Servicios personalizados
texto en 
Inglés (pdf)
Articulo en XML
Referencias del artículo
Enviar articulo por email
Citado por SciELO 
Similares en
SciELO 
Permalink
INTRODUCTION
Agriculture consumes 70% of fresh water withdrawals from rivers, lakes and aquifers; reaching up to 90% in some developing countries. The growing demand for food to meet the needs of the world's growing population is the main factor for increasing the consumption of water resources (UNESCO, 2009). In 2002, approximately 3 600 km3 of fresh water were used for human consumption, in all regions, with the exception of Europe and North America. Agriculture was the sector that consumed the most water, reaching 69% of all extraction (FAO, 2002).
In Cuba, agriculture is also the main consumer of available fresh water. The Statistical Yearbook of Cuba 2017 informs that, in this year, 6 661 million of m3 of fresh water were extracted and 3 420 million were consumed in agriculture, representing 51.3% of the total. From the 3 877 million m3 of the surface fresh water, 2 031 million m3 were used in agriculture, which represents 52.4%, a similar value to the consumption of groundwater that reached almost 50% of the total fresh water (ONEI, 2018a). Agriculture, as the main consumer of fresh water, works in reducing water consumption and one of the fundamental ways to achieve this propose is to increase the efficiency in the use of irrigation water to increasing water productivity.
The water volume demanded per ton of agricultural product, as well as the efficiency in its use during irrigation, are the main factors that condition the water consumption. Irrigation management determines when and how much to irrigate, based on crop water needs, soil characteristics and climatic conditions (Vázquez et al., 2017). However, do not use an irrigation schedule adjusted to the climate, the soil and the characteristics of the crop are one of the main causes of excessive use of irrigation water. In addition, the production units face the decrease in the volumes of water available due to climate change and the increase in areas under irrigation and therefore, the augment in the demand for water from existing reservoirs. The dams for irrigation use should contain less water in the future, due to decrease in rainfall and increase in temperature, resulting in less water available for plant growth.
Cuban state has invested substantial financial resources in expanding the areas under irrigation. This increase in the water demand can be solved by increasing the productivity of the irrigation water used. The agronomic productivity of water is defined as the ratio between the mass of the product harvested and the volume of water provided by the irrigation to obtain the product. Its calculation can be obtained from the crop agricultural yield and the water applied by irrigation, the total water applied (irrigation + effective rainfall) or the crop evapotranspiration. (González et al., 2015b).
Several authors have pointed out the importance that knowledge of water yield functions acquires in irrigation planning and operation (González et al., 2010; González et al., 2013, 2014; Duarte et al., 2015; Herrera y González, 2015). According to these authors, from water yield functions, rules can be developed, with economic technical criteria for the distribution of available water among crops, in order to maximize production or economic gain in conditions of water deficit. This research was carried out with the objective of determining the efficiency in the use of irrigation water, based on the calculation of the agronomic water productivity of some selected crops in the central region of Cuba.
MATERIALS AND METHODS
The investigation was carried out in the months of January and March 2018, processing the information of different varieties of potato (Solanum tuberosum), bean (Phaseolus vulgaris) and dasheen (Colocasia esculenta), grown in brown soils with carbonates and brown soils without carbonates. The climatic variables such as minimum, average and maximum temperature, as well as the reference evapotranspiration and rainfall were obtained from the Agrometeorological Station " Valle del Yabú ", located at 22° 27 '54 "north latitude and 79° 59' 51 "west longitude.
The irrigation technologies evaluated were spraying, with central pivot machines. Information from the production units was used for water consumption; water applied by irrigation, rainfall water and crop yields obtained during the period. The efficiency in the water use was determined from the calculation of water productivity. This was determined for water applied by irrigation and for total water applied, meaning the irrigation water plus the effective precipitations in the period (González et al., 2010).
The irrigation water productivity was determined by the following equation:
Where:
WP I |
irrigation water productivity (kg/m3); |
R |
crop yield (kg/ha); |
I |
gross irrigation water applied m3/ha |
Where:
WP T |
productivity of total water (total irrigation plus rainfall, kg/m3); |
T |
Total irrigation water applied (irrigation water applied plus effective rainfall) m3/ha. |
Rainfall during the periods studied were converted to effective rainfall, using the Savo method, according Pacheco & Pérez (2010).
RESULTS AND DISCUSSION
Table 1 shows the crops analyzed, the total area planted, the agricultural yield (R), the irrigation water applied (I), the sowing and harvest dates.
TABLE 1 Base data of each crop
| Crop | Irrigation water applied m3/ha | Sown area ha | Yield kg/ha | Date of sown | Date of harvest |
|---|---|---|---|---|---|
| Potato | 4500 | 8 | 25 000 | 5/1/2018 | 9/4/2018 |
| Bean | 1363 | 6 | 1 700 | 15/1/2018 | 15/4/2018 |
| Potato | 4800 | 8 | 29 900 | 28/12/2016 | 5/4/2017 |
| Bean | 3920 | 6 | 1 580 | 12/1/2017 | 12/4/2017 |
| Potato | 4800 | 14 | 27 600 | 26/12/2016 | 7/4/2017 |
| Potato | 4707.6 | 14 | 30 560 | 22/12/2016 | 20/3/2017 |
| Potato | 1126.7 | 11 | 17 880 | 8/1/2018 | 30/3/2018 |
| Potato | 3300 | 10 | 22 500 | 29/12/2015 | 20/3/2016 |
| Dasheen | 5100 | 10 | 20 000 | 20/3/2016 | 20/4/2017 |
| Potato | 3600 | 15 | 27 000 | 8/1/2014 | 10/4/2014 |
| Bean | 3600 | 12 | 1 210 | 11/2/2016 | 8/4/2016 |
| Potato | 3000 | 15 | 23 300 | 5/1/2018 | 31/3/2018 |
The relationship between yield and water applied by irrigation for the potato crop is shown in Figure 1, showing the tendency to increase yield with an increase in applied water. The determination coefficient R2 = 0.82 of linear equation make suitable for predictions. González et al. (2010), found magnitudes of the determination coefficient from 0.45 to 0.72. These results coincide with similar values and trends in the papers of González et al. (2010); González et al. (2011b) y Herrera et al. (2011).
FIGURE 1 Relationship between agricultural crop yield (R) and water applied by irrigation (I) for potato crop.
Table 2 shows the total water applied to all crops. Here it is observed an increase of the water applied in values of 478.8 to 1152.7 m3/ha due to the rain in potato and in bean an increase of 470.3 to 1106.3 m3/ha.
TABLE 2 Rainfall in the period (P), water applied to the crop (I), effective rainfall (Pe) and total water applied to the crops (T)
| Crop | I (m3/ha) | P (mm) | Pe (m3/ha) | T (m3/ha) |
|---|---|---|---|---|
| Potato | 4500 | 149.9 | 1106.3 | 5606.3 |
| Bean | 1363 | 149.9 | 1106.3 | 2469.3 |
| Potato | 4800 | 103.2 | 761.4 | 5561.4 |
| Bean | 3920 | 78.8 | 606.6 | 4526.6 |
| Potato | 4800 | 62.2 | 478.8 | 5278.8 |
| Potato | 4707.6 | 62.2 | 478.8 | 5186.4 |
| Potato | 1126.7 | 149.9 | 1106.6 | 2233.3 |
| Potato | 3300 | 176.1 | 1152.7 | 4452.7 |
| Dasheen | 5100 | 1026.5 | 6622.3 | 11722.3 |
| Potato | 3600 | 35.8 | 275.6 | 3875.6 |
| Bean | 3600 | 61.1 | 470.3 | 4070.3 |
| Potato | 3000 | 149.9 | 1106.6 | 4106.3 |
Relationship between yield and the total water applied is shown in Figure 2. Here an increase in yield can be seen with an increase in the total water applied to the crop. The curve fits a linear equation with a R2 coefficient value equal to 0.63.
FIGURE 2 Relationship between agricultural crop yield (R) and total water applied to the crop (T), for potato crop.
The irrigation water for the potato of 90 day in Villa Clara is 4 100 m3/ha, proposed by Duarte et al. (2015). When analyzing the average water applied by irrigation, it was found that 3 729 m3/ha were applied, a value lower than the proposed by Duarte et al. (2015). However, if the total water is taken into account, a value of 4 537.4 m3/ha was obtained, higher than the proposed value. This indicates that there has been no efficient use of water, because the effective rainfall of the period was not taken into account during the application of water. The average agricultural yield of the crop reached 25 467.5 kg/ha, higher than the average obtained during 2017 in the country, which was 21 740.0 kg/ha (ONEI, 2018b) and also higher than those in the years from 2012 to 2017, as reported by the Statistical Yearbook of Cuba (ONEI, 2018b).
The agronomic productivity of irrigation water in the potato crop was 6.82 kg/m3, but when considering the total water applied, the water productivity dropped to 5.61 kg/m3. Irrigation water productivity is within the range proposed by González et al. (2015a), who propose values between 6.25-26.7 kg/m3 and within the one presented by González et al. (2015b) for field experiments. However, in addition to the irrigation water, that contributed by rainfall, the productivity achieved is lower than the one proposed by the previous authors, manifesting the application of water excess to the plants and, therefore, decrease in the water use efficiency.
Pacheco y Pérez (2010), in field experiments in this area, evaluated the irrigation efficiency in the potato crop and obtained that an excess of water was applied. The potato was irrigated frequently high, every 3.5 days. They also identified as a problem not to establish irrigation schedules or irrigation programming adjusted to the evapotranspiration of the plant and the water contributed by the rain. Water agronomic productivity values coincide with the range proposed by Doorenbos & Kassam (1979), however, they are lower than those proposed by (Herrera et al., 2011), for the conditions of Cuba. It should be noted that this result of lower water productivity is obtained despite the very good agricultural yield obtained which was almost 3000 kg/ha higher than the average of the country.
For beans crop the irrigation water proposed by Duarte et al. (2015), reaches 3 000 m3/ha. The water applied by irrigation had a value of 2 961 m3/ha, similar in magnitude to the proposal, complying with the irrigation water proposed. With the application of this water volume, the average agricultural yield reached 1 490 kg/ha higher than 1 120 kg/ha achieved on average in Cuba during 2017 (ONEI, 2018b).
The productivity of water irrigation applied was 0.50 kg/m3, which is similar to the range of 0.53 to 0.97 kg/m3 found by (González et al., 2011a), in field experiments. Other similar values of water productivity, between 0.6 to 1.91 kg/m3, were reported by González et al. (2015a), and (Herrera et al., 2011). If during the period of crop establishment, the rainfall had been negligible, it could be said that an efficient use of the water was made, since the productivity obtained is very close to the proposal. However, when analyzing the total water that fell on the crop, it is found that an excessive application of water has been made (688.7 m3/ha more than the standard proposed by Duarte et al. (2015), water productivity in this case dropped to 0.40 kg/m3, showing inefficiency in water use. Other studies on the use of water in bean crop have shown a similar water consumption (González et al., 2017), calculated the irrigation water needs for beans, for similar conditions and found that they were satisfied with 2 518 m3/ha.
The norm of net irrigation for the cultivation of the dasheen according to Duarte et al. (2015), is 13 200 m3 / ha, higher than 11 722.3 m3 / ha of total water applied to the crop. With this water deficit of 1 477.7 m3 / ha, an agricultural yield of 20 000 kg / ha was obtained, obtaining an agronomic water productivity of 1.7 kg / m3, much lower than that of 5.9-11.3 kg / m3 reported by (González et al. (2014) & González et al. (2015a), however it is higher than that obtained from the calculation of water productivity from the average agricultural yield of the dasheen in Cuba , which is 15 280 kg / ha (ONEI, 2018b).
The relationship between total water applied and total water productivity is shown in Figure 3. This shows a decrease in total water productivity with an increase in total water applied. The adjustment of the curve to a polynomial equation with a value of the coefficient of determination R2 of 0.50 shows an acceptable value of the model.
FIGURE 3 Relationship between total water productivity (WPT) and total water applied (T), for all crops.
In the production unit analyzed, fixed irrigation schedules are applied; it is that from time to time a standard net irrigation water is applied. It is about maintaining this compliance without taking into account the crops real water needs and without applying an irrigation calendar, calculated according to the climatic and evapotranspiration conditions of the region. These practices cause inefficiencies in the use of irrigation water.
CONCLUSIONS
Inefficient use of water is made for crop irrigation; the total water applied was bigger than values proposed in the literature. In addition, water provided by the effective rainfall was not taken into account.
The agronomic productivity of the irrigation water applied on potato was 5.61 kg/m3, on bean 0.50 kg/m3 and on dasheen 1.7 kg/m3, in all cases lower than the productivity of water reported in the literature, which allows stating the inefficient use of water for irrigation.
