Al-Hira is located in the northwest of Libya, (Figure 1) and it’s a part of the important Djafara plain, one of the most important pastoral areas, near Al Azizia town with a longitude of 31˚N and a latitude of 13:01 E. Desert crops were encountered in most areas such as castor crops (Ricinus-Communis), ring crops (Typhaelephanfing), retama, bitter melon (Citrullus-Colocyntis) and prickly pear (Opuntia-Flcus-Indica).

Rain varied between 200 and 250 mm, a speed wind of 3 m/s is almost encountered, relative humidity recorded by the meteorological station was 80% during January and 30% during August for the period 1945-2006. The average annual air temperature is 26˚C (Table 1).

The combination of all these factors makes the soil granular and non-contiguous, making its light weight and conducive to wind transport, which leads to desertification of the region; the presence of sand dunes in the region is only a result.

Physical and chemical properties analysis shows that (El Zarroug and al., 2020) [4] :

- The percentage of Calcium Carbonate in the soil of the study area varies between 0.5% and 14.5%.

- Total dissolved salts shows acceptable values varying between 0.69 and 1.53 dS/m.

- Average field capacity and wilting point are very low, respectively less than 7 and 4%, which means that there is little capacity of soil moisture retention and gives an indication that the soil is sandy or predominantly sand induced by wind erosion (El Zarroug and al., 2020) [4] .

- The percentage of organic matter is very low (about 0.4%).

Salinities were measured in limited areas. While the salinities measured outside the irrigated area were around 1 dS/m; salinities inside irrigated areas reached even 6 dS/m under squash and tomato in August 2018. Even though these salinities can be considered acceptable for squash, barley and even tomato with some yield reduction, unfortunately any other crop with high added-value, non tolerant to salinity can’t be grown.

Measurements were done in February 2018. The transferred water salinity is high (about 4 dS/m) but aquifer is of good quality (1 dS/m), an integrated water resources management is necessary in this area in the aim to better manage irrigation (Daghari^b and al., 2020) [9] .

1) Case of tomato and squash irrigated with localized irrigation

Five farms were considered (2 for squash and 3 for tomato), tomato is the more important crop grown in the region. The discharge values are given in Table 2 and Table 3.

For vegetable crops, the irrigation equipment is newly installed but what is missing is the cleaning of the drippers. Indeed, the plugging is very clear on some drippers and we note the absence of filtration stations. The drippers are of the on-line type with a nominal flow rate of 2 l/h.

2) Case of olive trees irrigated by localized irrigation

Five olive farmers were considered. A strong variability of the flow rates is observed varying between 5.1 and 1.3 l/h (Table 4); we also note the absence of

filtration system or its failure. According to farmers, the nominal flow rate is 4 l/h. There are four drippers by tree.

Uniformity coefficients of 49% were calculated indicating the very poor use of irrigation water (Table 5). In this case, the drippers are of the on-line type, any lost or blocked dripper is replaced by another emitter, which does not necessarily have the same nominal flow rate as the faulty emitter. This resulted in very poor uniformity of irrigation. They use drippers with a nominal flow of 2 l/h intended for vegetable crops for irrigation of olive trees and vice versa.

The irrigation durations retained are almost 6 or 8 hours corresponding to the presence of the farmers on the plots and do not obey any hydraulic calculation especially since it is a very light soil where the field capacity and the wilting point vary between 11% - 2.8% and 8.2% - 1.8% respectively. Not only the irrigation equipment and the network must be reviewed, but the problem of irrigation management is also raised.

3) Case of wheat irrigated by hand-move sprinkler

To evaluate the sprinkler irrigation, two methods were used (at laboratory and field level):

- Laboratory method

Measured intensities at different distances from the axis of the sprinkler are given in Table 6.

The resulting intensity obtained in the middle of each of 3 zones Z₄, Z₃ and Z₂ (Figure 2) corresponding to the sum of the intensities coming from different sprinklers which spray the zone according to the spacing of the sprinkler (Table 6) was calculated. Zones Z₄, Z₃ and Z₂ are irrigated by respectively 4; 3 and 2 sprinklers. The resulting intensities calculated in the middle of zones Z₄, Z₃ and Z₂are respectively 8.8 mm, 10.2 mm and 7.6 mm. The theoretical uniformity coefficients calculated by Equation (2) are acceptable, it is about 90%.

- Field method

The field measurements of the rainfall intensities in 9 rain-gauges installed in the different zones Z₄, Z₃ and Z₂ gave the following respective intensities 5 mm/h, 10 mm/h and 4.5 mm/h with an overflow of the humidified zone to the outside the square A₁, A₂, A₃ and A₄ on the side of the sprinkler A₁ under the effect of the wind. Very fine droplets can be easily blown away. In the absence of the wind, the surface watered by a sprinkler is circular. As soon as the wind speed exceeds a certain threshold (4 m/s), this surface takes a more or less ovoid shape. The pressure was only 17 m lower than the nominal pressure (30 m). Low pressure causes a spreading of the water distribution with the formation of a double ring. A coefficient of uniformity of 64% was calculated by applying Equation (2).

The uniformity coefficient measured in the field is low compared to that calculated based on laboratory data in the absence of wind. The pressure is different, in addition to the presence of a fairly strong wind. Although the material used meets the standards, a good theoretical coefficient of uniformity of 90% was obtained in the laboratory, but the uniformity coefficient obtained in the field is only 63%. The management of sprinkler irrigation, the nominal conditions of use of irrigation equipment in this perimeter should be reviewed; the same remark as in the case of localized irrigation.

There was a significant decrease in the natural vegetation and degradation in most of the land in the study area. About 85% of the study area was classified as “moderately” or “severely” degraded. This is due to unmanaged agricultural practices and over-grazing. Irrigated area decreases from 18,000 to 12,000 ha between 1996 and 2008. The shrub vegetation decrease is very clear between 1988 and 2009 (from about 40,000 ha to only 26,000 ha), (Figure 3), (Mnsur, 2014) [10] .

An increase of bare soil is very clear jumping from 23,000 ha to about 35,000 ha. Sparse vegetation is constant (about 25,000 ha).

By comparing land cover maps of 1988 and 2009, the decrease of shrubs vegetation and irrigated areas is clear also (Figure 4 and Figure 5).

Sand dunes are sandy clusters of different shapes with a length between 13 meters and 460 meters approximately and important heights (Figure 6).

The results of the study area show that there is a significant reduction in the cultivated areas. These areas have changed and turned into non-cultivated areas and pastures. The study showed that there is a noticeable increase in the desertified area as shown in Figure 7.