The FAO Irrigation and Drainage Paper No.54 gives the Dual Crop Coefficient equation. This method requires a lot of climatic parameters to be input for each day of the study period. It is a very extensive process and some parameters may have to be interpolated. I am curious of other ways to estimate actual Et. The ultimate goal is to plug Et into a mass water balance to get drainage data, paired with tension-lysimeter nutrient concentration data to measure nutrient loads leaching past the root zone.
I tink you can use Penman equation or use the observation and measuring the pan class A
+ a RG thread
https://www.researchgate.net/post/How_can_one_predict_evapotranspiration_losses_in_a_small_catchment1
we can use SMAP for soil moisture retrieval. there are some product of smap like:
1-Radiometer TB and Daily Global Composite Radiometer Soil Moisture at 36 km resolution from 2015 until now.
2-Surface & Root Zone Soil Moisture and Carbon Net Ecosystem Exchange at 9km Resolution for 3- or 4 months in 2015.
finally, i think you can use SEBAL algorithm in remote sensing for ET calculation.
you can estimate potential evapotranspiration (ET) from meteorological data (e.g., only air temperature with Thorntwaite or Blaney-Criddle eqs) and then SMAP soil moisture (SM) data for obtaining actual ET:
actual ET ~ potential ET * SM/porosity
Hello Brooke,
Please see the NASA SIMS Project (Link). The beta web interface provides irrigation block specific crop basal ET estimates for the state of California in both data-layer and .csv format from current back to 2010. We will also produce a tool calculating stress which can calculate Ks based on input Irrigation, precip., and volumetric water content within the root zone. Please follow up with myself or the PI Forrest Melton.
https://ecocast.arc.nasa.gov/simsi/about/
Hello Brooke - do have both applied water and fertilizer records? How will you discern crop N uptake / loss as N2O and vadose zone leaching? Most importantly what scale and cropping system are you planning to work in? Many thanks!
I have used Thornthewaite-Mather approach years ago for ET. Although long dated by now, you might want to check out my thesis on researchgate 1975 (Missouri) and coauthor to a couple of papers on sewage irrigation and nutrient flux on some of the methods use and general discussion. Years ago, research at Hubbard Brook dealt with nutrient cycling and methodology as their are inputs with rainfall, organics from leaves and plants, and outputs in streamflow, leaching as you suggest as well as storage within the soil. Hubbard Brook studies at that time were the best on nutrient cycling discussions, but since then, others have continued and expanded this work, but I am not up to date on current research programs on this subject area, except to say that most experimental watershed and ecosystem type research are likely to have spent some effort on nutrient cycling. These studies can become quite complex, and your question suggested that climate readings may be too much, so a question might be how important are your interests, and perhaps installing measures below rooting zone to capture soil leachate may be more direct and simpler than trying to model all components of water and nutrient inputs and outputs for a complete water and nutrient cycling balance. Modeling is best verified and validated to each circumstance to be sure it is functioning as you would want.
Yes, i have applied fertilizer records and rainfall records. We did not irrigate and the field is not tile drained. The background of experiment is a small agricultural field in Southern Illinois with different cover crop treatments (legume, brassica, grass & oat mix, no cover crop) x different tillage treatments (conventional-till vs. no-till). I have tension lysimeters beneath the rooting zone and collected water samples under a soybean and corn rotation. I need Et to plug into the water balance equation to get a rough estimate of leaching..... There are a lot of complex parameters due to different crop types, textures within the field, topographies within treatments, etc.
Crop N uptake was measured by measuring the N in cover crop/cash crop/ and weeds on bare plots biomass. Root N content from biomass was also measured, but only for the first rotation as it was a separate study.
Soil samples were collected each spring and fall, and leachate would give idea of N concentrations in soil water that may pass the vadose zone (or more importantly the rooting zone in this case). If most pathways are covered, perhaps that could give a very rough estimate of N lost at N2o.
As for scale the plots are 18 m X 122 m long.
Most other literature reports daily leaching values. Not monthly, as some of the suggestions have been on this thread. I sampled every two weeks, so I would therefore have to interpolate the soil water nitrate values daily in between events as I have seen in other papers. Now I am beginning to see why there are not many studies that do this with multiple crop types.
It sounds like a very interesting dataset - sounds very similar to my current work in CA. Why do you need a modeled leaching fraction if you have measured lysimeter drainage value (which manufacture and model?). What is your working hypothesis and expected findings - it seems like you have multiple co-located studies. Calculating ET can be done relatively quickly if you have a ref. ET station? Nutrient leaching should be derived from measured drainage volume and NO3 concentration. Are you trying find the residual of N budget to calculate N2O flux? You should not have an issue doing this under multiple cropping types - PM me for further discussions
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