Paulo Cesar Ocheuze Trivelin

Ammonia volatilisation from urease inhibitor-treated urea applied to sugarcane trash blankets

Restricoes legais a colheita de cana-de-acucar com despalha a fogo estao causando um aumento da area cultivada com cana crua. Essa pratica gera uma espessa camada de palha de cana sobre o solo apos a colheita, o que dificulta a incorporacao de fertilizantes. Uma vez que grandes quantidades de amonia podem ser perdidas quando a ureia e aplicada superficialmente sobre a palha, e importante buscar alternativas para maximizar a eficiencia de uso do N-ureia. O inibidor de urease NBPT retarda a hidrolise da ureia e pode contribuir para diminuir as perdas de amonia por volatilizacao. Para quantificar essas perdas, foram instaladas câmaras coletoras de amonia em sete areas de producao de cana-de-acucar colhida sem queima; estas foram fertilizadas com sulfato ou nitrato de amonio, ureia ou ureia tratada com NBPT. Todos os fertilizantes nitrogenados foram aplicados superficialmente em doses de 80 ou 100 kg ha-1de N. As perdas de N foram muito pequenas quando se usou nitrato ou sulfato de amonio. Entretanto, as perdas por volatilizacao de amonia decorrentes do uso de ureia variaram de 1% (com dias chuvosos apos a adubacao) a 25% do N aplicado. O uso de NBPT proporcionou reducoes de 15 a 78% nas perdas por volatilizacao, dependendo das condicoes climaticas nos dias posteriores a aplicacao de N. A adicao de NBPT a ureia ajudou a controlar as perdas de amonia, mas o inibidor foi menos efetivo quando chuvas suficientes para incorporar a ureia no solo ocorreram somente 10 a 15 dias, ou mais, apos a aplicacao dos fertilizantes.

Decomposição e liberação de nutrientes da palhada de cana-de-açúcar em campo

A field decomposition and release of nutrients from trash of sugar cane mechanically harvested and without previous detrashing through burning was evaluated. During the experimental period ¾ August 1996 through August 1997 ¾ rainfall was 1,733 mm and mean maximum and minimum temperatures were 28.0 and 18.0oC, respectively. After one year the mass of trash remained on field decreased of approximately 20%, mostly derived from the decarboxylation of the cell content and hemicelulose. Among all structural carbohydrates only the hemicelulose decomposed. The percentage of K, Ca and Mg released in relation to the total nutrient content in original trash was 85, 44 and 39%, respectively. The N mineralization of the trash was not significant (18%) thus resulting in a negligible statistical difference among the N contents in original and remaining trash

BROMELIAD-LIVING SPIDERS IMPROVE HOST PLANT NUTRITION AND GROWTH

Although bromeliads are believed to obtain nutrients from debris deposited by animals in their rosettes, there is little evidence to support this assumption. Using stable isotope methods, we found that the Neotropical jumping spider Psecas chapoda (Salticidae), which lives strictly associated with the terrestrial bromeliad Bromelia balansae, contributed 18% of the total nitrogen of its host plant in a greenhouse experiment. In a one-year field experiment, plants with spiders produced leaves 15% longer than plants from which the spiders were excluded. This is the first study to show nutrient provisioning in a spider-plant system. Because several animal species live strictly associated with bromeliad rosettes, this type of facultative mutualism involving the Bromeliaceae may be more common than previously thought.

Degradação da palhada de cana-de-açúcar

Avaliou-se a influencia da aplicacao de ureia e vinhaca na degradacao da lignocelulose e na liberacao dos nutrientes da palhada de cana-de-acucar. Os tratamentos foram: vinhaca (dose equivalente a 100 m3 ha-1) aplicada sobre a palhada, combinada com ureia (dose equivalente a 100 kg ha-1) aplicada sobre a palhada ou enterrada no solo; mistura de cloreto de potassio (dose equivalente a 120 kg ha-1 de K2O) com ureia (dose equivalente a 100 kg ha-1) aplicada sobre a palhada ou enterrada no solo. Durante o periodo experimental, janeiro a novembro de 1997, a palhada recebeu uma lâmina de agua de 1.839 mm, sendo 923 mm de precipitacoes e 916 mm de irrigacoes. As medias das temperaturas maximas e minimas foram 28,4 e 15,5°C, respectivamente. Nao houve efeito dos tratamentos na degradacao da lignocelulose da palhada e na liberacao de nutrientes, verificando-se diferencas estatisticamente significativas apenas entre os resultados da palhada da cana recem colhida e os das remanescentes. Ocorreu reducao de massa de aproximadamente 80% para a hemicelulose e para o conteudo celular, e de 30 e 50% para a lignina e celulose, respectivamente. A porcentagem media de liberacao dos nutrientes N, P, K, Ca, Mg e S, em relacao ao total contido na palhada da cana recem colhida, foi de 18, 67, 93, 57, 68 e 68%, respectivamente.

Urea and sugarcane straw nitrogen balance in a soil-sugarcane crop system

Os objetivos deste trabalho foram avaliar a utilizacao do nitrogenio por soqueira de cana-de-acucar de duas fontes, ureia e palha de cana-de-acucar, e a recuperacao do N de ambas as fontes no sistema solo-planta. Os tratamentos foram estabelecidos em blocos casualizados, com quatro repeticoes: T1, mistura de vinhaca e ureia (100 kg ha-1 de N), aplicada em area total sobre o solo coberto com palha de cana-de-acucar marcada com 15N; T2, mistura de vinhaca e ureia (ureia marcada com 15N - ureia-15N; 100 kg ha-1 de N) aplicada em area total sobre o solo coberto com palha de cana-de-acucar nao marcada; e T3, ureia-15N (100 kg ha-1 de N) enterrada em sulcos laterais as linhas de cana-de-acucar, com previa aplicacao de vinhaca sobre o solo sem palha. A vinhaca foi aplicada no volume de 100 m3 ha-1 em todos os tratamentos. O experimento foi realizado em um Podzolico Vermelho-Amarelo (Paleudalf), entre outubro de 1997 e agosto de 1998, em Piracicaba, SP. A eficiencia de uso de N da ureia pela soqueira de cana-de-acucar foi de 21% e a de N da palha de cana-de-acucar foi de 9%. A principal contribuicao do N da palha de cana-de-acucar e a manutencao ou aumento do N orgânico do solo. A tendencia de menor acumulacao, pela cana-de-acucar, do N da ureia no tratamento com palha, foi compensada pela acumulacao de N proveniente da mineralizacao da palha. O N da palha ficou disponivel na segunda metade do ciclo da cultura.

UTILIZAÇÃO DE NITROGÊNIO DE ADUBOS VERDE E MINERAL PELO MILHO

Desenvolveu-se, na Estacao Experimental de Piracicaba - Instituto Agronomico (SAA-SP), de marco/94 a setembro/95, um experimento para avaliar o potencial de fornecimento de nitrogenio de adubos, verde e mineral, aplicados, de forma exclusiva ou combinada, na cultura do milho. Em uma primeira fase, produziram-se, simultaneamente, mucuna-preta sem marcacao isotopica no campo e adubo verde marcado com 15N em casa de vegetacao e, na segunda, a mucuna-preta foi incorporada ao solo, cultivando-se, em seguida, milho. O experimento constou dos seguintes tratamentos: testemunha, 15N-mucuna-preta (4,4 t ha-1 de materia seca e 25,8 g kg-1 de N), 15N-ureia (50 e 100 kg ha-1 de N) e as possiveis combinacoes de mucuna-preta e ureia marcadas ou nao com 15N. Esses foram dispostos em delineamento experimental de blocos ao acaso com quatro repeticoes. O solo forneceu a maior parte do N acumulado nas plantas de milho, seguido, em ordem decrescente, pela ureia e mucuna-preta. A contribuicao da ureia para o N acumulado nas plantas de milho foi proporcional a dose aplicada. O aproveitamento de nitrogenio da ureia pelo milho foi maior que o da mucuna-preta, sendo os melhores efeitos proporcionados pela combinacao das duas fontes.

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.

Utilization of nitrogen from green manure and mineral fertilizer by sugarcane

Given their potential for biological nitrogen fixation, legumes used as green manure are an alternative source of nitrogen to crops, and can supplement or even replace mineral nitrogen fertilization. The utilization of nitrogen by sugarcane (Saccharum spp.) fertilized with sunn hemp (Crotalaria juncea L.) and ammonium sulphate (AS) was evaluated using the 15N tracer technique. Amounts of 195.8 kg and 70 kg N per hectare, respectively, of sunn hemp and AS were added in the following treatments: without green manure and without AS; without green manure, with AS -15N; with green manure-15N and with AS; with green manure-15N, without AS; with green manure and with AS-15N. Four samples from the leaves +3 were collected and 2 m of the sugar cane row were harvested to estimate crop yield. The results for N contents (g kg-1), isotopic abundance of N (atoms % 15N) in leaf +3 samples, and sugarcane productivity were used to calculate cumulative N, nitrogen in the plant derived from the fertilizer-Ndff (% and kg ha-1), as well as percent recovery of fertilizer N (R%). Sugarcane was analysed and pol and total recovered sugar calculated. The highest Ndff percentages were observed eight months after sugarcane planting for treatments containing green manure without mineral N, and green manure with mineral N, at 15.3 and 18.4%, respectively. The best nitrogen recovery was observed during harvest, 18 months after planting; the treatment containing mineral fertilizer showed 34.4% recovery, while the sum between mineral N plus green manure N showed 40.0%. Treatments containing green manure plus mineral N changed soil attributes, by increasing Ca and Mg contents, sum of bases, pH, and base saturation, and decreasing potential acidity. In the plant, those treatments increased Ca and K contents.

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.