Soil enzyme activities in decomposition of different quality organic residues applied in a sandy soil for 14 years

Abstract

The objective of this study was to assess the activities of some decomposition enzymes in sandy soil continuously treated with different-quality organic residues over 14 years which led to different degrees of soil organic matter accumulation. There were 6 treatments including no organic input application (control), and plots treated to each organic input: groundnut (Arachis hypogeae) stover, freshly fallen tamarind (Tamarindus indica) leaf and petiole litter, freshly fallen dipterocarp (Dipterocarpus tuberculatus) leaf litter, and rice straw (Oryza sativa) annually applied at the rate of 10 Mg dry weight ha-1 y-1, while mixed groundnut + rice straw (at the ratio of 1:1 dry weight) was applied at the rate of 20 Mg ha-1 y-1. Highest activity of invertase was found in groundnut (high quality with high N, and low lignin and polyphenol contents) and tamarind (intermediate quality) treatments (0.40-0.41 mg GE g-1 soil DW h-1). Highest activity of B-glucosidase (59.5 g p-nitrophenol g-1 soil DW h-1) was also found in tamarind treatment. Highest activity of phenoloxidase was found in dipterocarp (low N, but high lignin and polyphenol contents) followed by the mixture of rice straw + groundnut, and tamarind in the range of 3.1-3.4 μmol substrate converted g-1 soil DW h-1. On the other hand, rice straw had the lowest activities of all enzymes among residue treatments. The results of this study served to show the link between enzyme activities and SOM accumulation (highest SOM under tamarind, and lowest under rice straw treatments), and bring about in-depth understanding of soil microbial functions in the decomposition of different-quality organic residues through enzyme activities.