Effect Of Furrow-to-ridge Ratios In Ridge- Furrow Mulching System On Dryland Spring Maize Growth And Soil Carbon Emission

Ridge–furrow mulching system?RFMS?,as a prospective rainwater harvesting system,is one of the most popular and widely applied field management techniques in the Loess Plateau area.The RFMS can vary the ratio of its alternating furrow and ridge to change the land surface and planting scheme for a better use of solar light and rainfall,which can also result in different soil microtopographic features and microenvironments.Meanwhile,these changes of soil surface properties are also drivers of soil CO2 emission.However,the way RFMS practice affects soil CO2 efflux is not well-studied and needs more investigation.Therefore,in this study,field experiments were conducted in 2014 and 2015 at the Changwu Agricultural Research Centre in Shaanxi Province,China to compare soil properties,maize growth,grain yield,water and nitrogen use efficiency and soil CO2 emission among different furrow:ridge width arrangement in RFMS comprised of three different furrow:ridge ratios,i.e.furrow:ridge=70:40 cm?RFMS40?,furrow:ridge=55:55 cm?RFMS55?and furrow:ridge=40:70 cm?RFMS70?,and conventional flat planting?CK,without mulching?.This study can not only enrich and deepen our understanding of ridge-furrow planting system,but also provide references and theoretical support for the development of water-saving management balanced between high production and low carbon emission in arid and semi-arid area.The main conclusions in this study were as follows:?1?The RFMS practice increased the soil temperature at 5,10 and 15 cm soil depths in the ridges duruing the vegetation stage throughout two growing seasons.This positive effect was intensified with increasing ridge width in RFMS,but no significant difference was found among RFMS40,RFMS55 and RFMS70.In comparison with CK,RFMS practice improved soil moisture in the furrow while decreased soil water content in the ridge,thus exhibited a significant difference between ridge and furrow soils.Besides,soil moisture in the furrow increased with increasing ridge width,but the difference between three furrow:ridge ratios was not statistically significant.RFMS practice changed soil bacterial alpha diversity greatly in comparison with CK,especially for the rhizosphere soil.But the impact of soil types?rhizosphere soil v.s.bulk soil?on soil bacterial communities was much higher than planting methods?CK v.s.RFMS?.After harvest,no significant difference in soil organic carbon content was found between CK and RFMS at 0-20 cm soil depth.?2?The plant height,stem diameter,leaf area index?LAI?and the leaf SPAD in RFMS were significantly higher than those of CK in both years.Stem diameter and LAI in CK plots reached their peaks almost 20 days later than that of RFMS during both years.Similarly,the aboveground biomass and root weight density were also higher in three RFMS ratios than that of CK.Aboveground biomass at the harvesting stage of RFMS40,RFMS55 and RFMS70were 26.0%,33.5%and 47.6%higher than CK averaged across two years,respectively.Among the three furrow:ridge ratios,aboveground biomass showed an increase with increasing ridge width which was not found in the root biomass.RFMS also increased the average grain-filling rate and prolonged the active grain-filling period and the effective grain-filling time.Changing the ratio of furrow and ridge also had a great impact on grain filling.Compared with RFMS40 and RFMS55,RFMS70 shortened the days and increased the average grain filling rate during the early grain-filling period,thus resulted in a higher grain weight.In comparison with CK,maize yield averaged across two years was increased by26.1%,36.4%and 50.3%under RFMS40,RFMS55 and RFMS70 treatments,respectively.Our results also showed that the great increase of yield under RFMS was accompanied by high kernel number per spike?R=0.92**?and high 100–kernel weight?R=0.97**?.?3?RFMS increased the soil water storage of 0-200 cm soil but did not decrease the evapotranspiration significantly.In comparison with CK,the 2-year average WUE was increased by 25.7%,38.7%and 53.9%under RFMS40,RFMS55 and RFMS70 treatments,respectively.In addition,RFMS also enhanced the nitrogen use efficiency in maize plant.At harvesting,nitrogen uptake in grain was significantly higher in RFMS than CK,although no difference was found in straw.The RFMS practice significantly increased nitrogen uptake efficiency?NupE?,nitrogen fertilizer productivity?Nfp?,nitrogen use efficiency?NUE?and nitrogen harvest index?NHI?,while changing furrow:ridge ratio had greater impact on NupE and Nfp.?4?Three RFMS practices increased soil respiration,and the significant difference was found between RFMS70 and CK in both years.RFMS also had a higher soil autotrophic respiration?R_a?and heterotrophic respiration?R_h?compared to CK,while no significant difference was found among all treatments.Besides,the ridge soils in three RFMS ratios exhibited a 14.0%,16.5%and 15.2%higher soil respiration than the furrow soils,respectively.Soil respiration in both CK and RFMS showed a high positive correlation with soil temperature and their relationship can be well-fitted by the exponential function.And soil temperature can explain the soil respiration variation in unmulched soils?CK and furrow?better than in the mulched ridge soils.Besides,the unmulched soils also exhibited a higher temperature sensitivity(Q₁₀)of soil respiration than the ridge soil.Aboveground biomass had a stronger relationship with the total soil respiration compared with root biomass in both CK and RFMS treatments,while root biomass was more strongly correlated with autotrophic respiration than with the total soil respiration.The two-year experiment showed that soil CO₂emission was increased by 10.6%,19.6%,and 20.4%under RFMS40,RFMS55,and RFMS70 treatments than CK,and carbon emission efficiency?CEE?was 13.6%,13.5% and24.1%higher than CK,respectively.During the whole growing season,maize field showed a strong carbon sink,and net ecosystem exchange was significantly higher in RFMS than in CK.Among three RFMS ratios,net carbon uptake in RFMS70 was 23.1% and 11.8%higher than RFMS40 and RFMS55,respectively.After taking carbon input in maize seeds during sowing and carbon losses during harvest into account,both CK and RFMS showed net carbon loss,without significant difference.However,RFMS70 exhibited lower carbon loss than CK,RFMS40 and RFMS55 in both years.In general,RFMS70 with high grain yield,water and nitrogen use efficiency,net carbon uptake and CEE is recommended for maize production in the Loess Plateau to have high crop yield and small climatic impacts.