Spring Nitrogen Uptake, Use Efficiency, and Partitioning for Growth in Iris germanica ‘Immortality’

This study investigated how spring nitrogen (N) application affects N uptake and growth performance in tall bearded (TB) iris ‘Immortality’ (Iris germanica L.). Container-grown iris plants were treated with 0, 5, 10, 15, or 20 mm N from 15NH415NO3 through fertigation using a modified Hoagland’s solution twice a week for 6 weeks in Spring 2013. Increasing N rate increased plant height, total plant dry weight (DW), and N content. Total N content was closely related to total plant DW. The allocation of N to different tissues followed a similar trend as the allocation of DW. In leaves, roots, and rhizomes, increasing N rate increased N uptake and decreased carbon (C) to N ratio (C/N ratio). Leaves were the major sink for N derived from fertilizer (NDFF). As N supply increased, DW accumulation in leaves increased, whereas DW accumulation in roots and rhizomes was unchanged. This indicates increasing N rate contributed more to leaf growth in spring. Nitrogen uptake efficiency (NupE) had a quadratic relationship with increasing N rate and was highest in the 10 mm N treatment, which indicates 10 mm was the optimal N rate for improving NupE in this study.

Nitrogen Source for Inflorescence Development in Phalaenopsis: II. Effect of Reduced Fertilizer Level on Stored Nitrogen Use

Plants of Phalaenopsis orchid are known for their great resilience and ability to flower under less than ideal conditions, including long periods without fertilization. Significant nutrient storage is thought to account for this characteristic; however, the use of stored nutrients in Phalaenopsis has not been fully studied. We used 15N-labeled Johnson’s solution to trace the use of stored nitrogen (N) and recently absorbed fertilizer N in Phalaenopsis given various fertilizer levels during forcing. By separately labeling fertilizer N applied to Phalaenopsis Sogo Yukidian ‘V3’ plants 6 weeks before and 6 weeks into forcing, we found in the inflorescence that the ratio of N derived from fertilizer applied 6 weeks before forcing to the N derived from fertilizer applied 6 weeks into forcing was 43% to 57%. With 90% reduction in fertilizer concentration during the reproductive stage, the ratio increased to 89% to 11%, indicating that stored N becomes a significant N source for inflorescence development when fertility becomes limited. Reducing fertilizer level during the reproductive stage from full-strength Johnson’s solution down to zero decreased the dry weight of newly grown leaves, reduced the number of flowers from 10.8 to 8.9, and slightly increased the time required between initiation of forcing and anthesis. However, the overall effect of reduced fertilization on the growth and flowering of Phalaenopsis Sogo Yukidian ‘V3’ plants in this study was slight, because under little or no fertilization, more stored N was mobilized and this was sufficient to meet most of the N demand for inflorescence development.

Nitrogen Source for Inflorescence Development in Phalaenopsis: I. Relative Significance of Stored and Newly Absorbed Nitrogen

Phalaenopsis orchid is a slow-growing crop that responds slowly to fertilization. In this study, we used 15N-labeled Johnson’s solution to investigate the accumulation and use of fertilizer nitrogen (N) during the vegetative and reproductive growth stages of Phalaenopsis Sogo Yukidian ‘V3’ with a focus on the nitrogen source for inflorescence development. Labeling of fertilizer applied to mature plants 6 weeks before forcing or at 6 weeks into forcing showed that in the inflorescence, the ratio of N derived from fertilizer applied 6 weeks before forcing to the N derived from fertilizer applied 6 weeks into forcing was 31% to 69%, which shows the importance of newly absorbed fertilizer for supplying the N needed for inflorescence development. The fate of fertilizer N applied during the small, medium, or large plant stage of vegetative Phalaenopsis Sogo Yukidian ‘V3’ was traced separately with 15N-labeling. The capacity of the plant to accumulate N after fertilizer application was different during the various stages of vegetative growth, with large plants having more N storage capacity as a result of their greater biomass. However, the percentage of the accumulated N that was later allocated to the inflorescence was similar regardless of the stage of fertilizer application: of the fertilizer N absorbed during various stages of the vegetative period, 6% to 8% was allocated to the inflorescence at the visible bud stage. This result highlights the mobility of N stored early on within the plant. By calculation, of the total N in the inflorescence at the visible bud stage, the N absorbed during the small, medium, and large plant stages contributed 7%, 11%, and 25%, respectively, whereas N applied after spiking made up the other 57%. This result indicates that both N stored during the vegetative stage and N applied during the reproductive stage contribute significantly to inflorescence development.

Effets d’amendements ligneux sur la disponibilité d’azote dans un sol sableux cultivé en pomme de terre

A field trial with potato (Solanum tuberosum L.) was conducted on a sandy soil to estimate N immobilization after applying tree clippings to the soil. N availability was evaluated by mineralizable N, N recovery coefficients and N derived from fertilizer. Fresh and composted tree clippings (50 t ha−1) were compared with an unamended control. In each principal treatment, nitrogen fertilizer was added at the rates of 0, 150, 200 and 250 kg N ha−1. Mineralizable N was lowest (P ≤ 0.001) in plots amended with wood residues by comparison to the unamended control. N recovery was 0.49 and 0.54 for fresh and composted residues, respectively, which indicates a higher N immobilization for fresh wood residues. N immobilization was estimated at 46 kg N ha−1 and increased in treatments receiving fresh tree clippings and also with increasing N rates. Moreover, a significant linear increase of N derived from fertilizer (P = 0.03) was observed with fertilizer N rates especially in amended treatments. Thus, the incorporation of ligneous material to the soil may have reduced the availability of soil mineralized N and potato growth depended mainly on N fertilizer addition. This study indicates that during the first growing season following the application of ligneous materials, N immobilization remained the main restricting factor on potato production. Key words: N availability, N derived from fertilizer, N immobilization, N recovery coefficient, potato, tree clippings, wood residues