Comparison of Different Nitrate Leaching Sensors

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In this post, I will deviate from my usual programming languages research topic and look at using sensors to detect concentration of N in either surface or ground water in NZ. This is in part related to my other project trying to create a marketplace of economic incentives for NZ farmers when it comes to optimising their environmental impact versus the long term economic cost (aka AgriDataTrade).

There are the following four options commercially available in NZ as of late 2020. I am not going to cover very very cheap conductivity based sensors available en masse on Ali Express and similar sites as these are not able technologically to gauge the actual presence of N in either soil or water despite what is advertised.

The major four options are:

  1. Hach HL4 is using pH light bulb, some pellets, conductivity sensor, and Nitrate sensor attachment. It is designed to be placed in running water - such as streams or rivers. It requires weekly calibration to ensure reliable Nitrate readings and the main Nitrate sensor needs to be replaced every 90 days (with a shelf life also being around 90 days). These cost around $8,000 NZD for a full set that can talk to your custom Arduino or similar board via either modbus or SDI12 interface. The advantage is that these are easily portable while the disadvantage is the frequent non-trivial callibration required to run them.
  2. Hydrometrics is using a custom designed UV sensor to be lowered into a pre-made bore and measures N concentration in the bore which needs to be drilled to reach the ground water level to produce a relevant reading. These do not need frequent calibration and can basically be left there for a year or more before much maintenance will be required. A cleaning mechnism using a simple pump is usually included. These cost around $10,000 NZD with around $2,500 NZD allocated to drilling an average sized bore. The disadvatnage is that these are not easilty portable as the bore is required for their operation. The advantage is that these are more precise without much requirement for calibration.
  3. Eco Detection is an up and coming company that produces an effective "field lab" that can be installed in the particular location for around $50,000 - $70,000 NZD and the water can either be manually added to be analysed (over the course of 20-30 minutes) or pumped automatically from a nearby location(s). This is also using UV technology and is definitely less portable than a single bore. However, it has an advantage if being able to get a result quickly and automatically in the field. The current accepted alternative is to collect water manually and send it ot the lab with each test cosing around $15-$20 NZ at ESR or similar places to find the levels of Nitrate, but also Phosphates, E-coli, etc.
  4. Trios makes several UV based sensors that can be deployed in rivers similar to Hach, in particular PICO (more versatile and around $20K) and NICO (more specific to N and around $10K). These are optical-based with a lense in the middle for the water to go through and require power to run. The data can be read using SDI12 or MODBUS.

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