Discussion on the calculation method of nitrogen use efficiency (NUE) in long-term field experiments under wheat and maize rotation systems. Effects of Plant Sizes on the Nitrogen Use Strategy in an Annual Herb, Helianthus annuus (Sunflower) Nitrogen use efficiency and its relationship with nitrogen nutrition characteristics of wheat varieties Responses of Physio-Biochemical Properties to N-Fertilizer Application and Its Relationship with Nitrogen Use Efficiency in Rice (Oryza sativa L.)