| The Loess Plateau is a typical semi-arid rainfed farming area and also one of the important bases for agricultural production and animal husbandry production in China.However,the shortage of land area and precipitation resources are limiting factors for the sustainable development in this area.Therefore,seeking efficient planting patterns is the key to improving forage yield and resource utilization efficiency.In this study,alfalfa（Medicago sativa L.）and four annual grasses namely forage maize（Zea mays L.）,sweet sorghum（Sorghum dochna（Forssk.）Snowden）,sudangrass（Sorghum sudanense（Piper）Stapf.）and Japanese millet（Echinochloa frumentacea（Roxb.）Link）were selected to consist 9 legume and grass monocropping and intercropping.The growth and development characteristics and component biomass,as well as water and land use efficiency of different forage grasses were monitored at key growing stages during the growing season.To provide references for exploring forage production system suitable for rainfed farming areas,the main results were as follow:（1）Intercropping mode affects the growth and development of gramineous forages and alfalfa:Compared with monocropping,except for Japanese millet,the effective accumulated temperature of gramineous forages under the four intercropping modes was higher,intercropping maize（IM）,intercropping Sweet sorghum（IS）and intercropping sudan grass（ID）increased by 51.9°C·d,34.0°C·d and 104.8°C·d,respectively.both intercropping and monocropping alfalfa showed that the effective accumulated temperature of the second cut was higher than that of their counterparts in the 1st and 3rd cut of alfalfa.Intercropping increased the effective accumulated temperature of alfalfa in the 2nd cut compared with monocrop.The growth and development characteristics of the corresponding forages varied with intercropping systems.In general,at the later stage of intercropping forage development,the leaf area and plant height of grass and alfalfa were lower than those of monocropping.Except for J（single crop Japanese millet）at maturity,the plant heights of M（single cropping maize）,S（single cropping sweet sorghum）,and D（single cropping sudangrass）were significantly different from intercrops（P<0.05）,specifically,the plant heights of M,S,and D increased by21.86%,27.73%,and 23.97%,respectively.The overall plant height of the three cropping of alfalfa was the 1st crop>the 3rd crop>the 2nd crop.At the jointing and flowering stage of grass（the 2nd growth period of alfalfa）,the leaf area of the middle leaves of IM and IS was significantly reduced（P<0.05）compared with that of monocropping,and the alfalfa（IAM）intercropped with maize.The leaf area of the top and middle of alfalfa（IAS）intercropped with sweet sorghum is larger than the leaf area of the same part of A,indicating that the intercropping of alfalfa with forage corn and sweet sorghum can improve alfalfa by changing the top leaf area to obtain a more suitable distribution of light energy resources,thereby improving the light energy utilization efficiency in the intercropping system.Intercropping reduced the maximum dry matter accumulation rates of grasses and alfalfa.The maximum dry matter accumulation rates of M,S,D and J ranged from 2.38 to 3.52 g·m-2·d-1,which were 19.51%,29.23%,76.88%and 85.94%higher than the intercrops,respectively.In the third growing period of alfalfa,among the alfalfa intercropping treatments,the dry matter accumulation rate of IAM was the highest,which was significantly higher than that of IAS and alfalfa intercropped with Sudan grass（IAD）（P<0.05）.Moreover,the average accumulation rate of the three crops of IAM in the whole year was the highest.（2）Alfalfa/annual gramineous forage intercropping increased the system productivity and affected the proportion of each component of gramineous forage in different periods.The annual yields of A/M,A/S,A/D and A/J were all significantly greater than those of their single-crop grasses.The above-ground biomass of M and D at maturity was significantly higher than that of intercropping（P<0.05）,and the above-ground biomass of M and D was 18.03%and30.48%higher than that of intercropping,respectively.The relationship between the aboveground biomass of the three cuts of alfalfa in each treatment is:1st cut>3rd cut>2nd cut,among which,the dry matter accumulation of the 1st cut of the intercropping treatment accounts for 40-50%of the dry matter accumulation of alfalfa in the whole year.During the entire growth period of gramineous forage,the actual total yield of each intercropping system was significantly higher than its expected yield（P<0.05）,and the Land Equivalent Ratio（LER）at the maturity was as follows:corn/alfalfa intercropping（A/M）>Hunan millet/alfalfa intercropping（A/J）>Sweet sorghum/alfalfa intercropping（A/S）>Sudan grass/alfalfa intercropping（A/D）>1,indicating that the intercropping mode can effectively improve the System productivity and land use efficiency.Except for the grasses at the seedling stage,the competitive ratios（CRga）of A/M,A/S,A/D and A/J were all greater than 1,indicating that forage maize,sweet sorghum,sudangrass and Hunan millet It has a dominant position in the competition with alfalfa and can obtain more growth resources.The yields of stems,leaves,sheaths,ears（fruits）and their total yields in the intercropping treatment were generally lower than those in the corresponding monocropping treatments,while the biomass distribution of feed maize components was less affected by intercropping.Combined with LER performance,the intercropping system of alfalfa and forage corn had the highest productivity and land use efficiency.（3）Alfalfa/annual grass intercropping can change the water consumption of the forage and improve the water use efficiency of the forage.The soil water content in the single cropping and intercropping treatments showed the same depth,and the soil water content decreased with the advancement of the forage growth period.At the mature stage of grasses,the average soil water content of A/M and A/J at 0-160 cm was 29.67%and 15.13%higher than that of grasses alone.The average soil water content of A/S and A/D at 0-160 cm was 27.63%and 22.04%lower than that of the grass monoculture.Soil water use（WU）of IJ,J and IM was significantly higher than that of other treatments（P<0.05）,and WU of D and ID was the lowest.At the maturity stage of grasses,the water equivalent ratio（WER）of intercropping forages was between 1.20 and 1.38,and the water use efficiency（WUE）of intercropping forages was in the order of A/S>A/D>A/M>A/J,indicating intercropping were able to improve the water use efficiency of forage grass compared with monocropping,and the intercropping of alfalfa and sweet sorghum has the highest water use efficiency. |
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