Efficacy of bio-composted agricultural wastes and biocontrol agents in improving soil fertility and controlling dry root rot in King mandarin (Citrus nobilis) orchards

Abstract

Importance of the work: Intensification of King mandarin cultivation has been
threatened by dry root rot (DRR) disease, causing unsustainable growth of this citrus fruit.
Objectives: To evaluate the efficiency of bio-fertilizers (BF) in combination with
different bio-control agents on improving soil properties and controlling DRR disease in
King mandarin orchards.
Materials and Methods: Rice straw waste material was composted with isolated fungi
from King mandarin orchards and rice fields. Five treatments were conducted in a
complete randomized design: 1): common farmer practice (the control); 2): recommended
inorganic fertilizers (RIF); 3): RIF plus BF inoculated with Trichoderma asperellum
(BF1); 4): RIF plus BF inoculated with Gongronella butleri (BF2); and 5): RIF plus BF
inoculated with Trichoderma sp. from a commercial source (BF3).
Results: BF amendment led to significant increases in soil organic matter, soil pH, labile
nitrogen, available phosphorus and exchangeable potassium compared to the control
with its high dose of inorganic fertilizers. There was a significantly lower density of
Fusarium solani and DRR suppression (40–82.5%) as result of BF amendment, with BF
plus isolated Trichoderma and Gongronella butleri being the most effective treatment.
Consequently, in the second year harvest, fruit yield increased by about 3.5 times that of
the control treatments (p < 0.05).
Main finding: Using rice straw as waste material to make bio-compost with isolated
strains of native fungi could be an optimal practice for improving soil fertility and soil
suppression to reduce DRR and enhance fruit yield, promoting an eco-friendly system in
King mandarin orchards.