Hazards of swine slurry: Heavy metals, bacteriology, and overdosing-Physicochemical models to predict the nutrient value.

In this work, 124 samples of slurry from 32 commercial farms of three animal categories (lactating sows, nursery piglets, and growing pigs) were studied. The samples were collected in summer and winter over two consecutive years and analyzed for physicochemical properties, macronutrient and micronutrient, heavy metals, and major microbiological indicators. The results were found to be influenced by farm type and to deviate especially markedly in nursery piglets, probably as a consequence of differences in pig age, diet, and management. The main potential hazards of the slurries can be expected to arise from their high contents in heavy metals (Cu and Zn), especially in the nursery piglet group, and from the high proportion of samples testing positive for Salmonella spp. (66%). Linear and nonlinear predictive equations were developed for each animal category and the three as a whole. Dry matter, which was highly correlated with N, CaO, and MgO contents, proved the best predictor of fertilizer value. Using an additional predictor failed to improve the results but nonlinear and farm-specific equations did. Rapid on-site measurements can improve the accuracy of fertilizer value estimates and help optimize the use of swine slurry as a result.

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.

Leaching techniques for saline wastes composts used as growing media in organic agriculture: assessment and modelling.

The purpose of this work was to examine solute release by the effect of leaching of a saline compost with two main objectives: (1) to identify the most efficient method for this purpose, in order to minimize the environmental impact of this process in terms of water consumption and (2) to study the composition of the leachates to manage them properly and avoid possible contamination. A laboratory method involving column leaching with distilled water (CL) and two field methods involving saturation leaching (SL) and drip leaching (DL) were compared to this end. In order to more accurately assess nutrient release and compare the three leaching techniques, the cumulative amounts of ions leached were processed by using an exponential growth model. All target ions fitted properly, and so did the curve for the ions as a whole. Salts were removed mainly by effect of the leaching of major ions in the substrate (Na(+), Cl(-), inorganic N, SO4 (2-) and K(+)). SL and CL proved similarly efficient and reduced the salt content of the substrate to an electrical conductivity below 2 dS m(-1) in the saturation extract, which is the optimum level for nursery crops. By contrast, the DL method provided poor results: salt contents were reduced to an electrical conductivity of only 8 dS m(-1) in the saturation extract, so the resulting substrate can only be useful to grow highly salt-tolerant crops.