Temporal physicochemical variations in burnt rice husk: Improvement of fertigation protocols in carnation crops
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abstract
The use of burnt rice husk (BRH) as a substrate in the cultivation of carnations in the Bogota plateau has increased greatly in recent years. Carnation has a relatively long crop cycle and throughout the growing season an intensive and continuous fertigation is supplied. Changes in physicochemical characteristics of the substrate that occur throughout the crop cycle are not fully known and therefore the present study aims to evaluate the behavior of certain parameters of burnt rice husk substrate throughout the carnation crop cycle (100 weeks). Detailed knowledge of this behaviour will allow growers to modify fertigation management accordingly. Substrate samples were taken from greenhouses in 3 different farms at 10-week intervals throughout the carnation crop cycle in order to determine pH, cation exchange capacity (CEC), exchangeable cations and percent base saturation. From these data the effective CEC and the variable charge were calculated, burnt rice husk presents very high initial values of exchangeable K leading to imbalance in the exchangeable bases, which must be corrected by applying adequate doses of Ca and Mg. After application of this amendment the substrate takes from 1 to 10 weeks to reach suitable balance. The CEC values increased with crop time on average from 23 to 36 cmol%2b·kg-1. This represents a 60%25 increase on the initial value, indicating that the fertigation frequency, composition and concentration should be modified with substrate age. The concentration of exchangeable Na also increased with time; however, this increase varied in the different farms studied. This behaviour is directly related to irrigation water quality, and may also be related to the fact that drainage water is reused in two of the farms. Knowledge of the physicochemical properties of BRH substrate can be useful for improving current fertigation protocols for carnation crops.
