Nitrogen Cycling in a Wheat Crop: Soil, Plant, and Aerial Nitrogen Transport¹

Abstract

An understanding of N cycling in the soil‐plant‐atmosphere components of wheat (Triticum aestivum L.) production systems is necessary to maximize yield and quality. The objectives of this study were to examine N cycling and observe the effects of N surplus and deficit on N absorption/desorption in the soil and atmosphere and to evaluate translocation within the plant. Soil, plant, and microclimate measurements were taken concurrently, and soil, plant, and atmospheric ammonia (NH3) transport determined. During the early vegetative phase, plant N concentration reached a maximum; however, during the remaining growth periods, N concentration decreased even though N uptake from the soil continued until plant maturity. More total N was translocated to grain from leaves than stems, and translocation from the leaves began earlier than that from stems. Isotope and total N studies showed that after anthesis about half of the grain N came from remobilization from leaves and stems and the other half directly from the soil. A progressively larger percentage of N came from mineralized organic matter as the season progressed. Nitrogen was lost as volatile NH3 from the plant after fertilizer application and during the senescence period. Prior to anthesis, atmospheric NH3 absorption was observed during a period when soil N was temporarily unavailable. About 21% equivalent of the applied fertilizer was lost as volatilized NH3. During the period of soil unavailability an amount equivalent to about 1% equivalent of the applied fertilizer was gained from atmospheric NH3 by plant absorption.

Nitrogen loss in Brachiaria decumbens after application of glyphosate or glufosinate-ammonium

“…V C 2 3 7 2 5 2 9 1 1 2 activities of the enzymes glutamine synthetase (GS) and glutamine:2-oxoglutarateaminotransferase (GOGAT), the main compounds responsible for ammonia assimilation in the nitrogen metabolism of higher plants, resulting in an increase of the ammonia emission potential (Morgan & Parton, 1989). Using 15 N as a tracer, Harper et al (1987) demonstrated that after wheat anthesis, one half of the nitrogen in the grain came from a remobilization of N stored in stems and leaves during the breakdown process of proteins and amino acids during the maturation period of leaves and stems, while the other half came from the soil.…”

Nitrogen translocation in wheat inoculated with Azospirillum and fertilized with nitrogen

“…Therefore, regardless of how the process originated (absorption or fixation), N incorporation took place after anthesis (Table 4) and behaved like late cycle absorbed N, and could have influenced the dry matter and probably the duration of leaf area without changing grain production (Thomas et al, 1978;Gifford et al, 1984). Probably both capacity and quantity of reproductive sinks (grain) became a limiting factor, since they are defined at a stage much earlier than the extra availability of N (Moll et al, 1982;Harper et al, 1987;Mac Kown & Sanford, 1988).…”

Perda de nitrogênio pela Brachiaria decumbens após a antese: relação com a umidade do solo

“…Isto porque, nos estádios reprodutivos (pós-antese -início da senescência), há aumento do potencial de emissão de NH 3 devido às mudanças no metabolismo do N no vegetal, uma vez que ocorre maior clivagem de proteínas e aminoácidos nesses estádios (MORGAN & PARTON, 1989). HARPER et al (1987) (HOOKER et al, 1980). Dessa maneira, o NO 2 seria a fonte para a volatilização de NO 2 e NO x via corrente transpiratória, resultando em perdas de N via parte aérea das plantas.…”

“…No entanto, DAIGGER et al (1976), cultivando trigo de inverno, encontraram perdas que variaram de 25 a 80kg ha -1 entre a antese e a colheita. Na pós-antese na cultura de soja, foram encontradas perdas de 5,9 a 76,9kg ha -1 de N (HARPER et al, 1987;PAPAKOSTA & GAGIANAS, 1991). Durante a senescência foliar, que tem início após o florescimento, o aumento da hidrólise de proteínas é acompanhado pela redução nas atividades das enzimas glutamina sintetase (GS) e glutamato sintase (GOGAT), com o aumento de atividade da glutamato desidrogenase (GDH), principais responsáveis pela assimilação de NH 3 no metabolismo do nitrogênio nas plantas superiores.…”