Effects Of Long-term Different Fertilization And Crop Residue Management On Methane And Carbon Dioxide Emission From Rice-wheat Rotated Purple Soils

Methane (CH4) and carbon dioxide (CO2) are the two most important greenhouse gases. Farmland ecosystem is one of the important anthropogenic emission sources of CH4and CO2. There are many factors affecting CH4and CO2emission on farmland ecosystem, such as farming systems, water managements, fertilization measures, etc. Purple soil is the most important agricultural soil type in Sichuan Basin, but there are few studies reporting the effects of fertilization and crop residue management on CH4and CO2emission. Therefore, we used a closed chamber technique to measure CH4and CO2fluxes during the wheat/rice growing seasons, in seven experimental plots established at the National Monitoring Base for Purple Soil Fertility and Fertilizer Efficiency in Beibei, Chongqing. These plots have been subjected to different treatments since1991, including no crop residue incorporation combined with no fertilization (R.), application of P and K fertilizers (PKR.), application of N fertilizer only (NR.), or application of N, P and K fertilizers (FnR.), and crop residue incorporation combined with no fertilization (R+), application of N, P and K fertilizers with normal rate (FnR+), or application of N, P and K fertilizers with1.5times higher N rate (FhR+). The amount of normal nitrogen application was135kg N·hm-2and straw returning rate was7.5t·hm-2. The main objective of this study was:1) to investigate the dynamic of CH4and CO2emission from purple soils under rice-wheat rotatation system;2) to understand the effects of long-term differentiated fertilization and crop residue incorporation on CH4and CO2emission from purple soils. The main results are as follow:Ⅰ. The dynamic change of CH4emissionIn wheat-growing season (from early November to the early May in the following year), the average of CH4emissions were-20.76±5.43μg C·m-2·h-1～7.10±10.82μg C·m-2·h-1on different fertilization treatments, which from R. was the lowest and that from FnR. was the highest in the season. The CH4fluxes appeared fluctuations with the passage of time and did not have significant difference among treatments (p>0.05).In rice-growing season (from late May to late August), CH4fluxes of different fertilization treatments appeared similar seasonal variation. The emission peaks appeared at the tillering stage and the grouting-mature stage. The average of CH4 emissions had obvious difference between treatments, which range was3.14±0.29mg C·m-2·h-1～18.73±2.24mg C·m-2·h-1. The CH4emission from FnR. was the lowest and that from FhR+was the highest.II. The dynamic change of CO2emissionCO2fluxes of different fertilization treatments appeared similar seasonal variation in rice-growing season. The emission peaks majorly appeared in drained stage of the late rice-growing. CO2fluxes of treatments showed a significant negative correlation with flood depth and a significant positive correlation with soil temperature (depth of5cm). The average of CO2emissions were between43±4.34mg C·m^2·h01to65±0.94mg C·m-2·h-1on different fertilization, which had obvious difference among treatments, it from R+was the lowest and from FnR.was the highest.III. Effect of long-term different fertilization and straw management on CH4emissions from purple soilsThe partial application PK fertilizers (PKR) and the NPK normal amount fertilizers (FnR) were measured several higher CH4emission values after strong rainfall in middle of the wheat-growing season, to lead that-cumulative emissions of CH4were positive values (0.19kg C·hm-2and0.54kg C·hm-2) and displayed the weak-emission sources. However, the cumulative emissions of CH4from the remaining treatments were between-1.00±0.50kg C·hm-2to-0.20±0.27kg C·hm-2, which displayed the weak-absorb sources. Fertilizer factors of treatments had no significant effect on CH4emissions in wheat-growing season (p>0.05). Nitrogen fertilizer (N), phosphate and potash fertilizers (PK), crop residue incorporation and their interactions were weak effect of CH4emissions.The cumulative emission of CH4from the no crop residue incorporation combined with no fertilization (R) was108kg C·hm-2, which was a little lower than that from PKR. in rice-growing season. When compared to R_and PKR_, the CH4emission from FnR. was decreased by31%to44%, indicating that application N fertilizer combined with PK fertilizers could inhibit CH4emissions from purple paddy soils under the condition of no crop residue incorporation. The CH4emissions from R+and FnR+were not significantly different (p>0.05), but were92%to99%higher than that from R., suggesting that crop residue incorporation could stimulate methane emission. The CH4emission from FhR+was102%higher than that from FnR+, further explanation that application high-level N fertilizer could stimulate CH4emission under the crop residue incorporation. The same, partial application N fertilizer under no crop residue incorporation could significantly stimulate CH4emission. Fertilizer factors in treatments had significantly different effects of CH4emissions, which from N fertilizer is the strongest effect on CH4emission, the PK fertilizers followed by N fertilizer, while which from the interactions between N fertilizer, PK fertilizers and crop residue incorporation were the weakest effect on CH4emission, suggesting that application PK fertilizers weakened the impact of N fertilizer on CH4emissions from rice paddy.IV. Effect of long-term different fertilization and straw management on CO2emissions from purple soilsThe cumulative emission of CO2from the no crop residue incorporation combined with no fertilization (R.) was1046kg C·hm-2. The CO2emission from PKR. and NR. were little lower than R., but that had no significant difference among the treatments (p>0.05). When compared to R., the CO2emission from FnR. was added to18%, suggesting that NPK normal amount fertilizers could stimulate CO2emission under the condition of no crop residue corporation. In contrast, the CO2emission from R+was19%decreased than R., which from FnR+and FhR+were not significantly different with that from R., suggesting that effects of crop residue incorporation combined with fertilization were complex on CO2emissions from paddy field. Comprehensive analysis of the CH4and CO2emissions in rice-growing season could conclude that there were more intermediate products even CO2transformed into CH4in soil under the organic matters decomposition process. Generally, fertilizer factors in each treatment had moderate effect on CO2emissions.