Effect of Cropping Systems on Enzyme Activity in a Marvyn Sandy Loam Soil.

Cover crops play an essential role in nutrient recycling in soil. Coupled with no-till cropping systems, cover crops increase soil organic matter content and enhance soil enzyme activity. We investigated the effect of two tillage systems (conventional and no-till) and two cover crops (black oat, Avena strigosa; crimson clover, Trifolium incarnatum; and their association) on arylamidase (EC 3.4.11.2), L-asparaginase (EC 3.5.1.1), and urease (EC 3.5.1.5) activities in tomato field plots following harvest. The cover crops were planted in November 2005 and early in May 2006, they were plowed and incorporated into soil (conventional tillage) or mowed and left on the soil surface (no-till). Broiler litter as source of N fertilizer was applied at a rate of 4.6 t ha^-1, triple super phosphate at 180 kg P₂O₅ ha^-1, and potassium chloride at 120 kg K₂O ha^-1 according to soil testing recommendations. Tomato (Lycopersicon esculentum Mill.) seedlings were transplanted and grown for 60 days. After harvest, ninety-six core soil samples were collected at incremental depths (0-5, 5-10, and 10-15 cm). In general arylamidase activity decreased with increasing soil depths in the no-till black oat plots from 47.4 (0-5 cm) to 15.4 µg β-naphthylamine g^-1 h^-1 (10-15 cm) while L-asparaginase and urease activities in the no-till plots remained constant throughout the soil profiles (26.9 and 16.5 µg NH₄⁺ - N g^-1 2h^-1, respectively). In the conventional tillage plots, arylamidase and urease activities were highest in the crimson clover-black oat mixture plots (29.0 µg β-naphthylamine g^-1 h^-1 and 18.3 µg NH₄⁺ - N g^-1 2h^-1, respectively). All the control plots (weed) showed lowest enzyme activities suggesting that cover crops significantly increased enzyme activities in soil.