| Conservation tillage maintains sustainable agricultural development through improving productivity, soil fertility, and sequestrating carbon in the soil and reducing the movement of agricultural inputs from the cropping area. Soil respiration dynamics were measured on conservation tillage measures, no tillage (NT), no tillage with straw mulch (NTS) and tillage with straw mulch (TS) were compared to tillage (T) in a maize (Zea mays L.)-winter wheat(Triticum aestivum L.)-vetch(Vicia sativa L.) rotation which was established in 2001 on the Loess Plateau, Gansu Province, China. Soil respiration was monitored using a LI-8150 CO2 analyzer on both the growing season and the freeze-thaw cycles. soil temperature, soil moisture, soil carbon content and soil nitrogen conten were measured as well. The results could put insight into the characteristics of soil respiration and carbon emissions under conservation tillage, and could provide scientific basis for the establishment of the sustainable development strategy in rainfed agricultural region. The main results showed:1. During each crop growth season, soil respiration dynamic had obvious regularity under tillage treatments in rotation system in sunny day, "unimodal type". During maize growth season, a peak under T and NT treatment appeared at 12:00. A peak delayed an hour under NTS and TS, and the peak value of TS treatment (4.33 μmolCO2·m-2·s-1) was 26.6%,20.6% and 33.2% higher, respectively, compared with the T, NT and NTS. During wheat growth season, respiratory peak appeared at the same time with maize. Under T treatment, the peak value (1.71 μmolCO2·m-2·s-1) was significantly 58.3%、20.4% and 71.0% higher than under TS, NT and NTS treatment. Soil respiration showed little change during vetch growth season. Rrespiratory peak value appeared at 13:00 under the T and NT treatment. Peak value were respectively 2.56 and 2.54 μmol CO2·m-2·s-1, while soil respiration changed slightly under TS and NTS treatment. Rangeability of daily soil respiration was smaller in rainy weather. At different times of the soil respiration value relatived to the average would appear different deviations which were high (15～98%), or low (7～77%).2. The winter soil occurred freezing and thawing alternation in one day. When thawing peak of soil respiration appeared at 14:00. Peak values were 0.77,1.08,0.8 and 1.05 μmolCO2·m-2·s-1 under T, TS, NT and NTS. During 18:00～19:00, as temperature reduced quickly, soil started freezing. When soil respiration rates respectively were 0.18,0.17,0.17 and 0.18 μmolCO2·m-2·s-1 as minimum, under T, TS, NT and NTS treatment.3. Soil respiration was affected by season, with the peak found during summer. Maximum soil respiration flux (2.31 μmolCO2·m-2·s-1) was found in the maize growing season with the minimum values (1.43 μmolCO2·m-2·s-1) found in the winter wheat growing season, the second (1.65 μmolCO2·m-2·s-1) found in the vetch growing season. Compared to traditional tilliage(T), NT treatment significantly reduced the soil respiration rate of 13.85% in the maize growing season. NT treatment reduced the soil respiration rate of 19.58% in winter wheat season. NTS treatment significantly reduced the soil respiration rate of 10.30% in the vetch growing season. Soil C emissions was 15.31～30.61 kgC·hm-2·d-1 for annual crop growing season. Soil C emissions were greatest under the TS treatment. Soil C emissions in the non-growth season accounted for 4.48～8.38% of the annual total.4. When rainfall (21.60～54.96 mm) occured, soil respiration decreased by 62.9-92.9% and 35.8-56.9% for T and NT treatments with the first rainfall instantly. After the rainfall, soil respiration decreased a further 31.5-81.9% and 15.7-59.9% for the NT and T treatments. Tillage treatments were 51.8% higher for tillage versus no-till treatments when soil moisture was at 18%. However when soil moisture reached 30%, tillage was 43% lower for soil respiration than no till. Under tillage, soil water content had a more dynamic impact on soil respiration. The critical value of soil moisture content restrained soil respiration was 24.2% for no-till and 20.7% for tillage treatments. A hydrothermal, double factor model can be used to simulate soil respiration under tillage.5. Soil respiration under various treatments, was no significant correlation with soil carbon and nitrogen significantly, but associated with soil temperature and moisture. The main factors affecting the soil respiration in different months are different. In March, when temperatures were low, soil temperature index model was the best choices to fit soil respiration. R2 was 0.81～0.89. From April to June, prior to rainfall occurrence, soil temperature and soil moisture both influenced soil respiration. The temperature-water double factor model was the optimal to fit respiration. In July, where rainfall was most prevalent, soil moisture had the greatest influence on soil respiration under TS, NTS treatment. Soil moisture quadratic equation model was better one. R2 was 0.71,0.68. While the temperature-water double factor model was the best to fit respiration under T and NT treatment, and the degree of fitting under NT treatment (R2= 0.53) was weaker than the fitting under T treatment (R2= 0.88).6. Annual Q10 values were 2.01,2.45,2.97 and 2.86 for T, NT, TS and NTS treatments, respectively. Monthly Q10 values were lowest when the soil temperature was at 25℃ at 0.23. Monthly Q10 values were at their highest when the soil temperature was at 15℃, with a value of 8.25.This study obtained dynamic and seasonal dynamic characteristics of soil respiration in three kinds of crop growing season under straw mulching and no-till treatment, based on a 14 years of conservation tillage rotation, through the continuous monitoring for 24 h. It obtained the change of soil respiration during the freezing and thawing period, and alternately cleared the influence on soil respiration by rain under drought condition. It made the accuracy of the estimated C emissions higher. It had significant innovation about soil respiration rate and temperature sensitivity under conversation tilliage. |
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