Application of appropriate level of nitrogen fertilization is a major objective to increase nitrogen use efficiency by rice varieties. Field experiments were conducted during 2016 and 2017 growing seasons to evaluate the efficiency of varying nitrogen fertilizer rates on growth and yield parameters, along with nitrogen use efficiency of some newly released rice varieties (Sakha 108) and some promising lines GZ9399-4-1-1-3-2-2, GZ10101- 5-1-1-1 and GZ10154-3-1-1-1. Five nitrogen levels (i.e. 0, 55, 110, 165 and 220 kg N ha-1) were used. The results from both growing seasons indicated that, Sakha 108 recorded the highest grain yield while GZ10154 and GZ10101 recorded the lowest grain yields. A linear increase in grain yield was observed with continuous rate increase of nitrogen from 0 to 220 kg ha-1, while 220 kg N ha-1 treatment showed maximum grain yield followed by 165 kg N ha-1, with control as minimum. Agronomic nitrogen use efficiency (AE) for studied rice genotypes varied significantly, and ranged from 3.63 to 32.9 and from 2.72 to 34.12 kg grain yield produced per kg of nitrogen applied in 2016 and 2017 respectively. Across N levels, GZ9399 recorded the highest values of AE for the nitrogen fertilizer rate of 165 kg N ha-1 in both seasons.

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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.

A field trial was performed in 2015 and 2016 rice seasons at the farm of Rice Research and Training Center, Sakha, Kafr El-Sheikh, Egypt to study the role of organic fertilizer i.e. compost rice straw 5 t ha -1 (CRS) and rice straw 5 t ha -1 (RS) plus control and potassium treatments namely 60 kg K 2 O ha -1 applied basally before planting (K1), 30 kg K 2 O ha -1 basally plus 2% potassium sulfate (K 2 SO 4 ) as foliar spray at panicle initiation (K2), 2% K 2 SO 4 as foliar spray at both panicle initiation (PI) and late booting (LB) periods (K3) plus control (K0) on the yield and its attributes as well as some of grain quality characters of Giza 179 rice variety. The experiment was laid out in a split-plot design with four replications. The organic fertilizer was allocated in the main plots while the sub-plots received potassium treatments. The studied characters were plant height, number of tillers, number of panicle hill -1 , panicle weight, panicle length, number of branches panicle -1 , number of filled grains panicle -1 and number of unfilled grains panicle -1 , 1000-grain weight, grain and straw yield and some grains quality characters i.e. hulling, milling and head rice percentage as well as available and uptake of potassium . The main results revealed that application of both compost rice straw (CRS) and rice straw (RS) gave the same greatest values of all the previous characters except panicle length which gave insignificant effect. Application of potassium fertilizer at the rate of 60 kg K 2 O ha -1 basally applied before planting (K1) or as foliar spray at the rate of 2% K 2 O at both panicle initiation (PI) and late booting (LB) produced the highest values of all the studied characters. As for the interaction between organic fertilizer and potassium treatments, results clarified that the combination of 5 t CRS ha -1 with each of 60 kg K 2 O ha -1 (K1) or 2% K 2 O as foliar spray at both PI and LB (K3) gave the same greatest values in number of panicles hill -1 , filled grains panicle -1 and grain yield, while panicle weight and straw yield reached to the maximum values when 5 t RS ha -1 was combined with K1 and K3. Hulling% reached the maximum value when treated with 5 t CRS ha -1 while both milling and head rice responded to 5 t RS ha -1 . Treatment of potassium applied as a foliar spray at both PI and LB (K3) produced the highest hulling and milling% while head rice% responded to K2 and K3. The combination of 5 t RS ha -1 with K1 or K3 gave the highest hulling and milling% while head rice reached the maximum value when each of CRS and RS was combined with each of K1, K2 and K3. Available K reached the maximum value at 30 days after transplanting. Availability of K was the highest under rice straw treatment followed by CRS. The uptake of K reached to the greatest value when either CRS or RS was combined with K1 treatment. It can be concluded that combination of 5 t CRS ha -1 with K3 (2% K 2 SO 4 as a foliar spray at both PI and LB) produced the greatest grain yield and saved about 40 kg K 2 O ha -1 . ...

Water shortage stress is the most critical abiotic factor reducing rice yield. Water deficit stress at whichever of the rice critical growth stage causes decline in yield. A field experiment was conducted at the Experimental Farm of Sakha Agricultural Research Station, Kafrelsheikh, Egypt during 2018 and 2019 seasons, to investigate the effect of four irrigation intervals (continuous flooding(I1), irrigation every six days(I2), nine days(I3) and twelve days(I4)) on performance of five genotypes (Giza 178, IR 69625A/Giza 178, IR 70368A/Giza 178, IR 69625A/Giza 179 and IR 69625A/Giza 181). Strip plot design, with four replications was used. The horizontal plots were assigned to irrigation treatments, while the vertical plots were assigned to rice genotypes. Different drought tolerance indices such as abiotic tolerance index (ATI), stress susceptibility index (SSI), mean productivity (MP), tolerance index (TOL) and stress susceptibility percentage index (SSPI) were tested in screening superior rice genotypes. The results showed that days to 50% heading, plant height, panicle length, panicle weight, number of effective tillers hill-1 , spikelet's number panicle-1 , number of branches panicle-1 , seed set (%), 1000-grain weight (g), number of filled grains panical-1 , grain yield t ha-1 , harvest index (%) and biomass weight t ha-1 were highly significantly affected by the interaction between irrigation intervals and genotypes. The highest values of grain yield were obtained by IR69625A/Giza 181 under continuous flooding irrigation during both seasons. Based on results of different drought tolerance indices, IR69625A/Giza 181 showed lowest values of ATI, SSI and TOL and the highest values of MP and SSPI and was identified as drought tolerant genotype.