M. E. López-Mosquera

Use of dairy-industry sludge as fertiliser for grasslands in northwest Spain : Heavy metal levels in the soil and plants

The suitability of dairy-plant sludge for fertilisation of a Cambisolic soil was investigated in northwest Spain. Soil properties (pH, electrical conductivity, organic matter content, NO3−, P, Ca, Mg, Na, K and Al) and soil and plant tissue heavy metal contents (Hg, Pb, Cd, Cu, Zn, Ni and Cr) were determined in 12 grassland plots fertilised over a 1–4-year period with dairy sludge and conventional fertiliser (cattle slurry and mineral fertilisers), and in six meadows fertilised with conventional fertilisers only. Heavy metal contents were also determined in plant tissues from different plots. There were no significant differences in soil heavy metal concentrations between the sludge-amended plots and the control plots, except for Pb concentration, which was significantly lower in the sludge-amended plots. A significant correlation between metal content in the soil and total sludge dose applied was detected only for Cr. Even in plots to which the dairy-plant sludge had been applied for 4 years, heavy metal levels in both soil and plants were within European Union and Spanish legislative limits (Council of the European Communities Council Directive of 12 June 1986 on the protection of the environment, and in particular of the soil, when sewage sludge is used in agriculture (86/278/EEC), Official J. Eur. Communities 1986;L 181:6–12; Royal Decree 1310/1990, del 29 de octubre por el que se regula la utilizacion de los lodos de depuracion en el sector agrario, BOE 1990;262:32339–32340.) However, a number of significant metal-metal correlations (Ni–Zn, Ni–Cr, Ni–Cu, Cu–Cr, Zn–Cr and Pb–Cd) were detected in both the sludge and the sludge-amended soils, but not the non-amended soils, suggesting that the sludge is an important source of these metals. In addition, soils that had received the dairy-plant sludge had significantly higher conductivity, probably because of the NaOH used for cleaning in dairy plants. Salinity-related variables (K, NO3−) were significantly correlated with Cr and Zn concentrations in plant tissues. These findings suggest a need to assess the possible long-term effects of dairy sludge application, with the aim of developing guidelines for its use as a fertiliser.

Characterization and Evaluation of Compost Utilized as Ornamental Plant Substrate

Two composts produced at different times of the year from garden waste, sewage sludge and wood ash were evaluated for use as ornamental plant substrates. The maturity and lack of phytotoxicity of both composts, as well as the absence of E. coli, were first confirmed by use of laboratory procedures and rapid test kits. A greenhouse experiment was then carried out with two ornamental species, Petunia sp. and Tagetes sp., to evaluate the suitability of the composts as plant substrates. The performance of the composts as well as mixtures of each with 25, 50 and 75% acid peat moss was compared with that of a commercial universal substrate. Addition of the peat to the composts improved some of the physical and chemical properties. However, the results of the pot experiments indicated that under the experimental conditions used, the compost produced from green waste was suitable for use as a plant substrate, without the need for addition of other components; this appears to be an effective way of utilizing the type of urban waste considered in the study.

Salt effect of dehydrated broiler litter on organic lettuce

Abstract This paper examined salinity changes in soil in a greenhouse over four cropping cycles of lettuce (two autumn-winter cycles followed by two spring-summer cycles), testing the effect of applying an organic fertiliser consisting of dehydrated broiler litter at variable rates from 267 to 1596 g m−2 and comparing this with two mineral fertilisers; ammonium nitrate applied at 58.5 g m−2 and Nitrofoska Stábil® applied at 100 g m−2. The electrical conductivity of the soil (ECe) increased with increased rates of the organic fertiliser. Also, the increased temperatures and evaporation in the spring-summer cropping cycles resulted in increased concentrations of the fertiliser components salts in the soil. However, ECe remained below 4 dS m−1 and, although the highest fertilisation rates led to ECe levels near the acceptable threshold for lettuce (1.3 dS m−1), the weights of the lettuce increased. This result suggested that the favourable effects of the organic fertiliser on soil properties offset its adverse effects on salinity. Long-term risks of salinization can be avoided by using dehydrated manure rates not exceeding 600 g m−2 in autumn and 1200 g m−2 in spring or 532 g m−2 at any time of the year where repeated applications are made.