Estado nutricional em nitrogênio da grama esmeralda avaliado por meio do teor foliar, clorofilômetro e imagem digital, em área adubada com lodo de esgoto

A intensidade da cor verde da folha pode ser alternativa para estimar a concentração de N na planta, devido à relação entre o teor de clorofila e o de N no tecido foliar. Objetivou-se neste trabalho avaliar índices da cor verde da grama esmeralda obtidos da análise da imagem digital e pelo uso do clorofilômetro para predizer o estado nutricional em N fornecido pelo lodo de esgoto. O experimento foi instalado e desenvolvido em uma propriedade comercial de grama esmeralda, localizada na cidade de Itapetininga (SP). O delineamento experimental foi em blocos casualizados, com quatro repetições e cinco doses de lodo de esgoto: 0, 10, 20, 30 e 40 Mg ha-1, base seca. As doses de lodo aplicadas correspondem a 100, 200, 300 e 400 kg ha-1 de nitrogênio disponível. Foram avaliadas as concentrações de N e a intensidade de coloração verde da folha pelo uso do clorofilômetro (ICV) e por meio da análise da imagem digital (G, H e ICVE) aos 45, 105 e 165 dias após a aplicação do lodo. Os valores de intensidade obtidos foram correlacionados com a concentração de N na lâmina foliar e com a taxa de cobertura do solo determinada nas mesmas épocas. A aplicação de doses de lodo de esgoto proporcionou aumento dos índices de cor verde e da concentração de N nas folhas da grama esmeralda. A concentração de N na lâmina foliar pode auxiliar a adubação nitrogenada em cobertura, pois proporcionou altas correlações com a taxa de cobertura do solo. O matiz (H) obtido com a imagem digital e a intensidade de cor verde da folha (ICV) obtida com o clorofilômetro correlacionaram-se com a concentração de N e com a taxa de cobertura do solo e, dessa forma, podem servir como índices na recomendação da adubação nitrogenada.The intensity of leaf green color can be an alternative to estimate the N concentration because of the relationship between chlorophyll level and N in leaf tissue. The objective of the work was to assess green index of the zoysiagrass from the digital imaging analysis and the use of chlorophyll meter to predict the nitrogen nutritional status in sewage sludge fertilized areas. The experiment was carried out on a commercial property of zoysiagrass, located in the county of Itapetininga, State of São Paulo. The experimental design was completely randomized, with five sewage sludge doses: 0, 10, 20, 30 and 40 Mg ha-1, on dry basis (equal to 0, 100, 200, 300 and 400 kg ha-¹) of N available and four replications. The N concentration and green hue intensity were evaluated by using chlorophyll meter (GHI) and by the digital image analysis (G, H and DGCI) at 45th, 105th and the 165th days after sewage sludge application. The intensity values were correlated with the N concentration in the leaf blade and with the soil cover rate determined in the same season. The application of sewage sludge doses increased the green rates and the N concentration in the Zoysia grass leaves. The N concentration leaf can help the nitrogen top-dressed application because it has high correlation with the soil cover rate. The hue (H) obtained with the digital image and green hue intensity (GHI) obtained with the chlorophyll meter are correlated with N concentration and with the soil cover rate and can serve as an index to assist in the recommendation of nitrogen fertilization

Dairy farm characteristics and managed flows of phosphorus

AbstractNonpoint sources of P pollution have been implicated in the declining water quality of many lakes in the northeastern U.S. Most of the agricultural nonpoint P contribution to surface waters comes from field runoff. Water quality may be improved by better understanding the movement, or flow, of P through a farm so that reasons for buildup of high soil P levels can be identified and remedies explored. In this study, the managed flows of P (P in imported and exported products) were estimated based on 1hour farmer interviews on 45 Vermont farms and 1 New York farm. Farm P inflow/outflow budgets were developed using information from the interviews. It was estimated that an average of 57% of the P brought onto the farms was not exported. Phosphorus imported in feed and minerals averaged 65% of the total P imports, while purchased fertilizer contributed to an average of 35% of the total farm P imports. Phosphorus was often fed in excess of the cow's nutritional requirements recommended by the National Research Council. Soil test P levels on two pairs of farms with similar animal densities and soil types reflected the large differences in the estimated net P accumulation. For all 46 farms, there was a significant relationship between net P accumulation and animal density (r2 = 0.59). Farms grouped by management operation type (confinement, pasture - based [non-organic], and pasture-based [organic]) were different in average farm size, animal density, P imports, net P accumulation, milk production, and predominant crop. Feeding of excess P results from the high P levels recommended by feed salesmen and nutritionists, who typically take into account the available home-grown forages and provide the suggested needs for purchases of concentrates and minerals. In a survey of seven Vermont dairy feed consultants and salespersons, rations were designed to feed cows as much as 50% more P than research has indicated is necessary.</jats:p

Mobilization of Cd upon acidification of agricultural soils: column study and field modelling

The potential effect of acidification of contaminated sandy soils on Cd transport in the unsaturated zone was assessed. Forty-eight soil profiles were sampled at five depths in a polluted field that was set aside in 1992. The Cd concentration in the top 30 cm of this field was, on average, 10 mg kg−1. A column experiment was carried out with one of the topsoil samples. Homogeneously packed columns were leached with 0.001 m CaCl2, adjusted to pH 3 or pH 5.7, at a pore water velocity of 6 cm day−1. The Cd and proton transport was predicted with coupled transport equations. The Cd transport was modelled by assuming local equilibrium and by using sorption parameters derived from batch experiments, while acidification was modelled with a kinetic approach, on the assumption that proton buffering was due to cation exchange and mineral weathering. Organic matter was the main contributor to the cation exchange capacity of these soils. Observed and predicted pH and Cd profiles in the columns agreed well. With the same model, the proton and Cd transport at field scale was calculated for each of the 48 profiles sampled (‘grid model’). It was predicted that the field-averaged Cd concentration in the seepage water will increase from 6 μg litre−1 at present to 200 μg litre−1 over 260 years, which greatly exceeds the maximum permissible concentration (MPC) in groundwater of 5 μg litre−1. Predictions of Cd transport using field-averaged soil properties yielded a later breakthrough time and a larger peak Cd concentration than predicted with the grid model, which illustrates the impact of spatial variability on solute transport. Continuation of liming practices is a possible solution to prevent breakthrough of Cd at concentrations far in excess of the MPC.F. Degryse, V. Vlassak, E. Smolders & R. Merck