EFFECT OF N- FERTILIZATION RATES AND SMALL-FLOWER UMBRELLA, (CYPERUS DIFFORMIS, L.) COMPETITION ON BROADCAST-SEEDED RICE, (ORYZA SATIVA, L.) PRODUCTIVITY AND NUTRIENTS UPTAKE

Two field experiments were conducted at Gemmeiza Agric. Res. Station, Gharbia Governorte, Egypt, during 2015 and 2016 summer seasons. The objective of this work was to study the effect of nitrogen fertilizer rates and small-flower umbrella (Cyperus difformis L.) competition on broadcast rice productivity and nutrient uptake. Each experiment included eighteen treatments. (The combination of three nitrogen fertilizer rates 50, 70 and 90 kg N fed -1 , and six of Cyperus difformis L. densities, i.e., zero, 10, 20, 40, 80 and 100 (naturally infestation) plant m -2 ). A split plot design, with four replications, was used. The results revealed that increasing nitrogen rates increased significantly the studied broadcast rice growth parameters, yield and its components, in both seasons. Where the application of 70 and 90 kg N fed -1 increased grain yield by 11.45 and 18.91 % in the first season and 12.92 and 18.92 % in the second season, respectively, compared to the lowest nitrogen fertilizer rate. Also, increasing nitrogen fertilizer rates had significant effect on most of NPK % of both broadcast rice and Cyperus difformis L. plants at 60 and 80 days after sowing. N, P and K % decreased with growth in both broadcast rice and Cyperus difformis L. plants and were higher in Cyperus difformis L. than broadcast rice in N% showing that Cyperus difformis L. plants is a major competitor of broadcast rice plants for N nutrient. Moreover, the addition of nitrogen fertilizer rates significant affected N, P and K %, NPK uptake and protein% in broadcast rice grain. Application of 70 and 90 kg N fed -1 increased protein % in grain broadcast rice by 9.54 % and 11.23 % respectively in the second season, compared to 50 kg N fed -1 . On the contrary, increasing Cyperus difformis L. density m -2 had an adverse effect on broadcast rice growth, yield and its components in both seasons. Increasing number of Cyperus difformis L. plants from 10 to 100 m -2 reduced the grain yield by 5.37 to 47.43 % in the first season and 7.98 to 48.88 %, in the second season compared to Cyperus difformis L. free treatment. Positive significant effects were detected for Cyperus difformis L. density m -2 on N, P and K % of both broadcast rice and Cyperus difformis L. plants at 60 and 80 days after sowing as well as broadcast rice grain contents of N, P and K and protein in both seasons. Increasing Cyperus difformis L. plants from 10 to 100 m -2 decreased grain protein % from 0.17 to 2.11 % in the first season and 0.17 and 1.09 % in the second season compared with Cyperus difformis L. free plots. The interaction between 90 kg N fertilization rate and zero Cyperus difformis L. plant m -2 gave the highest broadcast rice grain yield (4.21 and 4.15 ton fed -1 ) compared with 50 kg N fertilization rate and 100 Cyperus difformis L. plant m -2 which gave (1.84 and 1.71 ton fed -1 ) in the first and second seasons, respectively. The main findings of this investigation indicate that Cyperus difformis L. weed should be controlled to avoid broadcast rice grain yield losses due to its competition through integration between nitrogen fertilization and weed control treatments to get the highest grain yield of broadcast rice.