Growth Stage, Development, and Spatial Variability in Corn Evaluated Using Optical Sensor Readings^*

ABSTRACT

Knowing the exact stage of growth where expressed plant variability is at a maximum might lead to the identification of times when in-season fertilization could have the greatest impact. One field experiment was initiated to measure daily plant growth and spatial variability in corn (Zea mays L.) over the entire growth cycle using optical sensor readings (normalized difference vegetative index, or NDVI) collected every 0.05 m in length, 0.6 m wide from 4 corn rows, 27 m in length. Averaged over all 4 rows, plants were spaced 21 ± 7 cm apart. For each row and sensing date, the mean, standard deviation, and coefficient of variation (CV) were computed from the NDVI readings. Eighteen days after planting, NDVI values were near 0.20, and later peaked near 0.81, 54 days after planting at the 10-leaf growth stage (V10). Coefficients of variation were found to peak much earlier, 33 to 35 days after planting at the 6-leaf growth stage (V6), (31% to 34% during this period). Expressed spatial variability decreased from >30% at V6 to just under 10% at the 11-leaf growth stage (V11). Immediately following V11, a distinct increase in CVs was found just following the initiation of tasseling (VT), but lasted for only 2 days. Expressed spatial variability was greatest at the V6 growth stage, and this peak in the within-row-by-plant variability may be the precise growth stage at which treating that variability will have the greatest impact.

Notes

^*Contribution from the Oklahoma Agricultural Experiment Station and the International Maize and Wheat Improvement Center (CIMMYT).

^*2 consecutive days with evening frost accelerated senescence and physiological maturity.