In Egypt, rice is one of the major water consuming crops and most of Egyptian rice genotypes are grown under continuous flooding with about 5 cm depth of standing water throughout the growing season [1]. Most of Egyptian rice genotypes show better growth and higher productivity under continuous flooding conditions than under water deficit at certain growth stages [2]. Water resources in Egypt are limited to 55.5 × 109 m³/ year, with tremendous increase in the population, production has to be increased and irrigation water should be well managed for increasing water use efficiency [3]. In near future it is expected that, less water will be available for rice growing [4]. Some rice planted areas, especially at the end of the terminal irrigation channels in the northern part of the Nile Delta, suffer from irrigation water shortage during different growth stages [5]. Therefore, water input can be reduced by; reducing water depth to soil saturation and using different irrigation intervals [6]. Recently, the term “water-saving irrigation techniques” has been introduced, which recommends, (i) reducing the depth of ponded water from 5-7 cm to 2-3 cm height to reduce the amount of water used for irrigation (ii) keeping the soil just saturated by irrigation until the soil is wet [5,7].

to manage soil, fertilizer, and moisture regimes and to maximize rice production in a given environment. The application of the organic fertilizers such as the farmyard manure and composted rice straw could increase the soil organic matter contents which serve several advantages like conservation and slow release of nutrients, improve of soil chemical and physical conditions and preservation of soil moisture that help for high production. These advantages lead to increasing the fertility and productivity of the soil [8]. Alternate flooding and dry, gave highest rice grain yield and nitrogen uptake than continuous flooding. In flooded and saturated anaerobic soils, ammonium is the dominant form of available N. Most of the losses of nitrogen fertilizer (N) occur immediately after application into the floodwater through ammonia volatilization [9]. Some of the ammonia is nitrified in oxidized soil zones and in the floodwater [10]. Due to the difference in behavior of nutrients under flooded soil compared to irrigation intervals so, we need to know the best recommendation of fertilizers under irrigation intervals. A study was, therefore, carried out with water and fertilizer management to investigate the yield potential with following objectives 1) to find out the suitable irrigation practice, 2) to determine the suitable fertilizer package and 3) to study the combine effects of irrigation and fertilizer on growth, yield 4) discuss the chemistry of nutrients availability under water stress which may help in better nutrient management and consequently greater yields.

Field experiment was conducted at the Experimental Farm Sakha Agriculture Research Station, Kafr El-Sheikh, Egypt, during 2016 and 2017 rice growing season's (Figure 1). To study the impact of different water regimes and fertilizer treatments on yield and its attributes of Sakha 106 rice cultivar as well as the availability of NH₄⁺, NO₃⁺, P and K at different periods (30, 60 and 90 days after transplanting) and the best combination among studied factors. Five water treatments were used; continuous flooding (W1), continuous saturation (W2), irrigation every 6 days (W3), irrigation every 9 days (W4) and irrigation every 12 days (W5). The fertilizer treatments were, control without any fertilizer application (T1), 4.76 tons of farm yard manure (FYM) /ha (T2), 4.76 tons of composted rice straw (CRS)/ha (T3), 4.76 tons FYM +110 kg N /ha (T4), 4.76 tons CRS +110 kg N /ha (T5) and recommended dose of nitrogen, 165 kg N /ha (T6). Full dose of phosphorus 36.89 kg P₂O₅ ha^-1 as a superphosphate (15%) was applied as a basal dose during land preparation and incorporated well into the dry soil, while, zinc as zinc sulphate at the rate of 23.8 kg/ha was applied in the nursery after wet leveling. The experiment was laid out in a strip plot design with four replications; irrigation treatments were located in the main plots, while the fertilizers treatments were placed in the sub-plots. After 30 days from nursery, the seedlings were pulled and transferred to the permanent field and transplanted at the spacing 20 × 20 cm between rows and hills. The FYM and CRS treatments were applied during the land preparation. While nitrogen fertilizer was added as urea form (46.5% N) according to the experimental treatment. Two third of N was applied as basal application, and the other third was top dressed at 30 days after transplanting (DAT).

Figure 1: Map showing study area in Kafr El- Sheikh Governorate (Sakha region), North Egypt. It is part of the Egyptian Nile delta that is characterized by extensive rice cultivation. It is located between 31°06 0 40 00 and 31°06 0 0 00 North and 30°54 0 30 00 and 30°55 0 60 00 East.

The studied characters

Chlorophyll content of flag leaf (SPAD), number of tillers/m², number of panicles/m², panicle weight (g), number of filled grains/ panicle, straw yield (t/ha) and grain yield (t/ha). Plant sample were collected from each plot for collection of data on plant characters and yield components. The straw yield was estimated while; grain yield was adjusted at 14% moisture. All traits were measured according to the standard’s evaluation system used by the International Rice Research Institute (IRRI, Manila, Philippines) [11].

Some chemical analyses of soil used in this study before the experiments were presented in Table 1-3. Total soluble cations and anions, pH and Ec in soil paste extract were determined according to [12]. Soil samples were taken from each plot for all replications at 30, 60 and 90 days after transplanting (DAT), all samples were subjected to determination of available NH₄⁺, NO₃^-, P and K according to the methods of [13]. Collected data were subjected to statistical analysis according to procedure describe by [14]. Means were compared at p<0.05 Duncan's multiple test (MRT), which was adapted by [15]. Water use efficiency (WUE) was calculated as following equation:

WUE (kg ha^-1 m^-3)=Crop yield (kg ha^-1)/Water supply (mm or m³).

Table 1: Chemical analyses of the experimental soil before planting in 2016 and 2017 seasons.

Table 2: Some chemical analysis of the organic materials (farm yard manure and composted rice straw) used.

Table 3: Monthly temperature means (c°), relative humidity (RH %) and evaporation (mmd^-1) at study area in 2016 and 2017 seasons.

Chlorophyll content of flag leaf, number of tillers/m² and number of panicles/m², panicle weight (g), number of filled grains/panicle, straw and grain yield (t/ha) of Sakha 106 rice cultivar influenced by water regime and fertilizers treatments are presented in Table 4. Data demonstrated that the continuous flooding (W1) and saturation (W2) treatments gave the greatest values for all studied characters as compared with the other irrigation treatments. On the other hand, the irrigation every 12 days (W5) treatment significantly reduced the values of all the studied characters. The shortage of water might have caused a decrease in the activity of nodes and buds that reduces the emergence of tillers especially the effective tillers and number and area of leaves due to the decrease in cell division and elongation these results are harmony with those obtained [16].

Table 4A: Chlorophyll content of flag leaf, number of tillers/m², number of panicles/m ² and panicle weight (g) of Sakha 106 rice cultivar as affected by the irrigation intervals and fertilizer treatments in 2016. T1=control (without any fertilizer applications); T2=4.76 tons farm yard manure (FYM) /ha T3=4.76 tons composted rice straw (CRS)/ha; T4=4.76 tons FYM +110 N/ha; T5=4.76 tons CRS +110 N/ha; T6=and recommended dose of Nitrogen, 165 kg N/ha W1=Continuous flooding; W2=continuous saturation; W3=irrigation every 6 days; W4=irrigation every 9 days; W5=irrigation every 12 days; *=significant **=highly significant a, b and c are the letter are significant or not significant by different according to DMRT.

Table 4B: Chlorophyll content of flag leaf, number of tillers/m², number of panicles/m² and panicle weight (g) of Sakha 106 rice cultivar as affected by the irrigation intervals and fertilizer treatments in 2017. T1=control (without any fertilizer applications); T2=4.76 tons farm yard manure (FYM) /ha T3=4.76 tons composted rice straw (CRS)/ha; T4=4.76 tons FYM +110 N/ha; T5=4.76 tons CRS +110 N/ha; T6=and recommended dose of Nitrogen, 165 kg N/ha W1=Continuous flooding; W2=continuous saturation; W3=irrigation every 6 days; W4=irrigation every 9 days; W5=irrigation every 12 days; *=significant **=highly significant a, b and c are the letter are significant or not significant by different according to DMRT.

Data also, indicated that irrigation every 12 days decreased the chlorophyll content of flag leaf. Water stress leads to a reduction in the efficiency of physiological processes, including protein synthesis, photosynthesis which causes inhibition of the activities of many enzymes and leads to early senescence in leaves especially flag leaf. Consequently, decrease grain filling rate, panicle weight, number of filled grains and grain yield. These results agreed with those obtained [16-19]. As for the effect of fertilizer treatments, data in Table 4A and 4B revealed that the application of fertilizers treatments increased all the studied characters as compared with the control. The highest values of the most studied characters were obtained with T5 treatment without any significant difference with the application of T6 during the two growing seasons. It can be observed that the organic fertilizers and the composted rice straw combined with urea performed better than the application of organic fertilizers alone. It might be due to the role of nitrogen for improving the growth of plant, physiological process consequently yields and its component found that the decomposition of organic fertilizers improves the soil fertility and keep the water in the soil more time that increase the availability of nutrients [18]. It is clear from the result, the application of T5 treatment produced higher grain yield without any significant difference with T6 and save about one third of inorganic nitrogen as well as, improving soil fertility.

The interaction between irrigation intervals and fertilizers treatments on the chlorophyll content (SPAD) of the flag leaf of sakha 106 rice cultivar is presented in Table 5. The highest values of chlorophyll content were obtained with T5 and T6 fertilizer treatments when combined with W1 and W2 irrigation treatments without any significant differences among them in the two seasons. In contrast, the lowest value in chlorophyll content was observed when T1 was combined with W5. It could be attributed to the inadequate amount of both water and nitrogen fertilizer which led to the decrease in the availability and uptake of nitrogen.

Table 5: Chlorophyll content of flag leaf (SPAD) of Sakha 106 rice cultivar as affected by the interaction between irrigation intervals and fertilizer treatments in 2016 and 2017 seasons. T1=control (without any fertilizer applications); T2=4.76 tons farm yard manure (FYM) /ha T3=4.76 tons composted rice straw (CRS)/ha; T4=4.76 tons FYM +110 N/ha; T5=4.76 tons, CRS +110 N/ha; T6=and recommended dose of nitrogen, 165 kg N/ha W1=Continuous flooding; W2=continuous saturation; W3=irrigation every 6 days; W4=irrigation every 9 days; W5=irrigation every 12 days a, b and c are the letter are significant or not significant by different according to DMRT.

Nitrogen is one of constituent of chlorophyll and improves the activity of synthetase enzyme that increases the biosynthesis of chlorophyll. The decomposition of organic fertilizers gradually makes continuous supply of nitrogen and other nutrients to the plant during all growth stages and consequently increases the chlorophyll content of flag leaf. These results are in harmony the importance of N from the Nfertilizer application, as the main constituent of the chlorophyll and the enzymes that have direct impact on vegetative and reproductive phases of plants [20].

Number of tillers/m² as affected by the interaction between irrigation intervals and fertilizer treatments during the 2016 and 2017 seasons are presented in Table 6. The highest number of tillers/m² were found when W1, W2 and W3 were combined with T5 and T6 treatments in 2016 and 2017 seasons, followed by W4 when combined with the same two fertilizer treatments. While the lowest values were obtained from T1 combined with W5 treatments. The high performance of number of tillers might be due to adequate amounts of water and nutrients uptake especially nitrogen. The absorption of nitrogen always increases the uptake of both phosphorus and potassium that enhance the nods and buds to emerge more tillers as a result to increase in cell division and elongation. These results are in harmony with those obtained who found that the highest values of number of tillers/m² was achieved by using 165 kg N ha^-1 under flooded conditions and continuous saturations without any significant differences with 5 tons ha^-1 of composted rice straw +110 kg N ha^-1, while using 5 tons composted rice straw ha^-1 alone gave the lowest values of number of tillers/m² in both seasons [18].

Table 6: Number of tillers/m² of Sakha 106 rice cultivar as affected by the interaction between irrigation intervals and fertilizer treatments in 2016 and 2017 seasons. T1=control (without any fertilizer applications); T2=4.76 tons farm yard manure (FYM) /ha T3=4.76 tons composted rice

Regarding to number of panicles/m², panicle weight (g) and number of filled grain as affected by the interaction between irrigation intervals and fertilizer treatments are presented in Tables 7-9. Data indicated that the greatest values of the number of panicles/m², panicle weight (g) and filled grain/panicle were obtained when T5 and T6 combined with most of the irrigation treatments except W5. On the other hand, the lowest number of panicles/m², panicle weight (g) and filed grain/panicle were found when T1 was combined with W5 treatment.

Table 7: Number of panicles /m² of Sakha 106 rice cultivar as affected by the interaction between irrigation intervals and fertilizer treatments in 2016 and 2017 seasons. T1=control (without any fertilizer applications); T2=4.76 tons farm yard manure (FYM) /ha T3=4.76 tons composted rice straw (CRS)/ha; T4=4.76 tons FYM +110 N/ha; T5=4.76 tons CRS +110 N/ha; T6 =and recommended dose of nitrogen, 165 kg N/ha W1=Continuous flooding; W2=continuous saturation; W3=irrigation every 6 days; W4=irrigation every 9 days W5=irrigation every 12 days. a, b and c are the letter are significant or not significant by different according to DMRT.

Table 8: panicle weight (g) of Sakha 106 rice cultivar as affected by the interaction between irrigation intervals and fertilizer treatments In 2016 and 2017 seasons. T1=control (without any fertilizer applications); T2=4.76 tons farm yard manure (FYM) /ha T3=4.76 tons composted rice straw (CRS)/ha; T4=4.76 tons FYM+110 N/ha; T5=4.76 tons CRS+110 N/ha; T6=a and recommended dose of nitrogen, 165 kg N/ha W1=Continuous flooding; W2=continuous saturation; W3=irrigation every 6 days; W4=irrigation every 9 days; W5=irrigation every 12 days. a, b and c are the letter are signficant or not significant by different according to DMRT.

Table 9: Number of filled grains of Sakha 106 rice cultivar as affected by the interaction between irrigation intervals and fertilizer treatment in 2016 and 2017 seasons. T1=control (without any fertilizer applications); T2=4.76 tons farm yard manure (FYM) /ha T3=4.76 tons composted rice straw (CRS)/ha; T4=4.76 tons FYM+110 N/ha; T5=4.76 CRS+110 N/ha; T6=and Recommended dose of nitrogen, 165 kg N/ha W1=Continuous flooding; W2=continuous saturation; W3=irrigation every 6 days; W4=irrigation every 9 days; W5=irrigation every 12 days. a, b and c are the letter are significant or not significant by different according to DMRT.

The increases in number of panicles/m², panicle weight (g) and filled grains/panicle could be attributed to the presence of required amount of water with adequate amount of nitrogen whether added to the soil inorganic (urea) or combined with organic fertilizers (farmyard manure or composted rice straw) that cause an increase in nutrients availability and uptake, which led to improve the viability of leaves and late its senescence resulted in increase in photosynthesis and its products (assimilates). These assimilates translocate from source to the sink of plant, consequently increase the filling and percentage. These results are in harmony with those obtained [21].

It can be easily observed that the application of T5 and T6 caused a relief of the harmful of water stress and improved the crop growth. These results are in harmony with those obtained by who found that the application of 5 tons ha^-1 of rice straw +110 kg N ha^-1 recorded the maximum value of number of panicles/m², panicle weight (g) and filled grains/panicle and mitigation the hazard effect of water stress [22].

Straw yield (t/ha) as affected by the interaction between irrigation intervals and fertilizer treatments are presented in Table 10. Data demonstrated that the highest straw yield was found when T5 and T6 combined with most of irrigation treatments. The highest straw biomass might be due to the presence of adequate amount of both nitrogen fertilizer and water which led to increase the availability of NH₄⁺and its uptake. The increase in N absorption always increase the absorption of both phosphors and potassium, which increase both of number of tillers and leaves that significantly increase in straw yield. The tested fertilizer treatments with W5 reduced the hazard effect of water stress and increased straw yield and reach to the maximum value when each of T5 and T6 was combined with W4. These results agreed with those reported by who found that there are significant differences among fertilizer treatments on straw yield [23]. Data in Table 11 revealed that rice grain yield was significantly affected by the interaction between irrigation and fertilizer treatments in both seasons. The maximum grain yield was obtained when T5 and T6 fertilizer treatments were integrated with the first four irrigation treatments (W1, W2, W3 and W4) without any significant differences among them. This means that the application of both organic and inorganic fertilizers either individual or combination minimized the hazard effect of water stress up to irrigation every 12 days.

Table 10: straw yield (t/ha) of Sakha 106 rice cultivar as affected by the interaction between irrigation intervals and fertilizer treatments in 2016 and 2017 Seasons. T1=control (without any fertilizer applications); T2=4.76 tons farm yard manure (FYM) /ha T3=4.76 tons composted rice straw (CRS)/ha; T4=4.76 tons FYM +110 N/ha; T5=4.76 tons CRS +110 N/ha; T6=and recommended dose of 165 kg N/ha, W1=Continuous

Table 11: Grain yield (t/ha) of Sakha 106 rice cultivar as affected by the interaction between irrigation intervals and fertilizer treatments in 2016 and 2017 seasons. T1=control (without any fertilizer applications); T2=4.76 tons farm yard manure (FYM) /ha T3=4.76 tons composted rice straw (CRS)/ha; T4=4.76 tons FYM +110 N/ha; T5=4.76 tons CRS +110 N/ha; T6 and recommended dose of nitrogen, 165 kg N/ha W1=Continuous flooding; W2=continuous saturation; W3=irrigation every 6 days; W4=irrigation every 9 days; W5=irrigation every 12 days. a, b and c are the letter are significant or not significant by different according to DMRT.

The increase in grain yield might be due to the presence of the required amount of both water and nitrogen fertilizer especially under W1 and W2 treatments. The gradual decomposition of compost rice straw released nitrogen and other nutrients which make continuous supply to the plant at different stages of growth. Moreover, the organic fertilizers kept water in the soil longer as shown in W3 and W4 irrigation treatments [18]. These results are similar to those obtained by who found that irrigation intervals under fertilizer treatments had a highly significant effect on grain yield. He found that under continuous flooding, using 165 kg N ha^-1 produced the highest grain yield without any significant differences with using 5 tons composted rice straw ha^-1 +110 kg N ha under irrigation every 9 and 12 days. It could be concluded that using 4.76 tons CRS+110 kg N/ha (T5) combined with irrigation every 9 days (W4) is the best treatment because it well be saved about one third of inorganic fertilizer (urea) as well as, reasonable amount of irrigation water.

Water relations

Grain yield (t/ha), total water input (m³/ha), water saved (%) and water use efficiency (kg/m³) as affected by irrigation intervals and fertilizer treatments in 2016 and 2017 seasons are shown in Table 12. Data indicated that the highest grain yield was found under continuous flooding (W1) followed by W2 with all fertilizer treatments in both seasons. In the same time the total water input was so high and reach 15425.90 and 15632.00 m³/ha under W1 followed by 12560.36 and 12650.55 m³/ha under W2 in both seasons, respectively. The water use efficiency (WUE) was very low (0.51 and 0.52 kg/m³) and (0.62 and 0.63) with the same irrigation treatments in both seasons respectively.

Table 12: Grain yield (t/ha), grain yield reduction %, total water input (m³/ha), water saved (%) and water use efficiency as affected by irrigation intervals and fertilizer treatments in 2016 and 2017 seasons. T1=control (without any fertilizer applications); T2=4.76 tons farm yard manure (FYM)/ha T3=4.76 tons composted rice straw (CRS)/ha; T4=4.76 tons FYM +110 N/ha; T5=4.7 tons CRS +110 N/ha; T6=and recommended dose of nitrogen, 165 kg N/h W1=Continuous flooding; W2=continuous saturation; W3=Irrigation every 6 days; W4=irrigation 9 days; W5=irrigation every 12 days.

The fertilizer 4.76 tons CRS +110 N/ha (T5) with irrigation treatments W3 or W4 gave the highest values of grain yield without any significant differences with W1T5 and saved water about (23.64 and 24.76%) and (30.40 and 30.23%) for both season respectively. The same treatments (W3T5 and W4T5) recorded the highest value of WUE (0.90 and 0.91) and ((0.95 and 0.94 kg/m³) and lowest yield reduction (6.38 and 9.68%) and (10.03 and 13.02%) in 2016 and 2017 seasons respectively. These results are harmony with those obtained with [19, 24] who reported that the alternating wet and dry irrigation increasing water use efficiency. Data in the same table also, indicated that irrigation every 12 days caused strongly decreased grain yield and WUE under all fertilizer treatments in both seasons (Table 12).

Form these results and previous studies we can observed that there are different irrigation regimes for reduction of entering water to rice field, and increase WUE, such as soil saturation, and, alternating wet and dry irrigation (irrigation every 6 and 9 days) instead of a layer with deep 3-5 cm water. Also using mixed between organic and inorganic fertilizer with irrigation interval (9 days) significantly improves grain yield and WUE.

Nutrients availability in the soil

Concentration of NH_4⁺ available (ppm): The availability of ammonium (NH_4⁺) in the soil at 30, 60 and 90 days after transplanting (DAT) as affected by irrigation and fertilizer treatments are presented in Table 13. Data clarified that the highest available concentration of NH_4⁺ were recorded with W1 and W2 during all period of rice plant (30, 60 and 90 DAT) followed by W3 compared with W4 and W5 in 2016 and 2017 seasons. It could attribute to the fact that the presence of adequate amount of the water in the soil enhances nutrients availability and improved nutrients uptake by plants.

Table 13: Availability of NH₄⁺ concentration (ppm) in the soil at 30, 60 and 90 days after transplanting (DAT) as affected by irrigation intervals and fertilizer treatments in 2016 and 2017 seasons. T1=l control (without any fertilizer applications); T2=4.76 tons farm yard manure (FYM) /ha T3=4.76 tons composted rice straw (CRS)/ha; T4=4.76 tons FYM+110 N/ha; T5=4.7 tons CRS+110 N/ha; T6=and recommended dose of nitrogen, 165 kg N/ha W1= Continuous flooding; W2=continuous saturation; W3=irrigation every 6 days; W4=irrigation 9 days; W5=irrigation every 12 days. a, b and c are the letter are significant or not significant by different according to DMRT.

Data also, revealed that the available concentration of NH_4⁺ was higher at 30 DAT and 60 DAT, compared with availability of NH_4⁺ at 90 DAT during the two seasons. The highest value of NH_4⁺ available was observed at 30 DAT with W1 and W2 without any significant differences between them followed by W3. The same trend of NH_4⁺ availability was found at 60 and 90 DAT. The increase in NH_4⁺ availability under the first three irrigation treatments (W1, W2 and W3). It could be attributed to the adequate amount of water in the soil increase the availability of NH_4⁺ and improved NH₄⁺ absorption by plants because at the 30 DAT the rice canopy of plant still small, while at 60 DAT the rice canopy of plant reach the maximum growth consequently, the absorption of NH₄⁺ by plant dramatically increased so, the amount of NH₄⁺ in the soil solution tended to decrease. It can be easily notice that when the water cut off before harvesting the soil conditions transferred from anaerobic to aerobic that cause a conversion of NH₄⁺ into NO₃^-. These findings are in harmony with those reported by [25,26]. The T5 and T6 recorded the highest value of available NH₄⁺ followed by T4 in both seasons. This might be due to that incorporation of CRS or FYM with urea in the soil reduced the N losses beside stimulated both heterotrophic and phototrophic N fixation in flooded soil [27]. The lower N immobilization after incorporating composted in anaerobic system compared with aerobic system which increases inorganic N and also microbial N was replenished by N contained in root exudates and decomposing root debris [28].

The concentrations of NH₄⁺ available (ppm) at 30, 60 and 90 DAT as affected by the interaction between irrigation intervals and fertilizer treatments are illustrated in Figure 1. Data indicated that the application of fertilizer treatments (organic or inorganic form) under all irrigation treatments increased the available concentrations of NH₄⁺ compared with the control. The greatest value of concentrations of NH₄⁺ available was observed when both T5 and T6 combined with either W1 or W2 at the period of 30 DAT which reached to about 60 to 70 ppm, while the lowest value was obtained when T1 was combined with W5 treatment. It could be attributed under non-flooded conditions, rapid nitrification of the added fertilizer led to a rapid decrease in NH₄⁺ and a simultaneous increase in NO₃^- concentrations within the first 30 days [29]. Also, under flooded conditions,NH₄⁺ was the principal inorganic N form, as all NO₃^- originally present in the soils was rapidly lost, with time, NH₄⁺ concentrations tended to decrease under non-flooding conditions and increase in the presence straw under flooding conditions.

Concentration of NO₃^- available (ppm): The availability of nitrate (NO₃^-) in the soil at 30, 60 and 90 days after transplanting (DAT) as affected by irrigation intervals and fertilizer treatments are presented in Table 14. Data showed that the highest available concentration of NO₃^- was found with W5 followed by W4 at 30, 60 and 90 days from transplanting. This is mainly due to prolonging irrigation intervals up to 12 days which increased the aerobic conditions and higher amount of oxygen that lead to more nitrification producing plenty of NO₃^- beside its effect on increasing nitrate-N immobilization, also the reduction of NO₃^- to NH₄⁺ by microorganism [28]. Under aerobic conditions, a large part of immobilized N was released to the exchangeable and soluble phase within the first 10 days of incubation and rapidly converted into nitrate [30-32]. The largest concentration of NO₃^- available in soil was obtained at 30 DAT then decreased to the minimum at 60 DAT, followed with a slight increase at 90 DAT. This is due to the improving the aeration in the soil layers at 90 DAT and therefore nitrification process take place. These results are in agreed with those obtained [26,33]. It is clear from the data that utilization of T5 and T6 gave the maximum NO₃^- concentration without any significant differences with T3 and T4 treatments compared to the other treatments. These results agreed with the findings [21].

Table 14: Availability of NO₃^- concentration (ppm) in the soil at 30, 60 and 90 days after transplanting (DAT) as affected by irrigation intervals and fertilizer treatments in 2016 and 2017 seasons.

Significant interaction between irrigation intervals and fertilizer treatments were observed for available concentration of NO₃^- (ppm) during 2016 and 2017 seasons is illustrated in Figure 2. Results showed that the application of nitrogen fertilizers whether organic or inorganic increased concentration available of NO₃^- under all irrigation treatments compared with the control. The highest concentration available of NO₃^- were observed with T5 and T6 under W5 followed by the same fertilizer treatments under W4 in both seasons. Similar results were obtained by who found that application of composted rice straw and cellulose enhances nitrate immobilization under anaerobic conditions [34].

Figure 2: (A, B, C, D, E, F, J, H, I and g): Concentrations of NH₄⁺ available (ppm) in the soil at 30, 60 and 90 days after transplanting (DAT) as affected by the interaction between irrigation intervals and fertilizer treatments in 2016 and 2017 seasons.

Concentration of P available (ppm): Concentration of P available (ppm) as affected by the irrigation intervals and fertilizer treatments in 2016 and 2017 seasons are presented in Table 15. Generally, the available concentration of P was highest under continuous flooding than the other irrigation treatments in both seasons under study. The increase in phosphorus due to flooding conditions is attributed mainly to the reduction of iron, manganese and aluminum since their solubility increased with flooding and changing the soil condition from oxidation (before flooding) to reduction conditions (after flooding) [35]. The desorption of P held by Fe₃⁺ oxides and release of occluded P [8]. Data in the same table revealed that the application of any fertilizer treatments whether, organic or inorganic fertilizers increased phosphorus availability compared with the control. The highest phosphorus availability was observed with (T5) followed by T4. It could be attributed to the decomposition of compost and farm yard manure as organic fertilizers which release N, P, K and other nutrients. Data also, indicated that the P availability increased up to 30 DAT then decreased afterward (Figures 3 and 4). It could be attributed to fewer uptakes by plant because of the small growth at 30 DAT. The concentration of P available in the soil sharply decreased up to 90 DAT. This mainly due to the absorption of plant beside subsequent precipitation and desorption by soil minerals, also before harvesting

Table 15: Available of phosphorus (P) concentration (ppm) in the soil at 30, 60 and 90 days after transplanting (DAT) as affected by irrigation intervals and fertilizer treatments in 2016 and 2017 seasons. Control (T1), 2 tons FYM (T2), 2 tons CRS (T3), 2 tons FYM+110 N/ha (T4), 2 tons CRS+110 N/ha (T5), recommended dose of N (T6), Continuous flooding=(W1), continuous saturation=(W2), irrigation every 6 days=(W3), irrigation every 9 days=(W4) and irrigation every 12 days=(W5). a, b and c are the letter are significant or not significant by different according to DMRT.

Figure 3: (A, B, C, D, E, F, J, H, I and g): Available NO₃ concentrations (ppm) in the soil at 30, 60 and 90 days after transplanting (DAT) as affected by the interaction between fertilizer treatments and irrigation intervals in 2016 and 2017 seasons.

Figure 4: (A, B, C, D, E, F, J, H, I and g): Available P concentrations (ppm) in the soil at 30, 60 and 90 days after transplanting (DAT) as affected by the interaction between irrigation intervals and fertilizer treatments in 2016 and 2017 seasons.

Concentration of P available (ppm) in the soil as affected by the interaction between irrigation intervals and fertilizer treatments in 2016 and 2017 seasons is illustrated in Figure 3. The greatest concentration of P available recorded when T5, T6 and T4 were integrated with either W1 or W2 at 30 DAT, while the lowest value of P available was found when T1 combined with W5 in both seasons. These findings are in harmony with those obtained who found that rice straw incorporated and FYM with higher doses of fertilizer N increased the available P [37].

Concentration of K available (ppm): The effect of irrigation intervals and fertilizer treatments on K availability in the soil in both seasons is presented in Table 16. Data showed that the highest availability of K was found with W2 followed by W1 at 30, 60 and 90 DTA. Data also, indicated that the availability of K increased up to 30 DAT then decrease to the minimum at 60 DAT, followed by a slight increase at 90 DAT. The increasing in availability of K at the period of 30 DAT could be attributed to decrease in K absorption due to small growth in the canopy of tested rice cultivar, but with the increase the plant canopy the concentration of K gradually decreased. A slight increase in K availability at 90 DAT may be due to at this age the cut off water before harvesting transfer the soil from anaerobic to aerobic conditions moreover, alternate wet and dry under irrigation intervals (W3, W4 and W5). It is clear that all treatments under continuous saturation gave the largest amounts of K availability compared to the treatments under continuous flooding. This mainly due to the effects of leaching on K losses [21,38]. Data also, indicated that all fertilizer treatments increased the availability of K compared with the control at the three periods 30, 60 and 90 DAT. The maximum mean value of K availability was recorded with T5 followed by T4 compared with the other fertilizer treatments in both seasons (Figure 5).

Table 16: Available of potassium (K) concentration (ppm) in the soil at 30, 60 and 90 days after transplanting (DAT) as affected by irrigation intervals and fertilizer treatments in 2016 and 2017 seasons. Control (T1), 2 tons FYM (T2), 2 tons CRS (T3), 2 tons FYM+46 N/ha (T4) and 2 tons CRS+46 N/ha (T5) and recommended (T6), Continuous flooding=(W1), continuous saturation= (W2), irrigation every 6 days=(W3), irrigation every 9 days=(W4) and irrigation every 12 days=(W5). a, b and c are the letter are significant or not significant by different according to DMRT.

Figure 5: (A, B, C, D, E, F, J, H, I and g): Available K concentrations (ppm) in the soil at 30, 60 and 90 days after transplanting (DAT) as affected by the interaction between irrigation intervals and fertilizer treatments in 2016 and 2017 seasons.

Potassium availability (K) as affected by the interaction between irrigation intervals and fertilizer treatments at different period of tested cultivar (30, 60 and 90 DAT) in both seasons is presented in Figure 4. Data demonstrated that the combination between T3, T4 and T5 with all the irrigation treatments gave the highest availability of K at the three periods 30, 60 and 90 (DAT) compared with other fertilizer treatments. This could due to that the soil solution K is higher in composted rice straw treatments. The other reason could be higher increase in the soil solution Fe₂⁺ and Mn₂⁺ caused by organic fertilizers which release K from exchange complexes [36].

Soil saturation and alternating wet and dry irrigation (irrigation every 6 and 9 days) are very important for water saving strategy. In this study the fertilizer 4.76 tons CRS+110 N/ha (T5) treatment with irrigation every 6 days or 9 (W3 or W4) gave the highest values of grain yield without any significant differences with continues flooded (W1T5) and saved water about (23.64 and 24.76%) and (30.40 and 30.23%) for both season respectively. The same treatments (W3T5 and W4T5) also recorded the highest value of WUE (0.90 and 0.91) and ((0.95 and 0.94 kg/m³) and lowest with yield reduction (6.38 and 9.68%) and (10.03 and 13.02%) in 2016 and 2017 seasons respectively. Also this study concluded that using mixed between organic and inorganic fertilizers with irrigation interval (9 days) significantly improve grain yield and WUE. The highest amounts of nutrients (NH₄⁺ and P) availability were found under W1 followed by under W2, W3 and W4 especially with T5 fertilizer treatments. Whereas, the maximum values of NO₃^- availability was found under W5 followed by W4.