Effects Of Mixed Cropping Ratio And NPK Fertilizer On Production Performance And Soil Physical And Chemical Properties Of Sorghum Bicolor/dolichos Lablab Grassland

Legume/grass mixed sowing is an efficient production mode,which can make full use of the niche complementary effect of various grass species,improve grassland productivity,improve forage quality and increase soil nutrients.Reasonable mixed sowing ratio and fertilizer application are important measures for forage quality and high yield.As one of the important animal husbandry bases in China,the suitable proportion of legume/grass mixed sowing and reasonable fertilization amount in the arid region of Ningxia are not clear,which limits the further development of the potential of forage quality improvement and yield increase.In view of this,five different sowing rates(S₁₀:0 kg·hm^-2,S₁1:16.5 kg·hm^-2,S₁2:33.0 kg·hm^-2,S₁₃:49.5 kg·hm^-2,S₁₄:66.0 kg·hm^-2)of S₁orghum bicolor and Dolichos lablab were set in this experiment.Four N-P-K application levels(F₁:0-0-0 kg·hm^-2,F₂:75-120-90 kg·hm^-2,F₃:150-240-180 kg·hm^-2,F4:225-360-270 kg·hm^-2)were set under each mixed sowing mode.The effects of different sowing rates of Laba bean,mixed sowing of sweet sorghum and NPK application on grassland production performance,forage quality,soil physical and chemical properties and enzyme activity were studied.The main results were as follows:（1）The mixed sowing ratio of legume/grass and NPK application can significantly improve the grassland productivity.The treatment with the highest plant height was S₁₂F₂,reaching 317.67 cm;the tillering ability of sweet sorghum was the strongest under S₁₃F₃ treatment.S₁1F₃ treatment had the largest stem diameter（15.92 mm）;the treatments with the highest fresh-dry ratio and leaf-stem ratio were S₁₀F₂ and S₁₃F₃,respectively.With the increase of sowing rate and fertilizer application rate of Laba bean,the dry grass and total hay yield of sweet sorghum increased first and then decreased.The dry grass yield and total hay yield of sweet sorghum were the highest under S₁₃F₃ treatment,which were 32.62 and 36.04 t·hm^-2,respectively.Laba bean hay yield was the highest under S₁₁F₁ and S₁₂F₃ treatments;the maximum crude protein yield of mixed grassland reached 4.91 t·hm^-2,which was 31.69%higher than that of sweet sorghum monoculture.（2）The nutritional quality of forage could be improved by the mixture ratio of legume/grass and NPK application.The crude ash content was the highest under S₁₄F₁ treatment,reaching 11.13%;the crude protein content of S₁₄F₂ treatment was the highest,and the neutral detergent fiber content was the lowest,14.69%and 48.90%,respectively.The acid detergent fiber content of S₁₃F₂ treatment was the lowest（23.41%）,and the relative feeding value was higher（128.51）.（3）The combined application of nitrogen,phosphorus and potassium changed soil total nitrogen,organic matter,available potassium and available phosphorus content,and increased soil urease,catalase and invertase activities.In addition,soil nutrients and enzyme activities had surface aggregation.With the increase of soil depth,soil nutrient content and enzyme activity decreased.Through the redundancy analysis（RDA）of production performance,nutrient indexes and soil factors,it was concluded that urease,catalase and invertase had obvious positive effects on grassland production performance.The principal component analysis showed that the sowing rate of Laba bean was 49.5 kg·hm^-2 and the fertilization rate of nitrogen,phosphorus and potassium was 150-240-180 kg·hm^-2,which was beneficial to improve the production performance of grassland,improve the nutritional quality of forage,and increase soil nutrients and enzyme activity.It was suitable for demonstration and promotion in arid areas of Ningxia and other regions with similar climatic conditions and irrigation conditions.