MATERIALS AND METHODS

The study was carried out in a pasture in Arisu village of Van province between the years of 2004 and 2005. According to average climatic data, the study area has an average temperature of 9.0°C and a total precipitation of 387.7 mm. Between the years 2004 and 2005, an average temperature of 9.5 and 9.0°C and an average precipitation of 426.7 and 337.9 mm were recorded. The study was carried out according to randomized block design with three replications. Parcel size was determined to be 3x3 = 9 m² and parcel intervals were planned to be 1.5 m and block areas intervals were planned to be 2 m. In the study four different doses of nitrogen (0, 4, 8 and 16 kg da^-1) and three different doses of phosphorus (0, 6 and 12 kg da^-1) were used. As nitrogen source, ammonium nitrate and as phosphorus source triple super phosphate was used. Fertilizer doses were applied to parcels which were determined after the snows melted in early spring each year. Harvesting was made according to inflorescences period of the poaceae. Plant heights were measured and averages were taken from each parcel at 20 points before the harvest. Each parcel was harvested in full, measured in the field and green herbage yields were determined. Plant material in harvested parcels was dried in incubator at 105°C and dry weights were calculated. Crude protein yields of the dries material were identified using Kjeldahl device. In both years of the study, two harvests were performed in each parcel.

Data were analyzed using the general linear model of SPSS statistical software version 11.5. The analyses were performed according to randomized blocks design (Efe et al., 2000). Treatment means within each date were compared using Duncan’s multiple range test with a 0.05 level of significance (Duzgunes et al., 1987).

RESULTS AND DISCUSSION

Plant height: The effects of nitrogen and phosphorus applications on plant height are given in Table 1. According to the Table, in the first year of the study, the statistical effect of nitrogen applications on plant height was 1%; the effect of phosphorus applications was 5%. In the second year of the study, the reverse was the case.

In the first year of the experiment, in the first harvest, plant heights varied between 35.1 and 67.5 cm; in the second harvest, plant heights varied between 37.0 and 62.2 cm. According to the average of two harvests, the highest plant height values, in terms of nitrogen, were obtained from 8 and 16 kg da^-1 applications (59.5 and 58.7 cm, respectively). The lowest plant height was measured as 39.0 cm from the parcels in which no nitrogen was applied. As for the phosphor applications in harvest averages, although there was no significant difference between the parcels in which 6 kg da^-1 phosphorus was applied and the parcels in which no phosphorus was applied, the highest plant height was obtained from 52.3 cm and 6 kg da^-1 application. Nitrogen x phosphorus interaction was not statistically significant; however the highest plant height value (62.1 cm) was obtained from 8 kg da^-1 nitrogen and 12 kg da^-1 phosphorus (Table 1).

In the second year of the experiment, plant height values varied between 57.0 and 73.7 cm; in the second year, plant heights varied between 56.4 and 73.1 cm. According to the average of two harvests, the highest plant height obtained from 16, 8 and 4 kg da^-1 nitrogen applications were found to be 67.7, 67.4 and 64.8 cm, respectively. As for the phosphorus applications, the highest plant heights were found to be 68.6 and 68.5 from 12 and 6 kg da^-1 doses. Although nitrogen x phosphorus interaction was found to be insignificant in statistical analysis, the highest plant height (73.4 cm) was obtained from 8 kg da^-1 nitrogen and 12 kg da^-1 phosphorus interaction (Table 1).

Study results indicated that fertilizer applications increased vegetation heights. The researchers reported that nitrogen accelerated vegetative growth and phosphorus encouraged root development and tillage and thus plant growth is enhanced (Booker and Demir,1963; Kacar, 1984). In the second year, the significant effect of phosphorus on plant heights was supported by the approach of Booker and Demir (1963) and Kacar (1984).

Green herbage yield: In both years of the study, the effect of nitrogen and phosphorus applications on green herbage yield was found to be statistically significant at 1% level. In the first harvest in 2004, green herbage yields varied between 393.3 and 1730.0 kg da^-1 and in the second harvest, yields varied between 486.7 and 1656.7 kg da^-1. In the year 2005, in the first harvest, green herbage yields varied between 740.0 and 1490.0 kg da^-1; and in the second harvest, the yield varied between 653.3 and 1613.3 kg da^-1 (Table 2).

In the first year of the study, as for the average values of both harvests, the highest green herbage yield from 8 and 16 kg da^-1 nitrogen applications were 1423.1 and 1273.3 kg da^-1. As for phosphorus applications, the highest yield values were 1142.1 and 1092.1 kg da^-1 from 6 and 12 kg da^-1 dose applications respectively.

Table 1:	Effect of nitrogen and phosphorus application on plant height (cm)
Values with different letters show significant effect

Table 2:	Effect of nitrogen and phosphorus application on green herbage yield (kg da-1)
Values with different letters shows significant effect

Although nitrogen x phosphorus interaction was found to be insignificant, the highest yield (1596.7 kg da^-1) was obtained from 8 kg da^-1 nitrogen and 12 kg da^-1 phosphorus application (Table 2).

In 2005, according to the average nitrogen applications of two harvests, it was found that the highest yield was obtained from 16 and 8 kg da^-1 applications (1426.1 and 1218.3 kg da^-1, respectively). As for the phosphorus applications, the highest yield was obtained from 12 and 6 kg da^-1 applications (1335.8 and 1220.0 kg da^-1 respectively). In the second year of the experiment, nitrogen x phosphorus interaction was not found to be statistically significant. The highest green herbage yield (1551.7 kg da^-1) was obtained from 16 kg da^-1 nitrogen x12 kg da^-1 phosphorus interaction (Table 2).

Significant increases were observed in green herbage yield after increased doses of fertilizer applications. The difference between 8 and 16 kg da^-1 nitrogen and 6 and 12 kg da^-1 phosphorus applications was not found to be significant in terms of their effects on green herbage. Therefore, the dose of the fertilizer should be determined after economic considerations. The findings are consistent with the findings of Alinoglu and Mulayim (1976).

Hay yield: In both years of the study, the effect of nitrogen and phosphorus applications on hay yield was found to be statistically significant at the level of 1%. In the first year, hay yields varied between 106.6 and 303.9 kg da^-1 in the first harvest; 144.0 and 300.6 kg da^-1 in the second harvest. In the year 2005, the yield varied between 303.2 and 664.2 kg da^-1 in the first harvest; 309.0 and 668.6 kg da^-1 in the second harvest.

When the averages of two harvests in the first year were analyzed, the highest hay yield (263.3 kg da^-1) from nitrogen applications was obtained from 8 kg da^-1 application. The highest yield from phosphorus application was obtained from 12 and 6 kg da^-1 applications (218.2 and 217.6 kg da^-1 respectively). Nitrogen x phosphorus interaction was found to be significant at the level of 1% and the highest hay yield (286.5 kg da^-1) was obtained from 8 kg da^-1 nitrogen x 6 kg da^-1 phosphorus application (Table 3).

In the second year of the experiment, according to the averages of two harvests, the highest yield (602.7 kg da^-1) was obtained from 16 kg da^-1 nitrogen application. As for phosphorus applications, the highest yield was obtained from 12 and 6 kg da^-1 applications (549.6 and 537.7 kg da^-1 respectively). Nitrogen x phosphorus interaction was found to be statistically significant at the level of 1% and the highest hay yield (666.4 kg da^-1) was obtained from 16 kg da^-1 nitrogen x 12 kg da^-1 phosphorus application (Table 3).

According to the findings of the study, the fertilizers with nitrogen and phosphorus content to be applied on the pastures in the region significantly increased hay yield. High hay yield was achieved particularly with nitrogen fertilization. In their fertilization experiments on rangelands and pastures, the researchers concluded that nitrogen fertilizers rapidly increased herbage yield (Altin et al., 2005; Gokkus, 1989; Gokkus and Koc, 1995; Comakli et al., 2005). In the study it was found that 8 kg da^-1 nitrogen and 6 kg da^-1 phosphorus applications will be sufficient for the pastures and higher doses do not result in significant increase in the yield. The findings are similar to those reported by Buyukburc et al. (1991), Akdeniz (1992), Tahtacioglu et al. (1993) and Hatipoglu et al. (2001).

Table 3:	Effect of nitrogen and phosphorus application on hay yield (kg da-1)
Values with different letters shows significant effect

Table 4:	Effect of nitrogen and phosphorus application on crude protein yield (kg da-1)
Values with different letters show significant effect

Crude protein yield: In both years of the study, the effect of nitrogen and phosphorus fertilizer applications on crude protein yield was found to be statistically significant at the level of 1%. In 2004, in the first harvest, crude protein yield values varied between 7.7 and 34.4 kg da^-1; in the second harvest the yield varied between 10.1 and 33.1 kg da^-1. In 2005, the yield varied between 34.0 and 77.6 kg da^-1 in the first harvest and the yield varied between 31.9 and 82.0 kg da^-1 in the second harvest (Table 4). As for the average of both harvests in the first year, the highest crude protein yield (29.2 kg da^-1) was obtained from 8 kg N da^-1 nitrogen application; the highest phosphorus yield (23.1 kg da^-1) was obtained from 12 kg P₂O₅/da application. However, there was no statistical significance between the first and second doses of phosphorus. Nitrogen x phosphorus interaction was found to have a statistical significance of 1%. The highest crude protein yield (33.4 kg da^-1) was obtained from 8 kg da^-1 nitrogen x 12 kg da^-1 phosphorus application (Table 4).

In the second year of the study, as for the average of two harvests, the highest crude protein yield (67.8 kg da^-1) was obtained from 16 kg N da^-1 nitrogen application; the highest yield (66.1 kg da^-1) from phosphor applications was obtained from 12 kg P₂O₅/da application. However, the findings indicate that there was no significant difference between N₈ ve N₁₆ and P₆ and P₁₂ levels of nitrogen applications. In other words, with the increase in application levels, no proportional increase was achieved in the yield. Nitrogen x phosphorus interaction was found to be significant at the level of 1%. The highest crude protein yield (77.6 kg da^-1) was obtained from 16 kg da^-1 nitrogen x 12 kg da^-1 phosphorus application (Table 4).

Gokkus and Altin (1986) reported significant increases in protein yield with 10 kg da^-1 nitrogen and 5 kg da^-1 phosphorus doses. Akdeniz (1992) reported that they have obtained high crude protein yields with 15 kg da^-1 nitrogen and 5 kg da^-1 phosphorus applications. Polat et al. (2007) obtained highest crude protein yield from the applied doses of 200 kg ha^-1 N and 150 kg ha^-1 P. In light of these results, because the amount of nitrogen and phosphorus doses show variety in different ecologies and vegetations while determining these doses, the effect of different ecologies and vegetations should be considered. Therefore, conducting regional studies are important.

CONCLUSIONS

In this study which analyzed the effects of various nitrogen and phosphorus doses on herbage yield in natural pastures, it was determined that nitrogen and phosphorus doses significantly affected plant height, green herbage and crude protein yield. Parallel to increasing fertilizer doses, significant yield increases were observed in analyzed criteria. However, the difference between the highest dose of nitrogen (16 and 8 kg da^-1); and the difference between the highest dose of phosphorus (12 and 6 kg da^-1) was not significant. According to these results it was concluded that in natural pastures having the same ecology, 8 kg da^-1 nitrogen dose and 6 kg da^-1 phosphorus dose applications would be sufficient for economic and environmental aspects. Considering the current status of natural pastures, these areas should be conserved and the practices for increasing the density of the flora should be applied.