Precision agriculture is a farming management concept based on observing, measuring and responding to inter and intra-field variability in crops. It has the promise to produce more with less and better, giving benefit to potato farmers, potato value chains and society. But adoption is slower than expected. In this series I look at the state of art of precision agriculture applications in potato from a Dutch perspective. Let us have a look at variable rate planting density of potatoes.
A Fieldlab for Precision Farming (NPPL) was established in The Netherlands in 2018 to stimulate adoption of precision agriculture applications. It runs for four years and has now twenty-six participating farmers whom implement applications with the support of independent experts. E.g., arable farmers are applying variable rate planting density of potatoes. They are searching what approach fits best in their situation. The application consists in general terms of getting data on the variability of soil conditions, decision support on where to plant which density (prescription map), and actuation. Farmers can choose from a variety of data to start with. On the actuation side, modern planters can apply variable rate planting density per row. Management zoning software is available to make variable rate planting density prescription maps. The weakest part is the decision making on where to plant which density.
If you look close at the decision making, the planting density is generally adjusted to differences in yield potential within a field. Yield potential variation is shown in maps in irregularly shaped zones or regularly shaped grids. Yield potential maps can be based on data from soil sensors (EC, NIR, gamma radiation), remote optical sensors, and/or yield sensors. Furthermore, decision making applies data on tuber quality (number of sprouts that will emerge per tuber), desired number of stems per m2, shading of the field, and sprayer tramlines. Planting density is increased by several % on places of the field where growth conditions are expected to be unfavourable (shading, low EC, low water holding capacity) and reduced by several % where they are expected to be favourable (extra light, high EC, optimal clay content). The increase or decrease % is often based on expert judgement by the farmer or farm advisor, and often less than 10%. If you look in literature, you will find very few studies that quantify these % or validate the decision support models.
Despite clear decision support, farmers are interested in variable rate planting because they believe in it. It is logic reasoning that on places with high yield potential, more stems per m2 will provide more produce per m2. Yield increases of 5 – 10% by variable rate planting are expected (such numbers are mentioned in farmers magazines). The reason why there are so few scientific studies quantifying the yield increase, is that such studies are difficult to carry out and require large efforts. Study result depends e.q. on variation in soil of the experimental field and variation in the quality of the seed lot. Such studies would benefit from more precise yield sensors on potato harvesters.
Within the EU IoF2020 use cases 1.1, 1.5 and 1.9, a consortium works on a multi-vendor potato planting density webservice that delivers prescription maps that can be applied as task maps on planters of different machine brands. A user of the service has to define the specific soil and shading conditions of his field, the sprouting capacity of the tubers he uses and the desired stem density. The webservice will then calculate the planting density prescription map on the basis of the soil/yield potential map. Defaults are e.g. 0.6 cm less planting density when the clay content increase 1 %. This relation was derived from literature on experiments to determine the optimal planting density of three potato varieties on soils with different clay contents (ranging from 5 – 50 %) in The Netherlands. The webservice will be tested in 2020 and 2021 in The Netherlands, Belgium and Germany, and hopefully we can quantify the benefit of variable rate planting. We know already that the benefit can only be demonstrated if the seeds used are homogenous, meaning that the variation in number of sprouts per tuber does not differ much from one to the other. ●
Dr. Ir. Corné Kempenaar
Sr. Scientist @ WUR & Professor @ Aeres
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