Effects Of Water Regulation On Productivity And Water Use Of Artificial Grassland In Inland Arid Area Of Northwest China

In view of the prominent problems such as lack of water resources,serious grassland degradation,desertification and salinization in the northwest inland arid area,exploring a more water-saving and efficient artificial grassland planting and irrigation mode is one of the paths to support the sustainable development of local grassland animal husbandry and ecological environment.The study was carried out in the experimental base of Qiantan Village,Minghua Township,Sunan Yugur Autonomous County,Zhangye City,Gansu Province,in the typical northwest inland arid region in 2019 and 2020.Taking Bromus inermis and Medicago sativa as the research objects,three planting modes（Bromus inermis monoculture W,Medicago sativa monoculture M and Bromus inermis and Medicago sativa mixture H）and four water regulation gradients（sufficient irrigation T0（75%～85%θ_f）,mild water deficit T1（65%～75%θ_f）,moderate water deficit T2（55%～65%θ_f）and severe water deficit T3（45%～55%θ_f））were set to analyze the effects of different treatments on soil moisture and nutrients,quality,yield and water use of artificial grassland,and the artificial grassland was comprehensively evaluated based on TOPSIS method.The following main conclusions are drawn:（1）Irrigation amount and planting pattern have significant effects on water consumption of artificial grassland,and water consumption increases with the increase of irrigation amount.The water consumption of the first crop accounted for the largest proportion in the annual water consumption,with an average proportion of35.40%in two years.The average water consumption of M in two years increased by5.82%and 15.87%compared with H and W,respectively.The average water content of 0～120 cm soil layer decreased with the aggravation of water deficit,and the average water content was W>H>M under each water treatment.With the advancement of growth period,the vertical water content of soil profile in artificial grassland decreased first and then increased,and the soil water content was the lowest in the three planting modes from branching stage to budding stage.The contents of soil organic matter,nitrate and ammonium nitrogen in each treatment were the highest within 0–20 cm of topsoil;The organic matter accumulation of each planting pattern was the highest under T1 water treatment,and the organic matter accumulation of mixed planting was higher than that of single planting.The contents of soil nitrate and ammonium nitrogen decreased after the experiment,and the consumption of soil nitrate and ammonium nitrogen in mixed planting was significantly lower than that in single planting.（2）Compared with monoculture（P1）,mixed planting（P2）increased the crude protein content of Bromus inermis and Medicago sativa,and decreased the contents of acid detergent fiber（ADF）and neutral detergent fiber（NDF）.Moderate water regulation could improve the quality of forage.The average crude protein content of forage in P1 was the highest under T2 water treatment,which was 12.05%（W）and21.06%（M）,respectively.Under P2,WT2 was the highest（13.47%）;MT1 was the highest（22.35%）.With the increase of cutting stubble,forage crude protein content showed an increasing trend,ADF and NDF content showed a decreasing trend.Mixed planting could significantly increase the crude protein yield of grassland than monoculture of Bromus inermis,but there was no significant difference between mixed planting and monoculture of alfalfa.The crude protein yield of Bromus inermis monoculture under WT1 was the highest,with an average of 906.78 kg·hm^-2,and that of alfalfa monoculture under T0 was the highest,with an average of 3428.98 kg·hm^-2.There was no significant difference in crude protein yield between alfalfa monoculture and alfalfa monoculture under T0 and T1 water treatments.The ADF and NDF contents of the two forage species under P1 and P2 decreased first and then increased with the increase of water deficit,and the ADF and NDF contents were the lowest under T1 treatment.The variation of relative feeding value（RFV）of forage was consistent with that of ADF and NDF and the RFV of forage reached the maximum values under T1 water treatment,which were 121.13（P1W）,126.95（P2W）,120.34（P1M）and 124.20（P2M）.（3）With the increase of water deficit,the plant height of artificial grassland decreased gradually,but there was no significant difference between T0 and T1.Mixed planting significantly increased the plant height of Bromus inermis,with an average increase of 16.14%.But the effect on alfalfa plant height was not significant.With the increase of water deficit,the leaf area index（LAI）of artificial grassland gradually decreased,and the LAI of W was the lowest among the three grasslands,and the LAI of H was 2.32%higher than that of M on average.The hay yield of artificial grassland showed an increasing trend with the decrease of water regulation,and the yield of mixed planting was significantly higher than that of two single planting.The average annual yield of three planting modes was the highest under T0water treatment.The hay yield of each crop was in the order of the first crop>the second crop>the third crop;With the increase of water deficit,the yield contribution rate of Bromus inermis in mixed sowing decreased.The relationship between water consumption and yield of artificial grassland was quadratic parabola,and the maximum yield was 8077 kg·hm^-2 when W consumption was 635 mm.When the water consumption of M was 790 mm,the maximum yield was 17066 kg·hm^-2;The maximum yield was 18877.13 kg·hm^-2 when H consumption was 788 mm.When the water consumption exceeds the critical value of the three planting modes,the yield of artificial grassland will no longer increase.With the increase of water deficit,the water use efficiency of artificial grassland increased first and then decreased.The water use efficiency of each treatment reached the highest in the whole season under T1,which were 1.40 kg·m^-3（WT1）,2.41 kg·m^-3（MT1）and 2.91 kg·m^-3（HT1）,respectively.（4）Comprehensive evaluation of artificial grassland based on TOPSIS,according to the relative fitness ranking,HT1 is the best.It indicated that mild water regulation under mixed planting could not only obtain higher yield and quality,but also reduce irrigation amount and improve water productivity,which was a suitable planting and irrigation mode for artificial grassland in northwest inland arid area.