5:15 PM - 6:30 PM
[AGE27-P13] Monitoring of soil gas environment in soybean fields under different fertilizer managements
Keywords:Soybean, Soil gas environment, Monitoring, Soil respiration
It is known that significant amount of CO2 is released from the soil to the atmosphere. Previous studies showed that applied fertilizer influences the CO2 emissions from soils based on the field monitoring of soil gas environment. However, there are a few investigations about continuous monitoring of soil gas at minutes to hourly time interval. Therefore further understandings on effects of fertilizer managements on soil gas environment and GHG emission are required, eg., the response of soil respiration to rainfall events, and emission rate in response to type of the applied fertilizer. This study aims to clarify the effect of different fertilizer managements on the soil gas movement during the cultivation period.
Field monitoring was conducted at soybean fields in Koriyama City, Fukushima prefecture with 4 different treatments: no fertilizer (NF), cow manure (CM), chemical fertilizer (CF), and without crop (WC). The CO2 and O2 concentration at different depths (10, 25 cm) were monitored at every 1hr interval and recorded with data loggers (CR1000, Campbell Scientific). The CO2 concentration was measured using NDIR type CO2 concentration transducers (GMM221, Vaisala) and O2 concentration was measured using Galvanic oxygen sensors (CAP-SO-210, Apogee), respectively. Water content, soil temperature, and electrical conductivity at different depths (10, 18, 25 cm) were monitored at every 30 min interval using 5TE sensors (METER Group). The monitoring has been done from June 29 till November 12, when the soybeans were grown. Soil hardness profile was also measured using a digital penetration type soil hardness tester (DIK-5532, Daiki) during flowering and harvesting period. The soil samples were taken at 5, 10, 18 and 25 cm deep. Basic physical properties, gas diffusion coefficient, air permeability and amount of microbial biomass were measured using the soil samples. The monitored gas concentrations and gas diffusion coefficients were used to calculate gas fluxes at 0-10 cm and 10-25 cm deep.
The CO2 fluxes at each depth of the CM plot were smaller than those at the NF plot. This was because deeper layer of CM plot was more compacted and the soil water content was higher than the NF plot, inducing the reduction on the soil respiration. Similar behavior was observed at the CF plot where lower CO2 flux at 10-25 cm deep after September were observed than at the NF plot. This was also thought to be because shallower layer of the soil at CF plot was compacted and generally wet. The CO2 concentration at the WC plot were larger than those at NF plot. The soil hardness measurements showed that the surface soil of the WC plot was highly compacted, which inhibited CO2 emission to the atmosphere. Cumulative CO2 emission after August was well correlated to mean water content regardless of different fertilizer managements. In the comparison of soil gas dynamics between plots, the effects of water contents among the plots were more significant than effects of applied fertilizer. There were cases where the gas concentrations were different under wetting and drying processes before and after rainfall events even at the same soil water content condition. Hysteresis of soil gas diffusivity during wetting and drying and activation of microbial respiration induced by increase of soil water content were considered as possible reasons for these phenomena.
Field monitoring was conducted at soybean fields in Koriyama City, Fukushima prefecture with 4 different treatments: no fertilizer (NF), cow manure (CM), chemical fertilizer (CF), and without crop (WC). The CO2 and O2 concentration at different depths (10, 25 cm) were monitored at every 1hr interval and recorded with data loggers (CR1000, Campbell Scientific). The CO2 concentration was measured using NDIR type CO2 concentration transducers (GMM221, Vaisala) and O2 concentration was measured using Galvanic oxygen sensors (CAP-SO-210, Apogee), respectively. Water content, soil temperature, and electrical conductivity at different depths (10, 18, 25 cm) were monitored at every 30 min interval using 5TE sensors (METER Group). The monitoring has been done from June 29 till November 12, when the soybeans were grown. Soil hardness profile was also measured using a digital penetration type soil hardness tester (DIK-5532, Daiki) during flowering and harvesting period. The soil samples were taken at 5, 10, 18 and 25 cm deep. Basic physical properties, gas diffusion coefficient, air permeability and amount of microbial biomass were measured using the soil samples. The monitored gas concentrations and gas diffusion coefficients were used to calculate gas fluxes at 0-10 cm and 10-25 cm deep.
The CO2 fluxes at each depth of the CM plot were smaller than those at the NF plot. This was because deeper layer of CM plot was more compacted and the soil water content was higher than the NF plot, inducing the reduction on the soil respiration. Similar behavior was observed at the CF plot where lower CO2 flux at 10-25 cm deep after September were observed than at the NF plot. This was also thought to be because shallower layer of the soil at CF plot was compacted and generally wet. The CO2 concentration at the WC plot were larger than those at NF plot. The soil hardness measurements showed that the surface soil of the WC plot was highly compacted, which inhibited CO2 emission to the atmosphere. Cumulative CO2 emission after August was well correlated to mean water content regardless of different fertilizer managements. In the comparison of soil gas dynamics between plots, the effects of water contents among the plots were more significant than effects of applied fertilizer. There were cases where the gas concentrations were different under wetting and drying processes before and after rainfall events even at the same soil water content condition. Hysteresis of soil gas diffusivity during wetting and drying and activation of microbial respiration induced by increase of soil water content were considered as possible reasons for these phenomena.