| Global warming as the main characteristics of climate change is one of the most seriousglobal environmental problems humanity faced, The research has shown that the CO2emission in China has continuously increased and the sum of positive radiative forcingsproduced by greenhouse gases is responsible for climate waning. The internationalcommunity pays close attention to "climate crisis", nations should instead consider a globalcarbon tax or a “cap and trade” system that would allow countries to emit a given amount ofCO2or sell permits to other countries. China is the one of the largest emitter of greenhousegas pollution, facing unprecedented challenges and opportunities. Farmland ecosystem playsan important part in terrestrial ecosystem and global carbon cycle, and it has effects on theglobal carbon balance. Agriculture soil carbon pool can be interrupted strongly by anthropicactivity, such as tillage system and fertilization, and it also can be regulated at a relativelyshort time scale. Dryland ecosystem has important position in the agricultural ecosystem, andsummer maize is the main crops in China, so increasing maize crop yield has significantcontribution to food security of China. At present, studies on soil carbon emissions and carbonbalance in dryland summer maize field were rarely. Based on the above phenomenon, fieldexperiment was conducted in situ under dryland, to detective the effect of different farmlandmanagement practices on the dynamic changes of soil respiration rate, the relationshipbetween soil respiration rate and soil moisture and soil temperature, changes of soil organiccarbon and soil carbon banlance during the summer maize growing season, and our researchresults can serve as the basis for meeting greenhouse gas reduction targets, designing properand effective farmland management practices. The main research results are as follows.(1) Soil respiration rates have daily and seasonal regular changes under differentfarmland management practices. Soil respiration rate was frist increased then decreasedduring the whole crop period in all kind of tillage system. The miximum of soil respirationrate was DT, follwed by PT, RT, NT, and there are significant difference among them.Dynamic change of soil respiration under different N-fertilizer levels show as an asymmetricunimodal curve, the miximum of soil respiration occurred at52days after sowing, theminimum of soil respiration occurred at harvesting stage. In certain range of nitrogenapplication (0-320kg/hm2), with nitrogen application increased, soil respiration rate were all increased, the relationship between the total carbon flux release (Sr) and nitrogen applicationrate (n) meet the equation i.e. Sr=1204.09/(1+e-1.69-0.02n).(2) The effect of tillage practices on soil moisture was more significance at earlier stage(0-30days after sowing) than late growth stage (50-120days after sowing), it can be shownthat soil temperature of RT higher than DT and NT at the earlier stage of maize crop. Theregression model fitted by temperature and soil respiration rate could explained48.10%-59.36%of the seasonal variation under DT, and NT, RT and PT were13.31%-19.90%,23.30%-38.47%and50.72%-53.90%, respectively. The results also indicated that soiltemperature wae the key factor that affected the soil respiration rate in fertilized drylandsummer maize field, which could explained62.31%-78.66%of the seasonal variation; theaverage temerature sensitivities (Q10) were1.377-2.435, and the miximum was occurredduring jointing stage to heading stage, minimum was occurred at early and late growth stage.(3) Soil moisture affected by tillage practices had a greater effect on early growth stage(0-30days after sowing), along with the advance of growth of summer maize, differencebetween them narrowed gradually. Analysis of the relationship between the soil moisture andsoil respiration rate, both had no obvious correlation. Therefore, considering the effects ofsoil temperature and soil moisture on soil reapiration rate could improve the accuracy of soilreapiration rate in regional research. The regression model fitted by soil temperature and soilmoisture can explain31.46%-76.83%(in2010),21.26%-57.61%(in2011) of the diurnalchanges of soil respiration under different tillage systems, respectively, and79.63%-85.87%of the diurnal changes of soil respiration under different N-fertilizer levels.(4) With the increase of soil depth, soil organic matter (SOM) content gradually reduced.SOM content of DT was miximum in depth of0-20cm, followed were NT, RT and PT, andhad no significant difference (P>0.05). SOM content of PT and DT in depth of20-40cm werehigher significantly than NT (P<0.05), which also can be known in depth of40-60cm.Compared with controls, SOM content in all nitrogen treatments were enhanced, themaximum was increased by10.30%, and the minimum was increased by5.22%. SOMcontent in all nitrogen treatment in depth of20-40cm were lower than CK, which reduced by0.01%-10.30%; SOM content of80kg/hm2and160kg/hm2nitrogen treatment in depth of40-60cm increased0.01%and3.40%than that of CK, respectively, and240kg/hm2and320kg/hm2nitrogen treatment reduced by1.44%and1.68%, respectively.(5) The net primary productivity carbon was C4853.78-6091.49kg/hm2under differenttillage system, carbon emissions of soil microbial heterotrophic respiration of which were C1655.00-4372.90kg/hm2, and the net ecosystem productivity were followed as RT>NT>PT>DT. At the same time, the net primary productivity carbon was C4036.81-5093.52kg/hm2 under different N-fertilizer levels, carbon emissions of soil microbial heterotrophic respirationof which were2395.61-2854.80kg/hm2, and the net ecosystem productivity were followed asN3>N4>N2>CK>N1. Which indicated that dryland field of summer maize was an importantsink of atmospheric carbon dioxide (CO2).(6) In summer maize growing season, the net carbon flux of DT, NT, RT and PT were-48.45、-79.81、313.46、560.66kg/(hm2·a), respectively. From which we can see DT and NTdryland field of summer maize were a sink of carbon dioxide compared with RT, and PT wassource of carbon dioxide. And NT had a greater contribution than PT in the atmospheric CO2reduction. The net carbon flux of0kg/hm2,80kg/hm2,160kg/hm2,240kg/hm2and320kg/hm2N-fertilizer levels treatments were-48.45,-79.81,313.46,560.66kg/(hm2·a),respectively. Taking agriculture input into account,80kg/hm2and160kg/hm2N-fertilizerlevels treatments were a sink of carbon dioxide, and240kg/hm2and320kg/hm2N-fertilizerlevels treatments were source of carbon dioxide. With nitrogen addition increasing, drylandecosystem had a greater contribution in the atmospheric CO2reduction.(7) In general, although soil water storage was reduced to some degrees by RT and DT,they were conducive to downward infiltration of soil moisture and increased the water storageat middle and late stage. Moreover, in comparison to NT, RT and DT could properly improvesoil temperature at seedling and promote summer maize normal growth, enhance the grainyield of maize by3.35%and1.91%, respectively. Taking economic profits into account, thenet income were259.38Chinese Yuan (CNY) hm-2and138.48Chinese Yuan (CNY) hm-2greater in DT and NT than in RT, respectively. With the increase of nitrogen application, theyield of summer maize crop were increased, and nitrogen use efficiency and nitrogen partialproductivity were reduced gradually, there were no significant difference of crop yieldbetween240kg/hm2and320kg/hm2treatment. |
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