Verifiable Water Use Inventory Using ICT …
13
without considering runoff and percolation losses. Dr n-1 accounts for the soil moisture depletion of the previous day (mm), ER n is the effective rainfall of n day (mm)
whose calculation is described in the following subsection, I n is the real applied
irrigation depth and is measured with the water meter installed on field (mm), ETC
is the crop evapotranspiration (mm) estimated from the ET 0 data registered by the
nearest agroclimatic station and information on the state of development of the crop.
K s is a non-dimensional coefficient of water stress [3] that quantifies the reduction of
transpiration when water deficit in the soil exceeds RAW. As long as water depletion
in the root zone is less than RAW, the value of this coefficient is equal to 1.
Equation (5) calculates the depletion of soil moisture using the information
recorded by on-site moisture sensors.
Dr real,n = 1000 · (θ FC − θ real n−1 )
(5)
where θ FC represents the volumetric water content of soil at field capacity (m
3 /m
3 )
and θ real is the average volumetric water content (m
3 /m
3 ) recorded by on-site sensors
at a fixed time every day using Eq. (6):
θ real =
p
Z=1 θ z
n
=
θ Z1 + θ Z2
2
(6)
where Z identifies the sensor by its depth from the ground surface, so θZ1 and θZ2
represent the volumetric water contents recorded by the most superficial sensor and
the one located underneath, in the layer with higher root density, respectively. As
commented above, the function of the sensor located below Z2 is aimed at controlling
percolation occurrence.
To estimate soil water content, θ, the soil water retention curves are needed. These
curves are estimated from soil texture. Soil samples taken at sensor location depths
will be analyzed to determine soil texture using the US Department of Agriculture
(USDA) soil texture triangle. Then the soil water retention curves can be calculated
by the ROSETTA model [47]. The retention curves are used to estimate θ FC and θ PWP
while θZ1 and θZ2 are obtained from the sensors at sunset giving information about
the remaining water content in the soil after the daily evapotranspiration period.
Frequently, after irrigation, the water content in the soil exceeds FC for a while,
then the soil drains and the water content stabilizes. After irrigation, soil moisture
data recorded has high θ values as the soil has not drained yet and the crop has not
taken the water available yet. If this data is used, inaccurate irrigation scheduling
could be done. It is possible to change this parameter to suit other irrigation and crop
management criteria.
If the average moisture value exceeds a certain percentage of the FC value, x, (e.g.
20%), the moisture deficit at the end of the day, Dr n , will be considered 0 and the
soil is at field capacity. If θ real is lower than the set threshold, the value of Dr n will
be the higher between Dr real,n and Dr theorical,n , so the most limiting value was taken
to determine the irrigation timing Eq. (7)
13
without considering runoff and percolation losses. Dr n-1 accounts for the soil moisture depletion of the previous day (mm), ER n is the effective rainfall of n day (mm)
whose calculation is described in the following subsection, I n is the real applied
irrigation depth and is measured with the water meter installed on field (mm), ETC
is the crop evapotranspiration (mm) estimated from the ET 0 data registered by the
nearest agroclimatic station and information on the state of development of the crop.
K s is a non-dimensional coefficient of water stress [3] that quantifies the reduction of
transpiration when water deficit in the soil exceeds RAW. As long as water depletion
in the root zone is less than RAW, the value of this coefficient is equal to 1.
Equation (5) calculates the depletion of soil moisture using the information
recorded by on-site moisture sensors.
Dr real,n = 1000 · (θ FC − θ real n−1 )
(5)
where θ FC represents the volumetric water content of soil at field capacity (m
3 /m
3 )
and θ real is the average volumetric water content (m
3 /m
3 ) recorded by on-site sensors
at a fixed time every day using Eq. (6):
θ real =
p
Z=1 θ z
n
=
θ Z1 + θ Z2
2
(6)
where Z identifies the sensor by its depth from the ground surface, so θZ1 and θZ2
represent the volumetric water contents recorded by the most superficial sensor and
the one located underneath, in the layer with higher root density, respectively. As
commented above, the function of the sensor located below Z2 is aimed at controlling
percolation occurrence.
To estimate soil water content, θ, the soil water retention curves are needed. These
curves are estimated from soil texture. Soil samples taken at sensor location depths
will be analyzed to determine soil texture using the US Department of Agriculture
(USDA) soil texture triangle. Then the soil water retention curves can be calculated
by the ROSETTA model [47]. The retention curves are used to estimate θ FC and θ PWP
while θZ1 and θZ2 are obtained from the sensors at sunset giving information about
the remaining water content in the soil after the daily evapotranspiration period.
Frequently, after irrigation, the water content in the soil exceeds FC for a while,
then the soil drains and the water content stabilizes. After irrigation, soil moisture
data recorded has high θ values as the soil has not drained yet and the crop has not
taken the water available yet. If this data is used, inaccurate irrigation scheduling
could be done. It is possible to change this parameter to suit other irrigation and crop
management criteria.
If the average moisture value exceeds a certain percentage of the FC value, x, (e.g.
20%), the moisture deficit at the end of the day, Dr n , will be considered 0 and the
soil is at field capacity. If θ real is lower than the set threshold, the value of Dr n will
be the higher between Dr real,n and Dr theorical,n , so the most limiting value was taken
to determine the irrigation timing Eq. (7)