Plant Production Department. Escuela Politécnica Superior. University of Santiago de Compostela, 27002-Lugo, Spain
ABSTRACT
The use of sewage sludge as a fertilizer of grassland could be a good option for eliminating these residues and introducing organic matter and nitrogen in agricultural lands where the parameters used to be very low. Sewage sludge had a good level of nitrogen but potash content used to be low. The complement of sludge with inorganic fertilizer can be a good option for compensating these potash low levels. Nitrogen from sewage could not be incorporated into the soil at the beginning of the season due to low temperatures and mineral nitrogen had to be added. The aim of the present experiment was to test the addition of different doses of nitrogen and potash as inorganic fertilizer in order to complement the sewage sludge experiment and to study the effects of these treatments on pasture production and botanical composition. The results indicated that the use of nitrogen as a complement of low sewage sludge doses should be necessary. Higher organic doses produced a bad clover establishment.
Keywords: clover, pasture production, pasture establishment.
INTRODUCTION
The use of sewage sludge as a fertilizer is an economic and ecological way to eliminate these residues. However, its use is limited by law because of heavy metals. Knowledge about complementary inorganic fertilization in pasciculture would help to make decisions about adequate doses as a complement of the inorganic fertilizers. Sewage sludge used to have lower potassium levels which is an essential nutrient for Trifolium development (González and Mosquera, 1991) and therefore nitrogen absorption by the soil could be limited. The objective of the present experiment was to study the effect of different sewage sludge doses complemented with potash and nitrogen on pasture production and botanical composition evolution.
MATERIALS AND METHODS
The experiment was conducted in Northwest Spain (Galicia). Two pasture mixtures were tested: a) 25 kg ha-1 Dactylis glomerata cv Artabro; and b) 3 kg ha-1 Trifolium repens var Huia and 25 kg ha-1 Dactylis glomerata cv Cambria and 3 kg ha-1 Trifolium repens var Huia. Soil analyses prior to the start of the study showed an average pH of 6.3, a high available phosphorous status (P2O5: 28 ppm) and a medium available potassium status (K2O: 87 ppm).
Treatments were applied in small plots (2 x 4 m2) placed following a completely randomized design with four replicas. Treatments consisted of three sewage sludge doses: 26 030 kg/ha (L40), 52 060 (L80) and 78 090 (L120), the same doses plus potash (100 units): L40K, L80K and L120K and the same doses plus potash and first nitrogen (100 and 40 units, respectively): L40NK, L80NK and L120NK. Two control treatments were established: no fertilization (NF) and the fertilization usually used in the area 120 P2O5, 120 K2O and 40 kg N a week after sowing (Min).
The dates of cutting were 2 and 30 April. In each cut an area of 4 x 0.9 m2 was mown and weighed in the field. Grass which had been mown from each plot was sub-sampled for dry matter (100 g, 18 hours x 80ºC) and botanical composition (100 g) determinations.
Production and botanical composition variables were analysed by ANOVA.
RESULTS AND DISCUSSION
Pasture production for the first two harvests is presented in Figure 1. Pasture production was increased by sewage sludge application in the first harvest, but no residual effect was found in the second one. Pasture production was not significantly different in non-fertilized and mineral treatments. However, plots fertilized with sewage sludge at this moment produced two, four and five times more with L40, L80 and L120 than with NF treatment, respectively. This could be explained because of the slow nutrient release in the organic fertilization proportioned nitrogen at the first of spring.
Figure 1. Pasture production in the first (black shade) and second (white shade) harvest for each treatment.
Potash addition did not modify pasture production, so pasture production was 4 317 and 4 371 kg/ha for treatments with no potash and potash, respectively. However, the use of first nitrogen increased significantly pasture production in the first harvest as well as in the global period. These increments were 26, 21 and 12 percent in the lower, medium and high sewage sludge doses in comparison with the same sludge dose without first nitrogen application. These differences could be explained because nitrogen was a factor less limiting at higher doses.
Doses applied generally are from 25 000 to 140 000 kg per hectare depending on farmer needs and enterprise (which made soil and sewage sludge analysis in order to follow state normative) and usually no nitrogen is applied. The use of nitrogen for the pasture establishment when low organic doses are applied could be interesting.
Dactylis cultivar treatment did not affect pasture production and botanical composition.
The percentage of sown species was affected by the different treatments. An interaction between the sown species and fertilization was shown. Dactylis glomerata percentage was higher in organic fertilized treatments, being very low in non fertilized treatment. However, Trifolium repens showed the inverse answer, it was higher on treatments without fertilized and mineral and very low in treatments with 120 units of nitrogen. This could be explained because nitrogen fertilization usually reduces clover content because favoured grass develops (Frame and Newbould, 1986). The total sown species percentages were significantly higher in treatments NF, Min, L40, L40K, L40KN, L80, L80K and L80KN due to high clover content in low sludge doses (L40) and NF and Min and high sown grass percentage in medium sludge doses (L80). The low clover percentage in L120 treatments made the sown species content in those swards significantly lower in spite of higher grass content.
Cerastium glomerata was a species that did not like fertilization. It showed a higher percentage in the treatment with no fertilization and was significantly lower in treatments which received more than 80 units of nitrogen.
CONCLUSION
The use of nitrogen as a complement to organic fertilization contributed to increased pasture production mainly in low doses. On the other hand, higher organic doses of sewage sludge reduced clover content significantly.
ACKNOWLEDGEMENTS
Thanks are expressed to Aurora López Veigas and Divina Vázquez Varela for sampling and processing in laboratory and to Mª de las Mercedes Fernández Couto Gómez and J. M. Cainzos Calvo from GESTAGÜA S.A. for field assistance. This experiment was financed by CAICYT.
REFERENCES
Bontoux, L., Vega, M. & Papameletiou, D. 1998. Tratamiento de las aguas residuales urbanas en Europa: el problema de los lodos. Instituto de prospectiva tecnológica (Eds) IPTS, abril, report nº 23. Comisión Europea.
Frame, J. & Newbould, P. 1986. Agronomy of white clover. Advances in agronomy. 20:1-87.
González, A. & Mosquera, R. 1991. Respuesta de la pradera mixta a la aplicación de potasio y nitrógeno en Galicia. XXXI Reunión Científica de la Sociedad Española para el Estudio de los pastos. Murcia, 1991.
