Nitrogen fertilizer (15N) leaching in a central pivot fertigated coffee crop

Abstract

RESUMO Lixiviação de nitrogênio ( 15 N) do fertilizante em uma cultura de café fertirrigadaO nitrogênio possui uma dinâmica complexa no sistema solo-planta-atmosfera. Considerando o elevado custo dos adubos, é fundamental o desenvolvimento de manejos da adubação nitrogenada que visem ao melhor aproveitamento do N pelas culturas, como é o caso da fertirrigação e o mínimo impacto ambiental. Balanços hídricos e a lixiviação de N derivado do fertilizante são apresentados para um cafezal sob fertirrigação com uréia marcada com 15 N no oeste baiano, em três cenários para um ciclo da cultura 2008/2009: i) precipitação + irrigação no ano inteiro, ii) apenas precipitação; e iii) precipitação + irrigação apenas na estação seca. Nos balanços hídricos os componentes ascensão capilar e escoamento superficial foram considerados nulos por se tratar de solo arenoso em declive praticamente nulo, com lençol freático profundo. A irrigação foi realizada por pivô-central e no balanço hídrico o volume de controle conside- Nitrogen has a complex dynamics in the soil-plant-atmosphere system. N fertilizers are subject to chemical and microbial transformations in soils that can result in significant losses. Considering the cost of fertilizers, the adoption of good management practices like fertigation could improve the N use efficiency by crops. Water balances (WB) were applied to evaluate fertilizer N leaching using 15 N labeled urea in west Bahia, Brazil. Three scenarios (2008/2009) were established: i) rainfall + irrigation the full year, ii) rainfall only; and iii) rainfall + irrigation only in the dry season. The water excess was considered equal to the deep drainage for the very flat area (runoff = 0) with a water table located several meters below soil surface (capillary rise = 0). The control volume for water balance calculations was the 0 -1 m soil layer, considering that it involves the active root system. The water drained below 1 m was used to estimate fertilizer N leaching losses. WB calculations used the mathematic model of Penman-Monteith for evapotranspiration, considering the crop coefficient equal to unity. The high N application rate associated to the high rainfall plus irrigation was found to be the main cause for leaching, which values were 14.7 and 104.5 kg ha -1 for the rates 400 and 800 kg ha -1 of N, corresponding to 3.7 and 13.1 % of the applied fertilizer, respectively.

The Brazilian Cerrado: assessment of water and soil degradation in catchments under intensive agricultural use

“…However, the role that nitrogen leaching plays in agricultural Cerrado is inconclusive. In the eastern Cerrado, Bortolotto et al (2012Bortolotto et al ( , 2013 reported extremely high N-applications during fertigation (irrigation combined with fertilizer application) in coffee plantations at a rate of up to 800 kg N ha À1 a À1 . Most commonly, nitrogen fertilizer (for cotton up to 180 kg ha À1 N and maize~90 kg ha À1 ) is applied as urea with 1/3 of the total N rate during the seeding stage of the second crop (usually maize or cotton) after the soybean harvest.…”

“…Gücker et al (2009) provided evidence for nitrate leaching, that is, significantly high levels, in groundwater samples influenced by agriculture. In the eastern Cerrado, Bortolotto et al (2012Bortolotto et al ( , 2013 reported extremely high N-applications during fertigation (irrigation combined with fertilizer application) in coffee plantations at a rate of up to 800 kg N ha À1 a À1 . In field experiments, they confirmed that nitrate leaching and groundwater pollution would occur.…”

Enhanced Plant Rooting and Crop System Management for Improved N Use Efficiency

“…Among the reasons are that N fertilizer rates are relatively small compared with those used in Europe, USA, and China, farmers usually split N applications, and deep oxisols have positively charged clay particles in the subsoil, especially at low pH (Lopes and Guilherme, 2016). However, as the average crop yields increase in Brazil, so are the amounts of N fertilizers used, and consequently increased NO 3 À leaching losses have been reported (Bortolotto et al, 2012;Cantarella et al, 2003).…”

Nodulation, contribution of biological N2 fixation, and productivity of the common bean (Phaseolus vulgaris L.) inoculated with rhizobia isolates

“…However, the use of N-fertilizers increases the production costs and contributes to increased environmental risks, such as groundwater contamination with nitrite under irrigated production systems (Bortolotto et al, 2012) and the increase of greenhouse gas emission (Siqueira Neto et al, 2011). All of these indicate the need for alternative sources of N supply.…”