Usefulness of Leaf Greeness Intencity to Determine Sulfur Status of Corn.

Sulfur diagnostic tools are essential for rational use of S fertilizers. There is little information about the utility of leaf greenness intensity to detect S deficiency in corn. This work evaluates, under controlled high S-stressed conditions, i) the performance of leaf greenness intensity as an indicator of the degree of S deficiency in corn, and ii) the advantage of the upper leaves in relation to the middle leaves for S deficiency determination. A sand-pot experiment was conducted in greenhouse with corn at S rates of 0, 5, 10, 20, and 40 mg kg^-1 and sufficiency of other nutrients. Measurements of aboveground biomass (AB), total N and S concentration and chlorophyll meter readings (CMR) in upper and middle leaves, were performed at V6-V7, V11-V12, and V14-V15 growth stages. Sulfur application significantly increased AB, leaf S concentration, and CMR but decreased leaf N concentration. Significantly positive relationships were obtained between leaf S concentration and CMR but negative relationships between leaf N concentration and CMR. A sulfur sufficiency index (SSI) based on CMR measured in both plant leaves was significantly associated with AB. It was concluded that leaf greenness intensity could be useful for predicting/characterizing corn S status, although no significant advantage was found for taking CMR from the upper leaves since S deficiency symptoms during vegetative stages were generalized in the whole plant. More field work is needed to validate this methodology and develop interpretations and S recommendations.