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Résumé :
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The objectives of this research were to evaluate N cycling in a highly fertilized grassland in a humid temperate climate and to observe the effects of N surplus and deficit on NH3 absorption-desorption by the grass. Soil, plant, and weather measurements were taken concurrently and soil-plant-atmosphere N transport were determined. After N application, soil inorganic N decreased rapidly to background levels, due to possible microbial immobilization and plant N demand. Much of the immobilized N was remobilized during the growth period, but at insufficient rates to avoid N stress by the crop, as shown by absorption of NH3. During spring, 45% of the plant N was derived from applied fertilizer, with the balance obtained from mineralized organic N (49%) and absorption of NH3 (6%). During summer, fertilizer N accounted for 60% of accumulated grass N and NH3 absorption accounted for 11% of N not derived from fertilizer (4% of the total N), with the balance coming from mineralized organic N.
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