Submitted to: Crop Management at www.cropmanagement.org
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 23, 2009
Publication Date: December 11, 2009
Citation: Long, D.S., Eitel, J.U., Huggins, D.R. 2009. Assessing Nitrogen Status of Dryland Wheat Using the Canopy Chlorophyll Content Index. Crop Management [Online]. Available: http://www.plantmanagementnetwork.org/cm/element/sum2.aspx?id=8617 Interpretive Summary: Active light sensors with sensitivity in the red, far red, and near infrared (NIR) wavebands are now available for use with ground applicators to sense crop reflectance, measure crop nitrogen (N) response, and apply N fertilizer at the same time. These sensors rely upon the Normalized Difference Vegetation Index (NDVI) which is computed from the red and NIR wavebands in ratio. However, NDVI is poorly related with crop N status in water limiting environments. The objective of this study was to compare NDVI and the Canopy Chlorophyll Content Index (CCCI) for estimating the N status of dryland wheat. Canopy reflectance was measured in a small plot experiment with dryland wheat by means of an active three band sensor, and correlated with relative chlorophyll and leaf N contents. The CCCI was more highly correlated with these variables than the NDVI. Similar results were obtained in two production fields. A simple N response index is proposed using the CCCI to base late-season topdressing N applications and increasing grain protein concentration.
Technical Abstract: Ground-based, active light sensing relies upon the Normalized Difference Vegetation Index (NDVI) for assessing crop nitrogen (N) response and applying N fertilizer. However, NDVI may not work well in semiarid environments where biomass and yields depend upon plant water. This study evaluated the Canopy Chlorophyll Content Index (CCCI) for predicting leaf chlorophyll and N contents while minimizing non-N related crop variation. Ground reflectance was measured on wheat (Triticium aestivum L.) in a small plot experiment using an active sensor with sensitivity in red, red edge, and near infrared wavebands. Relative chlorophyll and N were measured in flag leaf samples. The CCCI was calculated from the Normalized Difference Red Edge (NDRE) index and NDVI in ratio. Index CCCI was more highly correlated with chlorophyll (r^2=0.46) and leaf N (r^2=0.31) than NDRE (r^2<0.17) or NDVI (r^2<0.10). Chlorophyll and leaf N were well described by CCCI in two farm fields (r^2<0.80), but NDRE or NDVI performed well in only one field. The CCCI shows promise over NDVI for predicting N status. A simple N response index is proposed using CCCI to base late-season topdressing for increasing grain protein in hard red wheat.