In this experiment various combinations of organic and inorganic fertilizers input for their residual impact on biochemical, biological and physic-chemical attributes of arable field was assessed. Table 1 exhibit that highest SOC contents under the OM (12.20 C kg-?1) followed by HOM (9.28 g C kg?1) treatment with significant (P ? 0.05) difference than control. Contents of total N in soil were statistically (P ? 0.05) higher with the OM (1.56 g N kg?1) and HOM (1.10 g N kg?1) treatments than NPK (0.80 g N kg?1), NP, NK, PK and CK. These results are in lined with the work of many researcher (Hopkins and Shiel, 1996; Malhi, Wang et al. (2005) who observed that relative to the control, biomass C and other nutrients (D-amino acids) had been increased by FYM and LFOM, and reduced by NPK treatment. Moreover, the presence of C and N contents in soil was attributed to the amount of crop residues, which in turn was associated with crop yield (Malhi, Wang et al. 2005). N-fertilizer application could decrease the acidic amino acids and increase neutral amino acid concentration in soil (Malhi, Wang et al. 2005). This strongly suggests that acidic amino acids are a source for N mineralization and that neutral amino acids represent storage pools for soil organic N and C (Malhi, Wang et al. 2005). Malhi, Wang et al. (2005) suggest that proper N fertilization may be an important consideration, as amino acids in soil increased considerably with N application (Malhi, Wang et al. 2005). Peroxidase could also be considered to enhance soil C and N mineralization via improving the bioavailability of reducing sugars and amino acids (Malhi, Wang et al. 2005).
The pH values were slightly lower than that of original soil (8.65), being highest in control (8.61) followed by NK (8.58) and PK (8.35) differing non significantly. The lowest pH was found under OM and NP treatments with a value of 8.01. Lowest pH of soil may be considered as favorable for accumulation of acidic to neutral amino acids.
Mass proportions of macroaggregates (M) were significantly (P ? 0.05) enhanced with manure amendments as 30.8% under HOM and 17.7% through NPK, while the lowest percentage (8.8%) was obtained from OM and NP. However, the proportions of microaggregates (m) were increased in the OM and NP treatments as compared to control and other treatments, showing results just the opposite to that of macroaggregates. Thus treatments of OM (71.5%) and inorganic fertilizer NP (70.1%) showed the highest mass proportion of microaggregates. Free silt + clay (SC) portion reflected significant reduction with HOM (14.1%) and NPK (19.4%)
The soils amended with OM resulted in a statistical increase (P ? 0.05) in L-aspartic acid followed L-alanine and L-lysine as compared to other amino acid and all other treatments as well as control. This was in a pace with that of Andersson and Berggren (2005) who studied that the dominating amino acids during their investigation were glycine, glutamine/histidine, aspargine/serine and aspartic acid other than arginine. So OM was found to be a best treatment among all other treatments. Which may be supported by the finding of Malhi, Wang et al. (2005) who consider OM as an important factor to sustain and improve soil quality and productivity. Similarly, our results also indicated that OM followed by HOM treatment was found to be the most effective among all other treatment for enhancing the D-amino acid contents. This was in contrast to that of Brodowski, Amelung et al. (2005) who suggested that the amount of D-amino acids can be declined bi-exponentially to about 30% with increasing number of years for cropping. As the years of arable cropping increased, the proportions of D-alanine and D-glutamic acid increased relative to the respective L-enantiomers. In contrast, the D=L-ratios of leucine and aspartic acid declined in the long-term cultivated plots, probably reflecting losses of old amino acid-N reserves at the most degraded arable land (Brodowski, Amelung et al. 2005).