The Carbon And Nitrogen Conversion Process Affected By Fertilization In Chinese Mollisols

Global warming, induced by the increase in CO2, CH4and N2O concentration is a key environmental question. The effect of C and N cycle in agricultural ecosystem on global change is the major base, and which affects the stability of agricultural ecosystem and environment. C and N cycle is the elementary process influenced by human activity. Mollisols region in China is the grain production base of China or "bread basket of China". The crop production was affected directly by C and N content in soil. It is an important question that the content of C and N is decreasing fastly. Nearly20years, peasant had applied much more chemical fertilizer to increase crop production, and affected the cycle of C and N in agricultural ecosystem.This study was conducted at the Hailun State Key Agro-ecological Experiment Station, Hailun County, Heilongjiang Province, China, to examine the effect of long-term fertilizer application on CO2and N2O emissions. Pot culture and field experiment were used to research the CO2and N2O emission with static state box during vegetative and un-vegetative period. The organic carbon partitioning and balance of C and N affected by long-term fertilization were studied by13CO2labelling to discuss the environmental benefit in agricultural ecosystem. Results as below,1) Long-term fertilization affected crop growth, in turn, soil respiration. The key factor to regulate soil respiration was air temperature.During corn growing season, the rate of soil respiration changes as corn growth, reached to the largest value at87d after germination, then decline to harvest. The rate of soil respiration and rhizosphere respiration were affected significantly by fertilization in an order of NPKOM>NPK>NP>NK>CK, while little effect on bulk soil respiration. Two peak values of soil respiration cumulant were appeared at jointing boot stage and milk ripe stage, while the peak value for bulk soil only at jointing boot stage. Compared NPK with NK treatment, application P had relative large effect on soil respiration. These suggested that P induced lower of soil respiration, at the same time, affected the photosynthate allocation to root. For soybean, the crop growth rate, soil respiration and rhizosphere respiration in NPKOM were larger than other fertilizer treatment.2) Long-term fertilization improved CO2and N2O emission during vegetative seasonCO2emission from soil showed single peak change as time, and affected by fertilization with an order of NPKOM>NPK>NP>NK>CK. The rate of CO2emission during un-vegetative season was lower, and account of5～20%of vegetative season. The largest rate of CO2emission was in NPKOM treatment. The CO2emission cumulant during vegetative reason accounted for83%of un-vegetative season. NPKOM induced mainly CO2emission during vegetative season, no significant effect during un-vegetative season. There was forward direction N2O emission during vegetative season, no regular emission during un-vegetative season. N2O emission was affected by fertilization in an order of NPKOM>NK>NPK>NP>CK. However, the N2O emission during vegetative season was larger than that during un-vegetative season. For NPKOM treatment, it is increased87mg N m-2and166mg N m-2by corn and soybean, while compared to NPK treatment, it increased by363%in NPKOM and17.6%in NK.3) Long-term fertilization affected photosynthate carbon partitioningPhotosynthetic carbon partitioning by corn was affected by fertilization. The largest partition percentage to shoots was76.1%in NK treatment at Day0, then changed to53.3%at Day7. The percentage of NPK changed from1.0%at Day0to3.5%at Day7. The52.9～94.4%of photosynthetic carbon allocated to roots was consumed by rhizosphere respiration, and the largeat value in NPKOM treatment up to94.4%å'Œ93.6%. Distribution of rhizodepoit carbon to water stable aggregates was affected by long-term fertilization. Rhizodepoit carbon induced>2mm size aggregate formation and decreased0.25～0.5mm size aggregate formation. The rhizodeposit carbon in CK treatment was allocated to>2mm,2～1mm and<0.25mm size aggregates, to0.5～2mm and<0.25mm size aggregates in NP, NK and PK treatment. NPKOM induced rhizodepoit carbon to0.5～1mm and<0.25mm size aggregates and decreased to1～2mm and0.25～0.5mm size aggregates.4) Long-term fertilization plays role in maintaining organic carbon balance in soilLong-term fertilization improved organic carbon input to soil and mineralization. Once level off, organic carbon content was increased448kg hm-2per year by NPKOM. The little amount of organic carbon input in CK, only was increased by754kg hm-2with larger mineralization output. Thinking the profit and loss of organic carbon, the amount of organic carbon decrease was1.7g kg-1at the rate of0.22g kg-1year-1after18years. Because of the close amount of C input and output in NPK and NP treatment during12～44kg hm-2a-1range, the soil C maintained balance and changes from27g kg-1to28g kg-1.5) Little effect of long-term fertilization on C and N reserve, while large effect on GWPThe contents of C and N in soil were affected by long-term fertilization. NPKOM increased Cand N content of0-60cm profile, while significant decreas of C and N content of0-20cm profile in CK. For the C and N reserve of0～100cm profile, the effect by fertilization was in an order of NPKOM>NPK>CK. Fertilization can adjust the direction of soil carbon loss. There were four variation phases of organic C content in NPKOM treatment, as quick decline, quick ascend, decline again and keep balance. NPKOM treatment showed a C reserve, no fertilizer improved significantly the GWPI. The value of GWPI was-6.5kg C hm-2in NPKOM treatment. There was no significant difference between NPK and NP for GWPI. These indicated that mixed application of organic and inorganic fertilizers is a friendly practice to environment.