الفهرس 
INTRODUCTION
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Abstract
The present work was carried out at the Agricultural Experimental Station of soil and water Department‚ Faculty of Agricultural‚ Assiut University‚ situated at 27 0 11’N latitude‚ 310 10’E longitude
The aims of this study were :1- To study the effects of irrigation systems surface drip irrigation, subsurface drip irrigation and modified surface irrigation on potato and maize production under the conditions of different deficit irrigation strategies. 2: To determining the best water deficit level for potato and maize production to save irrigation water using the subsurface drip irrigation, surface drip irrigation system and modified surface irrigation system and 3: To study the effects of deficit irrigation strategies on IWUE of potato and maize crops.
To achieve such goals field experiments were carried out:-
-The first experiment was carried on potato in the winter seasons of 2011/2012 with sub surface drip irrigation (SSDI) and surface drip irrigation (SDI).
-The second experiment was run using maize during the summer season of 2012 with sub surface drip irrigation (SSDI), surface drip irrigation (SDI), and modified surface irrigation system (MSI).
-The third experiment was carried out using potato in the winter season of 2012/2013 with sub surface drip irrigation (SSDI), surface drip irrigation (SDI), and modified surface irrigation system (MSI)..
-The fourth experiment was run using maize during the summer season of 2012 with sub surface drip irrigation (SSDI), surface drip irrigation (SDI), and modified surface irrigation system (MSI).
*The first and second experiments continues deficit irrigation levels (CDI) with four different deficit irrigation levels were applied. The levels were full irrigation (100%ETc), 85% of full irrigation (85%ETc), 70% of full irrigation (70%ETc) and 55% full irrigation (55%ETc) treatments..
*The third and fourth experiments were for application regulated deficit irrigation (RDI)which imposed with four different stages along growth season as four treatments (T1, T2, T3 and T4). For potato regulated deficit irrigation experiments, [(T1, T2, T3 and T4) at (26 -47, 48 - 70, 71 - 92 and 93 -113 days from planting)], respectively. For maize regulated deficit irrigation strategies experiments, [(T1,T2,T3 and T4) at (19-38, 39 -60, 61-80 and 81- 101 days from planting)], respectively.
A randomized complete block design with four replications in strip was used. Irrigation water amount of I100 treatment was calculated from reference evapotranspiration (ET0). Irrigation water amount of 100%ETC treatment for all experiments was calculated determined using the CropWat computer program and the recorded climatic parameter of the Assiut metrological station. The water amounts of the other treatments were calculated by using the corresponding percentages of deficit (85%, 70% and 55%) based on the water amount of 100% treatment for CDI potato2011/2012 and CDI maize 2012 experiments .And were calculated by using the corresponding percentages of deficit (80%) based on the water amount of 100% treatment for RDI potato2012/2013 and RDI maize 2013 experiments. Soil moisture distribution was measured using the gravimetric methods. Also, Soil moisture tension was measured with the WatermarkR sensor.
The obtained results could be summarized as it follows:
1- Potato continues deficit irrigation strategies experiment:
1.1. Effects of irrigation method and amount of irrigation water on the distribution of soil water content.
A- The distribution of soil water content is influence by the irrigation systems and amount of irrigation water applied.
B- For all treatments, under SSDI the highest soil water content was measured in the layers (15- 30 , 30 - 45cm) because the water supply retained in these layers. While in SDI the highest soil water content was measured in the layers (0- 15 , 15 - 30cm) because the water supply retained in these layers.
C- Locating the dripper under the soil surface, reduced the upward water movements, minimized the evaporation losses and delivered the water directly to the root zone.
D- Due to variation in amount of irrigation water between the treatments, the 100% of ETc treatment showed higher increase in the soil water content at 60 cm followed by (85% of ETc treatment, than 70% and 55% of ETc treatments, therefore, the gradient changes in soil moisture before and after irrigation depended on the amount of applied water at various depths.
E- Decreasing the volumetric moisture content for 70% and 55% ETC treatments at 45 and 60 cm depth was because the amount of water supply was less than field capacity and all added water retained in the upper layers.
1-2. Effects of irrigation methods and amount of irrigation water on potato production.
A- The main effects of irrigation methods and amount of irrigation water on tuber yield and total dry weight were significant (p≤0.01). The tuber yield produced by sub surface drip system was 17.28 % higher than produced by the surface drip system. The total yield dry weight of the subsurface drip system was about 20% higher than the yield of surface drip system.
B- Reducing the amount of irrigation water caused significant reduction in the potato tuber yield. The tuber yield was 7631.25, 9444.23, 11280.23 and 12258.45 kg /fed with applying 55, 70, 85 and 100% of ETc respectively, that were the yield reduced percentage were 8%, 23% and 38% of the yield produced by applying 85%, 70%, and 55% of the ETc as compared to applying 100% of ETc.
C- The interaction between subsurface and surface drip and ETc levels showed markedly differences. The total potato tuber yield per faddan increased with increasing applied water a ETc percentage within each drip system or between the two systems. The yield values of the subsurface drip were higher than those of the surface drip.
D- The highest potato tuber yield of 12953.25 kg /fed was obtained with applying 100% of ETc through subsurface drip, while the lowest value of 6750.00 kg /fed was produced when applying 55% of ETc through surface drip.
1-3. Effects of irrigation methods and amount of irrigation water on water use efficiency (WUE):
A- Sub surface drip irrigation (SSDI) was generally produced higher values of WUE than surface drip irrigation ( SDI). SSDI gave the highest yield because it increases water content within root zone.
B- Decreasing the water supply caused a significant decrease in the total yield, Increasing the amount of water from 667 (55% of ETc ), to 772 (70% of ETc ), to 877 (85% of ETc ) and (100 % of ETc ) increased the yield from 7631 to 9444 to 11280 and 12258 kg. The respective WUE were increased from 11.44 to 12.23, 12.86 and 12.47 kg/m3.
C- Water deficiency more than 30% of ETC could not be suggested due to the irrigation of potatoes at 70%ETC during the growing season which tends to significant losses in yield more than the water saving.
2- Maize continues deficit irrigation strategies experiments:
2-1 Effects of irrigation methods and amount of irrigation water on wetting pattern and water distribution.
A- The movement water within soil in horizontal and vertical direction is more homogeneous with SSDI than SDI, because the dripper were at the suitable depth.
B- The soil water content in surface drip irrigation (SDI) and modified surface irrigation ( MSI) was increased after irrigation with 100%ETc at depths 15 and 30 cm and reached to the field capacity, followed by 85% of ETc treatment.
E- The 70% of ETc treatment showed water content of 60% of soil moisture available water (SMAW) at 45 cm depth, while at 60 cm depth soil moisture available water (SMAW) was between 35% and 50%.
G- The water content of 55% of ETc treatment was %50 of soil moisture available water (SMAW) at depth 45 cm, while at 60 cm was 25% either as soil moisture available water (SMAW) or volumetric water content.
H- The highest soil water content under subsurface drip irrigation (SSDI) was recorded in middle two layers (15- 30 and 30 - 45cm). While a depth of 0-15 cm the soil moisture content showed very small.
2-2. Effects of surface drip, sub surface drip and modified surface irrigation, and amount of irrigation water (% of ETc) on maize growth and yield.
A- Subsurface drip irrigation SSDI was better than the surface drip irrigation SDI and the modified surface irrigation MSI, on dry matter accumulation rate .
B- The full irrigation 100% of ETc and continuous deficit irrigation up to of 85% of ETc under all irrigation methods (SSDI, SDI and MSI) gave the highest dry matter accumulation rate. The advantage of subsurface drip irrigation may due to the delivery of water directly to the root zone which reduced water loss by evaporation.
C- The main effects of irrigation systems (SSDI, SDI and MSI) on the straw, grain, the total shoot yield and grain / straw ratio of maize plants were significant (p≤0.01). Subsurface drip irrigation (SSDI) and surface drip irrigation (SDI) produced 14.9 and 4.8 % more than modified surface irrigation (MSI), respectively. Also total shoot dry weight was increased by 5.2 and 18.7% by using SDI and SSDI as compared by the MSI system, respectively.
D- The SDI and SSDI increased the grain yield by 6.3 and 30.5% as compared MSI, respectively. Also total shoot dry weight was increased by 5.2 and 18.7% by using SDI and SSDI as compared by the MSI system, respectively. The maize grain / straw ratio was increased by using SSDI from 0.32 to 0.36 as compared by SDI or MSI.
E- The descending order of the grain yield values the treatments was as it follows: SSDI 100% < SSDI 85% ≤ SDI 100% < MSI 100% ≤ SDI 85% < MSI 85% < SSDI 70% < SDI 70% ≤ MSI 70% ≤ SSDI 55% < SDI 55%≤ MSI 55%.
2-3 Effect of irrigation systems and continuous deficit irrigation, CDI
on irrigation water use efficiency by maize crop.
A- Sub surface drip (SSDI) had generally higher values than surface drip (SDI) and modified surface irrigation (MSI). SSDI gave the highest yield because it increases soil water content, best water supplies management and water distribution uniformity. Also, surface drip irrigation produced higher values of WUE than modified surface.
B- The highest value of WUETDM and WUEgrain was obtained from 85% of ETc treatment. while the lowest one was recorded for 70% and 55% treatments. Deficit irrigation saves water but reduces yield. Irrigating maize during growing season at 85% ETC reduced the grain yield & total yield by 7.27% & 7.67 and saved about 12.52% of irrigation water. Increasing the deficit irrigation resulted in a severe yield reduction. Giving 70% ETC reduced the grain yield & total yield by 49.24% & 40.78 and saved about 25.04% of irrigation water. . It’s twice as much as the amount saved by the treatments 85%, and seven times as a reduction in the yield.
C- The highest significant WUEgrain values obtained by the 85% and 100% of ETc which were of one significant level and were arranged as it follows: SSDI 85% < SSDI 100% < SDI 85% ≤ SDI 100% < MSI 85% < MSI 100% ≤ SSDI 70%. While the lowest IWUEgrain values were obtain by the 70% and 55% of ETc of all irrigation methods as it follow: SSDI 55% ≤ SDI 70% = MSI 70%< SDI 55% ≤ MSI 55%.
3- Potato regulated deficit irrigation strategies experiment.
3-1 Effects of irrigation method and continuous deficit irrigation, RDI on wetting pattern and distribution of soil water content.
A- The deficit irrigation was reflected as low values of moisture content in the soils at different depths, either before or after irrigation for all treatments.
B- The subsurface drip irrigation SSDI produced higher soil moisture content than surface drip irrigation or modified surface irrigation, especially in the depths of 30, 45 and 60 cm. Appling water under surface reduced evaporation and keep the water in the layer 30-60 cm.
C- The advantage of the SSDI is that it keeps the root zone are with regular balanced water, therefore it may give better growth. It is clear from figure that, the behaviors of the water potential was the same at the deficit period.
D- The advance of wetting front and the water distribution patterns in the wetting area underneath the trickle point source is greatly changed with the changes in initial soil moisture content in the wetting area as affected by application of RDI strategies during each deficit period the with all treatments along growth season.
3-2. Effects of irrigation methods and regulated deficit irrigation, RDI on potato tuber yield:
A- of the irrigation systems (SDI, SSDI and MSI) on the total tuber yield and all studied plant treats were significant at (p≤0.01). The tuber yield produced by subsurface drip irrigation (SSDI) and surface drip irrigation (SDI) was 24.2% and 16.7% more than modified surface irrigation (MSI), respectively. The dry yield weight of the subsurface drip irrigation and surface drip irrigation was abut 28% and 22% higher than modified surface irrigation (MSI), respectively.
B- The mine effect of reducing the amount of irrigation water during deficit period caused significant at (p≤0.01) in the potato tuber yield. The total tuber yield was 9437.5, 8637.5, 10112.5 and 11762.5 kg / fed with deficit irrigating periods treatments: T1 at 26 – 47, T2 at 48-70, T3 at 71-92 and T4 at 93-113 respectively, the water stress must not be imposed from tuber initiation until the tuber bulking at 26- 70 days because the water stress during that was most detrimental to biomass and tuber production.
3-2 Effect of irrigation systems regulated deficit irrigation, RDI on irrigation water use efficiency by potato crop:
A- The main effect of irrigation system on WUE were significantly (p≤0.01). Subsurface drip irrigation (SSDI) was higher values than surface drip irrigation (SDI) and modified surface irrigation (MSI). The WUE total tuber yield values were 12.08, 11.41 and 10.72 kg m3, respectively.
B- the WUE total tuber yield values were 11.77, 10.26, 8.37 and 9.41 for treatments T4, T3, T2 and T1, respectively.
4- Maize regulated deficit irrigation strategies experiment:
4-1 Effects of irrigation method and continuous deficit irrigation, RDI on wetting pattern and distribution of soil water content.
A- Vertical variability in soil column differs according to the irrigation system and the amount of water applied (fully irrigation or RDI) . B- Soil moisture potential values for all treatments is reverses the amount of total water supplied. B- The large peak of the upper and lower values of SWP due to the irrigation schedule will led to higher stress on the plant growth and may cause lower plant growth than drip irrigation.
4-2 Effects of irrigation systems and regulated deficit irrigation- RDI on yield and irrigation water use efficiency by maize crop .
A- The main effects of irrigation systems on the straw, grain and the total yield of maize plants were significant (p≤0.01). The grain yield of maize increased in SDI and SSDI by 6.3% and 21.4% as compared MSI, respectively. Also, total shoot dry weight was increased by 4.6% and 25.4% by using SDI and SSDI as compared by the MSI system, respectively.
B- The grain yield was 2443.59, 2710.21, 3242.42 and 3646.38 kg / fed with deficit irrigating periods treatments of T1, T2, T3 and T4 respectively, that were the yield reduced percentage by 11.1%, 25.7 % and 33 % of the grain yield produced by applying regulated deficit irrigation (RDI) with T3, T2 and T1 as compared to applying regulated deficit irrigation with T4.
C- deficit period by T1 at 19-38 days and T2 at 39-60 were more sensitive to deficit irrigation, while deficit period by T3 or T4 at 60-80 or 81-101 were lower sensitive stages to water stress.
D- The water stress must not be imposed from 19-60 days because it are main prong in the development and growth of the plant and affect mainly and proactively in the composition in the total yield and grain yield.
E- Subsurface drip irrigation (SSDI) was higher values than surface drip irrigation (SDI) and modified surface irrigation (MSI). The WUEgrain values were 1.33, 1.16, and 1.05 kg m3, respectively.
F- The highest values of WUEgrain and WUETDM were obtained by T4 at 81-113 days. While the lowest values of WUEgrain and WUETDM were obtained by T2 at 39 – 60 days and T1 at 19-38 days.
As a result of this study, it can be concluded:
Now a day, all over the world, the problem of limited water resources becomes crucial and indispensable. Deficit irrigation both, CDI and RDI is one of the important strategies that are now proposed to face such crisis. The decision of getting such a small reduction in yield with reducing the amount of irrigation water by 20% could be a good decision toward saving more water to irrigate more land and produce more food, oil and fiber required to cover the gap between production and demands. It is finally concluded that subsurface drip irrigation supplies water at a rate close to that of plant water uptake; therefore it is expected to improve the plant growth, increase the crop yield and reduce water losses from drainage below the root zone. In conclusion, deficit irrigation could be a feasible irrigation technique for maximizing the water productivity where the benefit from saving large amounts of water outweighs the decrease in total yield , These strategies can be recommended for irrigation of much important economic crops cultivation under arid and semi arid environments.