Amidohydrolases Activities in Conventional and Conservation Tillage Systems.
Said Hamido and K. Kpomblekou-A. Tuskegee University, 210 Campbell Hall, Tuskegee, AL 36088
Methyl bromide (CH3Br, MeBr) is used in crop production to manage most soil borne fungi, bacteria, nematodes, and weeds. It was phased-out in United States in 2005. Methyl bromide has many side effects on the ozone layer, animals, and people. Cover crops can be used as an alternative to methyl bromide in vegetable production to control weed population and improve soil health. We investigated enzyme activity in a tomato field preceded by black oat or crimson clover in conventional and conservation tillage systems. The cover crops were planted early in fall 2005, plowed and incorporated into soil (conventional tillage) or mowed and left on the soil surface (conservation tillage). Broiler litter as source of N fertilizer was applied at a rate of 4.6 t ha-1, triple super phosphate at 180 kg ha-1, and potassium chloride at 124 kg ha-1. Tomato (Lycopersicon esculentum Mill.) seedlings were transplanted and grown for 60 days. Ninety-six core soil samples were collected at incremental depths (0-5, 5-10, and 10-15 cm) using an auger to investigate enzyme activity. The moist soil samples were passed through a 2-mm sieve and kept at 4 ºC until use. The enzymes studied were those involved in hydrolysis of native and added organic nitrogen in soils (arylamidase, [α-aminoacyl-peptide hydrolase EC 18.104.22.168]; L-asparaginase,EC 22.214.171.124; L-glutaminase,EC 126.96.36.199; and urease, EC 188.8.131.52). Results showed that on average arylamidase activity increased from 3.23 in the control treatment to 10.1 μg β-naphthylamineg-1 h-1 in the black oat treatment plot.