Water limit is one of the major a biotic stress limiting plant production in worldwide. The research work of the present study was carried out at the Experimental Farm of the Rice Research and Training Center (RRTC), Sakha, Kafr El-Sheikh, Egypt, during the three successive rice seasons 2010, 2011 and 2012, to study the genetic effects on some of root system related to water limit and yield and its component traits under water limit condition. Six rice genotypes i.e. Giza 177, Sakha 101, GZ 7456-13-6-5-3, Sakha 105 (sensitive to drought stress), IRAT 112 and IRAT 170 (tolerant to drought stress), were chosen for this study. The results of this investigation revealed that both general and specific combining ability variances were found to be highly significant for all studied traits except root thickness, root dry weight and 1000-grain weight, indicating the importance of both additive and non-additive genetic variance in determining the inheritance of these studied traits i.e. root length, root volume, plant height, No. of days to heading, , No. of panicles/plant, No. of filled grains/panicle and grain yield/plant. With the exception of No. of panicles/plant and grain yield/plant, the GCA/SCA variances were found to be greater than unity for all the studied traits except for No. of panicles/plant and grain yield/plant, suggesting greater importance of additive genetic variance in the inheritance of these traits. Therefore, it could be concluded that selection procedures based on the accumulation of additive effect would be successful in improving of these traits. The results showed that IRAT 112 and IRAT 170 were highly significant and positive general combining ability effects for maximum root length, root thickness, root volume, root dry weight and yield and its component traits under water limit condition indicating that these genotypes could be considered as good combiners for the improvement of these traits i.e. Sakha 105 x IRAT 112 for maximum root length, Sakha 101 x IRAT 112 for root thickness, Giza 177 x IRAT 112 for root volume, IRAT 112x IRAT 170 for root dry weight and Sakha 101 x IRAT 170,Sakha 101 x IRAT 112 for grain yield/plant under water limit condition. Frequency distribution of phenotypes for each trait in F2 and their parents, all studied traits approximately fit normal distribution, F2 plants having phenotypic values greater than the higher parent and less than the lower parent (Transgressive Segregates) were observed for all studied traits.

Irrigation intervals and potassium levels were studied using Giza179, GZ7112 and Sakha106 rice genotypes at the experimental Farm of Rice Research and Training Center (RRTC) Sakha, Kafr El-Sheikh, Egypt, during 2012 and 2013 seasons. Four irrigation intervals treatments namely; continuous flooding (W), irrigation every 4 days (4W), irrigation every 8 days (8W) and irrigation every 12 days (12W), as well as five rates of potassium; 0 (K0), 36 (K1), 72 (K2), 108 (K3) and 144 (K4) kg K2O/ha were used. The field experiments were laid out in a split-spit design with four replications. The irrigation treatments were applied in the main plots, the rice genotypes were placed in the sub-plots and the potassium rates were put in the subsub plots. The main obtained results indicated that Giza179 produced higher grain yield and its attributes followed by GZ7112 rice line under continuous flooding (W) without any significant decrease in yield up to 8W and then significantly decreased under12W treatment. The amount of water saved due to increasing irrigation intervals compared to continuous flooding were (10.36 and 8.37 %) for Giza179 and (10.50 and 10.36%) for GZ7112 under 4W treatment and (17.81 and 23.66%) for Gzia179 and (13.33 and 18.44%) for GZ7112 with 8W treatment, while under 12W water saved was about 23.91 and 27.90 % with reduction in grain yield about 22.42 and 24.71 % in 2012 and 2013 seasons respectively. Over both season using Giza179 and GZ7112 rice genotypes which gave higher yield about (9.70 and 9.33 t/ha), water saved (20.73 and 15.88 %) and water use efficiency (0.90 and 0.81 kg/m 3) for both genotypes respectively. It means that the total water input ranged from 11260.88 and 10006.80 m 3 /ha (which equal about 4700 m 3 /fed) under 8W treatment using Gzia179 rice variety compared with national average which reaches to 1428.57 m 3 /ha (which equal about 6500 m 3 /fed). The application of potassium up to 108 K2O/ha (K3) significantly increased rice yield and relatively mitigated the undesirable effect of water stress resulted in increase the WUE and water saved %. *Average Requirement = Grain yield (kg/ha) ÷ Total water input (m 3 /ha).

One of the main problems of lowland rice cultivation and production is the shortage of irrigation water, which effects the vegetative growth rate and the amount of yield and its component. In this study, afield experiment was conducted to find out the impact of some plant growth regulating substance on rice cultivars namely; Giza179 cultivar and Giza177 cultivar grown under different irrigation intervals in 2015 and 2016 growing season sat the farm of Agricultural Research Station, Sakha, Kafrelsheikh, Egypt. The Experiment was conducted using Randomized Complete Block Design with Strip-split plot arrangements. Main plots consisted of the three irrigation intervals namely; irrigation every 4 days (I1), irrigation every 8 days (I2) and irrigation every 12 days (I3), while sub plots devoted torice cultivars while the sub-sub plots contained the four levels of plant growth regulators: T1: spraying by cytokinein with concentration of 20 ppm, T2: spraying by abscisic acid with concentration of 15 ppm (ABA), T3: spraying by proline with concentration of 80ppm, T4: control (without any spray).The recorded data were chlorophyll content (SPAD), plant height (cm) at harvest, number of panicle (m-2), panicle weight (g), number of filled grains/panicle, number of unfilled grains/panicle, 1000-grain weight (g), grain yield (t/ha) and straw yield (t/ha). The main results indicated that irrigation every 4 and 8-days intervals cause an increase in all the previous studied characters, while irrigation every 12 days significantly reduced it. Spraying the tested rice cultivars by three growth regulators increased all studied characters as compared with control treatment. spraying Giza 179 cultivar with Cytokinin under the different irrigation intervals surpassed Giza177 cultivar and gave the highest value in all the studied characters expect 1000-grain weight followed by ABA. Spraying the two tested cultivars by Cytokinin under irrigation every 12 days which cause water stress relief the harmful of stress in the plant and increase the yield by about 3.2 t/ha specially with Giza179 cultivar as compared with control (without any growth regulator). Moreover, the application of cytokinein extend irrigation intervals from irrigation every 4 days up to irrigation every 8 days without any significant reduction in the yield. these results are benefit for farmers which safer from shortage of irrigation water in their rice field.

The concentrations of cadmium (Cd 2+), nickel (Ni 2+) and Lead (Pb 2+) in different organs of rice plant were investigated by field experiments. Data showed that the highest yield of rice grain was recorded by the application of 21.42 tons farmyard manure (FYM) plus 357 kg urea.ha-1 as compared with the other treatments. Roots accumulated more Pb 2+ , Ni 2+ and Cd 2+ than straw and grains at harvest stage of rice growth. Pb 2+ , Ni 2+ and Cd 2+ concentration in rice plant organs (root, straw and grain) increased with increasing levels of FYM either alone or in combined with urea compared with the control. Pb 2+ concentrations in straw do not exceed the critical limits of pollution with FYM added to the soil either separated or combined with urea. However, rice grains were slightly polluted at 21.42 tons FYM plus 238 kg urea.ha-1 and 21.42 tons FYM plus 357 kg urea.ha-1. Ni 2+ concentration in rice grain and straw do not exceed the critical limits with all treatments .Cd 2+ concentration in rice straw do not exceed the critical limits of Cd 2+ at all addition levels of FYM added to the soil whether levels separated or integrated with urea, however Cd 2+ concentration in rice grain was polluted at 21.42 tons plus 238 kg urea.ha-1 , 14.28 tons FYM plus 357 kg urea.ha-1 and 21.42 tons FYM urea.ha-1. Integration of 14.28 tons FYM plus 238 kg urea.ha-1 do not exceed the critical limits of the concentration of Pb 2+ , Ni 2+ and Cd 2+ in different organs of rice plant.

This work targeted investigation of the efficiency of silica application on anatomical structures of the root system after 45 days from sowing and grain yield at maturity of the five rice varieties, Sakha104 (V1), Egyptian hybrid rice1 (EHR1) (V2), Sakha105 (V3), Giza178 (V4) and Giza179 (V5) under irrigation with drainage water (DW), having varied concentrations of Cd, Pb and Cr. Potassium silicate, potassium sulphate and silicon dioxide were sprayed individually as an aqueous solution at a concentration of 2% silica, applied twice 15 and 30 days after sowing. The collected results for the anatomical characteristics indicated that the highest values of cortex (650 length and 650 width μm), vascular bundle (750 length and 750 width μm), epidermis (241 μm) and xylem (175 length and 160 width μm) were recorded with application of Si as potassium silicate or silicon dioxide under the two types of irrigation water and in two consecutive growing seasons. Si application significantly increased shoots and root weight and length, and grain yield, compared to the Si‐untreated counterparts. The concentrations of Cd, Pb and Cr in harvested grains with application of potassium silicate or silicon dioxide under irrigation by DW were below the safety limits of 0.40, 0.20 and 1.00 ppm respectively.

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A field experiment was conducted in summer season 2007 at the farm of Rice Research and Training Center farm Kafr El-Sheikh to study the impact of FYM and urea and their combination with using drainage water for irrigation on availability of some heavy metals such as Lead(Pb), nickel (Ni), Cadmium (Cd). Results indicated that the highest values of available pb +2 , Ni +2 , Cd +2 were found with the combination of 150 kg urea plus the rate of 9 ton FYM.Fed -1 . Data indicated that ,the lowest values of available Cd 2+ ,Ni 2+ and pb 2+ in soil were found at flowering stage compared with the other stages at all treatments. The results of simple correlation coefficient ( r )between organic matter ( OM) ( y ) and each of available Pb +2 (X1), available Ni +2 ( X2) and available Cd +2 (X3 ) at harvest stages showed the character most closely associated with organic matter was the available Pb +2 (X1 ) (R= 0.9) . Multiple linear regressions showed that the prediction equation for organic matter was formulated as follows: Y = -0.8+ 0.224 X1 + 0.301X2 + 2.62 X3

To evaluate the role of growth promoting Rhizobacteria (PGPR) either added a single or combined with nitrogen fertilizer (urea) on yield and yield components of five Egyptian rice cultivars.i.e. Giza179, Sakha102, Sakha105, Sakha106 and Sakha103.Two field experiments were carried out at the farm of Sakha Agriculture Station during 2014 and 2015 growing seasons. Five fertilizer were application different combination between Rhizobacteria and nitrogen fertilizer; Recommended dose of N 165 Kg N/ha (T 1), Rhizo+1/4 recommended dose of nitrogen (T 2), Rhizobia only (T 3), Rhizo+1/2 recommended dose of nitrogen(T 4) and Rhizo+3/4 recommended dose of nitrogen(T 5).The Experiments were conducted using the Randomized Complete Block Design (RCBD) with splitplot arrangements. Split plot design was used with four replication. The main plots received the five rice cultivars while the fertilizer treatments were located in sub plots. The recorded data were chlorophyll content of flag leaf, plant height (cm) at harvest, number of tillers (m-2), number of panicles (m-2), panicle length (cm), panicle weight (g), number of filled grains/panicle, number of unfilled grains/panicle, 1000-grain weight (g), grain and straw yield (t/ha). Results indicated that the application of either Rhizo+3/4 dose of N (T 5) or recommended dose of N (urea) (T 1) gave nearly the highest value of growth characters, yield and yield components. While, Rhizobia application alone gave the lowest value of the previous studied characters. The results also clarified that the treatments of combined Rhizobacteria with 3/4 of recommended dose of urea produced nearly the same grain yield as recommended dose with very little difference between the tested cultivars. According to the results, it can save 1/4 of the recommended dose of nitrogen fertilizer (165 kg N/ha)without significant reduction in the yield beside minimized the economical and the pollution resulted from chemical fertilizers.