Effects Of Irrigation On Interspecific Relationship And Productivity Of Mixed Herbage In Arid Steppe

The cultivated grassland has potential value and realistic productivity,which can make up for the deficiency of insufficient grass yield due to degradation of natural grassland.The mixed grassland community has higher community functional diversity than the single species community,which has a certain positive effect on the community productivity.The mixed grassland often has higher resource utilization rate.Due to the lack of natural precipitation and the uneven distribution of time and space,the shortage of irrigation water has become a key factor affecting ecological restoration and the development of animal husbandry in the arid grassland of Gansu province.It is of great significance to study the mixed planting combination under different irrigation rates for the production practice in the region.In our study,Bromus inermis and Medicago sativa L.cv.Qingshui were used as experiment material.Different sowing patterns were established by single sowing（CK1:M.sativa,CK2:B.inermis）and mixed sowing（AB:M.sativa+B.inermis）.By setting three irrigation gradients（FW:soil water content accounts for 75%-85%of field water holding capacity;LW:soil water content accounts for 65%-75%of field water holding capacity;MW:soil water content accounts for 55%-65%of field water holding capacity）,we studied the effects of water quantity and seeding mode on the soil nutrient,growth characteristics,nutrient quality of herbage,the interspecific relationship,so as to establish a suitable forage combination mode for grass-legume mixture in arid steppe areas of Gansu province,and to provide a scientific theoretical basis for ecological restoration of arid steppe areas in inland China under artificial intervention conditions.The results as follow:（1）With the decrease of irrigation amount,the symbiosis ability between M.sativa and B.inermis become weaker（The first harvest:from 2.5 to 0.83;The second harvest:from 1.66 to 0.71）.The ability of M.sativa to expand the population by increasing tiller number was increased and it had potential inhibitory effect on tiller number of B.inermis.Under FW and LW treatment,the intra-species competition of B.inermis was greater than interspecific competition,which had a competitive advantage over M.sativa.However,under MW treatment,the competition of B.inermis was reduced.Therefore,the water deficit had a great impact on the competitiveness of the B.inermis.In moderate water deficit,the competitiveness of B.inermis was weakened,while that of M.sativa was enhanced.（2）Under the same sowing treatment,the leaf area,plant height and stem diameter of herbage increased with the increase of irrigation amount.Among different stubble times,the leaf area and plant height were arranged in size order:the first crop>the second crop,full irrigation could significantly increase the leaf area of the second crop（P<0.05）.The effects of different water gradients on the stem diameter of M.sativa were not significant,but moderate water irrigation significantly reduced the plant height of B.inermis at the first crop.The effects of full irrigation and light water irrigation on plant height were not obvious,which did not result in significant reduction in plant height.At the same irrigation level,the leaf area of mixed-planting treatment of M.sativa was smaller than that of monoculture treatment,while that of mixed-planting treatment of B.inermis was larger than that of monoculture treatment,but there was no significant difference between the two treatments.The sowing treatment had no significant effect on the stem diameter of M.sativa,except that it had significant effect on the B.inermis at jointing stage.Under the influence of mixed seeding effect,mixed seeding can reduce the effect of light water irrigation on the plant height of herbage,which is beneficial to the growth of plant height of forage grass.（3）The available nitrogen and available potassium decreased with the deepening of soil layer,and the soil water soluble salt increased with the deepening of soil layer.Under the same water treatment,soil nutrients showed that mixed planting was greater than monocultural planting.Compared with CK1 treatment,AB treatment increased soil organic matter,available nitrogen,available phosphorus and available potassium by 24.49%,9.55%,21.89%,27.86%,respectively.Compared with CK2 treatment,it was improved by 25.63%,39.6%,23.65%and 19.37%,respectively.The soil water soluble salt in 0-30cm are arranged in size order:CK2<AB<CK1,and the highest in CK1MW treatment was 6.05 g·kg^-1.Under the same sowing treatment,the available nitrogen,available potassium and soil organic matter in the 0-30cm soil layer presented a decreasing trend with the increase of water deficit.Under light water irrigation,the available phosphorus was the largest,followed by full irrigation,and it was the smallest in moderate deficient water.The soil water soluble salt increased with the increase of water deficit.（4）With the increase of cutting stubble,the yield,ADF and NDF of herbage presented change trend:the first stubble>the second stubble,and the crude protein content presented change trend:the first stubble<the second stubble.With the decrease of water deficit,the yield of hay increased gradually under the same seeding treatment,and was the highest under ABFW treatment in both M.sativa and B.inermis.The crude protein content of M.sativa in two crops was the highest under ABLW treatment（23.84%,24.54%）.ADF and NDF increase gradually with the increase of water deficit.With the same water treatment,the yield,crude protein,ADF and NDF of the M.sativa at first stubble in AB increased by 30.42%,6.27%,4.35%,0.97%,respectively,and that of increased by 24.4%,6.26%,5.99%,1.14%,respectively at the second stubble.As for B.inermis,the yield,crude protein,ADF and NDF at first stubble in AB increased by 33.93%,14.3%,17.37%,8.36%,respectively,and that of increased by 26.38%,14.19%,9.79%,10.65%,respectively at the second stubble.