Daily photosynthetically active radiation (PAR) is now available for Puerto Rico. PAR is estimated from net radiation using a regression equation developed in Florida (pre-fire equation, Sumner, 2001). Click here to access images and data
Relation between daily values of measured net radiation and photosynthetically active radiation (from Sumner, 2001).
Other daily hydro-climate variables for Puerto Rico
Sumner, D. M., 2001. Evapotranspiration from a cypress and pine forest subjected to natural fires in Volusia County, Florida, 1998-99. U. S. Geological Survey Water-Resources Investigations Report 01-4245. Washington, D.C.: U.S. Geological Survey.
I will be offering the following two courses this semester at UPR-Mayaguez. Please click the following links for the course fliers.
Please feel free to contact me if you would like additional information about either course.
Eric Harmsen, Professor
University of Puerto Rico
Dept. of Agricultural and Biosystems Engineering
Mayaguez, Puerto Rico 00681
email: firstname.lastname@example.org, email@example.com
websites: http://pragwater.com , http://bahai.org
Click here to read article
Water Lily: Like snorkels, the mouthlike stomata on water lily leaves point up, where they find the air they need.
From National Geographic Magazine, October 2012, http://ngm.nationalgeographic.com/2012/10/leaves/dunn-text
This article is very interesting, describing some of the evolutionary processes that created the wide diversity of plant leaves that exist over the surface of the Earth. It also discusses the process of photosynthesis as a unique mechanism for deriving food directly from the sun. The article, unfortunately, never once mentioned the extremely important temperature regulation mechanism of evapotranspiration, which is the other important function of the stomata (microscopic pores on the surface of leaves). The reader may find it interesting that only about 1% of the solar energy received by the leaf is used for photosynthesis. The other 99% is converted into other energy fluxes for maintaining the leaf temperature within a comfortable range. When sufficient water is present in the soil, virtually all of the solar radiation is converted into the latent energy flux (i.e., water vapor), which keeps the plant leaf cool, the same way perspiration is used to cool humans. Keeping cool is critically important for plants, to avoid heat stress and a reduction in their growth and yield (e.g., fruit, seed, etc.).
CROP WATER USE ( HARGREAVES ET EQUATION) NEW WOLFRAM ALPHA WIDGET. Reference: Hargreaves, G. H. and Z. A. Samani, Reference Crop Evapotranspiration from Temperature. Appl. Eng. Agric., ASAE. 1(2). 1985,. pp.96-99.
Widget Application: Suppose you want to schedule irrigation by replacing the water evapotranspired by your crop each day. 1. Click on the appropriate link to get yesterdays solar radiation for your location: Puerto Rico or Northern Caribbean, 2. Check the internet for the average daily air temperature at your location (average = (minimum + maximum)/2), 3. Get the appropriate crop coefficient for your crop from this link, and 4. Finally, enter solar radiation, air temperature and crop coefficient into the widget to estimate ET. Multiply ET x acres x 1069.0663 to get the number of gallons of water you need to apply to your field.