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Two sides of the same corn: in-soil nitrate sensing to reduce over-application of nitrogen

By Roger Burton - Last updated: Thursday, March 9, 2017

TractorUp to 70% of applied nitrogen in agriculture is wasted. Integration of technology such as optical interrogation, drones and satellite imaging with agricultural equipment is showing increases in yield and decreases in operating costs. With new sensing technologies, robust implementations and intelligent data handling and analysis, it is possible to greatly reduce this wastage.

Agricultural efficiency has been increasing steadily through improved fertiliser production, specialised crops and improvements to farming techniques in a similar way. Using fewer resources to achieve greater yields reduces the cost of production and potentially increases profit for the farmer.

As the single largest consumable expense for a farmer in the US, fertiliser deserves a special focus. High yield crops demand large amounts of nitrogen to achieve their potential and often fertiliser must be applied to prevent nitrogen stress. Measurements have been taken on how much nitrogen the plants need, but many factors affect how much needs to be applied and when.

  • Nitrogen levels in the ground vary significantly before application. Within a single field, some areas might be completely depleted while others need only a slight top-up.
  • After the nitrogen is applied, environmental conditions will affect how much of it remains as useful nitrates. Temperature, humidity, rainfall, sunshine, groundwater, soil type and soil moisture will all result in variations.
  • All of these same environmental factors will affect the speed of the growth of the crops and when it needs nitrates available to grow

Only one sure-fire method exists to ensure the maximum yield – over fertilise (see figure 2). Applying more fertiliser might result in more wastage, but the high cost of a yield reduction makes it worthwhile. To reduce the wastage, there are two technology breakthroughs waiting to happen, two sides from which the problem can be tackled.

Figure 1

Figure 1 – Unknowns in the nitrate levels in the soil and the losses that will occur after nitrogen application

Figure 2

Figure 2 – Without any extra information, over application can be caused by high nitrogen levels in the ground and low environmental losses

Side 1: real time nitrate sensing

I’ve said before how many different technologies are being pursued to try to facilitate real time nitrate sensing. As the applicator is being dragged through the soil, measure how much nitrate is in the soil so that the nitrogen application is only ever as much as is needed to get up to the required level (see figure 3).

Figure 3

Firgure 3 – By measuring the nitrate levels at the point of application, the level applied can be reduced or increased accordingly

Figure 4

Firgure 4 – If the environmental losses can be predicted, then the real amount of applied nitrogen required can be reduced further

This needs a sensor on the tractor which is able to detect to extremely low levels of nitrates (0-200 ppm) and respond in about a second. This combination of speed and resolution is a difficult challenge, even in laboratories.

Side 2: knowing the response of nitrate levels to environmental conditions

Nitrogen being applied is only the start. Not all of the nitrogen that is applied to the soil stays available for the plants to use. Monitoring long term levels in the soil in test fields and correlating fluctuations with environmental factors could enable the construction of a model that can be applied to any field. The likely losses due to environmental conditions can then be estimated, reducing the amount of nitrogen that is applied even further (see figure 4)

This needs long term monitoring; a sensor that can detect levels and communicate them for months at a time, without depleting nitrate levels through its detection method. Once this sensor has been created, correlation of the nitrate data with environmental data and extrapolation to applications in other fields with varying weather requires some clever processing.

The scale of this problem is not small and many different approaches are being investigated. What this really needs is an integrated approach. At Cambridge Consultants we are actively investigating nitrate detection methods, combining our knowledge of chemistry, fluidics and optical sensors with mechanical engineering and robust design to create solutions to the problems stated above.

Figure 5

Illustrated nitrogen levels vs nitrogen uptake. The green area shows nitrogen that is not used by the plants. This could be reduced using lower application levels and application at different times. To reduce these gaps, we need to measure or predict them before they happen


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AuthorRoger Burton


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