Nitrate Dynamic in a Tropical Mollisol Amended with Organic Manures, Planted with Sweet Corn, and Monitored with SPAD Readings

Two field experiments were conducted to evaluate the use of relative chlorophyll content (RCC) in sweet corn leaves as an indicator of nitrate concentration in soil. Study objectives were (1) to evaluate the effect of manure types (chicken and dairy), rates (0, 168, 336, and 672 kg ha −1 equivalent N), and application frequency (one and two applications) of organic amendments on (a) nitrate nitrogen (NO 3 -N) concentration within and below the crop root zone and (b) the RCC of sweet corn leaves and (2) to quantify the relationship between RCC and NO 3 -N concentrations. The results showed a significant increase in NO 3 -N concentrations within and below the root zone and plant leaf RCC under chicken manure treatments. Manure application rates and frequency had a significant effect on both NO 3 -N concentration within and below the root zone and leaf RCC. It appears that leaf RCC can be used as an indicator of NO 3 -N availability for sweet corn cultivated under the study conditions.