Competition And Compensation Of Potato-soybean Relay-cropping In Northwest Irrigation Districts

Intercropping is widely practiced in Northwest irrigation districts because of its significant overyielding and nutrition acquisition.Interspecies interactions was the intrinsic factor to coordinating resources use in intercropping systems.To further improving the resources use efficiency,coordination the relationship between interspecies competition and facilitation and utilization the spatial-temporal niche differentiation was current problem to be solved.Therefore,a study took the potato and soybean intercropping system as simple,with different cultivation systems and soybean varieties,was carried out in Gansu irrigation districts.Our works reported here are aiming at investigating the structure of growth period,the characteristics of crop growth and nutrient absorption,determining dry matter accumulation,nutrient accumulation and photosynthetic physiological characteristics,interspecific competition dynamics and niche differentiation characteristics,clarifying the resources saving mechanism of intercropping.Main results were summarized as the following:1.There was no significant difference of the structure of growth period between intercropped potato and sole potato under continuous intercropping system and different soybean varieties intercropping system.But there was significant difference of the structure of growth period between intercropped soybean and sole soybean under continuous intercropping system and different soybean varieties intercropping system.In comparison with sole cropping,intercropping led to delay reproductive growth stage of soybean but not change the whole growth period,the duration from plating to flowering was extended,but the duration from flowering to maturing was shortened.The co-growth stage of different soybean varieties was not affected by intercropping,but the reproductive co-growth stage?from flowering to maturing?was remarkable,?late maturing variety was 12 days,middle-maturing variety was 36 days,early-maturing variety was 42 days?.2.Compared with successive cropping and continuous intercropping system,dry matter of potato and soybean in rotatory intercropping system increased by 15.02%and 41.57%after three years and there was significant difference between intercropping and sole cropping.Interspecies interactions significantly affected the dry matter and nutrient accumulation of soybean in intercropping systems.Dry matter accumulation of inter-soybean relative to sole soybean was decreased by 43.74%at 60 days after soybean sowing,but there was no significant difference between different soybean varieties.Dry matter accumulation of late maturing variety was 35.54%-59.22%and 65.56%-70.81%higher than those under medium maturing and early maturing varieties at 80-100 days after soybean sowing,respectively.When the potato had been harvested?100 days after soybean sowing?,the dry matter accumulation of soybean in all intercropping systems increased,especially late maturing varieties,which became much closer to sole cropping,and the dry matter accumulation of inter-soybean relative to sole soybean was decreased by 32.34%,16.61%and 8.23%at soybean harvest,and there was significant difference between different soybean varieties.During the co-growth period,there was significant difference between late maturing variety and medium and early maturing variety.3.Compared with successive cropping and continuous intercropping system,nutrient accummulation of potato and soybean in rotatory intercropping system increased after three years,Nutrient N accumulation of potato and soybean inrotatory intercropping system increased by 12.89%and 55.78%,Nutrient P accumulation of potato and soybean inrotatory intercropping system increased by 1.78%and148.63%,Nutrient k accumulation of potato and soybean inrotatory intercropping system increased by 16.77%and 115.07%.Nutrient N accumulation of early,medium and late maturing varieties of inter-soybean relative to sole soybean was decreased by 41.44%,38.91%and 31.43%,respectively.Nutrient P accumulation was decreased by 25.36%,22.02%and 21.17%,and nutrient K was decreased by 35.6%,27.28%and 23.23%,respectively.After potato harvest,nutrient N decreased by 11.12%,12.16%and 5.89%,nutrient P decreased by 4.83%,5.48%and 4.87%,nutrient K decreased by 10.44%,7.85%and 5.36%,respectively.Potato-soybean intercropping systems not only was overyielding but also had nutrient acquisition advantage,showing the stronger intercropping superiority.Topsoil fertility was improved to some extent by different cultivation systems,Topsoil fertility of potato-soybean intercropping systems?IC or IR?had obvious decline after four years of continuous cropping compared with PM,SM and P-S.Yearly changes of different cultivation systems on available N,P and K were obvious difference from 2011 to 2014.Estimate of different cropping systems nutrient apparent balance,indicating that interspecies interactions was the important factor to coordinating nutrient use in intercropping systems and improving the nutrient use efficiency.4.Continuous intercropping systems had predominant advantage,crop yields of IC and IR treatments enhanced by 28.54%-254.07%and 39.39%-283.98%in comparison with PM and SM,respectively,and increased by 57.5%and 70.81%in comparison with P-S over four years respectively.There was no significant difference in system yield between IC and IR in 2011and 2012,but there was obvious difference in 2013 and 2014,the system yield of IC was significantly lower than IR,which decreased by 13.91%-24.71%.Compared with sole cropping,the yield of potato in intercropping system decreased by 5.24%-7.86%.There was no significant difference in yield of potato between intercropping and sole cropping,but there was obvious difference in yield of soybean between different varieties.The yield of inter-soybean relative to sole soybean was decreased by 41.49%,17.18%and 9.89%,respectively,and there was significant difference between late maturing and medium and early maturing soybean varieties.Average fresh-weight of potato in successive cropping and continuous intercropping system decreased after three years,but there is no difference in rotatory intercropping system in different years.Pods per plant of soybean in successive cropping and continuous intercropping system decreased after three years,but compared to 2011,pods per plant of soybean in rotatory intercropping system increased by 9.46%in 2014.Compared with sole cropping,the pods per plant,seeds per plant and seeds per pod of early-maturing soybean in intercropping system decreased by 24.15%,22.14%and 18.92%,respectively.However,Effective pods per plant,seeds per plant and seeds per pod of late-maturing soybean decreased by 5.66%,7.64%and 2.11%,respectively.5.The land equivalent ratio?LER?was greater than 1 under different cultivation systems and soybean varieties,indicating that intercropping increased the efficiency of land use and capacity of yield productivity.In potato-soybean intercropping system,the values of A_PS,CR_PS,K_PS and CC indicated that the potato was more competitive than soybean,late maturing variety was better than early maturing and medium maturing varieties to intercrop with potato,the interspecific competition in using resources was been weaken during the co-growth period,and it was beneficial to the compensation effect of soybean during the period after potato harvest.During the co-growth period,compared with medium maturing and early maturing varieties,the competitiveness of potato relative to soybean?A?of late maturing variety decreased by 27.17%and 30.61%,respectively.The nutrient N,P,K competitiveness of potato relative to soybean?CR?of late maturing variety was 9.34%-12.87%?0.45%-3.54%and 4.44%-13.94%lower than those under medium maturing and early maturing varieties,respectively.After potato harvest,the growth rate of late maturing variety was 128.13%and196.28%higher than those under medium maturing and early maturing varieties,respectively.N,P,K uptake under late maturing variety were 19.23%-44.19%,2.03%-17.44%and 7.62%-9.38%higher than those under medium maturing and early maturing varieties,respectively.