EFFECTS OF DAIRY-INDUSTRY SLUDGE FERTILIZATION ON MIXED FIELD PRODUCTION AND ON BOTANICAL COMPOSITION - M.E. López Mosquera, C. Moirón and E. Carral

Escuela Politécnica Superior, University of Santiago de Compostela, 27002 Lugo, Spain

SUMMARY

In a field sown in the autumn of 1995, an experiment was initiated in June of 1997, applying different doses of a dairy industry sludge (0, 80, 160 and 240 m³ ha^-1). The results obtained two months after the addition of sludge clearly show the increase in the forage production up to a dry weight of 5 400 kg ha^-1 for the highest dose. There was also an increase in the percentage of grasses in comparison to the percentage of clover and weeds as the dose increased.

Keywords: botanical composition, dairy sludge, forage production.

INTRODUCTION

In their productive process, dairy industries generate a milk waste and cleaning waste waters from the facilities of the factory that are later treated through a depuration system. The result is a product rich in organic matter, nutrients and with low heavy metal content (Moirón et al., 1997). The application of sludges of this type in agricultural lands has been made in the municipality of Vilalba (Lugo-Spain) since 1991. The first data on the production of grasses under trees, comparing plots fertilized with these sludges and those plots fertilized with a mineral source have been obtained (Carral et al., 1996). Also, the effects produced in chemical soil properties (Moirón et al., 1998), as well as the heavy metal accumulation in the soil have been studied in plants and fields fertilized with these sludges (Moirón et al., 1997). In order to know the short-term fertilizing effect based on the quantity applied and to value the possible risks of toxicity in the plant that can be originated with elevated applications, a test was made in a field in which different amounts of sludges of 0, 80, 160 and 240 m³ ha^-1 for a dry extract 13 gl^-1, after the first cut for silage, were applied. In the resulting second cut herbage, evaluations were made of production, the botanical composition and mineral content.

MATERIAL AND METHODS

The experiment was conducted in Goiriz-Vilalba (Lugo-Spain), a zone of warm temperate climate (Papadakis regime) and soil type Humic Cambisol (FAO, 1991). In autumn 1995 a field was sown with Lolium perenne cv. Barbestra, Lolium multiflorum cv. Barmult, Dactylis glomerata cv. Nicol, Trifolium repens cv. Huia and Trifolium pratense cv. Marino. Fertilization for establishment was 3 t ha^-1 dolomite and 600 kg ha^-1 of 8-24-16. In the spring, 250 kg ha^-1 of 9-17-28 was added as a maintenance fertilizer. Then a cut for silage was made in spring and the rest of the year the sward was grazed. In June 1997 0.4 ha were chosen out of a total of 4 ha. These were divided into four plots measuring 10 m wide by 100 m long. One out of the four dairy-sludge application rates (0, 80, 160 and 240 m³ ha^-1) was chosen. The liquid sludge was surface-applied by a tractor-drawn tank. The chemical properties of the sludge are summarized in Table 1.

Table 1. Dairy-sludge composition used in the experiment. Dairy-sludge dry mater content was 13 g l^-1.

* kg m^-3, + mg kg^-1

Vegetation samples were collected in July 1997. In each experimental plot, six randomly placed quadrats measuring 33 by 33 cm were used for vegetation sampling. The above ground biomass in each quadrat was clipped at ground level and separated into grass, clover and weed components. The plant material was dried at 65ºC for 48 hours and weighed and the weights were then converted to kg ha^-1. After extraction with sulphuric acid and hydrogen peroxide (Thomas et al., 1967), nitrogen and phosphorus in the herbage were determined by AutoAnalyser, K, Ca and Mg by AAS. Vegetation production, botanical composition and tissue analysis were analysed by ANOVA to determine differences among treatments.

RESULTS

Significant differences were observed in herbage production (dry weight) according to the amount of sludge applied, as shown in Figure 1. Concerning the botanical composition, there was an increase in the grass percentage compared to the control, having no differences for the doses of 80 and 160 m³ ha^-1. Although there was a decreasing trend for the clover biomass with higher sludge rates, this was not statistically significant. At the same time weed biomass decreased with the higher sludge rates (240 m³ ha^-1), as can be seen in Figure 2.

Regarding the plant mineral content, surprisingly, there were no significant differences between samples, except in the K content, which was greater in those plots fertilized with sludges than in the control ones. On the contrary, there were lower concentrations of Ca in the forage corresponding to the plot that had received the highest dose of sludge (Table 2).

Figure 1. Herbage dry matter production by rate of sludge applied (bars with different letters differed significantly at P<0.05).

Figure 2. Herbage botanical composition by rate of sludge applied (bars with different letters differed significantly at P<0.05).

Table 2. Mineral contents in herbage depending on the treatment. Values for the treatments represented with the same letter are not significantly different at the P<0.05 level.

ACKNOWLEDGEMENTS

The authors thank Besnier-Leche de Galicia, S.A. for their assistance and Moisés Carballeira who kindly lent us his land and time.

REFERENCES

Carral, E., Castelao, A., López, M.E., Moirón, X., Mosquera, R., Rigueiro, A. & Villarino, J. 1996. Effect of milk sewage sludge on pasture production. In: Grassland and land use systems, G. Parente (Publisher), 16^th EGF meeting, Italy, pp. 66–67.

FAO. 1991. The soil map of the world. FAO-UNESCO. Rome, 142 pp.

Moirón, C., Carral, E. & López-Mosquera, M.E. 1997. Contenu de metaux lourds dans des sols fertilises avec boues d'une industrie agroalimentaire. Experience pilote en Galice (NW Espagne). Deuxiéme Colloque International de Recherche sur Les Sous-Produits de Traitement et d'Epuration des fluides. Rennes. France.

Moirón, C. & López-Mosquera, M.E. 1998. Aplicación de residuos de una industria agroalimentaria: Efectos en el suelo. Agricultura Ecológica y Desarrollo Rural. Actas del II Congreso de la Sociedad Española Agricultura Ecológica SEAE. Pamplona. pp.443-448.

Thomas, R.L., Sheard, R.W. & Moyer, J.R. 1967. Comparison of conventional and automated procedures for nitrogen, phosphorus, and potassium analyses of plant tissue using a single digestion. Agron. Journal 59: 240-243.