Agro-Industry Sludge as a Potential Organic Fertilizer for Prompt Nitrogen Release

The aim of this study was to evaluate the sustainability of an agro-industry sludge as a nitrogen (N) fertilizer in perennial crops by assessing its dynamics of release of: 1) N as ammonium (NH₄⁺)- and nitrate (NO₃^?)-N, and 2) carbon as soil respiration. In incubation assay, application of agro-industry sludge promoted the maximum NH₄⁺-N concentration (50 mg kg^?1) 2 h after application, then it decreased with time until day 26. NO₃^?-N increased, reaching the maximum between day 60 and day 100, according to a second degree function. Agro-industry sludge showed a slower release of NO₃^?-N compared with urea. Soil basal respiration and cumulative amount of carbon dioxide were higher in sludge from day 71 on. In field, soil NO₃^?-N increased after fertilization treatments and was higher in Calcari Stagnic Cambisols soil. Sludge showed a potential lower environment impact in terms of mineral N release, than urea.     

Effect of time of application on nitrogen uptake,partitioning, and remobilization in walnut trees

Walnut tree requires a relatively high amount of nitrogen (N). To avoid loss in the environment, N uptake efficiency (NUE) should be optimized. The aims of this study were to evaluate the effect of time of N application on NUE, partitioning, and remobilization in walnut trees. Two-year-old trees were planted in 40-L pots and fertilized with 1 g of ¹⁵N-enriched (5 atom %) N at: 1) bud burst, 2) pistillate flower maturity, and 3) late summer. One week after fertilization, the percentage of N derived from fertilizer and NUE were higher in trees fertilized in late summer, than other timings. N uptake was linearly related to root dry weight. At May 2008 harvest, the N stored in trunk and twigs was remobilized to the developing leaves and to the roots. Late summer N application appeared to be the most effective in providing N for walnut spring new growth.     

Productivity and photosynthetic efficiency of outdoor cultures of Tetraselmis suecica in annular columns

In this study, 120-l annular columns were used to cultivate Tetraselmis suecica outdoors. The mass transfer at different aeration rates and the influence of the harvest rate on productivity and biochemical composition were investigated. The potential of the system was evaluated by estimating productivity at full-scale. Two different arrangements to simulate a full-scale plant and determine the “overall areal productivity” (OAP) were experimented with. In August 2003, one experimental column (full-scale column) was placed between seven dummy columns. All the reactors were positioned at a distance of 0.8 m wall to wall and centred at the vertices of equilateral triangles. A second experimental column (isolated column) was placed in a separate area under full sunlight. In August 2004, the columns were placed side by side in an east-west oriented row at a distance of 0.24 m wall to wall.In the first experiment, the mean volumetric productivity of the full-scale column was not significantly lower than that achieved by the isolated column (0.46 against 0.49 g l^− 1 day^− 1) in spite of the shading by the dummy units. The average OAP and efficiency of conversion of visible solar radiation (PE) were 36.3 g m^− 2 day^− 1 and 9.4%, respectively. In the second experiment, the full-scale column attained a mean volumetric productivity of 0.42 g l^− 1 day^− 1. The OAP and the PE were 38.2 g m^− 2 day^− 1 and 9.3%, respectively.