**2.2. Calculation of surface renewal (SR) and measuring Rn and G**

The calculation of SR is done using Eq. (1). This is a residual energy balance equation. The net radiometer and soil heat flux plate data will be measured every 5 minutes and then averaged and recorded at the end of each 30 minutes. Soil temperature data will be recorded at the end of each 30 minutes, and the change in soil heat storage (dS) above the heat flux plates can be computed as in Eq. (2):

$$\text{dS} = \text{VC} \times \left( \text{(T final} - \text{T initial)} / 1800 \right) \times \text{D} \tag{2}$$

where VC = apparent volumetric heat capacity of the soil; T final and T initial = final and initial temperatures for a 30 minute period, and D = 0.04 m = depth of the heat flux plate. The value 1800 is the number of seconds for each 30 minutes. The VC is calculated as the product of the apparent soil density and the specific heat. The soil heat flux density at 0.04 m depth (G0) is calculated as the mean of the two heat flux plate measurements. Then the soil heat flux density at the surface (G) was calculated as:

$$\mathbf{G} = \mathbf{dS} + \mathbf{G}\mathbf{o} \tag{3}$$

where ETc, is average crop maximum evapotranspiration per week; ETo is the average weekly

Water Replenishment in Agricultural Soils: Dissemination of the IrrigaPot Technology

Ks = ETa/ETc (7)

ETa = ks × ETc or ETo × kc × ks (8)

Water applied at each site was evaluated based on water held in the soil and data from production and harvest. Water-use efficiency is used as an important parameter to evaluate the performance of this technology. The water-use efficiency is calculated using harvest yield

the hydrologic balance, and real evapotranspiration is calculated from measurements using the technique of surface renewal. Rainfall data were measured using a rain gauge installed at the site. Irrigation water was measured and applied using a gauged watering bucket. In the article "Evaluating water productivity of tomato, pepper and Swiss chard under clay pot and furrow irrigation technologies in semi-arid areas of northern Ethiopia" more detail about the agronomic data was presented [13]. A comparative study has been undertaken between bar shaped clay pot and furrow irrigation on tomato, pepper and Swiss chard plots in Mekelle University Campus, Tigray, Ethiopia. Plant height for both tomato and pepper was measured every week using a ruler starting from 30 days of transplanting until maturity. The number of fruits per plant and yield were measured during the cropping season, and the results showed that there were five successive harvests of tomato and Swiss chard whereas

) is obtained from the analysis of

http://dx.doi.org/10.5772/intechopen.80605

81

where ETa is actual evapotranspiration and ks is the stress cofficient.

of water applied to the crop. Water consumed (m3

**2.5. Economic evaluation: comparison based on a cost/benefit relation (CBR)**

viable, and this also indicates that the technology used is economically efficient.

An analysis of cost/benefit relation (CBR) was done dividing the present value of the total benefit by the present value of the total cost for each farm; the larger the resulting index, the more efficient is the project. In general, a larger CBR indicates that the project is economically

Analysis of variance was conducted using a statistical program to evaluate the efficiency of water use, biomass production, crop yield, and plant height, width, and fruits, among other variables. Implementation of demonstration units of the Africa partnership was conducted with more than 60 farmers and 12 Agricultural Agents trained and provided with training

there were only two harvests from the pepper crop.

**2.6. Statistical analysis of field data**

manuals in the local language (**Figure 1**).

reference evapotranspiration.

**2.4. Water-use evaluation in Africa**

(kg) per m<sup>3</sup>

#### **2.3. Calculating surface renewal sensible heat flux**

Temperature data was collected at a frequency of 4 Hz and the time lags of r = 0.25 and 0.5 s were used in a structure function to determine the temperature ramp amplitude (Ar) and inverse ramp frequency (D + S) as described [8]. The uncalibrated sensible heat flux density (H′).

$$\mathbf{H'=q \times Cp \times \left( (Ar)/D + S \right)} \times \mathbf{Z} \tag{4}$$

where q is air density (kg m−<sup>3</sup> ); Cp = specific heat at constant pressure (J kg−<sup>1</sup> K−<sup>1</sup> ) of the air; and Z is measurement height (m). A calibration factor (f) was used to account for uneven heating below the temperature measurement height and other potential issues [9] and to convert the uncalibrated H′ to the actual sensible heat flux density.

$$\mathbf{H} = \mathbf{f} \times \mathbf{H'} \tag{5}$$

The 'f' values depend on the thermocouple size, sampling frequency, height above the ground, and the underlying vegetation [8–10]. A calibration factor was be determined using a linear regression of sonic anemometer H readings versus H′ data collected over a one-week period on the site.

Reference evapotranspiration (ETo) was based on FAO-penman Montheith [11, 12]. Determination of crop coefficient (kc) and actual and maximum evapotranspiration (ETa and ETc): from Eq. (1), LE can be related to ETc or ETa;

$$\mathbf{k}\mathbf{c} = \mathbf{E}\mathbf{T}\mathbf{c}/\mathbf{E}\mathbf{t}\mathbf{o}\tag{6}$$

where ETc, is average crop maximum evapotranspiration per week; ETo is the average weekly reference evapotranspiration.

$$\mathbf{Ks} = \text{ETa/ETc} \tag{7}$$

where ETa is actual evapotranspiration and ks is the stress cofficient.

$$\text{ETa = ks} \times \text{ETc or } \text{ETo} \times \text{kc} \times \text{ks} \tag{8}$$
