Effects Of Alfalfa-Grain (Oil) Crop Rotation On Soil Moisture,Fertilizer And Growth In The Loess Plateau

For the Loess Plateau drought, water deficit caused by long-term cultivation of alfalfaand underproduction caused by barren soil,an alfalfa-crop rotation trial had been conductedin the typical sub-humid and liable-drought region to investigate the soil moisture, soilnutrients, crop biological characteristics and crop yields after plowing alfalfa grassland,analyzing the economic and ecological benefit,aiming to provide a theoretical basis for thesustainable use of alfalfa grasslands in the Loess Plateau and to establish a stable agroecosystems. The main conclusions are as follows:1. Different alfalfa-crop rotation patterns had differences in restoring soil moisture, in theharvesting period after two years alfalfa-rotation experimental, alfalfa-leisure-rape (AFR)mode had the best water eco-environment, Which0⁵00cm layer soil moisture increased by6.7%than the2009autumn before plowing alfalfa grassland, but alfalfa-winter wheat-winterwheat(AWW) had the worst water eco-environment, showing a deficit state compared withthe stage of plowing alfalfa. In the fall of2011, all the rotation patterns0⁵00cm layer soilmoisture had recovered compared to the2009autumn, and the alfalfa-leisure-rape (AFR)rotation mode was still the best,alfalfa-winter wheat-winter wheat (the AWW) was still theworst mode,which respectively increased by32.5%,27.0%than the beforetime of plowingalfalfa, indicating that the alfalfa-crop rotation can alleviate the status of water overconsumption of alfalfa grass, and promote soil moisture recovery. After the two years rotation,the soil moisture recovery layer of AWW mode respectively appeared in120³20cm,0³60cm soil layer in harvest and autumn, the rest of the rotation mode respectively appeared in120³40cm and0³80cm soil layer.2. Alfalfa-crop rotation could increase soil nitrogen and organic matter than conventionalfarmland. After two-year rotation, the0⁶0cm layer soil average total nitrogen, soil averageorganic matter, soil average available nitrogen of the second year planting rape treatmentrespectively increased by0.08g·kg^-1～0.19g·kg^-1,0.41g·kg^-1～1.11g·kg^-1,3.70mg·kg^-1～10.61mg·kg^-1than that of continuous rape planting, compared with the fallow land,respectively increased by0.05g·kg^-1～0.16g·kg^-1,0.13g·kg^-1～0.83g·kg^-1,0.83mg·kg^-1～ 7.74mg·kg^-1. Meanwhile, the second year planting winter wheat respectively increased by0.10g·kg^-1～0.22g·kg^-1,0.56g·kg^-1～1.07g·kg^-1,4.48mg·kg^-1～7.13mg·kg^-1than that ofcontinuous cropping of winter wheat, and increased by0.04g·kg^-1～0.16g·kg^-1,0.43g·kg^-1～0.94g·kg^-1,2.65mg·kg^-1～5.30mg·kg^-1than the fallow land, indicating that the alfalfa-croprotation could enhance the soil fertility.3. Alfalfa grassland and alfalfa-crop rotation farmland0⁶0cm layer soil available P,available K were significantly lower than continuous cropping farmland and fallow land,showing that alfalfa was a more consumption of phosphorus, potassium plant. In the plantingprocess required for fertilizing P and K to maintain soil phosphorus and potassium balance.After plowing alfalfa grassland, because of the disturbance of the soil, soil nutrients showed adecreasing trend year after year, especially for two consecutive years planting the same crop,so people should try to avoid planting the same crop so as to maintain the soil nutrient balancebetter when conduct an alfalfa-crop rotation experiment.4. Alfalfa-crop rotation could promote the formation of soil mineralized nitrogen, the0¹00cm layer average ammonia nitrogen of rape and winter wheat rotation field were higherthan continuous growing alfalfa field, fallow and conventional farmland, all crop rotationtreatments for0¹00cm soil nitrate content also showed higher than conventional farmlandand fallow land, meanwhile, fallow-leisure-rape (AFR) and alfalfa-leisure-winter-wheat(AFW) treatment0¹00cm soil nitrate content was significantly higher than the continuousgrowing alfalfa, the rest of the rotation treatments' nitrate content was less than the continuousgrowing alfalfa, indicating that the alfalfa-crop rotation had a positive role to improve the soilnitrogen availability of follow-up crops in the drought areas.5. Alfalfa-crop rotation increased yields significantly. The two-year experiment showedthat crop yields and water use efficiencies of rotating rape treatments and winter wheattreatments were higher than the corresponding conventional farmland. In the first year ofrotation, the rape yield and water use efficiency of rotation cropping cropland respectivelyincreased by28.9percent and49.8percent than that of continuous rape planting, the winterwheat yield and water use efficiency increased by43.2%,36.7%than the continuous croppingfarmland. In the second year, rape yield of rotation cropping croplands increased by3.5%⁴1.7%and water use efficiency increased by1.4%³8.6%than the continuous rapeplanting land, winter wheat yield of rotation cropping croplands increased by47.3%⁵9.6%and water use efficiency increased by29.9%⁵0.4%than the continuous cropping farmland.6. Alfalfa-crop rotation could improve the plant height and increase dry matteraccumulation of subsequent crop, and then promote crop growth and development. Thetwo-year trial results showed that the rotation of rape and winter wheat could improve crop plant height and increase dry matter accumulation, showing a significant difference ascompared with the conventional farmland. Alfalfa-crop rotation also had a certain impact onyield components, could increase significantly spike numbers of winter wheat, and increasethe number of siliques per plant and grain number per silique of the rape, but has little effecton the thousand seed weight. Alfalfa-crop rotation could improve the photosyntheticperformance of crop, the alfalfa-rape-rape mode and alfalfa-leisure-wheat mode had the besteffect.7. Through analyzing ecological effects of different rotation models after alfalfa-croprotation, found that the ecological effects of alfalfa-leisure-rape rotation mode was best,having the highest water recovery content and the highest rates of nitrogen activation and lessconsumption of soil nutrients, while the alfalfa-wheat-wheat rotation mode was the worst,which water recovery effect was negative, and soil phosphorus, potassium, available nitrogen,total nitrogen and organic matter was consumed very much, so it was not conducive tomaintain the balance of soil nutrient8. Through researching on the economic benefits of different rotation models, found thatalfalfa-winter wheat-winter wheat mode had the highest net income, which was up to15473.5Yuan· hm^-2, while alfalfa-leisure-rape had the minimum net income, just was1329.7Yuan· hm^-2, there were contradictions between ecological effects and economic benefits.Generally speaking, one year fallow could alleviate the soil environment pressure caused bythe previous alfalfa, however, less per capita arable land resources in the Loess Plateau lead tomore contradictions between people and farmland resources, therefore there was moredifficult to implement in Agricultural production, and most of people tend to rotate crop toachieve a balance of economic and ecological benefits. Besides, it was essential to becombined with local ecological, economic status when choosing a suitable alfalfa-croprotation, and took a rational fertilization way according to the depletion of different rotationpatterns.