9Jeol G, Camon J A, Field C B. Production efficiency m sunflower: the role of water and nitrogen stress [J]. Remote Sensing of the Environment, 1997,62:176-188.
10Fredeen A L, Camon J A, Field C B. Response of photosynthesis and carbohydrate to limitation in nitrogen and water availability in field-grow sunflower[J]. Plant Cell and Environment,1991,14: 963-970.