Use of a chlorophyll meter to diagnose nitrogen status of 'Fuyu' persimmon leaves

Abstract

A possible relationship between leaf SPAD readings and nitrogen (N) concentrations was evaluated at different growing stages of 'Fuyu' persimmon trees under different N regimes in pots and in the field. When 5-year-old trees grown in pots received 0 to 40 g N over the growing season, leaf SPAD reading, N concentration, and specific leaf weight tended to increase with increasing N rate. The correlation between leaf SPAD reading and N concentration was statistically significant from late April to early November (R2 = 0.72 to 0.97). It was noted that the slope of regression line decreased as the season progressed. Similar significant correlations were found from pot-grown 4- to 7-year-old trees grown under various nutrient regimes (R2 = 0.67 to 0.96). Significant correlations were also confirmed with the leaves collected from 31 commercial orchards at different locations. The highest coefficient of determination was observed from the leaves collected at harvest time in both the pot and field experiments. Although the regression equations differed depending on the growing stage of trees, SPAD readings were found useful in estimating leaf N status at a specific time and in quickly judging the need for N application at that time. Seasonal changes of leaf SPAD readings from five well-managed orchards are presented as a reference guide for practical use.