NO3^--N/NH4^＋-N配比对紫花苜蓿营养品质及饲用价值的影响研究

Effects of NO_3^--N/NH_4^+-N ratio on the nutritional quality and feeding values of alfalfa

以"甘农3号"紫花苜蓿为试验材料,在室外防雨网室内,采用盆栽营养液砂培,在最佳氮素供应水平210mg/L基础上,研究NO_3^--N和NH_4^+-N混合的7种配比(1/7、1/3、3/5、5/5、5/3、3/1、7/1)对紫花苜蓿营养品质及饲用价值的影响。结果表明,NO_3^--N/NH_4^+-N=5/3处理的粗蛋白(CP)、蛋白总量(TP)、可消化干物质(DDM)及干物质采食量(DMI)总体上都显著高于其他配比处理(P<0.05),中性洗涤纤维(NDF)和酸性洗涤纤维(ADF)均显著低于其他配比处理(P<0.05),5/3处理有利于紫花苜蓿营养积累;从微量元素营养角度分析,以NH_4^+-N为主的混合态氮更有利于铁(Fe)、锰(Mn)和钼(Mo)的积累,且最适配比分别为NO_3^--N/NH_4^+-N=1/3、1/7和3/5,而以NO_3^--N为主的混合态氮则有利于锌(Zn)的积累,且最适配比为NO_3^--N/NH_4^+-N=3/1;用相对饲用价值(RFV)法评定,5/3处理RFV值显著高于其他配比处理(P<0.05),且各处理RFV均大于100,对照美国紫花苜蓿草产品的分级标准,其品质均达到2级以上水平,其中5/3和7/1处理紫花苜蓿的品质达1级水平。说明紫花苜蓿生长环境中速效氮以NO_3^--N为主,且比例接近NO_3^--N/NH_4^+-N=5/3时,最有利于紫花苜蓿优良营养品质的形成。

The effects of different ratios of NO3^--N/NH4^＋-N（1/7,1/3,3/5,5/5,5/3,3/1,7/1）on alfalfa（Medicago sativa cv.Gannong No.3）in terms of its nutritional quality and feeding values were studied in an outdoor rain-protected chamber.Alfalfa plants were cultivated in sand with an optimum nitrogen supply（210mg/L）.The results indicated that under the ratio of NO3^--N/NH4^＋-N（5/3）,the contents of crude protein（CP）,total protein（TP）,digestible dry matter（DDM）and dry matter intake（DMI）were significantly higher than their respective values in the other treatments（P〈0.05）,while the contents of neutral detergent fiber（NDF）and acid detergent fiber（ADF）were significantly lower than their respective values in the other treatments（P〈0.05）.Thus,the 5/3ratio was determined to be the best ratio for nutrient accumulation.From the perspective of microelement nutrition analysis,mixed nitrogen mainly with NH＋4-N was more beneficial for the accumulation of iron,manganese,and molybdenum,and the adaptation ratios were 1/3,1/7,and 3/5,respectively.Mixed nitrogen mainly with NO-3-N was more beneficial for the accumulation of zinc,and the adaptation ratio was 3/1.In the relative feeding values analysis,the RFV value in the 5/3treatment was significantly higher than those in the other treatments（P〈0.05）,and the RFV of all treatments was greater than 100.Referring to the classification standard of alfalfa grass products in America,the nutritional quality in all treatments was at least level 2,with that in the 5/3and 7/1treatments reaching level 1.When alfalfa was grown in an environment of available nitrogen mainly with NO-3-N and the ratio of NO-3-N/NH＋4-N was closer to 5/3,the alfalfa crop had good nutritional quality.