โ Scribed by R. P. Dick; P. E. Rasmussen; E. A. Kerle
No coin nor oath required. For personal study only.
Soil enzyme activities (acid and alkaline phosphatase, arylsulfatase, fl-glucosidase, urease and amidase) were determined (0-to 20-cm depth) after 55 years of crop-residue and N-fertilization treatment in a winter wheat (Triticum aestivum L.)-fallow system on semiarid soils of the Pacific Northwest. All residues were incorporated and the treatments were: straw (No), straw with fall burn (NoFB), straw with spring burn (NoSB), straw plus 45 k g N ha -1 (N45), straw plus 90 kg N ha -1 (N90), straw burned in spring plus 45 kg N ha -i (NnsSB), straw burned in spring plus 90 kg N h a -t (N90SB), straw plus 2.24 T ha-1 pea-vine residue and straw plus 22.4 T ha -1 of straw-manure. Enzyme activities were significantly (P<0.001) affected by residue management. The highest activities were observed in the manure treated soil, ranging from 36ยฐ70 (acid phosphatase) to 190070 increase in activity over the control (No). The lowest activities occurred in the NoFB (acid phosphatase, arylsulfatase and 8glucosidase) and N90 treated soils (alkaline phosphatase, amidase and urease). Straw-burning had a significant effect only on acid phosphatase activity, which decreased in spring burn treated soil when inorganic N was applied. Urease and amidase activity decreased with long-term addition of inorganic N whereas the pea vine and the manure additions increased urease and amidase activity. There was a highly significant effect from the residue treatments on soil pH. Arylsulfatase, urease, amidase and alkaline phosphatase activities were positively correlated and acid phosphatase activity was negatively correlated with soil pH. Enzyme activities were strongly correlated with soil organic C and total N content. Except for acid * Journal Paper No. 8072 of the Agricultural Experimental Station,
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