Effect Of Dense Planting On The Ecological Processes Of Productivity Formation And Greenhouse Gas Emissions In Maize/Pea Intercropping System

Intercropping,especially cereal/legume intercropping,has the advantage of high productivity and low greenhouse gas emission.Planting density has also been proved to be an important measures to adjust crop population structure and increase yield.However,there is a lack of theoretical basis,referring to whether carbon emissions can be reduced while productivity is improved when planting density and intercropping are integrated into the same system.It is of great significance to explore this mechanism for improving intercropping productivity and reducing greenhouse gases.Field experiment was conducted at Wuwei,northwest China,in 2014 and 2015.Two N fertilizer rates?low-N₀ and high�N₁?,three maize plant densities?low�D₁,medium�D₂,and high�D₃?and three planting patterns?sole maize-M,sole pea-P and maize/pea intercropping-M/P?were designed to create the different levels of source availabilities.The growth characteristics,greenhouse gas emission,interspecific relationship and resource utilization characteristics of monoculture,intercropped maize and pea were studied under different maize planting density in order to provide theoretical and practical basis for reducing greenhouse gas emission while improving the productivity of intercropping.The main results are as follows:1.The yield of intercropping increased significantly under close planting,and the compensatory growth effect of corn increased after pea harvest,The increase of maize planting density reduced the competitiveness of maize to pea in the co-growth period,but increased the compensatory effect of maize after pea harvest,and then formed a higher intercropping productivity.In the two-year experiment,the relative crowding index of maize/pea intercropping was greater than 1,and the land equivalent ratio?LER?of maize/pea intercropping was greater than 1.The yield of maize/pea intercropping increased by 34.0%and37.9%on average compared with that of monoculture system.The synergetic yield increase of planting density and maize/pea intercropping system was 9.3%.After pea harvest,intercropped maize quickly recovered its growth,its growth rate was significantly greater than that of corresponding monocropping,showing a strong ability to recover growth,and alleviating the loss caused by early competition.The compensation effect of intercropped maize was greater than 1.The stage of after pea harvest was the main growth period for intercropped maize to obtain high yield.2.Dense planting significantly reduced the greenhouse gas emissions of intercropping maize and pea.The carbon emission and N₂O-N emission of monoculture and intercropping decreased with the increase of maize planting density.Soil carbon emission of monoculture maize in D2 decreased by 12.6%than that in D₁,and D₃ decreased by 10.1%than that in D₂,while that of intercropped maize in D₂ decreased by 5.6%than in D₁,and 6.2%lower in D₂ than in D₃.Before the pea harvest,the carbon emission of intercropped maize decreased by 30.8%and 21.6%with the high planting density than that with low and medium planting density respectively,and that of monoculture maize decreased by 32.0%and 16.2%respectively.After the pea harvest,the carbon emission of intercropped maize decreased by 12.9%and 8.5%with the high planting densitythan that with low and medium planting density respectively,and that of monoculture maize decreased by 23.5%and 12.9%respectively.The N₂O-N emission of monoculture maize with D₂ decreased by 23.9%than that with D₁,and 17.2%lower with D₃than with D₂,The N₂O-N emission of intercropped maize with D₂ decreased by 13.8%than that with D₁,and 15.1%lower with D₃ than with D₂.Before pea harvest,the N₂O-N emission of intercropped maize decreased by 32.9%and 16.4%under high planting density than that under low and medium planting density respectively,and that of monoculture maize decreased by59.0%and 35.2%respectively.After pea harvest,the N₂O-N emission of intercropped maize decreased by 57.1%and 38.8%under high planting density than that under low and medium planting density respectively.The total soil carbon emission in the whole growth period of maize/pea intercropping decreased by 17.7%,10.2%and 5.3%respectively with the increase of maize planting density under the nitrogen application mode compared with the weighted average of soil carbon emission under the two monoculture systems.The carbon emission of maize and pea accounted for 70.2%and 29.8%respectively.The carbon emission of intercropped pea before harvest was larger,and its contribution to the total emission was 53.0%.Dense planting density was an effective measure to control the carbon emission of pea.The carbon emission of intercropped maize after pea harvest was an important source of its total carbon emission.The carbon emission of maize decreased with the increase of planting density.The total N₂O-N emission in the whole growth period of maize/pea intercropping decreased by 15.1%,10.5%and 12.7%respectively with the increase of maize planting density.In the intercropping system,the N₂O-N emission of intercropped maize accounted for 68.9%of the total emission of the system,and that of intercropped pea accounted for 31.1%.Maize was still the main source of N₂O-N emission of the soil in the intercropping system.The combination of dense planting density and maize/pea intercropping showed a better synergistic effect on reducing greenhouse gas emission and had great potential for carbon emission reduction.3.GWP of maize/pea intercropping decreased with the increase of maize planting density.GWP of monoculture maize decreased by 5.8%in D₂ than that in D₁,and 8.4%lower in D₃ than that in D₂.GWP of intercropped maize decreased by 8.8%in D₂ than that in D₁,and 10%lower in D₃ than that in D₂.Before pea harvest,GWP of sole maize decreased by 33.6%and 24.1%under high maize planting density than that under low and medium planting density respectively,and GWP of intercropped maize decreased by 42.6%and 23.5%under high maize planting density than that under low and medium planting density respectively.After pea harvest,GWP of sole maize decreased by 36.1%and 22.5%under high maize planting density than that under low and medium planting density respectively,and that of intercropped maize decreased by 36.8%and 28.0%respectively.Maize/pea intercropping can reduce GWP,and the GWP of maize/pea intercropping was 89.8%higher than that of sole pea,and 24.3%lower than that of sole maize.The GWP of maize/pea intercropping in the whole growth period decreased by 5.0%on average compared with that of pea and maize.In this study,the combination of maize/pea intercropping and dense planting density had a good synergistic effect on the warming potential of greenhouse gas emissions,and the collaborative emission reduction was7.9%.Before the pea harvest,the GWP of intercropped maize was 37.9%lower than that of monoculture maize,and after the pea harvest,the carbon emission of intercropped maize was23.8%higher than that of monoculture maize.The harvest of pea was an important growth period for regulating GWP of maize.4.Dense planting strengthened the advantage of intercropping resource utilization,improved and promoted the resource utilization efficiency of intercropping and reduced carbon emission.The increase of maize planting density improved the resource utilization efficiency of intercropped compound population and reduced carbon emission.The increase of maize planting density can make the crops make full use of the available water in the soil,and make the water left less in the soil at harvest.At the same time,reasonable increasing the maize planting density is one of the effective agronomic measures to reduce the ineffective water consumption in maize/pea intercropping system.The N use efficiency of maize/pea intercropping was 25.2%higher than that of sole cropping.The N use efficiency and N-fertilizer use efficiency of intercropping increased with the increase of planting density.In two years,the N-fertilizer use efficiency of intercropped pea with high planting density was lower than that of intercropped pea with high planting density,and the N-fertilizer use efficiency of intercropping pea with medium planting density was increased by 40.4%and17.9%respectively.The ability of intercropping to maintain the appropriate competitiveness is conducive to the improvement of nitrogen uptake and yield,the accumulation of pea and maize dry matter in the co-growth period,and the increase of maize competitiveness is an important guarantee to improve nitrogen utilization efficiency.The flowering and pod setting stage of pea is the key period to control the interspecific competitiveness and obtain high yield of intercropped crops.The combination of maize/pea intercropping and high planting density has a good synergistic effect on the emissions intensity of greenhouse gas,and the collaborative emission reduction is 7.1%.The greenhouse gas emission intensity of maize/pea intercropping was 11.7%lower than that of sole pea and sole maize.The increase of maize competitiveness in intercropping is an important factor to reduce the emissions intensity of greenhouse gas.