Responses of soil respiration to N fertilization in a loamy soil under maize cultivation

Abstract

To understand the effects of nitrogen fertilization on soil respiration in an intensively cultivated fluvo-aquic loamy soil, a field experiment was conducted in the Fengqiu State Key Agro-Ecological Experimental Station, Henan province, China. The experiment consisted of five treatments: unplanted and N-unfertilized soil (CK0), unplanted soil treated with 150 kg N ha- 1 (CKNL), maize (Zea mays L.) planted and N-unfertilized soil (N0), and planted soils fertilized with 150 kg N ha- 1 (NL) and 250 kg N ha- 1 (NH). Soil CO2 efflux during the maize growth season was significantly affected by soil temperature and also by soil moisture when the opposite effect of soil moisture below and above the optimum values was distinguished. There was a significant interdependence between soil temperature and soil moisture in the effect on soil CO2 efflux in the presence of maize plants. A logarithm transformed regression equation including soil temperature (T) and soil moisture (W) was developed as y = a + bT log(W). This equation accounted for 60-71% of the seasonal variation in soil CO2 efflux, which better depicted soil CO2 efflux than did a regression equation with soil temperature alone in the maize planted soils. Cumulative soil CO2 emissions in the CK0 and CKNL treatments were estimated as 229 ᠱ2 and 245 ᠱ7 g C m- 2, respectively during the experimental period and the application of N fertilizer slightly increased soil basal respiration by 6.5% through enhancing microbial biomass. In contrast, cumulative seasonal soil CO2 emissions were 7.4% lower in the NL (461 ᠳ3 g C m- 2) and NH (462 ᠱ3 g C m- 2) treatments than in the N0 treatment (498 ᠳ2 g C m- 2), indicating that N fertilization marginally significantly depressed soil respiration (p = 0.06). N application rates, however, did not exhibit any effects. Our results suggest that the effects of N fertilization on soil respiration mainly depended on the concentration of easily decomposed organic carbon in soil and N fertilization possibly reduced soil respiration in the planted soils when N released from the decomposition of native soil organic carbon roughly met the demand for maize growth.