Two field experiments were conducted at El-Serw Agricultural Research Station, Damietta Governorate, during 2008/2009 and 2009/2010 seasons, to study the effect of farmyard manure (0, 10, 20 and 30 m3/fad), plant densities (33600, 42000 and 56000 plant/fad), four biofertilizer treatments (without treated, inoculation seeds with Cerialine, Netrobine at 450 g/fad and 90 kg N/fad as a mineral fertilizer)and their interactions on growth and yield of sugar beet .
The obtained results indicated that farmyard manure had a significant effect on average values of root fresh weight, sucrose %, purity % and yields of top, root and sugar/fad in both seasons. Increasing farmyard manure rate up to 30 m3/fad significantly increased root fresh weight, top yield/fad, root yield/fad as well as sugar yield/fad but, decreased sucrose % and purity % as compared to control (without added farmyard manure) in both seasons.
Plant density significantly affected all studied traits in both seasons. The highest plant density 56000 plant/fad gave the highest values of sucrose %, purity %, top yield /fad, root yield /fad and sugar yield/fad, but it gave the lowest root fresh weight. On the contrary, the heaviest root was recorded with the lowest plant density 33600 plant/fad as compared with other studied plant densities in 2008/2009 and 2009/2010 seasons.
Results indicated that fertilization treatments had a significant effect on all studied characters in both seasons. Applying nitrogen as a mineral fertilizer at a rate of 90 kg N/fad gave the highest values of root fresh weight, top yield/fad, root yield/fad and sugar yield/fad as compared with all other fertilization treatment, in 2008/2009 and 2009/2010 seasons. In this connection, cerialine biofertilizer followed the mineral nitrogen of the mentioned previously traits.
The interaction between farmyard manure rates and plant densities, the interaction between farmyard manure rates and biofertilization treatments and the interaction between plant densities and biofertilization treatments were significantly affected all studied traits in both seasons. The interaction effect among farmyard manure, plant density and fertilization treatments was significant on all studied characters in both seasons. Plants received 30 m3/fad farmyard manure at the highest plant density 56000 plant/fad and fertilized by 90 kg N/fad gave the highest top yield/fad 33.65 and 39.28 tons, root yield/fad 40.76 and 39.20 tons as well as sugar yield/fad 7.11 and 6.75 tons compared to all other this interaction treatments in 2008/2009 and 2009/2010 seasons, respectively.
Generally, it could be recommended that applied farmyard manure at the rate of 30 m3/fad for sugar beet plants sown at plant density of 56000 plant/fad, and fertilized by 90 kg N/fad gave the highest root and sugar yield/fad at North Delta, Damietta Governorate, Egypt