| Integrating annual forage crops into fallow-winter wheat(Triticum aestivum L.)cropping system could enhance system productivity and resource use efficiency in the Loess Plateau.However,this region precipitation distribution is uneven in monthly and yearly,which leads to the forage-winter wheat system productivity are variable.Therefore,exploring the forage-winter wheat system productivity under variable rainfall scenarios,it has the theoretical and practical guiding significance for optimizing the planting structure and adapting to future climate change in the region.This study was carried out at the Qingyang Grassland Ago-ecosystems Field Research Station of Lanzhou University from 2016 to 2020.The traditional fallow-winter wheat as control,three annual forage crops of oat(Avena sativa L.),soybean(Glycine max L.),and vetch(Vicia sativa L.)were plating in the fallow season to create 3 annual forage crops-winter cropping systems.The rainfall-collection-redistribution device was used to simulate a 30%decrease in rainfall(R-30%),normal rainfall(CK),and a 30%increase in rainfall(R+30%)three rainfall scenario.Therefore,this experiment had four rotation systems,and three rainfall scenarios.We measured each treatment crop grow process,yield,soil water content,and soil nitrogen content;Meanwhile,combined with APSIM(Agricultural Production System Simulator)model,to reveal the precipitation variation how to effects on annual forage-winter wheat rotation system productivity,water and nitrogen utilization characteristics in the Loess Plateau.The main results are as follows:1.Clarification precipitation variation on crop growing process in annual forage-winter wheat rotation system.The forage and winter wheat growing process were significantly affected by the precipitation variations.The forage crops plant height,leaf area index(LAI),normalized difference vegetation index(NDVI),and light interception were significantly positive correlation with precipitation.However,the winter wheat growing process were influenced by the forage species and precipitation distribution.Compared to CK scenario,the R-30%scenario oat,soybean,and vetch light interception decreased by 12.4%,6.6%,and 12.8%(p<0.05).But the R+30%scenario fallow-winter wheat(F-W),oat-winter wheat(O-W),soybean-winter wheat(S-W),and vetch-winter wheat(V-W)systems winter wheat LAI were increased by24.9%,47.9%,31.7%,and 24.6 respectively(p<0.05).Integrating forage crops into fallow-winter wheat cropping system significantly influenced wheat growth,and the wheat growth influenced by the annual precipitation type.In dry year(annual precipitation less than 494 mm),compared to F-W system,the O-W,S-W,and V-W systems winter wheat plant height were decreased by 34.4%,19.5%,and 22.1%,light interception were decreased by 47.5%,5.7%,and 25.0%,respectively(p<0.05).In normal year(annual precipitation from 494 to 575 mm),the F-W,O-W,S-W,and V-W systems winter wheat NDVI were 0.80,0.79,0.81,and 0.80,respectively.In wet year(annual precipitation over 575 mm),planting oat,soybean,and vetch in fallow seasons did not influence on winter wheat growth.2.Identification precipitation variation on the system productivity in annual forage-winter wheat rotation system.The dry matter yield and crude protein yield of forage,winter wheat,and systems were significantly influenced by the precipitation variations,and it is a linear positive correlation with precipitation.Compared to CK scenario,the oat,soybean,and vetch dry matter yield were significantly increased by 14.2%,18.8%,and 18.2%,the F-W,O-W,S-W,and V-W systems wheat grain yield were significantly increased by 49.4%,50.0%,31.0%,and 52.0%,the system dry matter yield were significantly increased by 16.5%,12.1%,15.0%,and 11.7%,respectively,under R+30%scenario.But the R-30%scenario wheat grain yield decreased by19.8%,25.5%,18.1%,and 20.4%;the system dry matter yields were decreased by24.2%,23.7%,30.8%,and 33.7%(p<0.05).Integrating forage crop into fallow-winter wheat cropping system significantly enhanced productivity,and the winter wheat yield determined by the annual precipitation type.In dry year,compared to F-W,the O-W and V-W system wheat grain yield decreased by 63.8%and 28.3%(p<0.05),but the system dry matter yield increased by 26.2%and 11.3%(p<0.05),and the S-W system did not influence on wheat grain yield(p>0.05).In normal year,the F-W,O-W,S-W,and V-W system forage yields were 0.0,4.7,3.2,and 2.1 t hm-2,the wheat grain yield were 3.1,3.5,3.7,and 3.0 t hm-2,and the system dry matter yield were 11.0,15.9,14.6,and 12.9 t hm-2.In wet year,the forage oat,soybean,and vetch yield were 6.5,5.4,and 3.7 t hm-2.The F-W,O-W,S-W,and V-W system wheat grain yield were 4.5,5.0,5.6,and 4.2 t hm-2.Compared to F-W system,the O-W,S-W,and V-W system dry matter yield were increased by 39.7%,24.3%,and 24.3%(p<0.05).3.Quantifying precipitation variation on soil water content,water use,and water use efficiency in annual forage-winter wheat rotation system.The precipitation variation had a significant influence on water use in forage and winter wheat growing seasons.Compared to CK scenario,the F-W,O-W,S-W,and V-W systems water use were increased by 27.5%,31.4%,32.3%,and 30.1%under the R+30%scenario(p<0.05),respectively.But the R-30%scenario system water use decreased by 24.4%,27.7%,30.7%,and 24.4%(p<0.05),respectively.Integrating forage crops into fallow season significantly enhanced system water use efficiency.In dry year,compared to F-W,the O-W,S-W,and V-W systems soil water storage at winter wheat sowing stage 0-300 cm were decreased by 17.3%,10.3%,and 15.0%;but the system water use efficiency water use efficiency were increased by 41.1%,43.8%,and 17.7%,respectively(p<0.05).In normal year,the F-W,O-W,S-W,and V-W system forage water use efficiency were 0.00,24.77,21.69,and 12.01 kg hm-2 mm-1;the wheat water use efficiency were 7.69,12.68,11.54,and9.78 kg hm-2 mm-1;and the system water use efficiency were 20.25,30.33,27.55,and 23.79 kg hm-2 mm-1.In wet year,compared to F-W,the O-W,S-W,and V-W system water use efficiency were increased by 23.6%,30.8%,and 17.4%;and the system precipitation use efficiency increased by 39.7%,36.9%,and 24.4%(p<0.05).Integrating forage crops into fallow season could deplete amount soil water and decreased soil water storage at wheat planting stage,but it did not influence on the system water use.4.Exploring precipitation variation on nitrogen utilization in annual forage-winter wheat rotation system.The precipitation variation had significant influenced on nitrogen partial productivity in the forage,winter wheat,and system,which increased with the growing seasons precipitation.Compared to CK scenario,the F-W,O-W,S-W,and V-W systems nitrogen partial productivity were increased by 22.9%,34.5%,20.4%,and 33.8%,respectively,under the R+30%scenario;but under R-30%scenario system nitrogen partial productivity were decreased by 24.2%,23.7%,30.8%,and33.7%(p<0.05).Integrating forage crops into summer fallow period significantly enhanced the nitrogen partial productivity.In dry year,compared to F-W system,the O-W,S-W,and V-W system nitrogen accumulation were increased by 35.7%,134.4%,and 70.1%(p<0.05).In normal year,the F-W,O-W,S-W,and V-W system forage nitrogen partial productivity were 0.00,47.02,158.80,and 103.45 kg kg-1;the winter wheat nitrogen partial productivity were 26.14,28.82,30.94,and 25.03kg kg-1;and the system nitrogen partial productivity were 91.64,72.17,104.00,and91.79 kg kg-1.In wet year,compared to F-W system,the S-W and V-W system nitrogen partial productivity were increased by 17.3%and 23.8%;but the O-W system decreased by 6.6%(p<0.05).5.Based on the APSIM model,exploring more precipitation scenarios effects on productivity,water and nitrogen utilization in annual forage-winter wheat rotation system.Through the long-term 55 years simulation find that the precipitation variation significantly influenced the annual forage-winter wheat system yield,water use efficiency,and nitrogen partial productivity.In the normal years,the F-W,O-W,S-W,and V-W systems forage yields were 0.0,5.8,3.4,and 3.4 t hm-2,the winter wheat yields were 4.8,3.7,4.9,and 4.3 t hm-2,the system dry matter yields were 12.0,15.1,15.2,and 13.8 t hm-2,system water use efficiency were 22.6,28.7,27.6,and 25.4 kg hm-2 mm-1;the system nitrogen partial productivity were 100.0,68.8,108.2,and98.5 kg kg-1,respectively.In the dry years,compared to F-W,the O-W,S-W,and V-W system wheat grain yield decreased by 72.6%,51.4%,and 61.7%,respectively.In wet years,compared to F-W,the O-W,S-W,and V-W systems dry matter yield increased by 35.5%,19.5%,and 17.2%;the system water use efficiency increased by 35.4%,24.9%,and 15.8%,respectively.In conclusion,the precipitation variation significantly influenced the forage-winter wheat system productivity,water use efficiency,and nitrogen partial productivity.The oat-winter wheat system could obtain the highest dry matter yield,which significantly improve the system water use efficiency,precipitation use efficiency,and nitrogen accumulation.But the oat depleted amount result in soil water depletion,which lead to increasing the risk of decline in winter wheat yield.We recommend oat-winter wheat system under future climate scenarios with increased rainfall or regional applications with supplemental irrigation.The soybean-winter wheat system not only obtain a large amount of high-quality forage,but also fix the nitrogen,reduce fertilizers,enhance the water and nitrogen use efficiency,and improve the system productivity.Therefore,we recommended the soybean-winter wheat system to optimize planting structure,and promote the agricultural sustainable development in the Loess Plateau. |
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