CO₂ emitted from the arid farming land is an important source of greenhouse gases, nitrogen application is an effective approach to increase production of farming land, soil quality degraded, however, CO₂ emission will be increased by unreasonable fertilization. Therefore,it is an important problem need to be solved urgently now to reduce the greenhouse gas emissions of farming land by reasonable fertilization without crop yield loss.
An experiment was conducted in the crop planting station of Northwest A&F University in Yangling Shaanxi, P.R China to explore the effects of different types and dosages of nitrogen fertilizers on soil enzymatic activities and soil CO₂ emission in the arid farming land of summer maize and to elucidate the relationship of soil CO₂ emission and activities of urease, invertase, and catalase, which will provide evidence for carbon emission reduction in the arid farmland management mode of summer maize.
Nine treatment levels were set, including four levels each of available nitrogen (urea) and low-release nitrogen, specifically, 80 kg/hm² urea (N1), 160 kg/hm² urea (N2), 240 kg/hm² urea (N3), 320 kg/hm² urea (N4), 80 kg/hm² slow-release fertilizer (SR1), 160 kg/hm² slow-release fertilizer (SR2), 240 kg/hm² slow-release fertilizer (SR3), 320 kg/hm² slow-release fertilizer (SR4), and no-fertilizer treatment served as control (CK). The results showed that CO₂ emission and activities of urease, invertase and catalase in the fertilizer treatments were higher than those in no-fertilizer treatment (P<0.5). The averages of urease activity in urea and slow-release nitrogen treatments improved by 66.75% and 67.50% respectively compared with no-fertilizer treatment;The averages of invertase activity in urea and slow-release nitrogen treatments were 45.55% and 62.75% respectively higher than those in no-fertilizer treatment;The averages of catalase activity in urea and slow-release nitrogen improved 45.00% and 46.75% than those in no-fertilizer treatment;The averages of soil CO₂ emission in urea and slow-release nitrogen were higher 42.34% and 32.42% respectively than no-fertilizer treatment. The range of soil CO₂ emissions in slow-release nitrogen was smaller than in urea, which indicated that slow-release nitrogen fertilizer can improve effectively soil enzymatic activities and reduce soil CO₂ emissions. During the whole growth period, the same trends of three enzymes activities and CO₂ emissions were detected between the treatments of available nitrogen and slow-release nitrogen, but maximum values reached at different stage, i.e., at jointing stage for urease activity, at maturity stage for invertase activity, at tasseling stage for catalase activity, and at jointing stage for soil CO₂ emission. There were significant differences (P<0.5) between the CO₂ emissions of nitrogen and slow-release nitrogen, 459.12 mg·m^-2·h^-1 and 427.11mg·m^-2·h^-1 respectively. Correlation analysis showed that, a highly positive correlation existed between soil CO₂ emission and activities of urease, catalase and invertase. Correlation coefficients of soil CO₂ emission with activities of urease, catalase, and invertase were 0.79, 0.80, and 0.64, respectively. In conclusion, at the same application levels of available nitrogen, slow-release nitrogen fertilizer can improve effectively soil quality of arid farming land and reduce soil CO₂ emission compared with urease.