Luís Carlos Timm

Management effects on nitrogen recovery in a sugarcane crop grown in Brazil

The present studys objectives were to quantify the fertilizer-N and residue-N balances of a sugar cane crop under two trash management systems. The fate of nitrogen (N) derived from fertilizer (NdfF) and N derived from residue (NdfR) was studied comparing: (i) the traditional harvest system with trash burning before harvest (“trash burning”) and (ii) an alternative system without trash burning, in which crop residues are left on the soil surface (“trash mulching”). The experiment consisted of three treatments: (i) T1: at planting, the sugarcane crop was fertilized with 63 kg N ha−1 as 15N-labeled ammonium sulfate, and after the 1st harvest received unlabeled trash from T2; (ii) T2: at planting, the crop was fertilized with 63 kg N ha−1 as unlabeled ammonium sulfate. At the 1st harvest time, this treatment received the labeled trash from T1; (iii) T3: at planting, the crop was fertilized with 63 kg N ha−1 as 15N-labeled ammonium sulfate, and every year, immediately before cutting, the crop residues were burnt. After the first harvest fertilizer-N was applied over the total soil area at a rate of 80 kg N ha−1 as unlabeled ammonium sulfate. The results indicated that the trash remaining as a surface blanket resulted in an average N recycling of 105.0 kg ha−1 year−1, while the practice of burning the trash produced an average N loss from the system of 83.5 kg ha−1 year−1. At the first harvest, about 75% of the labeled N was recovered in the soil–plant system. The majority was found in the plant, indicating a high availability of the fertilizer-N for the crop. At the end of the third crop cycle (2nd ratoon crop harvest), the total output of fertilizer-N (export+burning) was 60% for the burnt-trash treatment, and only 42% (export) for the trash-blanket treatment. The N liberated from the residue is mainly immobilized in the soil, reflecting that sugarcane trash is an N source of slow availability to the crop. This study indicated that green cane harvesting followed by mulching leads to a more efficient recycling of the N applied to the system and therefore reducing fertilizer-N needs.

STATE-SPACE APPROACH FOR THE ANALYSIS OF SOIL WATER CONTENT AND TEMPERATURE IN A SUGARCANE CROP

The state-space approach is used to describe surface soil water content and temperature behaviour, in a field experiment in which sugarcane is submitted to different management practices. The treatments consisted of harvest trash mulching, bare soil, and burned trash, all three in a ratoon crop, after first cane harvest. One transect of 84 points was sampled, meter by meter, covering all treatments and borders. The state-space approach is described in detail and the results show that soil water contents measured along the transect could successfully be estimated from water content and temperature observations made at the first neighbour.

Field spatial and temporal patterns of soil water content and bulk density changes

Umidade (q) e densidade do solo (rs) influenciam importantes processos no solo e planta tais como: movimento de agua, compactacao do solo, aeracao do solo e desenvolvimento radicular. Baseado neste fato, questoes referentes a variabilidade espacial e temporal de q e rs para diferentes periodos do ano e diferentes fases de desenvolvimento da cultura do cafe tornam-se de extremo interesse. Este trabalho teve como objetivo caracterizar padroes espaciais e temporais de q e rs durante diferentes periodos do ano e verificar se existem mudancas temporais significativas de rs na superficie do solo quando submetida a ciclos de umedecimento/secagem. O experimento foi conduzido em campo cultivado com cafe em um solo classificado como Nitossolo Vermelho Eutrofico. O experimento iniciou-se em maio de 2001 com espacamento de 1,75 m entre linhas e 0,75 m entre plantas. Medidas de q e rs foram feitas metro a metro ao longo de 200 m usando uma sonda de superficie neutron/gama. Durante o periodo umido nao houve padroes de diferenca espacial para q, enquanto que para o periodo seco o contrario foi observado. Estes padroes podem ser associados a eventos de precipitacao alterando a estrutura de correlacao espacial para observacoes adjacentes de q. Para rs existem mudancas temporais na superficie do solo ao longo do periodo estudado como uma consequencia dos ciclos de umedecimento/secagem no campo.

Variability of water balance components in a coffee crop in Brazil

Establishing field water balances is difficult and costly, the variability of their components being the major problem to obtain reliable results. This component variability is presented herein for a coffee crop grown in the Southern Hemisphere, on a tropical soil with 10% slope. It was observed that: rainfall has to be measured with an appropriate number of replicates; irrigation can introduce great variability into calculations; evapotranspiration, calculated as a remainder of the water balance equation, has exceedingly high coefficients of variation; the soil water storage component is the major contributor in error propagation calculations to estimate evapotranspiration; and that runoff can be satisfactorily controlled on the 10% slope through crop management practices.

State-space approach to evaluate the relation between soil physical and chemical properties

A abordagem de espaco de estados e usada para avaliar a relacao entre propriedades fisicas e quimicas de um solo em uma area cultivada com cana-de-acucar. O experimento foi realizado em um Nitossolo situado em Piracicaba (SP). A cana-de-acucar foi plantada em uma area de 0,21 ha i.e., 15 linhas com 100 m de comprimento cada, espacadas de 1,4 m. Medidas da umidade do solo, materia orgânica, conteudo de argila e estabilidade de agregados foram feitas ao longo de uma transecao de 84 pontos, metro a metro. A abordagem de espaco de estados e usada para avaliar como a umidade do solo na posicao i e afetada por medidas de umidade do solo, materia orgânica, conteudo de argila e estabilidade de agregados na posicao i-1, em diferentes combinacoes, com o objetivo de contribuir para um melhor entendimento da relacao entre estas variaveis no solo. Os resultados mostram que a umidade do solo pode ser estimada usando esta abordagem, sendo a melhor performance encontrada quando as estimativas da umidade do solo na posicao i foram relacionadas com a umidade do solo, conteudo de argila e estabilidade de agregados na posicao i-1 e que as equacoes de espaco de estado descrevem a umidade do solo melhor do que qualquer equacao de regressao multipla equivalente.

Nitrogen dynamics in a soil-sugar cane system

Results of an organic matter management experiment of a sugar cane crop are reported for the first cropping year. Sugar cane was planted in October 1997, and labeled with a 15N fertilizer pulse to study the fate of organic matter in the soil-plant system. A nitrogen balance is presented, partitioning the system in plant components (stalk, tip and straw), soil components (five soil organic matter fractions) and evaluating leaching losses. The 15N label permitted to determine, at the end of the growing season, amounts of nitrogen derived from the fertilizer, present in the above mentioned compartments.

Densidade de um planossolo sob sistemas de cultivo avaliada por meio da tomografia computadorizada de raios gama

A sustentabilidade do arroz (Oryza sativa L.) irrigado em solos de varzea esta alicercada na utilizacao da rotacao e sucessao de culturas, fundamentais para o controle do arroz-vermelho e preto. Os reflexos sobre os atributos dos solos de varzea merecem estudos em especial sobre a compactacao do solo. O objetivo deste trabalho foi identificar camadas compactadas em Planossolo submetido a diferentes sistemas de cultivo e preparo, avaliando-se a densidade do solo (Ds) pela Tomografia Computadorizada de Raios Gama (TC). A analise foi realizada em um experimento de longa duracao, conduzido de 1985 a 2004, na Estacao Experimental da Embrapa Clima Temperado, Capao do Leao, RS, num delineamento experimental em blocos ao acaso, com sete tratamentos, cada um com quatro repeticoes (T1 - um ano de arroz com preparo convencional do solo seguido de dois anos de pousio; T2 - cultivo continuo de arroz com preparo convencional do solo; T4 - rotacao de arroz e soja (Glycine max L.) com preparo convencional do solo; T5 - rotacao de arroz, soja e milho (Zea maiz L.) em preparo convencional do solo; T6 - plantio direto de arroz no verao em sucessao do azevem (Lolium multiflorum L.) no inverno; T7 - rotacao de arroz sob plantio direto e soja sob preparo convencional do solo; T8 - testemunha: solo sem cultivo). A Tomografia Computadorizada de Raios Gama permitiu detectar que o plantio direto de arroz no verao em sucessao do azevem no inverno nao resultou na formacao de camadas compactadas; a utilizacao de dois anos de pousio, no sistema de producao de arroz irrigado, nao foi suficiente para evitar a formacao de uma camada superficial compactada; e a rotacao de arroz, soja e milho com preparo convencional do solo apresentou duas camadas compactadas (0,0 a 1,5 cm e 11 a 14 cm), indicando que essas podem limitar a producao agricola nesse sistema de producao em Planossolos.

State-space analysis of soil data: an approach based on space-varying regression models

The assessment of the relationship among soil properties (such as total nitrogen and organic carbon) taken along lines called transects is a subject of great interest in agricultural experimentation. This question has been usually approached through standard state-space methods by some authors in the soil science literature. Important limitations of the mentioned procedures used in practice are pointed out and discussed in this paper, specially those related to the model parameters, meaning and practical interpretation. In the standard state-space approach, based on an autoregressive structure, it does not present any parameters that express the variables relationship at the same point in space, but only at lagged points. Also, its model parameters (in the transition matrix) have a global meaning and not a local one, not expressing more directly the soil heterogeneity. Therefore, the objective here is to propose an alternative state-space approach, based on dynamic (space-varying parameters) regression models in order to avoid the mentioned drawbacks. Soil total nitrogen and soil organic carbon samples were collected on a Typic Haplustox. Samples were taken along a line (transect) located in the middle of two adjacent contour lines. The transect samples, totaling 97, were collected in the plow layer (0-0.20 m) at points spaced 2 meters appart. Results show the comparative advantages of the proposed method (based on an alternative state-space approach) in relation to the standard state-space analysis. Such advantages are related to a more adequate incorporation of soil heterogeneity along the spatial transect resulting in a better model fitting, and greater flexibility of the models building process with an easier interpretability of the local model coefficients.

Soil-plant interaction evaluated by the state-space approach.

The interaction soil-plant was evaluated using a state space approach (dynamic model) comparatively to a static regression model using both, standard and sequential estimations. Experimental soil data consisted of bulk density, macroporosity, microporosity and porosity of a dark red latosol, and plant data of root density in length per unit volume, of a forage-oat crop. Among these, only soil porosity had a good correlation with the root system density, which is the response variable of this study. A static regression model written in the state space form with a sequential estimation, gave a R2 coefficient of 0.69, comparatively to a conventional (non-sequential) regression model, which gave a R2 coefficient of only 0.59. This soil-plant relation was better described by a dynamic regression model, which gave a R2 coefficient greater than 0.98. These results indicate the advantage of the state space approach in relation to the other more conventional regression methods.

Soil spatial variability and the estimation of the irrigation water depth

A influencia da variabilidade espacial da umidade do solo em uma situacao pre-irrigacao e da capacidade de campo e avaliada no calculo da lâmina de irrigacao. O experimento constou de cultura de feijao (Phaseolus vulgaris L.) estabelecida em um ARGISSOLO da regiao de Piracicaba, SP, irrigada por pivo central, tendo as medidas de umidade sido feitas com sonda de neutrons, em uma malha de 20x4 pontos, espacados de 0.5 m. Em determinada situacao, os 80 valores de lâmina de irrigacao calculados apresentaram um coeficiente de variacao de 29.3%, para uma media de 18 mm, com valor minimo de 9 mm e maximo de 41mm. E concluido que a unica forma pratica de irrigacao e o uso de uma lâmina media devido a variabilidade inerente ao solo, e que a procura de melhores valores para a capacidade de campo nao implica em melhores estimativas da lâmina de irrigacao.