Consecutive Biochar Application Alters Soil Enzyme Activities in the Winter Wheat-Growing Season

Soil enzymes catalyze key biochemical processes in organic matter decomposition and nutrients cycles and are regarded as indicators of soil quality. In this study, we investigated the impact of 4 consecutive years of biochar (corncob; 360 degrees C) amendment on dynamics of enzyme activities (i.e., invertase, urease, catalase, and alkaline phosphatase) during the winter wheat (Triticum aestivum L.) growing period in Northern China. The experiment consisted of four treatments: control (CK), biochar rate at 4.5 t . ha(-1) . y(-1) (B4.5), biochar rate at 9.0 t . ha(-1) . y(-1) (B9.0), and crop straw return (SR). Four times throughout the wheat growth period (i.e., 5 Nov. 2010; 26 Mar. 2011; 25 Apr. 2011; 5 Jun. 2011), we determined the enzyme activities down to the 30-cm depth of the soil profile (i.e., 0-5, 5-10, 10-20, and 20-30 cm). Results showed that there were considerable fluctuations in enzyme activities across the observed period and depths. All enzyme activities decreased significantly in deeper soil horizons. High biochar amendment rates (B9.0) lead to the peak activities of invertase, urease, and phosphatase occurring in the 0- to 5-cm layer on 25 Apr. 2011 samples. The greatest catalase activity under B9.0 was found on 26 Mar. 2011 samples. In addition, the effect by B4.5 and SR on enzyme activities was variable and limited. These data support the conclusion that consecutive application of biochar for 4 years increased enzyme activities, which potentially influence soil nutrients dynamics under field condition, although the effects were dependent on sampling depth and time.