MANIPULATION OF INCEPTISOLS POND BOTTOM SOIL THROUGH ADDITION OF ULTISOLS AND VERTISOLS FOR REARING OF RED TILAPIA (Oreochromis sp.) LARVAE

Abstract

The pond bottom soil of Inceptisols mixed with Ultisols (I-U) and Vertisols (I-G) with the proportion of (70:30); (50:50); (30:70) showed the improvement of clay fractions >30% compared with the control (100% Inceptisols). These mixtures were given basal fertilizer (quail droppings manure with dosage of 2 tons/ha/month), Urea, and SP36. Cultivation system was divided into two stocked: fish ponds with 50 fish/m2 and ponds without fish. The best mix with the basal fertilizer was further treated with fertilization treatment (1 ton/ha/month of quail droppings manure) 3 times within 42 days of larval rearing. Physical and chemical soil analyses showed an increase of total soil porosity (> 50%), decrease of SG, BD, and permeability (medium), pH > 5, the CEC > 20 cmol (+) kg-1, and the C/N ratio < 6.5. The proportion of the best mix of 30% I : 70% U and 50% I : 50% G with 3 times of the fertilization frequency gave significant improvement of water quality, chlorophyll-a, diversity of plankton, benthic algae, fish growth, and total biomass. The presence of mineral montmorillonite on a mixture of 50% I : 50% G was a very good sign of the bottom soil fertility.