Expert view

Soil remains ‘black box’ in nitrogen advice

Once, a Chinese emperor told his gardener he wanted him to plant a certain tree in his garden. When the gardener warned it would probably take at least 1,000 years before that tree was fully grown, the emperor said: “Then we should not lose one single day.”

The proverb reminds me of where we are with farming technology. Sometimes it grows slowly, but you know the end result is going to be worth it.

Take nitrogen advice, for instance. It’s common practice to apply base fertiliser to cereals and potatoes and supplement it during the growing season.

Determining the exact requirements of a crop is partly down to the grower’s gut feeling and knowledge of leaf colour and size. The grower also takes the acreage into account and the amount of fertiliser already applied.

Photo credit: Jan Willem Schouten

Photo credit: Jan Willem Schouten

Measurements

But the grower measures, too. Soil temperature – past, present and future – determines mineralisation and release of nitrogen. Satellite, aircraft or drone images can rate the vegetation index from 0 (no vegetation, bare soil) to 1 (complete crop cover). Or the farmer can rely on machinery-mounted crop sensors to generate a reading.

Whatever the method used – traditional or technological – ultimately, the goal is the same: to maximise the potential of the soil and the crop variety it supports, at the lowest possible cost. The question is: do the vegetation index and the following automatically generated nitrogen advice add anything to the skill and rules of thumb growers have always relied on?

Photo credit: Koos Groenewold

Photo credit: Koos Groenewold

Data insights

I think they do. As the Dutch say: “meten is weten” (to measure is to know). Using the insights gained from data almost always leads to better and larger harvests. What I really want to know, though, is how many more potatoes does data use actually yield? How much money do you save?

This very hard to quantify, because the yield depends on many variable factors, from soil type and disease burden to the weather.

Nitrogen advice

Let’s focus on the difference in nitrogen advice, then. What amount is advised based on the vegetation index acquired through satellite, drone, aircraft or sensors and how much is down to the grower’s intuition?

Does the agronomist – having run an algorithm through his computer – think it is best to use a lot of nitrogen to ensure maximum yield of potatoes, or does he believe in crops that ripen in a timely fashion, give no problems at harvest and are not too susceptible to late blight (Phytopthera infestans).

Data for a breakthrough

Put simply, we cannot categorically say what the best piece of advice is.

With soil as the “black box” between theory and practice, gigantic data, rather than big data, is needed to produce reliable, yield-enhancing nitrogen advice. So, let’s embrace the pioneers who experiment with this. They deliver the data that will realise a breakthrough, sooner or later.