RESULTS

The mean values for the parameters of the agricultural soils under study at different altitudes are presented in Table 2. In this study, the mean value for the pH, percent organic C, content of mineralizable N, available phosphorous and available K in soil ranged from 5.3-6.2, 1.05 to 2.44, 166.84 to 323.4 kg ha^-1, 21.1 to 31.1 kg ha^-1 and 153.30 to 310.59 kg ha^-1, respectively. Also, the mean microbial biomass carbon for the soil sample ranged from 194.89 to 367.76 mg kg^-1 soil.

Data on pH revealed that soil of the Almora is acidic in nature. Lowest pH (5.3) was recorded at altitude of 3000-3500 feet followed by 5.5 at 4500-5000 feet of altitude. Percent organic C tended same as pH of the soil. Accordingly for all other soil chemical parameters studied, the maximum value was observed at higher altitude. The difference in mean value with altitude for all the parameters was statistically significant at p = 0.05 except the pH.

Statistical analysis of the data using ANOVA in MS Excel revealed that organic C possess a strong positive correlations with mineralisable nitrogen (r = 0.81**) and potassium (r = 0.84**). Also organic carbon was positively correlated with phosphorous content (r = 0.65*) (Table 3). Soil pH showed positive correlation with the organic carbon (r = 0.73*) and mineralisable N (r = 0.77*). The available phosphorous content of the soil was found to possess positive correlation with Total N content (r = 0.76*).

β-glucosidase, an important soil enzyme involved in carbon cycle, varied from 419.73 to 532.01 ppm pNP g^-1 soil h^-1 while the urease activity involved in nitrogen assimilation, ranged from 216.99 to 395.28 ppm urea hydrolysed g^-1 soil h^-1 (Table 2). Soil microbial biomass carbon in the agricultural soil at different altitudes also showed variation ranging from minimum value of 194.89 mg kg^-1 at 3000-3500 feet to maximum value of 367.76 mg kg^-1 at an altitude of 6500-7000 feet. The rise or fall in the microbial activity was variable. β-glucosidase possessed significant positive correlation with urease (r = 0.71*), available P (r = 0.75*) and with SMBC (r = 0.88**). Similarly, urease activity was also found to be positively correlated with available P (r = 0.84**). Altitude significantly influenced the enzymatic activities erratically and its activities was highest at 6500-7000 feet of altitude for both the enzymatic activities. Lowest activity of β-glucosidase and urease was recorded at 5000-6000 feet of height.

Table 2:	Effect of altitudes on soil health characteristics of Agricultural soil of Almora district
NS: Not significant

Table 3:	Simple significant correlations coefficients of different soil health properties
*Significant at p = 0.05, **Significant at p = 0.05

DISCUSSION

Altitude is one of the main topographic factors affecting the physicochemical and biological properties of the soil and hence the overall soil health. People of Uttarakhand and other hilly areas usually add waste product of plants in their fields to meet the nutrients requirements of the crops. They depend totally on the organic manures in the form of farm yard manures for their agriculture. But now a days some farmers also had started using chemical fertilizer specially, urea. Apart from it the increasing population density leads to the conversion of more forest land into agriculturable land.

The soil of the region show higher percent organic carbon as compared to the soils of plains. It is due to the addition of more organic waste as farm yard manure and leaf litter from plants in soil which plays a major role in increasing the carbon content of the soil. Also agriculturable soil at the high altitude has more carbon as compared to the soils at low altitude. This might be due to the conversion of forest in agriculturable land at high altitude while frequent agricultural practices at low altitude leads to the loss of organic matter from soil pool. This statement is in conformity to the findings of Abera and Belachew (2011). Hence, it has been observed that people at these altitude depends on more organic matters for the carbon source. As a result the addition of organic matter contributed to the soil N, P and K which caused highly significant positive correlation with content of percent organic C. It is true as the content of organic matter in the soil has lead to the increment of mineralisable nitrogen, phosphorous and potassium in the soil. A positive and significant correlation of organic carbon with nitrogen, phosphorous and potassium has been reported by other researchers (Rezende et al., 2004; Verma et al., 2010; Onweremadu, 2007).

Also the variation in the carbon content was significantly influenced by the variation in altitude. Consequently, the nitrogen, phosphorous and potassium content of the soil were also increased with altitude.

Addition of organic matter has been found to be good agricultural management to increase the content of organic carbon. The higher organic matter depicts the high carbon content. It has also been suggested by Pascual et al. (1997) and Uyanoz et al. (2005) that the higher biomass reflects the potential for soil’s organic matter mineralization. As a result the nutrient, i.e., N, P and K content of the soil increases. The microbial biomass carbon was found to be influenced by the altitude. The agricultural soil at higher altitude has higher microbial biomass carbon.

Waring and Schlesinger (1985) reported that microorganisms can mineralize up to 80% of dead plant materials. With the increasing awareness of the soil microbial activities many studies have been conducted in this regard. Temperature, pH, soil water content, land use changes and nutrient availability have been identified as key variables controlling soil microbial activities. These facts are in evident to the experimental findings of Anderson and Nilsson (2001), Allison et al. (2008), Ye et al. (2009), Venkatesan and Senthurpandian (2006), Kang et al. (2003), Jia et al. (2006) and Enowashu et al. (2009).

Debosz et al. (1999) and Eivazi and Tabatabai (1988) have stated that β-glucosidase activity in the soils is ideal to examine the importance of physico-chemical controls on the turnover of soil organic matter. β-glucosidase is synthesized by soil microorganisms in response to the presence of suitable substrate. It has been found in the current study that its activity is significantly influenced by the variation in altitude. It was maximum (32.01) at high altitude of 6500-7000 feet and comparatively lower at lower altitudes. It was due to the variation in substrate availability in soil. The enzymatic activity at an altitude of 3500-4500 and 4500-6000 has little variation in their activity which is statistically insignificant. This might be due to limitation of the substrate in soil or some other factors may be involved for this variation to occur. Enzymatic activities at high altitude seem to be more prominent due to the availability of substrate or may be supported by the other environmental factors. These environment factors may be temperature or pH of the soil for its high activity. Substrates in the form of organic matter are the source of carbon and nitrogen for the microorganism. Xu et al. (2000), Xue et al. (2003), Wang et al. (2006) and Liu et al. (2007) deserve to mention that the kind and number of soil microorganisms determine, to a certain extent, the source of soil enzymes. Activity of the β-glucosidase reflects the status of labile organic C turnover in the soil, confirmed by a positive correlation between β-glucosidase activity and organic carbon in soil.

Variation in altitudes greatly influences the activity of urease. Urease activity was found to be greater at high altitude as compared to the lower altitude. This is due to the presence of high organic matter content in the soil as a result of shifting cultivation and addition of huge amount of organic matter and leaf litter from the trees. Beri et al. (1978) had reported that soil urease activity is largely controlled by the organic carbon status of the various soils. The positive correlations of urease activity with organic carbon (r = 0.65) suggested that organic matter content accounted for most of the variations in soil urease activity. This was in accordance to the finding of Tabatabai (1977) who reported that urease activity was significantly correlated with organic carbon.

CONCLUSION

With the increasing concern about the soil health, researchers have started working various indicators for soil health assessment. The present study concludes that while going for a biological indicator it is necessary to keep in mind the influence of the altitude. Soil enzyme, a bioindicator, shows a great variation in its activity with the altitude.

ACKNOWLEDGMENTS

Authors thank GB Pant Institute of Himalayan Environment and Development (GBPIHED) for funding the research work. We also acknowledge Department of Soil Science and Agricultural Chemistry, Institute of Agricultural Science, BHU, Varanasi for providing the facilities for the research to be conducted.