Crop water use, which translates to crop evapotranspiration, is defined by FAO 56 as is the evapo-transpiration from disease-free, well-fertilized crops, grown in large fields, under optimum soil water conditions, and achieving full production under the given climatic conditions.
When designing an experiment to quantify crop water use in an intercrop grown under rainfed conditions, does the definition of crop water use justify me adding an irrigated duplicate as a treatment?
Dear Chimonyo
FAO 56 crop water use does not mention whether the crop is irrigated or rain fed. Here, if I understood properly, you are using two crops in the same field. For the intercrop system, crop water requirement may be computed for two crops with their respective growth stages and crop coefficients.
Crop water use defines only that amount of water used by a crop(s) growing within the area of influence of the measurements made to determine that water use. As such I would guess that a crop water use you may obtain under inter-crop system will be a proportionate average of the crops grown. As such, the quantification of water use cannot accurately be partitioned between rain and irrigation sources though of course discrete measurement of the two water sources can give a good idea of their contributory levels to the crops' crop water use.
Be aware that FAO crop ET assumes well-watered conditions (no water stress), ie Potential ET while rainfed agriculture can have periods of no rain leading to ET being less than FAO PET. If rainfall is scanty, then the use of an irrigated plot would furnish values of FAO PET. By the way, the FAO 56 assumes alfalfa is the crop, and for other crops one needs crop coefficients..
Thank for for all your input, to Mr Basharat, although FAO 56 does not mention water source, from this current discussion I assume for me to calculate crop ET it should be under STANDARD conditions which Amartya Saha has also alluded to. On the other hand, to Romulus Okwany, I wanted to avoid proportionate averages in the intercrop, but from discussions with professors that have worked on similar projects there are a lot of things I need to consider. Ideally measuring water balance within crop components and between them would be the best. However, I intend to have 3 crop components. I have been asked to look and the cost implication of having UPTO 5 access tubes per treatment :(
A succinct summary of the discussion so far, Mr. Chimonyo. You may need to do some literature review on the density of access tubes (neutron probe tubes?). But a general guide will be the size of your plots, the soil type and the irrigation uniformity. Homogeneity is a most irrelevant term in soil environment but if you have a small enough plot with fairly uniform soil type and high irrigation uniformity you can use fewer tubes. On the other hand the density of access tubes will increase substantially.
- Badges
- Science topic
- Similar topics
- Geoscience
- Remote Sensing