Mineralization dynamics in soil fertilized with seaweed-fish waste compost.

BACKGROUND: Seaweed and fish waste can be composted together to obtain fertilizer with high organic matter and nutrient contents. The nutrients, however, are mostly in organic form and must be mineralized to make them available to plants. The objective of this work was to establish a usage guideline for the compost by studying its mineralization dynamics. Also, the release of inorganic N and C from soil fertilized with the compost was monitored and modelled. RESULTS: C and N were released throughout the assay, to an extent significantly dependent on fertilizer rate. Mineralization of both elements fitted a first-order exponential model, and each fertilizer rate required using a specific fitting model. An increased rate favoured mineralization (especially of carbon). After 90 days, 2.3% of C and 7.7% of N were mineralized (and 23.3% of total nitrogen made plant available) with the higher rate. CONCLUSION: C mineralization was slow because organic matter in the compost was very stable. On the other hand, the relatively high initial content in mineral N of the compost increased gradually by the effect of mineralization. The amount of N available would suffice to meet the requirements of moderately demanding crops at the lower fertilizer rate, and even those of more demanding crops at the higher rate.

Fertilization of Pinus pinea L. seedlings with a sewage sludge-based compost.

Two experiments were conducted to evaluate the effect of a sewage sludge-based compost (SSC) on the growth and mineral composition of containerized Pinus pinea L. seedlings. In the first experiment, five different substrates were tested: four binary mixtures of SSC and peat (100% SSC, 75% SSC, 50% SSC and 25% SSC, by volume) without fertilization, and a control substrate (peat-based substrate + fertilizer). Seedlings growing in the 100% SSC substrate showed the lowest growth, a consequence of both the low water availability and the high electrical conductivity that made SSC unsuitable to be the only component of a growing-media for pine ;seedlings'. The 50% SSC substrate presented physical and chemical properties similar to the control substrate and near the acceptable range for a growing-media. Moreover, no significant differences were found between growth of seedlings from treatment 50% SSC (without mineral fertilization) and seedlings from control treatment (with mineral fertilization). In the second experiment, a fertilization assay was performed with two substrates selected from the first experiment (50% SSC and control). The two substrates were fertilized with three levels of a macronutrient fertilizer (0.5, 1.0 and 2.0 g L( -1)) and two levels of a micronutrient fertilizer (0 and 0.4 g L(-1) of fertilizer containing only micronutrients). Results obtained suggest that replacing 50% (by volume) of peat-based substrate by the sewage sludge-based compost allowed: maintenance of the commercial value of seedlings; reduction of the amount of peat used in the substrate; a need for only half the amount of macronutrient fertilizer applied in the basal fertilization; and omission of micronutrient fertilization.