Effects Of Soil Tillage On Crop Yield And Greenhouse Gas Emission Of Corn–Wheat Cropping System

Corn-wheat cropping system is one of the most important grain production systems in the world. The production of wheat and corn needs to increase to meet the future food demand of the growing population. In order to increase crop yield, excessive nitrogen(N) fertilizer has been applied for wheat and corn production, causing serious environmental problem due to the low N use efficiency(NUE). Meanwhile, agricultural lands are the main sources of anthropogenic emissions of N2 O and CH4, and agronomic practices play an important role in affecting the emissions. China by producing 17.9% of wheat and 23.8% of corn production in the world is one of the largest countries of wheat and corn production and carbon emission, and corn-wheat cropping system is a dominant system particularly in North China Plain. In order to further enhance crop yields and NUE, great efforts have been made on agronomic innovations such as soil tillage in this region. Although some field observations have been implemented about tillage impacts on crop yields and greenhouse gases(GHGs) emissions, but the integrative effects of tillage were not clear on crop yields, N use efficiency(NUE), soil characteristics and GHGs emissions in corn-wheat double cropping system. Therefore, a two-year field experiment with new combination of tillage practices was carried out in Dongping county, Shandong province in north of China with typically corn-wheat cropping system. The field experiment was started in the wheat season in 2012, four tillage treatments including no-tillage(N), rotary tillage(R), sub-soiling with no-tillage(SN) and sub-soiling with rotary tillage(SR) were carried out in wheat season of the first year, then for corn planting 2013, each plot was bisected, with one half maintained using no-tillage method and the other half converted to sub-soiling, resulting in eight treatment plots and two groups:(N-tillage group including the N-N, N-R, N-SN and N-SR; SR-tillage group including the SR-N, SR-R, SR-SN and SR-SR). The main plots were tillage in corn season, and the sub- plots were tillage in wheat season. The present study will provide important theoretical and technological supporting for corn-wheat cropping system with high yield, high NUE and low GHGs emissions. The main results are summarized as follows:1. Tillage practices significantly affected crop yields. The N-SR and also SR-SR plots significantly increased crop yield at seasonal and annual scales under the corn-wheat cropping system. The annual average yields of two years showed an order of N-SR> SR-SR> N-SN > SR-SN> SR-R> N-R> N-N> SR-N. Averagely during the entire cropping system, the No-tillage group had 1.55% higher grain yield than the SR-tillage group.2. Nitrogen uptake and NUE were significantly affected by tillage practices. The N-SR plot significantly increased N uptake, NHI and NFP at seasonal and annual scales under the corn-wheat cropping system across two years. During the entire cropping in wheat season averaged N uptake showed the order of N-SR> SR-R> SR-SR> N-N> SR-SN> N-R> SR-N> N-SN and averaged NHI showed the order of N-SR> SR-SN> SR-SR> N-SN> SR-R> N-R> SR-N> N-N, but annual averages of NFP showed the order of N-SR> SR-SR> SR-SN> N-R> SR-R> N-N> N-SN> SR-N. Across the entire cropping system, the No-tillage group in corn season had higher N uptake, NHI and NFP than those in the SR-tillage group(using SR tillage in corn and all tillage practices that we used in wheat season).3. The soil physical characteristics were significantly affected by tillage. In general, the N-N plot had the highest soil bulk density at the depth of 0-10, 10-20 and 20-30 in all treatments during the entire cropping system. At the wheat and corn maturity stage, the N-tillage compared to SR-tillage group had a higher soil bulk density at the depth of 0-10, 10-20 and 20-30 cm of the soil layer. The N-N tillage is the more effective tillage for increasing soil moisture in corn-wheat cropping system, followed by SR-N tillage, while there were no significant differences in soil moisture between the other tillage treatments.4. Tillage significantly affected the soil chemical characteristics. Total nitrogen(TN) concentration in all treatments at maturity stages of corn and wheat was higher at 0-10 cm compared to 10-20 cm of soil. The highest concentration of TN in corn and wheat season at the depth of 0-10 cm was detected in N-N tillage, but at the depth of 10-20 cm the N-SR had the highest TN concentration. In corn growing season SR-tillage group averagely at the depth of 0-10 cm and 10-20 had higher total nitrogen than the N-tillage group, while in wheat growing seasons the No-tillage group had higher TN at the depth of 0-10 cm and 10-20 cm higher than the SR-tillage group. The concentration of NH4+-N during the wheat growing season in soil at the depth of 0-10 cm was higher than that at the depth of 10-20 cm. The concentration of NH4+-N was varied between the treatments during the growing period, at the depth of 0-10 cm the soil NH4+-N concentrate in N-tillage group was higher than the SR-tillage group, while SR-tillage at the depth of 10-20 cm was higher compared to the N-tillage group. The concentration of NO3--N in soil at the depth of 10-20 cm was higher than the depth of 0-10 cm, generally during the wheat growing season at the depth of 0-10 and 10-20 cm SR-tillage group had higher NO3--N than the N-tillage group. The average of all treatments during the entire cropping system showed that the soil p H at the depth of 10-20 cm was 17.50% higher than that in 0-10 cm of soil. The soil p H at the depth of 0-10 cm in the N-tillage group was higher than that in the SR-tillage group in corn and wheat maturity stage, at the depth of 10-20 cm of corn maturity stage, soil p H in the N-tillage group was higher than the SR-tillage group but at wheat maturity SR-tillage group had a higher soil p H than the N-tillage group. The highest p H between all treatments at the depth of 0-10 and 10-20 was detected under N-N plot.5. The soil biological characteristics were significantly affected by tillage. The soil microbial biomass carbon in all treatments at the depth of 0-10 cm was higher than that at the depth of 10-20 cm. The N-N tillage had the highest concentrations of microbial biomass carbon at the depth of 0-10 and almost 10-20 cm during the wheat growing season. The microbial biomass nitrogen was higher under the N-N and N-R plots during wheat growing season at the depth of 0-10 and 10-20 cm. At the maturity stage of wheat and corn, at the depth of 0-10 cm soil organic carbon was higher than the depth of 10-20 cm soil in all treatments. For two years, the highest concentration of soil organic carbon at the depth of 0-10 and 10-20 cm was detected in N-N plot. Generally, soil organic carbon concentration in the N-tillage group at corn and wheat maturity stage was higher than the SR-tillage group. The nitrification capacity at the anthesis stage of the wheat growing season in 2013-2014 in 0-20 cm of soil under N-tillage group was 18.78% higher than the SR-tillage group at anthesis stage. Between all treatments the N-N plot had the highest nitrification capacity and N-SR had the lowest. The denitrification capacity in the SR-tillage group was 4.67% higher than that in the N-tillage group. The highest denitrification capacity in was detected under the N-R plot and the lowest was SR-SR plot.6. The N2 O emissions during the whole first year was significantly affected by tillage, while in the second year there were no significant effects of soil tillage practices on N2 O emissions(P>0.05). Averagely during the entire cropping system, N2 O emissions were higher under SR-tillage group compared to N-tillage group and the highest N2 O emissions between all treatments was detected under the SR-SR tillage and the lowest was under the N-N tillage. No significant differences in CH4 emissions could be observed in wheat, corn and annual cropping seasons in both years(P>0.05). The average cumulative CH4 emissions of two years in double cropping systems showed the trend of the SR-tillage group> N-tillage group. During the entire cropping system, area and yield scaled GWP were higher under SR-tillage group compared to the N-tillage group and the highest area and yield scaled GWP between all treatments was detected under the SR-SR tillage and the lowest was under N-N tillage. Generally SR-tillage had higher area and yield scaled GWP than the N-tillage group.