PhD Oral Defence: Development of equipment to characterize soil attributes in different agricultural settings

PhD Oral Defence of Eko Leksono, Bioresource Engineering

In Indonesia, sugarcane and oil palm are cultivated commonly in organic or sandy clay loam soils. The usual way to determine fertilizer demand relies on cumulative randomized grid sampling. As a result, the fertilizer prescription becomes relatively uniform across the whole farm. In fact, spatial variability of various soil properties is often diverse across the field; therefore, it is necessary to develop the PA methodology to provide a better understanding of soil chemical attributes in the field. First, a soil apparent electrical conductivity (EC_a) inversion algorithm was needed to depict the general characteristics of top organic soil. Subsequently, from soil ECa inversion input, sampling schemes were built to further examine the soil chemical properties. Thus, reliable manual and automatic soil sensing platforms were needed. Both platforms, developed in this research, rely on the Direct Soil Measurement (DSM) principle and they facilitate multiple soil chemical analyses (pH, nitrate) using multiple Ion-Selective Electrodes (ISEs). The manual system was based on a modified generic soil sampler to accommodate portability, whereas the automatic system, called On-the-spot Soil Analyzer (OSA), was designed to operate as a vehicle attachment. Both systems were successfully tested in the field for their operation and for determining soil pH (R² of 0.53 to 0.88) and Nitrate (R² of 0.72 to 0.84).

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