Rafael Otto

Stalk yield and technological attributes of planted cane as related to nitrogen fertilization

A still unclear question related to sugarcane cropping refers to the low response of the planted cane to nitrogen fertilization. Two experiments were carried out in areas under a Typic Hapludox, located in Pirassununga, Sao Paulo State, Brazil, and an Arenic Kandiudult, located in Jaboticabal, Sao Paulo State, Brazil, with the objective to evaluate planted cane response to nitrogen fertilization at planting. The experimental design was organized as random blocks and treatments consisted of three N rates (40, 80, and 120 kg ha-1 N-urea) and a control without N. Nitrogen fertilizers were applied to the bottom of the planting furrow and then incorporated into the soil. During the maximum growth stage, +1 leaf samples were collected from all experimental plots to evaluate the crop nutritional status. In the Pirassununga experiment, N fertilization at planting increased N, K, Mg, and S contents in the leaves and increased the stalk yield, without effect in the technological attributes. Conversely, no stalk yield response was observed at the Jaboticabal experiment, but N fertilization benefited the stalk technological attributes. The N rates increased the sugar yield per hectare in both experiments. The highest margin of agricultural contribution was obtained at the rate of 40 kg ha-1 N.

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.

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.

Root system distribution of sugar cane as related to nitrogen fertilization, evaluated by two methods: monolith and probes

Poucos estudos com cana-de-acucar avaliaram o sistema radicular da cultura, apesar de sua importância. Esse fato e devido, em grande parte, a dificuldade de avaliacao e a elevada variabilidade dos resultados. Objetivou-se com este trabalho avaliar um metodo de avaliacao do sistema radicular da cana, por meio de sondagem, a fim de avaliar a massa, a distribuicao e as raizes metabolicamente ativas em funcao da adubacao nitrogenada de plantio. Para isso, foi conduzido experimento em um Latossolo Vermelho distrofico tipico textura media, em Jaboticabal/SP, no esquema de blocos ao acaso com quatro repeticoes e quatro tratamentos: controle (sem N), 40, 80 e 120 kg ha-1 de N aplicado na forma de ureia no sulco de plantio, utilizando a cultivar SP81 3250. Uma semana antes da colheita, foi aplicada solucao de ureia-15N na base de colmos das plantas de cana-de-acucar, para marcacao do sistema radicular com metabolismo ativo. Foram abertas trincheiras de 1,5 m de largura e 0,6 m de profundidade entre duas linhas de cana, para permitir a amostragem de raizes por dois metodos: monolitos (0,3; 0,2 e 0,15 m de largura, profundidade e comprimento, respectivamente) retirados da parede da trincheira e sonda (0,055 m de diâmetro interno). Para cada metodo foram coletadas 15 amostras por parcela. As amostras de raizes foram separadas do solo por peneiramento (malha de 2 mm) e secas em estufa, obtendo-se assim as massas de raizes secas. A amostragem de raizes com sonda resultou em massa de raizes que nao diferiu da avaliacao em monolito, indicando que esse metodo pode ser usado para avaliacoes da massa de raizes de cana-deacucar, porem nao foi eficiente em avaliar tanto a distribuicao das raizes no perfil do solo quanto a massa de rizomas, devido ao pequeno volume amostrado. A adubacao nitrogenada de plantio nao promoveu maior acumulo de raizes na cana-planta, mas causou mudancas na distribuicao do sistema radicular no solo. A ausencia da adubacao nitrogenada promoveu melhor distribuicao do sistema radicular no perfil do solo, com 50, 34 e 16 % nas camadas de 0 a 0,2, 0,2 a 0,4 e 0,4 a 0,6 m de profundidade, respectivamente; nos tratamentos fertilizados, em media, as raizes concentraram-se na camada superficial, com 70, 17 e 13 % para as mesmas camadas. As raizes metabolicamente ativas concentraram-se no centro da touceira, totalizando 40 % da massa total de raizes, independentemente da fertilizacao nitrogenada (sem N ou 120 kg ha-1 N).

Fitomassa de raízes e da parte aérea da cana-de-açúcar relacionada à adubação nitrogenada de plantio

This work evaluated the root and shoot sugarcane (Saccharum spp.) development in plant cane cycle, related to nitrogen (N) rates applied at planting. Two experiments were carried out using randomized block designs, one in a Typic Eutrustox and other in an Arenic Kandiustults. Treatments were a control without N, and 40, 80 and 120 kg ha-1 N applied in furrow at planting, with four replicates. The root and shoot masses were evaluated in three periods (October 2005, February 2006 and June/July 2006). Shoots were collected in 2 m of furrow, and the roots were collected using a probe (internal diameter of 0.055 m) until 0.6 m depth. The nitrogen fertilization at planting increased the development of cane roots and shoots in Typic Eutrustox. However, there was no growth increase of sugarcane roots and shoots in the Arenic Kandiustults where a large amount of organic N from cultural residues had been incorporated into the soil. The phase of larger root development of one and half year old plant cane was from October to February, with decrease of the root mass from February to July.

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.

Contribution of N from green harvest residues for sugarcane nutrition in Brazil

Brazil is recognized as a prominent renewable energy producer due to the production of ethanol from sugarcane. However, in order for this source of energy to be considered truly sustainable, conservation management practices, such as harvesting the cane green (without burning) and retaining the trash in the field, need to be adopted. This management practice affects mostly the nitrogen (N) cycle through the effect of trash on immobilization–mineralization of N by soil microorganisms. The aim of the experiments reported here was to evaluate N recovery from trash (trash‐N) by sugarcane during three ratoon crop seasons: 2007, 2008 and 2009. Two field experiments were carried out, one in Jaboticabal and the other in Pradopolis, in the state of Sao Paulo, Brazil. The experiments were set up in a randomized block design with four replications. Within each plot, microplots were installed where the original trash was replaced by trash labelled with 15N, and maintained up to the fourth crop cycle. Trash‐N recovery was higher in the Jaboticabal site, the most productive one, than in the Pradópolis site. The average trash‐N recovery across the two sites after three crop cycles was 7.6 kg ha−1 (or 16.2% of the initial N content in trash), with the remaining trash‐N being incorporated into soil organic matter reserves. While these results indicate that the value of trash for sugarcane nutrition is limited in the short term, maintaining trash on the field will serve as a long‐term source of N and C for the soil.