A field experiment was conducted during the two successive summer seasons of 2009 and 2010 in using clayey soil at the farm of Rice Research and Training Center, Sakha District, Kafer El-Sheikh Governorate, Egypt, to investigate the effect of rice straw incorporation in the soil under continuous flooding and continuous saturation on availability of some nutrients in the soil (ammonium, nitrate, phosphorus and potassium) and rice yield. Utilization of 165 kg N ha -1 gave the highest values of rice grain yield but without any significant differences with 5 tons rice straw ha -1 + 110 kg N ha -1 . The largest amounts of nutrients (NH4 + and P) availability were found with continuous flooding. While, the highest values of NO3 and K availability were found under continuous saturation. The continuous flooding treatment gave more grain yield as compared with continuous saturation treatment.

Sustainable agriculture is a prerequisite for food and environmental security. Chemical fertilization, especially nitrogenous fertilization, is considered the most consumed for field crops. In rice crops, plants consume much less than half of the applied N-fertilizer. In the current investigation, multiple N environments were generated by applying different N doses of urea fertilizer to a permanent transplanted field for two successive summer growing seasons at a rice research and training center, Kafrelsheikh, Egypt. A set of 55 genotypes consisting of 25 Jabonica, 4 Tropical Japonica, 20 Indica, and 6 Indica/Japonica were transplanted under no N (0N), Low N (LN), medium N (MN), and High N (HN) (i.e., 0, 48, 96, and 165 Kg N ha−1, respectively). Highly significant differences were detected among the tested genotypes. AMMI analysis of variance revealed the existence of the genotype via nitrogen interaction (GNI) on yield performance. The GNI principal components (IPCA) IPCA1 and IPCA2 scores were significant and contributed values of 71.1 and 21.7, respectively. The highest-ranked genotypes were MTU1010, IR22, SK2046, SK2058, IR66, and Yabani LuLu based on their grain yield means (30.7, 29.9, 29.5, 29.3, 28.8, and 28.5 g plant−1). These genotypes were grouped into the same SCL according to the stability analysis ranking matrix. Based on AMMI analysis and biplots, MTU1010 and Yabani LuLu showed yield stability across environments. Meanwhile, the which-won-where biplot showed that IR22 was superior under unfavorable N-levels and MTU1010 was stable across the different environments. These findings are considered to be of great importance to breeders for initiating low-nitrogen-input breeding programs for sustainable agriculture.

Phosphorus is a macronutrient that plays number of important roles in plants. It is a component of nucleic acids, so it plays a vital role in plant reproduction, of which grain production in an important result. Intensive cropping system, high phosphorus consumer crops, high yielding rice varieties and high soil pH restricted P availability resulted in low rice yield. The experiment was carried out at farm of Sakha Agriculture Research Station, Kafrelsheikh during 2014 and 2015 summer seasons, in clayed alkaline soil, the study aimed to find out the effect of different levels of phosphorus fertilizer on yield and yield attributes of rice in low soil phosphorus. The treatments consist of four cultivars; Egyptian hybrid rice one (EHR1), Sakha102, Sakha106 and Giza179 and five phosphorus (P) fertilizer levels Viz. 0, 12, 24, 36 and 48 kg P 2 O 5 . ha -1 as single super phosphate (15.5 % P 2 O 5 ). Split plot experiment design with four replications was used. At heading some growth parameters were measured yield and yield attributes were estimated. Nitrogen and phosphorus uptake were determined.The studied varieties were certainly differed regarding their yield and yield attributes as well as nitrogen and phosphorus uptake. The Egyptian hybrid rice one (EHR1) apparently surpassed others studied varieties in growth, grain yield and most of yield components characteristics.All the studied parameters of rice varieties differed significantly with the application of phosphorus fertilizer. Plants grown without added phosphorus gave the lowest grain yield. The higher phosphorus levels exhibited higher grain yield. A significant interaction between varieties and phosphorus levels in respect of yield and yield attributes of rice were observed. The highest grain yield was recorded with Egyptian hybrid rice one at 48 kg P 2 O 5 . ha -1 .It could be concluded that high yielding rice varieties, EHR1 and Giza 179 responded to phosphorus fertilizer up to 48 kg P 2 O 5 /ha -1 . Furthermore, the medium yielding varieties; Sakha102 and Sakha106 performed better with P level of 36 kg P 2 O 5 /ha -1 . The application of phosphorus for rice after heavy phosphorus consumer crop and high pH soil is imperative to fetch high rice grain yield.

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Two field experiments were conducted at the Experimental Farm of Rice Research and Training Center, Sakha, Kafer El-Sheikh, Egypt during the rice growing seasons of 2009 and 2010 to evaluate the response of different rice genotypes namely, GZ8455, GZ8450, GZ7576, GZ8479, GZ8126, GZ7769, GZ7764 and GZ6522 (Sakha105) to various nitrogen levels (0, 40, 80, 120, 160, 200, 240, 280 and 320 Kg N ha-1). Yield and yield attributes were determined at maturity. A wide variation in nitrogen response was observed in the eight rice genotypes. GZ6522 produced the highest grain yield followed by GZ8455 and GZ8126. Grain yield and most of yield attributes generally increased with increasing nitrogen levels up to 160 kg N ha-1 .