Detection of N, P, K fertilizers in agricultural soil with NIR laser absorption technique

Soil is a complex medium that contains minerals, organic matter, micro-organisms, air and water. Recent studies have shown that soil fertility is declining in many farmlands due to insufficient fertilization. Over-fertilization results in groundwater pollution or toxic accumulation of chemicals in the soil. The aim of this experiment is to adjust fertilization based on crop needs and soil properties and to reduce the amount of fertilizer in soil without diminishing yield. The soil analysis technique focus on photon absorption characteristics of the major soil nutrients (nitrogen, phosphorus and potassium). The soil samples under test were first oven dried and and then mixed with four types of fertilizer [KNO3, TSP, (NH₄)₂SO₄, NPK] in the concentration range of 0.02-10%. Near IR laser beam pass through the closed loop Mach-Zander Interferometer to reduce fluctuations related to beam path and interacts with soil sample. When IR radiations are focused onto a sample, the molecules in the sample will increase their vibration energy by absorbing energy at specific frequencies depending on the molecular geometry, bond strengths and atomic masses. The scattered beam is thus modified, creating a signature of the targeted object with peaks at the absorbing frequencies. This technique provided rapid, non-destructive and simultaneous determination of nitrogen, phosphorus and potassium concentrations in soil fertilizer mixtures.