USE OF CROP CANOPY SIZE TO ESTIMATE CROP COEFFICIENT FOR VEGETABLE CROPS

Authors: Trout, Thomas; Gartung, Jimmie

Submitted to: Environmental and Water Resources Institute World Congress Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 2/10/2006
Publication Date: 5/21/2006
Citation: Trout, T.J., Gartung, J.L. 2006. Use of crop canopy size to estimate crop coefficient for vegetable crops. Environmental and Water Resources Institute World Congress Proceedings. Omaha, NE May 21-25,2006

Interpretive Summary: Efficient irrigation is critical to get maximum benefit from limited water supplies. Good information about crop water requirements is needed to precisely schedule irrigation. Most horticultural crops are grown with irrigation. Planting time, plant density, variety, and cultural practices vary widely for horticultural crops, so it is difficult to estimate water requirements for each situation. Canopy cover, as an indicator of intercepted sunlight, is related to crop water use. We used a weighing lysimeter to measure daily crop water use and a multi-spectral camera to measure canopy cover for two vegetable crops – head lettuce and bell pepper, and related canopy cover to water use. The ratio of crop water use coefficient to canopy cover declined from about 4 with small canopy cover (0.1) to about 1.3 for a mature crop with canopy cover of 0.9. The relationship was similar for these two crops. Because light interception other than at mid-day will depend on the canopy structure, adjustment may be needed for canopy structure. A generalized canopy cover: crop coefficient relationship would allow weather-based irrigation scheduling for a wide range of horticultural crops based on canopy measurements, and possibly based on remotely-sensed vegetation indices.

Technical Abstract: Planting time, plant density, variety, and cultural practices vary widely for horticultural crops. It is difficult to estimate a basal crop coefficient that can incorporate these variations. Canopy cover, as an indicator of intercepted sunlight, is related to crop water use. We used a weighing lysimeter to measure daily crop water use and a multi-spectral camera to measure canopy cover for two vegetable crops – head lettuce and bell pepper, and related canopy cover to basal crop coefficient. The ratio of crop coefficient to canopy cover declined from about 4 with small canopy cover (0.1) to about 1.3 for a mature crop with canopy cover of 0.9. The relationship was similar for these two crops. Because light interception other than at mid-day will depend on the canopy structure, adjustment may be needed for canopy structure. A generalized canopy cover:basal crop coefficient relationship would allow weather-based irrigation scheduling for a wide range of horticultural crops based on canopy measurements, and possibly based on remotely-sensed vegetation indices.