Isotopic composition of maize as related to N-fertilization and irrigation in the Mediterranean region

Abstract

Nitrate leaching as a result of excessive application of N-fertilizers and water use is a major problem of vulnerable regions. The farming of maize requires high N fertilization and water inputs in Spain. Isotopic techniques may provide information on the processes involved in the N and C cycles in farmed areas. The aim of this work was studying the impact of sprinkler and furrow irrigation and N input on maize (Zea mays L.) yields, and whether isotopic composition can be used as indicator of best farming practices. Trials were set up in Tudela (Spain) with three rates of N fertilization (0, 240 and 320 kg urea-N ha -1 ) and two irrigation systems (furrow and sprinkler). Yield, nitrogen content, irrigation parameters, N fate and C and N isotope composition were determined. The rate of N fertilization required to obtain the same yield is considerably higher under furrow irrigation, since the crop has less N at its disposal in furrow irrigation as a result of higher loss of nitrogen by NO 3 --N leaching and denitrification. A lower δ 13 C in plants under furrow irrigation was recorded.The δ 15 N value of plant increased with the application rate of N under furrow irrigation. Key words: Zea mays L., furrow irrigation, nitrogen, sprinkler irrigationComposição isotópica do milho relacionada à fertilização nitrogenada e método de irrigação na região do Mediterrâneo RESUMO: A lixiviação de nitratos resultante da aplicação excessiva de fertilizantes nitrogenados e o uso excessivo de água são problemas sérios em regiões vulneráveis. A cultura do milho(Zea mays L.) na Espanha exige altos níveis de fertilização nitrogenada e irrigação. Técnicas isotópicas podem prover informações sobre os processos envolvidos nos ciclos do N e do C em área agrícolas. Avaliou-se o impacto da irrigação por aspersão ou sulco e adição de N na produtividade do milho e se a composição isotópica pode ser usada como indicador de melhores práticas de manejo da produção agrícola. Os ensaios foram realizados em Tudela, Espanha, utilizando três níveis de fertilização nitrogenada (0, 240 e 320 kg ureia-N ha -1 ) e dois sistemas de irrigação (sulco e aspersão). Foram determinados produtividade, teor de nitrogênio, parâmetros de irrigação, fixação de N e C e composição isotópica dos grãos. Os níveis de N exigidos para obtenção de produtividades idênticas são maiores sob a irrigação em sulcos, uma vez que nestas condições as perdas de nitrogênio pela lixiviação de NO 3 --N e denitrificação são maiores e, consequentemente, a disponibilidade de N é menor. Foi registrado menor δ 13 C nas plantas irrigadas por sulcos. Os valores do δ 15 N nas plantas irrigadas por sulcos aumentaram com os níveis de fertilização nitrogenada. Palavras chave: Zea mays L., irrigação por sulco, nitrogênio, irrigação por aspersão

C-N elemental and isotopic investigation in agricultural soils: Insights on the effects of zeolitite amendments

“…Concerning maize (cropped in 2014), the C contents varied from 36.0 to 46.4 wt% in the stems and from 36.7 to 40.8 wt% in the grains; the relative isotopic compositions ranged from -15.4 (10CZ) to -13.8 (5NZ-15NZ) ‰ in the stems and from -13.9 (5NZ) to -12.6 (10CZ) ‰ in the grains. These values are conforming with those typical of C4 photosynthetic pathways worldwide, and particularly with those of maize plants from other Mediterranean occurrences; data coherently show physiological differences between stems and grains, with the latter systematically 13 C-enriched, leading to intra-plant isotopic fractionation in the order of δ 13 C 1.0-1.5 ‰, comparable to what observed by Lasa et al (2011).…”

“…Distinct fertirrigation practices in fact influence the C discrimination factor (Δ 13 C) (Lasa et al, 2011;Bogaard et al, 2013;Maxwell et al, 2014) expressed as [(Ra-Rp)/(1+Rp/1000)] where Ra and Rp are the deviation of the C isotopic composition from the reference standard (Vienna Pee Dee Bee Belemnite) of atmospheric air and plant, respectively. The advantage to use "Δ" notation instead of "δ" is that the first can be used for directly express the consequences of biological processes, since it is independent of the isotopic composition of the standard (Farquhar et al, 1989).…”

“…The advantage to use "Δ" notation instead of "δ" is that the first can be used for directly express the consequences of biological processes, since it is independent of the isotopic composition of the standard (Farquhar et al, 1989). For this reason, the measurement of Δ 13 C has been identified as a suitable indicator of the plant physiological status, especially in C3 plants where the variation in the Δ 13 C is generally higher (Farquhar et al, 1989;Lasa et al, 2011;Maxwell et al, 2014).…”

“…This in turn implies that plants grown on organic fertilizers have higher δ 15 N with respect to plants grown under unfertilized or under chemical N-fertilizers (Choi et al, 2002;Choi et al, 2003;Bateman et al, 2005;Yun et al, 2006;Szpak et al, 2012;Szpak, 2014). It is also known that site specific conditions such as water and nutrients availability, soil salinity and soil compaction can cause important variation in the carbon (C) discrimination factor (Δ 13 C), giving information on the physiological status of plants (Lasa et al, 2011;Maxwell et al, 2014).…”

Belowground carbon allocation patterns as determined by the in-growth soil core 13C technique across different ecosystem types

“…On the other hand, plants grown on NH 4 -enriched zeolites registered a higher δ 15 N, approaching that of the pig slurry employed for enriching the zeolites, confirming that this material can constitute a N pool for plants at least for two cultivation cycles. The distinct agricultural practices seem to be reflected in the plant physiology, as recorded by the carbon discrimination factor (Δ 13 C) which generally increases in plots amended with natural zeolites indicating better water/nutrient conditions (Lasa et al, 2011) Since the pioneering efforts of Emiliani (1955) and Shackleton (1967), oxygen and carbon isotopic records derived from measurements of fossil foraminiferal shells have played a pivotal role in palaeoceanography, addressing a large range of questions regarding the evolution and history of the ocean and climate.…”