| Climate is the main determinant that influences agriculture production and crop layout in arid and semiarid region.It is of great significant for choosing appropriate agrotypes and proper farming practices after analyzing the regional micrometeorology characteristics and yearly changing trends.Sown pasture is an important part of ecological construction and agricultural production in semiarid loess hilly-gully region.It is also important for selecting proper sown pasture types and management methods after comparing the biomass production,soil water and soil nutrient contents of different sown pastures.The yearly change of microclimatic factors at lowland,and the biomass production,soil water and nutrient content were compared between lowland and slopland at Ansai loess hilly-gully region.The main results are as follows:1.Characteristics of microclimatic factors at Ansai lowland:the yearly averaged air temperature and aridity index during 1970-2007 are 9.11℃and 1.46,respectively.The 10-year averaged temperature showed low-low-high-high from 1970 to 2007,and the values were 0.31℃and 0.45℃smaller,and 0.11℃and 0.94℃bigger consecutively compared with the 38-year mean.The yearly rainfall was between 275mm(1997) and 688.9mm(1983),and showed rising undulatedly during 1970-1983,while decreased undulatedly during 1984-2000, and went up during 2001-2007.Heavy rainfall happened mainly in August.Surface water evaporation occurred mostly during May and August,and monthly evaporation was 80-140mm. Yearly total solar radiation(TSR) was 5168.85MJ/m~2.Photosynthetic active radiation(PAR) and net radiation(E~*) accounted for the TSR 19%and 18%respectively.The northeaster was the main wind.Month averaged wind speed was 0.93m/s,and the wind speed was the strongest (1.34m/s) in April while weakest in July(0.68m/s).The monthly air pressure change curve was parabolic,and January was the highest(901.8hPa) and July was the lowest(888hPa).2.Soil water characteristics of sown pastures:The change of soil water content in 0-100cm soil depth of lowland sown pasture was more active,and which was the active layer;soil water content in 100-350cm soil depth was related with the root system consumption,and was hypo-active layer;the seasonal change of soil water content in 350-500cm was small,and which was relatively stable layer.The soil drying phenomenon was distinctive in 350-500cm soil layer of switchgrass and alfalfa.In 2004-2005,the soil water storage in 0-200cm decreased from Aril to September,while increased from September to November.There were great differences among pastures in soil depth below 200cm,but the seasonal change was similar.The 0-100cm soil water content in late autumn was higher than in springtime at slope pasturelands,and there were no evident soil water stress in 100-500cm in each pastureland.3.Biomass production and soil nutrition content:The aboveground biomass production order of the lowland pastures was switchgrass(Panicum virgatum L.)＞alfalfa(Medicago sativa L.)＞milkvetch(Astragalus adsurgens Pall.)＞Lespadeza davurica(L.davurica)＞sainfoin (Onobrychis viciaefolia Scop.).The water use efficiency(WUE) of switchgrass was highest (25.1kg/hm~2·mm),next were alfalfa and milkvetch,and those of L.davurica and sainfoin were the lowest,which were 5.1kg/hm~2·mm and 4.4kg/hm~2·mm respectively.The root biomass order in 0-150cm of the above five pastures was same as WUE.The main soil depth for root distribution was 0-20cm,and it accounted for 60-66%of leguminous species,while it was 49.5%for switchgrass.Soil total nitrogen content(TNC),soil organic carbon content(OCC), soil organic carbon reserves(OCR) and fixed organic carbon(FOC) of each sown pasture at lowland and slope land were higher that bare land.Soil TNC,OCC and OCR of lowland pastures were higher than slopeland pastures,while soil FOC was lower than the latter.At lowland soil TNC in alfalfa was the highest,while at slopeland old world bluestems had the highest.Pasture cultivation improved soil available nitrogen and potassium. |
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