DETERMINATION OF AVAILABLE MACRONUTRIENTS, NA, CL, PH AND EC IN COIR SUBSTRATE INCUBATED WITH MINERAL FERTILIZERS

Coconut fiber has been considered an adequate alternative material as substrate for soilless potted plants under semi or protected cultivation. Several water extracts are used for the determination of pH, EC and available nutrients in substrates for plants, but there is little information about the relations among them for a more correct plant nutrient evaluation. The objective of this research was to compare current procedures of water extraction for the chemical analysis of coir substrate incubated with conventional NPK and slow-release fertilizers (SRF). Samples were collected at 20, 60 and 120 days of incubation and submitted to the following water extraction methods: 1:1.5 v/v; 1:2 v/v; 1:5 v/v; 1:10 m/v; and saturation extract. NPK showed a faster nutrient-releasing rate compared to the SRF. The substrate did not present excess sodium or high electrical conductivity (EC). However, pH decreased with period of incubation independently of treatment. The initial pH was increased in the conventional NPK-fertilizer and decreased in the SRF treatments. Ammonium and nitrate presented a different behavior along the time, according to fertilizer source. Phosphorus concentrations were not influenced, however, EC and all other macronutrients in the coir substrate were significantly affected by the water extraction methods. The best methods for the substrate analysis were the saturation and 1:1.5 water extracts for nutrient evaluation purposes.