Carlos Eduardo Faroni

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.

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.

Produtividade de colmo e sacarose em resposta à adubação nitrogenada da cana-de-açúcar, sob preparo reduzido

The objective of this work was to evaluate the agroindustrial production of sugarcane (millable stalks and sucrose yield) after successive nitrogen fertilizations of plant cane and ratoons in a reduced tillage system. The experiment was carried out at Jaboticabal, SP, Brazil, on a Rhodic Eutrustox soil, during four consecutive crop cycles (March 2005 to July 2009). Plant cane treatments consisted of N-urea levels (control, 40, 80, and 120 kg ha-1 N + 120 kg ha-1 P2O5 and K2O in furrow application). In the first and second ratoons, the plant cane plots were subdivided in N-ammonium nitrate treatments (control, 50, 100, and 150 kg ha-1 N + 150 kg ha-1 K2O as top dressing over rows). In the third ratoon, N fertilization was leveled to 100 kg ha-1 in all plots, including controls, to detect residual effects of previous fertilizations on the last crops cycle. Sugarcane ratoon was mechanically harvested. A weighing truck was used to evaluate stalk yield (TCH), and samples were collected in the field for analysis of sugar content (TSH). Increasing N doses and meteorological conditions promote significant responses in TCH and TSH in cane plant and ratoons, in the average and accumulated yield of the consecutive crop cycles.

Utilization of Boron (10B) derived from fertilizer by sugar cane

The response to B in agricultural systems of sugar cane is still an unexplored issue; B application has however recently been widely publicized and used with a certain degree of frequency. The use of 10B-labeled fertilizers may further contribute to clarify this practice. With the objective of evaluating sugar cane use of B (10B) derived from fertilizer (boric acid), an experiment was conducted under field conditions in the 2005/2006 growing season. The experiment consisted of the installation of microplots (2 x 1.5 m) where 4 kg ha-1 B (boric acid with 85.95 % in 10B atoms) dissolved in water was applied 90 days after planting (May 2005). The solution was applied to the soil on both sides of the plant row at a distance of 20 cm. After harvest (June 2006) the B content and 10B abundance in % atoms in all parts of the sugar cane plants (stalks, dry leaves, tips and roots) were determined. Results showed that the total B accumulated was 471 g ha-1 in the entire plant (35 % in the stalks, 22 % in the dry leaves, 9 % in the tips and 34 % in the roots). The sugar cane plants used on average 14 % of the total accumulated B in the above-ground part (44 g ha-1) and 11 % in the roots (19 g ha-1), totaling 13 % in the entire plant (63 g ha-1). The recovery of 10B-fertilizer by sugar cane plants was low, around 2 % of the total applied amount.

Estado nutricional da cultura de cana-de-açúcar (cana-planta) em experimentos com 15N

Estudos com isotopos estaveis sao cada vez mais comuns pela qualidade e confiabilidade dos resultados obtidos e por nao apresentarem risco ao homem e ao ambiente. No entanto, e necessario o uso de microparcelas para diminuir o custo do projeto. Por suas areas serem muito reduzidas em relacao a parcela onde esta inserida, o objetivo deste trabalho foi comparar o estado nutricional de plantas das microparcelas com as do restante das parcelas experimentais, na fase de maximo desenvolvimento da cultura da cana-de-acucar, em experimentos com doses de N. Foram instalados tres experimentos, no Estado de Sao Paulo, com tres doses de N e uma testemunha, com quatro repeticoes, em delineamento em blocos completos casualizados. Nas parcelas, de 48 linhas de 15 m cada, foram instaladas microparcelas de 3 m2 com fertilizante-15N. Na epoca de maximo desenvolvimento da cultura foram coletadas folhas-diagnostico para a avaliacao de seu estado nutricional em todas as parcelas e microparcelas. Nessas folhas foram determinados os teores de macronutrientes, e os resultados foram submetidos a analise de variância. Foram comparados, em cada area experimental e de forma conjunta, os resultados das parcelas com os das microparcelas quanto aos teores foliares dos nutrientes e, quando significativo o efeito das doses de N na variacao desses, foram feitas regressoes. Nao houve diferenca entre os teores de N, P, Ca, Mg e S das folhas-diagnostico entre as parcelas e as microparcelas, as quais foram consideradas representativas da area experimental. A adubacao nitrogenada aumentou os teores dos nutrientes nas folhas-diagnostico, o que deve ser considerado na avaliacao nutricional da cultura quando este tipo de experimento for realizado.Studies with stable isotopes are becoming more common due to the increased safety of operation and quality and reliability of results. However, the use of microplots is required to decrease the costs of such studies. Since microplots are small compared to regular plot areas, the purpose of this study was to investigate whether nutritional data based on microplot samples can adequately represent the whole area, in a comparison of the nutritional status of microplot sugar cane plants at their maximum development stage with those of the regular plots in experiments with N rates. Three experiments were set up, with three N rates (40, 80, and 120 kg ha-1 N) and a control, with four repetitions, in a randomized complete block design, in the state of Sao Paulo. Microplots of 3 m2 containing 15N-fertilizer (5.04% atom 15N) were included in the main plots formed by 48 lines of sugar cane spaced 1.5 m apart. At the time of maximum development stage, diagnostic leaves were collected in the main and microplots to evaluate the nutritional status of plants by analyzing the total concentration of macronutrients. There were no differences in N, P, Ca, Mg, and S concentrations in the diagnostic leaves from the main and microplots, so that the latter can be considered representative of the experimental area. Higher nitrogen fertilizer rates induced increased concentrations of not only N, but also of P, Ca, Mg, and S in the diagnostic leaves.