*3.3.1 Delineation of calculations of evaporation*

Mostly, very little discussion is there in different research papers regarding the calculative part of the evaporation. Hence, the repetition of the carried-out work under differentially textured soils/agroclimatic conditions is quite difficult. As far as the calculative part, different lysimeters were installed in different plots receiving differently established methods/techniques.

#### **Figure 9.**

*Step-wise technique of evaporation delineation with mini-lysimeters (a) Fitting of lysimeter in experimental plot, (b) use of chain-pulley for removing it from plots, (c) removed lysimeter, (d) weighing of lysimeters within the plots receiving differential treatments [23].*

in the plastic pipe. When water applied to a particular plot equipped by a particular treatment, sensor placed in the pipe starts recording and displaying the quantity of water entered in the plot in liters which could be further be used in calculating the irrigation water productivity of differently treated plots. As there is no electric supply in the remote agricultural fields, hence a battery is required for its power. Further, calibrations are required before using it by filling the water in a Known volume of drum and in case of any discrepancy, a correction factor must be applied for further calculations for applied irrigation amounts in the agricultural water management experiments so that correct irrigation water productivities will be

Evaporation generally is known as the unproductive loss of the water from any surface, namely, soil or water or leaf, when liquid water changed to vapor form in the presence of the certain energy, and is affected by establishment methods [8, 12, 20, 29, 42] as mulched plots experienced lesser evaporation losses. However, through the stomata of the leaf, loss of liquid water to atmosphere in gaseous form coined as productive loss, delineated as "transpiration (T)" as under transpiration pull along with water nutrient also enters into the plants through the roots which further results in higher grain yields. Therefore, for having higher production of the plants, higher transpiration is required; thus, every effort is made to divert a greater fraction of the ET share of the soil moisture to the T component [15, 39]. Generally, lysimeters are used for delineating the evaporation, while transpiration is delineated after subtracting other water loss factors from rainfall + irrigation. Lysimeters [41, 42] comprised of two pipes of PVC, the outer (0.16 m) being wider than the inner (0.102 m) in diameter while both of the same length (0.20 m). Porous end cap is used to seal the inner one from downward side, while the outer one was opened from both sides for making soil environment homogeneous in mini-lysimeter and the outer field. Cylindrical auger is used for making space in the field for fitting wider outer pipe (0.20 m long), in which inner soil-filled pipe (duly closed from

delineated under different treatments.

*Area Velocity Flow Meter for calculating the irrigation water applied.*

downside with an end caps) is placed.

**12**

**3.3 Evaporation (E)**

**Figure 8.**

*Soil Moisture Importance*

Let us suppose.

Day 1 (Mass of the Lysimeter + Soil) = A g.

Day 2 (Mass of the Lysimeter + Soil) = B g. Evaporated moisture mass after 1 day = A-B = X g (suppose it is 15 g).

1 g = 1 cm<sup>3</sup> (15 g = 15 cm3 ).

For calculating evaporated water in 24 hours under differential treatments, the differential lysimeter weight in cm3 needs to be divided by the lysimeter area (п r 2 ) cm2 where r is the radius. Let us suppose radius was 7.5 cm.

Hence, evaporated water = 15 cm<sup>3</sup> /3.14 � 7.5 cm � 7.5 cm = 0.085 cm.

Delineation of moisture evaporated from a particular treatmental plot during the last 24 hours is quite important. The "cm" units are converted into "mm" by multiplying it by 10. Therefore, in the above case, 0.85 mm (0.085 � 10 = 0.85 mm) of evaporation is there. With this way, the performance of different RCTs in reducing evaporation and thereby promoting the transpiration could be delineated in a particular region (**Figure 10**).

## **3.4 Drainage (D)**

Drainage is the loss of irrigation or rain water in the downward direction beyond the rhizosphere. Therefore, drained away water could never be used up by the plants. Hence it needs to be checked for providing more moisture to the rhizosphere. In wheat, generally, drainage losses are assumed to be negligible or near to 100 mm, while in the rice season, drainage losses are of significance (>2000 mm). For calculating the drainage losses in the rice season, electronic tensiometers are installed at 450 and 600 mm assuming rhizosphere up to 500 mm [15]. For a drainage calculation, unsaturated hydraulic conductivity needs to be delineated by using the disk permeameter, which is used throughout the soil profile (**Figure 11**).

Now, for calculating the flux using Darcy's law (Eq. (6)), delineation of the unsaturated K of the transitional layer on a daily basis is very important, which is further expressed as deep drainage.

$$\mathbf{q} = \mathbf{K} \Delta \mathbf{H} / \mathbf{L} \tag{6}$$

where Q is the flux, K is the unsaturated hydraulic conductivity, and ΔH/L is the hydraulic gradient.

Hydraulic gradient (ΔH/L) changed to the suction gradient (ΔΨt/L), for tensiometers

$$\mathbf{q} = \mathbf{K} \Delta \mathbf{\Psi} \mathbf{t} / \mathbf{L} \tag{7}$$

Sometimes under field conditions, different length tensiometers had to be used depending upon their availability; hence, a correction factor is applied to nullify this

*Working of electronic tensiometers (a) Fitting of tensiometers in the field, (b) filling of water in tensiometers,*

*(c–e) installed tensiometers,( f) measuring of matric potential using digital soil spec [24].*

*Delineation of Soil Moisture Potentials and Moisture Balance Components*

*DOI: http://dx.doi.org/10.5772/intechopen.92587*

Correction Factor ¼ Tensiometer reading–9*:*8 ∗ ð Þ *Tensiometer length* row number*=*100

Generally, the tensiometer reading is in kPa, but for the soil water balance studies, readings in "cm" are necessary, which are converted by multiplying kPa reading with 10. After filling reading in Eq. (5), flux (q)/drainage loss in different

(11)

effect.

**15**

**Figure 10.**

plots could be easily delineated.

where Ψt is the total potential which is the sum of matric and gravitational potentials, namely, Ψm + Ψg, which are delineated as in cm and kPa, respectively. kPa is easily converted into cm by multiplying it with 10. Disk permeameter (**Figure 11**) is generally used for estimating unsaturated hydraulic conductivity values up to 0–150 cm. For estimating water drained deep through the soil profile, Eq. (4) is used.

$$\mathbf{q} = \mathbf{K} \Delta \mathbf{\Psi} \mathbf{t} / \mathbf{L} \tag{8}$$

$$\mathbf{q} = \mathbf{K}\Delta\Psi\mathbf{A} - \Delta\Psi\mathbf{B}/\mathbf{L} \tag{9}$$

q ¼ K*:*fð Þ Tensiometer readings at 45cm � 45

� ð Þ Tensiometer readings at 60cm � 60 *=*15 (10)

*Delineation of Soil Moisture Potentials and Moisture Balance Components DOI: http://dx.doi.org/10.5772/intechopen.92587*

#### **Figure 10.**

Let us suppose.

*Soil Moisture Importance*

1 g = 1 cm<sup>3</sup> (15 g = 15 cm3

in a particular region (**Figure 10**).

further expressed as deep drainage.

**3.4 Drainage (D)**

(**Figure 11**).

hydraulic gradient.

tensiometers

**14**

Hence, evaporated water = 15 cm<sup>3</sup>

Day 1 (Mass of the Lysimeter + Soil) = A g. Day 2 (Mass of the Lysimeter + Soil) = B g.

).

cm2 where r is the radius. Let us suppose radius was 7.5 cm.

Evaporated moisture mass after 1 day = A-B = X g (suppose it is 15 g).

last 24 hours is quite important. The "cm" units are converted into "mm" by

For calculating evaporated water in 24 hours under differential treatments, the differential lysimeter weight in cm3 needs to be divided by the lysimeter area (п r

Delineation of moisture evaporated from a particular treatmental plot during the

Drainage is the loss of irrigation or rain water in the downward direction beyond

delineated by using the disk permeameter, which is used throughout the soil profile

Now, for calculating the flux using Darcy's law (Eq. (6)), delineation of the unsaturated K of the transitional layer on a daily basis is very important, which is

where Q is the flux, K is the unsaturated hydraulic conductivity, and ΔH/L is the

Hydraulic gradient (ΔH/L) changed to the suction gradient (ΔΨt/L), for

where Ψt is the total potential which is the sum of matric and gravitational potentials, namely, Ψm + Ψg, which are delineated as in cm and kPa, respectively. kPa is easily converted into cm by multiplying it with 10. Disk permeameter (**Figure 11**) is generally used for estimating unsaturated hydraulic conductivity values up to 0–150 cm. For estimating water drained deep through the soil profile, Eq. (4) is used.

q ¼ K*:*fð Þ Tensiometer readings at 45cm � 45

the rhizosphere. Therefore, drained away water could never be used up by the plants. Hence it needs to be checked for providing more moisture to the rhizosphere. In wheat, generally, drainage losses are assumed to be negligible or near to 100 mm, while in the rice season, drainage losses are of significance (>2000 mm). For calculating the drainage losses in the rice season, electronic tensiometers are installed at 450 and 600 mm assuming rhizosphere up to 500 mm [15]. For a drainage calculation, unsaturated hydraulic conductivity needs to be

multiplying it by 10. Therefore, in the above case, 0.85 mm (0.085 � 10 = 0.85 mm) of evaporation is there. With this way, the performance of different RCTs in reducing evaporation and thereby promoting the transpiration could be delineated

/3.14 � 7.5 cm � 7.5 cm = 0.085 cm.

q ¼ K*:*ΔH*=*L (6)

q ¼ K*:*ΔΨt*=*L (7)

q ¼ K*:*ΔΨt*=*L (8) q ¼ K*:*ΔΨA � ΔΨB*=*L (9)

� ð Þ Tensiometer readings at 60cm � 60 *=*15 (10)

2 )

> *Working of electronic tensiometers (a) Fitting of tensiometers in the field, (b) filling of water in tensiometers, (c–e) installed tensiometers,( f) measuring of matric potential using digital soil spec [24].*

Sometimes under field conditions, different length tensiometers had to be used depending upon their availability; hence, a correction factor is applied to nullify this effect.

Correction Factor ¼ Tensiometer reading–9*:*8 ∗ ð Þ *Tensiometer length* row number*=*100 (11)

Generally, the tensiometer reading is in kPa, but for the soil water balance studies, readings in "cm" are necessary, which are converted by multiplying kPa reading with 10. After filling reading in Eq. (5), flux (q)/drainage loss in different plots could be easily delineated.

where Øi is the volumetric soil moisture (cm<sup>3</sup> cm�<sup>3</sup>

*Delineation of Soil Moisture Potentials and Moisture Balance Components*

depth under consideration, moisture (cm) is determined by

evapotranspiration water from evaporation to transpiration.

For Db determination, generally, core method [22] was used. Under this method, undisturbed metallic soil cores are used for calculating the Db, and fresh core weight was measured. Then, fresh soil + cores weight was recorded, and then, both fresh soil and cores are dried for 1 day in an oven at 105°C. For Db, the dried weight of soil is divided with the internal volume of the metallic cores [15]. Further for a specific

In a specific depth of soil, soil moisture cmð Þ¼ Øi � soil profile depth (14)

Further, for delineating soil profile moisture up to 150 cm, each depth value of

By adopting above methodology for calculating different soil moisture components, namely, rainfall, irrigation, evaporation, transpiration, seepage, drainage, and change in profile soil moisture, one could easily delineate the soil moisture components or validate the performance of a particular resource conservation technology, namely, happy seeder, laser leveler, tensiometers, direct-seeded rice, etc., in improving the yield potentials by partitioning the maximum share of the

Underground water is globally declining down which in itself is a matter of great

concern. Further, population pressure is rising day by day whose requirements whether of food, fiber, etc. should be met out from the ever-diminishing resources, namely, water and land. Climate change further complicated the whole scenario by one or other way. Thus, under this whole current scenario, it is very much important to first have knowledge regarding soil moisture movement under the impacts of different soil moisture potentials, namely, matric potential, solute potential, and gravitational potential, so that irrigation water is applied as required for having higher water-use efficiency for which tensiometers may serve the purpose under the field conditions. Further, many RCTs are being proposed in the water-stressed regions for establishing the wheat-rice cropping sequence with claim to have higher water-use efficiency and, thus, higher land and water productivity. But a careful observation delineates that all of these RCTs are not universally applicable; rather their performance varied as per differential sand, silt, and clay ratios, soil slope, and agroclimatic conditions. Therefore, the first idea regarding different soil water potentials and then, secondly, rechecking of different recommended RCTs in a diversion of maximum share of green water from E to T are required. For this, estimating different soil moisture balance components and therefore their instrumental/calculative part needs more attention in the budding scientists more particularly dealing with the agricultural water management experiments in the water-

soil moisture is added up to have soil profile moisture (cm), which is further multiplied by 10 to get soil moisture of the whole profile in mm, the required units

moisture; and Db is the bulk density.

*DOI: http://dx.doi.org/10.5772/intechopen.92587*

for the soil moisture balance.

stressed regions of the globe.

No conflict of interest is expressed by the authors.

**Conflict of interest**

**17**

**4. Conclusion**

); W is the mass basis soil

**Figure 11.** *Disk permeameter for delineation of un-saturated hydraulic conductivity [23].*
