| In recent years,alfalfa had cultivated widely on the loess plateau and its planting area accounts for 90% of artificial grassland area,since the planting industrial structural adjustment and the implementation of returning farmland to grassland.During initial stage,alfalfa yield was high and stable due to the supplement of rainfall and the storage soil water,but the strong consumption characteristics of alfalfa led the deep soil moisture close to wilting moisture, after growing several years,alfalfa grassland would form permanent evapotranspiration soil layer, which led to the recession of alfalfa grassland.Soil desiccation and the degradation of alfalfa grassland was increasingly serious,so the problem of soil moisture recovery and efficient using of land became increasingly prominent.By the way of fallow during rainy season and little water consumed crops rotation could overcome and relieve alfalfa's strong water consumption effect,and improve and restore deep soil moisture.In this research, based on the measurement of yield,soil moisture and soil nutrients of alfalfa grassland and soil moisture of rotation crops. EPIC mode's 0509 edition which was develped by USA scientist Williams was applied to simulate the potential productivity and the changes of deep soil water of semi-humid area Zhenyuan and semi-arid area-Guyuan from 1960 to 1990,and semi-arid prone to drought area-Haiyuan from 1960 to 1995,to choose the best alfalfa-crop rotation for different rainfall areas of Loess plateau,at the same time,we compared the differences of soil water recovery effects of different rainfall areas with its best alfalfa-crop rotation pattern,these works could provide the basic scientific foundations for sustainable way of using alfalfa grassland and stable yield of crops on dryland in Loess Plateau. The progresses of this study were as following:1 Field experimental results showed as following:(1) The field soil water and nutrients investigation results of three rainfall areas showed that:In Zhenyuan,the mean soil moisture of 11 year-old alfalfa grassland of 0～300cm soil layers was 9.89%,which was close to the wilting mositure 9.00% ,and soil total nitrogen, total phosphorus, total potassium contents of 15 year-old alfalfa grassland were lower than that of 10 year-old alfalfa,so the best planting year of alfalfa grassland of Zhenyuan was no more than 11 year; In Guyuan, the yield of 7 year-old alfalfa grassland declined sharply and became to degradation, the mean soil moisture of 8 year-old alfalfa grassland of 0～300cm soil layers was close to the wilting mositure 5.00%,and the deep layers soil nutrients of 6～7 year-old were deficienct seriously,so the best planting year of alfalfa grassland of Guyuan was 7 years; In Haiyuan, the yield of 7 year-old alfalfa grassland declined sharply,and the mean soil moisture of 7 year-old alfalfa grassland of 0～300cm soil layers decreased seriously which was close to the wilting mositure 4.50%,besides,soil nutrients of 6～7 year-old were deficienct seriously,so the best planting year of alfalfa grassland of Haiyuan was 6 years.(2) The field soil water investigation results of rotation crops of three rainfall areas showed that:In Zhenyuan,10 year-old alfalfa grassland's soil water storage capacity of 0～1000cm was 1607.84mm, soil water of fully recovery should be 2015.00mm,soil water should restored was 407.16 mm, the average soil moisture restoration rate was 77.15mm/a, 5.28 years rotation could recover the soil mositure,so the reasonable rotation pattern of Zhenyuan was"10 years alfalfa→over 5～6 years crop";In Guyuan,7 year-old alfalfa grassland's soil water storage capacity of 0～1000cm was 777.19mm,soil water of fully recovery should be 1560.00mm,soil water should be restored was 782.81 mm,the average soil moisture restoration rate was 80.88mm/a,9.68 years rotation could recover the soil mositure,so the reasonable rotation pattern of Guyuan was"7 years alfalfa→over 9～10 years crop";In Haiyuan,6 year-old alfalfa grassland's soil water storage capacity of 0～1000cm was796.88mm, soil water of fully recovery should be 1397.50mm,soil water should be restored was 600.62mm,the average soil moisture restoration rate was 25.14mm/a,23.89 years rotation could recover the soil mositure,so the reasonable rotation pattern of Haiyuan was"6 years alfalfa→over 23～24 years crop".2 EPIC0509 simulation results showed as following:(1) The simulation results of three rainfall areas showed that:In Zhenyuan,water potential productivity increased gradually from 1 to 7 years,after that alfalfa grassland began to degradation since the water stress days increased,soil available water declined and the formation of soil dry layer,the alfalfa yield of 11 year-old only accounts for 36% of 7 year-old alfalfa,the soil water consumption of 9～11 year-old alfalfa grassland was deeper than 10m,there was serious soil desiccation,so alfalfa grassland of Zhenyuan should be rotated by crops after planting 9～10 years;In Guyuan,water potential productivity of 7 years decreased sharply,at the same time,stable soil dry layer was formed in 1～6m and soil available water waved on low level, so alfalfa grassland of Guyuan should be rotated by crops after planting 6～7 years;In Haiyuan,the trend of water potential productivity was same to Guyuan, soil available water waved on low level during 6～7 year-old alfalfa grassland, stable soil dry layer was formed in 1～6m of 5 year-old alfalfa grassland,while it was formed in 1～8m of 6 year-old alfalfa grassland, so alfalfa grassland of Haiyuan should be rotated by crops after planting 5～6 years;(2) The simulation results of alfalfa-corp rotation in three rainfall areas showed that:In Zhenyuan,the yield of 15 year-old crop declined sharply, and the soil water restored completely before planting 15 years corp,so the reasonable alflalfa-crop rotation pattern of Zhenyuan was"10 years alfalfa→15 years Ww-Ww-Ss";In Guyuan,the yield of 16 year-old crop declined evidently,and the SWRI of 16 year-old crop was 0.92,the soil water restored excellently,so the reasonable alflalfa-crop rotation pattern of Guyuan was"7 years alfalfa→16 years P-P-Sw";In Haiyuan,the yield of 22 year-old corp bagan to wave on low level,and the SWRI of 24 year-old crop was 0.84,the soil water restored excellently,so the reasonable alflalfa-crop rotation pattern of Haiyuan was"6 years alfalfa→24 years P-P-Sw".In conclusion,based on the validation of field data,using EPIC model to simulate the effects of three rainfall areas could make up for the shortcomings of field experiment,made the reserch results more comprehensive and reliable. |
PDF Full Text Request