Effects of intensive vegetable production on the hydrolyzable carbon, nitrogen and sulphur of a British Columbia Humisol

Acid hydrolysis was used to examine organic matter (OM), C, N and S in adjacent uncultivated and cultivated (40 yr) sections of a humisol. Paired soil samples were collected along two transects, both of which included deep organic soil and an exposed mineral ridge. About one-third of the OM was hydrolyzed. Cultivation had no effect on hydrolysis of the deep organic soil, whereas the amount hydrolyzed was significantly reduced by 4.1% in the ridge samples. Total C hydrolyzed ranged from 22.8 to 26.9% with no effect caused by cultivation or transect position relative to the ridge. In contrast, 71.1–80.4% of total N and 39.1 to 49.3% of total S were hydrolyzed. Cultivation significantly reduced the proportion of total N hydrolyzed in the deep organic soil and the proportion of total S hydrolyzed in both the deep organic soil and the ridge sections. On a total soil weight basis, cultivation reduced the amount of OM, C, N and S hydrolyzed in the ridge samples by 43, 38, 44 and 39%, respectively, but had much less effect on the deep organic soil samples. For the most part the distribution of N forms was similar for the four transect sections. Most of the S hydrolyzed was in the hydriodic acid-reducible sulphur (HI-S) form. The hydrolyzates from the cultivated soil samples had higher C-S:HI-S ratios. The amount of S hydrolyzed in the OM was not affected by cultivation, whereas residue-S was increased by 35.1 to 64.7%. The problems encountered with S hydrolysis analysis were discussed. Key words: Cultivation, humisol, hydrolysis, organic matter, carbon, nitrogen, sulphur