Is there a table with the amount of water that we need to irrigate in one hectare, according the readings of the PQS 1 PAR quantum sensor (PAR Lite) daily?
We do not have charts or tables indicating irrigation requirements for various plots of land (i.e. based on differing vegetation and climatic factors). There are many scientific publications that refer to evaporation rates from crops, but none, to our knowledge, that specifically link PAR readings from our sensor to irrigation.
With the PQS 1 (PAR Lite), can I derive the crop evaporation from the net radiation?
There is something as a "reference crop evaporation" or "actual evaporation" that can be derived from net radiation (solar plus thermal) together with surface temperature, soil and vegetation data. Unfortunately we don't have the information how to do it. There is a simpler approach in which the expected evaporation is coupled to the total dose of global radiation as measured by a horizontal pyranometer.
If the metoffice gives such figures for your area it should be of importance to know the relation between PAR intensity and total global irradiance for at least a solar spectrum at air mass 1.5 (solar elevation 53°).
This relation is for:
Clear sky: 681 W/m² total, 308 W/m² in the 400 to700 nm band 1408 µmol/s.m² PAR
Light cloud cover: 200 W/m² total, 109 W/m² in the 400 to 700 nm band 493 µmol/s.m² PAR
Be aware that many green leaves are highly reflective for near IR but absorb strongly in the 400 to 700 nm band (PAR region). For evaporation only W/m² counts and for photosynthesis only photons counts.
How many PQS 1 PAR quantum sensors (PAR Lite radiometers_ do you advise to use in a greenhouse?
Normally 1 should be enough. If in the greenhouse the conditions differ, like different glass type, shielding or glass cover, it is advised to use more than one PQS 1 PAR quantum sensor per typical condition.
Can I use a PQS 1 (PAR Lite) meter under water?
Yes, however the depth is limited to 2 meters. Please also take the “breaking of light on the water surface” in consideration. This affects the calibration factor.
If I use a PQS 1 PAR quantum sensor (PAR Lite radiometer) under water, can I connect a data logger to it?
Yes, however the data logger needs to be placed on the surface (it is weather resistant, but cannot be lowered into the water).
What is the advised calibration frequency for a PQS 1 (PAR Lite)?
We advise to re-calibrate the PQS 1 (PAR Lite) radiometer every two years.
PAR readings at noon increase by the order of 0.001 umol/m²s. Can you tell me whether small readings like this are likely to be accurate? If not, what is the effective lower irradiance limit detectable by this sensor?
0,001 µmol represents a voltage of 5nV (nano Volt). As you can understand this very low voltage cannot be measured with a data logger. Besides the absolute error from the data logger, the PQS 1 PAR quantum sensor (PAR Lite) also has some specifications to consider.
There is the non- stability, non linearity, temperature dependence and the quantum response. Measurements under 1 µmol/m²s are not to be trusted as accurate. (effective limit)