紫花苜蓿种子生产中临界氮稀释曲线模型的建立与应用

Establishment and Application of Critical Nitrogen Dilution Curve in Alfalfa(Medicago sativa L.) Seed Production

为了验证临界氮稀释曲线模型在紫花苜蓿种子生产中的适用性,探讨以氮营养指数评价紫花苜蓿氮营养状况的可行性,以敖汉苜蓿和公农1号苜蓿为材料,设置4个氮肥处理(0、45、90、135kg N/hm^2),于返青期施肥,并在现蕾期、开花期、结荚期和成熟期分别测定苜蓿地上部生物量和氮浓度值,建立了制种苜蓿的临界氮稀释曲线模型,并在此基础上建立氮营养指数模型来判断苜蓿氮素营养状况。结果表明,随着施氮量的增加,紫花苜蓿地上部生物量并未出现显著性的增加,表明苜蓿生长将不受氮素制约。因此选择地上部生物量的平均值作为最大干物重,确定临界氮浓度值并建立了临界氮稀释曲线模型。两个苜蓿品种的临界氮稀释曲线模型分别为Nc=3.352W^(0.391)(敖汉苜蓿)和Nc=2.673W^(0.485)(公农1号苜蓿)。根据氮营养指数模型推荐的施肥量为敖汉苜蓿在现蕾期和开花期共施45kg N/hm^2,在结荚期追施90kg N/hm^2;公农1号苜蓿在现蕾期不施肥,在开花期、结荚期和种子成熟前追施45kg N/hm^2。利用临界氮稀释曲线模型和氮营养指数模型可以很好地预测制种苜蓿植株氮营养状况,且模型的建立为苜蓿种子生产管理中适时合理施肥提供了新的方法。

In order to verify the applicability of critical nitrogen （N） dilution curve in alfalfa seed pro- duction, and explore the feasibility of N nutrition index （NNI） in evaluating N nutrition status of alfalfa, a field experiment with four N fertilizer treatments （0, 45, 90, and 135 kg N/hm2） was carried out with two cultivars of Aohan and Gongnong No. 1 at returning green period, and the above ground biomass and N concentration were determined in the budding, flowering, podding, and maturing stage. The results showed that the above ground biomass did not increase significantly with N fertilizer application increasing, and indicated that the growth of alfalfa did not affected by N application level. Then the average above ground biomass and N concentration were used to calculate critical N concentration （Nc）, and established the critical N dilution curve model for alfalfa seed production. The critical N dilution curve model of two alfalfa cuhivars were as follows： Nc= 3. 3521W0.3916 （Aohan） and Nc= 2. 6737W0.4857 （Gongnong No. 1）. At the end, Nc and measured N concentration were used to establish the NNI, and evaluate N nutrition status of alfalfa. The results indicated that the optimum N application rate of Aohan was a total of 45 kg N/hm2 in budding stage and flowering stage,90 kg N/hm2 in podding stage. The optimum N application rate of Gongnong No. 1 was 45 kg N/hm2 in flowering stage, podding stage and maturing stage separately. Therefore, critical N dilution curve and NNI could be used directly to estimate the plant Nc and plant N status in alfalfa. Thus these models could be used to predict the dynamic precision fertilization and provide a theoretical basis for optimal N management of alfalfa for seed production.