Effects Of Long-term Fertilization On Yield,Quality And Soil Properties Of Forage Sweet Sorghum And Its Mechanism

Long-term application of fertilizers affects the variation of chemical and physical properties of cropland soil,and the nutrient quality,nutrient uptake,yields of sweet sorghum.However,few report about the effect of long-term application of fertilizers on the properties of irrigated-brown desert soil,forage quality,nutrition use efficiency and feeding value of sweet sorghum in northwestern China has been found.In this paper,8 fertilization methods such as CK(control plot),NK(nitrogen+potassium),NP(nitrogen+phospho rus),NPK(nitrogen+phosphorus+potassium),PK(phosphorus+potassium),M(single farmyard manure),NPKM(nitrogen,phosphorus and potassium combined with farmyard manure)and 1.5 NPKM(nitrogen+phosphorus+potassium+1.5 times of farmyard manure)were designed during 2008?2018 to study the effect of 11 year-long-term fertilization on the agricultural trait,yield,quality,nutrient distribution in organs and dynamics of soil chemical properties,the correlation between the using efficiency of nutrients and fertilizers,yield and photosynthesis,nutrient quality and forage value were also explored.The effect of the irrigated-brown desert soil properties in different fertilization treatments on the yields,growing characters and quality components of sweet sorghum were discussed,the optimum fertilization method to increase the bio-mass yield and forage quality together was determined.The results showed:(1)The plat height and stalk of sweet sorghum were affected by the different fertilization,but the leave numbers and average Brix of sweet sorghum stalk were not affected by different fertilization.The effect of different fertilizer treatments on yields differed.The yield for CK without fertilization decreased by(68.52%),the treatments M,NP,NK and NPK had not clear effects on yields,while PK,NPKM and1.5NPKM significantly increased the yields by 7.98%,2.81%and 2.10%,respectively,after 11-year fertilization.The sugar Brix showed decreasing trend for all fertilized and controlled treatments.The chemically fertilized treatments decreased the sugar Brix more,among all treatments.Long-term cultivation without nitrogen fertilizer was not favorable for stem sugar accumulation,PK increased the yields without increasing the stem sugar Brix.In contrast,M and NPK enhanced the stem sugar Brix,but did not enhance the yields.NPKM had the highest biomass yield(94.81 t/hm~2)with the highest sustainable yields index and quite higher sugar Brix(17.88%).(2)The nitrogen and phosphorus contents in sweet sorghum grain and the nitrogen and potassium contents in sweet sorghum straw decreased over years.Fertilization had no obvious effect on the distribution of N,P and K,the distribution order of N,P and K in grain was N>K>P,and that in straw was K>N,P.The accumulation of N,P and K in straw was higher than that in grain,the aboveground accumulations of N and K for NPKM were higher than those for other treatments.The utilization efficiencies of N,P,K fertilizers for sweet sorghum were as K,P>N.The utilization efficiencies of N,P,K differed significantly for treatments,the utilization efficiency of N ranged at 7.56?25.02%.Statistics showed that yields had positively correlation with N,P,K in straw.The stem sugar Brix had positively correlation with N in straw and negatively correlation with P and K in straw.(3)Long-term fertilization had non-significant effect on soil p H.Treatments M,NPKM and PK had lower soil p H than the CK,the decrement for M was the greatest.All treatments increased the soil TS significantly,compared with the initial contents,indicating the accumulation of salt on the soil surface by the effect of fertilization,the effect of treatments with nitrogen was more obvious than those without nitrogen.Long-term cultivation without fertilization reduced soil SOM,but the long-term fertilization slightly increased the soil SOM.The treatments NPK and NK effectively enhanced the soil AN,while treatments without nitrogen significantly decreased the AN.Besides,long-term fertilization decreased the soil available potassium(AK)and total phosphorus(TP)significantly.The single application of chemical fertilizers(NK,NP,PK,NPK)and control plot(CK)reduced the soil total nitrogen(TN).Biomass yield was positively correlated with SOM,AN,AP,AK,TN and TP,and negatively correlated with p H and TS.Sugar Brix for treatments was also negatively correlated with soil p H and TS,while it was positively correlated with soil AN.The nutrient demand of sweet sorghum differed for different growing stages,the nitrogen and potassium demands were higher than phosphorus demand in pre-flowering stage.(4)The water use efficiency(WUE),net photosynthetic rate(Pn),stomatal conductivity(Gs)and chlorophyll(SPAD)showed consistent changing law from flowering stage to maturation stage,and exhibited the best performance in filling stage.The demand of sweet sorghum for different fertilizers during different growing stage was different,and the fertilization favored the photosynthesis.The treatment NPKM was the most favorable treatment for enhancing photosynthesis condition,biomass stability and high production.(5)The different treatments had not significant impact on the forage quality of sweet sorghum,the changing laws of forage quality index were:crude fiber in grain>crude fiber in straw,crude ash in straw>crude ash in grain,soluble carbohydrates in straw>soluble carbohydrates in grain.Fertilization significantly increased the straw crude protein,soluble carbohydrates and crude fiber.NK increased the grain starch more than other treatments did,but decreased the tannin in grain.The treatments NPKM significantly increased the carbohydrates,dry matter in straw,but decreased NDF,ADF and crude ash contents.The NPKM performed higher digesting rate and forage quality over other treatments.In brief,considering to enhance the fertilization efficiency,forage quality,high production rate and biomass stability,the treatment NPKM is the best sustainable fertilization method for the irrigated-brown desert soil in the northwest arid region.The research provided valuable data for enhancing forage quality and sustainable cultivation of sweet sorghum in irrigated-brown desert soil.