) than the integral harvesting system for trash recovery rates higher than 30 %. Varying trash recovery fraction, stalks productivity and mean transport distance for both integral harvesting and baling systems, sensitivity analyses showed that higher trash recovery fractions associated with higher stalks yields and long transport distances favors baling system, mainly due to the reduction of bulk load density for integral harvesting system under those conditions.

Input of sugarcane post-harvest residues into the soil

Sugarcane (Saccharum spp.) crops provide carbon (C) for soil through straw and root system decomposition. Recently, however, sugarcane producers are considering straw to be removed for electricity or second generation ethanol production. To elucidate the role of straw and root system on the carbon supply into the soil, the biomass inputs from sugarcane straw (tops and dry leaves) and from root system (rhizomes and roots) were quantifi ed, and its contribution to provide C to the soil was estimated. Three trials were carried out in the State of Sao Paulo, Brazil, from 2006 to 2009. All sites were cultivated with the variety SP81 3250 under the green sugarcane harvest. Yearly, post-harvest sugarcane residues (tops, dry leaves, roots and rhizomes) were sampled; weighted and dried for the dry mass (DM) production to be estimated. On average, DM root system production was 4.6 Mg ha -1 year -1 (1.5 Mg C ha -1 year -1 ) and 11.5 Mg ha -1 year -1 (5.1 Mg C ha -1 year -1 ) of straw. In plant cane, 35 % of the total sugarcane DM was allocated into the root system, declining to 20 % in the third ratoon. The esti- mate of potential allocation of sugarcane residues to soil organic C was 1.1 t ha -1 year -1 ; out of which 33 % was from root system and 67 % from straw. The participation of root system should be higher if soil layer is evaluated, a deeper soil layer, if root exudates are accounted and if the period of higher production of roots is considered.

Contribution of nitrogen from sugarcane harvest residues and urea for crop nutrition

Sugarcane (Saccharum spp.) harvested without burning provides a substantial amount of remains (trash) on soil profiles which can be decomposed and release nutrients contributing to reduce fertilizer needs. The contribution of nitrogen (N) from sugarcane plant residues and fertilizer in sugarcane nutrition was assessed. Plant cane treatments were micro plots of 15N-labeled urea, sugarcane trash and root system; the last two to simulate the previous crop residues incorporated into the soil after crop renewal. For ratoons, N-ammonium nitrate (N-AN) micro plots, 150 kg ha-1 of N-AN and control (0 kg ha-1) were set up to evaluate the contribution of trash in N supply and quantify the effects of N-fertilizer on N-trash mineralization. The N balances derived from each 15N source were calculated after four crops and resulted in: 15N-urea applied at planting, 31 % was recovered by plant cane, 12 % by the following ratoons, 20 % remained in the soil and 37 % was not found in the soil-system (NOC). For crop residues 15N-trash + roots 26 % was recovered by sugarcane, 51 % remained in soil, and 23 % was NOC. N-fertilizer applied to ratoons nearly doubled the amount of N from green harvest residues recovered by sugarcane; 17 vs. 31 %. Water balances and crop evapotranspiration were correlated with 15N-sources recoveries and cumulative N recovery presented a positive correlation with evapotranspiration (2005 to 2009). The 15N balances indicated that crop residues are supplementary sources of N for sugarcane and may contribute to reduce N fertilizer needs since trash is annually added to the soil.

Nitrogênio proveniente da adubação nitrogenada e de resíduos culturais na nutrição da cana-planta

The objective of this work was to evaluate the recovery, by plant cane, of the nitrogen ( 15 N) from urea and from sugarcane (Saccharum spp.) crop residues - straw and root system - incorporated into the soil. The experiment was settled in 2005/2006 with the sugarcane cultivar SP81 3250. At planting, microplots of 2 m length and 1.5 m width were installed, and N applications were done with 80 kg ha -1 N (urea with 5.05% in 15 N atoms) and 14 Mg ha -1 crop residues - 9 Mg ha -1 of sugarcane straw (SS) and 5 Mg ha -1 of root system (RS), labeled with 15 N (1.07 and 0.81% in 15 N atoms, respectively). The total N accumulation by plants was determined during the crop cycle. Although the N use by shoot from crop residue mineralization (PA and SR) increased significantly over time, this source hardly contributed to crop nutrition. The recovery of the 15 N-urea, 15 N-SS and 15 N-RS by plant cane was 30.3±3.7%, 13.9±4.5% and 6.4±0.9%, respectively, representing 15.9, 4.7 and 1.4% of total nitrogen uptake by shoot. Index terms: Saccharum, sugarcane, 15 N, roots, urea.

Mineralização da palhada e crescimento de raízes de cana-de-açúcar relacionados com a adubação nitrogenada de plantio

O experimento foi realizado em canavial comercial, com a variedade SP81 3250, na Usina Sao Martinho (Pradopolis-SP), em Latossolo Vermelho-Escuro de textura argilosa, com o objetivo de avaliar a mineralizacao da palha de cana-de-acucar e sua composicao apos um ciclo de desenvolvimento da cultura. Foi utilizado um delineamento experimental de blocos completos casualizados, com quatro repeticoes. Sacos de telas que continham palha marcada em 15N (1,07 % de atomos de 15N), em quantidades equivalentes a 9 t ha-1 de materia seca, foram colocados entre as fileiras de cana-planta, em todos os tratamentos (0, 40, 80 e 120 kg ha-1 de N). Apos 14 meses (de junho 2005 a agosto 2006), foram retirados os sacos para a quantificacao do material seco remanescente e para determinacoes de N, de isotopos de 15N e do teor de C, por espectrometria de massas. A decomposicao da palhada nos sacos foi maior nos tratamentos adubados com N e o balanco de massa subestimou a liberacao do N da palha em comparacao com os dados obtidos com a tecnica isotopica. Apos 14 meses, verificou-se que 37 a 65 % da materia seca do material da palhada remanescente sobre o solo eram compostos por restos de raizes da cana cultivada durante esse periodo, pela contaminacao por solo e por microrganismos que se desenvolveram na palhada, indicando que os processos ocorridos durante a decomposicao da palhada sao mais dinâmicos do que os avaliados pelo balanco de massas.