Abstract
The effect of rice-husk char (potentially biochar) application on the growth of transplanted lettuce (Lactuca sativa) and Chinese cabbage (Brassica chinensis) was assessed in a pot experiment over a three crop (lettuce-cabbage-lettuce) cycle in Cambodia. The biochar was the by-product of a rice-husk gasification unit and consisted of 28.7% carbon (C) by mass. Biochar application rates to potting medium of 25, 50 and 150 g kg−1 were used with and without locally available fertilizers (a mixture of compost, liquid compost and lake sediment). The rice-husk biochar used was slightly alkaline (pH 7.79), increased the pH of the soil, and contained elevated levels of some trace metals and exchangeable cations (K, Ca and Mg) in comparison to the soil. The biochar treatments were found to increase the final biomass, root biomass, plant height and number of leaves in all the cropping cycles in comparison to no biochar treatments. The greatest biomass increase due to biochar additions (903%) was found in the soils without fertilization, rather than fertilized soils (483% with the same biochar application as in the “without fertilization” case). Over the cropping cycles the impact was reduced; a 363% increase in biomass was observed in the third lettuce cycle.
Highlights
Rice-husk char (RHC) is a waste by-product of gasification and, due to an absence of demonstrated use for the RHC, lack of knowledge of the properties of the char, and the lack of enforcement of waste management regulations, the material tends to accumulate adjacent to the gasification units [1]
A negative impact on plant growth from an individual substrate component may be counteracted by other positive effects from the biochar addition, for example, an increase in cation exchange capacity (CEC) under certain conditions
Rice-husk biochar applied at rates between 50–150 g kgí1 in pot trials led to a highly positive effect on lettuce and cabbage growth both with and without local organic fertilizers in a sandy, acidic soil typical for Cambodia
Summary
Rice-husk char (RHC) is a waste by-product of gasification and, due to an absence of demonstrated use for the RHC, lack of knowledge of the properties of the char, and the lack of enforcement of waste management regulations, the material tends to accumulate adjacent to the gasification units [1]. There has been increasing interest in finding appropriate uses of such RCH [2], and the purpose of this research was to explore the potential of RHC as a form of biochar with attendant benefits when introduced into agricultural soils. Little research is available on the agronomic impacts of RHC, with two published studies for impacts on rice productivity in Cambodia [3,4] suggesting that yield increases of 30 to 40% are feasible with 30 to. One of the purposes of the study reported here was to test the growth pattern of vegetables at high levels of RHC in pots in order to ascertain whether an upper application-threshold became evident beyond which further RHC addition, alongside other soil amendments, becomes counter-productive. Following common practice and locally available resources, we tested the impact of RHC and RHC with combinations of these other soil amendments
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