|DUESTERHAUS, JAMEY - Collaborator|
|BOOKER, J - Texas Tech University|
Submitted to: Agricultural Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/2/2014
Publication Date: 11/6/2014
Citation: Lascano, R.J., Duesterhaus, J.L., Booker, J.D., Goebel, T.S., Baker, J.T. 2014. Field measurement of cotton seedling evapotranspiration. Agricultural Sciences. 5(13).
Interpretive Summary: Information on much water a cotton seedling uses on a daily basis and under field conditions is scarce because it is a difficult value to measure. The main problem is that most of the available methods to measure cotton water use lack the sensitivity that is required and the methods that can measure cotton seedling water use are expensive. By elimination, the only available method that is both accurate and inexpensive is the gravimetric method that simply requires a repeated measure of the weight of a known soil volume as a function of time. To do so requires to isolate a soil volume that can be repeatedly weighed that has a plant growing in the isolated soil volume. This is called a weighing lysimeter and we designed and built one that was weighed with load cells connected to a datalogger to have a continuous record of the water use of a cotton plant under field conditions. We verified that the plants inside the lysimeter were no different than the cotton plants in the immediate area of where the lysimeters were positioned. This was done by measuring and comparing the leaf area and root length on plants in the lysimeters with nearby plants. Our results indicated that the method we used provided an accurate measure of the water use of cotton seedlings for the first 30 days after seed emergence.
Technical Abstract: Information on cotton evapotranspiration (ET) during the seedling growth stage and under field conditions is scarce because ET is a difficult parameter to measure. Our objective was to use weighable lysimeters to measure daily values of cotton seedling ET. We designed and built plastic weighable micro-lysimeters (ML) that were 0.35 m deep with a soil volume of 6 300 cm3. The soil core was obtained in-situ by pushing the ML well casing into the soil using a commercial soil sampler. The soil core was weighed with tension and compression type load-cells, where a change in mass of 18 g d-1 was equivalent to a water evaporation of 1 mm d-1. We compared load-cell measurements of changes in mass to values measured with a portable field scale by linear regression analysis, and the slope was equal to 1, indicating no statistical difference (P = 0.05) between the two measurements. We measured and compared seedling height, root length and leaf area of cotton plants in the ML with cotton plants in the surrounding area and this comparison showed that the ML used was suitable to measure cotton seedling ET for the first 30 days after seed emergence. The RMSE for crop height was 0.09 cm, for LAI 0.03 m2 m-2 and 6.5 cm for root length. Also, soil temperature at a 0.1 m depth was statistically (P = 0.05) the same in and outside the ML’s. For two planting dates, we measured daily values of soil water evaporation (E) and cotton seedling ET. The day following an irrigation event, E was ~ 9 mm d-1 and quickly declined the following days. Results showed that ML’s provide an accurate tool to measure water losses from the soil and cotton plants with a leaf area index of < 0.2.