This study was carried out during 2015 and 2016 seasons on mature Balady mandarin trees budded on sour orange rootstock at the Experimental Orchard, Department of Horticulture, Faculty of Agriculture, Menoufia University. The main target of this study was examining the effect of yeast, seaweed and farmyard manure extracts as a partial replacement of the inorganic N fertilizers on fruiting of Balady mandarin trees. Adjusting the best proportion of inorganic N fertilization used with any of these biostimulants is considered another goal. The experiment was arranged in a complete randomized block design with three replications, one tree for each, and it consisted of nine treatments. The obtained results could be summarized as follow :
Increasing inorganic N percentages from 50 to 100 % either when applied alone or when applied with any of the three biostimulants (yeast, seaweed extract and farmyard manure) materially caused a gradual promotion on the yield expressed in weight (kg) and number of fruits per tree. A positive effect on the yield was observed with using the suitable N through 50 to 75 % inorganic N source in combined with using yeast, seaweed or farmyard manure extracts. The best biostimulants in this respect applied with inorganic N was seaweed extract followed by farmyard manure and yeast occupied the last position with using any of these biostimulants. They were remarkably enhanced with using the suitable N through 50 to 75% inorganic N in combined with using any biostimulants comparing with using N via inorganic source alone. The promotion on fruit quality was associated with increasing percentages of inorganic N from 50 to 100% as well as application of any of the three biostimulants. For improving yield quantitively and qualitatively as well as protecting our environment from pollution, it is advised to fertilize Balady mandarin trees grown under Menoufia region with the suitable N (1000 g/ tree/ year) through 50 % inorganic source plus spraying seaweed extract at 0.25 % four times (Feb., April, June and Aug.).