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ORGANIC FERTILIZATION ON HIGHLAND PASTURES - A. Rigueiro-Rodríguez, R. Mosquera-Losada and L. Díaz-López


Departamento de Producción Vexetal, Escuela Politécnica Superior, Universidad de Santiago de Compostela, 27002-Lugo, Spain

SUMMARY

The experiment was conducted in Pol (Lugo) (NW of Spain). The objective of this experiment was to compare the use of sewage sludge at different doses on pasture production growing under Pinus radiata D. Don forest. The experimental land used was at 450 m above sea level and had a slope of 20 percent. The soil was acid (pH around 4.5) and had low levels of nutrients. The experiment tested three fertlization doses (nitrogen at a rate of 40, 80 and 120 kg ha -1) combined with two doses of lime (none and 2.5 t ha -1). The sowing mixture was Lolium perenne cv. Brigantia, Dactylis glomerata cv. Artabro and Trifolium repens cv. Huia. The use of organic fertlization and lime application increased pasture production. Trifolium content was positively affected by lime application.

INTRODUCTION

The large areas of forest (1 000 000 ha) and shrubs (1 000 000 ha) in Galicia make it interesting to study the possibility of recycling materials like sewage sludge as tree fertlizer because of the new European Commission Directive that will reduce the disposal of sewage sludge at sea and in landfill. Furthermore, the introduction of fertlization in woodland increases pasture production (Rigueiro et al., 1998) and therefore reduces fire risk and produces meat output which will generate an improvement in farm income. For these reasons, the present experiment aimed to test four sewage sludge doses, with liming in two doses, in highland sown pastures.

MATERIALS AND METHODS

The experiment was conducted at Pol in Lugo (NW of Spain). A grass mixture (25 kg of Lolium perenne cv. Brigantia + 10 kg of Dactylis glomerata cv. Artabro and 4 kg of Trifolium repens cv. Huia) was sown in autumn 1997. Soil analyses before sowing revealed a poor fertility status since available nitrogen, phosphorous and potash were 0.28 percent, 4 ppm and 63 ppm, respectively. Pasture was established under five year old pines (density of 1 667 trees/ha). Botanical composition previous to grass and legume sowing was composed by shrubs (Erica sp, Calluna vulgaris, Daboecia cantabrica, Ulex europaeus and Ulex galli) which contributed to fire risk in the area. After shrubs were removed, half of the experimental plots received liming at a rate of 2.5 t/ha. All the plots were fertlized with 120 units of P2O5 and 100 units of K2O. After inorganic fertlization the mixture was directly sown and was fertlized with nitrogen two weeks later.

Four treatments were established in every liming dose (SC: without lime and CC: with lime) and consisted of four sewage sludge doses L0: 0, L1: 19 919, L2: 39 838 and L3: 59 757 kg of sewage sludge per hectare in April. The treatments were randomly distributed in plots of 96 m2.

Table 1. Soil heavy metal composition (soil real), soil maximum content allowed by directives (soil allowed) and heavy metals applied with different sewage sludge doses (Sludge L1, L2 and L3) and maximum heavy metal content on sludge allowed by normative (sludge allowed).

(ppm)


Cd

Cu

Ni

Pb

Zn

Hg

Cr

Soil

real

0

3.3

2.6

7

6.6

0

13

allowed

1

50

30

50

150

1

100

Sludge

allowed

0.15

12

3

15

30

0.1

3

L1

0.024

1.21

0.1

1.01

4.84

0.007

0.19

L2

0.049

2.43

0.2

2.02

9.68

0.014

0.38

L3

0.072

3.63

0.3

3.03

14.52

0.021

0.57

Four randomized samples of 0.09 m² per plot were taken at the same time as harvesting in June. Samples were transported to the laboratory and stored at 4ºC. Samples were hand separated to determine botanical composition by weight.

RESULTS AND DISCUSSION

Soil heavy metal contents in the Galician highlands, heavy metal of soil and sludge allowed by diectives and heavy metals applied with each sewage sludge dose are presented in Table 1. All the parameters are into the range established by the directive.

Soil heavy metal content and allowed as well as maximum established doses and used doses were utilized in order to calculate the number of annual applications of sludge for determination of heavy metal limits for agronomic use of sludge. Calculations are shown in Table 2. Maximum annual doses allowed by law are too high for agronomic use, for this reason high doses (120 kg N/ha quickly released) can be applied more times than maximum. No soil washing was taken into account for these calculations. The heavy metals were ordered (according to limits) as Hg followed by a second group of Cu, Cd and Pb and a third group of Ni, Cr and Zn. The number of times that sewage sludge could be applied was underestimated as soil washing and pasture extraction were not taken into account. Usual doses in highlands did not use more than 40 units of nitrogen per hectare which allows a theoretical 40 sludge application. However, improvements in sludge quality, with a reduction of Hg concentration, would permit 120 applications.

Pasture production and the percentage of sown and most common unsown species are presented in Table 3. There was only one cut in the spring that produced around 2 750 kg DM per hectare; this is a normal value in the mountain area. Pasture production was positively and significantly affected by sludge fertlization and liming. This response could be explained by the nutrient supplement of sludge.

Table 2. Number of applications of three tested doses of sewage sludge, calculated with a maximum annual allowance of heavy metals.


Cd

Cu

Ni

Pb

Zn

Hg

Cr

Allowed

20

11

27

8

14

3

87

L1

120

115

786

127

354

40

1 343

L2

60

57

393

63

177

20

671

L3

40

38

262

42

118

13

447

Table 3. Pasture production (Prod. t/ha) and percentage of Dactylis glomerata (Dg), Lolium perenne (Lp), Trifolium repens (Tb), Sown species (Sown), Arrhenatherum elatius (Arrhen) and Agrostis curtisii (Agrostis) and total explained (%Tot) in the pasture.

Nitrogen

L1

L2

L3

L0

Sig. Diff.

Liming SC

CC

Sig. Diff.

Production









(t / ha)

2.75

2.46

3.5

2.23


2.42

3.06


Dg

27b

25b

39c

24a

*

26.97

21.84

ns

Lp

3c

5abc

13b

1a

***

2.25

9.60

***

Tb

2.77

6.35

4.52

3.41

ns

0

8.43

***

Sown

33.71b

36.71b

57.21c

10.64a

***

29.31

39.83

ns

Arrhen

43.11

11.54

26.23

24.9

ns

17.54

35.36

ns

Agrostis

8.32c

30.32b

2.14a

42.51c

***

29.44

12.21

*

%Tot.

85.14

78.57

85.58

78.5


76.29

87.40


Differences between the high doses of sewage with respect to no fertlization were 1.2 t which represented a 57 percent increase in production. Liming pasture produced around one tonne more than plots that had not received liming, which meant a difference of 26 percent. Pasture production was related to the presence of sown species in the different treatments, as expected. Dactylis glomerata, Lolium perenne, Arrhenatherum elatior and Agrostis curtisii represented 82 percent of total species present in the pasture.

The percentage of sown grasses were significantly affected by sludge dose but no effect of liming was detected. Both Lolium perenne and Dactylis glomerata were positively related with sewage application, that is to say that the application of 59 670 kg of sludge per hectare increased the sown grass content by 45.5 percent. Sowing should always be joined with fertlization in the Galician mountains because the absence of this practice leads to a low percentage of sown grass species, Rigueiro et al (1998). Dactylis glomerata had a better establishment than Lolium perenne as the latter is a species with higher soil fertility and climatic condition requirements (Piñeiro and Pérez, 1990), in spite of having a high sowing rate. Trifolium repens was not significantly affected by sewage sludge dose. However, it was significantly absent in pastures with no limed soils, Rigueiro et al (1998). The pH of none limed and limed plots was around 4.5 and 5.8, respectively. Liming did not affect the percentage of Dactylis glomerata in the pasture, however the absence of this treatment reduced significantly the Lolium content in the pasture. Agrostis curtissii seemed to substitute sown grasses as this species represented the highest percentage on plots without liming or sewage sludge application.

In conclusion, the use of sewage sludge in highlands will improve pasture production and it is convenient to introduce more quality species with the exception of Trifolium if no liming is applied. The use of sewage sludge in highlands will be limited in time by Hg content.

ACKNOWLEDGEMENTS

Thanks are expressed to Aurora López Veigas and Divina Vázquez Varela for sampling and processing in the 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 Xunta de Galicia.

REFERENCES

Rigueiro, A., Mosquera, R. & López, D. 1998. Estudio del uso de lodos de depuradora en la instalación de praderas bajo pinar. XXXVIII Reunión Científica para el Estudio de los Pastos.

Piñeiro, J. & Pérez, M. 1990. ¿Raigrás inglés o dactilo para pastos de larga duración en Galicia? Reunión Científica de la Sociedad Española para el estudio de los pastos. 286-293.


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