| The experiment was conducted in 2005-2014 summer maize growing seasons in pool cultures and field conditions at the Experimental Station of shandong agricultural university. In 2010-2011 summer maize growing season, the experiment was conducted in pool cultures with straw mulching combined and 2 summer maize plant types; In 2012-2013 summer maize growing seasons, the experiment was conducted in pool cultures with straw mulching and 3 plant densities; In 2005-2014 summer maize growing seasons, the experiment was conducted in field conditions with conservation tillage methods and straw returned or not. From the above experiments, to study the effect of straw mulching(plant type and density) and cultivation measures(straw returned) on water use efficiency(WUE), the difference of returning straw mulching and carbon emissions, as well as the crops carbon sequestration and carbon sinks etc. The results can provide theoretical basis for agricultural sustainable development in North China.The main results were as follows:1 Carbon sequestration and carbon sink effect in summer maize conservation tillage fieldBoth tillage measures and straw returne were significantly affect the carbon sequestration and carbon sequestration in summer maize growing seasons. In 2011-2014 summer maize growing seasons, the highest carbon uptake was found in straw returned with deep loosening treatment, and the lowest was found in without straw returned with conventional tillage treatment. The same result was found in carbon sequestration, which showed that the highest value was found in t straw returned with deep loosening treatment, and the lowest was found in no straw returned with conventional minimum tillage treatment. It is obvious that straw returned with deep loosening treatment not only absorb a large amount of carbon, but also will be accumulated more carbon in the grain.Effect of tillage methods on soil organic carbon accumulation was not consistent. From 2011 to 2012, the soil organic carbon in both no tillage and minimum tillage fields was increased; however, from 2013 to 2014, it was decreaded. The result also showed that the soil organic carbon was much higher in straw mulching field than in straw returned field. Hence, soil organic carbon could accumulated significantly only under the conditions that conservation tillage combined with straw mulching.2 Soil respiration and carbon source effect in summer maize conservation tillage fieldSoil tillage significantly affected the soil CO2-C emissions. The soil CO2-C emissions in straw returned with conventional tillage treatment was higher than that in straw returned with no tillage treatment by 5.88%, and the emission rate in day time was much higher than that in night time.From summer maize planting to flowering, the soil CO2-C emissions rate was increased, and the highest value was found at flowering stage, then it was decreased.Compared with conventional tillage, in 2011 and 2012, the soil CO2-C emission rate in no tillage treatment was reduced by 10.0% and 12.5%, and in deep loosening treatment was reduced by 5.0% and 5.0% respectively. No matter in what kind of tillage methods, straw return could significantly increase the soil CO2 emissions. Compared with no straw return treatments, the soil CO2 emissions in no tillage and conventional tillage treatments were enhanced by 20.0% and 13.6% in 2011, and by 26.3% and 25.0% in 2012, respectively. In 2011 and 2012 summer maize growing seasons, the soil CO2-C emission in conventional tillage treatment were 1.14 and 1.09 times than those in no tillage treatments.Results showed that adding straw could significantly increase the soil organic carbon content. Under the condition of no straw powder added, the soil organic carbon was significantly higher in the treatment of relative humidity was 55% than those were 65% and 65%, and the differences between 65% and 75% relative humidity were not significant differenct. After adding straw powder, soil CO2-C cumulative release quantity was increased with the increasing of relative humidity. No matter adding straw powder or not, the lowest soil CO2-C cumulative release quantity was found at 25℃. The soil CO2-C cumulative release quantity was much higher at 35℃ than at 30℃; however, the difference was not significant.Plant densities had no significant effect of soil respiration; however, the soil respiration in straw mulching treatments was significantly decreased. Hence, the soil CO2 emissions in stwaw mulching was significantly decreased. Compared with non-mulching treatments, the soil CO2 emissions quantities in mulching treatments were significantly decreased. In 2012 and 2013 summer maize growing seasons, both soil respiration rate and soil CO2 flux was much lower in mulching treatments than in non-mulching treatments. In 2012, compared with non-mulching treatments, the soil CO2 flux in mulching treatments at high, medium, and low plant densities was reduced by 41.78%, 20.56% and 34.97%; In 2013, it was reduced by 14.41%, 10.99% and 14.41%, respectively. It is obvious that straw mulching could reduce CO2 emissions efficiently.3 Straw mulching and summer maize plant types can affect both carbon and water use efficiencyStraw mulching affected the growth of summer maize in early growth stage; however, promote in the middle and later. Therefore, the summer maize leaf area index(LAI) in mulching and non-mulching treatments was not differ significantly. Compared with non-mulching treatments, photosynthetic rates in both Danyu 86 and Denghai 661 were improved. With the increasing of straw amount applied, the aboveground dry matter ccumation of summer maize was increased; however, the accumulation rules in different plant types were different: after the straw mulching, both ear and leaf dry weight in Danyu 86 were increased simultaneously; while in denghai 661, mainly increased the ear dry weight. Compared with non-mulching treatment, summer maize grain yield was increased significantly at mulching rate at 0.6 and 1.2 kg/m2. In 2011 summer maize growing season, the grain yield was significant higher in denghai 661 than in Dan yu 86, the main reason was that both ears number and lines number were increased significantly.Evapotranspiratin in both Danyu 86 and Denghai 661 was not significant difference. However, straw mulching could affect stomatal conductance in spike leaves Compared with non-mulching treatments, the stomatal conductance in both Danyu 86 and Denghai 661 were significantly decreased at straw mulching rate at 0.6 and 1.2 kg/m2.4 The effect of straw mulching and plant densities on summer maize grain yield and water use efficiencyUnder the condition of medium density, straw mulching could increase the photosynthetic active radiation(PAR) interception rate in spike leaves of summer maize. Under the condition of non-mulching conditon, both of summer maize stems and leaves dry weight were decreased with the decreasing of plant density; Under the condition of straw mulching, the highest stems and leaves dry weight were attained in medium density. Straw mulching had no significant differences on spikes weight in different plant densities. Straw mulching also had no significant difference on grain yield in high plant density; however, significant differences were found in both medium and low plant densities, the main reason was that 1000-kernels weright was significantly enhanced. The WUE in mulching treatment was significantly improved, and especially in medium density.5 Soil carbon analysis in long-term conservation tillage farmland 2005-2014In 2005-2014, the soil organic carbon was much higher in straw returned treatments than in no straw returned treatments; and the soil organic carbon was much higher in conservation tillage than in conventional tillage. Carbon sequestration potential order is as follows: zero tillage with straw returned(PZ) > deep loosening with straw returned(PS) > conventional tillage with straw returned(PC) > no-till without straw returned(AZ) > deep loosening with straw returned(AS) > conventional tillage(AC), the carbon sequestration potential was much higher in straw returned treatments than in without straw returned treatments, and the carbon sequestration potential was much higher in conservation tillage than in conventional tillage. Compared with conservation tillage, the carbon sequestration potential in PC, AZ, PZ, AS, and PS was increased by 77.18%, 74.90%, 87.42%, 41.06%, and 82.72%, respectively. It is obvious that conservation tillage can improve the soil carbon sequestration potential.The results show that conservation tillage combined with straw return could improve the soil organic carbon and carbon sequestration potential. To sum up, straw return or straw mulching combined with conservation tillage technology could improve the carbon and water use efficiency of winter wheat and summer maize. The results can provide theorerical basis for water-saving, high yield, and low carbon agriculture in North China. |
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