黄土高原半湿润区苜蓿—粮食作物轮作效应模拟研究
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摘要
紫花苜蓿是多年生豆科牧草作物,在黄土高原半湿润区大面积栽培。苜蓿具有强烈的耗水性能,导致半湿润区苜蓿草地发生干燥化,草地退化较为严重。为了克服和缓解苜蓿草地高强度耗水效应,逐步提高和恢复苜蓿草地深层土壤湿度,需要采取雨季休闲或轮作耗水量较小的粮食作物等措施,促进干燥化苜蓿草地的更新和高效再利用。
本研究采用野外实地测定和EPIC模型模拟相结合的方法研究了黄土高原半湿润区苜蓿草地土壤干燥化特征和草粮轮作土壤水分恢复效应。首先,对黄土高原半湿润区镇原不同生长年限苜蓿草地深层土壤水分进行了测定,分析了不同生长年限苜蓿草地深层土壤干燥化特征。同时,对连作10年苜蓿翻耕后轮作不同生长年限粮食作物农田的深层土壤水分进行了测定,探讨了采用不同年限草粮轮作方式对苜蓿草地土壤水分恢复效果。其次,选取黄土高原半湿润区镇原为试验站点,组建逐日气象要素序列、典型土壤剖面理化性状、作物生长参数等一系列数据库,借助EPIC0509模型,模拟研究了1～16年生苜蓿草地水分生产力和土壤干燥化效应,并设置了10年生苜蓿与21年“连作春大豆”、“连作冬小麦”、“连作春玉米”、“冬小麦→冬小麦→春大豆(WWS)”、“冬小麦→冬小麦→春玉米(WWC)”、“春大豆→春大豆→冬小麦(SSW)”和“春大豆→春大豆→春玉米(SSC)”等7种草粮轮作的长周期定量模拟试验,对苜蓿草地轮作不同类型粮食作物后的逐年产量变化以及深层土壤干层湿度恢复规律进行了动态模拟分析,依据试验结果,选择出了适应半湿润区的最优草粮轮作方式。研究取得的进展:
1.镇原实测结果:
(1)黄土高原半湿润区15～28年生苜蓿草地0～1 000 cm土层土壤湿度平均为10.20%,土壤干燥化速度34.2 mm·a~(-1),土壤干层最大分布深度超过了1 400 cm。苜蓿草地适宜翻耕和轮作粮食作物的生长年限为10年生。
(2)苜蓿草地翻耕并轮作3～25年粮食作物后土壤干层湿度能够逐步恢复,土壤干层恢复厚度为583 cm,土壤湿度恢复度为83.3%,达到极好恢复程度,土壤湿度恢复速率为77.3 mm·a~(-1)。通过粮草轮作方式使15年生苜蓿草地土壤湿度恢复到当地土壤稳定湿度需要8年以上。有利于土壤水分恢复的适宜粮草轮作模式是“10年生苜蓿→8年以上粮食作物”。
2.模拟结果:
(1)苜蓿草地产量和土壤水分变化模拟结果表明,10年生苜蓿草地0～1000 cm土层土壤有效含水量波动较小,土壤湿度趋于不稳定,土壤发生严重干燥化,导致草地产量下降。所以苜蓿生长10～12年后,应采取草粮轮作等适当措施来缓解土壤水分亏缺加剧。
(2)不同草粮轮作方式下土壤湿度恢复模拟结果表明,草粮轮作利于干燥化苜蓿草地土壤水分的恢复,土壤水分恢复效果与轮作年限成正比。在7种轮作方式中,连作春大豆、轮作WWS和SSW达到完全恢复程度所需年限为15年,连作冬小麦、轮作WWC和SSC达到完全恢复程度所需年限为21年,7种轮作方式中WWS土壤水分恢复状况最为显著,轮作方式比连作方式的恢复效果要好。
(3)不同草粮轮作方式下粮食作物产量模拟结果表明,在整个轮作过程中,产量呈现“倒U”型。苜蓿草地翻耕后种植15年左右的粮食作物为宜,此时土壤水分就已经恢复到了较好水平。
(4)不同草粮轮作方式下土壤养分演变模拟结果表明,种植苜蓿对土壤有机碳和有机氮的积累起到了促进作用,有机碳和有机氮积累与苜蓿生长年限成正比,有机磷、活性磷和NO_3-N含量则略有降低。7种轮作模式中的粮食作物均消耗土壤有机碳、有机氮和有机磷,损耗最大的是冬小麦,损耗最小的是春大豆,二者轮作则有利于冬小麦田有机质含量的积累。表明WWS轮作模式有利于土壤养分的均衡。
(5)综上所述,既要考虑到不同轮作模式下土壤湿度和水分生产力的变化动态,又要结合养分变化动态,得出“10年生苜蓿→15年WWS”为黄土高原半湿润区的最优草粮轮作方式。
Alfalfa(Medicago sativa L.)is a perennial legume grass which was cultivated widely on semi-humid areas of the loess plateau.Due to its strong consumption of soil water,soil desiccation and grassland degradation happened quite frequently at this zone.In order to overcome and slow down the effects of high-intensity water consumption,then promote deep soil moisture to recover gradually,We found that these kinds of grasslands should be treated through fallow during rainy season or rotated with cereal grains that consumed little soil water, which helped to update and efficiently reuse the dried alfalfa grassland.
We used the field soil water observation combined with EPIC model simulation to study soil desiccation characters of alfalfa grassland and effects of its water recovery on the semi-arid areas of the loess planteau.Firstly,we investigated soil moisture on different growth age alfalfa grasslands and analysed soil desiccation characters,at the same time,the deep soil moisture of 10-year-old alfalfa field after rotated with different years crops were measured, and effects of soil water restoration by alfalfa-grain rotation were explored.Secondly, we used EPIC0509 model developed by USA to simulate the productivity and soil desiccated effects of 1~16-year-old alfalfa at Zhenyuan station,on the basis of creating different kinds of databases,such as the daily weather elements series,the typical profile of physicochemical properties of soil,the crop growth parameters,the field tillage mearsures,the fertilizer characteristic parameter and cropping system database.Seven disposals were designed, concluding 21 years continuous cultivation of spring soybean,winter wheat and spring corn, and the same years of rotation,which were"winter wheat-winter wheat-spring soybean (WWS)","winter wheat-winter wheat-spring corn (WWC)","spring soybean-spring soybean-winter wheat (SSW)","spring soybean-spring soybean-spring corn(SSC)"and so on,after plowing 10-year-old alfalfa.Which could help quantitatively analysis the dynamic change of annual yield and the restoration rule of soil moisture in deep soil layer.According to the quantitative simulation of long period results,we could select the optimal alfalfa-grain rotation pattern that adapted to Zhenyuan station.
The main progresses were as follows:
(1)Field experimental results in Zhenyuan showed as following:
A: The mean soil moisture in the 0~1 000 cm soil layers of alfalfa fields 15~28 years old at semi-humid zones was 10.20%,the soil desiccation rate 34.2 mm per year and the maximum distribution depth of desiccated soil layer over 1 400 cm,and only 10 years old or younger alfalfa fields were fit for tillage and crop rotation.
B: Soil moisture in the desiccated soil layer of the alfalfa fields could be restored gradually after 3~25 years of tillage and crop rotation,with the thickness of the desiccated soil layers reduced to 583 cm or by 77.3 mm·a~(-1) and the average soil water restoration index (SWRI)reaching up to 83.3%,an extremely significant level.It took at least 8 years for a 15 year-old alfalfa field to restore its soil moisture to a stable level(15.5%)common in the region by following alfalfa-grain crop rotation.Therefore,alfalfa-grain crop rotation for over 8 years was a suitable pattern to restore soil moisture in 10-year-old alfalfa fields.
(2)EPIC model simulation results showed as following:
A: The simulation results of the productivity and soil moisture change of alfalfa fields on semi-humid of the loess plateau showed that,after alfalfa 10 years’growth,the available water content in 0~1 000 cm soil layers fluctuated at a low value,soil desiccation was serious,which resulted in the instability of alfalfa yield and soil moisture situation.Therefore,proper measures should be taken to ease soil water deficit when alfalfa was planted for 10 to 12 years,such as alfalfa-grain crop rotation.
B: The simulation results of soil moisture restoration under different alfalfa-grain rotation measures showed that,the restoration effects of alfalfa-grain crop rotation were excellent,the longer the year,the better the effects.Among the seven disposals,the year for continuous cultivation of spring soybean,WWS and SSW to reach full restoration degree was 15 years,and it needed 21 years for continuous cultivation of winter wheat,WWC and SSC.We could find that WWS has the remarkable restoration of soil moisture,and the effect of rotation was better than other continuous cultivation of crops.
C: The simulation results of cereal crop yield under different alfalfa-grain rotation measures showed that,The yield played "inverted U"-type movement.15-year was suitable for crop rotation after alfalfa plowed in terms of yield components.Because the soil water restoration reached to a good level at this time.So we could plant alfalfa again after 15-year crops rotation.
D: The simulation result of soil nutrient evolution showed that,planting alfalfa was conductive to the accumulation of soil organic carbon and organic nitrogen.The year of alfalfa were longer,it would accumulate more,however,that was different for organic phosphorus, labile phosphorus and NO_3-N.Seven disposals all consumed soil organic carbon,organic nitrogen and organic phosphorus.And the continuous cultivation of winter wheat had the maximun loss of organic carbon,while the continuous cultivation of spring soybean had the least loss.Then if spring soybean rotated with winter wheat,which could relieve the loss of organic matter.All of those indicated that"WWS"was beneficial to balance soil nutrient.
E: In sum,we must think over soil moisture dynamics and soil nutrient dynamics combined with yeild dynamics by various rotation measures,then determined the suitable alfalfa-grain rotation pattern for Zhenyuan,which was"10 years alfalfa→15 years WWS".
本研究采用野外实地测定和EPIC模型模拟相结合的方法研究了黄土高原半湿润区苜蓿草地土壤干燥化特征和草粮轮作土壤水分恢复效应。首先,对黄土高原半湿润区镇原不同生长年限苜蓿草地深层土壤水分进行了测定,分析了不同生长年限苜蓿草地深层土壤干燥化特征。同时,对连作10年苜蓿翻耕后轮作不同生长年限粮食作物农田的深层土壤水分进行了测定,探讨了采用不同年限草粮轮作方式对苜蓿草地土壤水分恢复效果。其次,选取黄土高原半湿润区镇原为试验站点,组建逐日气象要素序列、典型土壤剖面理化性状、作物生长参数等一系列数据库,借助EPIC0509模型,模拟研究了1～16年生苜蓿草地水分生产力和土壤干燥化效应,并设置了10年生苜蓿与21年“连作春大豆”、“连作冬小麦”、“连作春玉米”、“冬小麦→冬小麦→春大豆(WWS)”、“冬小麦→冬小麦→春玉米(WWC)”、“春大豆→春大豆→冬小麦(SSW)”和“春大豆→春大豆→春玉米(SSC)”等7种草粮轮作的长周期定量模拟试验,对苜蓿草地轮作不同类型粮食作物后的逐年产量变化以及深层土壤干层湿度恢复规律进行了动态模拟分析,依据试验结果,选择出了适应半湿润区的最优草粮轮作方式。研究取得的进展:
1.镇原实测结果:
(1)黄土高原半湿润区15～28年生苜蓿草地0～1 000 cm土层土壤湿度平均为10.20%,土壤干燥化速度34.2 mm·a~(-1),土壤干层最大分布深度超过了1 400 cm。苜蓿草地适宜翻耕和轮作粮食作物的生长年限为10年生。
(2)苜蓿草地翻耕并轮作3～25年粮食作物后土壤干层湿度能够逐步恢复,土壤干层恢复厚度为583 cm,土壤湿度恢复度为83.3%,达到极好恢复程度,土壤湿度恢复速率为77.3 mm·a~(-1)。通过粮草轮作方式使15年生苜蓿草地土壤湿度恢复到当地土壤稳定湿度需要8年以上。有利于土壤水分恢复的适宜粮草轮作模式是“10年生苜蓿→8年以上粮食作物”。
2.模拟结果:
(1)苜蓿草地产量和土壤水分变化模拟结果表明,10年生苜蓿草地0～1000 cm土层土壤有效含水量波动较小,土壤湿度趋于不稳定,土壤发生严重干燥化,导致草地产量下降。所以苜蓿生长10～12年后,应采取草粮轮作等适当措施来缓解土壤水分亏缺加剧。
(2)不同草粮轮作方式下土壤湿度恢复模拟结果表明,草粮轮作利于干燥化苜蓿草地土壤水分的恢复,土壤水分恢复效果与轮作年限成正比。在7种轮作方式中,连作春大豆、轮作WWS和SSW达到完全恢复程度所需年限为15年,连作冬小麦、轮作WWC和SSC达到完全恢复程度所需年限为21年,7种轮作方式中WWS土壤水分恢复状况最为显著,轮作方式比连作方式的恢复效果要好。
(3)不同草粮轮作方式下粮食作物产量模拟结果表明,在整个轮作过程中,产量呈现“倒U”型。苜蓿草地翻耕后种植15年左右的粮食作物为宜,此时土壤水分就已经恢复到了较好水平。
(4)不同草粮轮作方式下土壤养分演变模拟结果表明,种植苜蓿对土壤有机碳和有机氮的积累起到了促进作用,有机碳和有机氮积累与苜蓿生长年限成正比,有机磷、活性磷和NO_3-N含量则略有降低。7种轮作模式中的粮食作物均消耗土壤有机碳、有机氮和有机磷,损耗最大的是冬小麦,损耗最小的是春大豆,二者轮作则有利于冬小麦田有机质含量的积累。表明WWS轮作模式有利于土壤养分的均衡。
(5)综上所述,既要考虑到不同轮作模式下土壤湿度和水分生产力的变化动态,又要结合养分变化动态,得出“10年生苜蓿→15年WWS”为黄土高原半湿润区的最优草粮轮作方式。
Alfalfa(Medicago sativa L.)is a perennial legume grass which was cultivated widely on semi-humid areas of the loess plateau.Due to its strong consumption of soil water,soil desiccation and grassland degradation happened quite frequently at this zone.In order to overcome and slow down the effects of high-intensity water consumption,then promote deep soil moisture to recover gradually,We found that these kinds of grasslands should be treated through fallow during rainy season or rotated with cereal grains that consumed little soil water, which helped to update and efficiently reuse the dried alfalfa grassland.
We used the field soil water observation combined with EPIC model simulation to study soil desiccation characters of alfalfa grassland and effects of its water recovery on the semi-arid areas of the loess planteau.Firstly,we investigated soil moisture on different growth age alfalfa grasslands and analysed soil desiccation characters,at the same time,the deep soil moisture of 10-year-old alfalfa field after rotated with different years crops were measured, and effects of soil water restoration by alfalfa-grain rotation were explored.Secondly, we used EPIC0509 model developed by USA to simulate the productivity and soil desiccated effects of 1~16-year-old alfalfa at Zhenyuan station,on the basis of creating different kinds of databases,such as the daily weather elements series,the typical profile of physicochemical properties of soil,the crop growth parameters,the field tillage mearsures,the fertilizer characteristic parameter and cropping system database.Seven disposals were designed, concluding 21 years continuous cultivation of spring soybean,winter wheat and spring corn, and the same years of rotation,which were"winter wheat-winter wheat-spring soybean (WWS)","winter wheat-winter wheat-spring corn (WWC)","spring soybean-spring soybean-winter wheat (SSW)","spring soybean-spring soybean-spring corn(SSC)"and so on,after plowing 10-year-old alfalfa.Which could help quantitatively analysis the dynamic change of annual yield and the restoration rule of soil moisture in deep soil layer.According to the quantitative simulation of long period results,we could select the optimal alfalfa-grain rotation pattern that adapted to Zhenyuan station.
The main progresses were as follows:
(1)Field experimental results in Zhenyuan showed as following:
A: The mean soil moisture in the 0~1 000 cm soil layers of alfalfa fields 15~28 years old at semi-humid zones was 10.20%,the soil desiccation rate 34.2 mm per year and the maximum distribution depth of desiccated soil layer over 1 400 cm,and only 10 years old or younger alfalfa fields were fit for tillage and crop rotation.
B: Soil moisture in the desiccated soil layer of the alfalfa fields could be restored gradually after 3~25 years of tillage and crop rotation,with the thickness of the desiccated soil layers reduced to 583 cm or by 77.3 mm·a~(-1) and the average soil water restoration index (SWRI)reaching up to 83.3%,an extremely significant level.It took at least 8 years for a 15 year-old alfalfa field to restore its soil moisture to a stable level(15.5%)common in the region by following alfalfa-grain crop rotation.Therefore,alfalfa-grain crop rotation for over 8 years was a suitable pattern to restore soil moisture in 10-year-old alfalfa fields.
(2)EPIC model simulation results showed as following:
A: The simulation results of the productivity and soil moisture change of alfalfa fields on semi-humid of the loess plateau showed that,after alfalfa 10 years’growth,the available water content in 0~1 000 cm soil layers fluctuated at a low value,soil desiccation was serious,which resulted in the instability of alfalfa yield and soil moisture situation.Therefore,proper measures should be taken to ease soil water deficit when alfalfa was planted for 10 to 12 years,such as alfalfa-grain crop rotation.
B: The simulation results of soil moisture restoration under different alfalfa-grain rotation measures showed that,the restoration effects of alfalfa-grain crop rotation were excellent,the longer the year,the better the effects.Among the seven disposals,the year for continuous cultivation of spring soybean,WWS and SSW to reach full restoration degree was 15 years,and it needed 21 years for continuous cultivation of winter wheat,WWC and SSC.We could find that WWS has the remarkable restoration of soil moisture,and the effect of rotation was better than other continuous cultivation of crops.
C: The simulation results of cereal crop yield under different alfalfa-grain rotation measures showed that,The yield played "inverted U"-type movement.15-year was suitable for crop rotation after alfalfa plowed in terms of yield components.Because the soil water restoration reached to a good level at this time.So we could plant alfalfa again after 15-year crops rotation.
D: The simulation result of soil nutrient evolution showed that,planting alfalfa was conductive to the accumulation of soil organic carbon and organic nitrogen.The year of alfalfa were longer,it would accumulate more,however,that was different for organic phosphorus, labile phosphorus and NO_3-N.Seven disposals all consumed soil organic carbon,organic nitrogen and organic phosphorus.And the continuous cultivation of winter wheat had the maximun loss of organic carbon,while the continuous cultivation of spring soybean had the least loss.Then if spring soybean rotated with winter wheat,which could relieve the loss of organic matter.All of those indicated that"WWS"was beneficial to balance soil nutrient.
E: In sum,we must think over soil moisture dynamics and soil nutrient dynamics combined with yeild dynamics by various rotation measures,then determined the suitable alfalfa-grain rotation pattern for Zhenyuan,which was"10 years alfalfa→15 years WWS".
引文
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