Effects Of Long-term Conservation Tillage On Soil Melioration,carbon Storage And Greenhouse Gas Mitigation Of Wheat Field On Weibei Arid Plateau

Located in the south of the Loess Plateau,the Weibei arid plateau is an important crop production region.Low water use efficiency?WUE?and poor fertility are the main limiting factors for the crop production in that region.Excessive plow,harrow and N fertilizer have stressed the deterioration of the ecology,e.g.,water and soil erosion,soil degradation,leaching of N-NO.Thus,from the autumn of 2007,we established a long-term field experiment to study the cultivation and ecological effects of tillage,fertilization,and rotation at the Heyang Dryland Agriculture Research Station of Northwest A&F University,in Ganjing town,Heyang county,Shaanxi.To better understand the effect of fertilization,tillage and rotation tillage,12 cropping patterns,nine of which were fertilization-tillage patterns with three fertilization?conventional rate[CF],low rate[LF],and recommended rate[RF]?×three tillage?no tillage[NT],subsoiling tillage[ST],and plow tillage[PT]?,and three of which were rotation tillage patterns?NT/ST[NS],ST/PT[SP],and PT/NT[PN]?under RF,were selected in a continuous winter wheat field to study their effects on yield,water/fertilizer use efficiency,soil physical/chemical properties,and GHGs emission.We obtained the following main results:1.The effect of conservation tillage on continuous winter wheat grain yield and water/N use efficiency in the Weibei arid plateau.Average yield,WUE,precipitation use efficiency?PUE?,and Partial factor productivity of applied N?PFP_N?across 10 years were 4514.9 kg·ha^-1,14.3 kg·ha^-1·mm^-1,8.3kg·ha^-1·mm^-1,and 30.1 kg·kg^-1 under NS,which were15.3%,14.3%,8.3%,and 30.1%higher compared to PT,respectively.They decreased by the order of NS,SP,ST,and PN,and the first three cultivation patterns had steady and promising yield.The differences of yield,WUE,and PUE between fertilization were RF>CF>LF,PFP_N changed in the order of LF>RF>CF,among which,RF had the potential of higher yield.2.Effect of conservation tillage on soil physical properties?1?Compared to PT,Soil water storage?SWS?was increased by 4.9%-6.9%under ST in dry fallows,and under NT by 2.5%-6.4%and 9.6%-16.5%in wet and in dry fallows,respectively.Among all continuous/rotation tillage patterns,NT produced the greatest SWS,whereas the highest precipitation storage efficiency?PSE?being up to 21.67%was under NS.Though SWS under RF was lower,there was no significant differences of PSE between fertilizations.Conservation tillage and in season conservation tillage composing rotation tillage improved soil water content at 0-200 cm depth at the sowing stage.Soil water content in 60-140 cm layer varied more dramatically under RF and/or conservation tillage than other treatments.Grain yield was positively correlated with soil water content at the sowing stage and tillering stages as well as soil water consumption during the heading-grain filling period,and negatively correlated with the consumption during the sowing-tillering period.?2?Bulk densities?BK?in up 80 cm layers were 1.04-1.68 g·cm^-3,with no unanimous and significant effect of fertilization or tillage.Compared with ST and PT,NT migrated plow pans downward and together with RF decreased BK at 0-30 cm depth.Compared to CF,BK was increased under RF in 10-30 cm layers,and under LF in 30-40 cm layer.The BK under NS in 0-30 cm layers was lowest than all the other tillage/rotation tillage patterns.?3?Capillary porosity?C-pore?in 0-5 cm layer was 51.2%and 41.7%under RN and RS,respectively,9.2%and 1.4%higher compared to RF combined with PT?RP?.But in LF and CF treatments,the C-pore under NT was lower than under PT.The C-pore in 40-80 cm layers was improved by 2.7%-11.3%under NT and ST compared to PT,and in 0-40 cm layers it was improved by 0.4%-10.0%when N rate had been increased.Patterns NS and SP were beneficial for C-pore improvement in the whole 0-80 cm layer.?4?The contents of mechanical-stable aggregates and water-stable aggregates in 0-5 cm layer were 89.4%and 65.8%,mean weight diameter were 19.7%and 32.4%higher compared to CP.The content of mechanical-and water-stable macroaggregates in 0-40 cm layer were higher under NT compared with other continuous tillage treatments,while ST was helpful to improve the content in 40-80 cm layer.The RF treatment was beneficial for the stability improvement of mechanical-stable aggregate in 0-40 cm and 60-80 cm layers but decreased the content of water-stable aggregates at 40-80 cm depth.NS appeared more effective in the content improvement of mechanical-and water-stable aggregates at 0-80 cm depth,while SP and PN would just improve the stability of water-stable aggregates.3.Effect of conservation tillage on soil chemical properties of continuous winter wheat field in the Weibei arid plateau.?1?Soil organic material?SOM?content in 0-10 cm layer changed by the order of NT>ST>PT,and the order of CF>RF>LF,with the highest content of 1.9%under CN.In the treatments of LF and RF,SOM storage in 0-100 cm layer was 0.1-1.2 kg?m^-3 lower under conservation tillage compared with PT,while in the CF treatment it was 1.5-2.6 kg?m^-3higher under conservation tillage compared with PT.Under different fertilization treatments,SOM storage in 0-100 cm layer was ranked in the order of CF>LF>RF.Under NT,quantities of macro-aggregate carbon in 0-80 cm layers were 34.0-38.4 t?ha^-1for the three fertilization treatments,being higher than ST and PT.Macro-aggregate carbon quantity in 0-5 cm layer was higher under ST compared to PT,whereas total macro-aggregate carbon quantity in 0-80 cm layers was lower under ST compared to PT.The Effects of fertilization and tillage on the quantities of micro-aggregate carbon and silt-and-clay carbon were not obvious,but soil disturbance and RF increased their ratios in the total aggregate carbon.?2?In the three fertilization treatments,NT and ST increased total-N content in 0-10 cm layer by 2.7%-21.8%,and increased available-N content by 7.7%-323.6%,compared to PT(7.5 g?kg^-1 and 12.4 mg?kg^-1,respectively).While in the RF treatment,total-N storage at0-100 cm depth was decreased under conservation tillage compared to PT,due to the higher stratification ratio.The storage of total-N decreased by the order of CF>LF>RF,and the storage of available-N decreased by the order of CF>RF>LF.N-NO was the majorcomponent of available-N,and the variation trends of them were similar.Leaching of N was intensified under CP.There was no significant difference of variation trend between each pattern.?3?The highest stratification ratios of total-P?TP?and available-P?AP?reached 1.76 and4.41,respectively.The contents of TP and AP in 0-10 cm layer were 0.8 g?kg^-1 and 22.5mg?kg^-1,while the contents in 80-100 cm layer were only 37.1%and 11.7%of those in the top layer,respectively.Compared to PT,conservation tillage treatments improved TP content and AP content by average 15.2%and 35.4%,and increased AP storage in 0-100 cm layer by9.2%,but decreased TP storage in 0-100 cm layer besides NT and NS.The differences of TP and AP storage between fertilization treatments were RF>CF>LF and CF>RF>LF,respectively.?4?Under conservation tillage treatments,contents of total K?TK?in 0-10 cm layer ranged between 11.1 g?kg^-1 and 12.2 g?kg^-1,having been increased by 4.3%-12.8%compared to PT,and TK storage in 0-100 cm layer ranged between 16.6 kg?m^-3 to 18.4 kg?m^-3,being0.4%-7.5%higher compared to PT.The storage of TK under RF was lower compared to CF and LF.Among all conservation tillage/rotation tillage treatments,only NT and NS improved the available-K?AK?contents in top layer and AK storage in 0-100 cm compared to PT.The storage of AK under LF was higher compared to RF and CF?P>0.05?.4.Effect of conservation tillage on Greenhous gases?GHGs?emission and carbon ecological footprint in the Weibei arid plateau.?1?The CO₂ fluxes in the continuous winter wheat field ranged between 49.5 mg?m^-2?h^-1and 635.1 mg?m^-2?h^-1,with the lowest emission rate in the winter,and the higher emission rate in the wheat rapid growth period as well as the hot and wet fallow period.The lowest average flux was observed under NT,whose annual total emission ranged between 14.52 t?ha^-1 and16.53 t?ha^-1,being 14.7%-18.7%lower compared to PT.NS produced the second lowest emission quantity,then was ST.Under the same tillage practice,LF generated the lowest CO₂emission,and RF generated the highest emission.In spit of this,RN relieved the annual emission by 16.9%through less soil disturbance.?2?Being the sink of CH₄,average absorption rate across 2015-2017 under all cultivation patterns in the Weibei arid agroecosystem ranged between 8.0?g?m^-2?h^-1 and 138.1?g?m^-2?h^-1,with the lowest flux in winter and the highest flux in the Jointing-grain filling period.Under the same tillage practice,there was no significant difference of average flux between fertilization treatments.For the three fertilization treatments,total absorption quantities under NT and NS were decreased by 19.6%-23.7%,and 4.8%-8.3%,respectively.Total absorption quantities between tillage/rotation tillage practices ranked in the order of PT>SP>PN>ST>NS>NT.?3?In the present study,N₂O fluxes ranged between 2.5?g?m^-2?h^-11 and 160.6?g?m^-2?h^-1,with severe fluctuation.N fertilization and NT intensified the N₂O emission rate,thus the pattern with the highest flux(CN,1.3 kg?ha^-1)produced 74.0%more emission compared to the pattern with the lowest flux?LN?.N₂O flux under NS was next to that under NT,and there was no significant difference between SP,PN and PT.?4?Mineral fertilization caused 48.2%-79.0%of total indirect emission during the agriculture practice,while consumption of fossil fuel was the second emission source?averaged 31.3%of total emission?.Annual indirect emission quantity under CN was the highest?1456.5 kg?CO₂-eq?among all patterns,being 1.26-fold that under LN.Global warming potential?GWP?generated from the emission of N₂O,CH₄ and agriculture-related indirect emission accounted for 1.4%,0.6%,and 5.5%in the carbon ecological footprint.Compared to other patterns,CP generated the highest greenhouse effect,average annual carbon ecological footprint under which was 21.5 t?CO₂-eq?ha^-1,being 1.4-fold that under LN.Carbon ecological footprint per yield was the lowest under RF compared to CF and LF,of which,NS and NT(both being about 4.3 tCO₂-eq?ha^-1?t^-1)decreased 26.5%compared to CP.The 10-year field experiment revealed that RF combined with conservation tillage had effectively improved the grain yield,WUE,fertilizer use efficiency,soil structure,held relatively higher fertility in the upper layers,enhanced the nutrient absorption of crop from soil,relieved GHGs emission,decreased carbon ecological footprint per yield.Among all cultivation patters,due to the better ecosystem services for both yield improvement and GHGs mitigation,NS produced the highest comprehensive benefits,and would be the most suitable cultivation pattern for the continuous winter wheat production in the Weibei arid plateau and the same agroecosystems.