Sudan grass and pearl millets productivity under different irrigation methods with fully irrigation and stresses in arid regions

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1 Japanese Society of Grassland Science Japanese Society of Grassland Science ISSN ORIGINAL ARTICLE Sudan grass and pearl millets productivity under different irrigation methods with fully irrigation and stresses in arid regions Saleh M. Ismail 1,3, Fathy S. El-Nakhlawy 1 and Jalal M. Basahi 2 1 Arid Land Agriculture Department, Faculty of Meteorology, Environment and Arid Land Agriculture, King Abdulaziz University, Jeddah, Saudi Arabia 2 Hydrology and Water Resources Management Department, Faculty of Meteorology, Environment and Arid Land Agriculture, King Abdulaziz University, Jeddah, Saudi Arabia 3 Soils and Water Department, Faculty of Agriculture, Assiut University, Assiut, Egypt Keywords Drought; forage crops; irrigation systems; water use. Correspondence Saleh M. Ismail, Arid Land Agriculture Department, Faculty of Meteorology, Environment and Arid Land Agriculture, King Abdulaziz University, Jeddah, Saudi Arabia. smii2001@gmail.com Received 21 October 2016; accepted 2 July doi: /grs Abstract A field experiment was conducted at the Agriculture Research Station of King Abdulaziz University to study the response of sudan grass (Sorghum sudanensis L.) cv. California Gold and pearl millet (Pennisetum glaucum L.) cv. KN-10. productivity to different irrigation methods and water application under arid conditions. Three irrigation methods including surface drip (SD), sub-surface drip (SSD) and sprinkler irrigation (SPI) were investigated. Under each irrigation method, one full irrigation treatment (100% of water requirement [WR]) and two water stress treatments (75% WR and 50% WR) were studied. Sudan grass and pearl millet crops were cultivated under each water regime for two consecutive seasons and cut several times for evaluating the production and irrigation water use efficiency (IWUE). Results revealed that SSD produced the highest forage yield under full and stress treatments in both crops followed by SD. SPI produced the least forage yield compared with SD and SSD in 2014 and 2015 seasons. Decreasing water application decreased yield production and increased IWUE under SD and SSD but decreased them under SPI. Increasing number of cuts decreased yield and IWUE in both crops. Under full and stress treatments, sudan grass produced higher forage yield than pearl millet. Irrigation water use efficiency was the best under SSD followed by SD and SPI, respectively. Irrigation water use efficiency of 100 and 75% were significantly similar in both investigated crops. Introduction Kingdom of Saudi Arabia is one of the countries suffering from a severe water scarcity problem. Most of the water resources in the Kingdom come from groundwater, which is non-renewable water and is exploited as the major source of irrigation. Irrigation activities are used for 80 to 88% of the total water consumption in the Kingdom (Sadik and Barghouti 1994). Moreover, the volume of water used for irrigation has tripled from about 6.8 km 3 in 1980 to about 21 km 3 in 2006 (FAO-Aquastat, 2009). Under such circumstances, adoption of optimum water management practices assumes prime importance for attaining national food and water security. In view of the high investment costs of developing irrigation facilities and limited availability of irrigation water, it should be used most efficiently. Irrigation methods and amount of irrigation water applied to crops play significant role in optimizing crop production and water use efficiency. Sudan grass (Sorghum sudanensis L.) and pearl millet (Pennisetum glaucum L.) are among the best suitable forage crops for areas with hot weathering conditions, limited water resources and light-texture soil like that of the western region of Saudi Arabia. Both crops can provide two to three cuts to meet the green fodder requirement of milch animals. Under suitable climatic conditions, 2017 Japanese Society of Grassland Science, Grassland Science, 64,

2 Forage productivity under water stress S. M. Ismail et al. pearl millets have great capacity of rooting, which enables the producers to take two or three cuts of green forage (Maiti and Rodriguez 2010). When harvesting sudan grass as hay, it also recovers well after cutting and three or four cuts can be taken in one season especially when regularly irrigated. Both crops are adapted under different adverse conditions such as drought, salinity and soil poor in nutrients (Dakheel et al. 2009; Newman et al. 2010). The western region of Saudi Arabia is characterized by warm weather throughout the year with high temperature compared to other parts. These weather conditions encourage the growers to grow sudan grass and pearl millets in December as green forage (Ismail 2012). Besides the adaptability of both crops to drought stress, they were also characterized by high nutrition values. Pearl millet is rich in protein and energy while poor in fiber and lignin concentration. Crude protein can range from 9 to 11% in unfertilized soils and to 14 to 15% under nitrogen-fertilized conditions. It is also rich in calcium, iron and has balanced amino acids, but its sulfur-containing amino acid concentration is low. Crude protein of grass species like sudan grass is highly affected by nutrient contents of soil where the fertile soil increases the fodder crude protein. The crude protein of some grasses can range from high value (15 25%) to low (3 5%) (Al-Soqeer and Al-ghumaiz 2012). The current research tried to achieve the greatest aboveground biomass production per unit of water for sudan grass and pearl millet crops. Therefore, the objectives of the study were to: (i) measure growth parameters and quantify forage production of both crops in each cut under irrigation methods and water application; and (ii) evaluate irrigation water use efficiency under investigated irrigation methods and water application treatments. stress treatments (75% WR and 50% WR). The sub-sub plots were cultivated with two forage crops named as sudan grass cv. California Gold. and pearl millet cv. KN- 10. The seeds were sown on 18 December 2013 for the first growing season and on 10 December 2014 for the second growing season. Seeds were cultivated in hills with 20 cm distance between hills and rows for the three investigated irrigation systems. After complete germination, two plants were kept in each hill. Before the starting of the experiment, soil was prepared through ploughing, harrowing and leveling. Then superphosphate and potassium fertilizers in form of P 2 O 5 and K 2 O were incorporated with the soil with a rate of 120 and 100 kg ha 1 respectively. Irrigation systems instillation In SSD, the field was leveled and the dripper lines were installed at 10 cm deep on 40 cm between two adjacent dripper lines. The distance between drippers is 30 cm. The type of the dripper line was RAIN BIRD LD Landscape drip 0.6 (Rain Bird, California, USA). The downstream end of each dripper line was connected to a manifold for convenient flushing. Inlet pressure on each tape was about 1.5 bars. The system used 125-micron disk filter. The water source was from containers always full of water from the main irrigation network. The layout of SD was the same as SSD except for the positions of dripper lines, where they were install on soil surface. In SPI, 2045-PJ Maxi-Bird TM rotator (Rain Bird) was used. The inlet pressure on the system was worked with 2.2 bars. With this pressure, the radius of the rotator was adjusted to be 6 m with a maximum discharge of 0.68 m 3 h 1. Materials and methods Experimental location, design, treatments and cultural practices Field experiments were carried out for two consecutive growing seasons of 2013/2014 and 2014/2015 at the Agriculture Research Station of King Abdulaziz University located at Hada Al-Sham village, 110 km northeast of Jeddah, KSA. The soil texture was classified as sandy loam. The climate of the area is arid, with high temperatures during the summer season. The design of the experiment was split plot with four replicates. The sub-sub plot size was m. The main plots comprised three irrigation methods including surface drip (SD), sub-surface drip (SSD) and sprinkler (SPI). The sub-plots contained three water application treatments, one with fully irrigation (100% water requirements [WR]) and two as Water requirement calculation Before calculating water requirements and after installing irrigation systems, the irrigation efficiency was calculated for each irrigation method and found to be 90% for SD and SSD but due to the effect of wind in the experimental area the efficiency of SPI was about 75%. The required amount of irrigation water including system irrigation efficiency for 100% WR was calculated by CROPWAT model based on the metrological data of the area as follows: ET c ¼ K c ET 0 where: ET c = crop evapotranspiration (mm day 1 ) ET 0 = reference evapotranspiration (mm day 1 ) K c = crop coefficient. Reference evapotranspiration was calculated using Penman-monteith equation as described by Allen et al Japanese Society of Grassland Science, Grassland Science, 64, 29 39

3 S. M. Ismail et al. Forage productivity under water stress (1998). In addition, crop coefficient values for sudan grass and pearl millet listed by Allen et al. (1998) were used. Average 5-year metrological data for the experimental area during the growth periods are presented in Table 1. After water requirements were calculated the control unit (timer) was adjusted for the required time that supplied the calculated required amount of water under each irrigation method. As the daily water requirement was calculated as 100% WR, it reduced to 75% WR and 50% WR in the second and third water stress treatments, respectively. Total water supply for each cut was obtained by the summation of the daily water supply, while seasonal water supply was obtained by the summation of the total water supply of all cuts during each growing season. Under the current study, actual water supply for pearl millet and sudan grass was the same. Data collection Three cuts were harvested during each growing season from SD and SSD while only two cuts were harvested under the SPI system. The period of each cut during the first growing season was 64, 42 and 37 days for the first, second and third cuts, respectively, while it was 58, 41 and 37 days for the first, second and third cuts during the second growing season, respectively. The collected data for each crop in each cut included total water supply for each cut, seasonal water supply, plant height, leaf to stem ratio and fresh and dry forage yields based on ton ha 1. Statistical analysis The collected data of each cut for each crop were statistically analyzed using the analysis of variance procedures and mean separation using revised least significant differences (RLSD) test based on the used Experimental Design as in El-Nakhlawy (2010) using SAS program. Table 1 Average of 5-years metrological data in the experimental area during the growth period of the experiment Month Minimum temperature ( C) Maximum temperature ( C) Relative humidity (%) Wind speed (km day 1 ) Rainfall (mm) December January February March April May Results Water requirements and supply Total water requirements and total supply of each cut for sudan grass and pearl millet crops are presented in Table 2. The results indicated that the total water supply of the first andsecondcutswasalmostsimilarbutlessthanthatinthe third cut where it was the highest. The total water supply was reduced by reducing water supply where the highest water supplywasfoundtobe100%wrfollowedby75%wrand 50% WR, respectively. Similar behavior was recorded in SPI. Results of SPI clearly showed that total water supply was higher than that of SD and SSD in the first and second cut. However, SPI failed to produce any biomass during the third cut so that the system was turned off. Results of seasonal water supply presented in Table 2 show that the highest seasonal water supply was found in 100% WR treatment followed by 75% WR and 50% WR treatments, respectively, in all investigated irrigation methods. Seasonal water supply of SD and SSD was higher than that of SPI. Yield and growth attributes of pearl millet crop: Effect of irrigation system Results presented in Table 3 indicated that SSD increased plant height compared to SD; however, the differences between them were not significant in the first and third cuts but significantly short in the second cut in 2014 and 2015 growing seasons. Plant height under SPI was significantly shorter than the SD and SSD in both seasons in the first and the second cuts. Results of leaf/stem ration were significantly similar in investigated irrigation methods in all cuts in both growing seasons. Results of fresh and dry forage yields presented in Table 3 clearly indicated that the highest significant fresh and dry forage yields were obtained from SSD in all cuts in both growing seasons followed by SD. The least fresh and dry forage yields in all cuts of both growing seasons were obtained from SPI. Results also indicated that fresh and dry yield productions were gradually decreased in subsequent cuts along the growing season in all investigated irrigation methods. Effect of water stress treatments Effects of investigated fully and water stress treatments on the studied traits are presented in Table 3. No significant differences were found between 100% WR and 75% WR treatments in all cuts in both growing seasons. 50% WR 2017 Japanese Society of Grassland Science, Grassland Science, 64,

4 Forage productivity under water stress S. M. Ismail et al. Table 2 Total water requirement and actual supplied for sudan grass and millet under different irrigation methods and water application for two growing seasons of 2014 and 2015 SD and SSD SPI Cut number Water application treatments Total water requirement per cut (mm) Actual water supply per cut (mm) Total required mm per cut Actual supply mm per cut st 100% % % nd 100% % % rd 100% % % Seasonal 100% % % Table 3 Means of plant height (cm), leaf/stem ratio and fresh and dry forage yields (t ha 1 ) of Millet under the effects of different irrigation methods and water application as average of three cuts during 2014 and 2015 seasons Plant height (cm) Leaf/Stem ratio Fresh forage yield (t ha 1 ) Dry forage yield (t ha 1 ) Cut number Variables Treat st Irrigation method SD 95.0 a 99.7 a 0.50 a 0.77 a 29.1 b 29.8 b 13.5 b b SSD a a 0.52 a 0.64 a 36.3 a 36.9 a 17.2 a 15.9 a SPI 75.3 b 75.3 b 0.56 a 0.81 a 13.0 c 13.1 c 6.3 c 6.2 c Water application treatments 100% 99.7 a a 0.51 a 0.73 a 32.8 a 32.9 a 15.4 a 16.4 a 75% 87.7 ab 93.3 ab 0.52 a 0.71 a 25.1 b 26.2 b 12.3 b 11.9 b 50% 85.7 b 87.0 b 0.55 a 0.78 a 20.5 c 20.7 c 9.3 c 9.6 c 2nd Irrigation method SD 85.3 a 84.7 a 0.54 a 0.61 a 17.1 b 17.9 b 8.2 a 8.6 b SSD 99.7 a 98.0 a 0.53 a 0.76 a 19.7 a 21.8 a 9.2 a 11.4 a SPI 54.7 b 56.7 b 0.50 a 0.45 a 4.6 c 4.8 c 2.2 b 1.9 c Water application treatments 100% 89.3 a 88.7 a 0.53 a 0.68 a 17.0 a 18.3 a 8.0 a 9.2 a 75% 78.7 ab 80.3 ab 0.54 a 0.59 a 14.1 b 14.8 b 6.9 b 7.0 b 50% 71.7 b 70.3 b 0.50 a 0.55 a 10.3 c 11.5 c 4.6 c 5.8 c 3rd Irrigation method SD 73.7 a 68.0 a 0.44 a 0.46 a 10.8 b 10.0 a 5.2 a 4.8 b SSD 80.7 a 77.0 a 0.56 a 0.66 a 13.5 a 11.5 a 7.3 b 6.1 a SPI Water application treatments 100% 57.3 a 52.3 a 0.36 a 0.38 a 10.9 a 9.6 a 6.0 a 4.6 a 75% 51.3 ab 49.0 ab 0.32 a 0.39 a 8.4 a 8.1 a 4.1 b 4.2 a 50% 45.7 b 43.7 b 0.31 a 0.34 a 4.9 b 3.8 b 2.4 c 2.0 b Means of the same characteristic/cut/season followed by the same letter (s) are not significantly different according to revised least significant differences (RLSD) (P < 0.05). SD, surface drip; SPI, sprinkler; SSD, sub-surface drip. treatment produced the shortest plants in all cuts during both growing seasons. Leaf/stem ration were not significantly affected by investigated water application treatments in all cuts and both growing seasons, (Table 3). Fresh and dry forage yields were significantly affected by water supply. The highest fresh and dry yields in both growing seasons in the first and second cuts were obtained from 100% WR treatment followed by 75% WR and 50% WR respectively. In the third cut, no significant differences were shown in fresh yield under the effects of 100% WR and 75% WR in both growing seasons (Table 3) Japanese Society of Grassland Science, Grassland Science, 64, 29 39

5 S. M. Ismail et al. Forage productivity under water stress Effects of the interaction between irrigation methods and water application treatments Results of the effects of interaction between irrigation systems and water application on plant height, leaf/stem ratio and fresh and dry forage yields are presented in Table 4. Results clearly revealed that the effect of the interaction were not significant on leaf/stem ratio. Plant height, fresh forage yield and dry forage yield were significantly affected by the interaction between irrigation methods and water supply. Within each cut, no significant differences were found in plant height means, fresh or dry forage yield per ha using 100% WR under SD and SSD and these were the highest means compared with the other treatments means by RLSD (0.05) as shown in Table 4. Yield and yield attributes of sudan grass Effect of irrigation system Results of plant height of sudan grass presented in Table 5 in all cuts of both growing seasons clearly show significant differences between investigated irrigation methods. The highest significant plant height was found in SSD followed by in SD. The shortest plant height was recorded in SPI. No specific trend can be found for the behavior of leaf/ stem ration in all cuts of 2014 and 2015 growing seasons as affected by different irrigation methods and the results were significantly similar (Table 5). Sudan grass fresh and dry forage yields results from all cuts in 2014 and 2015 growing seasons presented in Table 5 indicated that SSD Table 4 Effects of the interaction between irrigation methods and water supply on plant height, leaf/stem ratio and fresh and dry forage yields (t ha 1 ) of millet as average of three cuts during 2014 and 2015 seasons Cut number Irrigation methods Water application treatments Plant height (cm) Leaf/Stem ratio Fresh forage yield (t ha 1 ) Dry forage yield (t ha 1 ) st SD 100% % % SSD 100% % % SPI 100% % % nd SD 100% % % SSD 100% % % SPI 100% % % rd SD 100% % % SSD 100% % % RLSD (0.05) between NS NS cuts 9 irrig. method 9 water application treatments RLSD (0.05) between irrig. method 9 water application treatments per cut NS NS NS, not significant according to revised least significant differences (RLSD) (P < 0.05). SD, surface drip; SPI, sprinkler; SSD, sub-surface drip Japanese Society of Grassland Science, Grassland Science, 64,

6 Forage productivity under water stress S. M. Ismail et al. Table 5 Means of plant height (cm), leaf/stem ratio and fresh and dry forage yields (t ha 1 ) of sudan grass under the effects of different irrigation methods and water application as average of three cuts during 2014 and 2015 seasons Plant height (cm) Leaf/Stem ratio Fresh forage yield (t ha 1 ) Dry forage yield (t ha 1 ) Cut number Variables Treat st Irrigation method SD b b 0.52 a 0.61 a 31.4 b 30.1 b 10.9 b 11.8 b SSD a a 0.57 a 0.55 a 37.9 a 36.2 a 14.4 a 13.7 a SPI 87.7 c 89.0 c 0.34 a 0.50 a 17.5 c 19.2 c 6.1 c 9.6 c Water application treatments 100% a a 0.46 a 0.53 a 35.5 a 35.7 a 13.6 a 14.7 a 75% a a 0.54 a 0.58 a 29.1 b 28.6 b 10.0 b 11.3 b 50% b b 0.44 a 0.54 a 22.1 c 21.2 c 7.9 c 9.1 c 2nd Irrigation method SD b b 0.50 a 0.61 a 23.1 b 23.5 b 7.8 b 3.2 b SSD a a 0.56 a 0.55 a 28.7 a 27.6 a 9.8 c 4.3 a SPI 73.3 c 65.3 c 0.35 a 0.37 a 9.4 c 8.5 c 4.2 c 1.3 c Water application treatments 100% a a 0.51 a 0.53 a 27.9 a 27.3 a 9.4 a 4.3 a 75% a 98.0 ab 0.45 a 0.53 a 20.3 b 19.1 b 7.9 b 2.2 b 50% 87.3 b 82.3 b 0.46 a 0.47 a 13.1 c 13.2 c 4.5 c 2.3 c 3rd Irrigation method SD 85.3 b 79.7 b 0.43 a 0.47 a 15.9 a 14.6 b 5.5 a 9.9 b SSD a a 0.44 a 0.49 a 17.5 a 18.1 a 6.0 a 11.4 a SPI Water application treatments 100% 73.0 a 72.3 a 0.29 a 0.34 a 14.4 a 14.7 a 4.8 a 9.6 b 75% 61.0 ab 61.3 ab 0.29 a 0.30 a 10.0 b 9.9 b 3.5 b 6.4 b 50% 55.3 b 52.0 b 0.29 a 0.32 a 9.1 b 8.1 b 3.2 b 5.3 b Means of the same characteristic/cut/season followed by the same letter (s) are not significantly different according to revised least significant differences (RLSD) (P < 0.05). SD, surface drip; SPI, sprinkler; SSD, sub-surface drip. was the best irrigation method since the highest yield production was obtained from it. Large quantities of fresh and dry forage yield per ha were also obtained under SD but the yield per ha were significantly less than that produced by SSD and higher than that produced by SPI. The least fresh and dry forage yields were obtained from SPI in the two cuts in both growing seasons. Results also indicated that the fresh and dry forage yields of investigated irrigation method were gradually decreased from cut 1 to cut 3 where the highest yield per ha obtained from cut 1 followed by cut 2 and cut 3 in SSD and SD respectively while was from cut 1 followed by cut 2 in SPI. Effect of water application treatments Results of plant height, leaf/stem ratio and fresh and dry forage yields of sudan grass as affected by different water supply are presented in Table 5. The treatment of 100% WR produced the highest plant height compared with 75% WR and 50% WR treatments in all cuts of both growing seasons. However, the increase in plant height was not significant between 100% WR and 75% WR treatments. As well, plant height of 75% WR and 50% WR were significantly similar. Leaf/stem ratios were not significantly different in all investigated water supply treatments of all cuts for both growing seasons. Increasing water supply increased the production of fresh and dry forage yield. The highest fresh and dry yields were obtained from 100% WR treatment followed by 75% WR and 50% WR, respectively, during the first two cuts of the 2014 and 2015 growing seasons. In the third cut, fresh and dry forage yields were the highest in 100% WR treatment followed by 75% WR treatment; however, the differences between 75% WR and 50% WR were not significant (Table 5). Effects of the interaction between irrigation system and water application treatments The effect of the interaction between irrigation methods and water supply are presented in Table 6. Results indicated that leaf/stem ratio was not significantly affected by the interactions in both growing seasons. Plant heights were the tallest in the 100% WR followed 75% WR of SSD within each cut of both growing seasons then, followed by 100% WR of SD, 50% WR of SSD, 75% WR and 50% WR of SD, respectively. The shortest plants were produced from SPI where 100% WR treatment were the highest followed by 75% WR and 50% WR treatments, respectively, within each cut. The maximum fresh and dry forage yields were obtained from 100% WR treatment of SSD in each cut of 2014 and 2015 growing seasons. No significant differences Japanese Society of Grassland Science, Grassland Science, 64, 29 39

7 S. M. Ismail et al. Forage productivity under water stress Table 6 Effects of the interaction between irrigation methods and water supply on plant height (cm), leaf/stem ratio and fresh and dry forage yields (t ha 1 ) of sudan grass as average of three cuts during 2014 and 2015 seasons Cut number Irrigation method Water application treatments Plant height (cm) Leaf/Stem ratio Fresh forage yield (t ha 1 ) Dry forage yield (t ha 1 ) st SD 100% % % SSD 100% % % SPI 100% % % nd SD 100% % % SSD 100% % % SPI 100% % % rd SD 100% % % SSD 100% % % RLSD (0.05) between NS NS cuts*irrig. method*water application treatments RLSD (0.05) between irrig. method*water application treatments per cut NS NS NS, not significant according to revised least significant differences (RLSD) (P < 0.05); SD, surface drip; SPI, sprinkler; SSD, sub-surface drip. in fresh forage yield per ha were found under the SD with 100% WR and 75% WR with SSD within the first and the second cuts in both seasons. Also, similar results were detected for the dry forage per ha in the first season as shown in Table 6. Fresh and dry forage yield of 75% WR of SSD and 100% WR of SD were almost similar in the first cut but significantly less than that of 100% WR treatment of SSD in both growing seasons followed by 75% WR of SD, 50% WR of SSD and 50% WR of SD, respectively, in 2014 and 2015 growing seasons. Fresh and dry forage yields during the second and third cuts of both growing season followed almost a clear trend. The highest production obtained from 100% WR treatment of SSD followed by 100% WR of SD, 75% WR of SSD, 75% WR of SD, 50% WR of SSD and 50% WR of SD respectively. SPI water application treatments produced the least fresh and dry forage yields in the first and second cuts of both growing seasons compared to SSD and SD (Table 5). Results also clearly revealed that the highest plant height and fresh and dry forage yields were obtained from the first cut followed by the second and third cuts in 2014 and in 2015 growing seasons respectively. Irrigation water use efficiency (IWUE) Irrigation water use efficiency (IWUE) kg m 3 ha 1 in the current study was estimated by dividing the fresh forage yield in kg ha 1 by depth of water applied including rainfall in m 3. Results of IWUE for pearl millet and sudan grass are presented in Table 7. Effect of irrigation methods Sub-surface drip was superior in increasing IWUE compared with SD and SPI. The production per unit of water of 2017 Japanese Society of Grassland Science, Grassland Science, 64,

8 Forage productivity under water stress S. M. Ismail et al. Cut number Variables Treatments Millet Sudan grass st Irrigation method SD 13.9 b 12.0 b 15.1 b 12.1 b SSD 17.6 a 15.2 a 18.2 a 14.7 a SPI 4.7 c 4.1 c 6.5 c 6.2 c Water application treatments 100% 11.1 b 9.5 b 12.0 b 10.2 ab 75% 11.4 b 10.2 b 13.1 ab 11.0 ab 50% 13.7 a 11.6 a 14.6 a 11.7 a 2nd Irrigation method SD 8.4 b 7.6 b 11.1 b 9.8 b SSD 9.7 a 9.4 a 13.9 a 11.6 a SPI 1.8 c 1.7 c 3.5 c 2.7 c Water application treatments 100% 6.1 b 5.7 a 9.8 a 8.4 a 75% 6.7 ab 6.0 a 9.6 a 7.8 a 50% 7.2 a 6.9 a 9.1 a 8.0 a 3rd Irrigation method SD 4.4 b 3.7 a 7.0 b 5.6 b SSD 5.8 a 4.1 a 7.7 b 6.7 a SPI 0.0 c 0.0 b 0.0 c 0.0 c Water application treatments 100% 3.8 a 3.0 a 4.6 b 4.1 a 75% 3.9 a 3.3 a 4.3 b 3.7 a 50% 3.4 a 2.5 a 5.7 a 4.5 a Table 7 Means of irrigation water use efficiency (IWUE) (kg m 3 ha 1 ) for millet and sudan grass under the effects of different irrigation methods and water supply during 2014 and 2015 seasons Means of the same characteristic/cut/season followed by the same letter (s) are not significantly different according to revised least significant differences (RLSD) (P < 0.05). SD, surface drip; SPI, sprinkler; SSD, sub-surface drip. SSD was the highest in all cuts of both growing seasons compared to SD and SPI. Results of IWUE also showed gradual decrease in IWUE by increasing the number of cuts where the IWUE pearl millet was almost twice and three times more in the first cut than that of the second and third cut, respectively, either for SSD or SD. A similar trend was found also in SPI. The IWUE of the first cut under SPI was almost 2.5 more than that of the second cut. A similar trend was also found for sudan grass under all irrigation methods; however, the reduction in IWUE by increasing number of cuts was less than that of pearl millet (Table 7). Effect of water application treatments Results clearly show that increasing water regimes decreased IWUE. The highest significant IWUE for the first cut for pearl millet crop was obtained from 50% WR treatment in the 2014 and 2015 growing season followed by 75% WR and 100% WR where the differences between them were not significant (Table 7). Irrigation water use efficiency of 50% WR in sudan grass crop was the highest followed by 75% WR and 100% WR treatments. However, the differences between 50% WR and 75% WR treatments and between 75% WR and 100% WR treatments were not significant. Irrigation water use efficiency in the second and third cuts for both crops were almost significantly similar in all water application treatments except for pearl millet in the second cut of 2014 and for sudan grass in the third cut of The highest IWUE either for pearl millet in the second cut or for sudan grass in the third cut was obtained from 50% WR treatment followed by 75% WR and 100% WR treatments, respectively. Effect of the interactions between irrigation system and water application treatments Results of IWUE in kg m 3 ha 1 as affected by the interaction between irrigation methods and water supply for pearl millet and sudan grass crops are presented in Figure 1. Results clearly revealed that IWUE obtained in 2014 was higher than that of 2015 for both crops. Irrigation water use efficiency of sudan grass was higher than IWUE of pearl millet in all irrigation methods. The highest IWUEs were obtained from 50% WR treatment followed by 75% WR and 100% WR treatments of SSD in both crops and then followed by the same sequence under SD. The least seasonal IWUE was obtained from SPI with huge reduction compared either with SSD or with SD (Fig. 1). The highest IWUE under SPI was obtained from 100% WR treatment followed by 75% WR and 50% WR treatments, respectively. Discussion Water requirements and actual supply Results of actual water supply were higher than calculated water requirements. The results were due to the applied Japanese Society of Grassland Science, Grassland Science, 64, 29 39

9 S. M. Ismail et al. Forage productivity under water stress Figure 1 Seasonal irrigation water use efficiency (IWUE) as affected by interaction between irrigation methods and water regimes for millet and sudan grass crop of two growing seasons. SD, surface drip; SPI, sprinkler; SSD, sub-surface drip. required irrigation time. The timer of each treatment, which automatically controlled water supply, was programmed to open irrigation networks for the specified calculated time. However, when the calculated time contains part of a minute, the timer was programmed to work for the nearest higher complete value: i.e. if the calculated irrigation time is 10.3 min, the timer is programmed to run 11 min. As the running time was higher than the calculated time, the actual water supply was higher than the calculated water requirements. Results clearly indicated that water supply per cut in SPI was higher than that in SD and SSD. The results might be due to low water use efficiency of SPI, which was 75% compared to the 90% efficiency of SD and SSD. Also, the weather of the experimental area was hot so that a high quantity of irrigation water was evaporated in air. Moreover, the experimental area sometimes suffers from wind effects during the growing season. Total water supply of the third cut in SD and SSD was higher than that of first and second cuts because the growing period of the third cut was characterized by relatively high daily water requirements compared with that of the first and second cuts. Seasonal water supply for SD and SSD were higher than that of SPI while the depth of water applied per cut in SPI was higher than that of SD and SSD. The results might be due to the number of cuts per season. In SD and SSD, three cuts were obtained per season while only two cuts per season were obtained from SPI. The Plants of pearl millet and sudan grass grown under SPI were very weak and short during the second cut, which gives indication that they can t produce any biomass during the third cut so that the number of cuts under SPI was terminated after the second cut while they continue for the third cut under SD and SSD. Total water supply of each cut and seasonal water supply was reduced by decreasing water regimes compared to 100% WR treatment. The results are logical and expected because the water supplies in both stress treatments were only 75% and 50% of that water supplied in 100% WR treatment, (Ismail and Almarshadi 2013). Forage yield in relation to investigated irrigation methods The best production and IWUE in pearl millet and sudan grass crops were obtained from SSD, followed by SD and the least production and IWUE were from SPI. In SSD, no water lost by surface evaporation that may increase the available water in the root zone area compared to the other irrigation methods. As a result, growth parameters expected to be enhanced and increase yield production. Due to the enhancement of growth parameters by SSD it is expected to be reflected in forage yield since at the end yield is the result of growth parameters and consequently high IWUE (Abu-Suwar and Bakri 2009; Ismail and Almarshadi 2013). SD increased the yield and IWUE of pearl millet and sudan grass crops compared with SPI. The results could be attributed to the surface root area of the plant, which is responsible to supply the majority of plant water requirements (Ismail and Ozawa 2007). In SD especially under stress treatments, the water reached directly to the plant surface root and diverted to the plant to recover the majority of its requirement. As a result, yield of forage increased under SD compared with SPI. The least forage production and IWUE were obtained from SPI. The results could be attributed to two reasons. The first one was that high wind speed affected the experimental area several times during the growth period. When wind speed is high, the efficiency of SPI is greatly reduced because the water distribution is interrupted and heterogeneously distributed among the cultivated area, resulting in low production. The second reason was high 2017 Japanese Society of Grassland Science, Grassland Science, 64,

10 Forage productivity under water stress S. M. Ismail et al. temperature of the experimental area might evaporate part of the irrigation water in the air, consequently less water than required was applied and resulted in yield reduction. Similar results were published by Almarshadi and Ismail (2011). Forage yield in relation to irrigation water supply Decreasing water supply decreased forage yield, the highest production obtained from 100% WR followed by 75% WR and 50% WR, respectively. Generally, the growth and yield production of forage crops are of great concern with improved soil conditions including water availability in the soil, since water deficiency restricts normal crop growth resulting in enormous economic loss. Under the conditions of this experiment, decreasing water regime to 75% WR and 50% WR reduced the available soil moisture in the root zone. An inadequate amount of available water in the soil disturbs various physiological processes in plants and finally the forage yield, (Fuertes-Mendizabal et al. 2012; Madani et al. 2012; Ismail and Almarshadi 2013; Almarshadi and Ismail 2014). Results of IWUE revealed that decreasing supply of required water increased IWUE in SD and SSD. Irrigation water use efficiency was found to increase as a result of decreasing losses, because the IWUE values are affected by reducing deep percolation, canopy interception, soil type and cultural and management practices (Al-Jamal et al. 2001). Increasing yields with a minimal water supply sharply increase IWUE. This may be due to the ability of these forage crops to use water effectively from the soil profile (Lindenmayer et al. 2008). Irrigation water use efficiency increased under soil moisture stress and with practicing deficit irrigation (Dorji et al. 2005; Ismail 2012). In SPI, IWUE was reduced by reducing water supply. The results could be attributed to the application of a reduced amount of irrigation water by SPI that was characterized by low application efficiency in hot weather. Such conditions largely reduced the available soil moisture, consequently, suspending various morphological and physiological processes in plants and finally reducing yield and IWUE (Fuertes-Mendizabal et al. 2012; Madani et al. 2012; Almarshadi and Ismail 2014). Conclusion Sub-surface drip irrigation method produced the tallest plants and the highest forage yield under fully and stress water treatments (100% WR, 75% WR and 50% WR) in pearl millet and sudan grass crops, followed by SD. Sprinkler irrigation method produced the shortest plants and the least forage yield compared with the other investigated irrigation methods in the 2014 and in 2015 growing seasons. Decreasing water supply decreased yield production but increased IWUE under SD and SSD, while decreasing them under SPI. Increasing the number of cuts sharply decreased yield and IWUE of both crops. Under full and stress water treatments, sudan grass produced higher forage yield than pearl millet crops. Irrigation water use efficiency was the best under SSD followed by SD while the least IWUE was recorded in SPI. Irrigation water use efficiency of 100% WR and 75% WR were significantly similar in both crops, which mean either of them can be used depending on the availability of water. In conclusion, growing sudan grass or pear millet as the second choice crop under SSD with full water requirement or 75% WR maximized forage production and IWUE under dry land conditions. Acknowledgments This project was funded by the Deanship of Scientific Research (DSR) at King Abdulaziz University, Jeddah, under grant no. G.276/155/1434. The authors, therefore, acknowledge with thanks DSR for technical and financial support. 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