*2.7. Application E*ffi*ciency and Water-Use E*ffi*ciency*

Application efficiency (ηA) is defined as [3]:

$$
\eta\_{\rm A} = \frac{\mathbf{V\_n}}{\mathbf{V\_b}} = \frac{\ell\_\mathbf{n}}{\ell\_\mathbf{b}} \tag{5}
$$

where Vn is the volume of water stored in the root zone and Vb is the total volume of water applied. The first is obtained with the expression Vn =<sup>n</sup> Ar, where <sup>n</sup> is the net irrigation depth, defined according to the crop irrigation requirements, and Ar is the irrigated area considered. The second is obtained as Vb = <sup>b</sup> Ar, where <sup>b</sup> is the gross irrigation depth. The net irrigation depth was calculated with the FAO-56 Penman–Monteith evapotranspiration method [22] and the crop phenology was estimated using the FAO methodology [23].

The water-use efficiency (WUE) is the relationship that exists between the biomass present in a crop per unit of water used by it, although recent studies refer to this term as the productivity of irrigation water [11,24]. This relationship is an indicator that allows us to calculate the economic value of the irrigation water in the area. High values of this index will indicate that we are managing to produce a greater amount of organic matter with less use of water. In this work we focus on the productive component of the harvest, which is why we will use the dry biomass yield (<15% of moisture) obtained in kg of the product per m3 of water used:

$$\text{WUE} = \frac{\text{dry biomass yield (kg)}}{\text{total volume of water applied } (\text{m}^3)} \tag{6}$$

#### **3. Results and Discussion**

## *3.1. Soil Texture*

Soil texture is an indicator of the amount of water that soil can store and, consequently, the irrigation interval with which crops must be watered. Figure 2 shows the general classification of textures found in the study area. The predominant soils were loam (21.33%), silty clay loam (18.26%), silty loam (16.44%), and sandy loam (11.71%). This measure allowed us to detect the soils in which more water was used and explain the reasons why the application efficiencies were lower than other soils with similar or different textures.

**Figure 2.** Soil textural classification in the studied areas.

## *3.2. Irrigations Test*

During the study, 475 irrigation tests were carried out on a surface in different phenological stages of the crops: sowing, growth, flowering, and fruiting. The crops in which they were made were corn *(Zea mayz*), sorghum (*Sorghum vulgare*), and barley (*Hordeum vulgare*) in the spring–summer (S–S) and autumn–winter (A–W) cycles (2014–2019). The results show that, in 25% of the cases, the irrigation depth applied by irrigation is 30 cm, which represents an application efficiency of 43%, while 50% of the farmers apply an average irrigation depth of 23 cm per irrigation (η<sup>A</sup> = 69%), and the remaining 25% applies an irrigation depth greater than 40 cm, which in some cases has reached up to 98 cm, which is equivalent to an application efficiency ranging from 16 to 40%.

The irrigation depth applied is directly related to the amount of water that reaches the plots, since the average value is close to 58 L/s, but there is a minimum value of 3.78 L/s that goes up to the maximum value of 160 L/s. This brings with it a very strong problem for the farmer, since he wants to apply the same furrow laying regardless of the flow that he has at the entrance of the plot, which leads to the irrigation time per hectare being 2–6 days and, consequently, there are low application efficiencies.

#### *3.3. Irrigation Design*

With the information of the established crop and the phenological stage in which it was found, the length of the borders or furrows, the parameters found in the irrigation tests (Ks and Hf), and the net irrigation depth to be applied in the next laying was calculated with the Equation (4). The entry flow in the plot was divided by the result obtained and the number of furrows per laying was found with which it should be watered for that specific crop and plot. The plots were split in half to apply traditional and designed irrigation.

As an example, in the case of Plot 778 (Table 1), the results of the evaluation and design were (1) for growing corn, 12 cm needed to be applied but the farmer applied 35.46 cm (η<sup>A</sup> = 33.84%); (2) once the advance and recession phase had been calibrated, the optimal flow was calculated with Equation (4); (3) with these data, the farmer is told that with the flow he has at the entrance of the plot, he must only open 44 furrows instead of the 52 with which he had been irrigating in the traditional way; (4) the farmer had a reduction of 120 min in the irrigation time per set and consequently a reduction of 22.86 in the irrigation depth; and (5) finally, he had an increase in application efficiency, going from 33.84 to 95.23%.

**Table 1.** Results of the design of Plot 778 (η<sup>A</sup> is the application efficiency).


With this methodology developed to obtain the optimal flow in each border or furrow of the plots, it was achieved that the irrigation time required to apply the expenses that have been designed decrease by more than half (Figure 3), where for example in soils with a silty loam texture, where previously the farmer took an average of 35 h per hectare, now it does so in less than 10 h. In the loam and silty clay loam texture plots, they exceed 25 h/ha and, in some cases, they have reached up to 89 h/ha. In general, in the plots where the study was carried out, it was found that the irrigation times decreased.

Irrigation times per hectare decreased significantly, but these times are a function of the expense that farmers receive at the entrance to the plot, so it is not the same to irrigate a hectare with 50 L/s to another that has an expense of 10 L/s. However, the same farmers stated that their lines are progressing evenly, but the only drawback they see is that now they must be more attentive. In some areas where the design was carried out, they had lengths of more than 300 m, and in these cases recommendations were given to modify the irrigation line, otherwise the irrigation will be deficient and the efficiencies will be questionable, despite the advice and design that under these conditions could be generated.
