Effects Of Growing Leguminous And Non-Leguminous Crops On Soil Respiration And N₂O Emission From Soil

The change of soil respiration and N2O emission from soil influence the concentration of greenhouse gases, thus affect global warming. In order to know effects of growing leguminous and non-leguminous crops on soil respiration and N2O emission from soil, we conducted a pot experiment planted soybean{Glycine max) and cotton (Gossypium spp). The soil respiration rate and N2O emission rate during crop growing season were sampled by static closed chamber method and analyzed by gas chromatography.There were significant correlations of quadratic function between soil respiration rates and growing days of crops. While the seasonal changes of soil respiration rate in bare soils were not significant and their correlations to days after sowing were weak. During the growth of soybean, the soil respiration rate in soybean-planted soil was20.6-1055.2mg C m-2h-1, however in bare soil was1.6～43.4mg Cm-2h-1. The total soil respiration in soybean soil was11.5times as high as that in its corresponding bare soil. The respiration rate for growing stages was seedling <branching <ripening <flowering-podding <filling stages, the soil respiration during filling and flowering-podding stages contributed82%of the total soil respiration, but the days of the growing stages accounted for only38.7%of the entire growth period. The total rhizosphere respiration was seedling <branching <ripening <flowering-podding <filling stages. Its contribution to soil respiration ranged from3.2%to95.8%, and it had the same rule as in rhizosphere respiration. During the growth of cotton, the soil respiration rate in cotton-planted soil was19.6～446.1mg C m-2h-1, however in bare soil was18.2～45.1mg C m-2h-1. The total soil respiration in cotton soil was4.9times as high as that in its corresponding bare soil. The respiration rate for growing stages was seedling <boll opening <buding <flowering and boll forming stages, soil respiration during budding, flowering and boll forming stages contributed77.8%of the total soil respiration, but the days of the growing stages accounted for only44.7%of entire growth period. The high total rhizosphere respiration was in flowering and boll forming stages, low in seeding stages. Its contribution to soil respiration ranged from21.8%to88.0%, and it has the same rule as in rhizosphere respiration. The maximum soil respiration rate in soybean planted soil was2.4times as high as and appeared earlier than that in cotton planted soil. The total respiration, the average soil respiration rate, the total rhizosphere respiration, and the average rhizosphere respiration rate in soybean planted soil were1.77,2.34,2.03and2.68times as high as those in cotton planted soil, respectively. And31-84days after sowing, the total respiration and total rhizosphere respiration in soybean soil were2.35and2.56times as high an that in cotton soil. The exponential correlation between soil respiration rates and air temperatures was significant in growing plants soil, but not in bare soils.During the growth of soybean, the N2O emission rate in soybean-planted soil was0.78-77.6mg N m-2h-1, however in bare soil was11.7～136.3mg N ni-2h-1.In soybean-planted soil, the first43days, middle43days and the last7days contributed63.6%,15.3%and20.9%of the total N2O emission, respectively. In low N application soil, the first43days, middle43days and the last7days contributed25.6%,66.0%and8.4%of the total N2O emission, respectively. And the total N2O emission in low N application soil was3.2times as high as that in soybean planting soil. During the growth of cotton, the N2O emission rate in soybean-planted soil was2.60-275.4mg N m-2h"1, however in bare soil was18.7-406.2mg N m-2h-1.In cotton-planted soil, the first65day and the last58days contributed96.3%and3.7%of the total N2O emission, respectively. In high N application soil the last58days and first65days contributed37.4%and62.6%of the total N2O emission, respectively. And the total N2O emission in high N application soil was3.1times as high as that in cotton planting soil. The most N2O emission focused in the beginning time in the soybean and cotton planting soil. But in SPS, the N2O emission rate had been increased in the period of decline, while the CPS was still in the low quality. The N2O emission of HBS was significant high than LBS. The negative correlation between N2O emission rate and air temperatures was not significant in growing plants soil, but distinctly positive correlation in bare soils. Also the correlation in HBS was significant high than LBS.The growth of soybean and cotton influence the soil respiration and N2O emission from soil differently. They not only controlled by growth, but also affected by N application and temperature. In soybean-planted soil, symbiotic azotifications affected the soil respiration, and root rot in the period of decline increased the N2O emission.