^(13)C analysis of cow tail hair and farm slurry can be used to implicitly distinguish between different dairy production systems

Background Public interest in the way food is produced on the farm and processed along the food-production chain is increasing.The analysis of isotopic signatures(^(13)C)in cow tail hair provides a method to reconstruct the dietary proportion of maize in cow diets.Based on this,we further investigated whether there is a relationship between isotopic signatures in cow tail hair or farm slurry and the proportion of maize of the total utilized agricultural area per farm[%].We did an on-farm survey on 17 dairy farms in coastal Northwest Germany and collected cow tail hair from dairy cows and slurry samples on each farm.The farms differed in their feeding regime(C_(3) vs.C_(4) plants),their site conditions(sandy soil=‘Geestland’;organic soil=‘Peatland’;clayey soil=‘Marshland’),and in the area cultivated with maize as a proportion of the total utilized agricultural area per farm.Results We found a positive relationship between δ^(13)C values in both cow tail hair and slurry and the annual dietary proportion of maize(R^(2)=0.67;and R^(2)=0.63).Furthermore,we confirmed that there was a relationship betweenδ^(13)C values in cow tail hair and area of maize as a proportion of the total utilized agricultural area per farm(R^(2)=0.69).Conclusion Our findings suggest a general applicability of using isotopic signatures(^(13)C)along a wide gradient of site conditions and productions systems in practice.

林牧系统的树木中豆科植物的比例减少并不影响其内部的氮吸收效率

在以豆科植物为主的草地中,豆科植物通过生物固氮为草地提供氮(N)。以往对林牧系统的研究发现,树木附近的豆科植物比例下降,将导致N供应以及树间草坪收获的牧草中N浓度的空间变化。在自然生态系统中,氮吸收效率(NRE)随着养分限制而增加,所以在树木附近豆科植物比较稀缺。本研究验证了以下假设,即树木附近的NRE增加,补偿了豆科植物相对于牧草中N浓度的损失。为此,本研究分析了5年前建立的巷道种植系统中,分布在林木间的两种由豆科草本植物为主的植被组成。研究结果表明,豆科植物的比例向树线方向下降了45%,因此,活的和枯死的牧草中的N浓度也下降了,但平均仅下降了15%。由于N浓度降低以及靠近树木的牧草质量下降,N产量最多下降了50%。尽管树木附近的豆科植物减少,但无论植被组成如何,NRE都不受树线的影响。此外,与未管理的生态系统相比,收获之间的落叶间隔较短的林牧草地中管理草坪的内部N循环的相关性较低。豆科植物的比例控制着活的和枯死的草本植物的N浓度,而与林牧系统中的树木遮阴无关。