Nitrogen (N) leaching below the crop-rooting zone represents not only a valuable loss of nutrients for the plant, but also a potential pollution source of groundwater. The objective of this work was to quantify leaching losses of native N and that derived from fertilizer in an Oxisol that was cultivated with sugarcane (Saccharum officinarum) during the crop plant cycle. The sugarcane was planted and fertilized with urea in the planting furrow, with 120 kg ha -1 of N. In order to determine the fate of the fertilizer -N, four microplots with 15 N enriched fertilizer were installed. Input and output of N at the depth of 0.9 m were quantified from the flux density of water and the N concentration in soil solution. During the evaluation period the rainfall was 141 mm less than the historical average (1,315 mm), and the climate was drier than normal in January. The average concentration of mineral N in soil solution was 1.8 mg L -1 . The abundance of 15 N was very high at the beginning (first week) of the assessment period and remained approximately constant (0.453 atom% of 15 N) until the end of the period. The internal drainage was 91 mm of water and the N leaching loss was 1.1 kg ha -1 of N, with only 54 g ha -1 derived from fertilizer. Therefore, under high demand of N by the crop in a system without burning before planting, the leaching of N was not considerable, mainly because the surplus of water between the months of December and March was lower than expected and also because the extraction of nitrogen by the crop was high. Key words: Saccharum spp., sustainability, solute transport, environmental quality, pollution Nitrogênio lixiviado num Latossolo cultivado com cana-de-açúcarRESUMO: A lixiviação de nitrogênio (N) abaixo da zona radicular representa uma valiosa perda do nutriente para as plantas e uma fonte potencial de poluição do lençol freático. Quantificaram-se as perdas de N por lixiviação num Latossolo Vermelho Amarelo cultivado com cana-de-açúcar (Saccharum officinarum) durante o ciclo agrícola de cana-planta. A cultura foi implantada e fertilizada no sulco com 120 kg ha -1 de N-uréia. Para conhecer o destino do fertilizante, foram instaladas quatro microparcelas onde o fertilizante era marcado com o isótopo 15 N. As entradas e saídas de N a 0,9 m de profundidade foram quantificadas diariamente pela densidade de fluxo de água e a concentração de N da solução no solo. No período de avaliação, a precipitação pluvial foi 141 mm menor que a média histórica (1.315 mm) sendo janeiro mais seco que o normal. A concentração de N mineral média foi 1,8 mg L -1 . A abundância de 15 N foi superior à abundância natural do isótopo, especialmente no início do período de avaliação, permanecendo logo constante (0,453% de 15 N). A drenagem interna foi de 91 mm de água e a perda por lixiviação foi 1,1 kg ha -1 de N com apenas 54 g ha -1 derivados do fertilizante. Portanto, com elevada demanda de nutrientes e elevada incorporação de restos culturais, não foram registradas perdas apreciáveis de N por lixiviação d...
RESUMOO estudo do balanço de água no solo com cana-de-açúcar, cultivada em larga escala no Brasil, é essencial para o manejo agrícola, visando ao aumento de produtividade e à redução de riscos de poluição. Este estudo objetivou avaliar os componentes da equação do balanço de água em dois Latossolos cultivados com cana-de-açúcar (cana-planta), localizados nos Municípios de Jaboticabal e Pirassununga (São Paulo). Na área experimental de Jaboticabal, o estudo foi realizado entre os dias 30 de setembro de 2005 e 12 de julho de 2006, e constou de dois tratamentos: T 1 (sem adubação nitrogenada) e T 2 (120 kg ha -1 de N). Em Pirassununga, o estudo foi feito entre os dias 28 de setembro de 2005 e 08 de junho de 2006, mas apenas o tratamento T 2 . O delineamento experimental foi o de blocos aleatórios, com quatro repetições. O volume de controle utilizado para o balanço de água teve como limite superior a superfície do solo e como limite inferior outra paralela à primeira, localizada em profundidade de 0,90 m. As variações de armazenagem, as entradas (precipitação pluvial e ascensão capilar) e as saídas de água (evapotranspiração real e drenagem interna) nesse volume de solo, nas áreas experimentais de Jaboticabal e Pirassununga, foram determinadas em 13 e 10 períodos, respectivamente. Ambas as áreas estudadas eram planas e não irrigadas. Na área de Jaboticabal, em todo o período, tanto a perda de água por drenagem interna quanto o ganho por ascensão capilar foram maiores no tratamento T 2 (-191,69 mm/5,33 mm e -238,37 mm/24,60 mm para T 1 e T 2 , respectivamente); não houve diferença significativa de produtividade (145 e 146 t ha -1 para T 1 e T 2 , respectivamente), nem de evapotranspiração real (1.058 mm para T 1 e 1.028 mm para o T 2 ) entre os tratamentos nesse ciclo de cana-planta, fazendo com que as plantas não adubadas apresentassem a mesma eficiência do uso da água (14 kg m -3 ) que as adubadas. Na área de Pirassununga, a drenagem interna e a ascensão capilar foram de -110,9 e 0,67 mm, respectivamente, e a eficiência de uso da água
Mollisols of Santa Fe have different tilth and load support capacity. Despite the importance of these attributes to achieve a sustainable crop production, few information is available. The objectives of this study are i) to assess soil physical indicators related to plant growth and to soil mechanical behavior; and ii) to establish relationships to estimate the impact of soil loading on the soil quality to plant growth. The study was carried out on Argiudolls and Hapludolls of Santa Fe. Soil samples were collected to determine texture, organic matter content, bulk density, water retention curve, soil resistance to penetration, least limiting water range, critical bulk density for plant growth, compression index, pre-consolidation pressure and soil compressibility. Water retention curve and soil resistance to penetration were linearly and significantly related to clay and organic matter (R2 = 0.91 and R2 = 0.84). The pedotransfer functions of water retention curve and soil resistance to penetration allowed the estimation of the least limiting water range and critical bulk density for plant growth. A significant nonlinear relationship was found between critical bulk density for plant growth and clay content (R2 = 0.98). Compression index was significantly related to bulk density, water content, organic matter and clay plus silt content (R2 = 0.77). Pre-consolidation pressure was significantly related to organic matter, clay and water content (R2 = 0.77). Soil compressibility was significantly related to initial soil bulk density, clay and water content. A nonlinear and significantly pedotransfer function (R2 = 0.88) was developed to predict the maximum acceptable pressure to be applied during tillage operations by introducing critical bulk density for plant growth in the compression model. The developed pedotransfer function provides a useful tool to link the mechanical behavior and tilth of the soils studied.
Indicators synthesizing the state of the structural quality and the function of the porous system are useful for assessing soil production capacity as well as the way it may serve natural ecosystems. This research aimed (i) to determine indicators of the state and function of the porous system, (ii) to use them to derive a global index to characterize the soil physical quality, and iii) to establish a reference pore-size distribution curve for Mollisols from the province of Santa Fe (Argentina). Sixty water retention curves (WRC) of A and B horizons of Mollisols, with clay varying between 119 and 538 g kg . Both the high silt content and low organic matter content confer on the soil characteristics with low stability, excess of small pores and low porosity of the macropore domain. Consequently, the capacity to quickly drain the water excess and allow root proliferation was not optimal, possibly due to the high silt or clay content and the low sand content, characteristic of the soil matrix of these Mollisols.
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