Relationship between readings of chlorophyll meter (Minolta SPAD 502) at differents crop corn stages and grain yield.

There exists a close association between N content and chlorophyll content, and theretore, crop N status can be evaluated using a chlorophyll meter. The objective of this work was to determine the relationship between corn yield and either absolute readings of a chlorophyll meter (Minolta® SPAD 502) or N sufficiency index (ISN), along crop cycle. The experiment was carried on at Balcarce during 1995/96 and 1996/97, without water or P limitations and with different corn hybrids for each year. Treatments were made at difterent rates and moments of N fertilization. Chlorophyll meter readings were taken weekly since six-leaf stage (V6) until 15 d after flowering. The correlation between absolute meter readings at V6 and corn yield was low and high for the first and the second year, respectively. However, after V6 and in both years there was a high association between either meter readings after or ISN and crop yield. Threshold meter readings after V6 to get 95% of maximum yield were 51.5- 61 and 57-54 SPAD units for 1995/96 and 1996/97, respectively. For both years, 95% of maximum yield was reached when ISN was between 0.97 and 0.98. It is concluded that the chlorophyll meter is an appropriate tool to check N availability for corn. especially at advanced crop stages.

Key words: corn-nitrogen-chlorophyll-stages-yield.