Eduardo Mariano

Ammonia losses estimated by an open collector from urea applied to sugarcane straw

The quantification of ammonia (NH3) losses from sugarcane straw fertilized with urea can be performed with collectors that recover the NH3 in acid-treated absorbers. Thus, the use of an open NH3 collector with a polytetrafluoroethylene (PTFE)-wrapped absorber is an interesting option since its cost is low, handling easy and microclimatic conditions irrelevant. The aim of this study was to evaluate the efficiency of an open collector for quantifying NH3-N volatilized from urea applied over the sugarcane straw. The experiment was carried out in a sugarcane field located near Piracicaba, Sao Paulo, Brazil. The NH3-N losses were estimated using a semi-open static collector calibrated with 15N (reference method) and an open collector with an absorber wrapped in PTFE film. Urea was applied to the soil surface in treatments corresponding to rates of 50, 100, 150 and 200 kg ha-1 N. Applying urea-N fertilizer on sugarcane straw resulted in losses NH3-N up to 24 % of the applied rate. The amount of volatile NH3-N measured in the open and the semi-open static collector did not differ. The effectiveness of the collection system varied non-linearly, with an average value of 58.4 % for the range of 100 to 200 kg ha-1 of urea-N. The open collector showed significant potential for use; however, further research is needed to verify the suitability of the proposed method.

Nutrient Partitioning and Stoichiometry in Unburnt Sugarcane Ratoon at Varying Yield Levels

Unraveling nutrient imbalances in contemporary agriculture is a research priority to improve whenever possible yield and nutrient use efficiency in sugarcane (Saccharum spp.) systems while minimizing the costs of cultivation (e.g., use of fertilizers) and environmental concerns. The main goal of this study was therefore to investigate biomass and nutrient [nitrogen (N), phosphorus (P), and potassium (K)] content, partitioning, stoichiometry and internal efficiencies in sugarcane ratoon at varying yield levels. Three sites were established on highly weathered tropical soils located in the Southeast region of Brazil. At all sites, seasonal biomass and nutrient uptake patterns were synthesized from four sampling times taken throughout the sugarcane ratoon season. In-season nutrient partitioning (in diverse plant components), internal efficiencies (yield to nutrient content ratio) and nutrient ratios (N:P and N:K) were determined at harvesting. Sugarcane exhibited three distinct phases of plant growth, as follows: lag, exponential–linear, and stationary. Across sites, nutrient requirement per unit of yield was 1.4 kg N, 0.24 kg P, and 2.7 kg K per Mg of stalk produced, but nutrient removal varied with soil nutrient status (based on soil plus fertilizer nutrient supply) and crop demand (potential yield). Dry leaves had lower nutrient content (N, P, and K) and broader N:P and N:K ratios when compared with tops and stalks plant fractions. Greater sugarcane yield and narrowed N:P ratio (6:1) were verified for tops of sugarcane when increasing both N and P content. High-yielding sugarcane systems were related to higher nutrient content and more balanced N:P (6:1) and N:K (0.5:1) ratios.

Incubation methods for assessing mineralizable nitrogen in soils under sugarcane

Considerar a mineralizacao do nitrogenio (N) da materia orgânica do solo e questao fundamental para o manejo eficiente dos fertilizantes nitrogenados nos sistemas agricolas. A incubacao aerobia de longa duracao e o metodo de referencia para estudos que envolvem a calibracao de metodos quimicos de extracao, a fim de estimar o N potencialmente mineralizavel do solo. Contudo, a tecnica e laboriosa e de alto consumo de tempo e custo. Os objetivos deste trabalho foram determinar o N mineralizavel do solo na profundidade de 0-60 cm e avaliar a possibilidade de adotar a incubacao anaerobia de curta duracao no lugar da aerobia de longa duracao, para estimar a mineralizacao liquida de N em solos cultivados com cana-de-acucar. Utilizaram-se cinco solos, coletados nas camadas de 0-20, 20-40 e 40-60 cm, em locais que nao receberam fertilizacao previa com N. As amostras de solo foram incubadas aerobiamente a 35 oC, durante 32 semanas, e anaerobiamente (saturadas com agua) a 40 oC, por sete dias, para determinar a mineralizacao liquida de N do solo. Os teores de areia, silte e argila apresentaram alta correlacao com os indices usados para predizer o N mineralizavel. O N mineralizavel do solo foi mais bem estimado na profundidade de 0-40 cm, enquanto a camada de 40-60 cm apresentou baixa mineralizacao liquida de N em ambos os procedimentos de incubacao. Na incubacao anaerobia, estimou-se adequadamente o N mineralizavel do solo, correlacionando-se com o N mineralizado acumulado e o N potencialmente mineralizavel do solo, ambos obtidos por meio da incubacao aerobia. A manutencao do N-NH4+ preexistente da amostra melhorou a estimativa do N mineralizavel por meio da incubacao anaerobia.

Boro em solos de várzea do sul de Minas Gerais e a cultura do feijoeiro

Aiming to evaluate the bean (Phaseolus vulgaris L.) plant response to boron application in lowland soils, an experiment was conducted in greenhouse conditions, involving four soils (0-20 cm), Low Humic Glei (LHG), Aluvial (A), Humic Gley (HG) and Bog soil (O), the last being artificially drained, all collected in Lavras, MG, Brazil. The experimental design was totally randomized, with four replications, in a 4x7 factorial scheme, consisting of the 4 soils and of 7 B doses (0; 0.25; 0.5; 1.5; 3.0; 6.0 and 10.0 mg dm-3). The soils received dolomitic lime, macro and micronutrients, and the respective doses of B, and were incubated for 24 days. Before seeding, the soils were sampled and analysed for B (hot water). Two plants were cultivated in 3 dm3 pots; at grain maturation the plants were harvested and the dry matter of grains, the number of pods per plant, and the number of grains per pod were evaluated. The results showed significant responses of the bean plant to the applied boron. The B doses, promoting 90% of the maximum yield, varied from 1.04 to 1.25; for maximum yield, varied from 2.50 to 2.85; and for 10% reduction of the yield due to toxicity, varied from 4.54 to 5.33 mg dm-3. The ranking of the productive potential of the soils for 90% of the maximum yield was the following: Humic Gley > Aluvial = Bog > Low Humic Gley.

Adaptation and Validation of Colorimetric Methods in Determining Ammonium and Nitrate on Tropical Soils

ABSTRACT Inorganic nitrogen (N) determination in soil extracts is a useful tool in studying soil–N interactions. The main method used worldwide is the steam distillation, but colorimetric methodologies show advantages of being quick, simple, sensitive, and higher yield. However, they are subject to disruption when the extract has interfering organic N, limiting its application in tropical soil. The aim of this study is to evaluate colorimetric methods for the determination of NH4+ (through Berthelot reaction) and NO3− + NO2− (through Griess-Ilosvay reaction) in saline extracts of tropical soils by addition of activated charcoal during the extraction process. It is recommended to use extraction solution of 2 mol L−1 potassium chloride (KCl) and reaction time of 30 min. Validation parameters confirmed the best performance of the colorimetric methods, revealing results favorable to the addition of the activated charcoal in the extraction process to increase the accuracy and precision of the colorimetric methods.